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.

Association among craniofacial morphology, ethnicity, and risk of pediatric sleep-related breathing disorders: A multicenter study.

INTRODUCTION: Craniofacial morphology and ethnicity may be risk factors for sleep-related breathing disorder (SRBD) in children but have not yet been assessed in an international multicenter study. The objectives of this study were to assess the association among craniofacial features, self-reported ethnicity, and risk of SRBD in children undergoing orthodontic treatment. METHODS: Children aged 5-18 years who presented for orthodontic evaluation were enrolled in the United States, South Africa, South Korea, Saudi Arabia, and Japan. The risk of SRBD was defined as answering ≥0.33 positive responses to the Pediatric Sleep Questionnaire. Craniofacial features included measurements in sagittal and vertical dimensions to evaluate the cranial base, maxillomandibular and dental relationships, and nasopharyngeal airway dimensions. Logistic regression was performed to assess the association among craniofacial features, ethnicity, age, body mass index, and risk of SRBD. RESULTS: Data were obtained from 602 patients from 5 sites. A total of 76 patients (12.6%) had a risk of SRBD. The mean age was 12.5 years. Male gender (odds ratio [OR], 1.9; 95% confidence interval [CI], 1.0-3.4; P = 0.041), Middle Eastern ethnicity (OR, 10.2; 95% CI, 4.1-25.4; P = 0.001), body mass index (OR, 1.1; 95% CI, 1.04-1.10; P = 0.001), gonial angle (OR, 0.91; 95% CI, 0.85-0.98; P = 0.011), and inferiorly positioned hyoid (OR, 1.1; 95% CI, 1.0-1.2; P = 0.002) were significantly associated with the risk of SRBD. CONCLUSIONS: In an ambidirectional cohort study across 5 sites, male gender, Middle Eastern ethnicity, body mass index, gonial angle, and inferiorly positioned hyoid were associated with the risk of SRBD in children undergoing orthodontic treatment.

Multinational study on profile preference of laypersons.

BACKGROUND: This study aimed to assess the facial profile preferences of lay people in seven locations from different countries and whether their place of residence, sex, age, race, education, or income influenced the decision. METHODS: After altering the lip and nose in 1 mm increments in the sagittal and sagittal/vertical directions, 50 profile silhouettes with white-like facial features were rated by evaluators. The soft tissue values were integrated into the profiles, and profile preferences were identified for each location. An ANOVA with post hoc Tukey test was used to compare the differences in mean preference in each location. A multivariable regression model was used to assess the effect of the demographics of the evaluator on preference. RESULTS: Thirteen profiles were ultimately analyzed. The mean for profile preference was significantly different across locations (P < 0.0001). For evaluators in the United States and Lebanon, the most preferred profile had the original lip and original nose. In Switzerland and South Africa, retrusive lips, and a small and less upturned nose was most preferred. In Japan and Saudi Arabia, the most preferred profile had the original lip and a protrusive nose that was less upturned. A protrusive lip with a small, upturned nose was preferred in Turkey. Profile change (P < 0.0001), location (P < 0.0001), sex (P < 0.0001), and race (P = 0.02) were significant confounders; in contrast, age, education, and income were not significant. CONCLUSIONS: Profile preference is different among the seven locations. For the most part, lay people prefer profiles within one SD from white norms. Also, an upturned nose is the least favored in most of the locations. Sex and race are also significant confounders. CLINICAL RELEVANCE: An orthodontic treatment plan decision is affected by an individual's preference for their facial appearance. This study helps clinicians understand how racial and regional differences may affect patients' preferences and, therefore, their expectations for orthodontic treatment results.

Three-dimensional morphometric analysis of anterior cranial base in growing patients.

INTRODUCTION: The growth of the sphenoethmoidal and sphenofrontal suture in the anterior cranial base (ACB) terminates around 7 years old; therefore, ACB is used as a reference structure for superimposing radiographs in 2-dimensions (2D) and 3-dimensions (3D). The data in the literature regarding the cessation of growth of ACB in 3D is insufficient. The study aimed to evaluate the volumetric changes of ACB in growing patients on cone-beam computed tomography (CBCT) data in 3D. METHODS: The CBCT sample was obtained from a repository of scans of subjects (n = 30) aged 6-11 years with no craniofacial anomalies or growth-related disorders. CBCTs were taken at 2 time points (approximately 12 months apart). The mean age at the initial scan (T1) was 8.4 ± 0.89 years, and the follow-up scan (T2) was 9.6 ± 0.99 years. The bones of the ACB were segmented, and 3D models of the bones were generated using Mimics software. The volumetric measurement was performed on the 3D-rendered model. Linear measurements were performed on the slices. RESULTS: The volumetric analysis of the ACB between T1 and T2 showed a significant change (P <0.0001). There were no significant differences in volumetric changes of the ACB between the male and female subjects. The linear measurements on the right side of the cranial base showed continued growth between T1 and T2. CONCLUSIONS: In the studied sample, growth-related changes of ACB were observed through volumetric analysis after 7 years old.

