Genetic and environmental impact on mandibular growth in mono- and dizygotic twins during adolescence: A retrospective cohort study.

INTRODUCTION: This study aimed to discover the genetic and environmental factors that contribute to the mandibular development of untreated monozygotic and dizygotic twins. MATERIAL AND METHODS: The sample, taken from the Forsyth Moorrees Twin Study, included 52 untreated monozygotic twins (36 male, 16 female) and 46 untreated dizygotic twins (23 male, 23 female). At the ages of 12 and 17, lateral cephalograms were collected and traced to assess total mandibular length, mandibular ramus length, mandibular corpus length, gonial angle, SNB, and bony chin prominence. The genetic and environmental components of variation were assessed using multilevel mixed-effects structural equation modelling. RESULTS: At 12 years of age, high additive genetic influences were observed for total mandibular length (74%), gonial angle (76%), SNB (41%), and bony chin prominence (64%), whereas strong dominant genetic components were observed for corpus length (72%), and mandibular ramus length was under unique environment influence (54%). At 17 years of age, only total mandibular length (45%), ramus length (53%), gonial angle (76%), and bony chin prominence (68%) were under strong additive genetic control, while the remainder were under strong dominant genetic control. CONCLUSIONS: Although monozygotic and dizygotic twins share at least a portion of their DNA, additive, dominant, or environmental components were discovered during adolescence. Nonetheless, by the age of 17, the majority of the mandibular traits are under either additive or dominant genetic impact.

Facial dysmorphology in children exposed in pregnancy to anticonvulsant medications correlates with deficits in IQ.

Some children exposed at conception to the antiepileptic drugs (AEDs) phenytoin (PHT), phenobarbital (PB), and carbamazepine (CBZ) have changes in their midface and fingers. It has been suggested that the anticonvulsant-exposed child with these subtle changes in facial features (the "anticonvulsant face") has a greater likelihood of having deficits in IQ in comparison with children exposed to the same anticonvulsants who do not have these features. 115 AED-exposed children (40, PHT; 34, PB; and 41, CBZ) between 6.5 and 16 years of age and 111 unexposed children matched by sex, race, and year in school were evaluated. The evaluations were (WISC-III), physical examination with measurements of facial features and digits and photographs. The AED-exposed children had cephalometric radiographs, but not the unexposed. Each parent had a similar examination of face and hands plus tests of intelligence. These AED-exposed children showed an increased frequency of a short nose and anteverted nares, features of the "anticonvulsant face." Lateral skull radiographs showed a decrease in the angle between the anterior cranial base and nasal bone, which produces anteverted nares. Mean IQs were significantly lower on one or more IQ measures for the children with these facial features. Shortening of the distal phalanges and small fingernails correlated with the presence of a short nose in that child. The findings in 115 children exposed at conception to either phenytoin, phenobarbital, or carbamazepine, as monotherapy, confirmed the hypothesis that those with a short nose and anteverted nares had a lower IQ than exposed children without those features.

Maxillary dimensions and arch shape with palatally displaced canines.

BACKGROUND/OBJECTIVES: The aim of this study was to explore the effect of palatally displaced canines on maxillary dimensions and arch shape. METHODS: Occlusal and skeletal landmarks were plotted on cone beam computed tomography (CBCT) images of 156 orthodontic patients: 78 with palatally displaced canines (PDC) (27 left, 28 right, and 23 bilateral) and 78 controls using Mimics™ (Materialise, Belgium). Arch forms were created, and arch width, depth, and skeletal dimensions were measured. T-test (P < 0.05) was used to compare the groups. Geometric Morphometrics (GM) analysis was used to compare the groups and to explore the pattern of covariation between two sets of landmarks. RESULTS: The unilateral PDC group showed an increased first premolar, second premolar, molar widths, and an increased molar depth. No significant difference was found in arch form. The skeletal measurements were generally larger in the PDC group, but the transverse measurements were the most significant. Discriminant Function Analysis (DFA) with cross-validation allowed an accurate classification of 85.9% of the control group and 66.7% of the PDC group. The Mahalanobis distance displayed significant differences among three combinations of groups. Strong covariance was found between the second premolar and all other landmarks. LIMITATIONS: The small sample sizes of the stratified groups precluded recognition of statistical significance. CONCLUSIONS: Patients with unilateral PDC displayed significantly wider first, second premolar, and first molar widths, and increased first molar depths. There were no significant differences in arch form; however, GM showed significant differences between the groups and a prominent covariance function for the 2nd premolars.

Effects of counterclockwise bimaxillary advancement surgery and relapse on upper airway.

