Abstract
A novel way was adopted to graft zinc oxide (ZnO) with urethane-modified dimethacrylate (UDMA) in order to utilize them as reinforcing agents in resin-based dental composites. Experimental novel composites were synthesized having UDMA-grafted and nongrafted ZnO, at a concentration of 0 wt.%, 5 wt.%, and 10 wt.%. The same concentrations of ZnO were also incorporated in Filtek Z250 XT (3 M ESPE, USA). The antibacterial behavior was evaluated against Streptococcus mutans by direct-contact test at one, three, and seven days of incubation. The compressive strength and Vickers microhardness were tested as per ISO 9917 and ISO/CD6507-1, respectively. For abrasive wear resistance, mass loss and roughness average after tooth-brushing cycles of 24,000 at custom-made tooth-brushing simulator were evaluated using noncontact profilometer. Data analysis was carried out using post hoc Tucky’s test and nonparametric Kruskal–Wallis test. Direct contact test revealed that the antibacterial potential of novel and commercial composites was increased with an increase in the concentration of grafted ZnO as compared with nongrafted, whereby the potential was the highest at day seven. There was a significant decrease in compressive strength and Vickers hardness of commercial composites on addition of grafted ZnO while there was no significant difference in the strength of experimental novel composite. The abrasive wear of commercial and experimental composites was within clinical limits. Low-temperature flow-synthesis method was successfully employed to synthesize grafted and nongrafted ZnO. The UDMA-grafted ZnO can be incorporated into dental composites without decreasing their strength and these composites can be used to combat secondary caries.
Highlights
It is desirable for current dental restorative materials to have antibacterial properties, as the occurrence of plaque accumulation on resin-based composites (RBCs) is higher, subsequently, leading to secondary caries formation [1, 2]
The broad band between 3600 and 3000 cm−1 attributed to the stretching vibration of the OH group, after grafting, the band shape changed to a prominent peak (3450–3350 cm−1) assigned to the N–H group due to the presence of urethane-modified dimethacrylate (UDMA)
The UDMA-grafted zinc oxide (ZnO) showed mass loss from 90 to 290 °C due to loss of moisture and the initial decomposition of UDMA. Another drastic mass loss was noted at 560 °C, which was due to the final decomposition of UDMA, and at 1000 °C mass loss was 34.2%. This confirmed the presence of UDMA on the surface of ZnO and the total mass loss of UDMA was approximately 28%, which was close to the initial weight percentage of UDMA
Summary
It is desirable for current dental restorative materials to have antibacterial properties, as the occurrence of plaque accumulation on resin-based composites (RBCs) is higher, subsequently, leading to secondary caries formation [1, 2]. The issue with these antibacterial agents is that after sometime, their effect diminishes, subsequently there is an adverse effect on the mechanical properties of the restoration [6, 7]. Another approach is the inclusion of quaternary ammonium that inactivates only the bacteria coming in direct contact with active molecules that are immobilized or incorporated as the functional group. Silver and titanium oxide (TiO2) nanoparticles had shown discoloration [11] and decreased shear bond strength with increasing the concentration of TiO2 [12]
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