Short-term effects of oral appliances with equal bite-raising distance but with varying protrusions on occlusal force, contact area and load center.

The purpose of this study was to demonstrate how short-term wearing of an oral appliance (OA) with equal bite-raising distance but with varying protrusions affects occlusal force, contact area and load center. Twelve young healthy volunteers participated. With the appliance, the mandible was protruded 0%, 45%, 60% and 75% of maximum protrusion capacity, with 10 mm bite-raising between the first molars. The occlusal force, contact area and load center at maximum voluntary clenching were measured before wearing the OA, at 1 h, 3 h and 6 h during wearing, and 1 h after removal. When compared to the values before wearing the OA, occlusal force was significantly lower at 1 h, 3 h and 6 h during wearing in the case of no mandibular protrusion, and at 3 h and 6 h after for 45%, 60% and 75% of maximum mandibular protrusion (P < 0.05). Occlusal contact area was significantly smaller at 1 h and 6 h during wearing in the case of no protrusion, and at 6 h during wearing in the case of 45% of maximum protrusion (P < 0.05). There was a tendency for anterior shift in the location of the occlusal load center at 3 h and 6 h during wearing of the OA with any level of maximum protrusion. No significant change in these three measurements was found at 1 h after removal of the OA. The present study demonstrated that wearing an OA had only a marginal and transient influence on oral functions when their changes were compared before and after wearing the OA.