Genetic and environmental impact on variation in the palatal dimensions in permanent dentition: a twin study.

The objective of this study was to assess the relative contributions of genetic and environmental factors to variation in palatal parameters in twins with completed maxillary growth. The subjects of this study comprised digital dental casts of 50 monozygotic and 35 dizygotic twin pairs. The subjects' average age was 17.95 ± 2.83 years. Zygosity determination was carried out using 15 specific DNA markers and an amel fragment of the amelogenin gene. The interdental distances were measured between selected dental landmarks at the occlusal and gingival planes. The palatal height, surface area and volume were measured between the gingival plane and the midpalate suture. High heritability estimates were observed for all transverse intra-arch measurements. The palate height (a2 = 0.8), dental arch width in the molar area (a2 = 0.86), palatal surface area (a2 = 0.61) and palate volume (a2 = 0.69) were under strong additive genetic control. Moderate genetic dominance was observed for dental arch widths at the gingival line in the canine (d2 = 0.5) and premolar regions (d2 = 0.78-0.81). Sexual dimorphism was shown, with males exhibiting a greater arch width, palate surface area and volume than females (p < 0.01). The majority of palate parameters variation in twins was controlled by genetic effects, and most were highly heritable.

Heritability of cephalometric variables of airway morphology in twins with completed active growth.

BACKGROUND: The interplay between genetic and environmental impacts on dental and facial morphology has been widely analyzed, but little is known about their relative contributions to airway morphology. The aim of this study was to evaluate the genetic and environmental influences on the cephalometric variables of airway morphology in a group of postpubertal twins with completed craniofacial growth. MATERIALS AND METHODS: The materials comprised lateral head cephalograms of 94 pairs of twins (50 monozygotic, 44 dizygotic) with completed craniofacial growth. Zygosity was determined using 15 specific DNA markers. The computerized cephalometric analysis included 22 craniofacial, hyoideal, pharyngeal structural linear and angular variables. Genetic analysis and heritability estimation were performed using maximum likelihood genetic structural equation modeling (GSEM). Principal component analysis (PCA) was used to assess the correlations between cephalometric measurement variables. RESULTS: Upper airway dimensions showed moderate to high genetic determination (SPPW-SPP and U-MPW: a2 = 0.64 and 0.5, respectively). Lower airway parameters showed only common and specific environmental determination (PPW-TPP a2 = 0.24, e2 = 0.38; LPW-V c2 = 0.2, e2 = 0.63; PCV-AH c2 = 0.47, e2 = 0.28). The relationship between the maxilla and the hyoid bone (for variables PNS-AH, ANS-AH d2 = 0.9, 0.92, respectively) showed very strong additive genetic determination. The size of the soft palate was affected by additive and dominant genes. Its length (SPL) was strongly influenced by dominant genes, while its width (SPW) showed a moderate additive genetic influence. Owing to correlations in the behavior of variables, the data could be expressed in 5 principal components that jointly explained 36.8% of the total variance. CONCLUSIONS: The dimensions of the upper airway are strongly determined by genes, while the parameters of the lower airway depend mainly on environmental factors. TRIAL REGISTRATION: The protocol has been approved by the Kaunas Regional Ethical Committee (No. BE - 2-41., May 13, 2020).

Heritability of mandibular cephalometric variables in twins with completed craniofacial growth.

OBJECTIVES: To determine genetic and environmental impact on mandibular morphology using lateral cephalometric analysis of twins with completed mandibular growth and deoxyribonucleic acid (DNA) based zygosity determination. MATERIALS AND METHODS: The 39 cephalometric variables of 141 same gender adult pair of twins were analysed. Zygosity was determined using 15 specific DNA markers and cervical vertebral maturation method was used to assess completion of the mandibular growth. A genetic analysis was performed using maximum likelihood genetic structural equation modelling (GSEM). RESULTS: The genetic heritability estimates of angular variables describing horizontal mandibular position in relationship to cranial base and maxilla were considerably higher than in those describing vertical position. The mandibular skeletal cephalometric variables also showed high heritability estimates with angular measurements being considerably higher than linear ones. Results of this study indicate that the angular measurements representing mandibular skeletal morphology (mandibular form) have greater genetic determination than the linear measurements (mandibular size). CONCLUSIONS: The shape and sagittal position of the mandible is under stronger genetic control, than is its size and vertical relationship to cranial base.

Relationships between Malocclusion, Body Posture, and Nasopharyngeal Pathology in Pre-Orthodontic Children.