OBJECTIVE: The aim of this study was to evaluate the long-term volumetric changes of the upper airway compartments in response to counterclockwise bimaxillary advancement surgery with multi-piece maxillary osteotomy, and to analyse the relationship between the postoperative stability of the maxillomandibular skeletal complex, and the volumetric airway changes over-time. METHODOLOGY: Twenty-seven sets of pre (T0), post (T1) and follow-up (T2) (20.15 months) CBCT scans were used. The upper airway was isolated into five compartments: soft and bony nasal cavity (SNC, BNC), nasopharynx (NP), oropharynx (OP) and hypopharynx (HP) using Mimics V.22 software. The volumetric changes and the correlation between the airway change and the skeletal movements were analysed using repeated measure ANOVA, and Pearson's correlation coefficient, respectively. RESULTS: The results showed a significant decrease in SNC and BNC (10.94% and 7.69%, p < .05) at T1. However, SNC presented a significant recovery (11.73%, p < .05) at T2. NP, OP and HP segments presented significant and stable increases over time (10.41%, 53.62%, 24.70%, p < .05). CONCLUSIONS: This surgical approach produced a significant increase in OP and HP volumes in short and long term without a significant relapse, NP showed a significant increase in long term only, SNC and BNC volumes showed a significant decrease post-surgery which was only partially maintained for BNC.

Longitudinal changes in the dental arch width and symmetry in identical and fraternal twins.

INTRODUCTION: This study aimed to assess growth-related dental and symmetry changes in the dental arch within and between identical and fraternal twins in mixed and permanent dentition. METHODS: Three-dimensional scanned dental models of eligible subjects were selected from the Forsyth-Moorrees Twin Study sample. This retrospective cohort study was carried out on 36 identical (18 pairs) and 28 fraternal (14 pairs) twins in mixed dentition and 36 identical (18 pairs) and 38 fraternal (19 pairs) twins in permanent dentition stages on the basis of the availability of the dental casts scanned each year from each group (Table I). Linear measurements from dental casts were performed in patients aged 8-16 years. Student t test and Pearson's correlation were used to compare the symmetry between and within the identical and fraternal twins. The resemblance and heritability patterns were retrospectively obtained from the Pearson correlation coefficient and Falconer's heritability test (H2 = 2 × b). Adjusted mixed-effects estimates and 95% confidence intervals were calculated to test the association between age and dental parameters for both mixed and permanent dentition groups. RESULTS: Intercanine and intermolar widths significantly increased (P <0.05) during the mixed dentition but became stable after 13 years old. No statistically significant differences were found in arch symmetry between the 2 groups (ie, identical and fraternal) in any of the included measurements. Evaluation of the resemblance and heritability pattern showed nonsignificant results for all variables measured (H2 range, -0.67 to 0.56). CONCLUSIONS: The dental arch becomes wider at a higher rate in the canine region than the molar region in both the mixed and early permanent dentition. The dental arches of twins develop symmetrically, and their growth is not mainly affected by genetics. Asymmetrical teeth will maintain their relative position to reference planes throughout growth.

Heritability of facial soft tissue growth in mono- and dizygotic twins at 12 and 17 years of age: A retrospective cohort study.

OBJECTIVE: The purpose of this investigation of untreated monozygotic and dizygotic twins was to identify the genetic and environmental components to the facial soft tissue growth. SETTINGS AND SAMPLE POPULATION: The sample consisted of 52 untreated monozygotic twins (36 male and 16 female) and 46 untreated dizygotic twins (23 male and 23 female) from the Forsyth Moorrees Twin Study (1959-1975). MATERIALS AND METHODS: Lateral cephalograms were taken at 12 and 17 years of age and traced to analyse facial convexity, nasolabial angle, upper and lower lip thickness, upper and lower lip profile and nose prominence. The genetic and environmental components of variance were analysed with structural equation modelling for multilevel mixed-effects model. RESULTS: At 12 years of age, strong additive genetic influence was seen for facial convexity (70%), upper lip profile (66%) and nose prominence (65%), whereas strong dominant genetic components were found for upper lip thickness (56%). Nevertheless, under unique environment influence were nasolabial angle (58%), lower lip profile (51%) and lower lip thickness (64%). At 17 years of age, only upper lip thickness (55%) and nose prominence (84%) were under strong additive genetic control, while the rest of the variables were under strong dominant genetic control. The only exception was lower lip thickness (61%), which is still influenced by the unique environment. CONCLUSION: Although monozygotic/dizygotic twins share at least part of their genome, at both times either additive, dominant or environmental components were found. Nevertheless, at 17 years of age most of the variables are either under additive or dominant genetic influence.

Knowledge of evidence-based research methodology amongst orthodontic postgraduate residents in four universities: An international survey.

AIM: The aim of this international survey was to assess knowledge concerning the design, conduct, critical appraisal and synthesis of clinical studies among senior orthodontic postgraduate residents. MATERIALS AND METHODS: Senior postgraduate residents from four universities in Europe and the United States were invited to complete a custom questionnaire. The overall correct answer score and proportion of residents correctly answering each of the 10 questions within the survey were analysed with descriptive statistics, analysis-of-variance, chi-squares test and linear regression at 5%. RESULTS: A total of 46 residents with mean age of 30.4 years scored an overall % correct score of 48.8%±13.8%, with the % of correct answers to each question ranging from 7 to 89%. The worst-answered questions pertained to correctly characterizing sensitivity and specificity (7%), number needed to treat (9%), credibility of trial synthesis in meta-analysis (35%) and publication bias (37%). The vast majority of postgraduate students could correctly identify entities that can be blinded in a randomized trial (89%), statistical power of a trial (74%) and proper methods for random allocation sequence (67%). No statistically significant differences were found among the four included universities, while residents having obtained another degree apart from dentistry scored better than others (+9.5%; 95% confidence interval: 0.6% to 18.5%; P=0.04). CONCLUSIONS: Postgraduate residents in orthodontics possessed moderate knowledge on evidence-based methodology. Efforts should be reinforced to assimilate research methodology perspectives in the postgraduate curricula of universities, in order to further augment critical training of orthodontic specialists.

