Glass ionomer cements functionalised with a concentrated paste of chlorhexidine hexametaphosphate provides dose-dependent chlorhexidine release over at least 14 months

Objectives
The aim of this study was to create prototype glass ionomer cements (GICs) incorporating a concentrated paste of chlorhexidine–hexametaphosphate (CHX–HMP), and to investigate the long-term release of soluble chlorhexidine and the mechanical properties of the cements. The purpose is the design of a glass ionomer with sustained anticaries efficacy.

Methods
CHX–HMP paste was prepared by mixing equimolar solutions of chlorhexidine digluconate and sodium hexametaphosphate, adjusting ionic strength, decanting and centrifuging. CHX–HMP paste was incorporated into a commercial GIC in substitution for glass powder at 0.00, 0.17, 0.34, 0.85 and 1.70% by mass CHX–HMP. Soluble chlorhexidine release into artificial saliva was observed over 436 days using absorbance at 255 nm. Diametral tensile and compressive strength were measured after 7 days’ setting (37 °C, 100% humidity) and tensile strength after 436 days’ aging in artificial saliva. 0.34% CHX–HMP GICs were tested for their ability to inhibit growth of Streptococcus mutans in vitro.

Results
GICs supplemented with CHX–HMP exhibited a sustained dose-dependent release of soluble chlorhexidine. Diametral tensile strength of new specimens was unaffected up to and including 0.85% CHX–HMP, and individual values of tensile strength were unaffected by aging, but the proportion of CHX–HMP required to adversely affect tensile strength was lower after aging, at 0.34%. Compressive strength was adversely affected by CHX–HMP at substitutions of 0.85% CHX–HMP and above.

Conclusions
Supplementing a GIC with CHX–HMP paste resulted in a cement which released soluble chlorhexidine for over 14 months in a dose dependent manner. 0.17% and 0.34% CHX–HMP did not adversely affect strength at baseline, and 0.17% CHX–HMP did not affect strength after aging. 0.34% CHX–HMP GICs inhibited growth of S. mutans at a mean distance of 2.34 mm from the specimen, whereas control (0%) GICs did not inhibit bacterial growth.

Clinical Significance
Although GICs release fluoride in vivo, there is inconclusive evidence regarding any clinical anticaries effect. In this study, GICs supplemented with a paste of chlorhexidine-hexametaphosphate (CHX–HMP) exhibited a sustained release of chlorhexidine over at least 14 months, and small additions of CHX–HMP did not adversely affect strength.