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.

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.

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.

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.

Analysis of nasal airway symmetry and upper airway changes after rapid maxillary expansion.

INTRODUCTION: The objectives of this study were to assess the changes in right vs left nasal cavity volumes and minimum cross-sectional width, nasopharyngeal, and oropharyngeal volumes of the upper airway in response to rapid maxillary expansion (RME). METHODS: Pretreatment and posttreatment cone-beam computed tomography scans of 28 patients with a mean age of 9.86 ± 2.43 years and 20 age- and sex-matched controls were digitized and linear, angular, and volumetric measurements were obtained. RESULTS: Nasopharyngeal volume, right, and left nasal cavity volumes, and minimum cross-sectional widths increased significantly 2 years post RME (P <0.05). These measurements did not show any significant increase in the control group (P >0.05), whereas the oropharyngeal volume increase for both groups was comparable (P = 0.92). In the experimental group, the right and left nasal cavity volumes were not significantly different at baseline or posttreatment. However, the change that occurred was significantly larger for the left nasal cavity. This change for the control group was more significant for the right nasal cavity. Maxillary right and left molar inclinations were positively correlated to the nasal cavity volume, showing that the more buccally inclined the maxillary molars were, the smaller the nasal cavity volume. CONCLUSIONS: Nasopharyngeal and right and left nasal cavity volumes and minimum cross-sectional widths increase significantly after RME in young children. Expansion decreases the degree of difference in volume between the right and left nasal cavities. The buccal inclination of maxillary molars is correlated with nasal cavity volume.

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.

Longitudinal assessment of salivary vitamin D binding protein during orthodontic tooth movement.

BACKGROUND: Vitamin D is critical for bone physiology. In this study, we quantified Vitamin D Binding Protein (VitDBP) levels in saliva as a measure of Vitamin D during orthodontic tooth movement. METHODS: In this longitudinal study, saliva samples were collected from 73 orthodontic patients for 4 timepoints for the first six months of orthodontic treatment, along with dental casts at the beginning and the end of the study period. The saliva was measured for VitDBP as a biological marker for bone apposition and clinical tooth movement. We used the absolute change in Little's Irregularity Index as a quantitative measure for alignment. In addition, we measured the levels of alkaline phosphatase (ALP) in saliva as a marker of bone turnover. RESULTS: Both low (< 2.75 ng/ml) and high (> 6.48 ng/ml) VitDBP levels were associated with reduced tooth movement. Significant (p < 0.05) seasonal changes in VitDBP using a two-season year model were found with lower levels observed in the summer (Apr-Sept) than in the winter (Oct-Mar). CONCLUSIONS: Clinically significant orthodontic tooth movement is associated with an optimal range of VitDBP in saliva. Normal levels of VitDBP correlated with more orthodontic tooth movement, suggesting a "normal" range of salivary content of VitDBP. Given the strong trend that is independent of the confounding factors (ex. age, race or gender), the predictive value or salivary VitDBP for tooth movement should be studied in larger cohorts in future studies.

Genetic and environmental components of vertical growth in mono- and dizygotic twins up to 15-18 years of age.