Heritability of nasal characteristics assessed using lateral cephalograms.

INTRODUCTION: The midface and nasal bones have a significant influence on facial esthetics. Being able to predict the ultimate size of a growing patient's nose may influence the orthodontic treatment plan. Our study aimed to determine whether significant heritability exists between parents and children using multiple soft and hard tissue measurements of nasal dimensions. METHODS: This cross-sectional study comprised 47 Western European families from the Forsyth Moorrees Twin Study. The lateral cephalograms of each parent and postpubertal child were evaluated using 14 cephalometric variables. The resemblance and heritability patterns were estimated from the Pearson correlation coefficient and Falconer's heritability test (ie, h2 = 2 × ß estimate). RESULTS: We found significant heritability between 1 or both parents to sons, daughters, or both children for 11 measurements. Daughters were more strongly influenced by their mothers than fathers, and sons showed relatively few features strongly heritable from either parent. The nasal bone length and ANB were strongly heritable with the mother, and the nose length alone was strongly heritable with the father. In addition, 4 of the 6 measurements that were significantly heritable for daughters were horizontal measurements. CONCLUSIONS: Many nasal dimensions are significantly heritable. However, fathers more strongly influenced their daughters than sons, but mothers and daughters shared stronger and more numerous traits than fathers and daughters. Finally, horizontal traits were significantly more heritable between parents and daughters than sons.

Cephalometric Variability Among Siblings: A Pilot Study.

OBJECTIVE: To determine whether multiple siblings resemble one another in their craniofacial characteristics as measured on cephalometric radiographs. METHODS: This study was conducted retrospectively using the Forsyth Moorrees twin sample. A total of 32 families were included, each with ≥4 postpubertal siblings, totaling 142 subjects. Only 1 monozygotic twin was included per family. Headfilms were digitized, skeletal landmarks were located, and 6 parameters that indicated sagittal jaw relationships and vertical status were measured. Diverse statistical approaches were used. Dixon's Q-test detected outliers in a family for a given parameter. Manhattan Distance quantified similarity among siblings per parameter. Scatter plots visually displayed subject's measure relative to the mean and standard deviation of each parameter to assess the clinical relevance of the differences. RESULTS: A total of 11 families (34.4%) had no outliers on any parameter, 13 families (40.6%) had outliers on 1 parameter, and 8 families (25%) had outliers on ≥2 parameters. We identified 29 individuals with at least 1 outlying measure (20.4%). Among these, only 2 individuals (1.4%) were significantly different from their siblings for more than 1 measurement. Although the majority of the families did not demonstrate any statistical outlier, the ranges of the measurements were clinically relevant as they might suggest different treatment. For example, the mean range of SNB (Sella-Nasion-B point) angles was 7.23°, and the mean range of MPA was 9.42°. CONCLUSION: Although families are generally not dissimilar in their craniofacial characteristics, measurements from siblings cannot be used to predict the measurements of another sibling in a clinically meaningful way.

Does rapid maxillary expansion enlarge the nasal cavity and pharyngeal airway? A three-dimensional assessment based on validated analyses.

OBJECTIVES: To evaluate the three-dimensional changes following rapid maxillary expansion (RME) of the nasal cavity (NC) and pharyngeal airway (PA) in growing patients, using innovative and validated evaluation methods and to investigate whether a correlation between skeletal expansion and increase in airway volume exists. SETTINGS AND SAMPLE POPULATION: Records of patients who had cone beam computed tomography taken before and after orthodontic treatment with or without RME were retrospectively collected and divided into two groups: (a) RME, 39 patients (mean age 10.40 ± 1.74 years); and (b) control, 29 patients, matched for age (mean age 11.07 ± 1.45 years) and follow-up period. MATERIAL AND METHODS: Total and partial volumes of the NC and the PA were calculated. The PA centerline was determined to assess the minimal cross-sectional area and hydraulic diameter. Paired and unpaired t test were applied to compare the difference between time points and between groups. One-way ANOVA and post hoc Tukey's tests were used to compare subgroups with respect to changes in palatal width and lacrimal ducts distance. RESULTS: All of the NC, PA and skeletal parameters were significantly enlarged after RME. The NC volume and inter-molar distance in the RME were significantly larger compared to the control group. The initially lower mean values of minimal cross-sectional area and hydraulic diameter in the RME group when compared to the control group normalized after RME treatment. CONCLUSIONS: Based on validated analyses, the NC volume increase was evident after RME in the long term after controlling for growth.