Long-term occlusal tooth wear at the onset of permanent dentition.

OBJECTIVES: This study quantified the long-term occlusal wear in the natural posterior teeth and the associations per tooth type within the dentition. METHODS: The sample included 70 orthodontically treated subjects (52 females and 18 males; median age, 14.3 years), followed for a 12.7-year period. They were consecutively selected with no tooth wear-related criteria. Post-treatment (T1) and follow-up dental casts (T2) were scanned and superimposed through three-dimensional methods. Occlusal wear volume of posterior teeth and tooth wear patterns were investigated through non-parametric statistics and analysis of covariance. RESULTS: There were no significant differences between contralateral teeth. The average occlusal wear per posterior tooth was 2.3 mm3, with 65.2% of teeth showing values greater than 1 mm3. Males, mandibular teeth, and first molars exhibited slightly greater wear levels than females (median, 2.57 and 2.21 mm3, respectively; p = 0.005), maxillary teeth, and first or second premolars, respectively. In all first premolars and in the mandibular second premolars, the buccal cusps were primarily affected with no other distinct patterns. There were weak to moderate correlations between tooth types, apart from certain strong correlations detected in males. CONCLUSIONS: Posterior tooth wear was highly prevalent after a 13-year period starting at the onset of permanent dentition. The detected patterns are in accordance with the concept of canine guidance occlusion that is transforming into group synergy through function. CLINICAL RELEVANCE: The widespread tooth wear occurrence and the high intra- and inter-individual variability underline the need for individual patient monitoring to identify high-risk patients at early stages.

Cervical headgear effectiveness in distalizing molars in relation to patient compliance.

OBJECTIVES: The purpose of this study was to measure the effectiveness of the cervical headgear for distalizing first permanent maxillary molars in relation to hours of use. METHODS: This was a one-centre, prospective, clinical study conducted at the Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece. Participants (N = 26; 17 females, 9 males) were patients with no history of orthodontic treatment, no syndromes or clefts, and Angle's Class II malocclusion, where the treatment plan included a cervical headgear. They were instructed to wear the appliance for at least 12 h per day. A TheraMon® microsensor was embedded in the headgear's strap to objectively measure wear-time. To measure tooth movement, pre- and post-treatment digital models were superimposed, using the palate as a reference area; translation and rotation were measured along three axes. Superimposition and movement measurements were made with the Viewbox 4 software. RESULTS: Average treatment time and headgear wear were 130 days and 55 days, respectively, i.e. 10.1 h/day. During this period, distal movement averaged 1.75 mm with high variability (min 0.2 mm, max 4.5 mm). Distal tipping and rotation had an average of approximately 5 °C. Cumulative headgear wear was significantly correlated with distal movement (r2 = 0.32, P < .002), distal tipping (r2 = 0.27, P < .01), and distal rotation around the long axis of the tooth (r2 = 0.20, P < .05). CONCLUSION: Compliance is critical for having a successful clinical outcome. Distalization of the molar with a cervical headgear is correlated with the cumulative hours of appliance use, with hours per day being a weaker predictor.

Third molar agenesis relates to human craniofacial form.

OBJECTIVE: To investigate the association between the number of third molars and craniofacial shape. SUBJECTS AND METHODS: The study sample comprised 470 individuals (194 males and 276 females), out of whom 310 (124 males, mean age: 14.6 years and 186 females, mean age: 14.1 years) had a full permanent dentition including third molars and 160 (70 males, mean age: 13.7 years and 90 females, mean age: 13.9 years) had at least one missing third molar. Pre-orthodontic treatment cephalometric images were digitized using 127 landmarks to describe the shape of the entire craniofacial configuration, the cranial base, the maxilla, and the mandible. The shapes of the various configurations were described by principal components (PCs) of shape. The effect of third molar agenesis on craniofacial shape was evaluated with multivariate regression models, considering shape PCs as the dependent variables, and age and sex as predictors. RESULTS: There was a strong association between third molar agenesis and the shape of all craniofacial configurations in both sexes. Individuals with missing third molars presented a less convex craniofacial configuration, a shorter anterior facial height and a more retrusive maxilla and mandible. In cases with third molar agenesis only in one jaw, shape differences were also evident in the opposing jaw. LIMITATIONS: Interpretation of study outcomes should take into consideration the two-dimensional data and the analysis of only white-European subjects. CONCLUSIONS: There is a strong association between third molar formation and craniofacial shape. The effect is rather generalized than local and is potentially linked to an ongoing evolutionary mechanism that leads to smaller and fewer teeth, as well as smaller craniofacial configurations, in modern humans.

