Background/Objectives: Eccentric bruxism is a complex parafunctional activity that involves grinding of teeth and occurs more frequently during sleep. This study aimed to assess differences in condylar parameters (sagittal condylar inclination -SCI and Bennett angle -BA) and mandibular and condylar kinematics during functional and parafunctional movements in bruxers and non-bruxers and to assess a digital method for quantifying eccentric bruxism using an optical jaw tracking system (Modjaw^®). Methods: The study group included subjects diagnosed with eccentric bruxism according to validated clinical diagnostic criteria. A control group of non-bruxer subjects with demographic characteristics similar to the study group was considered. Each participant underwent Modjaw^® examination twice to assess the recordings’ repeatability. The anterior guidance, mastication, and simulated eccentric bruxism were recorded. The SCI and BA were computed. The trajectories of interincisal inferior point (IIP), left condyle (LC), and right condyle (RC) in the frontal (F), sagittal (S), and horizontal (H) planes were outlined in rectangles to calculate areas of mastication and areas of eccentric bruxism (mm²). Intraclass correlation coefficient (ICC) was used to assess the recordings’ repeatability. Comparisons between groups were performed using Student’s t- and Mann–Whitney tests. The receiver–operator characteristic (ROC) curve was used to assess the diagnostic quality of the digital method. Results: Twenty bruxers (10 F and 10 M) and 20 non-bruxers (10 F and 10 M) were included. The ICC had values higher than 0.85. SCI, BA, and area of mastication for IIP, LC, and RC were similar between the groups (p > 0.05). The area of eccentric bruxism was significantly wider in the bruxers (p < 0.001). According to the ROC curve, the following cut-off areas (mm²) for eccentric bruxism were found in F, S, and H planes: IIP (18.05, 13.43, 16.28); LC (3.74, 10.83, 3.35); and RC (4.21, 10.63, 2.9), corresponding to sensitivity > 0.8, specificity > 0.75 and area under the curve (AUC) > 0.85. Conclusions: Mandibular and condylar kinematics during functional movements were similar in bruxers and non-bruxers. A novel digital method for quantifying eccentric bruxism was found using Modjaw^®, which could serve as a tool for early detection of eccentric bruxism before the onset of clinical consequences.

Bruxism is a parafunctional behavior that involves clenching and grinding of the teeth, as well as increased masseters activity with or without contact with the teeth. It can happen during the day or at night. Diagnostic tools for bruxism include self-assessment questionnaires, clinical evaluation forms and polysomnography. Stress and anxiety represent two psychological factors that have been frequently related to bruxism. Twenty students in dental medicine were included in this study and a self-assessment questionnaire together with a clinical evaluation form were used as diagnostic tools for bruxism. Consequently, two groups developed: group A or non-bruxers and group B or bruxers. A questionnaire of perceived stress and anxiety levels was applied for both groups. The average score for group A was 20.8 and for group B was 31.8 with a statistically significant difference (p=0.0062, T-test). Higher perceived stress level was associated with a higher risk of bruxism, along with higher anxiety level, parafunctions, and poor sleep quality. In order to accurately diagnose bruxism, a comprehensive clinical examination and, if feasible, a polysomnography ought to be performed after completing a self-assessment questionnaire.