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).

Relations of laterality and chewing sidedness in twins.

OBJECTIVES: To study, whether there are associations between chewing side preference and other lateralities, whether there is a genetic origin for preferred chewing side (PCS), relations to sex, birth order and orthodontic treatment. MATERIALS AND METHODS: The study included 113 twin pairs, 57 pairs monozygotic, 47 pairs same sex dizygotic and 9 pairs of opposite sex. The lateralities of preferred chewing side, footedness and eyedness were assessed by functional tests and handedness was checked by asking. RESULTS: Right-handed, -footed and -eyed as separated groups, and true-right sided (combined), were evenly distributed by preferred chewing side. By contrast, left-handed, -footed, -eyed and non-right sided used more left or both sides when chewing. Birth order affected preferred chewing side among monozygotic: the first-born twin was more likely to have the preferred chewing side on the non-right, whereas second-born twins used right side. Gender, zygosity and orthodontic treatment were not statistically significant factors. LIMITATIONS: Examination of chewing sidedness could have been done in several different ways to provide a definite result. Sample size of opposite sex twins was very small. CONCLUSIONS: Preferred chewing side generally seemed to follow the side where other lateralities occur; however, monozygotic twins seemed to be more receptive to it. True-right sided were more evenly distributed than non-right sided by the preferred chewing side.

Smile aesthetics as perceived by dental students: a cross-sectional study.

BACKGROUND: An aesthetic smile has a number of components, and people generally equate a good dental appearance with success in many areas of life. The features that determine smile aesthetics could provide significant insights into post-treatment satisfaction and may predict a patient's objectives when undergoing treatment. The purpose of this study was to evaluate how smile characteristics are perceived by dental students. METHODS: The study was performed in 431 local and international dental students at the Lithuanian University of Health Sciences. The study data were collected using a three-part questionnaire. The first part of the questionnaire included sociodemographic items, i.e., student gender, age, nationality, and years of study; the second consisted of questions about facial aesthetic features; and the third elicited responses to photographs of 17 different smiles retrieved from the Lithuanian University of Health Sciences Clinic of Orthodontics database. The smile aesthetics were evaluated according to their dentolabial, dentogingival, dental, and dental arch characteristics using a 5-point numeric rating scale (1, best; 5, worst). The data were analysed using the Pearson's chi-square and Mann-Whitney U tests. RESULTS: The study included 336 local and 95 international dental students (132 men [30.6%], 299 women [69.4%]). Significantly more women than men focused on a person's teeth when communicating (41.5% vs.32.6%, p < 0.005). Women were more critical than men when evaluating gingival smile, the 'golden proportion', occlusal cant, and dental crowding. The most unfavourable smile characteristics were identified in the dental analysis category, with hypodontia ranked as the worst smile feature (mean numeric rating scale score 4.71). CONCLUSION: Among dental students, the most distracting characteristics of a smile when determining its attractiveness were hypodontia, gingival smile, a reversed curvature of the occlusal plane, and dental crowding.

Relationship between malocclusion, soft tissue profile, and pharyngeal airways: A cephalometric study.

BACKGROUND AND OBJECTIVE: The recent years have been marked by a search for new interrelations between the respiratory function and the risk of the development of malocclusions, and algorithms of early diagnostics and treatment have been developed. The aim of the study was to evaluate the relationships between hard and soft tissues and upper airway morphology in patients with normal sagittal occlusion and Angle Class II malocclusion according to gender. MATERIALS AND METHODS: After the evaluation of clinical and radiological data, 114 pre-orthodontic patients with normal or increased ANB angle, were randomly selected for the study. The cephalometric analysis was done by using the Dolphin Imaging 11.8 computer software. RESULTS: Comparison of the cephalometric values of soft tissue and airway measurements performed statistically significant negative correlation between the width of the upper pharynx and the ANB angle was found: the ANB angle was decreasing with an increasing width of the upper pharynx. The airways showed a statistically significant negative correlation between the width of the lower pharynx and the distance from the upper and the lower lips to the E line. Logistic regression analysis was performed to evaluate significant factors that could predict airway constriction. The upper pharynx was influenced by the following risk factors: a decrease in the SNB angle, an increase in the nose tip angle, and younger age; while the lower pharynx was influenced by an increase in the distance between the upper lip and the E line and by an increase in the upper lip thickness. CONCLUSIONS: During critical period of growth and development of the maxillofacial system, the patients with oral functional disturbances should be monitored and treated by a multidisciplinary team consisting of a dentist, an orthodontist, a pediatrician, an ENT specialist, and an allergologist. Cephalometric analysis applied in our study showed that Angle Class II patients with significantly decreased facial convexity angle, increased nasomental, upper lip-chin, and lower lip-chin angles, and upper and lower lips located more proximally to the E line more frequently had constricted airways.

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.

Comparing Facial 3D Analysis With DNA Testing to Determine Zygosities of Twins.

