Correlation Between the Tragus-Incisal Distance and Interocclusal Rest Distance

Purpose: To evaluate correlations of arch size and sex with the interocclusal rest distance (IORD), as well as to estimate proportional variance. Materials and Methods: A total of 106 participants were examined. The participants, 38 men and 68 women, were aged 22 to 30 years, were fully dentate, had no signs of abnormal abrasion, and had intact posterior occlusal contacts. Measurements of interocclusal rest distance and tragus-incisal distance were recorded, and the rest angle created between the tragus-incisal distance in maximum intercuspation and in resting vertical dimension were calculated according to the cosine formula. Correlation between the size of the mandible (tragus-incisal distance, mean of left and right sides) and the IORD were calculated using Pearson correlation coefficient. Correlations for sex (calculated separately for male and female) and rest angle were also assessed. Results: The mean (SD) tragus-incisal distance values were 123.38 (6.77) mm for all participants, 120.01 (4.64) mm for women, and 130.72 (5.24) mm for men. The mean (SD) IORD values were 2.76 (1.3) mm for all participants, 2.13 (0.9) mm for women, and 3.87 (1.17) mm for men. The mean (SD) rest angle values were 1.26 (0.55) degrees for all participants, 1.02 (0.41) degrees for women, and 1.7 (0.49) degrees for men. Pearson correlation coefficient between IORD and tragus-incisal distance was significant (P <.05). According to t test, there was a significant difference between men and women for IORD, tragus-incisal distance, and rest angle (P <.01). Conclusion: A correlation exists between IORD and arch size.