Centric-Relation Bite as a Condylar Positioning Device in Bimaxillary Surgery

The repositioning of the proximal segment during bimaxillary surgery is critical for the maintenance of  temporomandibular joint function. A change in the position of the condyle after surgery results in an increase in the occurrence of internal derangement of the  temporomandibular joint, a loss of mandible angle, an increase in relapse, condyle sagging, and a loss or reduction of mastication, among other effects. In bimaxillary surgery, it is more difficult to reposition the condyle than during single-jaw surgery of the mandible. The dental occlusion changes during orthodontic treatment and is affected by neuromuscular function, gravity, level of consciousness and postural habits. The aim of this study was to evaluate preoperative and postoperative condylar positions among patients treated with bimaxillary surgery using a CR bite and simple device.

The patients comprised 20 adults who received bimaxillary surgery between August 2008 and July 2011. The amount of condylar displacement was measured by pre-/post-operative tomography analysis using Centric Relation(CR) Bite and wire in the surgery. The CR bite of each patient in an upright, conscious posture was obtained using Dawson’s bilateral manipulation method. Using an RP model previously created using 3D CT, a set of 3 reference points was generated. One (point A) was placed on the upper part of the estimated osteotomy line at the maxilla, and another (point B) was placed on the lateral cortical surface of the proximal segment of the mandible. The wire was bent approximately to fit points A and B. The third reference point (point C) was set using the same wire on the proximal segment approximately 1 cm from point B. The length of A-B and A-C was equal, and the same wire was used. Two different wires for the right and left side were prepared.                                    

The change in temporomandibular joint space was verified by measuring superior, anterior, and posterior joint space before and after surgery. A survey for temporomandibular joint(TMJ) sound, pain and locking was performed. 

The 20 tomographies were analyzed using Wilcoxon signed rank tests, and the surveys were analyzed using McNemar tests. No significant changes were observed in the anterior/superior/posterior joint space of the TMJ (p>0.05). No significant changes were observed in TMJ sound (p>0.05). The change in TMJ pain and locking was significantly decreased post-operation (p<0.05). 

Gerressen et al. and Fabio et al. reported that a manual positioning technique enabled equally stable results in orthognathic surgery. Previously published articles have advocated the use of condylar positioning devices or intraoperative imaging records only in the case of presurgical TMJ dysfunction or insufficient surgical experience. However, there has been a significant increase in the posterior displacement of CR from the conscious upright to the anesthetized supine position because the device is more precise than a surgeon’s hand and the possibility of mistakes remains even for expert surgeons. Manipulation of the condylar segments requires significant manual manipulation experiences. 

The condylar repositioning method used in this study is simple and procedure requires only 2-3 minutes; thus, it would not have a large influence on operative time and the TMD symptoms remained unchanged. Due to these reasons, this method may be a feasible and useful method for repositioning condyles.

 Reference

1. Costa F, Robiony M, Toro C, et al. Condylar positioning devices for orthognathic surgery: a literature review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:179-90 

2. Gerressen M, Stocbrink G, Riediger D, Ghassemi A. Skeletal stability following bilateral sagittal splint osteotomy(BSSRO) with and without condylar positioning device. J Oral Maxillofac Surg 2007;65:1297-302