Effects of polyphosphates and fluoride on hydroxyapatite dissolution: A pH-stat investigation

Area of Science:

• Biomaterials science
• Dental materials research
• Surface chemistry

Background:

• Hydroxyapatite (HA) is the primary mineral component of teeth.
• Understanding factors influencing HA dissolution is crucial for preventing dental erosion.
• Phosphate salts and fluoride are common agents investigated for dental protection.

Purpose of the Study:

• To evaluate the impact of sodium trimetaphosphate (TMP) and sodium hexametaphosphate (HMP), with or without fluoride (F), on hydroxyapatite (HA) dissolution.
• To assess the influence of salivary coating on the protective effects of these agents.
• To determine the immediate and sustained effects on HA dissolution rates.

Main Methods:

• Hydroxyapatite discs were subjected to an erosion-like model using a pH-stat system.
• HA discs were treated with various concentrations of HMP, TMP, and fluoride, alone and in combination.
• Experiments were conducted both with and without a pre-applied layer of human saliva.
• Dissolution rates were measured before and after treatments, with statistical analysis using ANOVA.

Main Results:

• All tested solutions significantly reduced HA dissolution compared to the baseline.
• A synergistic inhibitory effect on dissolution was observed specifically between fluoride and 1% HMP.
• Higher concentrations (8%) of HMP, and combinations of HMP with fluoride, demonstrated longer-lasting inhibitory effects.
• The presence of salivary coating significantly enhanced the protective effect across all tested groups.

Conclusions:

• Fluoride, phosphate salt type (HMP vs. TMP), concentration, and the presence of salivary coating all influence the reduction of HA dissolution.
• Combinations of HMP and fluoride, particularly at higher concentrations and with salivary coating, offer significant and sustained protection against HA dissolution.