A method for evaluating skeletal relapsing force during maxillomandibular fixation after orthognathic surgery: a...

Although skeletal relapse after orthognathic surgery can be considered primarily the results of unbalanced tension in the surgically modified stomatognathic system (i.e., skeletal relapsing force [SRF] acting on the mandibular segment), no study of SRF has been reported and its nature still remains unclarified. This article presents a practicable method for evaluating SRF during the fixation period with the use of a foil strain gauge fixed to the upper arch wire between the central incisors, with a preliminary result after mandibular advancement by sagittal split ramus osteotomy to demonstrate the value of this method for studying SRF. The pattern and degree of SRF were shown to vary during the postoperative period and in accordance with experimental situations, including the mandibular resting posture, swallowing, clenching, and speaking. On day 3, a constant SRF of 550 gm existed even in the resting posture and was increased by 450 gm to a maximum of about 1 kg on swallowing; clenching and speaking also produced an increase. Thus it was inferred that SRF arose not only from surgically stretched perimandibular connective tissues but also from intermittent physiologic muscle actions. The constant SRF subsided gradually with time, and after day 33, swallowing as well as clenching no longer increased the SRF, which indicates that the critical period for postoperative skeletal stability was the first few weeks, during which muscle readaptation and primary bone healing occurred. It was concluded that this method of evaluating SRF, which is capable of immediately revealing any tendency to relapse or the progress of soft tissue adaptation and bone healing, could be used as an effective research tool.