Methods: Bovine enamel specimens (3mm by 3mm) were prepared and baseline surface microhardness (SMH) measurements taken using a Knoop diamond with load of 50g for 10 secs. Specimens were stratified into three groups (n=10) and mounted in impression material. Each group was initially treated with sterilised whole human saliva for 2h to form a pellicle and then underwent a pH cycling protocol as follows: toothpaste slurry, 1:3 toothpaste:water (3mins), 1% w/w citric acid, pH 3.8 (2mins) and sterilised whole saliva (60mins). The cycling protocol was repeated 12 times and then the SMH was re-measured. The mean percentage change in SMH was calculated for each group. The toothpaste treatments were: non-fluoride control (A), 1450ppm SMFP (B), 1450ppm SMFP with enzyme (C), 2% HAP+1450ppm SMFP (D) or 2% HAP+1450ppm SMFP with enzyme (E). The enzyme treatment was as follows: bovine alkaline phosphatase type VII-L was added to toothpaste slurry at a final concentration of 100 U/ml and samples were incubated at 37oC for 20mins before addition into the pH cycling protocol.
Results: The mean percentage change in SMH (s.d.) for each treatment group was: A 52.8 (3.36); B 34.8 (1.44), C 26.7 (1.63), D 20.6 (1.41) and E 13.4 (1.55). Statistical analysis (ANOVA, Tukey-Kramer) showed that all treatments were significantly different (p<0.05) to each other.
Conclusions: A 2% HAP plus 1450ppm SMFP toothpaste provides greater enamel demineralisation protection than fluoride alone.