OBJECTIVES: To determine the additive genetic and environmental contributions to the vertical growth of craniofacial structures. MATERIALS AND METHODS: The sample consisted of 64 untreated monozygotic (44 male, 20 female) and 61 untreated dizygotic twins (32 male, 29 female). Lateral cephalograms taken at 15 and 18 years of age were traced to analyze the sella-nasion-nasal line angle (SN-NL), nasal line-mandibular line angle (ML-NL), sella-nasion-mandibular line angle (SN-ML), sella-nasion-sella-gnathion angle (Y-axis), posterior face height/anterior face height (PFH/AFH), and lower anterior face height/anterior face height (LAFH/AFH). The genetic and environmental components of variance were analyzed with structural equation modeling for multilevel mixed effects. RESULTS: At 15 years of age, strong dominant genetic control was seen for NL-ML (81%), LAFH/AFH (73%), and Y-axis (57%), whereas strong additive genetic components were found for PFH/AFH (78%), SN-NL (58%), and SN-ML (57%). Unique environmental factors accounted for 18-42% of observed variance, with SN-NL being affected the most (42%). At 18 years of age, only LAFH/AFH (86%) was under strong dominant genetic control, whereas the remainder were under additive genetic influence. The sole exception was SN-NL, which changed from additive to unique environmental influence. CONCLUSIONS: Either additive or dominant genetic components were found at 15 or 18 years of age for most vertical variables. Environmental factors accounted for about 10-40%, with SN-NL being mostly affected.

Alternative Approaches to Adenotonsillectomy and Continuous Positive Airway Pressure (CPAP) for the Management of Pediatric Obstructive Sleep Apnea (OSA): A Review.

Continuous positive airway pressure (CPAP) is considered first-line treatment in the management of pediatric patients without a surgically correctible cause of obstruction who have confirmed moderate-to-severe obstructive sleep apnea (OSA). The evidence supports its reduction on patient morbidity and positive influence on neurobehavioral outcome. Unfortunately, in clinical practice, many patients either refuse CPAP or cannot tolerate it. An update on alternative approaches to CPAP for the management of OSA is discussed in this review, supported by the findings of systematic reviews and recent clinical studies. Alternative approaches to CPAP and adenotonsillectomy for the management of OSA include weight management, positional therapy, pharmacotherapy, high-flow nasal cannula, and the use of orthodontic procedures, such as rapid maxillary expansion and mandibular advancement devices. Surgical procedures for the management of OSA include tongue-base reduction surgery, uvulopalatopharyngoplasty, lingual tonsillectomy, supraglottoplasty, tracheostomy, and hypoglossal nerve stimulation. It is expected that this review will provide an update on the evidence available regarding alternative treatment approaches to CPAP for clinicians who manage patients with pediatric OSA in daily clinical practice.

Vertical growth in mono-and dizygotic twins: A longitudinal cephalometric cohort study.

OBJECTIVE: The aims of this longitudinal analysis of untreated monozygotic and dizygotic twins were to investigate vertical changes of the craniofacial structures during growth, to determine the concordance between genetically twins and to assess the genetic component for the various aspects of vertical growth. SETTINGS AND SAMPLE POPULATION: The sample consisted of 34 pairs of untreated monozygotic twins (23 male, 11 female) and 30 untreated dizygotic siblings of multiple birth (8 male, 8 female and 14 mixed) from the Forsyth Moorrees Twin Study (1959-1975); lateral cephalograms taken from 6 to 18 years of age were analysed at 3-year intervals. MATERIALS AND METHODS: Cephalograms were traced, and longitudinal changes between twins in six angular and proportional vertical cephalometric variables (SN-NL, ML-NL, SN-ML, y-axis, PFH/AFH and LAFH/AFH) were analysed with intraclass correlation coefficients and linear regression modelling. RESULTS: The concordance between monozygotic/dizygotic twins at 18 years of age was moderate to high with intraclass correlation coefficient values between 0.51 and 0.66. Additionally, sex differences in concordance at 18 years of age were found for three variables. High heritability (66%-79%) was observed for 5 of the 6 variables (LAFH/AFH, ML-NL, y-axis, SN-ML, PFH/AFH), while SN-NL showed limited heritability (34%). CONCLUSIONS: Although monozygotic/dizygotic twins share at least part of their genetic material, differences in the vertical dimension were found. This supports the complex developmental mechanism of the human face and the varying influence of genetic and environmental factors.

Facial soft tissue growth in identical twins.

INTRODUCTION: The aims of this longitudinal analysis of untreated monozygotic twins were to investigate the change of the facial soft tissues during growth, to determine the concordance of soft tissue growth patterns between genetically identical twins, and to assess the genetic component of soft tissue development. METHODS: The sample consisted of 33 pairs of untreated monozygotic twins (23 male, 10 female) from the Forsyth Moorrees Twin Study (1959-1975); lateral cephalograms taken from 6 to 18 years of age were analyzed at 3-year intervals. Cephalograms were traced, and longitudinal changes in the soft tissue profile between twins were analyzed with intraclass correlation coefficients and linear regression modelling. RESULTS: The concordance between monozygotic twins at 18 years of age was moderate to high with intraclass correlation coefficients values between 0.37 and 0.87. Additionally, female twins showed higher concordance at 18 years of age than did male twins for all included variables. However, about 10% to 46% of the twin pairs had large differences in their soft tissue parameters, even after the growth period. CONCLUSIONS: Although monozygotic twins possess the same genetic material, differences in the soft tissues were found. This supports the complex developmental mechanism of the human face and the varying influence of genetic and environmental factors.

