Daniel W. Boston

Preliminary Evidence That Bioactive Cements Occlude Artificial Marginal Gaps.

PURPOSE The objective of this preliminary laboratory study was to explore whether bioactive dental cements have the ability to seal marginal gaps as compared with other classes of dental cements. MATERIALS AND METHODS Tooth discs (dentin/enamel) were positioned adjacent to a second disc of one of five possible dental cements (two bioactive and three conventional) and separated by a 50-μm Mylar film, creating a controlled gap between the two discs. The edges of the tooth segments were abraded to expose dentin such that the dentin interface was positioned opposite the cement. The artificial gap assembly was stabilized with adhesive and composite resin. Artificial gap assemblies for each cement type were immersed in a phosphate-containing, simulated body fluid (phosphate buffered saline) for up to 8 months. Occlusion of artificial marginal gaps (including deposition of crystal-like, mineralized deposits within the gaps) was observed and scored categorically during the observation period. Deposition of radiodense material within the artificial marginal gap space was confirmed by micro-computerized tomography analysis. RESULTS There was no evidence of marginal gap occlusion for the three conventional control cements, whereas both bioactive, surface apatite-forming cements demonstrated occlusion of the artificial marginal gaps. CONCLUSIONS The preliminary findings of this initial study suggest the possible capability of surface apatite-forming, calcium-based, bioactive dental cements to seal or reseal artificial marginal gaps in simulated aqueous physiological conditions. CLINICAL SIGNIFICANCE The results of this laboratory study, although preliminary in nature, suggest a new functional property for bioactive dental materials, namely the ability to significantly improve marginal stability with tooth/restorative material interface. Such behavior in a restorative material could improve the survival and serviceability of dental restorations.

Effects of a 36% tooth bleaching gel on zinc phosphate cement

PURPOSE To assess the effect of a 36% hydrogen peroxide bleaching gel on the roughness, microhardness, indentation modulus, and micromorphology of zinc phosphate cement aged 24 h or 1 week, compared to cement not exposed to bleaching gel. METHODS Dynamic indentation was performed for microhardness and indentation modulus. Contact profilometry was performed for surface roughness. Scanning electron microscopy assessed micromorphology. Means for microhardness, indentation modulus, and roughness were analyzed for differences among groups (No. 1 = 24 h/control; No. 2 = 24 h/treatment; No. 3 = 1 week/control; No. 4 = 1 week/treatment). RESULTS Means (SD) for groups 1-4 respectively: Vickers Microhardness (HV): 34.2(8.7)a, 32.8(10.9)a, 24.8(5.0)b, 41.5(7.4)c; Indentation Modulus (EIT, GPa): 14.2(6.9)a,b, 10.6(3.6)a, 11.2(3.8)a, 14.7(2.8)b; and Surface Roughness (Ra, microns): 1.08(0.38)a, 1.21(0.55)a, 1.55(0.21)b, 1.52(0.29)b. Means labeled with the same superscript were not statistically significantly different. Scanning electron microscopy of groups 1 and 2 revealed similar details. Group 3 surfaces had plate-like crystals not present on the group 4 surfaces. CONCLUSIONS Bleaching gel exposure increased hardness and indentation modulus and caused limited changes in surface morphology, but the cement was not adversely affected by the bleaching protocol.