05 NaF.[21] clearly Group 2 : Specimens were stored in 10��C cola in a refrigerator (Arcelik 4252N; Arcelik A.S. Istanbul, Turkey). A new bottle of cola was used in each period to maintain an acceptable level of carbonic gas. Group 3 : Specimens were stored in 37��C cola and held in a water bath at 37��C. A new bottle of cola was used in each test period. Group 4 : Specimens were stored in 70��C coffee solution, which was prepared with 2.8 g of coffee, weighed using a sensitive balance (1620c sensitive balance; Precisa, Zurich, Switzerland), added to 150 ml of boiling distilled water and held in a water bath at 70��C (OLS 200; Grant Instruments Ltd, Cambridge, England). Coffee solution was freshly prepared before each period. Group 5 : Coffee solution was prepared as described for group 4 and cooled to 37��C.

Specimens were stored in this solution and held in a water bath at 37��C (OLS 200; Grant Instruments Cambridge, England). Specimens were immersed in the test solutions for 15 min three times a day (morning, afternoon, and night) for 30 days. The specimens were kept immersed in 1.2 ml of artificial saliva at 37��C in an incubator (EN 120 incubator; N��ve) in the intervals between cycles. All specimens were stored in light-proof containers and the solutions were changed for each test period. The temperatures were measured with a digital thermometer. After 30 days of immersion in the solutions, the specimens were rinsed with distilled water for 5 min and blotted dry with absorbent paper before the final measurements.

The pH values of beverages at different temperatures were measured using a pH meter (HI 221; Hanna Instruments, Cluj-Napoca, Romania). The pH value was 4.85 for 70��C coffee, 5.04 for 37��C coffee, 2.72 for 10��C cola, and 2.48 for 37��C cola. Color measurements The color of specimens was measured at baseline and after 30 days immersion using a VITA Easyshade (Vident, Brea, CA, USA) spectrophotometer, with the CIELAB scale L*, a*, and b*. ��E* was calculated by the following equation: ��E* = [(��L) 2+ (��a) 2+ (��b) 2]1/2. All color measurements were performed three times for each specimen. The device was calibrated before the measurement of each specimen. Surface roughness measurements All the specimens were subjected to roughness testing using a contact profilometer (Surfcorder SE 1700; Kosaka Corp.

, Tokyo, Japan) equipped with a 5-mm-radius diamond-tipped stylus that was attached to a pickup head. The stylus traversed the surface of the specimen at a constant speed of 0.5 mm/s with a force of 4 mN and automatic return. Each specimen was traced in four parallel locations near the center across the finished and/or polished surface with an evaluation length of 4 mm. Five measurements in different directions were recorded for each specimen. Leveling of all parts of the apparatus was achieved by adjusting the pickup head knob. A calibration block was AV-951 used periodically to check the performance of the device.