BACKGROUND: The aim of the study was to assess the accuracy of commercially available software in estimating anterior tooth root inclination from digital impressions of the crowns of the teeth. SUBJECTS AND METHODS: Following sample size calculation and application of inclusion and exclusion criteria, 55 anterior natural teeth derived from 14 dry human skulls were selected. Impressions were taken and plaster study models were fabricated. Plaster models were scanned using the high-resolution mode of an Ortho Insight 3D laser scanner. The teeth on the digital scans were segmented and virtual roots were predicted and constructed by the Ortho Insight 3D software. The 55 natural teeth were removed from the dry skulls and scanned using the Identica extraoral white-light scanner in order to calculate their actual root angulation. The teeth were scanned twice, once to acquire the crown and the cervical part of the root, and a second time to acquire the remaining part of the root, including the apex. The two scanned segments were joined in software by superimposing them along their common part. The accuracy of the digital models generated by the Ortho Insight 3D scanner in predicting root angulation was assessed by comparing these results to the corresponding measurements of the 55 natural teeth. The long axes of the tooth models obtained from the software prediction and the scanning of the actual teeth were computed and the discrepancy between them was evaluated. The error of the methods was evaluated by repeating the measurements on 14 teeth and showed an acceptable range. RESULTS: The predicted tooth angulation was found to differ significantly from the actual angulation, both statistically and clinically. The angle between the predicted and actual long axes ranged from 2.0 to 37.6°(average 9.7°; median 7.4°). No statistically significant difference was found between tooth categories. CONCLUSIONS: Further investigations and improvements of the software are needed before it can be considered clinically effective.

OBJECTIVES: To evaluate the hard tissue and facial profile changes in matched extraction and non-extraction Class I patients by the use of geometric morphometrics. SUBJECTS AND METHODS: From a parent sample of 542 Class I patients, previously subjected to discriminant analysis, a subsample of 68 borderline cases was obtained, 34 treated with extraction and 34 without extraction of 4 first premolars. Geometric morphometric methods (Procrustes superimposition and Principal Component Analysis) were applied on cephalometric tracings to assess the validity of the discriminant analysis in successfully identifying a morphologically homogeneous group and to evaluate inter- and intra-group skeletal and facial profile shape changes. RESULTS: No significant pre-treatment shape difference between the two groups was found, thus validating the discriminant analysis. The non-extraction group showed increase in hard tissue facial height (P < 0.001), with slight lower lip retrusion and upper lip protrusion (P = 0.027). The extraction group showed retraction of the hard tissue and facial profile outline (P < 0.001). Permutation tests for post-treatment inter-group differences resulted in P = 0.054 for the soft tissue outline and P = 0.078 for the hard tissue skeletal component. CONCLUSIONS: The evidence indicates that borderline cases treated with four premolar extractions will exhibit lip retrusion compared to non-extraction treatment.

Superimpositions of serial 3D dental surface models comprise a powerful tool to assess morphological changes due to growth, treatment, or pathology. In this study, we evaluated the effect of artifacts on the superimposition outcome, using standard model acquisition and superimposition techniques. Ten pre- and post-orthodontic treatment plaster models were scanned with an intraoral scanner and superimposed using the iterative closest point algorithm. We repeated the whole process after manual removal of plaster artifacts, according to the current practice, as well as after re-scanning the cleaned models, to assess the effect of the model acquisition process derived artifacts on the superimposition outcome. Non-parametric multivariate models showed no mean effect on accuracy and precision by software settings, cleaning status (artifact removal), or time point. The choice of the superimposition reference area was the only factor that affected the measurements. However, assessment of individual cases revealed significant differences on the detected tooth movement, depending on artifact removal and on the model acquisition process. The effects of all factors tended to decrease with an increase in the size of the superimposition reference area. The present findings highlight the importance of accurate, artifact-free models, for valid assessment of morphological changes through serial 3D model superimpositions.

OBJECTIVES: Three-dimensional (3D) bioprinting, a method derived from additive manufacturing technology, is a recent and ongoing trend for the construction of 3D volumetric structures. The purpose of this systematic review is to summarize evidence from existing human and animal studies assessing the application of 3D printing on bone repair and regeneration in the craniofacial region. DATA & SOURCES: A rigorous search of all relevant clinical trials and case series was performed, based on specific inclusion and exclusion criteria. The search was conducted in all available electronic databases and sources, supplemented by a manual search, in December 2017. STUDY SELECTION: 43 articles (6 human and 37 animal studies) fulfilled the criteria. The human studies included totally 81 patients with craniofacial bone defects. Titanium or hydroxylapatite scaffolds were most commonly implanted. The follow-up period ranged between 6 and 24 months. Bone repair was reported successful in nearly every case, with minimal complications. Also, animal intervention studies used biomaterials and cells in various combination, offering insights into the techniques, through histological, biochemical, histomorphometric and microcomputed tomographic findings. The results in both humans and animals, though promising, are yet to be verified for clinical impact. CONCLUSIONS: Future research should be focused on well-designed clinical trials to confirm the short- and long- term efficacy of 3D printing strategies for craniofacial bone repair. CLINICAL SIGNIFICANCE: Emerging 3D printing technology opens a new era for tissue engineering. Humans and animals on application of 3D printing for craniofacial bone repair showed promising results which will lead clinicians to investigate more thoroughly alternative therapeutic methods for craniofacial bone defects.

Forensic anthropologists are frequently faced with the challenge of individualizing and sorting commingled remains in a variety of scenarios. A number of protocols have been proposed to standardize the methodological approach to individuating commingled remains, some of which are focused on pair-matching. A recent study by Karell et al. (2016) proposed a virtual method for pair-matching humeri using a semi-automatic procedure that gave encouraging results. With regards to the phalanges, there are only a handful of studies focusing on identifying and siding phalanges, as well as exploring their directional and functional asymmetry. Yet, they are still as important as every other bone when sorting commingled human remains in various situations, such as archaeological common burials and mass graves, commingled decomposed remains resulting from atrocities, accidents or natural disasters. This study investigates a new method for pair-matching, a common individualization technique, using digital three-dimensional models of bone: mesh-to-mesh value comparison (MVC) as proposed by Karell et al. (2016). The MVC method digitally compares the entire three-dimensional geometry of two bones using an iterative closest point (ICP) algorithm to produce a single value as a proxy for their similarity. The method is automated with the use of Viewbox software 4.1 beta for a simultaneous comparison of all possible pairs. For this study, 515 phalanges from 24 individuals of mixed ancestry were digitized using CT scans and the 3D modeling program AMIRA 5.3.3. The models were also hollowed (internal information of compact and trabecular bone removed) to test the method with simulated surface scan models. The subsequent data-over 73,000 comparisons-were assessed using sensitivity and specificity rates via ROC analysis to indicate how well the automated version of MVC pair-matched phalanges. The best bone in terms of pair-matching was the proximal phalanx of Digit 3 with 87.5% sensitivity and 92.4% specificity rates at a threshold value of 0.488 for the unhollowed bones. The specificity drops slightly (91.1%) when the hollowed models are compared. To compare the performance of the method in all phalanges, the specificity was set to 95%-allowing for a 5% acceptable error-and the adjusted sensitivity was compared. The highest sensitivity, namely 68.8%, was noted for Digit 2 proximal phalanx for both unhollowed and hollowed models. Thus far, our preliminary results indicate that the MVC method performs well when pair-matching phalanges, though it is less accurate than pair-matching other types of bones. The introduction of 95% specificity threshold allows for rejecting pairs in great confidence, which could, for instance, significantly reduce the number of DNA comparisons required for the remaining possible matches. In addition, the similar results obtained from hollowed and unhollowed models indicate that the internal information included in the unhollowed models adds little to the identification of true pairs. This means that if a CT scan is not available, the method could be applied to surface models produced by light and laser scanners as well. While additional work needs to be done to verify these preliminary results, this research has the potential to expand the repertoire of individualization methods.

Background: To assess the accuracy of digital models generated using commercially available software to predict anterior teeth root inclination characteristics and compare the results to relevant data obtained from CBCT images. Material and Methods: Following sample size calculation and after application of inclusion and exclusion criteria, pre-treatment maxillary and mandibular plaster models and the corresponding CBCT scans of 31 patients attending a private orthodontic clinic were selected. The subjects were 10 males and 21 females with age range 12 to 40 years. Plaster models were scanned using the high resolution mode of an Ortho Insight 3D scanner and CBCT scans were taken using a Kodak 9500 Cone Beam 3D System machine. The teeth on the digital scans were segmented and virtual roots were predicted and constructed by the Ortho Insight 3D software. The long axes of the predicted roots and the actual roots, as segmented from the CBCT images, were computed using best-fit lines. The inter-axis angle was used to assess error in root inclination prediction by the software. Mann-Whitney and Kruskal-Wallis tests were used. Intra-examiner error was evaluated using the Bland-Altman method. Results: The maximum disparity in angle between images derived from digital models and CBCT data was almost 40 degrees (upper left canine). The upper and lower canines produced the worst results, followed by the lower lateral incisors. The upper central incisors showed the best results, although the maximum angle of difference exceeded 20 degrees (with the median around 8 degrees). Conclusions: Root morphology imaging prediction is not a primary function of this software and this study confirmed its limitation as a sole tool in routine clinical applications. At present these predictions cannot be considered accurate or reliable unless correlated clinically with a radiographic image. Digital models, CBCT, tooth root inclination prediction software.

Objectives: To assess the effectiveness, clinical performance, and potential adverse effects of early anterior crossbite correction through opening of the bite. Subjects and methods: The sample consisted of 16 consecutive patients (8.0 ± 0.9, range: 6.2-9.3 years) with dental anterior crossbite in the mixed dentition who were treated through posterior bite opening. Patients were prospectively followed until a minimum of 6 months post-treatment and there were no drop-outs. Results: In 14 patients (87.5 per cent), the anterior crossbite was corrected. Results remained stable without any retention regime. Active treatment of the successfully treated cases lasted 2.5 months (range: 0.6-8.9). Crossbite correction of central incisors was achieved by a 2.05 mm (range: 0.97-5.45) forward movement and 9.25° (range: 2.32-14.52°) buccal inclination of the crowns (P < 0.05). The antagonists showed spontaneous adaptation of their position in the opposite direction (P < 0.05). No important adverse effects were recorded. Limitations: This was a non-comparative controlled study, on a limited sample. Conclusions: Bite opening is a promising, simple, and non-compliance approach for early dental anterior crossbite correction. The technique of 3D superimposition and analysis of digital models used here, allowed precise evaluation of single tooth movement in all three planes of space.

