Effect of 4 Medium Used in In-Vitro Composite Wear Testing

Wear remains a problem for developing new dental restorative materials and a consistent method has yet to be developed that will predict the materials in vivo performance. Purpose: No published studies have examined third body mediums used in in-vitro composite wear testing since De Gee (1986).  Objectives: This study measures the wear of four different composites using four different mediums.  Methods: 4mm thick flat composite specimens (n=8) were prepared and polymerized with a curing light (583mWatz/cm3) in 2mm intervals. Specimens were mounted in a brass holder and stored at 37°C for 48 hours. After storage, specimens were loaded into an Alabama Wear Testing Device.  Third body medium was weighed, crushed, and combined according to the protocol of previous studies.  The test was run for 10,000 cycles at 72 Hz applying a 75N force. The volumetric loss through wear of the specimens was determined using a non-contact light profilometer (Proscan 2000).  Medium particles were characterized by hardness (nano-indentor) and particle size (particle size analyzer).  Wear volumes (mm³) of composite materials were compared for each medium using a two factor ANOVA and Tukey's test (alpha = 0.05).

Results: 

	PMMA	Glass	Poppy	Millet
Z-100 (3M ESPE)	.00037(7E-5)	1.36(.082)	.018(.018)	.0020(.0031)
Filtek Supreme (3M ESPE)	.0019(.001)	1.34(.15)	.017(.029)	.057(.049)
Estelite (Tokuyama)	.0019(.0011)	.87(.073)	.0026(.0036)	.034(.062)
Esthet-X (Dentsply-Caulk)	.0037(.002)	1.19(.15)	.01(.0083)	.015(.033)

The ANOVA revealed that materials showed different amounts of wear and Tukey's test differentiated materials into significantly different groups when using PMMA and glass beads as a medium (p <0.001) but not poppy or millet seeds as a medium. Glass bead slurry produced significantly more wear than all other mediums. Conclusions: Variability in volumetric wear from poppy and millet seeds is best explained by particle size variation.  The amount of volumetric wear produced by each medium is best predicted by the hardness of its particles.