Methods: HA disc dissolution was measured in 14 mM citric acid (pH 3.20) over 30 min periods at 36°C using a pH stat. Baseline dissolution rate for each disc was determined from the mean of three initial measurements. Discs were then exposed to (i) 0.10% SDP (ii) 0.10% PDP (iii) 1.00% PDP or (iv) 300 mgL-1 fluoride for 120 s under gentle agitation. Following rinsing with deionised water, the disc dissolution rate was measured again in fresh acid solution over successive 30 min periods until the baseline rate had been recovered.
Results: Fluoride treatment significantly reduced the HA dissolution rate versus baseline by 14% in the first instance (p<0.05), but inhibition did not persist beyond the first post-treatment acid exposure (30 min). Treatment with 0.10% SDP or PDP also resulted in a statistically significant reduction in dissolution rate versus baseline (p<0.05) of 26 and 34% respectively; PDP was significantly more effective than the SDP. The reduction in HA dissolution by 0.10% MAP was persistent to 60 and 120 min post-treatment respectively for SDP and PDP. Treatment with 1.00% PDP resulted in more sustained inhibition of dissolution compared to the other treatments, with statistically significant suppression of dissolution observed for at least 210 min post-treatment (p<0.05). Conclusions: In this pH stat model, a single treatment with 0.10% MAP confers a greater inhibition of HA dissolution than 300 mgL-1 fluoride. Moreover the dissolution inhibition afforded by MAP is more long-lasting than that of fluoride, and for PDP was dose dependent.
Funding provided by GlaxoSmithKline