Afshin Falsafi

Mechanisms of setting reactions and interfacial behavior of a nano-filled resin-modified glass ionomer

OBJECTIVES In order to improve the short-comings of glass ionomers such as polishability and esthetics while preserving their excellent clinical bonding effectiveness, nanofiller technology has been introduced in a paste-paste resin-modified glass ionomer (nano-filled RMGI, Ketac Nano, KN, 3M ESPE). One objective of this study was to investigate if the introduction of nanotechnology had any significant effect on the setting reaction of the nanoionomer compared to a control RMGI, Vitremer (VM, 3M ESPE). Another objective was to determine the mechanism of bonding of KN in combination with its primer (KNP) to the tooth. METHODS Fourier-Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were performed on KN and VM during the setting of the GIs. FTIR and XPS were also used to study the reaction of the primer of KN (KNP) with hydroxyapatite (HAP). Shear adhesion to dentin and enamel was measured with KN and compared with several RMGIs and one conventional glass ionomers (CGI). The interfaces were examined with scanning electron microscopy (SEM). RESULTS FTIR data show that KN undergoes both acid-base and methacrylate setting reactions of classical RMGIs. XPS and FTIR studies of the interaction KNP with HAP shows the formation of calcium-polycarboxylate bond. Shear adhesion and failure mode of KN to enamel and dentin were similar to the other RMGIs and CGI. SEM images of KN with tooth structure showed a tight interface with a thin but distinct layer of 2-3 microns attributed to the primer. This was also observed for VM but not for the other three materials. CONCLUSIONS KN showed two setting reactions expected in true RMGIs. The adhesion with dentin and enamel was similar to other glass-ionomers. The formation of calcium-polycarboxylate was also evident. This chemical bonding is a significant factor in the excellent long-term adhesion of these materials.

Fluoride release and dentin caries inhibition adjacent to resin-modified glass-ionomer luting cements

The objectives of this investigation were to compare the fluoride release and caries inhibition ability of resin-modified glass ionomer (RMGI) luting cements. Methods: Materials used for dentin caries inhibition were 3M ESPE RelyX(superscript TM) Luting Plus Cement (REP) paste-paste RMGI, RelyX(superscript TM) Luting Cement (RLC) powder-liquid RMGI and Filtek(superscript TM) Z250 composite/Adper(superscript TM) Single Bond adhesive (ZSB). Rectangular slots (6×2×1 mm) were prepared in 24 dentin blocks cut from 8 bovine roots, and filled with ZSB, RLC, and REP. The specimens were immersed in 10 ml acetic acid solution pH 5.0 (37℃, 3 wks) to create artificial dentin lesion, then sectioned into 400 μm slices and subjected to microradiography. Mineral loss (△Z) was calculated from mineral profiles at 0.5 and 1.0 mm from the material margin, and statistically analyzed (ANOVA, Fishers, p＜0.05). Fluoride release from cured cement discs (20×1 mm; n=8) in distilled water was measured after 1, 7, 14, 28, 90, 180, and 365 day using F-specific electrode and TISAB buffer. A conventional GIC, Ketac(superscript TM) Cem, was used as a control for this experiment. Results: Z250 is not fluoridated and did not exhibit F release. The sustained F release from REP and REC were comparable to each other and higher than from the control conventional GIC. Both RMGIs showed pronounced inhibition zones in dentin adjacent to cement margin. △Z values at 0.5 mm and 1.0 mm from RLP and RLC were significantly less compared to ZSB. △Z values were not significantly different in RLP and RLC groups at 1.0 mm. Conclusion: Both the powder-liquid and paste-paste RMGIs, RelyX Luting and RelyX Luting Plus cements respectively, released comparable amounts of fluoride, and, in contrast to the composite, demonstrated inhibition zones at the adjacent dentin when subjected to in vitro demineralization. Both cements inhibited mineral loss in dentin compared to the composite up to 1.0 mm adjacent to the bonded interface.