Occlusal irregularities and their relationships to bite force

Objective: To assess the orthodontic treatment need or outcome, various occlusal indices have been developed with the scoring of morphological occlusal irregularities. However, properties of those irregularities have not been discussed. The present study was designed to evaluate the functional property of those occlusal irregularities from the point of maximum bite force (MBF). Methods: Subjects examined were 180 healthy male young adults with complete dentition. Nine occlusal indices with high validity and reliability and approved by many orthodontic societies and dental associations were selected, i.e. TPI, HMAR, OI, DAI, PAR, ICON, HLD/CalMod, OGS/ABO and DI/ABO. Their 65 occlusal irregularities were divided into 17 categories and scored according to their original instructions. MBF was analyzed using the pressure sensitive sheet. Correlation between scores of occlusal irregularities and MBF were analyzed by Spearman's rank correlation analysis. Results: Significant correlation were detected for some occlusal irregularities in those categories as buccolingual malalignment in the posterior teeth, overbite, anteroposterior relationship of posterior teeth, three-dimensional relationship of posterior teeth, occlusal contacts, and over jet in the anterior and posterior regions. Interestingly, other occlusal irregularities in the same category showed different levels of significance, owing to the different scoring methods. By the stepwise multiple regression analysis, 63 % of the variation of MBF were explained by four occlusal irregularities. In the current study, OGS/ABO and DI/ABO were the only indices whose total scores demonstrated significant correlation with MBF. Conclusions: Among 65 occlusal irregularities of nine occlusal indices, those irregularities participating in occlusal contacts of the posterior teeth could significantly take part in MBF.