Surface area improvement with grooves and boxes in mandibular molar crown preparations

Axial-wall inclination has been shown to affect the stability of a cemented restoration in function, resulting in early restoration failure.

The purpose of this study was to evaluate surface area improvement with the use of supplemental grooves in tooth preparations for complete crowns.

The surface area preparation improvement in combinations of unfavorable/marginal height and axial-wall inclinations was quantified. A right regular pyramid was used to simulate a single mandibular molar tooth preparation with known axial-wall inclinations and vertical heights. Various combinations of these 2 variables allowed the calculation of surface areas with a formula for the area of a pyramid, cones, and right triangles through geometric/trigonometric manipulations. The pyramidal model system had a 9-mm square base with marginal and unfavorable vertical heights, 3 or 4 mm, and axial-wall inclination angles from 2 to 25 degrees. Conical-shaped grooves of varying lengths and widths, depending on height and axial-wall inclinations, were introduced with a tapered fissure bur. The percentage of surface area gained or lost through the supplementation with tapered grooves and boxes served as the dependent variables, alpha-factors (1) through (5).

Significant area gains were demonstrated in all alpha-level comparisons. The greatest change was found in the 4-mm height grouping, as a positive 35.2% gain in the 25-degree level with 4 grooves.

Axial-wall groove and box supplementation were shown to improve the surface areas of simulated mandibular molar preparations with unfavorable axial-wall inclination and vertical height levels.