Accurate gingival recession quantification using 3D digital dental models.

OBJECTIVES: To develop and validate a method for accurate quantitative assessment of gingival recessions based on superimposition of serial 3D digital models. MATERIALS AND METHODS: Gingival recessions of mild (0.5-2 mm) and increased (3-7 mm) severity were simulated on stone casts and surface models were created. The outlines of the gingival margins of the mild (A) and severe recessions (B) were compared to the original gingival margins following 3D best fit superimposition through a gold standard technique (GS), which used intact adjacent structures, and the tested method (CC), which used single tooth crowns at the position of recessions, as superimposition reference. The primary outcome was the distance between the most apical point of each corresponding gingival margin along the respective tooth long axis. RESULTS: For mild recessions, the median difference of the test methods (CC_A) from the reference method (GS_A) was 0.008 mm (IQR: 0.093; range: - 0.143, 0.147). For severe recessions, the median difference of the test method (CC_B) from the reference method (GS_B) was 0.009 mm (IQR: 0.091; range: - 0.170, 0.198). The proposed method (CC) showed very high intra- and inter-operator reproducibility (median: 0.025 and 0.033 mm, respectively). CONCLUSIONS: The suggested method offers highly accurate monitoring of gingival margin changes and diagnosis of gingival recessions using 3D digital dental models. The method is applicable irrespective of changes in tooth position or form, allowing for assessments over any time span. CLINICAL RELEVANCE: The accurate detection and visualization of gingival margin changes in 3D will enhance diagnosis and patient-doctor communication.

Intrauterine growth restriction affects bone mineral density of the mandible and the condyle in growing rats.

OBJECTIVES: To investigate in growing rats the effect of intrauterine growth restriction (IUGR) on the bone mineral density of the mandible and tibia, as well as the quality of the mandibular and condylar bone. METHODS: Twelve male rats were born IUGR by mothers sustaining 50% food restriction during pregnancy. Twelve control male rats were born by mothers fed ad libitum. Dual-energy X-ray absorptiometry (DEXA) of the tibia, proximal tibial metaphysis and the mandible, biochemical markers, histology and histomorphometrical analysis on the mandibular and subchondral bone of the condyle were performed. RESULTS: IUGR significantly affected bone mineral density (BMD) of both tibial and mandibular bones. IUGR rats had significantly lower osteocalcin values (p=0.021) and phosphorus (p=0.028), but not 25-OH vitamin D (p=0.352). Bone area percentage in the mandible was significantly lower (51.21±5.54) in IUGR compared to controls (66.00±15.49), and for subchondral bone of the condyle for IUGR (47.01±6.82) compared to controls (68.27±13.37). IUGR had a significant reduction in the fibrous layer, but not the proliferating layer, with the hypertrophic layer significantly increased. CONCLUSION: Maternal restricted nutrition during gestation can affect BMD of the mandible and the tibia of the offspring animals.

Drug-induced sleep endoscopy improves intervention efficacy among patients treated for obstructive sleep apnea with a mandibular advancement device.

PURPOSE: To compare the short-term treatment effect of a mandibular advancement device (MAD) with and without previous drug-induced sleep endoscopy (DISE) on polysomnography (PSG) and other sleep apnea-related treatment outcomes (Short Form Health Survey [SF-36] and Epworth Sleepiness Scale [ESS]) among adults with mild, moderate, and severe obstructive sleep apnea (OSA). We hypothesized that using DISE would improve the efficacy of MADs on the sleep apnea parameters. METHODS: The study sample consisted of patients with OSA who were unable or unwilling to tolerate a CPAP device, divided into an experimental (with DISE) and a control (without DISE) group. RESULTS: Of 50 patients with OSA, 40 men (80%), mean age was 48.8 ± 12,3 years. The mean apnea-hypopnea index (AHI) score of both groups decreased significantly between baseline and the 8-week follow-up titration PSG with MAD in situ, from 31.7 ± 17.3 (mean ± SD) apnea-hypopnea episodes/h to 7.0 ± 6.4/h (p < 0.0001) in the experimental group, and from 22.5 ± 16.6 episodes/h to 11.4 ± 8.0/h (p < 0.024) in the control group. Capillary oxygen saturation (SpO2) levels did not change significantly between the two timepoints for either group. The SF-36 (p < 0.023) and ESS (p < 0.036) results of both groups improved significantly between baseline and the 8-week follow-up after starting MAD treatment; however, the improvement in quality of life was significantly more pronounced in the experimental group than in the control group (p < 0.0001). CONCLUSION: DISE provides a significant benefit to patients with OSA undergoing MAD treatment. It can be used as a valuable prediction tool in clinical practice for the management of patients with OSA, even those with moderate and severe disease.