OBJECTIVES: This study aimed to investigate size and shape variation of human premolars between Indigenous Australians and Australians of European ancestry, and to assess whether sex and ancestry could be differentiated between these groups using 3D geometric morphometrics. MATERIALS AND METHODS: Seventy dental casts from each group, equally subdivided by sex, were scanned using a structured-light scanner. The 3D meshes of upper and lower premolars were processed using geometric morphometric methods. Seventy-two landmarks were recorded for upper premolars and 50 landmarks for lower premolars. For each tooth type, two-way ANOVA was used to assess group differences in centroid size. Shape variations were explored using principal component analysis and visualized using 3D morphing. Two-way Procrustes ANOVA was applied to test group differences for ancestry and sex, and a "leave-one-out" discriminant function was applied to assess group assignment. RESULTS: Centroid size and shape did not display significant difference between the sexes. Centroid size was larger in Indigenous Australians for upper premolars and lower second premolars compared to the Australians of European ancestry. Significant shape variation was noted between the two ancestral groups for upper premolars and the lower first premolar. Correct group assignment of individual teeth to their ancestral groups ranged between 80.0 and 92.8% for upper premolars and 60.0 and 75.7% for lower premolars. DISCUSSION: Our findings provide evidence of significant size and shape variation in human premolars between the two ancestral groups. High classification rates based on shape analysis of upper premolars highlight potential application of geometric morphometrics in anthropological, bioarcheological and forensic contexts.

Aim : To evaluate the shape of the craniofacial complex in patients with tooth agenesis and compare it to matched controls. Subjects and methods : The sample comprised 456 patients that were allocated to three groups: the agenesis group of 100 patients with at least one missing tooth, excluding third molars, the third molar agenesis group (3dMAG; one to four missing third molars) of 52 patients and the control group (CG) of 304 patients with no missing teeth. The main craniofacial structures depicted on lateral cephalograms were digitized and traced with 15 curves and 127 landmarks. These landmarks were subjected to Procrustes superimposition and principal component analysis in order to describe shape variability of the cranial base, maxilla and mandible, as well as of the whole craniofacial complex. For statistical analysis, permutation tests were used (10 000 permutations without replacement). Results : Approximately half of the sample's variability was described by the first three principal components. Comparisons within the whole sample revealed sexual dimorphism of the craniofacial complex and its structures (P < 0.01). Differences between the agenesis group and matched controls were found in the shape of all craniofacial structures except for the cranial base (P < 0.05). Specifically, patients with agenesis presented with Class III tendency and hypodivergent skeletal pattern. However, the comparison between the 3dMAG and matched CG revealed no differences. Conclusion : The shape of the craniofacial complex differs in patients with tooth agenesis suggesting that common factors are implicated in tooth development and craniofacial morphology.

Aim: There is great variation of growth among individuals. The question whether patients with different skeletal discrepancies grow differently is biologically interesting but also important in designing clinical trials. The aim of the present study was to evaluate whether growth direction depends on the initial craniofacial pattern. Subjects and method: The sample consisted of 350 lateral cephalograms of 175 subjects (91 females and 84 males) followed during normal growth without any orthodontic treatment. The examined ages were 12 (T1) and 14 (T2) years. The cephalograms were obtained from the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection (Burlington, Fels, Iowa, and Oregon growth studies). We digitally traced 15 curves on each cephalogram, comprehensively covering the craniofacial skeleton, and located 127 points on the curves, 117 of which were sliding semilandmarks and 10 fixed. Procrustes alignment, principal component analysis and two-block partial least squares analysis were performed, after sliding the semilandmarks to minimize bending energy. Results: The first 10 principal components (PCs) described approximately 71 per cent of the total shape variance. PC1 was related to shape variance in the vertical direction (low/high angle skeletal pattern) and PC2 was mainly related to shape variance in the anteroposterior direction (Class II/Class III pattern). PC3 was mainly related to the shape variance of the mandibular angle. All subjects shared a similar growth trajectory in shape space. We did not find any correlation between the initial shape and the magnitude of shape change between T1 and T2, but males showed a greater shape change than females. The direction of shape change was moderately correlated to the initial shape (RV coefficient: 0.14, P < 0.001). Conclusions: The initial shape of the craniofacial complex covaried weakly with the direction of shape change during growth.

Objective: To assess shape covariation of the palate and craniofacial complex (CFC) in children and adolescents. Methods: Pre-treatment lateral cephalometric radiographs and corresponding maxillary casts of 100 children (8-10 years) and 100 adolescents (15-20 years) were digitized. Exclusion criteria were previous orthodontic treatment, craniofacial syndromes, mouth breathing, finger sucking, crossbite, tooth agenesis, and tooth impaction. Palatal shape was described with 239 surface and curve semilandmarks and craniofacial shape with 10 fixed landmarks and 117 curve semilandmarks. Procrustes superimposition and principal component analysis were applied for evaluation of shape variability. Shape covariation between palate and CFC was assessed with partial least squares analysis. Results: The first five principal components explained 77 per cent (palate) and 60 per cent (CFC) of total shape variability. The palate varied mainly in height (adolescent group) and width-length (both groups), whereas the CFC varied mainly in the vertical dimension. Significant covariation was found between the craniofacial and palatal components (RV coefficient: 0.27, children; RV: 0.23, adolescents). Variation of the CFC in the vertical and anteroposterior direction was mainly related to variation in the height-width and the width-length ratio of the palate, respectively. Limitations: The use of lateral cephalometric radiographs eliminated the transverse dimension from the craniofacial shape analysis. The study was cross-sectional, so the observed intergroup differences should be interpreted with caution. Conclusions: Covariation strength and pattern were similar in children and adolescents. The closer a subject was to the high-angle end of the variability spectrum, the higher and narrower was the palate, and conversely.

Objectives: To evaluate the patterns of covariation between palatal and craniofacial morphology in Class II subjects in the early mixed dentition by means of geometric morphometrics. Methods: A cross-sectional sample of 85 Class II subjects (44 females, 41 males; mean age 8.7 years ± 0.8) was collected retrospectively according to the following inclusion criteria: European ancestry (white), Class II skeletal relationship, Class II division 1 dental relationship, early mixed dentition, and prepubertal skeletal maturation. Pre-treatment digital 3D maxillary dental casts and lateral cephalograms were available. Landmarks and semilandmarks were digitized (239 on the palate and 121 on the cephalogram) and geometric morphometric methods (GMM) were applied. Procrustes analysis and principal component analysis (PCA) were performed to reveal the main patterns of palatal shape and craniofacial skeletal shape variation. Two-block partial least squares analysis (PLS) assessed patterns of covariation between palatal morphology and craniofacial morphology. Results: For the morphology of the palate, the first principal component (PC1) described variation in all three dimensions. For the morphology of the craniofacial complex, PC1 showed shape variation mainly in the vertical direction. Palatal shape and craniofacial shape covaried significantly (RV coefficient: 0.199). PLS1 accounted for more than 64 per cent of total covariation and related divergence of the craniofacial complex to palatal height and width. The more a Class II subject tended towards high-angle divergence, the narrower and higher was the palate. Conclusions: Class II high-angle patients tended to have narrower and higher palates, while Class II low-angle patients were related to wider and more shallow palates.

Serial 3-dimensional dental model superimposition provides a risk-free, detailed evaluation of morphological alterations on a patient's mouth. Here, we evaluated accuracy and precision of five palatal areas, used for superimposition of maxillary 3D digital dental casts. Sixteen pre- and post-orthodontic treatment dental casts of growing patients (median time lapse: 15.1 months) were superimposed on each palatal area using the iterative closest point algorithm. Area A (medial 2/3 of the third rugae and a small area dorsal to them) was considered the gold standard, due to high anatomical stability. Areas B, C, and D added a distal extension along the midpalatal raphe, an anterior extension to the second rugae, and the remaining palatal surface, respectively. Area E was similar to A, located more posteriorly. Non parametric multivariate models showed minimal or no effect on accuracy and precision by operator, time point, or software settings. However, the choice of superimposition area resulted in statistically significant differences in accuracy and clinically significant differences in detected tooth movement (95% limits of agreement exceeding 1 mm and 3°). Superimposition on area A provided accurate, reproducible, and precise results. Outcomes were comparable for area B, but deteriorated when alternative areas were used.

OBJECTIVE: To assess the maxillary second molar (M2) and third molar (M3) inclination following orthodontic treatment of Class II subdivision malocclusion with unilateral maxillary first molar (M1) extraction. MATERIALS AND METHODS: Panoramic radiographs of 21 Class II subdivision adolescents (eight boys, 13 girls; mean age, 12.8 years; standard deviation, 1.7 years) before treatment, after treatment with extraction of one maxillary first molar and Begg appliances and after at least 1.8 years in retention were retrospectively collected from a private practice. M2 and M3 inclination angles (M2/ITP, M2/IOP, M3/ITP, M3/IOP), constructed by intertuberosity (ITP) and interorbital planes (IOP), were calculated for the extracted and nonextracted segments. Random effects regression analysis was performed to evaluate the effect on the molar angulation of extraction, time, and gender after adjusting for baseline measurements. RESULTS: Time and extraction status were significant predictors for M2 angulation. M2/ITP and M2/IOP decreased by 4.04 (95% confidence interval [CI]: -6.93, 1.16; P  =  .001) and 3.67 (95% CI: -6.76, -0.58; P  =  .020) in the extraction group compared to the nonextraction group after adjusting for time and gender. The adjusted analysis showed that extraction was the only predictor for M3 angulation that reached statistical significance. M3 mesial inclination increased by 7.38° (95% CI: -11.2, -3.54; P < .001) and 7.33° (95% CI: -11.48, -3.19; P  =  .001). CONCLUSIONS: M2 and M3 uprighting significantly improved in the extraction side after orthodontic treatment with unilateral maxillary M1 extraction. There was a significant increase in mesial tipping of maxillary second molar crowns over time.