BACKGROUND: Malocclusion, body posture, and breathing pattern may be correlated, but this issue is still controversial. The aim of the study was to examine the relationship between the type of malocclusion, body posture, and nasopharyngeal obstruction in children aged 7-14 years. MATERIAL AND METHODS: The study group comprised 94 patients aged 7-14 years (mean±SD: 11.9±2.1 years); 44 (46.8%) males and 50 (53.2%) females. All patients passed an examination performed by the same orthodontist (study model and cephalometric radiograph analysis), orthopedic surgeon (body posture examined from the front, side, and back), and otorhinolaryngologist (anterior and posterior rhinoscopy and pharyngoscopy) in a blind manner. RESULTS: Postural disorders were observed in 72 (76.6%) patients. Hypertrophy of the adenoids was diagnosed in 54 (57.4%) patients, hypertrophy of the tonsils in 85 (90.3%), nasal septum deviation in 51 (54.3%), and allergic rhinitis in 19 (20.2%) patients. There was a statistically significant correlation between presence of kyphotic posture and a reduction in the SNB angle, representing sagittal position of the mandible. Also, there was a statistically significant association between kyphotic posture and nasopharyngeal obstruction (54.1% of patients with nasopharyngeal obstruction were kyphotic, compared with 25% of patients with no nasopharyngeal obstruction; p=0.02). Kyphotic posture and reduced SNB angle were more common among males. CONCLUSIONS: We concluded that: 1) there was a significant association between the sagittal position of the mandible (SNB angle) and a kyphotic posture; 2) kyphotic posture was significantly more common among patients with nasopharyngeal obstruction.

Mandibular morphology in monozygotic twins: a cephalometric study.

BACKGROUND: The understanding of relative effects of genetics and environmental factors on mandible growth would increase effectiveness of orthodontic therapy and treatment planning. The purpose of this study was to clarify whether the skeletal morphology of mandible is phenotypically alike in two individuals in a pair of young adult monozygotic (MZ) twins. METHODS: The 90 twin pairs were classified as MZ by 15 specific DNA markers and Amel fragment. Cephalometric analysis of mandible morphology using 27 parameters was done and Pearson's intra-pair correlation coefficient for each variable was calculated. RESULTS: The highest correlations of cephalometric variables between two individuals in the same MZ twins pair was in the total mandibular and corpus length (r=0.94). The lowest correlations was established for depth of antigonial notch (r=0.65) and articular angle (r=0.68) in female pairs. Statistically significant differences (p ≤ 0.05) of intra-pair correlation coefficients between genders was found only for total mandibular length (distances Co-Gn and Ar-Gn). CONCLUSIONS: Mandibular length has highest intra-pair correlation coefficient among similar linear cephalometric variables in MZ twins. The females demonstrated greater variability of mandible skeletal cephalometric measurements within the MZ twin pair than the men.

An interdisciplinary study of orthodontic, orthopedic, and otorhinolaryngological findings in 12-14-year-old preorthodontic children.

BACKGROUND AND OBJECTIVE: Malocclusion, the body posture, and the breathing pattern may correlate, but this issue is still controversial. The aim of the study was to examine the relationship between the type of malocclusion, the body posture, and the nasopharyngeal obstruction in 12-14-year-old children. MATERIAL AND METHODS: The study group consisted of 76 orthodontic patients (35 boys, 41 girls) aged 12-14 years (mean age, 12.79 years [SD, 0.98]). All the patients were examined by the same orthodontist (study model and cephalometric radiograph analysis), the same orthopedic surgeon (body posture examined from the front, the side, and the back), and the same otorhinolaryngologist (anterior and posterior rhinoscopy and pharyngoscopy) in a blind manner. RESULTS: The prevalence of a poor body posture and a nasopharyngeal pathology was high in the present study. In total, 48.7% of the orthodontic patients had a kyphotic posture and 55.3% a rib hump in the thoracic region. The nasopharyngeal pathology was diagnosed in 78.9% of the patients. The patients with the kyphotic posture had a higher mandibular plane angle (MP-SN) and a lower sagittal position of the mandible SNB angle. A deeper overbite correlated with shoulder and scapular asymmetry. The kyphotic posture was diagnosed in 55.0% of the patients with the nasopharyngeal pathology. CONCLUSIONS: The sagittal body posture was related to the vertical craniofacial parameters and hypertrophy of the tonsils and/or the adenoids. The study showed no relationship between the degree of crowding, the presence of a posterior cross bite, orthopedic parameters, and a breathing pattern.