Assessment of four different tooth preparation techniques for porcelain fused to metal crown: An in vitro study

Introduction: Tooth preparation for full veneer crowns has to be a fine balance between conservation of remaining tooth structure and provision of sufficient thickness of restorative material. Therefore, due consideration needs to be given to the selection of technique of tooth preparation. Aim: Comparative evaluation of the preparation details of four different techniques of tooth preparation for porcelain fused to metal crown. Materials and Methods: One hundred and sixteen maxillary right central incisor typodont teeth were divided into four groups (A, B, C, and D) of 29 each and subjected to different tooth preparation techniques. Group A teeth were prepared using the freehand technique and served as the control group. Group B, C, and D teeth were, respectively, prepared using a silicone index, an appropriate depth gauge bur, and a vacuum-formed template. Contrasting colored silicone was injected into a silicone index of unprepared teeth to identify the amount of reduction in tooth structure accomplished. The index was bisected along the midline and imaged using an electron microscope. The preparation depth was measured in millimeters at five locations: cervical third of the labial surface, mid-labial, incisal, mid-palatal, and cervical third of the palatal surface, using image analysis software. The mean preparation depth in millimeters for each surface was then calculated. The data were analyzed using one-way analysis of variance and Scheffe’s post hoc test. Results and Discussion: Group A exhibited significantly less preparation depth on the labial surface compared to Groups B, C, and D. Teeth in Group B demonstrated accurate labial and incisal preparation depths, although there was a tendency for excessive palatal reduction. Conclusion: The freehand technique is unreliable for tooth preparation for porcelain fused to metal crowns because of the likelihood of underpreparation of the labial surface.