Wear of visible light-cured restorative materials and removable partial denture direct retainers

This study measured the in vitro wear of visible light-cured restorative materials and removable partial denture direct retainers.

An aluminum test die was produced by replicating the facial contours of an extracted human molar (model). The replica's cervical contour was modified by placement of a restorable Class V cavity preparation. The test die became a fixed component of a testing apparatus. The restorative materials tested were Z100 (fine particle filled resin composite), Silux Plus (microfilled resin composite), and Photac-Fil (hybrid glass ionomer). Cast round, half round, I bar, and wrought-wire retainers were designed to engage a 0.254-mm undercut. Caliper measurements of the wear of restorative materials were made at intervals during testing, and after 7,500 retainer placements and removals. The measurements of material- and retainer-wear were subjected to ANOVA and Tukey tests.

Generally, retainers with round profiles caused less wear of the restorative materials than those featuring flat contact surfaces. Wear of the materials ranged from 14 +/- 5.5 microns (Silux Plus by cast round) to 70 +/- 10.0 microns (Photac-Fil by cast half round). Mean wear of retainers, however, ranged only from 2 +/- 4.5 microns for six of 12 possible retainer-material pairings up to 12 +/- 4.5 microns (cast half round by Z100).

Regardless of their design features, the direct retainers of this study exhibited little wear when paired with any of the restorative materials. Overall, material wear appeared to be greater than retainer wear by a factor of five. When paired with practically any retainer type, the hybrid glass ionomer (Photac-Fil) exhibited more wear than either of the two resin composites (Z100 or Silux Plus). Although not established clearly, retainers with round profiles (wrought-wire and cast round) appeared to produce less wear of restorative materials than their I bar and cast half round counterparts.