Risk factors for low molar bite force in adult orthodontic patients.

The aim was to analyse which parameters in a standard orthodontic material are most important for identifying factors for low bite force. Such analyses have not previously been reported in adult orthodontic patients. The sample comprised 95 adults (67 females and 28 males) aged 18-55 years sequentially admitted for conventional orthodontic treatment. All subjects had moderate to severe malocclusions. Bite force was measured by a pressure transducer, craniofacial dimensions and head posture were measured on profile radiographs, number of teeth in contact were evaluated with a plastic strip in intercuspidal position, and symptoms and signs of temporomandibular disorders (TMD) were evaluated by TMD screening. Associations were assessed by Spearman correlations, Wilcoxon signed-rank sum test, and multiple stepwise regression analyses. Associations were found between bite force and craniofacial dimensions as mandibular prognathia (S-N-Pg, P < 0.05; S-N-sm, P < 0.05), sagittal jaw relationship (SS-N-Pg, P < 0.05), mandibular inclination (NSL/ML, P < 0.05), and mandibular plane angle (ML/RL, P < 0.01) and between bite force and TMD symptoms (P < 0.05) and TMD signs (P < 0.05). Multiple regression analysis showed that gender (P < 0.001), TMD symptoms (P < 0.01), and mandibular plane angle (P < 0.001) were the most important factors for the magnitude of the bite force in adult orthodontic patients (R (2) = 0.32). The results showed that particularly women with TMD symptoms and an increased mandibular plane angle are at risk of having low bite force. This may prove valuable in the clinic, especially in orthodontic cases with an increased need for vertical anchorage during treatment.