Microhardness of in vitro caries inhibition zone adjacent to conventional and resin-modified glass ionomer cements

Objective. This study was conducted to correlate Knoop and triangular hardness numbers by measuring the microhardness of in vitro caries-inhibited and -demineralized dentin adjacent to a conventional and two resin-modified glass ionomer cements.Methods. Box-shaped cavities were prepared on bovine root dentin and restored with either Fuji II, Fuji II LC, or Vitremer. The teeth were then decalcified in an acid buffered solution of 50 mmol l−1 acetic acid adjusted to pH=4.5 for 3 days. Knoop and triangular microhardness indentations were performed perpendicular to the surface and parallel to the cavity wall, in the demineralized lesion and inhibition zone. Calcium and phosphorous contents of the outer lesions and inhibition zones were compared using energy-dispersive X-ray spectrometry (EDS). The correlation between Knoop and triangular hardness was analyzed by correlation coefficient. The statistical significance of hardness data was analyzed by one-way ANOVA and Fisherʹs PLSD test (p<0.05).Results. Triangular hardness (HT) correlated well with Knoop hardness number (KHN) (r2=0.81, p<0.05). The microhardness of the inhibition zone created by Fuji II was of 59.2±3.8 HT and was statistically significantly higher than the zone produced by Fuji II LC and Vitremer. Fuji II LC and Vitremer produced inhibition zones with similar microhardness [48.3±3.5 HT and 44.0±7.6 HT, respectively (p>0.05)]. Calcium and Phosphorous were present in the inhibition zone, but did not exist in the demineralized lesion.Significance. Knoop and triangular hardness numbers correlated significantly (p<0.05), and the latter seems to be a promising alternative method for measuring very narrow surfaces. Despite the fact that all glass ionomer materials used in this study were effective in producing an acid-resistant layer, microhardness and intensity of these layers were material dependent.