Interactions between glass ionomer cement and alkali metal fluoride solutions: the effect of different cations

Evaluation of ion release and the recharge ability of glass-ionomer cement containing BioUnion filler using an in vitro saliva-drop setting assembly

OBJECTIVE

A glass-ionomer cement (GIC) containing BioUnion filler has been reported to release Zn²⁺ under acidic conditions and to inhibit oral bacteria on its surface. However, previous results are based on in vitro experiments under static conditions. This study aimed to assemble an in vitro saliva-drop setting to simulate in vivo conditions of the oral cavity and to investigate the ion releasing and recharging properties of the GIC containing BioUnion filler.

METHODS

The effective concentrations of Zn²⁺ and F^- against Streptococcus mutans and saliva-derived multi-species biofilms were determined. Artificial saliva was dropped on the GIC containing BioUnion filler using the in vitro saliva-drop setting assembly and was periodically replaced with acetic acid. Ion release/recharge properties were investigated by measuring the release concentrations of Zn²⁺ and F^-.

RESULTS

The concentration of Zn²⁺ released from the BioUnion filler-containing GIC during seven days with repeated exposure to acid could be maintained at the level to inhibit S. mutans and saliva-derived multi-species biofilm formation. Moreover, the BioUnion filler-containing GIC could be recharged with Zn²⁺ and F^- by the application of a tooth gel containing Zn²⁺ and F^-. The release concentration of Zn²⁺ after recharging was significantly higher than the effective concentration of Zn²⁺ to hinder S. mutans and saliva-derived multi-species biofilm formation on material surfaces.

SIGNIFICANCE

The GIC containing BioUnion filler was shown to have the potential to inhibit biofilm formation in the oral cavity. In addition, recharging Zn²⁺ and F^- would further enhance the effect of the GIC containing BioUnion filler.

Uptake of fluoride ions by the glass component of glass ionomer cement

OBJECTIVES

The uptake of F(-) ions by glass ionomer cement (GIC) has been extensively studied but the precise location of the F(-) ion in the GIC structure has not been reported. The aim of this study is to use model materials to elucidate the possible locations. GIC consists of residual particles of aluminosilicate glass surrounded by depleted glass in an ionically crosslinked polymeric matrix. This study evaluates uptake by both unreacted glass particles (RAW) and particles acid-treated to produce a depleted glass surface (DEPLETED).

METHOD

Three glasses, previously studied as cements, were tested at the particle size used in GICs. LG30 contained Al, Ca, O, P, and Si; LG26 also contained F and AH2 contained Na as well. To produce depleted surfaces they were immersed in acetic acid washed and dried at room temperature. Test samples (N=5) were immersed in KF solution (900ppm F). Control solutions without glass were used. Both were stored at 37C for 48h. F concentrations were measured using ISE with TISAB IV.

RESULTS

Uptake was Control-test expressed in micromol/g glass. RAW LG30=56 (16); LG26=35(17); AH2=17(31). DEPLETED LG30=285(41); LG26=431(42); AH2=286(50). The levels of F uptake by DEPLETED were comparable to those found with GICs formed with these glasses.

CONCLUSIONS

The glass particles of GIC, and particularly the depleted zones surrounding them, can account for an appreciable amount of the F uptake observed with cements but do not show the same relation between F content and F uptake previously observed with cements.

Ion processes in glass ionomer cements

Ion processes are involved in many aspects of glass-ionomer cements. The ions released from the glass take part in the formation of the cement matrix. Although this process has been investigated, particularly using model cement systems, no study provides a complete matrix composition. Combining results from different studies enables an approximate composition to be derived. The importance of Phosphorous in controlling ion release from the glass surface has been identified in a number of studies. The release of ions from the set cement into water (and other aqueous liquids) has been much reported, particularly for fluoride. Over most of the release periods studied (i.e. from >7 days up to 3 years), release of F ion is related to t1/2 indicating a diffusion-controlled process. Other ions, except possibly Na+ also show this relationship. The amount of cumulative F release whilst maintaining this relationship indicates that more F than is in the matrix is involved. Ion chromatography would probably elucidate the precise form of the ionic species released. Glass-ionomer cements take up ions from solutions in which they are immersed. The levels are much higher than required to produce as internal/external equilibrium. Studies using dynamic SIMS and XPS give some information on ion location and elemental association. It is suggested that ToF SIMS would elucidate these further. Re-release of uptaken ions can vary considerably for different cements and ion species. Surface disruption of glass ionomers is caused by both F ion and monofluorophosphate ion and occurs much more readily in F containing cements than in F free ones. The mechanism of this process has not been elucidated. Analysis of the ions released from the cement as disruption occurs should provide an indication of the site of attack.

The effects of adding fluoride compounds to a fluoride-free glass ionomer cement on subsequent fluoride and sodium release

Studies have shown that ions in a glass ionomer matrix are 1-10% of the amounts present in the original glass. To measure more precisely the release from a cement matrix, known amounts of ions were added to LG30 glass which was fluoride and sodium-free. Cement without additions acted as the control. 1.4-1.6% of each of sodium, calcium and aluminum fluorides were added to three portions of control blend. The sodium and fluoride release into deionised water from five discs of each cements blend was measured for 8 months. This represented complete release for sodium but not for fluoride. Traces of fluoride and sodium in the glass produced low but measurable amounts indicating about a third of the fluoride and substantially all sodium present in LG30 was released. The addition of calcium fluoride had no significant effect on sodium or fluoride release and aluminium fluoride minimal effects. Adding sodium fluoride significantly enhanced release of both ions although fluoride release was less than from a glass containing 5% fluoride. Only small proportions of the additions, 2-5% of the fluoride and 13% of sodium, were released. Sodium and fluoride appeared to be released independently. For LG30 cements additives were poor at supplying extra ions.