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Linear and rotational changes in large mandibular advancements using three or four fixation screws
C A Knaup1, T R Wallen, D S Bloomquist
1Department of Orthodontics, School of Dentistry, University of Washington, Seattle.
The International Journal of Adult Orthodontics and Orthognathic Surgery
|January 1, 1993
Summary
Four fixation screws in mandibular advancement surgery led to greater bone movement but similar stability compared to three screws. Relapse rates were not affected by screw number or specific preoperative conditions.
Area of Science:
- Oral and Maxillofacial Surgery
- Orthognathic Surgery
- Biomechanical Analysis
Background:
- Bilateral sagittal ramus osteotomy (BSR0) is a common procedure for large mandibular advancements.
- Surgical stability and relapse are critical concerns following BSR0.
- The role of fixation methods, specifically screw number, on stability requires further investigation.
Purpose of the Study:
- To evaluate the rotational and linear stability of mandibular segments after BSR0 for large advancements.
- To compare outcomes between fixation using three versus four bicortical screws.
- To identify factors influencing relapse and continued advancement post-surgery.
Main Methods:
- Retrospective cephalometric analysis of 41 patients undergoing BSR0.
- Grouping patients based on fixation: three vs. four 2-mm bicortical screws.
- Matching groups for advancement amount and analyzing postoperative changes.
Main Results:
- The four-screw group achieved significantly larger advancements relative to the cranial base.
- Postoperative change patterns were similar between the three- and four-screw groups.
- No increased relapse rate was observed in patients with high mandibular plane angles, genioplasties, mandibular constriction, or open bites; screw number did not impact these changes.
Conclusions:
- While four screws may allow greater initial advancement, stability and relapse patterns are comparable to three screws in BSR0.
- Preoperative patient factors and screw fixation number did not significantly influence relapse rates.
- Specific factors independent of screw fixation were identified as influencing relapse and continued advancement.