Frequency of mandibular tori in the present-day Japanese

Abstract

The frequency and morphology of mandibular tori and the correlations between their development and environmental factors (number of teeth, degree of crowding, degree of dental attrition) were examined in plaster casts of present-day Japanese dental patients and students. A total of 224 patients (118 males aged 13–77, average age 50; 106 females aged 15–81, average age 49) and 113 students (60 males aged 17–36, average age 20; 53 females aged 18–29, average age 19) were included in the examinations. Before the examinations, we defined a new torus grading system with four categories. There were no statistically significant differences between males and females and between the left and right sides in the distribution of torus classes and positions. Palpable tori were found in 76.6% of patients and 72.0% of students. Perceptible tori were found in 70.3% of patients and 58.0% of students. Tori were most frequently found below the first and second premolars. In students, the torus class and size negatively correlated with the degree of crowding and positively correlated with the degree of dental attrition. In patients, torus class and size positively correlated with the degree of dental attrition, the number of teeth, and age. From these results, we suggest that mandibular tori are promoted by masticatory stress and other factors correlated with age.