Biomechanical impact of odontogenic cyst–associated impacted mandibular third molars on mandibular angle fragility: a finite element analysis

Background

Impacted mandibular third molars are recognized as predisposing factors for mandibular angle fractures. When associated with odontogenic cystic lesions, progressive bone loss may further compromise structural integrity; however, quantitative biomechanical evidence remains limited.

This study aimed to evaluate the effect of cyst-associated impacted mandibular third molars on mandibular angle fragility using finite element analysis.

Methods

A comparative three-dimensional finite element study.

The primary predictor variable was cyst volume associated with an impacted mandibular third molar (no cyst [Model 1], small cyst [Model 2], medium cyst [Model 3], and large cyst [Model 4]).The primary outcome variables were maximum principal stress (P1), minimum principal stress (P3), and von Mises equivalent stress measured in the mandibular angle region.

Loading direction (ipsilateral, contralateral, symphyseal), cortical surface location (buccal vs lingual), and predefined anatomical measurement points were included as biomechanical covariates.Four standardized mandibular finite element models were constructed with identical material properties and mesh parameters. A static 2000 N load was applied under three loading conditions. Stress values were recorded from twelve predefined cortical points in the mandibular angle region. Absolute stress magnitudes and percentage differences relative to the control model were compared to assess volume-dependent effects.

Results

Cyst-associated models demonstrated volume-dependent stress amplification compared with the control model. Under ipsilateral loading, tensile stress in selected cortical regions increased several-fold in the largest cyst model, with marked elevation of both tensile and compressive stress magnitudes. Contralateral and symphyseal loading produced localized stress increases, although to a lesser extent. The mandibular angle, particularly cortical regions adjacent to the cyst, exhibited progressive mechanical weakening as cyst size increased.

Conclusion

Odontogenic cystic lesions associated with impacted mandibular third molars significantly reduce the biomechanical resistance of the mandibular angle in a volume-dependent manner. Early detection and appropriate management of cystic pathology may help prevent trauma-related angle fractures.