Statement of problem: Inadequate preparation of teeth for metal ceramic crowns can significantly influence the ultimate form and longevity of the definitive restoration, as well as adversely affect the supporting tissues.
Purpose: The purpose of the study was to determine the effect that 3 different tooth preparation techniques had on an operator's ability to appropriately and consistently prepare teeth for metal ceramic crowns.
Material and methods: Thirty typodont maxillary central incisor teeth were mounted individually and randomly allocated to 3 equal groups (A, B, and C). One operator was asked to prepare each tooth for a metal ceramic crown. 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 a silicone index and a suitable depth gauge bur, respectively. A silicone index of the unprepared tooth, into which contrasting silicone was injected to occupy the space created by tooth preparation, was sectioned in the midline. Images of the sectioned index were captured with an optical microscope (resolution +/- 0.02 mm), which was attached to a personal computer. A calibrated image analysis program was used to measure the depth of preparation (in millimeters) at 5 points (labial cervical, mid-labial, incisal, mid-palatal, and palatal cervical) on 2 occasions. These results were pooled and averaged to give a mean labial and palatal preparation depth (in millimeters) and incisal edge reduction. The data were analyzed by use of a 1-way analysis of variance and Scheffe's post hoc statistical test (P<.05).
Results: The mean depths of labial and palatal preparation for Groups A, B, and C were 1.28 and 0.47 mm; 1.46 and 0.56 mm; and 1.45 and 0.63 mm, respectively. The difference between the groups' labial preparation depth was not significant (P=.06), but the difference for palatal preparation depth was significant (P=.01). The mean incisal reduction was 3.00 mm for Group A, 2.74 mm for Group B, and 2.13 mm for Group C (P=.00).
Conclusion: Within the limitations of this study, it was concluded that preparation of teeth for metal ceramic crowns without the use of devices to help gauge reduction depth can result in insufficient labial reduction and incisal overreduction.