OBJECTIVES: This study aimed to quantify the patterns of shape variability and the extent and patterns of shape covariation between the upper and lower dental arch in an orthodontic population. METHODS: Dental casts of 133 white subjects (61 males, 72 females; ages 10.6-26.6) were scanned and digitized in three dimensions. Landmarks were placed on the incisal margins and on the cusps of canines, premolars, and molars. Geometric morphometric methods were applied (Procrustes superimposition and principal component analysis). Sexual dimorphism and allometry were evaluated with permutation tests and age-size and age-shape correlations were computed. Two-block partial least squares analysis was used to assess covariation of shape. RESULTS: The first four principal components represented shape patterns that are often encountered and recognized in clinical practice, accounting for 6-31 per cent of total variance. No shape sexual dimorphism was found, nevertheless, there was statistically significant size difference between males and females. Allometry was statistically significant, but low (upper: R(2) = 0.0528, P < 0.000, lower: R (2) = 0.0587, P < 0.000). Age and shape were weakly correlated (upper: R(2) = 0.0370, P = 0.0001, lower: R (2) = 0.0587, P = 0.0046). Upper and lower arches covaried significantly (RV coefficient: 33 per cent). The main pattern of covariation between the dental arches was arch width (80 per cent of total covariance); the second component related the maxillary canine vertical position to the mandibular canine labiolingual position (11 per cent of total covariance). LIMITATIONS: Results may not be applicable to the general population. Age range was wide and age-related findings are limited by the cross-sectional design. Aetiology of malocclusion was also not considered. CONCLUSIONS: Covariation patterns showed that the dental arches were integrated in width and depth. Integration in the vertical dimension was weak, mainly restricted to maxillary canine position.

The commingling of human remains often hinders forensic/physical anthropologists during the identification process, as there are limited methods to accurately sort these remains. This study investigates a new method for pair-matching, a common individualization technique, which uses digital three-dimensional models of bone: mesh-to-mesh value comparison (MVC). The MVC method digitally compares the entire three-dimensional geometry of two bones at once to produce a single value to indicate their similarity. Two different versions of this method, one manual and the other automated, were created and then tested for how well they accurately pair-matched humeri. Each version was assessed using sensitivity and specificity. The manual mesh-to-mesh value comparison method was 100 % sensitive and 100 % specific. The automated mesh-to-mesh value comparison method was 95 % sensitive and 60 % specific. Our results indicate that the mesh-to-mesh value comparison method overall is a powerful new tool for accurately pair-matching commingled skeletal elements, although the automated version still needs improvement.

BACKGROUND: The anterior component of occlusal force (ACF), considered to result from the mesial inclination of teeth relative to the occlusal plane, has been estimated by indirectly measuring contact point tightness (CPT) through interproximal insertion of metal strips. ACF has been observed concurrently with a posterior component, whose theoretical origin is difficult to explain. OBJECTIVES: Evaluate ACF by measuring CPT directly, and integrate current data to propose a theoretical basis for ACF. MATERIALS AND METHODS: The sample comprised 14 females (age: 22.3±2.8) and 16 males (age: 20.8±2.5). Our device consisted of two force sensors: one for measuring maximum bite force (MBF) (overall thickness: 4mm), and one for measuring CPT directly (0.2mm thick), inserted between the lower first molar and second premolar. ACF was computed as the difference in CPT between the biting (at 75 per cent of MBF) and non-biting conditions. RESULTS: Averages of MBF, CPT, and ACF were 666.67 [standard deviation (SD): 36.06], 6.74 (SD: 1.17), and 20.59 (SD: 4.60) N, respectively. ACF, CPT, and MBF were higher in males by approximately 28, 18 and 7 per cent, respectively. A positive correlation was observed between ACF and MBF (R (2): 0.64). CPT was also significantly correlated to MBF (R (2): 0.40). Biomechanical analysis indicates that previously offered explanations do not unriddle the concurrent increase of CPT at anterior and posterior contact points. CONCLUSIONS: ACF was related to bite force by a logarithmic model. We speculate that CPT increases during biting through a combination of mesial tipping of teeth and mandibular bending.

BACKGROUND: The objective of this study was to investigate whether multistranded fixed retainers prevented overeruption of unopposed mandibular second molars in maxillary first molar extraction cases. METHODS: The panoramic radiographs of 65 Class II Division 1 Caucasian Whites (28 females, 37 males) consecutively treated with bilateral maxillary first molar extraction and the Begg technique, and with records taken after treatment (T1) and in retention (T2), were withdrawn from private practice records. After appliance removal, mandibular second molars were retained with sectional wires till at least T2 in case of lack of occlusal contact with the antagonist. The subjects were assigned to study-retention and control-nonretention groups based on the retention status of mandibular second molars. Radiographic analysis was carried out to determine inclination of mandibular molars and the resulting movement of second molar centroids. Parametric and nonparametric tests were performed to assess the changes between T1 and T2. RESULTS: No statistically significant differences in molar inclination were observed between groups and timepoints (P > 0.05). There were no statistically significant differences in molar movement percentages (P > 0.05) irrespective of whether fixed retention had been used or not. CONCLUSIONS: No significant eruption occurred in unopposed mandibular second molars bonded with fixed sectional retainers compared to molars partially occluded with the antagonists without fixed retention. Given the study limitations, fixed retention should be considered with caution in restricting tooth overeruption in unopposed molars.

INTRODUCTION: Morphologic homogeneity is desirable in sample selection of clinical studies that evaluate methods of treating craniofacial discrepancies in orthodontics. The purposes of this study were to assess sample selection criteria commonly used in the orthodontic literature regarding their effectiveness in achieving morphologic homogeneity, and to propose a method that can guarantee selection of a homogeneous sample, for which the degree of homogeneity and the average skeletal pattern can be specified a priori. METHODS: Pretreatment lateral cephalograms from 170 consecutive patients (82 boys, 88 girls) aged 7 to 17 years were used. Sixteen skeletal and 4 dental landmarks were digitized and processed with Procrustes superimposition and principal component analysis. The sample was bootstrapped to a virtual population of 10,000 subjects by random sampling from the normal distribution for each principal component. A systematic literature search of randomized controlled trials showed that the most prevalent sample selection criteria, in addition to molar relationship, included overjet, ANB, and SN-GoGn. Each criterion was applied to the virtual population. The morphologic homogeneity of the samples was assessed as the percentage of shape variance of each sample relative to the shape variance of the population. RESULTS: The first 3 principal components incorporated approximately 53% of shape variability. The evaluated criteria achieved low or moderate morphologic homogeneity scores (range, 28%-63%), and the selected patients were widely spread in the shape space. Although the criteria are commonly applied for selecting samples with skeletal discrepancies, a considerable number of subjects with an average shape were selected. The proposed procedure entails selecting a skeletal pattern appropriate for the study's purpose, setting limits in shape space within which the sample should be confined, and testing candidate patients against these limits. The patients within these boundaries have, by definition, a similar shape to the selected skeletal pattern and form a homogeneous sample. CONCLUSIONS: The cephalometric variables that have been used in randomized controlled trials do not result in samples of high morphologic homogeneity. The proposed method guarantees high morphologic homogeneity. The extent of homogeneity, the average shape of the sample, and the sample's relationship to the general population's average can be specified a priori.

OBJECTIVES: Chewing efficiency may be evaluated using cohesive specimen, especially in elderly or dysphagic patients. The aim of this study was to evaluate three two-coloured chewing gums for a colour-mixing ability test and to validate a new purpose built software (ViewGum©). METHODS: Dentate participants (dentate-group) and edentulous patients with mandibular two-implant overdentures (IOD-group) were recruited. First, the dentate-group chewed three different types of two-coloured gum (gum1-gum3) for 5, 10, 20, 30 and 50 chewing cycles. Subsequently the number of chewing cycles with the highest intra- and inter-rater agreement was determined visually by applying a scale (SA) and opto-electronically (ViewGum©, Bland-Altman analysis). The ViewGum© software determines semi-automatically the variance of hue (VOH); inadequate mixing presents with larger VOH than complete mixing. Secondly, the dentate-group and the IOD-group were compared. RESULTS: The dentate-group comprised 20 participants (10 female, 30.3±6.7 years); the IOD-group 15 participants (10 female, 74.6±8.3 years). Intra-rater and inter-rater agreement (SA) was very high at 20 chewing cycles (95.00-98.75%). Gums 1-3 showed different colour-mixing characteristics as a function of chewing cycles, gum1 showed a logarithmic association; gum2 and gum3 demonstrated more linear behaviours. However, the number of chewing cycles could be predicted in all specimens from VOH (all p<0.0001, mixed linear regression models). Both analyses proved discriminative to the dental state. CONCLUSION: ViewGum© proved to be a reliable and discriminative tool to opto-electronically assess chewing efficiency, given an elastic specimen is chewed for 20 cycles and could be recommended for the evaluation of chewing efficiency in a clinical and research setting. CLINICAL SIGNIFICANCE: Chewing is a complex function of the oro-facial structures and the central nervous system. The application of the proposed assessments of the chewing function in geriatrics or special care dentistry could help visualising oro-functional or dental comorbidities in dysphagic patients or those suffering from protein-energy malnutrition.

