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Restoring the vertical dimension of mandibular incisors with bonded ceramic restorations
Abstract:
Mandibular incisors are difficult to restore with conventional anterior crowns due to their small axial diameters. Crown preparation risks pulp exposure and results in a thin core of dentine. An experiment was designed to determine if increasing the thickness of ceramic to restore incisal edges affects the load at the point of restoration failure. Forty-eight mandibular incisors were randomly divided into four groups. The incisal edges of the teeth in three groups were reduced so that the coronal height was 7.5 mm (Group A), 6.5 mm (Group B), and 5.5 mm (Group C). Group D was designated as the experimental control. A fifth group (Group E), independent of the random sample, was introduced to the study for discussion purposes and was characterized by each of the incisors having an intact incisal edge of enamel. Groups A, B and C were prepared in a standard fashion for ceramic veneer restorations that were constructed to restore the vertical height of each tooth to 8.5 mm. Prior to cementation, the preparation surfaces were analysed and the relative surface areas of enamel and dentine were calculated. The ceramic restorations were cemented using a resin luting agent. The teeth were then thermocycled prior to loading at 135 degrees C until failure. The mean fracture load was 305 N (SD 134 N) for Group A, 403 N (SD 101 N) for Group B, 515 N (SD 296 N) for Group C, 587 N (SD 187 N) for Group D and 395 N (SD 129 N) for Group E. As determined by analysis of variance followed by a Sheffè multiple comparison test there was a significant difference (p < or = 0.01) between Group A and Group D. There were no significant correlations of load at failure with the percentage of exposed dentine, enamel surface area, total preparation surface area, and the incisal surface area. The patterns of failure of the fractured specimens were also analysed. There were significantly (p < or = 0.05) greater fractures of the ceramic restorations when they were bonded with the minimum incisal thickness of ceramic.