Primary dentition unilateral crossbite in relation to functional lateralities.

PURPOSE: The aim of this study was to explore primary dentition unilateral crossbite malocclusion prevalences in functionally true right-sided and nonright-sided children, with the latter having 1 or more left-sided or indeterminate functions (eye, hand, foot). METHODS: The transversal relationship of the primary teeth was determined from dental casts of 1,835 young African American (60%) and Caucasian (40%) children in a cross-sectional sample at a mean age of 8.5 years. Hand, foot, and eye preferences (right, left, or indeterminate) were recorded at the age of 4 years during the same collaborative perinatal study. The prevalences of left and right crossbites were compared between true right-sided and mixed or completely nonright-sided children using chi-square analysis. RESULTS: Unilateral crossbite occurred in 140 cases with a complete set of laterality tests: 65 were right-sided and 75 left-sided. True right-sided children had more bilaterally symmetric occlusions and less crossbite on the right side than those having nonright-sidedness in their functions, with the differences being statistically significant (P<.01). CONCLUSIONS: These results point to anatomical relationships between the structures supporting the occlusion, the asymmetric neurocranium, and the cranial base. This suggests variable unilateral compensatory growth after unbalanced fetal asymmetry, modified by sidedness and the growth-stimulating effects of early lateralized functions and oral habits.

Sagittal occlusal relationships and asymmetry in prematurely born children.

The aim of this investigation was to examine the effect of pre-term birth on sagittal occlusal relationships. The subjects were 328 prematurely born white and black children and 1804 control children who participated in the cross-sectional study of the Collaborative Perinatal Project (USA) in the early 1960s and 1970s. Dental examinations, including dental casts and photographs, were performed at the age of 6-12 years. The sagittal occlusion of the permanent molars and the canine relationship was recorded by examining and measuring the hard stone casts. The pre-term and comparison groups were divided by sex and race. A significantly greater prevalence of pre-normal canine relationships was found in the pre-term group than in the controls (P < 0.001). The incidence of a bilateral symmetrical canine relationship was 60.3 per cent in both the pre-term and control groups, but in the pre-term group the girls had better symmetry than the boys. Asymmetry occurred significantly more often on the left side (P < 0.001), especially in the control boys, but this was not so clear in the pre-term group. The prevalence of mesial molar occlusion was greater in the pre-term group. These results suggest that premature birth and the consequent exceptional adaptation from intra- to extra-uterine nutrition may influence dental occlusal development. This emphasizes the importance of early functional activity and differences in masticatory muscle activity and the largely unknown phenomenon of early catch-up growth. Individual differences in neonatal factors, in the need for intubation and other medical care are also of importance. Pre-term birth may also interfere with the development of symmetry and lateralization.