BACKGROUND: Mesial protraction of mandibular posterior teeth requires increased anchorage to avoid undesired tooth movements. Orthodontic mini-implants have become a popular and successful way to increase skeletal anchorage in such cases. However, mini-implants may cause injury to adjacent teeth or anatomical structures and may lead to tissue inflammation. Induced ankylosed primary teeth have been used in the past as abutments for the protraction of the maxilla in cases of maxillary retrognathism. However, this technique has not been described in the literature for the protraction of mandibular molars. The aim of this paper is to present, through a case report, an alternative to mini-implant devices to maximize anchorage in the mandible by inducing ankylosis on a primary molar. FINDINGS: A 13-year-old female with class II right malocclusion, deep bite, and congenitally missing right second premolars was referred for orthodontic treatment. Treatment plan involved removal of the primary teeth and mesial protraction of the posterior. In the mandible, ankylosis was induced on the retained primary second molar by extraction, bisection, replantation of the mesial part after endodontic treatment, and bonding of a rigid splint. Ankylosis was diagnosed after 10 weeks and a closing T-loop sectional wire was inserted to move the permanent first molar mesially. At 6 months, the remaining space was closed using elastic chain on a rectangular stainless steel wire with tip-back bends, supported by class II elastics. CONCLUSIONS: Induced ankylosis of primary teeth can be an alternative to orthodontic mini-implants in selected cases, with minimal risks and maximum biocompatibility.

OBJECTIVES: The 2D:4D ratio is sexually dimorphic and is considered a proxy of prenatal androgen levels, or, according to recent evidence, is related to genes involved in ocular and palate development. Our aim was to investigate correlation between the 2D:4D ratio and the shape of the craniofacial skeleton in a population of prepubertal children. METHODS: We conducted a cross-sectional study in a group of 58 male and 59 female prepubertal children aged 7-12 years. Craniofacial shape was evaluated using 15 skeletal landmarks on lateral cephalometric radiographs and fingers were measured with a computer-assisted procedure that involved tracing the finger outline. Geometric morphometric analysis was applied to the craniofacial landmarks and multivariate regression between digit ratios and craniofacial shape was computed in shape space and form space. RESULTS: The male 2D:4D ratio was smaller than the female ratio (Cohen's d: 0.275 left hand, 0.126 right hand), but the difference was not statistically significant. Craniofacial shape did not show sexual dimorphism, but males were larger than females. No correlation was found between digit ratio and craniofacial shape in prepubertal children, either for the whole sample or for any of the two sex groups. CONCLUSIONS: As several factors might be involved in the development and growth of both the craniofacial complex and fingers, the 2D:4D ratio, a putative proxy for fetal sex-hormone levels, is probably unable to impose a measurable effect within the variation of a normal population. Future research needs to examine an adult sample for potential covariation arising after the pubertal growth spurt.

The occurrence of mutual genetic loci in morphogenesis of the face and teeth implies shape covariation between these structures. However, teeth finalize their shape at an early age, whereas the face grows and is subjected to environmental influences for a prolonged period; it is therefore conceivable that covariation might modulate with age. Here we investigate the extent of this covariation in humans by measuring the 3D shape of the occlusal surface of the permanent first molars and the shape of the craniofacial complex from lateral radiographs, at two maturations stages. A sample of Greek subjects was divided into two groups (110 adult, 110 prepubertal) with equally distributed gender. The occlusal surfaces of the right first molars were 3D scanned from dental casts; 265 and 274 landmarks (including surface and curve semilandmarks) were digitized on the maxillary and mandibular molars, respectively. The corresponding lateral cephalometric radiographs were digitized with 71 landmarks. Geometric morphometric methods were used to assess shape variation and covariation. The vertical dimension of the craniofacial complex was the main parameter of shape variation, followed by anteroposterior deviations. The male craniofacial complex was larger (4.0-5.7%) and was characterized by a prominent chin and clockwise rotation of the cranial base (adult group only). Allometry was weak and statistically significant only when examined for the sample as a whole (percent variance explained: 2.1%, P = 0.0002). Covariation was statistically significant only between the lower first molar and the craniofacial complex (RV = 14.05%, P = 0.0099, and RV = 12.31%, P = 0.0162, for the prepubertal and adult groups, respectively). Subtle age-related covariation differences were noted, indicating that environmental factors may influence the pattern and strength of covariation. However, the main pattern was similar in both groups: a class III skeletal pattern (relative maxillary retrusion and mandibular protrusion), hyperdivergency, forward rotation of the posterior cranial base and upward rotation of the anterior cranial base were associated with mesiodistal elongation of the lower molars and height reduction of their distal cusps. This pattern mimics phylogeny in humans, where flexion and counterclockwise rotation of the cranial base, considered advantageous to survival, co-occur with tooth reductions that cannot be easily explained in evolutionary terms. The similarity of the phylogenetic and covariation patterns seems to support the pleiotropic gene hypothesis.

Dental casts of 160 Greek subjects (80 males, 80 females) were scanned by a structured-light scanner. The upper and lower right first molar occlusal surface 3D meshes were processed using geometric morphometric methods. A total of 265 and 274 curve and surface sliding semilandmarks were placed on the upper and lower molar surfaces, respectively. Principal component analysis and partial least square analysis were performed to assess shape parameters. Molars tended to vary between an elongated and a more square form. The first two principal components (PCs), comprising almost 1/3 of molar shape variation, were related to mesiodistal-buccolingual ratios and relative cusp position. Distal cusps displayed the greatest shape variability. Molars of males were larger than those of females (2.8 and 3.2% for upper and lower molars respectively), but no shape dimorphism was observed. Upper and lower molar sizes were significantly correlated (r(2) = 0.689). Allometry was observed for both teeth. Larger lower molars were associated with shorter cusps, expansion of the distal cusp, and constriction of the mesial cusps (predicted variance 3.25%). Upper molars displayed weaker allometry (predicted variance 1.59%). Upper and lower molar shape covariation proved significant (RV = 17.26%, P < 0.0001). The main parameter of molar covariation in partial least square axis 1, contributing to 30% of total covariation, was cusp height, in contrast to the primary variability traits exhibited by PC1 and PC2. The aim of this study was to evaluate shape variation and covariation, including allometry and sexual dimorphism, of maxillary and mandibular first permanent molar occlusal surfaces.

Blending of chewing gums of different colours is used in the clinical setting, as a simple and reliable means for the assessment of chewing efficiency. However, the available software is difficult to use in an everyday clinical setting, and there is no possibility of automated classification of the patient's chewing ability in a graph, to facilitate visualisation of the results and to evaluate potential chewing difficulties. The aims of this study were to test the validity of ViewGum - a novel image analysis software for the evaluation of boli derived from a two-colour mixing ability test - and to establish a baseline graph for the representation of the masticatory efficiency in a healthy population. Image analysis demonstrated significant hue variation decrease as the number of chewing cycles increased, indicating a higher degree of colour mixture. Standard deviation of hue (SDHue) was significantly different between all chewing cycles. Regression of the log-transformed values of the medians of SDHue on the number of chewing cycles showed a high statistically significant correlation (r² = 0.94, P < 0.01). ViewGum eliminates drawbacks of previous two-colour chewing gum test methods by the simplicity of its application. The newly developed ViewGum software provides speed, ease of use and immediate extraction of clinically useful conclusions to the already established method of chewing efficiency evaluation and is a valid adjunct for the evaluation of masticatory efficiency with two-colour chewing gum.

This investigation aimed to quantify craniofacial variation in a sample of modern humans. In all, 187 consecutive orthodontic patients were collected, of which 79 were male (mean age 13.3, SD 3.7, range 7.5-40.8) and 99 were female (mean age 12.3, SD 1.9, range 8.7-19.1). The male and female subgroups were tested for differences in mean shapes and ontogenetic trajectories, and shape variability was characterized using principal component analysis. The hypothesis of modularity was tested for six different modularity scenarios. The results showed that there were subtle but significant differences in the male and female Procrustes mean shapes. Males were significantly larger. Mild sexual ontogenetic allometric divergence was noted. Principal component analysis indicated that, of the four retained biologically interpretable components, the two most important sources of variability were (i) vertical shape variation (i.e. dolichofacial vs. brachyfacial growth patterns) and (ii) sagittal relationships (maxillary prognatism vs. mandibular retrognathism, and vice versa). The mandible and maxilla were found to constitute one module, independent of the skull base. Additionally, we were able to confirm the presence of an anterior and posterior craniofacial columnar module, separated by the pterygomaxillary plane, as proposed by Enlow. These modules can be further subdivided into four sub-modules, involving the posterior skull base, the ethmomaxillary complex, a pharyngeal module, and the anterior part of the jaws.

INTRODUCTION: Our objective was to investigate potential associations between maxillary sinus floor extension and inclination of maxillary second premolars and second molars in patients with Class II Division 1 malocclusion whose orthodontic treatment included maxillary first molar extractions. METHODS: The records of 37 patients (18 boys, 19 girls; mean age, 13.2 years; SD, 1.62 years) treated between 1998 and 2004 by 1 orthodontist with full Begg appliances were used in this study. Inclusion criteria were white patients with Class II Division 1 malocclusion, sagittal overjet of ≥4 mm, treatment plan including extraction of the maxillary first permanent molars, no missing teeth, and no agenesis. Maxillary posterior tooth inclination and lower maxillary sinus area in relation to the palatal plane were measured on lateral cephalograms at 3 time points: at the start and end of treatment, and on average 2.5 years posttreatment. Data were analyzed for the second premolar and second molar inclinations by using mixed linear models. RESULTS: The analysis showed that the second molar inclination angle decreased by 7° after orthodontic treatment, compared with pretreatment values, and by 11.5° at the latest follow-up, compared with pretreatment. There was evidence that maxillary sinus volume was negatively correlated with second molar inclination angle; the greater the volume, the smaller the inclination angle. For premolars, inclination increased by 15.4° after orthodontic treatment compared with pretreatment, and by 8.1° at the latest follow-up compared with baseline. The volume of the maxillary sinus was not associated with premolar inclination. CONCLUSIONS: We found evidence of an association between maxillary second molar inclination and surface area of the lower sinus in patients treated with maxillary first molar extractions. Clinicians who undertake such an extraction scheme in Class II patients should be aware of this potential association and consider appropriate biomechanics to control root uprighting.

