Stacy Geisler DDS, PhD
The authors concluded that relapse following bilateral sagittal split osteotomy of the mandible is multifactorial.
1) What is the amount of horizontal relapse following mandibular advancement with bilateral sagittal split osteotomy utilizing rigid internal fixation? 2) What factors contribute to skeletal relapse?
An electronic search of four databases using terms related to orthognathic surgery from 1974 to 2007 was conducted. Forty-three articles were identified; however only twenty-four trials met all inclusion and exclusion criteria. A quality assessment was also conducted for each of the trials as described by Jaded et al and Petren et al.
Only one prospective, randomized clinical trial (RCT) was of adequate methodological quality to meet inclusion and exclusion criteria. This trial evaluated short (6 months) and long term (24 months) skeletal relapse between two groups of patients undergoing bilateral sagittal split osteotomy (BSSO) advancement of the mandible without genioplasty. Rigid internal fixation (RIF) utilizing three bicortical screws was compared to wire fixation. The authors of this trial found that RIF produced a more stable outcome as compared to wire fixation. Since none of the remaining twenty-three trials employed a randomization strategy between interventions, they were determined to range from medium to low methodological quality.
All trials included in the systematic review attempted to assess short term and long term relapse as measured at cephalometric B point for three forms of RIF following BSSO advancement of the mandible utilizing bicortical screws, bioresorbable bicortical screws and mini-plates. The majority of studies did not adjust for confounding variables such as genioplasty or surgical splints in their analysis, making a meta-analysis impossible due to heterogeneity between studies. In addition, standardization of cephalometric landmarks used to measure outcome variables was not consistent between the different studies evaluated in the systematic review.
The authors of the systematic review concluded that BSSO for mandibular advancement is a good treatment option for skeletal Class ll malocclusions but less stable for mandibular set-backs in both the long and short term. The etiology of relapse appears to be multifactorial with high mandibular plane angle patients exhibiting more horizontal relapse and those with a low mandibular plane angle exhibiting more vertical relapse. Advancements greater than 6 to 7 mm are more prone to horizontal relapse. The authors concluded that there were minimal differences between bicortical screws of titanium, stainless steel or bioresorbable material compared to miniplates in the short term but patients treated with bicortical screws, as compared to mini-plates, exhibited greater long term relapse.
Source of Funding:
Importance and Context:
Decreasing the risk of both short and long term skeletal relapse for patients undergoing BSSO of the mandible is important since it minimizes risk for additional surgery which can be costly for the patient and operating surgeon.
Strengths and Weaknesses of the Systematic Review:
While the authors of this systematic review had clearly stated inclusion and exclusion criteria of which wire fixation (WF) was excluded a priori, the authors violated their own criteria by including 6 studies that evaluated RIF and WF in their systematic review including the only randomized clinical trial which evaluated cortical screw fixation as compared to wire fixation for BSSO of the mandible. In addition, the authors concluded that bicortical screws as compared to mini-plates demonstrated greater risk of long term relapse but the strength of evidence was limited as there were no randomized clinical trials to support this conclusion.
Strengths and Weaknesses of the Evidence:
The pool of twenty-four studies of moderate to low quality lacked adjustment for important confounding variables such as genioplasty and the use of a splint. The lack of randomization between interventions and standardization between the trials for measuring post-surgical relapse prevent strong conclusions being drawn from these studies. The evidence was strong however from the only randomized clinical trial which demonstrated that RIF exhibited better stability as compared to non-rigid fixation and that mandibular advancements greater than 5 mm were less stable over time as compared to smaller advancements. The authors were also able to demonstrate that proximal segment control also affected long-term skeletal stability.
Implications for Dental Practice:
Based on one randomized clinical trial, the available evidence indicates that rigid fixation improves skeletal stability of the mandible following BSSO mandibular advancement. This review was not able to answer what type of rigid fixation (bicortical screw type or mini-plate) best improves stability and decreases risk of relapse. Surgeons utilizing rigid fixation with BSSO advancement of the mandible should be aware of the potential for relapse following this procedure, especially when advancements greater than 5 mm are planned.