Finite element analysis of stress in removable lower complete denture under vertical and oblique occlusal forces

Frequent fractures of complete removable dentures during mastication in the anterior zone cannot be explained by bite forces in this area, because occlusal forces on the incisors are small. It appears that the mechanism of fracture must be from lateral mastication forces. The hypothesis of the study was that, under stable support of a complete removable denture on the foundation, its fracture in the anterior segment is possible due to stress generated under masticatory forces typical for denture wearers. This study analyzes stress distribution in removable complete dentures (designed in Exocad), using the finite element method (FEM, Nx Siemens). The denture was loaded on the first molars with bilateral vertical forces of 100 N and oblique forces of 140 N at an angle of 45˚. Under oblique bilateral mastication forces the anterior zone exhibited nominal stresses originating from tension on the lingual side and compression on the labial side. These values were significantly lower than the material's strength, even under conservative criteria for semi-brittle polymer in tension-dominant zones. The study also showed that the stress in properly manufactured dentures without defects or excessively sharp grooves did not reach the fatigue strength of the denture materials. This negated the hypothesis that denture fracture in the anterior segment is possible under such conditions. Further investigation is required, incorporating factors such as denture foundation resiliency, misfit, occlusal imbalance, and potentially different loading patterns to fully elucidate intraoral failure modes.