In this longitudinal study, the craniofacial morphology and evaluated soft tissue profile changes, at 6 and 12 years of age in patients with complete bilateral cleft lip and palate (CBCLP) were compared. Lateral cephalograms from 148 patients with CBCLP, treated consecutively at three European cleft centers, Gothenburg (n (A) = 37), Nijmegen (n (B) = 26), and Oslo (n (C) = 85), were evaluated. Eighteen hard tissue and ten soft tissue landmarks were digitized. Paired t test, Pearson's correlation coefficients, and multiple regression models were applied for statistical analysis. ANOVA and Tukey-B, as a post hoc test, were used to evaluate the increments and compare centers. Hard and soft tissue data were superimposed using the generalized Procrustes analysis. For Nijmegen, the increments of the variables SNA, ANB, SN-NL, SN-ML, NL-ML, Snss, and Snpg were significantly different than the two other centers (p = 0.041 to <0.001). SNPg increments were significantly different between Nijmegen and Oslo (p = 0.002). The three cleft centers followed different treatment protocols, but the main differences in craniofacial morphology until 12 years of age were the growth pattern and the maxillary and upper incisor variables. Follow-up of these patients until facial growth has ceased, which may elucidate components for improving treatment outcome.

OBJECTIVES: To evaluate the effectiveness of non-steroidal anti-inflammatory drugs (NSAIDs) in managing pain arising from orthodontic interventions, such as archwire or separators placement. DATA SOURCES: Medline and Cochrane databases searched in February 2010 and updated in July 2010 using orthodontics and pain as the search terms. Additional studies located from Google Scholar, Clinical Trials and the reference lists of retrieved articles. STUDY SELECTION: Randomized controlled trials comparing NSAID to placebo using visual analogue scale (VAS) scores. DATA SYNTHESIS: Of the 1127 studies identified through database searches, seven were included for meta-analysis. Treatment effects (Hedges' g using random effects model) and 95% confidence intervals (CI) of the pain VAS scores were evaluated at 2, 6 and 24 h after intervention, during chewing and biting activities. Pain level at 2 h differed between the ibuprofen and placebo groups during biting (95% CI: -0.178 to -0.046), but not during chewing (95% CI: -0.551 to 0.148). At 6 h, the ibuprofen group exhibited lower pain levels during both activities (chewing 95% CI: -0.640 to -0.123, biting 95% CI: -0.857 to -0.172). At 24 h, no statistically significant difference could be detected between ibuprofen and placebo (chewing 95% CI: -0.642 to 0.112, biting 95% CI: -0.836 to 0.048). No statistically significant difference was found between ibuprofen and acetaminophen at any time point. CONCLUSION: Ibuprofen appears to lower orthodontic pain compared to placebo at 2 and 6 h after separators or archwire placement, but not at 24 h, when pain peaks.

INTRODUCTION: The aim of this study was to assess the changes in inclination of the maxillary second (M2) and third (M3) molars after orthodontic treatment of Class II Division 1 malocclusion with extraction of maxillary first molars. METHODS: Two groups of subjects were studied. The experimental group consisted of 37 subjects, 18 boys and 19 girls (mean age, 13.2 ± 1.62 years). The inclusion criteria were white origin, Class II Division 1 malocclusion, overjet ≥4 mm, no missing teeth or agenesis, and maxillary M3 present. All patients were treated with extraction of the maxillary first molars and the Begg technique. Standardized lateral cephalometric radiographs were taken at the start of active treatment (T1) and at least 3.7 years posttreatment (T2). The control group was drawn from the archives of the Nittedal Growth Material (Oslo University, Oslo, Norway) and included 54 untreated Class I and Class II subjects,18 boys and 36 girls (mean age, 13.4 ± 1.99 years) followed up for a minimum of 3.6 years. M2 and M3 inclinations relative to the palatal plane (PP) and functional occlusal plane (FOP) were measured and compared between groups and time periods. RESULTS: M2 to PP inclination improved significantly in both the control group (M2-PP at T1, 17.7° ± 5.81°, and at T2, 11.9° ± 4.61°) and the experimental group (M2-PP at T1, 26.7° ± 5.75°, and at T2, 6.9° ± 6.76°). There were also significant increases of the mesial inclination of M3 in the control group (M3-PP at T1, 30.1° ± 8.54°, and at T2, 19.6° ± 9.01°) and extraction group (M3-PP at T1, 32.2° ± 7.90°, and at T2, 12.8° ± 7.36°). By using the FOP as the reference system, no significant change in the inclination of M2 was observed in the control group, whereas, in the extraction group, although more distally inclined at T1, M2 ended up mesially inclined at T2 (M2-FOP at T1, 14.2° ± 4.62°, and at T2, -6.2° ± 6.10°; P <0.0001). M3 inclinations were similar between the groups at T1 (M3-FOP control, 17.3° ± 9.35°; M3-FOP experimental, 19.6° ± 7.37°), and these improved significantly in both groups. However, M3 uprighting was almost 4 times greater in the extraction group (M3-FOP from T2-T1, 5.6° vs 19.9°). The greatest distal inclination of M3 at T2 in the extraction group was 9.4°, a value attained by only 43% of the control group. CONCLUSIONS: Extraction of the maxillary first molars in Class II Division 1 patients results in significant uprighting of M2 and M3 and facilitates the normal eruption of M3.

INTRODUCTION: The dilemma of extraction vs nonextraction treatment, along with the uncertain potential of orthodontic treatment to control vertical dimensions, still remains among the most controversial issues in orthodontics. The aim of this study was to evaluate 2 contradictory treatment protocols for hyperdivergent Class II Division 1 malocclusion regarding their effectiveness in controlling vertical dimensions. METHODS: The subjects were retrospectively selected from 2 orthodontic offices that used contrasting treatment protocols. The patients had similar hyperdivergent skeletal patterns, malocclusion patterns, skeletal ages, and sexes. Group A (29 patients) was treated with 4 first premolar extractions and "intrusive" mechanics (eg, high-pull headgear), whereas group B (28 patients) was treated nonextraction with no regard to vertical control (eg, cervical headgear, Class II elastics). Twenty-seven landmarks were digitized on lateral cephalometric radiographs before and after treatment, and 14 measurements were assessed. Geometric morphometric methods were also implemented to evaluate size and shape differences. RESULTS: As expected, the maxillary and mandibular molars translated mesially and the mandibular incisors uprighted in group A but remained approximately unchanged in group B. The vertical positions of the molars and the incisors were similar between groups before and after treatment, although they were altered by treatment or growth. No significant differences were observed in the posttreatment skeletal measurements between the 2 groups, including vertical variables, which remained unaltered. Permutation tests on Procrustes distances between skeletal shapes confirmed these results. CONCLUSIONS: This study demonstrated the limitations of conventional orthodontics to significantly alter skeletal vertical dimensions. More important factors are probably responsible for the development and establishment of the vertical skeletal pattern, such as neuromuscular balance and function.

INTRODUCTION: Correlations between cephalometric measurements are frequently assumed to represent biologic associations. However, a significant portion of such correlations might arise from purely geometric dependencies, when measurements share common landmarks. Analytic calculation of this topographic component is difficult. The purpose of this study was to propose a permutation method for evaluating the topographic component of cephalometric correlations. METHODS: The method consisted of creating a virtual sample of cephalometric tracings (landmark configurations) from the original biologic sample under investigation. Each novel landmark configuration was constructed by assigning coordinates to the cephalometric points; the coordinates of each point were taken randomly from the original sample, each from a potentially different subject. Correlation analysis was performed separately on both samples and the results compared. Biologic meaning was ascribed only when there was a significant difference in correlation values between the samples. Confidence intervals for assessing statistical significance were calculated by using a randomization approach. The method was tested on a sample of 170 radiographs to evaluate the correlation between cranial base angle (NSBa) and angles SNA and SNB, as well as between ANB angle and the Wits appraisal. RESULTS: No biologic association was found between ANB and Wits, or between NSBa and SNA. The biologic correlation between NSBa and SNB was statistically significant but low (r(2) = 12%). CONCLUSIONS: Topographic associations between cephalometric measurements are ubiquitous and difficult to assess. The proposed method enables evaluation of their relative strength without the need for analytic solutions.

The present study investigates whether the human mandible is sexually dimorphic during early postnatal development and whether early dimorphic features persist during subsequent ontogeny. We also examine whether mandibular dimorphism is linked to dimorphism of dental development. Dense CT-derived mandibular meshes of 84 females and 75 males, ranging from birth to adulthood, were analyzed using geometric morphometric methods. On the basis of the specimen's chronological ages and mineralization stages of the deciduous and permanent teeth, we compute dental age as proxy for dental development by the additive conjoint measurement method. By birth, males have, on average, more advanced age-specific shapes than females. However, sex differences decrease quickly as females catch up via a different association between shape and size. This leads to an almost complete reduction of sexual dimorphism between the ages of 4 and 14. From puberty to adulthood, males are characterized by allometric shape changes while the shape of the female mandible continues to change even after size has ceased to increase. Dimorphism of dental maturation becomes visible only at puberty. Sexual dimorphism, concentrated at the ramus and the mental region during the earliest ontogenetic stages and again at adulthood, is not associated with the development of the teeth. At puberty there is a simultaneous peak in size increase, shape development, and dental maturation likely controlled by the surge of sex hormones with a dimorphic onset age. We argue that the infant and adult dimorphism of the mental region may be associated with the development of supralaryngeal structures.

The aim of this study was to compare craniofacial morphology and soft tissue profiles in patients with complete bilateral cleft lip and palate at 9 years of age, treated in two European cleft centres with delayed hard palate closure but different treatment protocols. The cephalometric data of 83 consecutively treated patients were compared (Gothenburg, N=44; Nijmegen, N=39). In total, 18 hard tissue and 10 soft tissue landmarks were digitized by one operator. To determine the intra-observer reliability 20 cephalograms were digitized twice with a monthly interval. Paired t-test, Pearson correlation coefficients and multiple regression models were applied for statistical analysis. Hard and soft tissue data were superimposed using the Generalized Procrustes Analysis. In Nijmegen, the maxilla was protrusive for hard and soft tissue values (P=0.001, P=0.030, respectively) and the maxillary incisors were retroclined (P<0.001), influencing the nasolabial angle, which was increased in comparison with Gothenburg (P=0.004). In conclusion, both centres showed a favourable craniofacial form at 9-10 years of age, although there were significant differences in the maxillary prominence, the incisor inclination and soft tissue cephalometric values. Follow-up of these patients until facial growth has ceased, may elucidate components for outcome improvement.

