Laboratory Measurement of Toothpaste Wear

Objective:Radiotracer Method (J D Res 1976) has been and is now the primary laboratory method for the measurement of toothpaste abrasion. Methods:One of the strengths of the Radiotracer Method is the direct comparison of test materials to calcium pyrophosphate abrasivity reference material. The resistance of human dentin to toothpaste wear varies substantially between teeth and even within the same tooth. Results:By sandwiching an unknown test material between two determinations of calcium pyrophosphate reference abrasive, the strength of the comparison is strengthened. The sensitivity of the Radiotracer Method permits multiple determinations on the same tooth; thus a pre- and post-reference calcium pyrophosphate sandwich on both sides of the test material is possible multiple times on the same tooth. In contrast to the Radiotracer method, the profilometry method can be used for about three such calcium pyrophosphate sandwich determinations on the same tooth. A profilometry determination includes a pre-brushing baseline and post-brushing scans followed by a flattening of the brushed tooth surface. The variation in wear values for individual human dentin specimens brushed with calcium pyrophosphate reference can be a factor of 10 or more, thus multiple determinations are necessary to obtain reasonable method sensitivity. A large sheet of cast acrylic can be cut into uniform of about 20 X 50mm strips cut to fit various cross brushing machines. Conclusion:Since cast acrylic is uniform throughout a very large sheet, the calcium pyrophosphate wear measurement can be used for comparison with many individual test measurements made on the same acrylic sheet. This approach decreases the laboratory work per test specimen while increasing the sensitivity of the determination. The direct comparison of the wear of an unknown test material with the calcium pyrophosphate reference abrasive remains at the heart of laboratory measurement of toothpaste wear.