Structure, Properties and Performance Relationships of Different Ion-leachable Resin Composites

Abstract

A common cause of failure of resin composite (RC) dental restorations is recurrent caries, due to bacterial ingress and demineralisation between tooth walls and RC. RC systems with potential re-mineralising ability and sufficient properties could address this problem. Ion leachable (IL) 45S5 bioactive glass (BG) is a candidate filler phase and source of Ca2+ and PO43- ions. This was incorporated into experimental composites along with two strontium-fluoro-alumino-silicates that correspond to glass compositions of Fuji IX® (F9) and Fuji IX Extra® (F9X) and function as fluoride sources. We analysed the in situ IL-glass phase (amorphous by XRD), chemical compositions (by XRF) and morphology (average size 1-10 m). Then, we formulated and studied RC systems (13 formulations) with filler phase comprised of 72 wt% silanated barium borosilicate inert glass (BBS, control), with progressive substitutions of 10, 15, 20 or 25 wt% with un-silanated BG, F9X, or F9 dispersed in a Bis-GMA:TEGDMA (50:50 w/w) photo-polymerised matrix. The amount of ions released had a direct correlation with ILG proportions in RCs. BG-RCs released higher Ca2+ and PO43- ions (5 and 2.5 mmol/L, respectively) in acidic than neutral pH. Due to the presence of surface oxides, BG fillers in RC reduced the transmitted light (by 17 %) and impaired the immediate degree of polymerisation. Minimal increase in the un-silanated filler proportions (10-25 wt.%) did not affect the flexural strength (FS) of ILG-RCs. But the high solubility of 45S5 glass fillers resulted in high water sorption (80-100 µg/mm3), and thus, reduced flexibility (25-50 MPa), and surface hardness (20-35 VHN) of RCs. By contrast, adding F9X or F9 glasses to RC had no effect on the water sorption (30-38 µg/mm3). FS was minimally affected and comparable (80 MPa) to the reference resin composite (0-ILG%). Both F9X- and F9-series were able to release similar amounts of fluoride ions (0.5-1 mmol/L). The short-term fluoride release (3 d) was higher in acidic than neutral pH. However, the pH of the immersed solutions had no significance on cumulative fluoride release after 60 d (p>0.05). Ion release and strength properties were determined mainly from ILG solubility and proportion in RC. The results obtained show IL-resin composite systems as candidate restorative materials, particularly for the lower increment in a two-step cavity restorative procedure. The ability of BG restorative composites to raise pH and release Ca2+ and PO43- propose these materials as potential means of remineralisation at tooth-filling interfaces. Further in-vitro investigations are needed to validate these possibilities.