Incisor compliance following operative procedures: a rapid 3-D finite element analysis using micro-CT data.

PURPOSE: New methods are available for the rapid generation of 3-D finite element models of dental structures and restorations. Validation of these methods are required. The aim of the present study is to utilize stereolithography and surface-driven automatic meshing to generate models of specific restorative conditions, and to examine these models under loading. The data generated are compared to existing experimental data in an attempt to validate the model.

MATERIALS AND METHODS: An intact maxillary central incisor was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different tooth preparations (endodontic access, veneer, proximal, and Class III preparations) and restorations (Class III composites). The different parts were then imported in a finite element software package to create 3D solid models. A 50-N point load perpendicular to the tooth's long axis and centered on the incisal edge was applied either on the buccal or palatal surface. The surface strain was obtained from selected nodes corresponding to the location of the strain gauges in the validation experiments.

RESULTS: The increase in crown flexure (compared to the unaltered tooth) ranged from near zero values (conservative endodontic access, removal of proximal enamel) to ca 10% (aggressive endodontic access, conservative Class III preparations), 23% and 34% (moderate and aggressive Class III preparations, respectively), and 91% (veneer preparation). Placement of Class III composite resin restorations resulted in 85% recovery of the original crown stiffness. 3D FEA data correlated well with existing experimental data. In two situations, smaller FEA strains were recorded compared to the experimental strains, perhaps due to enamel cracking under the strain gauges. This artefact was not simulated by the FEA models.

CONCLUSION: Experimental data validated the FEA models. The described method can generate detailed three-dimensional finite element models of a maxillary central incisor with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications.