Influence of Voluntary Clenching on Spinal Range of Motion Depends on Occlusal Contact State

Purpose: The aim of this study was to clarify the effects of voluntary moderate clenching on the range of motion of the spine depending on the occlusal contact state. Method: Participants were 46 healthy men with no missing teeth except for wisdom teeth, and no medical history of musculoskeletal neurological or orthopedic surgery. Using a pressure-sensitive film, the participants were divided into those with a lateral difference in occlusal contact area of less than 10% (good occlusal balance group) and those with 10% or more (occlusal imbalance group). A spinal shape analyzer was used to measure the curvature of the spine in the static standing posture and the standing forward bending posture. The evaluation indices were thoracic kyphosis angle (TKA), lumbar lordosis angle (LLA), sacral inclination angle (SSA), and spinal inclination angle (SIA), and the range of motion for each alignment configured on the analyzer software. Two measurement conditions were compared: mandibular resting position (RP) and voluntary 50% maximal clenching (50% MVC) in the intercuspal position. Differences in range of motion for each spinal align- ment due to occlusal balance and clenching were analyzed with a split-plot design. Results: LLA, SSA, and SIA showed significant differences in occlusal balance and clenching factors. In the good occlusal balance group, LLA, SSA, and SIA were significantly lower in 50% MVC condition than in RP condition. In the occlusal imbalance group, there was no difference between the presence or absence of clenching in any spinal alignment. Conclusion: As a result of this study, it was clarified that the effect of clenching on the range of motion of the spine during trunk flexion differs depending on the occlusal contact state. In other words, it was suggested that voluntary clenching restricts trunk flexion in participants with good occlusal balance.