Sociomedical and oral factors affecting masticatory performance in an older population.

OBJECTIVES: To assess the sociomedical and oral factors affecting masticatory performance in a community-dwelling older population. MATERIALS AND METHODS: Community-dwelling persons over 60 years were investigated using medical and dental oral interviews, oral and denture examination (natural teeth, tooth mobility, number of occluding tooth pairs, and removable dentures' prevalence and quality), and evaluation of masticatory performance using a mixing ability test. RESULTS: A total of 130 participants with a mean age of 73.9±8.5 years were recorded. Fifty-eight (44.6%) used various types of removable prostheses. Twenty were edentulous and used a pair of complete dentures. Univariate analyses revealed statistically significant associations (p≤0.05) between masticatory performance and aging, marital status, subjective chewing ability, use of removable dentures, use of various combinations of complete dentures, pain caused by maxillary denture, number of teeth, tooth mobility, posterior chewing pairs, all chewing contacts natural or prosthetic, retention of mandibular partial dentures, and dentures' occlusion. The multivariable quantile regression analysis revealed that fewer natural teeth (95% CI: -0.02-0.01, p<0.001), being edentulous and using a pair of complete dentures (95% CI: 0.09-0.35, p=0.001), and larger percentage of severely mobile teeth (95% CI: 0.07-0.82, p=0.020) were associated with lower masticatory performance. CONCLUSIONS: Poor masticatory performance in older adults was associated with fewer teeth, being edentulous and using a pair of complete dentures, and increased prevalence of severe tooth mobility. CLINICAL RELEVANCE: Retaining the natural dentition and preventing and treating periodontal disease are important measures to maintain masticatory performance in older adults.

Oral factors and adherence to Mediterranean diet in an older Greek population.

PURPOSE: The aim of this study was to investigate the effect of oral factors on adherence to the Mediterranean diet in an older population METHODS: 130 persons over 60 years visiting Open Care Community Centers for Older People participated in this study. Oral interviews recorded demographic and sociomedical information, subjective oral complaints, and dental habits. Adherence to Mediterranean diet was assessed using the MDI_BNC4H index (range: 0-14). An oral examination was performed, and evaluation of the masticatory performance was carried out using a two-color chewing gum that was digitally analysed. RESULTS: The mean age of the study participants was 73.9 ± 8.5 years. The score of adherence to the Mediterranean diet ranged from 3 to 9 (5.6 ± 1.4). 58 participants used removable prostheses, while 20 used a pair of complete dentures. Univariate analyses revealed that the parameters that negatively significantly, or marginally significantly, affected the level of adherence to the Mediterranean diet were lower masticatory performance (p = 0.050), larger number of drugs per day (p = 0.056), higher BMI (p = 0.043) and smoking (p = 0.053). The multivariable analysis revealed that lower adherence to the Mediterranean diet was significantly associated with higher BMI (p = 0.047) and lower masticatory performance (p = 0.050). CONCLUSIONS: Increased masticatory performance was an independent predictor of better adherence to the Mediterranean diet in an older population.

A randomized, 3-month, parallel-group clinical trial to compare the efficacy of electric 3-dimensional toothbrushes vs manual toothbrushes in maintaining oral health in patients with fixed orthodontic appliances.

