Effect of perforation size and furcal lesion on stress distribution in mandibular molars: a finite element analysis

To compare the effect of furcal perforations of various sizes on the biomechanical response of mandibular first molars with or without periodontal bone loss at the furcal region via three-dimensional (3D) finite element analysis (FEA).

The 3D geometric basic model was reconstructed from the micro-computed tomographic images of an extracted mandibular first molar. Five different models were constructed from this molar in group 1 as follows: intact molar model, root filled (RCF) model and three models with furcal perforations (1, 2 and 3 mm in diameter) repaired with a calcium silicate-based cement (CSC). In group 2, a lesion simulating bone resorption at the furcal region was modelled on the models in group 1. A force of 200 N was applied to simulate normal occlusal loads. Static linear FEA was performed using the Abaqus software (Abaqus 6.14; ABAQUS Inc., Providence, RI, USA). The maximum principal stresses (P_max ) and maximum displacement magnitude were evaluated.

The range of P_max values of the models in group 1, from high to low, was as follows: RCF + 3 mm perforation > RCF + 2 mm perforation > RCF + 1 mm perforation > RCF > intact model, and the range of P_max values of the models in group 2 was as follows: RCF + 3 mm perforation + furcal lesion > RCF + 2 mm perforation + furcal lesion > RCF + 1 mm perforation + furcal lesion > RCF + furcal lesion > intact model + furcal lesion. All of the models in group 2 exhibited lower P_max values and higher maximum displacement magnitude than their counterparts without lesions in group 1.

The size of the furcal perforation affected the accumulation and distribution of stress within the models. Mandibular molar teeth with large furcal perforations treated with a calcium silicate-based cement may be associated with an increased risk of fracture whether or not accompanied by bone resorption.