Influence of anthropometry, TMD, and sex on molar bite force in adolescents with and without orthodontic needs

Bite force has been studied as representative of functional indices of mastication and its value may have diagnostic significance in disorders of the musculoskeletal system of facial bones. This study aimed to evaluate bite force in adolescents with and without orthodontic needs considering presence of temporomandibular disorders (TMD) as well as anthropometry: craniofacial dimensions and body mass index (BMI).

A total of 80 subjects were screened (61 females, 19 males; 18 ± 3 years old). Unilateral molar bite force was measured using a digital dynamometer with a fork thickness of 12 mm. Direct anthropometry was used to quantify craniofacial measurements. Dental Health Component of the Index of Orthodontic Treatment Need (IOTN-DHC) and the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were used to classify samples according to malocclusion and to TMD, respectively. Data were analyzed using normality tests, Mann-Whitney U test, and multiple linear regression analyses with stepwise backward elimination, controlling for the presence of malocclusion and TMD (p ≤ 0.05).

The cephalic index was greater in females with malocclusion and the longitudinal cranial diameter was reduced in females with malocclusion. BMI was not different between normal and malocclusion groups for either gender. Bite force was negatively related with vertical dimension of the face, and positively related with facial width and facial index. The model explained 32% of bite force variability, considering the sample size (coefficient of determination R ² = 0.324).

Even when orthodontic needs and TMD signs and symptoms are present, stronger bite force is still observed in males and in subjects with smaller anterior facial heights and wider facial widths.