Evaluation of three different tooth preparation techniques for metal ceramic crowns by comparing preparation depths: An in vitro study

AIM: To determine the effect of three different tooth preparation techniques had on operator's ability to appropriately and consistently prepare teeth for metal ceramic crowns. MATERIALS AND METHODS: Ninety maxillary left central incisor typodont teeth were allocated to three equal groups (A, B and C) of thirty and mounted in standard working model one at a time. A freehand approach was used to prepare the teeth in Group A, which acted as a control. Groups B and C were prepared with the assistance of silicon index and suitable depth gauge burs, respectively. A silicon index of unprepared teeth, into which contrasting colored silicon injected to occupy the space created by tooth preparation, was sectioned in the midline. Images of sectioned index were captured with optical microscope attached to a personal computer. A calibrated image analysis software was used to measure the depth of preparation (in millimeters) at five points (labial-cervical, mid-labial, incisal, mid-palatal and palatal cervical) on two occasions. These results were pooled and averaged to give a mean labial, incisal and palatal preparation depths in mm. The data were analyzed by one-way analysis of variance and Scheffe's post-hoc statistical test. RESULTS: The mean depth of labial and incisal preparation for Groups A, B and C was 1.23 and 1.72 mm, 1.45 and 1.96 mm, 1.47 and 1.95 mm, respectively. The difference between the groups’ labial preparation depth was significant as well as the difference between groups’ incisal preparation depth. The mean palatal preparation was 0.46 mm for Group A, 0.54 mm for Group B and 0.59 mm for Group C. CONCLUSION: Teeth preparation for metal ceramic crowns without any assistance can lead to under-preparation of labial and incisal surface. CLINICAL SIGNIFICANCE: Whenever possible, considerable importance should be given to the use of index or depth gauge burs for preparing teeth for receiving metal ceramic crowns.