Development and application of a new abrasion testing device.
BACKGROUND
Wear of gypsum materials is a significant problem in the fabrication of accurately fitting cast prosthetic devices. Unfortunately, there is little agreement on how to measure it.


OBJECTIVE
This study was designed to evaluate the efficacy of a newly designed abrasion device and to develop a test methodology that provides a clinically relevant measure of material loss from gypsum material.


METHODS
In this study, a unique benchtop microabrasion/microimpact device was created. The device consists of a vertical arm with a variably loaded stylus and a reciprocating table that moves the specimen under the stylus. Type IV gypsum samples (Silky Rock, Whip Mix Corp, Louisville, Ky.) were made with 1 mm vertical, 45-degree angled ridges used to represent crown margins. Samples (n = 30) were separated 1 hour after pouring and allowed to bench set for 24 hours or 7 days. Three loads (15, 50, and 75 g) were used, and the resulting defect was evaluated after 5, 10, 15, or 20 cycles of loading. Changes in mass and volume were recorded.


RESULTS
At both 24 hours and 7 days, there was an increase in both mass and material volume loss with increasing load on the stylus (P<0.0001). There was no significant change in mass after 5 cycles of loading (P<0.05), but an increase in the volume loss occurred because of compaction of the walls of the defect (P<0.0001).


CONCLUSIONS
Under these conditions, the increasing load had a greater effect than the number of load cycles on gypsum brittle fracture.
Lindquist
T J
TJ
University of Iowa, Iowa City, Iowa 52242, USA. Terry-Lindquist@uiowa.edu
Stanford
C M
CM
D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry; D003735:Dental Casting Technique; D003748:Dental Equipment / Q000706:statistics & numerical data; D003764:Dental Materials / Q000737:chemistry; D004867:Equipment Design / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D008422:Materials Testing / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D013997:Time Factors
D003764:Dental Materials; D002133:Calcium Sulfate