Fluoride release from glass ionomer cements and resin composites coated with a dentin adhesive

Abstract

Objectives: This laboratory study compared the effect of surface coatings on patterns and amounts of fluoride released from four glass ionomer cements and two fluoride-containing resin composites.

Methods: Twelve cylinders of each material were prepared in a polyethylene mold. The experimental groups (n=6) were coated with one layer of an adhesive resin (3M Scotchbond Multipurpose Adhesive), while the control groups (n=6) remained uncoated. Cumulative fluoride release into deionized water was measured on days 1, 2, 3, 7, 14, 21 and 28 using an ion analyzer. Total fluoride release after 28 days was analyzed for significant differences among materials using one-way ANOVA and Student–Newman–Keuls test (p<0.05).

Results: The total amounts of fluoride release from the coated samples were found to be significantly less than the uncoated samples for all materials, except Solitaire. The uncoated samples released a total amount of fluoride of between 2.3 and 85.4 ppm, while the coated samples released a total amount of fluoride of between <0.2 and 24.1 ppm. Similar patterns of fluoride release were found in coated and uncoated samples.

Significance: The results indicated that the application of a dentin adhesive coating did not completely prevent fluoride release from glass ionomer cements and fluoridated resin composites, although the amounts were significantly less. Clinically, it suggests that a continued release of fluoride from glass ionomer cements and fluoridated resin composites is possible after placing a thin layer of resin adhesive. The clinical significance of these findings is not known.

Introduction

Glass ionomer cements (GICs) are widely used in dentistry because of a variety of beneficial properties. Chemical diffusion-based adhesion to enamel and dentine, fluoride release, biocompatibility with tooth structure, simple application, esthetic appearance, acceptable abrasion resistance and capacity to be retained on unsupported enamel or non-undercut cavities are some of their favorable properties [1]. The two main reasons that have made GICs very popular are their permanent ionic bond to tooth structure, and their capacity to release fluoride, making them useful materials to replace dentin when used as bases in deep cavities [2], [3]. GICs have also been recommended for use as bases in conjunction with resin composites, and the so-called ‘sandwich’ or ‘laminate’ technique has become a common practical procedure to take advantage of GICs in combination with resin composites for restorations [4], [5].

When using a conventional GIC, its bond strength to the resin composite has been found to be limited by the low cohesive strength of the GIC [4]. Resin-modified glass ionomer cements (RM-GICs) have been recommended as bases to support an overlying resin restoration because of their enhanced physical and mechanical properties [2], [6]. In order to increase the bond strength of RM-GICs to dentin, and retain the other benefits when used in combination with resin composites in the laminate technique, it has been recently suggested that an adhesive bonding resin be applied to the dentin prior to the placement of a RM-GIC/resin composite restoration [3]. This study demonstrated that shear bond strengths of several RM-GICs were higher when a dentin adhesive was used, compared to their application directly to the dentin. However, the placement of a dentin adhesive prior to the application of a GIC results in the loss of direct contact of the GIC and the cavity wall. This ‘barrier’ may affect the ion exchange that normally occurs between a GIC and tooth structure when setting, which is responsible for the transfer of fluoride and other ions to the tooth.

It has been determined in many previous studies that GICs and RM-GICs have the capacity to slowly and steadily release fluoride over extended periods of time [7], [8], [9], [10], [11], [12], [13]. Amounts of fluoride release in deionized water have been found to range between almost 100 ppm to less than 10 ppm at 28 days in some conventional GICs [14], [15], between almost 50 to 7 ppm or less at 28 days in RM-GICs [7], [10], [14], and between 1 ppm or less to undetected limits (below 0.02 ppm) in some fluoridated resin composites [7], [15]. Fluoride release is an important property of those restorative materials, as it has been postulated to have anticariogenic potential by protecting both surrounding tooth structure and adjacent teeth against caries and demineralization [16], [17], [18], [19], [20]. It has also been postulated to enhance remineralization of early demineralized lesions of enamel [21], [22], [23], [24], [25], [26], and increase enamel resistance to subsequent acid attacks [23], [25], [26], [27]. Therefore, it would be desirable to continue placing them where associated with dentin margins of the cavity walls, compared with other materials. However, it is unknown whether the prior application of an adhesive resin to dentin affects the release of fluoride and its claimed anticariogenic potential. A previous laboratory study has reported fluoride release through fluoride-containing resin adhesives [28]. However, only one study has investigated fluoride release through surface coatings of non-fluoride-containing resin adhesives and varnishes [29].

The aim of this laboratory study was to compare the patterns and amounts of fluoride release from two GICs, two RM-GICs and two new fluoride-containing resin composites, coated with a layer of non-fluoride-containing dentin adhesive, to determine whether these surface coatings affect the capacity to release fluoride.