Surface area improvement with grooves and boxes in mandibular molar crown preparations.
BACKGROUND
Axial-wall inclination has been shown to affect the stability of a cemented restoration in function, resulting in early restoration failure.


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


METHODS
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).


RESULTS
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.


CONCLUSIONS
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.
Bowley
John F
JF
Postdoctoral Prosthodontics Division, Boston University Goldman School of Dental Medicine, Boston, MA 02118, USA. jbowley@bu.edu
Lai
Wen-Fu T
WF
D001696:Biomechanical Phenomena; D003442:Crowns; D017268:Dental Prosthesis Retention; D006801:Humans; D008334:Mandible; D008962:Models, Theoretical; D008963:Molar / Q000033:anatomy & histology*; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000295:instrumentation / Q000379:methods*