Most Stable BSSO Advancement Fixation Method
For BSSO advancement in young adults and adolescents with Class III malocclusion, use three bicortical positional screws in an inverted-L pattern, as this provides superior biomechanical stability compared to miniplate fixation or hybrid techniques.
Primary Fixation Recommendation
The inverted-L pattern with three bicortical screws demonstrates the highest resistance to both vertical and lateral forces during mandibular advancement. 1 This configuration involves:
- One bicortical screw placed in the retromolar region
- Two additional bicortical screws positioned inferiorly in an inverted-L configuration
- All screws achieving bicortical purchase for maximum stability 1
The biomechanical superiority of this technique has been demonstrated in controlled laboratory testing, where the inverted-L group showed significantly higher resistance (P < .01) to vertical cantilever loading compared to miniplate fixation. 1
Alternative Acceptable Fixation Methods
Both titanium and biodegradable bicortical screws provide equivalent long-term stability for BSSO advancement. 2 If the inverted-L pattern is not feasible due to anatomic constraints:
Miniplate with additional bicortical screw (hybrid technique): Adding a single bicortical positional screw in the retromolar region significantly optimizes the resistance of standard miniplate fixation, approaching the stability of the inverted-L pattern for lateral forces. 1
Standard miniplate fixation: Four-hole plate with four monocortical screws provides adequate stability but demonstrates the lowest load peak scores compared to bicortical techniques. 1 This method remains acceptable when bicortical fixation is contraindicated.
Clinical Equivalence Data
Multiple clinical studies demonstrate no significant difference in postoperative stability between bicortical screws and miniplate fixation at 6-month follow-up. 3, 4 However, these clinical studies may not capture the biomechanical advantages evident in laboratory testing, particularly under extreme loading conditions. 1
The choice between titanium and biodegradable poly-L-lactic/polyglycolic acid copolymer screws does not affect skeletal stability, with both materials showing equivalent outcomes without wound healing complications. 2
Factors Affecting Stability (Independent of Fixation Method)
Greater advancement magnitude correlates with increased postoperative instability regardless of fixation technique. 3, 4 This positive correlation (P = .0002 to P = .018) means:
- Advancements exceeding 10mm require more vigilant monitoring
- Consider adjunctive measures (rigid intermaxillary fixation, extended elastic therapy) for large advancements
- Patient counseling should address realistic expectations for minor relapse 3, 4
Younger patients demonstrate greater postsurgical relapse. 4 Increasing age associates with smaller amounts of postsurgical change, making fixation choice even more critical in adolescent populations.
Low mandibular plane angle (ML/NSL < 25°) predicts both larger surgical movement and greater postsurgical instability (P = .0008 and P = .0195). 4 These patients benefit most from the superior biomechanical stability of the inverted-L bicortical technique.
Special Considerations for Adolescents
For adolescents approaching skeletal maturity with severe maxillomandibular discrepancy, BSSO advancement with maxillomandibular advancement (MMA) is appropriate when functional impairment exists. 5 The classical procedure consists of bilateral sagittal split ramus osteotomies with rigid internal fixation combined with Le Fort I osteotomy. 6
An advancement of 10-15mm of both maxilla and mandible is necessary to effectively treat associated obstructive sleep apnea when maxillomandibular abnormality exists. 6 This magnitude of advancement makes the inverted-L bicortical fixation pattern particularly important for stability.
Critical Pitfalls to Avoid
Underestimating the biomechanical demands: While clinical studies show equivalence between techniques, laboratory data reveals significant differences under loading conditions that may occur during early function. 1
Relying solely on miniplate fixation for large advancements: When advancing >7-8mm, strongly consider bicortical techniques or hybrid fixation. 1
Ignoring patient-specific risk factors: Low mandibular plane angle and younger age both increase relapse risk independent of fixation method. 4
Inadequate bicortical engagement: When using bicortical screws, ensure complete engagement of both cortices; partial engagement negates the biomechanical advantage. 1
Surgery-First Approach Stability
BSSO with rigid internal fixation using the surgery-first approach demonstrates excellent stability with minimal horizontal relapse (<1mm) at 6 months. 7 This validates that proper rigid fixation technique maintains stability even without pre-surgical orthodontic decompensation, though this data primarily applies to setback rather than advancement procedures.