Comparison of wear behavior of occlusal device materials manufactured by different processes

Abstract

Statement of problem: Occlusal devices have been used for therapeutic and diagnostic purposes. Although their effectiveness in preventing tooth wear has been reported, research regarding the wear of the occlusal device when opposing different materials is lacking.

Purpose: The purpose of this in vitro study was to measure and compare the volumetric wear of conventionally processed, milled, and 3-dimensionally (3D) printed occlusal device materials when opposed by human enamel, lithium disilicate, and 4 mol% yttria-stabilized zirconia.

Material and methods: Milled polymethyl methacrylate (ProArt CAD Splint; Ivoclar AG), printed resin (Next Dent Ortho Rigid), and conventional heat-polymerized polymethyl methacrylate (Vitacrilic Clear; Fricke International, Inc) were tested. Fifteen Ø14×2-mm disk-shaped specimens were fabricated from each manufacturing process. Each material group was divided into 3 groups of 5 specimens and tested against each of the 3 antagonist materials, human enamel, zirconia (IPS e.max ZirCAD MT; Ivoclar AG), and lithium disilicate (IPS e.max CAD; Ivoclar AG) shaped into a spherical stylus. Each specimen was subjected to 50 000 mastication cycles using an oral wear simulator (Oregon Health Sciences University (OHSU) Wear Machine), with a frequency of 1.1 Hz and a maximum 50-N load with vertical load and horizontal movement. The surfaces of the substrate and styli were before and after wear testing using a laboratory scanner (E4 scanner; 3Shape A/S). The surfaces of each specimen before and after wear testing were analyzed using a software program (WearCompare; Leeds Digital Dentistry). The volume difference between the before and after scans were determined for both the substrate and the stylus and analyzed using a 2-way ANOVA. The statistical significance between groups was determined using the Tukey-Kramer HSD test (α=.025).

Results: The results of the 2-way ANOVA showed that the antagonist material (P<.01) significantly influenced the resulting volumetric wear of the occlusal device materials, whereas the substrate material (P=.03) had no significant effect. The interaction between substrate type and antagonist material (P=.42) also did not significantly affect volumetric wear. Only the material type of the opposing antagonist material (P<.001) influenced the volume loss, whereas the substrate type (P=.05) and interactions (P=.93) between these 2 factors were statistically similar.

Conclusions: Significant differences in wear were found among printed, milled, and heat-polymerized polymethyl methacrylate occlusal device materials. The wear of these materials was influenced by both the type of material used and the antagonist materials. The printed occlusal device material exhibited the least amount of wear.