Cervical column morphology and craniofacial profiles in monozygotic twins

Frontal sinus dimensions can differ significantly between individuals within a monozygotic twin pair, indicating environmental influence on sinus sizes

CONCLUSION

The study showed that the size of the frontal sinus is not determined solely by genotype, but that other factors, e.g. environment, seem to affect the size as well. Environmental factors may include, for example diseases, trauma, allergies, acquired conditions, nutrition or medicine use.

OBJECTIVES

The purpose of the study was to compare sinus dimensions between individuals within a monozygotic twin pair.

METHODS

Profile radiographs were obtained from 42 pairs of monozygotic twins, 18 male and 24 female pairs (aged 18-23 years) with no known skeletal deviations in the cranium or general diseases. For each individual the size of the frontal sinus was analyzed on a profile radiograph and compared with the sinus size of the corresponding twin. The variation between twins was estimated using a random effects model for each gender.

RESULTS

The sinus sizes varied considerably between twins. The standard deviation between female pairs was 2.98 mm and between male pairs 5.36 mm. The variations in sinus sizes between females and males within twin pairs were not significantly different (p = 0.86 for height and p = 0.83 for width, F test). Still, within one female twin pair and within two male twin pairs, sinus sizes varied significantly between the two individuals.

The Morphology of the Sella Turcica in Monozygotic Twins

The purpose was to compare the sella turcica morphology of individuals within pairs of monozygotic twins with normal karyotype and to analyze the similarity between the observed morphology and the morphology of non-twins at the same age with normal karyotype. Profile radiographs from 84 individuals of 42 twin pairs (18 male and 24 female pairs, aged 18–23 years) comprised the material. Sella turcica measurements from non-twins aged 6–21 years were used as normal reference. Length, depth and diameter of the sella turcica were measured and controlled by re-measurements. Pearson's correlation coefficient was used for comparison of individuals within twin pairs. For comparison of twins and non-twins, normal standard values for length, depth and diameter were subtracted from the twin values. For the mean values of these differences, confidence limitspvalues andtvalues were calculated. The study showed that the size of the sella turcica may be partly similar and partly dissimilar within the pair of monozygotic twins. Statistical evaluation of the data showed correlations between length, depth and diameter of the sella turcica between the two twin individuals in the same twin pair. Differences in sizes are observed between individuals in the twin material and individuals in the non-twin material. As a conclusion, the twin males were more similar within the twin pair, but deviated more from the non-twin material than the females. Female twins had more discrepancy within the twin pair, but deviated less from the non-twin material than the males.

Associations between the Cervical Vertebral Column and Craniofacial Morphology

Aim. To summarize recent studies on morphological deviations of the cervical vertebral column and associations with craniofacial morphology and head posture in nonsyndromic patients and in patients with obstructive sleep apnoea (OSA). Design. In these recent studies, visual assessment of the cervical vertebral column and cephalometric analysis of the craniofacial skeleton were performed on profile radiographs of subjects with neutral occlusion, patients with severe skeletal malocclusions and patients with OSA. Material from human triploid foetuses and mouse embryos was analysed histologically. Results. Recent studies have documented associations between fusion of the cervical vertebral column and craniofacial morphology, including head posture in patients with severe skeletal malocclusions. Histological studies on prenatal material supported these findings. Conclusion. It is suggested that fusion of the cervical vertebral column is associated with development and function of the craniofacial morphology. This finding is expected to have importance for diagnostics and elucidation of aetiology and thereby for optimal treatment.