SA2 - Occlusal Scheme Shapes the Success of Mandibular Fracture Plating Systems: Toward a Better Understanding

Abstract: Objective: Current mandibular fracture biomechanics are still predominantly interpreted through Champy's classic tension-compression model, which assumes a standardized mandible and uniform anterior loading.¹ These simplifications ignore how individual occlusal schemes, dentition patterns and craniofacial forms may reshape local tension-compression environments at fracture sites, potentially weakening the rationale for current plating recommendations. This study uses patient-specific three-dimensional finite element analysis to test whether variations in bite-force location, dentition type, and craniofacial morphology produce distinct stress-distribution patterns in intact and fractured mandibles. Our goal is to relate these patterns to plate positioning and configuration, clarifying their implications for optimizing fixation techniques and reducing mechanical complications.

Methods: A three-dimensional finite element model of a mandible was reconstructed from a CT scan of a craniomaxillofacial skeleton with Class I occlusion and no dentofacial deformity. Three dentition states (complete, posterior bilateral and posterior unilateral partial edentulism) were combined with 2 craniofacial morphologies (short and long face, with long-face cases represented by half maximal bite force) to generate patient-specific scenarios. Forces from 6 masticatory muscle groups, based on published magnitudes and directions, were applied to simulate central incisor and unilateral first molar biting.² For each loading condition, intact mandibles and unilateral or bilateral fractures (subcondylar, angle, body, and parasymphyseal patterns) were modelled, and stress distributions along fracture planes were extracted for comparison.

Results: Finite element analysis showed that stress patterns at common mandibular fracture sites are highly dependent on bite target location. In posterior bilateral partial edentulism, central incisor loading produced tension along the superior margin and compression inferiorly at body and parasymphyseal fractures, whereas unilateral first molar loading inverted this pattern, with superior compression and inferior tension along the same fracture line. Bilateral fractures exhibited complex, asymmetric fields, with a tension zone developing along the inferior border on the loaded side and along the superior border contralateral to the bite. Craniofacial morphology (short vs long face) primarily scaled stress magnitude and displacement but did not materially alter distribution patterns. Figure 1 displays the central-incisor condition; Figure 2 shows the corresponding first-molar condition, highlighting the tension-compression reversal when the fracture line coincides with the molar load axis.

Conclusion: These finite element simulations demonstrate that mandibular fracture mechanics are driven by patient-specific occlusal loading, dentition and craniofacial form rather than fixed bone behavior. Central incisor versus first-molar biting produced opposite tension-compression patterns along identical fracture paths, suggesting that plating guided solely by classic Champy lines may be mismatched in some occlusal schemes. Clinical data from Ellis and colleagues show that patients with mandibular angle fractures, even on a soft diet, instinctively favor posterior molar chewing with reduced bite force on the fractured side, consistent with a neuromuscular tendency to avoid incisor loading by shortening the lever arm and limiting fracture-site motion.³ Integrating patient-specific occlusion, dentition, and fracture configuration into plate selection and positioning may therefore improve fixation stability and warrants further clinical validation of these modelling findings.


References:

1. Champy M, Lodde JP, Jaeger JH, Wilk A. Biomechanical basis of mandibular osteosynthesis according to the F.X. Michelet method. Rev Stomatol Chir Maxillofac 1976;77:248.

2. Meyer C. Determination of the external forces applied to the mandible during various static chewing tasks. Journal of Cranio-Maxillofacial Surgery 1998;26:331-341.

3. Tate G, Ellis III E, Throckmorton G. Bite forces in patients treated for mandibular angle fractures: Implications for fixation recommendations. J Oral Maxillofac Surg. 1994;52:1734-1736.