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.