The primary aim of the present study was to assess morphological covariation between the face and the basicranium (midline and lateral), and to evaluate patterns of integration at two specific developmental stages. A group of 71 children (6-10 years) was compared with a group of 71 adults (20-35 years). Lateral cephalometric radiographs were digitized and a total of 28 landmarks were placed on three areas; the midline cranial base, the lateral cranial base and the face. Geometric morphometric methods were applied and partial least squares analysis was used to evaluate correlation between the three shape blocks. Morphological integration was tested both with and without removing the effect of allometry. In children, mainly the midline and, to a lesser extent, the lateral cranial base were moderately correlated to the face. In adults, the correlation between the face and the midline cranial base, which ceases development earlier than the lateral base, was reduced. However, the lateral cranial base retained and even strengthened its correlation to the face. This suggests that the duration of common developmental timing is an important factor that influences integration between craniofacial structures. However, despite the apparent switch of primary roles between the cranial bases during development, the patterns of integration remained stable, thereby supporting the role of genetics over function in the establishment and development of craniofacial shape.

The purpose of this study was to propose a growth-based structural superimposition method for assessment of cervical vertebral fusion and evaluate variations and abnormalities of the upper cervical vertebrae. Standardized lateral cephalograms of 156 patients (69 males and 87 females, age range 6-20 years), representing a skeletally heterogeneous orthodontic population, were used. Primary criterion for sample selection was the existence of at least two lateral cephalograms, one taken before orthodontic treatment, which depicted the first four cervical vertebrae. The abnormalities of the vertebrae were estimated by visual assessment and structural superimposition. Lateral cephalometric analysis was conducted in order to correlate vertebral anomalies to skeletal pattern. Descriptive statistics were calculated for all variables and interobserver agreement was evaluated using the kappa statistic. Four patients (2.6 per cent) were found to have secondary ossicles in close relationship to the first cervical vertebra, while in 7.4 per cent, the vertebral arteries of the atlas were surrounded by a complete ring-shaped osseous structure. Three cephalograms showed atlas posterior arch dehiscence. After visual examination, 14 patients were provisionally identified as presenting fusion between the second and third cervical vertebrae. However, growth-based superimposition of the radiographs disclosed that no patient showed actual fusion, even though the lateral cephalometric analysis revealed sufficient extreme skeletal patterns, which have been previously related to vertebral fusion. The findings of this study demonstrated a low percentage of atlas anomalies. It was not possible to correlate skeletal pattern to fusion of cervical vertebrae because no fusions were found. Subjective visual examination of a single cephalogram may result in false-positive findings of fusion and growth-based superimposition is recommended.

Comparison of the early development of the mandibular symphysis between primates and modern humans is of particular interest in human palaeontology. Using geometric morphometric methods, we explored and compared the ontogenetic shape changes of 14 chimpanzee mandibles (Pan troglodytes) against 66 human CT-scanned mandibles over the age range from fetal life to the complete emergence of the deciduous dentition in a visualization incorporating the deciduous tooth arrangement. The results reveal that the symphysis is anteriorly inclined in the youngest chimpanzee fetuses but develops an increasingly vertical orientation up until birth. At the same time, the anterior teeth reorient before a vertical emergence, and a symphyseal tuber appears on the labial side. When the deciduous canine emerges, the symphysis inclines anteriorly again, exhibiting the adult characteristic slope. These two phases are characterized by a repositioning of the simian shelf. Unlike chimpanzees, the human symphysis remains vertical throughout fetal development. However, the combination of morphological changes observed in chimpanzee fetuses is similar to that of modern humans after birth, as the mental region projects forward. By elongating the alveolar process, the inclination of the chimpanzee symphysis could be a key event for emergence of the deciduous canine, as space is lacking at the alveolar ridge in a vertical symphysis once the deciduous incisors and molars have emerged. The repositioning of the simian shelf suggests that the suprahyoid muscles have a significant influence on the anterior growth of the symphysis. The anteroposterior positioning of the basal symphysis in both species may be related to hyoid bone position during ontogeny.

The aim of the present study was the determination of the levels of osteoprotegerin and soluble RANKL in blood serum and in gingival crevicular fluid relative to the degree of orthodontic root resorption in a rat model. Blood samples and gingival crevicular fluid were collected from fourteen 6-month-old male Wistar rats weighing 350-500 g. A 25-g closed orthodontic coil spring was inserted between each upper right first molar and the upper incisors. After 21 days of loading, both upper first molars (treated and control) were extracted and studied under microcomputed tomography scanning. Statistical analysis demonstrated a positive linear correlation between the initial concentration of RANKL in blood serum and the degree of root resorption. The ratio of the initial concentrations of osteoprotegerin to RANKL in blood serum proved to be an independent prognostic factor of the degree of root resorption. The initial concentration of RANKL in gingival crevicular fluid showed a negative correlation to the initial concentration of RANKL in blood serum and for a finite range of initial concentrations of osteoprotegerin in gingival crevicular fluid, the dental root seemed protected against extreme external root resorption. Finally, the concentration of osteoprotegerin in blood serum decreased significantly in cases of severe root resorption.

Studies have suggested that dental development substantially influences the variation of mandibular morphology and growth in primates. As a contribution to the methodology of such studies, we introduce a novel approach to quantifying the covariation between teeth and mandible. This was done showing fluctuations in the magnitude of this covariation within a sample of modern human mandibles at different postnatal ages. Dense CT- derived mandibular surface meshes of 73 females and 71 males, ranging in age from birth to adulthood, were processed by methods of geometric morphometrics. Each specimen's deciduous and permanent teeth were rated for mineralization stage. Form-space principal component analysis of the morphometric data was used to produce a single metric variable that best explains mandibular-form variation. This variable was then used to quantify the developing teeth, all together, through the use of the additive conjoint measurement method. This new metric variable corresponds to the dental prediction of the mandibular-form variation. Finally, we examine the covariation of the two over the full range of mineralization stages. We found a strikingly tight association between mandibular form and dental maturation up through the full emergence of the deciduous dentition (about age 2 years), followed by an equally striking decline in that association in later developmental stages, particularly for girls. The onset of the decline of the teeth-mandible relationship coincides with the onset time of the adult-like pattern of mastication and speech. The increasingly functional diversity may lead to more independence between dental development and mandibular growth than during the first two years.

INTRODUCTION: Cervical vertebrae shape has been proposed as a diagnostic factor for assessing skeletal maturation in orthodontic patients. However, evaluation of vertebral shape is mainly based on qualitative criteria. Comprehensive quantitative measurements of shape and assessments of its predictive power have not been reported. Our aims were to measure vertebral shape by using the tools of geometric morphometrics and to evaluate the correlation and predictive power of vertebral shape on skeletal maturation. METHODS: Pretreatment lateral cephalograms and corresponding hand-wrist radiographs of 98 patients (40 boys, 58 girls; ages, 8.1-17.7 years) were used. Skeletal age was estimated from the hand-wrist radiographs. The first 4 vertebrae were traced, and 187 landmarks (34 fixed and 153 sliding semilandmarks) were used. Sliding semilandmarks were adjusted to minimize bending energy against the average of the sample. Principal components analysis in shape and form spaces was used for evaluating shape patterns. Shape measures, alone and combined with centroid size and age, were assessed as predictors of skeletal maturation. RESULTS: Shape alone could not predict skeletal maturation better than chronologic age. The best prediction was achieved with the combination of form space principal components and age, giving 90% prediction intervals of approximately 200 maturation units in the girls and 300 units in the boys. Similar predictive power could be obtained by using centroid size and age. Vertebrae C2, C3, and C4 gave similar results when examined individually or combined. C1 showed lower correlations, signifying lower integration with hand-wrist maturation. CONCLUSIONS: Vertebral shape is strongly correlated to skeletal age but does not offer better predictive value than chronologic age.

This case report describes the treatment of a patient whose maxillary left first premolar was impacted horizontally, and both maxillary canines were transposed relative to the first premolars. The patient was treated without extractions, and both canines were brought to their correct positions in the maxillary arch. Treatment mechanics during the various stages are discussed.

OBJECTIVE: Fluctuating dental asymmetry is considered a sensitive indicator of environmental stress. We used fluctuating asymmetry of teeth in Greek children to assess the effect of the Chernobyl accident to the Greek population, which received relatively large radiation exposure compared to other European countries. DESIGN: Sixty dental casts were divided into two groups according to date of birth prior to or after the Chernobyl accident. The intercuspal distances of the mandibular first permanent molars were measured with digital calipers. We followed the data analysis procedure proposed by Palmer and Strobeck (2003). RESULTS: Fluctuating asymmetry was found at levels above measurement error in all traits except for the buccal measurement. Overall, there were no significant differences in the fluctuating asymmetry between the two groups, after removal of outliers. CONCLUSIONS: These results suggest that environmental radioactivity from the Chernobyl incident did not significantly affect the symmetry of lower permanent molar intercuspal distances in the specific population, even though increased levels of radionuclides have been reported in teeth and other tissues.

Abstract Pataky, K., Villanueva, G., Liani, A., Zgheib, O., Jenkins, N., Halazonetis, D. J., Halazonetis, T. D. and Brugger, J. Microcollimator for Micrometer-Wide Stripe Irradiation of Cells Using 20-30 keV X Rays. Radiat. Res. 172, 252-259 (2009). The exposure of subnuclear compartments of cells to ionizing radiation is currently not trivial. We describe here a collimator for micrometer-wide stripe irradiation designed to work with conventional high-voltage X-ray tubes and cells cultured on standard glass cover slips. The microcollimator was fabricated by high-precision silicon micromachining and consists of X-ray absorbing chips with grooves of highly controlled depths, between 0.5-10 microm, along their surfaces. These grooves form X-ray collimating slits when the chips are stacked against each other. The use of this device for radiation biology was examined by irradiating human cells with X rays having energies between 20-30 keV. After irradiation, p53 binding protein 1 (53BP1), a nuclear protein that is recruited at sites of DNA double-strand breaks, clustered in lines corresponding to the irradiated stripes.

