Zinc-Ion Release and Recharge Ability of GIC Containing BioUnion filler

Objectives: Caredyne-Restore (GC), a newly developed glass-ionomer cement for restoration of root surface caries, contains BioUnion filler which releases zinc ion (Zn²⁺) characteristically under acidic conditions. The aim of this study was to assess the ability of Caredyne-Restore to release and recharge Zn²⁺ in vitro. The effects of Zn²⁺ released from Caredyne-Restore to inhibit Streptococcus mutans biofilm were also evaluated.
Methods: On the set specimen of Caredyne-Restore, artificial saliva (pH 7.0) was dropped at 4 mL/hr using a peristaltic pump, replacing with an acetic acid at pH 4.5 for 1 hr, periodically. The concentration of Zn²⁺ released into the dropwise was measured by absorptiometry using colorimetric reagent, and compared with those for saliva only dropping group. To evaluate Zn-recharging ability, the specimen was immersed in 0.1 wt% zinc chloride solution for 5 min during saliva/acid-dropping procedure, and Zn²⁺ release profile was determined. To confirm effective concentrations of Zn²⁺ to inhibit biofilm, resin composites specimen was incubated in S. mutans suspension for 24 hrs with the addition of Zn²⁺ at 0 (control) - 15 ppm, and biofilm formation was assessed by CLSM with Live/Dead staining.
Results: Significant increase in the concentration of Zn²⁺ released was found by acid-dropping to the specimen (Student’s t-test, p<0.05). The release of Zn²⁺ was significantly increased by recharging, and the concentration was maintained above 5 ppm with the protocol to recharge twice during 24-hr period. The biofilm formed in the presence of Zn²⁺ at 5 ppm or greater was significantly thinner than the control (ANOVA, Tukey’s HSD test, p<0.05), and dead cells were observed by Zn²⁺ at 10 ppm or greater.
Conclusions: This in vitro study using the saliva-drop setting demonstrated that Caredyne-Restore released Zn²⁺ under acidic conditions and such ability can be maintained at the level to inhibit biofilm formation by recharging with zinc ion solution.