PURPOSE To establish the accuracy of measuring the gonial angle on an orthopantomogram (GAO), as defined by the anatomic relationship between the inferior and posterior borders of the mandible. Furthermore, to examine the relationship between GAO and maximum occlusal force (MOF) in the premolar and molar regions of healthy young adults. MATERIALS AND METHODS Orthopantomograms of dry mandibles were obtained in three orientations in the sagittal plane, to represent variation in image acquisition in clinical settings. The GAO was measured using image-processing software, and reliability was analyzed using the intraclass correlation coefficient. Then, GAO, MOF, gender, and body mass index (BMI) were measured in a cohort of healthy young adult volunteers. MOF was measured using an Occlusal Force Meter GM 10 device. The relationships between GAO, MOF, sex, and BMI were examined using the Pearson correlation coefficient and multiple regression analysis. RESULTS In five dry mandibles, there was a high correlation between the GAOs measured in the different orientations (p < 0.001). In 58 healthy volunteers (31 women and 27 men, mean age 24.6 years), the mean GAO was 123.3° ± 7.5°. The mean MOFs at the first premolar, second premolar, and first molar teeth were 256.4 N ± 128.3 N, 319.0 N ± 171.7 N, and 487.5 N ± 227.2 N, respectively. Men had significantly greater MOF than women at all teeth. The GAO was significantly inversely correlated with MOF at the second premolar (r = -0.376, p = 0.005) and first molar teeth (r = -0.479, p < 0.001). Multiple regression analysis showed that GAO was a significant explanatory factor for MOF at the second premolar and first molar teeth (p = 0.012 and 0.001, respectively). CONCLUSIONS GAOs were measured accurately on the orthopantomograms taken in this study and were a reliable predictor of MOF between the second premolar and first molar teeth. A smaller GAO was associated with a greater MOF at the second premolar and first molar teeth.