High-accuracy digital model design for full crown tooth preparation

Aim: Precise tooth preparation is necessary for successful restorative treatments. In the narrow oral space, achieving such precision with traditional manual operation is impeded by visual deviation, human eye blind zones, and hand-orientation errors. To overcome these drawbacks, a mini-robotic system for tooth preparation was developed to manipulate an ultra-short-pulse laser beam for the automatic shaping of a target tooth into a prepared tooth. Automatic tooth preparation is based on three-dimensional (3D) data. The present study was conducted to investigate the basic principles for digitally designing full crown tooth preparations and to quantitatively evaluate the associated design precision. Materials and methods: Cone beam computed tomography (CBCT) and dental model surface scan data were obtained from 20 volunteers. Using these data, a complete and systematic process for the digital design of full crown tooth preparations was conducted. The study included 40 cases with two design types. Software-derived measurements of prepared occlusal thickness, shoulder width, and axial convergence angle were compared with the design preparation data. Results: The design precision for shoulder width exceeded that for occlusal ablation depth, which exceeded that for axial convergence angle. One-way ANOVA analysis results confirmed no significant differences in the design precision of full crown preparations with different tooth morphologies, and the independent samples t test results showed no significant difference among the design standards. The mean errors for occlusal ablation depth, shoulder width, and axial convergence angle were 0.0096 ± 0.0108 mm, 0.0006 ± 0.0004 mm, and 0.1201 ± 0.1288 degrees, respectively. Conclusion: The design route of the full crown computer-aided design (CAD) software reported on in this article is highly feasible and accurate. Keywords: digital model, computer-aided design, accuracy evaluation, restorative treatment, teeth morphologies, tooth preparation