INTRODUCTION: Clinical assessment of facial type and facial proportions is an important element of orthodontic diagnosis and subsequent treatment planning. Because of the subjective nature of this procedure, it is important to identify factors that could affect final judgment. One such factor that has been shown to affect facial perception in general might be the configural relationship of internal parts of the face. Our aim in this study was to assess whether configural changes in a face affect the subjective evaluation of facial type. METHODS: The frontal photographs of 2 white boys, aged 12 years, with harmonious face were used. The photographs were manipulated by computer to produce realistic images of faces with various configural relationships of the features. The modifications were interocular distance enlarged by 3 mm or reduced by 3.6 mm, mouth width enlarged by 4.5 mm or reduced by 4.2 mm, and mouth moved vertically upward or downward by 2.8 mm. Two images with a true change of the frontal facial height by 4 mm were also produced. The images were presented in pairs to 20 experienced orthodontists. Each judge evaluated 36 pairs of images (including pairs of identical images), all belonging to the same patient, in a random sequence. The judges were unaware of the changes that had been made to the photographs and were asked to evaluate which of the 2 faces appeared longer. RESULTS: The judges correctly identified pairs of identical images with an accuracy of 42%. Reduction of the interocular distance and downward movement of the mouth caused the illusion of a longer face. The opposite changes had the reverse effect. Enlargement of the width of the mouth did not appear to influence the subjective impression of facial type, but reduction of mouth width had a statistically significant result, giving the impression of a longer face. CONCLUSIONS: Configural relationships among the constituent features of a face can influence our judgment about external facial proportions. Because of the importance of these factors in treatment planning, clinical evaluation of faces should be accompanied by objective assessment (measurement) of photographs, so that any illusory visual effects can be identified.

INTRODUCTION: Soft-tissue facial outline has been studied by conventional cephalometric methods, and differences between the 2 sexes have been identified, mainly related to size and timing of growth. However, shape per se was not sufficiently evaluated, especially regarding variability, age-related changes, and sexual dimorphism. The purpose of this study was to evaluate shape variability and sexual dimorphism of the soft-tissue outline by using morphometric methods. METHODS: Pretreatment lateral cephalograms from 170 consecutive patients (82 male, 88 female) aged 7 to 17 years were used. Fifteen skeletal and 22 soft-tissue landmarks were digitized and processed with Procrustes superimposition and principal component analysis. The principal components (PCs) of the soft-tissue shape were analyzed in relation to age and sex. RESULTS: The first 8 PCs explained approximately 90% of the total shape variability. The first coefficient (PC1) related to lip, nose, and chin prominence and included 36% of total shape variability. It was significantly correlated to age, but with a low coefficient of determination (r2 = 13%). The second coefficient (PC2) related to facial convexity and explained 18% of shape variability. The next 2 coefficients were mainly related to lower lip shape. Statistically significant sexual dimorphism was detected, but the overall shape differences between the average profiles of boys and girls were minor and barely detectable visually. Shape dimorphism was present both before and after the age of 12 years. CONCLUSIONS: Shape variability related mainly to relative lip protrusion, convexity of the face, and lower lip shape. Shape differences between the sexes seemed to exist even before the pubertal growth spurt, but they were small. Age changes in shape appeared more significant.

The purpose of this study was to use quantitative methods to measure the size and shape of the sella turcica and thus establish normative reference standards that could assist in a more objective evaluation and detection of pathological conditions. Standardized lateral cephalograms of 184 healthy Greeks (91 males and 93 females) were used. The age range was between 6 and 17 years. Conventional measurements included three different heights of the sella turcica (anterior, posterior, median), its length, and width, measured in relation to the Frankfort reference line. In addition, the area of sella turcica was calculated. Morphometric methods were used to assess shape. The tracings were superimposed using the Procrustes method, and the average shape was computed. Principal component analysis (PCA) was used to assess shape variability. The data were correlated with centroid size, age, and gender. Unpaired t-tests were used to determine gender differences. Sella height anteriorly was the only variable found to be significantly different between the genders, being larger in females by 0.5 mm. Linear and area measurements were found to be significantly correlated with age, but all correlations were low (r(2) below 8 per cent). Sella turcica shape, as described by PCA, was different between males and females, mainly at the posterior aspect of the sella outline. However, although there was an extensive overlap between the genders, and differences were minimal. Age was not found to be correlated with the shape coefficients, although, in the female group, the first principal component of shape was marginally not significant. Allometry was observed in both genders, the sella showing a tendency towards a flatter and wider shape with increase in size. The results of this study constitute quantitative reference data that could be used for objective evaluation of sella shape.

INTRODUCTION: Prediction of soft-tissue outline shape from skeletal remains is useful in forensics and archaeology. The inverse problem, the assessment of underlying skeletal relationships from the external appearance, is pertinent in orthodontics. The purposes of this study were to assess the correlation between craniofacial shape and shape of the soft-tissue profile outline and to determine the extent to which it might be possible to predict the latter from the former. METHODS: Lateral cephalograms from 170 consecutive orthodontic patients were used, and 17 skeletal, 2 dental, and 22 soft-tissue landmarks were digitized and processed by using Procrustes superimposition and principal component analysis. The principal components of the skeletal and soft-tissue shapes were entered into the correlation analysis. RESULTS: Significant correlations were found between the skeletal and the soft-tissue components. The use of 7 anterior skeletal landmarks (not including the nasal bone) resulted in a predictive power (coefficient of determination) of 38% of the variability of soft-tissue shape. This increased to almost 50% by adding nasal and incisor points but showed only a slight further improvement by incorporating posterior skeletal landmarks. CONCLUSIONS: Anterior skeletal and dental landmarks can be used to predict soft-tissue profile shape with a 50% power in children and adolescents.

INTRODUCTION: The purpose of this investigation was to study the shapes of the condyle and the glenoid fossa in patients with Class II Division 1, Class II Division 2, and Class III malocclusions. METHODS: Axially corrected tomograms of 189 patients were used (109 Class II Division 1, 47 Class II Division 2, and 33 Class III). Five points on the condyle and 7 on the outline of the fossa were digitized. Size was assessed by the centroid size of each structure, and measurements of shape were made by principal component analysis of the Procrustes residuals. RESULTS AND CONCLUSIONS: Inspection of the principal components of shape showed that shape variability of the condyle was mainly related to inclination of the condylar head; shape variability of the fossa was related to inclination of the eminence and fossa height. Centroid size was correlated to age in the Class III group only. Condylar and fossa shapes were found to be different between the groups; the Class III group had a more elongated and anteriorly inclined condylar head and a wider and shallower fossa. In the Class III group, the condyle was closer to the roof of the fossa. The 2 Class II divisions differed only in the position of the condyle in the fossa, which was situated more anteriorly in the Class II Division 1 group.

Computed tomography is entering the orthodontic specialty as a mainstream diagnostic modality. Radiation exposure and cost have decreased significantly, and the diagnostic value is very high compared with traditional radiographic options. However, 3-dimensional data present new challenges and need a different approach from traditional viewing of static images to make the most of the available possibilities. Advances in computer hardware and software now enable interactive display of the data on personal computers, with the ability to selectively view soft or hard tissues from any angle. Transfer functions are used to apply transparency and color. Cephalometric measurements can be taken by digitizing points in 3-dimensional coordinates. Application of 3-dimensional data is expected to increase significantly soon and might eventually replace many conventional orthodontic records that are in use today.

INTRODUCTION: The purpose of this study was to record and analyze the dynamic nature of spontaneous smiles. METHODS: Fifteen children (9 girls and 6 boys; average age, 10.5 years) were filmed with a hidden camera while they watched a funny cartoon video. Spontaneous smiles were recorded, and the video frames were digitized. Time-graphs of the measurements were constructed, and plots of the movement of the mouth points were drawn. RESULTS: Facial measurements showed that the upper lip elevated by 28%, relative to the rest position, and the mouth increased in width by 27%. The corners of the mouth moved laterally and superiorly at an angle of approximately 47 degrees . Time analysis showed that the smiles developed in a staged fashion. The first stage (attack phase) was the shortest, lasting an average 500 ms. It was followed by a sustaining phase that included waxing and waning. The smile ended with a fade-out stage. The second and third stages were of variable duration and could be interrupted by the attack phase of a subsequent smile. CONCLUSIONS: The dynamics of the spontaneous smile and the findings of this study raise concerns about the validity of a single photographic capture for esthetic assessment and treatment planning.

This article demonstrates morphometric methods by applying them to an orthodontic sample. A total of 150 pretreatment cephalograms of consecutive patients (84 female, 66 male) were traced and digitized. Fifteen points were used for the analysis. The tracings were superimposed by the Procrustes method, and shape variability was assessed by principal component analysis. Approximately 70% of the total sample variability was incorporated in the first 5 principal components. The most significant principal component, accounting for 29% of shape variability, was the divergence of skeletal pattern; the second principal component, accounting for 20% of shape variability, was the anteroposterior maxillary relationship. It is recommended that Procrustes superimposition and principal component analysis be incorporated into routine cephalometric analysis for more valid and comprehensive shape assessment.

