Effect of pH Variations in a Cycling Model on the Properties of Restorative Materials

Abstract

SUMMARYThis study evaluated the effect of cycling various pH demineralizing solutions on the surface hardness, fluoride release and surface properties of restorative materials (Ketac-Fil Plus, Vitremer, Fuji II LC, Freedom and Fluorofil). Thirty specimens of each material were made and the surface hardness measured. The specimens were randomized into five groups according to the pH (4.3; 4.6; 5.0; 5.5 and 6.2) of the demineralizing solution. The specimens were submitted to pHcycling for 15 days. The specimens remained in the demineralizing solution for six hours and in the remineralizing solution for 18 hours. Then, the surface hardness (SH) was remeasured and the surface properties were assessed. Fluoride release was determined daily. Data from SH and the percentage of alteration in surface hardness were analyzed by analysis of variance (p<0.05); the Kruskal-Wallis test was performed for the fluoride release results. When hardness was compared, the variation in pH led to a positive correlation for glass ionomer cements and a negative correlation for fluoride release. For polyacidmodified resin composites, a negative correlation was found with regards to fluoride release; no significant correlation was observed for hardness. Surface properties were influenced: an acidic pH led to a greater alteration, except for polyacid-modified resin composites. When considering the individual needs of patients in the clinical setting, it is important to know the behavior of restorative materials in the oral environment under pH variations. Laboratory Researchglass ionomer cements but did not influence polyacid-modified resin composites.

Effect of Chemical and Mechanical Degradation on Surface Roughness of Three Glass Ionomers and a Nanofilled Resin Composite

“…29 This method involves six hours of acid challenge and 18 hours of remineralization per day, which is a reasonable estimate for subjects who frequently consume sugar. 29 Moreover, Silva and others 22 showed that the surface properties of restorative materials were influenced by pH variation in the demineralizing solution of pH cycling. The acidic pH led to a greater alteration in hardness and surface morphology of GI cements.…”

“…The pH-cycling regime used in the current study was an in vitro chemical degradation method that simulated alterations in the pH of the oral cavity and mimics clinical conditions whereby there is always a dynamic between demineralization and remineralization. 22 The method of acid challenge by the dynamic pH-cycling model used in the current study was proposed by Featherstone and others. 29 This method involves six hours of acid challenge and 18 hours of remineralization per day, which is a reasonable estimate for subjects who frequently consume sugar.…”

“…The specimens were first immersed in 5 mL of demineralization solution for six hours at 378C, rinsed with distilled deionized water, and then stored in 5 mL of remineralization solution for 18 hours at 378C. 22 These experimental conditions were repeated for 10 uninterrupted cycles of demineralization and remineralization. The solutions were changed every day.…”

“…22 The demineralization solution contained 2.0 mM calcium and 2.0 mM phosphate in a buffer solution of 74.0 mM acetate at pH 4.3. The remineralization solution consisted of 1.5 mM calcium and 0.9 mM phosphate in a buffer solution of 0.1 mM Tris (hydroxymethyl-aminomethane) at pH 7.0.…”

“…The dynamic variations in the oral pH, due to cariogenic challenges, can develop superficial degradation of restorative materials from the low pH. 16,22 Furthermore, some studies 15,23,24 have demonstrated that materials can be more susceptible to brushing abrasion at lower pH values. The acidic storage medium erodes the surface of conventional GI, for example, and causes hydrolysis and dissolution mainly in the polyalkenoate matrix.…”