Buccolingual angulation and intermolar width changes in the maxillary first molars of untreated growing children.

INTRODUCTION: Buccolingual inclinations of the maxillary permanent molars and intermolar widths increase with growth for Class I subjects. Changes for untreated Class II subjects have not yet been assessed. The aim of this study was to test the hypothesis that changes in palatal inclination of the maxillary molars and intermolar width throughout growth vary between Class I and Class II molar occlusions. METHODS: Patients were selected from the Forsyth/Moorrees Twin Study. Dental models taken for 6 consecutive years of 55 untreated subjects (28 with Angle Class I and 27 with Angle Class II occlusion) were scanned. The images were superimposed on the palatal rugae, and the angle between a reference plane and the buccolingual inclination plane was used to calculate the buccolingual molar inclination at each time point. The distance between lingual groove points was used to calculate the intermolar width. RESULTS: All molars showed increasing palatal inclinations over the 6 years. The change for each time interval was statistically significant. Class I subjects demonstrated significantly greater palatal inclination at each time point. The molar inclination changed by means of 4.99° for Class I subjects and 6.25° for Class II subjects. Intermolar width increased continuously (P <0.001) and was significantly greater (P <0.05) for Class I patients. CONCLUSIONS: These results suggest that palatal inclination of the maxillary permanent first molars occurs continuously between ages 9 and 14 years, with Class II subjects showing greater changes. The intermolar width increases steadily during this time, with Class II subjects having a narrower intermolar width and less change over time.

Postoperative Positional and Dimensional Changes of Mandibular Canal after Bilateral Sagittal Split Set-Back Osteotomy.

OBJECTIVE: This preliminary study was planned to provide information about preoperative mandibular canal (MC) position and the postoperative positional changes of MC and length in three dimensions, with the purpose of providing some assistance in reducing inferior alveolar neurosensory disturbance (IAND). METHODS: MC was examined on CBCT data using SimPlant Pro Standalone 13.0. MC locations were measured in all dimensions, with respect to mandibular bony borders. RESULTS: The results showed that MC is frequently located in the midthird of the ramus anteroposteriorly and superoinferiorly and in the midthird of the corpus superoinferiorly. Postoperatively, ramus width was increased, ramus length was decreased significantly, and MC was repositioned laterally and inferiorly. MC length was decreased on both sides, non-correlated with the set-back amounts. CONCLUSION: Preoperative results may be beneficial for the prediction of MC position for surgeons, and postoperative results will be used for the following studies to correlate postoperative positional changes with IAND.

Rapid-maxillary-expansion induced rhinological effects: a retrospective multicenter study.

Conventional dental-borne rapid maxillary expansion (RME) leads to a widening of the airways, followed by improved nasal breathing. Although combined skeletal-dental appliances are nowadays being inserted increasingly often and provide a force at the center of resistance in the nasomaxillary complex, no study exists so far that shows whether this treatment may improve the expansionary effect on the airways. In this study, low-dose computed tomography (CT) images from 31 patients (average age 14.63 ± 0.38 years) were examined retrospectively. Both records (T0 = before expansion and T1 = immediately after maximum expansion) were taken in a time interval of 25 days to avoid growth influence. Five patients were treated with Hyrax RME, 6 patients with Hybrid RME, and 20 patients with acrylic cap RME. The total airway volume increased highly significantly (mean +7272.6 mm(3); P < 0.001, power = 0.998), representing an average airway expansion of +11.54 % (2.35 %/mm activation). While the nasopharynx and oropharynx showed highly significant expansion (P < 0.000, power = 0.999), the airway at the laryngopharynx did not change significantly (P > 0.779, power = 0.05). Although the patients were significantly older in the Hybrid RME group (P = 0.006), the positive rhinological effects were comparable within all groups of different appliances (P > 0.316). Hybrid RME may, therefore, be an advisable procedure in patients with nasomaxillary impairment and pronounced patient's age.