Clinical trials comparing activator and headgear treatment have shown comparable effectiveness in the total result achieved, but the mechanism of correction is still uncertain. Most studies have used conventional cephalometric methods to evaluate treatment effects, and this might be a factor for the inconclusive results. The aim of this retrospective investigation was to compare the effects of activator and cervical headgear treatment with a superimpositional cephalometric method that could discern between vertical and horizontal effects as well as skeletal, dental, and rotational treatment results. The sample consisted of 2 groups of Class II Division 1 patients, treated without extraction by the same clinician (22 patients were treated with a modified activator-type functional appliance, and 30 patients were treated with a combination of cervical headgear and fixed edgewise appliances). Lateral cephalometric radiographs taken at the beginning of treatment and after Class II molar correction were evaluated conventionally and with a superimpositional method. Regarding the conventional cephalometric measurements, the only difference in the anteroposterior dimension between the 2 treatment modalities was the significantly reduced SNA angle in the headgear group. Both appliances appeared to produce minimal changes in FMA and GoGn-SN angles, and there were no statistically significant differences between the treatment groups. Regional superimpositions showed differences in the movement of molars: the maxillary molar was found to move more posteriorly and inferiorly in the headgear group. Conversely, the mandibular molar was found to move toward the occlusal plane more in the activator group. Assessment of mandibular skeletal changes showed that the mandible moved anteriorly by approximately 1 mm more in the activator than in the headgear group. The overall effect of the 2 appliances was found to be clinically comparable. However, the individual components of change showed differences characteristic of each appliance.

Estimated natural head position, or natural head orientation (NHO), has been proposed as a preferred reference position for assessing facial morphology. However, because this position is subjectively defined by the orthodontist, it could be influenced by facial form, which would be an undesirable attribute. The aim of this study was to assess whether NHO is influenced by facial morphology. Lateral photographs of 14 patients were used. Each was warped to produce 2 new images, with the chin positioned backwards or forwards relative to the original (+/-2 degrees change of the soft tissue N-Pg line). All 42 images were placed in circular frames and shown to 7 experienced orthodontists, who were asked to orient them to NHO. Image orientation between the 3 chin positions was measured and compared. The results showed that NHO depended on chin position. Images with protrusive chins were positioned with the head rotated more downwards (Frankfort plane 3.10 degrees relative to horizontal) than were images with retrusive chins (Frankfort plane 4.98 degrees ). The difference in head orientation measurements was half of the difference in chin position (1.88 degrees for a chin change of 4 degrees ). These findings call into question the validity of NHO for diagnosis because it depends on the same factor it aims to assess. Use of NHO would result in underestimating the true skeletal relationships.

The soft tissue profile has been studied extensively in orthodontics, primarily from lateral cephalometric radiographs, under the assumption that the form of the soft tissue outline largely determines the esthetics of the whole face. The purpose of this study was to assess the relative contribution of the shape of the soft tissue profile outline on the attractiveness of the face, as seen from the profile view. Pretreatment color profile facial photographs of 20 female patients were used. The photographs were scanned, and the soft tissue outlines were digitized. The average outline of the 20 original photographs was then calculated and used as a template for modifying the photographs with computer warping methods. This resulted in 20 warped photographs, all with the same soft tissue outline. Three additional photographs were constructed with 1 face-the composite average of the 20 original photographs-and 3 hairstyles from 3 of the original pictures. The photographs were printed and presented to 10 laypersons and 10 orthodontists for scoring. Scoring was performed on 2 occasions separated by at least 1 week. On the first occasion, the original photographs of 10 of the patients and the warped photographs of the other 10 patients were shown. At the next session, the remaining 10 original and 10 warped photographs were shown. The 3 composite photographs were interspersed with the 20 pictures shown to the judges in each scoring session. Judges were asked to score facial attractiveness on a scale of 0 to 10. The judges were unaware of both the computer modification of the photographs and the purpose of the study. Good agreement was noted between the judges, although the orthodontists tended to be more influenced by the profile outline than did the laypersons. The 3 averaged composite photographs were consistently given the highest scores. The modified photographs were given higher scores than their original counterparts, showing that facial attractiveness is influenced by soft tissue outline form. However, the score improvement was not sufficient to reach the level of the composite images, especially for faces initially judged as being unattractive. This shows that factors other than profile outline shape may be more influential in facial esthetics.

Advances in computer vision have started to infiltrate the specialty of orthodontics. During the past few years, a number of new products have appeared that are capable of extracting the 3-dimensional (3-D) structure of an object just by "looking." Examples include laser scanners for creating 3-D models of the face, and hand-held scanners for creating virtual models of the teeth. Such noninvasive methods will surely evolve rapidly and be applied to a multitude of diagnostic and therapeutic modalities, changing the way we think and practice. This article introduces the basic principles behind such technology so that we can better appreciate its advantages, limitations and possibilities. From the large number of methods for acquiring 3-D shapes from images, 4 were selected and are described below. For more comprehensive coverage, see the book by Klette et al (1).

The mode of action of the activator appliance is still unclear. Apart from a possible mandibular growth enhancing effect, some investigators believe that orthopedic forces may be applied to the maxilla, contributing to Class II correction by inhibition of maxillary growth. In addition, orthodontic forces may arise that produce dentoalveolar changes. The purpose of this study was to measure the magnitude of anteroposterior intermaxillary forces during wear of the activator appliance. Ten consecutive patients with Class II dental and skeletal relationships were treated with a modified activator appliance. The appliance had maxillary and mandibular segments that could be detached from each other during the measuring session. A force transducer was placed at the anterior part of the maxillary segment, and the anteroposterior force exerted by the mandibular segment was measured. Measurements were taken in the upright and reclined position at every patient visit for a period of 6 months. Results indicated that intermaxillary forces were generally in the orthodontic range (median values of 100 gf at the upright position and 123 gf at the reclined position). A wide variation in force levels was noted, both between patients and for the same patient during the experimental period. No statistically significant change in force levels was observed during the 6 month period and no difference was noted between upright and reclined posture.

The analysis of force systems from an ideal arch has shown that the ratio of the moments produced by a straight wire connecting two malaligned brackets depends on the ratio of the angulations of the brackets to the interbracket axis. Although this result permits assessment of the relative forces and moments, prediction of future tooth movement requires knowledge of the position of center of resistance as well. In this study, the forces and moments produced by a straight portion of an arch wire were transferred from the brackets to the center of resistance. The purpose was to compare the force system at the brackets to the force system at the center of resistance and to assess whether bracket geometry can be applied to predict initial tooth movement. A computer model was used to simulate two teeth connected by a straight portion of wire. Forces and moments were calculated with the use of equations derived from elementary beam theory. The results show that the force system at the center of resistance may be of an entirely different "geometry" type than that at the bracket. Factors that influence the force system include the interbracket distance, the angulation of the teeth, the length of the tooth root, and the width of the bracket.

One of the main problems in assessing the mode of action of various treatment modalities is the method of measuring the treatment change. The purpose of the present study was to develop a cephalometric method that would permit a detailed evaluation of the individual growth processes (skeletal and dental) that contribute to the overall change in occlusal relationship. The change in molar relationship was resolved in five components, i.e. translation of the maxilla, of the upper molar, of the mandible, of the lower molar, and rotation of the mandible. These movements were recorded using regional superimposition of various structures, with the aid of a computer program. Derotation of the mandible was performed to remove any confounding effects of total mandibular rotation on the interpretation of the measurements. The results show that assessment of treatment effects can be carried out by comparison of the five resulting vectors.

The purpose of this investigation was to study the factors that may affect the position of the center of resistance and center of rotation. A two-dimensional computer model of the periodontal ligament was developed. The model permitted the simulation of an isotropic (responding in the same manner regardless of the direction of the applied force) and nonisotropic periodontal ligament and allowed changes in root shape and in position and direction of force application. The center of resistance was found to depend on the distribution of root surface area. For a model of the upper central incisor, it was located at 42% of the root length measured from the alveolar crest. The presence of anisotropy in the periodontal ligament significantly affected the position of the center of resistance, which was in this case also affected by the direction of the applied force. Forces passing through the center of resistance produced translation of the modeled tooth in a direction not necessarily the same as the direction of the applied force. Tipping forces produced much larger stresses than forces causing translation. Simulation of periodontal involvement resulting in loss of attachment increased the stresses exerted on the periodontal ligament. The model permitted easy assessment of various factors that may influence the position of the center of resistance of teeth and revealed a potentially large variability in the position of the center of resistance and center of rotation, caused by variation of the properties of the periodontal ligament.

The purpose of the present investigation was to study the effects of rapid maxillary expansion on the pressures exerted by the cheeks on the maxillary arch. The sample consisted of 15 patients (five males, ten females) who received either a Hyrax or Haas type expansion appliance for treatment of a bilateral maxillary constriction of more than 5 mm. The median age of the sample was 12 years. Buccal pressures were measured at the upper first molar on the left and right side, before and after active expansion, and also after an average of 3-4 months of retention with the appliance in place. Buccal pressures on the maxillary first molar averaged approximately 3 g/cm2 before expansion and increased significantly to a value of approximately 9 g/cm2 after expansion. Pressure change was approximately 0.6 g/cm2 for each millimetre of expansion. During the 3-4-month period of stabilization of the appliance, the pressures remained at the post-expansion levels and no adaptation of the soft tissues was observed. These results lead to the conclusion that cheek pressures on the maxillary arch may be implicated in the relapse occurring after rapid expansion, even after the usual 3-month period of stabilization.

The purpose of this study was to provide quantitative data on the shape of the mandible at the period around the pubertal growth spurt and to test the hypothesis that early mandibular shape may influence the amount and direction of subsequent mandibular growth. Longitudinal data from lateral cephalograms of 55 white female and 39 white male subjects were used. The mandibular outline from articulare to gnathion was analyzed into cosine curves, according to the Fourier equation. The resulting Fourier coefficients, representing mandibular outline shape, were analyzed statistically in relation to age, sex, craniofacial pattern, and mandibular growth rotation. Statistically significant growth changes of the Fourier coefficients were observed, especially during the postpubertal period, indicating a decrease in the gonial angle with age. Sex-related differences in shape were observed at all ages, male subjects showing a more rounded shape of the mandible than female subjects. Mandibular shape, as represented by the Fourier coefficients, was correlated to cephalometric variables, indicating mandibular inclination, but only poorly to cephalometric variables, indicating anteroposterior jaw relation. Total rotation of the mandible during growth could not be predicted by mandibular shape.