Association between severity of malocclusion and parameters of oral functions in permanent dentition with various malocclusion: case-control study

Abstract

ABSTRACT Purpose It has been reported that people with malocclusion have poor masticatory function, including decreased bite force and masticatory efficiency, but the relationship between the severity of malocclusion and oral function remains unclear. The purpose of this study was to clarify the relationship between the severity of malocclusion and various oral function parameters using the Dental Health Component (DHC) of the Index of Orthodontic Treatment Need (IOTN), which quantitatively evaluates the state of malocclusion. Materials and methods A total of 138 permanent dentition patients (39-men, 99-women; aged 15–59 years) who visited Tsurumi University Dental Hospital were included in the study. The severity of malocclusion was determined using IOTN-DHC grading, and patients were classified into three groups. All patients underwent oral function tests before orthodontic treatment, including masticatory efficiency, occlusal force, occlusal contact area, lip pressure and tongue pressure. The relationship between malocclusion severity and oral function was statistically analysed. Results Firstly, we compared the medians of each oral function values among three groups and found statistically significant lower value in group 3, the worst IOTN-DHC grading group, as compared to group 1. Correlation analysis revealed correlations between malocclusion severity and oral functions, such as lip pressure, masticatory efficiency and tongue pressure. In addition, masticatory efficiency was correlated with occlusal contact area, tongue pressure and lip pressure. Conclusions Our results suggest that oral function is lower in patients with severe malocclusion and masticatory efficiency is related not only to dental occlusion but also to the function of surrounding soft tissues, such as the tongue and lips.