Finite element study on the effect of bruxism on the fracture resistance of maxillary zirconia fixed partial dentures with varying anterior inter-implant distances.

Abstract

<h4>Objective</h4>This study aims to investigate the effect of bruxism on the fracture resistance of maxillary zirconia fixed denture prostheses (FDP) with different inter-implant distances and different occlusion types.<h4>Methods</h4>We developed four finite element models that reflect maxillary fixed dental prostheses in patients with bruxism. The original version retains the prosthesis using six implants positioned at the canines, premolars, and first molars. The second one features implants positioned at the lateral incisors, canines, and second premolars. The development of two supplementary models, 3 and 4, included a reduction of the cusp height by 0.35 mm. Angle's classification, encompassing classes I, II, and III, directs the application of pressures to all models subjected to parafunctional habits, including bruxism.<h4>Results</h4>Model 1 exhibited the lowest values for FDP and bone deformation, measuring 77 μm and 27 μm, respectively. Model 3 followed with values ranging from 71 to 73 μm for FDP and 25 to 26 μm for bone deformation. In contrast, Models 2 and 4 demonstrated higher values, with Model 2 showing particularly elevated measurements of 104 μm for FDP and 43 μm for bone deformation. In Models 2 and 3, the Von Mises stress in the FDP was less than 500 MPa, suggesting a less risk of fatigue, whereas Models 1 and 4 surpassed this threshold. Models 1 and 3 exhibited physiological bone stress, whereas Models 2 and 4 demonstrated unsafe levels indicative of potential structural damage. Class I and II occlusions exhibited stable, low-stress profiles, while Class III occlusions resulted in increased shear and torque due to anterior occlusal displacement. This underscores the importance of occlusion-specific prosthetic design to mitigate peri-implant stress.<h4>Conclusions</h4>The distribution of implants in Models 1 and 3 may enhance stability and extend longevity. A 350-micron reduction in occlusal surface height was associated with reduced stress and deformation in the models, which may enhance the lifespan of the FDPs. Therefore, reducing the occlusal surface height of FDP is recommended for patients with bruxism.<h4>Clinical significance</h4>It is recommended that clinicians construct maxillary zirconia FDPs with a broader implant distribution and a cusp inclination of (≤ 15º) for better outcomes in patients with bruxism. This configuration enhances prosthetic stability and reduces stress, thereby increasing longevity. Clinical protocols may encompass strategic implant placement, reduction of cusp height, and individualized occlusal design.