Effects of repeated use of tungsten carbide burs on the surface roughness and contact angles of a CAD-CAM PMMA denture base resin

Abstract

Statement of problem. The surface roughness (Ra) and wettability of complete denture base materials must meet certain clinical requirements. Although computer-aided design and computer-aided manufacturing (CAD-CAM) systems have recently become popular for the fabrication of complete dentures, the effects of the repeated usage of milling burs on the surface properties of CAD-CAM denture base acrylic resins have not yet been fully investigated. Purpose. The purpose of this in vitro study was to evaluate the effects of new and used burs on the Ra and contact angles (wettability) of a CAD-CAM polymethylmethacrylate (PMMA) denture base material. Material and methods. A total of 40 O2x10-mm disks were fabricated from 1 brand of CAD-CAM PMMA resin (Polident). Half of the specimens (group N) were milled with a new tungsten carbide bur set, while the other half (group U) was milled with a used tungsten carbide bur set. Moreover, half of the specimens (groups NT and UT) were subjected to thermocycling before Ra and contact angle testing. Ra was tested by using a profilometer, and the surfaces were also examined by scanning electron microscopy (SEM). The contact angle was measured by using the sessile drop method. Data were analyzed with the Kruskal-Wallis and Dunn Pairwise Comparison tests (alpha=.05). Results. The mean contact angle was highest for group U (80 degrees) and lowest for group UT (66 degrees) (P<.05). Ra values were highest for group N (1.3 mu m) and lowest for group U (0.93 mu m) (P<.05). Conclusions. Specimens milled with new tungsten carbide burs had lower mean contact angles and higher Ra values than specimens milled with used burs. The contact angles of CAD-CAM PMMA resin specimens milled with used burs decreased significantly after thermocycling. Regardless of whether or not thermocycling was performed, contact angle values decreased as Ra values increased.