Effect of Wearing an Oral Appliance on Range of Motion of Spine during Trunk Flexion

Purpose: The aim of this study was to clarify the effect of wearing an oral appliance on the range of motion of the spine during trunk flexion in elite-level athletes. Method: Participants were 15 elite-level female handball players (24.9 ± 2.0 years). A single-layer mouthguard was fabricated using a 2.0-mm-thick thermoplastic sheet that all teeth were adjusted to make even contact upon light clenching. Spinal curvature was measured in the static standing posture and standing forward-bending posture by using a spinal shape analyzer. The evaluation indices were thoracic kyphosis angle (TKA), lumbar lordosis angle (LLA), sacral inclination angle (SSA), and spinal inclination angle (SIA). Measurements were made under three conditions: mandibular resting position (RP), clenching in the intercuspal position (ICP), and clenching while wearing a mouthguard (MG). Differences in spinal curvature due to occlusal conditions were compared using repeated measure analysis of variance. Results: LLA, SSA, and SIA showed significant differences between RP and ICP, and between RP and MG, with RP having the greatest range of motion. There was no significant difference in any spinal alignment between ICP and MG. TKA was not significantly affected by occlusal condition. Conclusion: This study was clarified that lumbar lordosis angle, sacral inclination angle, and spinal inclination angle during trunk flexion decreased with clenching, regardless of the presence or absence of an oral appliance. Therefore, it was suggested that clenching contributes to trunk stabilization and may affect flexibility.