Biomechanical analysis of mandibular second molar with varying distal alveolar bone defects: a finite element study with two illustrative clinical cases

The level of alveolar bone distal to the mandibular second molar, following the extraction of the mandibular third molar, may affect the biomechanical performance. This study aimed to analyze the biomechanical performance of the mandibular second molar under different coaptation forces in the presence of different levels of distal alveolar bone defects. Three-dimensional finite element models of the left mandibular second molar were crafted to inspect five levels of defects in the distal mesial alveolar bone (0%, 20%, 40%, 70%, and 100%). Loading directions were established at 45° and vertical orientations with a maximum force of 5 MPa. A set of 50 distinct finite element models was constituted. The study measured the displacement of the distal enamel endpoints and the principal stresses of dentin and enamel to decipher the biomechanical attributes of the mandibular second molar amidst various levels of distal alveolar bone defects. The tooth displacement gradually rose proportionally to the increased levels of distal bone defects. When the distal roots remained partially shielded, the varied values of dentin stress across different levels of alveolar bone loss were relatively marginal, highlighting the possible supportive role of the remaining alveolar bone in the root of the tooth. Conversely, complete root exposure precipitated a substantial escalation in dentin stress. Two clinical cases were presented to illustrate the potential clinical application of the finite element findings. Following the extraction of the third molar, it is recommended to promptly undertake selective occlusal adjustment where clinically indicated or bone augmentation based on the clinical examination and severity of alveolar bone loss centered at the distal region of the second molar. After this, enhancing the occlusal relationship through appropriate orthodontic management can be beneficial.