The rate of abrasion of dental surfaces during short periods of time is difficult to measure clinically, but one quantifiable method is the use of the Bruxcore bruxism monitoring device. The aim of this study was to estimate the interobserver and intraobserver variation in the Bruxcore system using different reading methods. Fifteen volunteers used individually fabricated Bruxcore devices during 4 consecutive nights, and this procedure was repeated after 6 weeks. The abraded areas of the 30 Bruxcore devices were measured by two observers on two occasions and with three methods: microscope without a reference scale; microscope with a reference scale; and a computer-aided system. Intraobserver variation was small (5%), but interobserver variation was statistically significant for all three methods. The computer-aided system was superior to the other two methods. The interaction between Bruxcore values and observers was statistically significant for the microscope methods but not for the computer method. This was a desired property, indicating stability of the computer-aided method over the range of Bruxcore values observed. Small measurement errors, independent of the size of the measurements, can be expected using a trained observer and a computer-aided method for reading the Bruxcore bruxism monitoring device.