INTRODUCTION: The aim of this single-blinded, parallel-group, randomized clinical trial was to compare the efficacy of electric 3-dimensional (3D) toothbrushes and manual toothbrushes in removing plaque and reducing gingival inflammation in orthodontic patients. METHODS: Eighty adolescents with fixed orthodontic appliances in both arches were randomized at a 1:1 ratio, with an equal number of both sexes, in this examiner blinded, parallel clinical trial. Eligibility criteria included subjects aged between 12 and 16 years, good general health, nonextraction orthodontic treatment, and plaque-induced gingivitis, excluding patients with active caries or periodontitis, tooth agenesis, syndromes, disabilities, and craniofacial deformities, ≥2 cervical and/or proximal fillings, dental prostheses or dental implants, and subjects smoking or using antibiotics or medication predisposing to gingival enlargement. Patients were assigned to use either an electric 3D orthodontic toothbrush (Oral-B Pro-1000 with Oral-B Ortho head; Procter & Gamble, Cincinnati, Ohio) or a manual toothbrush (Oral-B Orthodontic brush; Procter & Gamble) and instructed to brush twice daily for 2 minutes. The main outcomes were: (1) plaque removal, assessed with the Modified Silness and Löe plaque index and the Modified Full Mouth Plaque Score, and (2) gingival inflammation reduction, assessed with the Modified Silness and Löe Gingival Index and the Modified Simplified Gingival Index. Measurements were taken at baseline, 1, 2, and 3 months. Randomization was achieved with 2 random sequences, one for each brush, written and sealed in opaque numbered envelopes. Blinding was possible for outcome assessment only. RESULTS: Considerable variability was observed among patients in the values of all dependent variables. There was no difference between interventions over time for any of the outcomes, and the main effects for treatment and time were also not statistically significant. For Modified Silness and Löe plaque index, the interaction was 0.001 (95% confidence interval, -0.011 to 0.013; P = 0.89). CONCLUSIONS: No difference in plaque removal efficacy and gingival inflammation reduction was found between the electric 3D and manual toothbrushes in adolescents with fixed orthodontic appliances. Therefore, orthodontists should focus on enhancing their patients' dental awareness and oral hygiene, along with professional prophylaxis and other oral hygiene aids, independently of the brush used. REGISTRATION: This trial was registered at ClinicalTrials.gov (Identifier: NCT02699931). PROTOCOL: The protocol was not published before trial commencement. FUNDING: Electric and manual toothbrushes and toothpastes for all participants were provided by Procter & Gamble (Oral-B). Miscellaneous costs were covered by the participating departments.

Relapse 1 week after bracket removal: a 3D superimpositional analysis.

OBJECTIVES: To measure tooth movement 1 week post-treatment and assess potential correlation with changes invoked during treatment. SUBJECTS AND METHODS: Thirty-eight patients were recruited (19 males, 19 females). Polyvinyl siloxane impressions were taken after bracket debonding (T1) and 1 week later (T2) and digitally scanned. During this period no retention was used. The digital casts were superimposed on structures of the hard palate. Translation and rotation of the first molars, canines, and central incisors were recorded. Additionally, movement of these teeth was assessed from the beginning (T0) until the end of treatment (T1). The correlation between the post-treatment relapse (T1-T2) and tooth movement during treatment (T0-T1) was investigated via the Spearman correlation coefficient. RESULTS: Relapse was detected and reflected changes in tooth position during treatment. For the first molars (right, left) the correlation between treatment and post-treatment tooth movement was evident in the transverse direction (r = -0.38, P = 0.020; r = -0.32, P = 0.052), tipping (r = -0.40, P = 0.015; r = -0.34, P = 0.034) and the antero-posterior direction (r = -0.31, P = 0.061; r = -0.36, P = 0.027); for the canines (right and left), as rotation around their long axis (r = -0.55, P = 0.003; r = -0.58, P = 0.002); for central incisors (right and left) in the antero-posterior direction (r = -0.55, P = 0.000; r = -0.48, P = 0.03), transverse direction (r = -0.43, P = 0.07; r = -0.32, P = 0.047), and rotation around their long axis (r = -0.53, P = 0.001; r = -0.28, P = 0.089). CONCLUSIONS: Post-treatment changes in tooth position were mostly related to tooth movement during treatment. The reported correlations may help clinicians predict short-term relapse, evaluate long-term retention need, and design individualized retention schemes.

A geometric morphometric evaluation of hard and soft tissue profile changes in borderline extraction versus non-extraction patients.

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.

Three-dimensional (3D) geometric morphometric analysis of human premolars to assess sexual dimorphism and biological ancestry in Australian populations.

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.

Early anterior crossbite correction through posterior bite opening: a 3D superimposition prospective cohort study.

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.

Morphometric covariation between palatal shape and skeletal pattern in children and adolescents: a cross-sectional study.

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.

Craniofacial shape differs in patients with tooth agenesis: geometric morphometric analysis.

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.

Geometric morphometric analysis of craniofacial growth between the ages of 12 and 14 in normal humans.

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.

Morphometric covariation between palatal shape and skeletal pattern in Class II growing subjects.

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.

Shape variation and covariation of upper and lower dental arches of an orthodontic population.

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.