In vitro caries inhibition at the enamel margins of glass ionomer restoratives developed for the ART approach

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Abstract

Objectives: To assess the ability of conventional glass ionomer cements manufactured specifically for the atraumatic restorative treatment (ART) approach to inhibit the in vitro demineralization of enamel.

Methods: Twenty-four sound permanent premolar teeth, extracted for orthodontic reasons, had cervical cavities (4×2×1.5mm3) prepared in enamel. These were restored with Fuji IX, Fuji IX GP, Ketac-Molar and Compoglass, and then thermocycled 300 times between 5–55°C before being placed in a demineralizing solution (0.1 M lactic acid with 1 g/l dissolved hydroxyapatite at pH 4.7) for four weeks. Buccolingual planoparallel sections were cut axially through the restorations, and subsequently lapped to approximately 100 μm thickness. The sections were examined with a polarized light microscope, and lesion measurements made using image analysis software. ANOVA and coefficients of variance were used to compare the findings.

Results: Compoglass and Ketac-Molar showed significantly less surface erosion than did the other two cements (p<0.0001). Inhibition of enamel demineralization immediately adjacent to the restoration margins was more frequent with the glass ionomer cements (20.5–25.0%) than with Compoglass (13.0%). However, the widths of the inhibition zones varied between materials and sites.

Conclusions: Fluoride ion release from the restorative materials afforded some degree of protection to the adjacent enamel against in vitro demineralization.

Introduction

Recently, several hand-mixed conventional glass ionomer cements (GICs) have been manufactured specifically for the atraumatic restorative treatment (ART) technique or approach [1]. Minimal cavity preparations using hand instruments and newer more-viscous aesthetic GICs are part of the ART approach, which has been developed to provide urgently needed treatment for dental caries where conventional methods of dental care are either not available or are too costly. However, the newer GICs also have a role in dental care for patients in industrialized countries.

Fluoride was initially incorporated into early GIC glasses to modify the setting reaction [2], but it was subsequently demonstrated by many workers that the leaching of fluoride ions from the cements was associated with an in vitro reduction in enamel demineralization. Reports have shown that the newer more-viscous GICs release substantially less cumulative fluoride ions than less-viscous aesthetic restorative GICs and resin-modified GICs [3], [4], [5], [6], [7], [8], [9], [10], [11]. The effect of the lower fluoride ion release on the ability of the more-viscous GICs to inhibit dental caries in adjacent tooth tissues is not known, and several in vitro studies have shown variations among different restorative materials in their inhibition of caries-like lesions in enamel. Generally, non-fluoride ion releasing restorative materials have had no or minimal inhibition and, although the degree of inhibition associated with fluoride ion releasing materials may not necessarily be directly related to the levels of release, any significant effect is usually restricted to the immediate vicinity of the restoration margins, and the findings can be confounded by the direction of the enamel prisms [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23].

Part of the requirements of a restorative material used with the ART approach is its ability to remineralize carious tissue remaining after hand excavation [24] and to prevent secondary caries [25], [26]. This in vitro study examines the ability of two GIC restoratives manufactured for use with the ART approach to inhibit the demineralizing effects on enamel from an artificial caries challenge.

Section snippets

Artificial caries challenge

Human permanent premolar teeth, recently extracted as part of orthodontic treatments, were stored in 0.1% thymol phosphate buffered saline solution. Soft tissues and deposits were removed with hand scaling and with pumice slurry in a rotating brush. The cleaned buccal and lingual enamel surfaces were examined at 12× magnification with a stereoscopic SMZ microscope (Nikon, Tokyo, Japan) to choose sites without caries, cracks or intrinsic staining, particularly from fluorosis and tetracyclines.

Surface loss of restorative material

The overall mean depth of surface loss of material adjacent to the cavity walls was 27±40(SD) μm, as shown in Table 2. This overall loss was fairly similar at the cervical and coronal margins of the preparations. However, as shown in Table 3, the erosion for the hand-mixed Fuji IX (51±41μm) and the encapsulated Fuji IX GP (51±50μm) was significantly greater than that for the encapsulated Ketac-Molar (9±21μm) and Compoglass (7±16μm), p<0.0001.

Inhibition of enamel demineralization adjacent to cavity margins

All sites showed some birefringence patterns in the

Surface loss of restorative material

All restorative materials showed some surface loss due to erosion from the demineralizing solution. However, the effects were significantly less for Ketac-Molar and Compoglass, Table 3. Other in vitro studies have also shown the deleterious effects of moisture and acidic solutions on GIC solubility [4], [7], [27]. However, surface hardening of Fuji IX GP has been shown to occur when the cement was stored in human saliva [28], which may reduce its surface erosion in vivo. Resistance by GICs to

Conclusions

Within the limits of this in vitro study it was found that:

  • 1.

    The two viscous aesthetic conventional GICs marketed for use with the ART approach, and the compomer, conferred some protection to the adjacent enamel against an artificial caries challenge.

  • 2.

    The GICs showed more instances (20.5–25.0%) of inhibition of demineralization than did the compomer (13.0%) immediately adjacent to the restorations. However, there was considerable variation among the materials in the widths of the inhibition zones

Acknowledgements

Dr M.S. Gale is gratefully acknowledged for writing and testing the image analysis software. Financial assistance from a Hong Kong RGC award (10201736323) and a University of Hong Kong award (10201736324) are also gratefully acknowledged, as was the supply of commercial materials from the manufacturers, and the assistance of Dr W.T.C. Lam, Prince Philip Dental Hospital.

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