Comparison of Body Position Perception, Tongue Pressure and Neck Muscle Endurance in Patients with Bruxism and Temporomandibular Joint Dysfunction: Occlusal Splint Users and Non-Users

Background: This study aimed to investigate the association between occlusal splint use and several key parameters, including body position perception, tongue pressure, temporomandibular joint dysfunction (TMD) severity, jaw functional limitation, and neck muscle endurance. Methods: A total of 157 individuals diagnosed with bruxism were screened, and 52 eligible participants were enrolled and divided into two groups: occlusal splint users (n = 26) and non-users (n = 26). Body position perception was assessed with a digital inclinometer, tongue pressure was measured using the Iowa Oral Performance Instrument (IOPI), and neck muscle endurance was evaluated by the Cranio-Cervical Flexion Test (CCFT). TMD severity and jaw functional limitation were assessed via the Fonseca Anamnestic Questionnaire and Jaw Functional Limitation Scale-20, respectively. Gender-based analyses showed higher TMD severity and mandibular limitation scores in females using occlusal splints than in males. Results: No statistically significant differences were found between the splint and non-splint groups in body position perception, tongue pressure and neck muscle endurance (p > 0.05). However, significant differences were observed in the Jaw Functional Limitation Scale (CFKS) subscales. Splint users reported higher functional limitations in chewing, mobility, and expression compared to non-splint users (all p = 0.000), with small effect sizes (d = 0.23–0.29). Conclusions: Occlusal splint use was not associated with better proprioception, orofacial muscle function, or TMD-related symptoms compared with non-splint users. However, splint users were associated with higher mandibular functional limitation based on CFKS subscale scores.