The aim of this study was to compare facial 3D analysis to DNA testing in twin zygosity determinations. Facial 3D images of 106 pairs of young adult Lithuanian twins were taken with a stereophotogrammetric device (3dMD, Atlanta, Georgia) and zygosity was determined according to similarity of facial form. Statistical pattern recognition methodology was used for classification. The results showed that in 75% to 90% of the cases, zygosity determinations were similar to DNA-based results. There were 81 different classification scenarios, including 3 groups, 3 features, 3 different scaling methods, and 3 threshold levels. It appeared that coincidence with 0.5 mm tolerance is the most suitable feature for classification. Also, leaving out scaling improves results in most cases. Scaling was expected to equalize the magnitude of differences and therefore lead to better recognition performance. Still, better classification features and a more effective scaling method or classification in different facial areas could further improve the results. In most of the cases, male pair zygosity recognition was at a higher level compared with females. Erroneously classified twin pairs appear to be obvious outliers in the sample. In particular, faces of young dizygotic (DZ) twins may be so similar that it is very hard to define a feature that would help classify the pair as DZ. Correspondingly, monozygotic (MZ) twins may have faces with quite different shapes. Such anomalous twin pairs are interesting exceptions, but they form a considerable portion in both zygosity groups.

Multifactorial etiology of Torus mandibularis: study of twins.

OBJECTIVE: The aim of this study is to investigate the multifactorial etiology of mandibular tori analyzing the influence of genetics, occlusal overload, various clinical variables and their interactions. METHODS: Overall, plaster casts of 162 twins (81 twin pairs) were analyzed for the presence or absence of mandibular tori. Atypical wear facets on canine tips or incisors were recorded to diagnose bruxism. Angle Class, any kind of anterior open bite and positive, negative or flat curve of Wilson were recorded. Zygosity determination was carried out using a DNA test. RESULTS: Mandibular tori were found in 56.8% of the cases. In 93.6% of all monozygotic twin pairs both individuals had or did not have mandibular tori (κ=0.96±0.04; p<0.001), compared to 79.4% concordance of mandibular tori in dizygotic co-twins (κ=0.7±0.12; p<0.001). Prevalence of mandibular tori was significantly higher in the group of bruxers (67.5%) compared to non-bruxers (31.3%) (p<0.001). Significant association between mandibular tori and negative or flat curve of Wilson in the maxillary second premolars and first molars was found (OR=2.55, 95% CI (1.19-5.46), p=0.016). In all monozygotic bruxers, 97.1% showed concordance of mandibular tori presence in both co-twins compared to 78.9% dizygotic bruxers, and this difference is statistically significant (p=0.007). CONCLUSION: Our results suggest that the mandibular tori are of a multifactorial origin. Mandibular tori seem to have genetic predisposition, and may be associated with teeth grinding as well as with negative or flat CW in region of maxillary second premolar and first molar.

The prevalence of malocclusion and oral habits among 5-7-year-old children.

BACKGROUND: Digit sucking, tongue thrust swallowing, and mouth breathing are potential risk factors for development of malocclusion. The purpose of this study was to verify the prevalence of different occlusal traits among 5-7-year-old children and assess their relationship with oral habits. MATERIAL AND METHODS: The study included 503 pre-school children (260 boys and 243 girls) with a mean age of 5.95 years. Different occlusal traits were verified by intraoral examination. Oral habits were diagnosed using data gathered from clinical examination of occlusion and extra-oral assessment of the face, combined with a questionnaire for parents. RESULTS: The study demonstrated that 71.4% of the children presented with 1 or more attributes of malocclusion and 16.9% had oral habits. The vertical and sagittal malrelation of incisors, as well as spacing, were the predominant features. This study showed that digit suckers have higher incidence of anterior open bite (P=0.013) and posterior crossbite (P=0.005). The infantile type of swallowing demonstrated strong association (P=0.001) with anterior open bite. CONCLUSIONS: Non-nutritive sucking habits and tongue thrust swallowing are significant risk factors for the development of anterior open bite and posterior crossbite in pre-school children.

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.

Assessment of skeletal and dental pattern of Class II division 1 malocclusion with relevance to clinical practice.

Class II division 1 malocclusion represents the most common skeletal discrepancy which orthodontists see in daily practice. The understanding of the morphology is a key element in planning dentofacial orthopedic treatment for this type of malocclusion. The purpose of the present study was to examine prepubertal children with Class II division 1 malocclusion and to evaluate maxillary and mandibular skeletal positions in comparison with normal growth standards by means of cephalometric measurements used by clinical practitioners. For the study casts and cephalograms of 86 consecutive patients with Class II division 1 malocclusion were used. The Class II division 1 malocclusion demonstrates broad variation in its skeletal and dental morphology. The retrognathic mandible (60%), maxillary prognathism (55.8%) and reduce vertical skeletal jaw relationship is the most common characteristic of Class II division 1 malocclusion. The optimal correction of the anteroposterior and vertical dental and skeletal discrepancies could be designed on the base of individual diagnosis for every Class II division 1 patient.