Hoa T. Bui

Long-term adhesion and mechanism of bonding of a paste-liquid resin-modified glass-ionomer

OBJECTIVES The contribution of chemical bonding of the polycarboxylic acid in classical powder/liquid conventional glass ionomers (GI) and resin-modified glass-ionomers (RMGI) has been attributed to the excellent long-term bond strengths and clinical retention. RMGIs have been recently introduced as paste/liquid systems for convenience of clinical usage. The objective of this study was to investigate the long-term bond strengths and mechanism of adhesion of paste-liquid RMGI in order to ascertain whether similar characteristics are retained. METHODS Long-term shear adhesion to dentin and enamel was measured on two paste-liquid RMGIs and one powder/liquid RMGI. Scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were carried out on the paste-liquid RMGI Vitrebond Plus (VBP) and compared with the classical powder/liquid RMGI Vitrebond (VB). RESULTS VBP maintains adhesion to dentin and enamel over long times; its long-term adhesive performance is equivalent to VB. FTIR data confirm that VBP exhibits the carboxylate crosslinking reaction of a true glass ionomer. SEM images show evidence of micromechanical bonding at the interface between VBP and the tooth. XPS and FTIR data show that the methacrylated copolyalkenoic acid component present in VB and VBP chemically bonds to the calcium in HAP. SIGNIFICANCE The new paste-liquid RMGI liner, VBP, shows equivalent adhesion to its powder-liquid predecessor, VB. The adhesion mechanism was attributed to micromechanical and chemical bonding. This chemical bond is a significant factor in the excellent long-term adhesion of these materials.

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.