Study Of The Prevalence Of Unilateral Posterior Crossbite And Effects On The Masticatory Function

Unilateral posterior crossbite is a relatively common malocclusion. An incidence ranging between 7% and 23% of the population has been found by many foreign authors. But there is no article about the prevalence of unilateral posterior crossbite in China. Among different malocclusions, unilateral posterior crossbite is thought to have a stronger impact on the normal functioning of the masticatory system. Previous findings have suggested that persons with unilateral posterior crossbite contracted their jaw muscles asymmetrically, and that they exerted lower bite force, a reduced thickness of the masseter muscle, asymmetries growth of mandibular and mandibular shifts have also been reported. Unilateral posterior crossbite has been considered as a risk factor for temporomandibular disorder. In this study we made an epidemic survey to investigate the prevalence of unilateral posterior crossbite among children with deciduous dentition and adolescents with permanent dentition in Xi'an city. We also recorded EMG data from the left and right masseter and anterior temporalis muscles. Masticatory movement was registered during unilateral chewing of a piece of gum. The impact of unilateral posterior crossbite on mastictory function has been analyzed in my study, and it may provide some proofs for diagnose and treatment of unilateral posterior crossbite.1408 children from three kindergartens were underwent an oral health examination. The prevalence of unilateral posterior crossbite was analyzed. Unilateral posterior crossbite was found in 132 participants (9.38%). 31 participants were found to have unilateral posterior crossbite and anterior crossbite. Finger sucking is strongly associated with the occurrence of unilateral posterior crossbite. Parents and dentists should pay more attention to children's finger sucking, some reasonable methods should be taken to prevent and abstain this habit. 1635 adolescents from three middle schools were underwent an oral health examination. The prevalence of unilateral posterior crossbite was analyzed. The prevalence of UPXB at the permanent dentition is 7.40%, this may be explained by the self-correction of UPXB. We also found a significant association between UPXB and TMD, so we think UPXB is a risk factor for TMD. Early treatment should be carried out to prevent TMD.20 subjects (11 males and 9 females) with unilateral posterior crossbite and 11 subjects whose UPXB have been treated were selected in this study. 20 subjects with individual normal occlusion were used as control. We recorded EMG data from the left and right masseter and anterior temporalis muscles. Masticatory movement was registered during unilateral chewing of a piece of gum. Compared to the control group, masseter and temporal muscle activities in unilateral posterior crossbite group were lower in maximum bite and bilateral chewing. Under maximum bite and lateral chewing, ASMM and ASTA in unilateral posterior crossbite group were significantly higher than those in control group. ASMM and ASTA in subjects with only one posterior tooth crossbite were lower than subjects with several teeth crossbite. Reverse sequencing chewing cycle is prevalent among patients with unilateral posterior crossbite. It was found that the percentage of reverse sequencing during chewing on the crossbite side was significantly higher than that on the unaffected side. We also found a significant reduction in reverse sequencing after orthodontic therapy. We conclude that orthodontic correction can eliminate reverse sequencing in the chewing cycle, early treatment should be taken to recover masticatory function.Unilateral posterior crossbite is a relatively common malocclusion. It is thought to have a stronger impact on the correct functioning of the masticatory system. So parents and dentists should pay more attention to it. Clinicians should carry out early treatment of unilateral posterior crossbite in order to recover masticatory function so as not to disturb normal growth.