Relationship between masticatory cycle morphology and unilateral crossbite in the primary dentition.

Occlusion is an important factor that affects chewing. Unilateral posterior crossbites (UPXBs) have been reported to be one of the most prevalent malocclusions in the primary dentition and patients with UPXBs show abnormal condylar motion on the crossbite side in the mediolateral direction during mastication. The aims of this study were to investigate the characteristics of common chewing cycles in the primary dentition in children with UPXBs, when chewing gum on the UPXB side and on the non-UPXB side, and to compare the average chewing pattern with a group of children with a normal buccal relationship. Twenty children in the primary dentition with a UPXB (6 boys, mean age 5.3 ± 1.2 years, and 14 girls, 4.8 ± 1.3 years of age; 9 with a left and 11 with a right UPXB) and 10 children with a normal occlusion were randomly selected. Chewing movements were recorded with the Sirognathograph computer analysing system (COSIG II). All children were asked to chew gum on both sides. The chewing patterns were averaged and analysed in two projection planes and compared using a Student's t-test with respect to the relationship between chewing pattern and occlusion. Significance was set at P ≤ 0.05. Children with a UPXB showed a difference between the chewing pattern on the UPXB and non-UPXB sides. Greater lateral deviation in the chewing cycle was observed on the working side when chewing on the non-UPXB side. The closing angle was found to be more pronounced towards the non-working side when chewing on the UPXB side and the time spent in maximal intercuspation showed reduced values when chewing on the same side. Children with a UPXB opened their mouths wider and showed greater chewing cycles in the sagittal and horizontal projection planes while chewing on the UPXB side and also in the frontal projection while chewing on both the UPXB and the non-UPXB sides in comparison with the control group, P ≤ 0.05. Children with a UPXB produced chewing cycles with a shorter rest position and more frequently in a reverse direction when chewing on the UPXB side in comparison with children with a normal occlusion and with the non-UPXB side. Based on the results of this study, early treatment is recommended to normalize the masticatory chewing cycle pattern to ensure normal growth and development of the orofacial system.