Genetic and environmental influences on third molar root mineralization.

OBJECTIVE: To assess the genetic and environmental influences on the variability of human third molar (M3) root mineralization stages via a twin study. DESIGN: The study sample consisted of 162 same-sex twins (66 dizygotic and 96 monozygotic, mean age: 17.9 years) with normal growth and development. Panoramic radiographs were evaluated to assess root mineralization stages of the upper and lower third molars, using the method of Demirijian et al. (1973). Zygosity was established using 15 specific DNA markers. RESULTS: Females developed their third molar roots earlier in life than males. Monozygotic twins (MZ) demonstrated higher intra-pair correlations for M3 root development stages than did DZ twins. An ACE model with additive genes, as well as common and specific environmental factors, provided the best explanation of variation in M3 root development. The mineralization of M3 roots showed highly additive genetic determination, varying from 60 to 63%, whereas a common environment contributed from 25 to 27%, and a specific environment only accounted 14% of the total variation, at most. CONCLUSIONS: A considerable proportion of the total variability of the third molar root mineralization rate can be attributed to additive genetic effects, while common and specific environmental effects have a smaller, yet significant, impact.

The Impact of Genetics and Environmental Factors on the Position of the Upper Third Molars.

PURPOSE: The purpose of this study was to estimate the importance of heredity in the position of the upper third molars. MATERIALS AND METHODS: Panoramic radiographs and lateral cephalograms of same-gender twins were analyzed. The determination of zygosity was performed by means of DNA tests with polymerase chain reaction for the amplification of short tandem repeats and 15 specific DNA markers. Data were estimated by the relative influence of additive genetic factors (A), nonadditive genetic factors (D), the common or shared environment (C), and unique environmental factors (E). RESULTS: The study sample consisted of 212 twins: 80 dizygotic and 132 monozygotic twins. The genetic analysis showed that the best-fitting model for the size of the molars and their angulations was AE (additive genetic factors and unique environmental factors), in which the additive genetic factors had up to 84% influence and specific environment had up to 40%. Therefore, the ACE (additive genetic factors, common or shared environment, and unique environmental factors) model showed higher significance for the tooth eruption level. The heritability estimates were up to 59%, specific environment contributed up to 16%, and common environment reached 30%. CONCLUSIONS: Genetic factors play a key role in the position of the upper third molars.

Impact of genetics on third molar agenesis.

The purpose of this investigation was to determine the impact of heritability on third molar agenesis in twins. The study sample consisted of 284 same sex twins (172 monozygotic and 112 dizygotic), whose mean ages were 19.7 ± 4.3 and 18.9 ± 4.8 years, respectively. The monozygotic group consisted of 36.3% males and 63.7% females, while the dizygotic group consisted of 50.1% males and 49.9% females. The zygosity of the twins was established using 15 specific DNA markers. The prevalence of third molar agenesis in monozygotic twins was 19.6%, which was higher than in the dizygotic twins group (15.50%) (p = 0.004). In both groups, third molar agenesis was more frequent in the maxilla than in the mandible (p = 0.000). Agenesis of the maxillary third molars was mostly affected by additive genetic factors (62-63%), with the common environment and the specific environment accounting for up to 25% and 13%, respectively. In contrast, agenesis of the lower third molars was associated with a higher additive genetic determination (81-83%), with the specific environment accounting for 17% to 19%. The study's conclusion is that the formation of the third molars follicle is strongly controlled by additive genetic factors.

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.

Oral bony outgrowths: prevalence and genetic factor influence. Study of twins.

OBJECTIVE: The aim of the study was to verify the influence of a genetic factor on the etiology of oral bony outgrowths and to determine the prevalence and type of oral bony outgrowths (tori and exostoses) among a group of Lithuanian twins. MATERIALS AND METHODS: In total, 162 twins (81 twin pairs) were analyzed for the presence or absence, type, and size of oral bony outgrowths. Statistical analysis was carried out to find the prevalence of bony protuberances and the relationship between zygosity and occurrence of oral bony enlargements. Zygosity of twins was confirmed by DNA analysis. RESULTS: 59.9% of the subjects had oral bony outgrowths. Mandibular tori were found in 56.8% and palatal tori in 1.8% of the sample. Palatal exostoses and mandibular exostoses were present in 1.8% and 3.1% of the sample, respectively, whereas maxillary exostoses were not found. A higher percentage of tori and exostoses were found in the group of older subjects (>18 years old, p=0.025). No significant difference was found between men and women in the prevalence of bony outgrowths. High κ and r values (0.91±0.062) showed very good concordance of oral bony outgrowths between monozygotic and moderate concordance (0.58±0.141) between dizygotic co-twins (p<0.001). The calculation of heritability estimate verifies dominant influence of genetic factor on the etiology of oral bony outgrowths (h(2)=0.658). CONCLUSION: The most common bony outgrowth was torus mandibularis. Our results show that the genetic factor is dominant in the etiology of oral bony outgrowths.

Heritability estimates of dental arch parameters in Lithuanian twins.

BACKGROUND: The genetic influence on dental arch morphology may be country-specific, thus it is reasonable to check the estimates of genetics across different populations. The purpose of this study was to evaluate the heredity of dental arch morphology in the sample of Lithuanian twins with accurate zygosity determination. MATERIAL AND METHODS: The study sample consisted of digital dental models of 40 monozygotic (MZ) and 32 dizygotic (DZ) twin pairs. The estimates of heritability (h(2)) for dental arch breadth and length were calculated. RESULTS: All dental arch breadths and lengths were statistically significantly larger in men than in women. Arch length differences between genders were less expressed than largest breadth differences. In the upper jaw the largest genetic effect was found on the arch breadth between lateral incisors. The heritability of dental arch length demonstrated similar differences between upper and lower jaw with mandible dental arch length being more genetically determined. CONCLUSIONS: The largest genetic impact was found on the upper dental arch breadth between lateral incisors. Similar, but lower heritability is inherent for canines and first premolars of the upper jaw and first premolars of the lower jaw. It also can be noted, that arch breadths between posterior teeth show lower heritability estimates than between anterior teeth on both jaws. The dental arch in the upper jaw has more expressed genetic component than in the lower jaw.

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.

Typical renal-coloboma syndrome phenotype in a patient with a submicroscopic deletion of the PAX2 gene.

We present a patient with optic nerve hypoplasia, secondary strabismus, mild deafness, abnormal external ear helices, and renal hypoplasia. The clinical phenotype was consistent with renal-coloboma syndrome, but no point mutation in the PAX2 gene could be identified. High-resolution array comparative genomic hybridization (aCGH) analysis showed that this patient has a submicroscopic deletion on chromosome 10, affecting the entire coding region of the PAX2 gene. This finding provided the molecular confirmation of the patient's clinical diagnosis and showed that, in addition to point mutations, deletions of the PAX2 gene contribute to the etiology of the renal-coloboma syndrome.