New Models to investigate Erosion Protection by toothpastes

Objectives:

Profilometry is a common tool to investigate tooth surface wear. Current studies, however, apply rather harsh conditions and investigate surface losses of 50 or even 100µm. The purpose of this study was to compare the erosion inhibiting potential of 2 toothpastes with varying active systems in vitro under mild conditions.

Methods:

A prototype paste containing a Hydroxyapatite-Protein-Composite (HPC) (P1) served as test. An HPC free silica toothpaste of comparable formula served as control (P2). Both pastes contained 1450 ppm fluoride as NaF. Bovine enamel specimens were mounted in cold cure epoxy resin, polished flat and randomly divided into 2 groups of four. During treatment reference areas were covered by adhesive tape. The specimens were subjected to a cyclic treatment of 20min exposure to Coke and 3 consecutive treatments with the pastes (1min brushing, 1:1 slurries, 150g load). In between brushing applications, specimens were kept in artificial saliva (37°C, minimum of 5h). This cycle was repeated 11 times. The amount of eroded enamel (wear) was measured in µm using a Scantron Proscan 3D profilometer with customized software after 5 and 11 cycles. The statistical significance of the data was confirmed using the T-test.

Results:

Paste	P1	P2
Wear after 5 cycles (MW±SD)	-0.69±1.40µm	-9.47±0.61µm
Wear after 11 cycles (MW±SD)	-3.09±1.99µm	-19.77±1.17µm

Conclusions:

The model allows to accurately monitor erosion inhibition and is subject to small standard deviations. Under the conditions employed the HPC-containing paste effectively protects enamel from erosive damage compared to the fluoride control. The erosion roughly proceeds linearly. The protective effect can be interpreted as a steady state between build up (neomineralization) of calcium phosphate by HCP and acid wear.