Trauma-Induced Stress Distribution in Primary Incisors Restored With Preformed Zirconia Crowns: 3D Finite Element Analysis.

Background/aims: Preformed zirconia crowns have emerged as the preferred choice for restoring damaged primary incisors. However, they differ from natural teeth in their biophysical properties and can potentially alter the overall response of crowned teeth to a traumatic load. This in silico study aimed to compare the response of three different traumatic loading conditions for the (i) natural (M1) and (ii) zirconia-restored tooth models (M2) models.

Methodology: A 3D dynamic finite element (FE) analysis was performed, and minimum dynamic loads required for fracture and coronal portion disjunction of both tooth models were applied in frontal, oblique, and incisal directions. Stress concentrations, von Mises stresses, fracture patterns, and displacements were compared at different periods of the loading pulse.

Results: The computed minimum threshold loads resulting in fracture of the natural tooth model were 82 N, 166 N, and 171 N for the frontal, oblique, and incisal impacts, respectively. Fracture of the coronal portion started at 1.8 and 1.68 ms in natural tooth and zirconia-restored tooth models, respectively. Complete disjunction of coronal and radicular portions occurred earlier in the zirconia-restored tooth model (2.46 ms) than in the natural tooth model (4.5 ms) for frontal impact. The maximum von Mises stresses causing fracture ranged from 254 to 314 MPa for both models, following assigned element erosion criteria. The zirconia-restored tooth model did not experience fracture during an oblique impact.

Conclusion: The stress concentration patterns were seen to be altered in the zirconia-restored tooth model. On incisal impact, the permanent tooth germ in the natural tooth model displayed stress concentrations that were not seen in the zirconia-restored tooth model.