Abstract:

Objective To prepare the strontium and nitrogen co-doped titanium dioxide （Sr-N-TiO₂）/nano hydroxyapatite （n-HA） composite resins， to evaluate its basic properties， antibacterial properties， remineralization abilities， and biosafeties， and to clarify the antibacterial mechanism of the new type of composite resins. Methods Sr-N-TiO₂ and n-HA were mixed as the reinforcing fillers. The composite resins were prepared and were divided into control group and three experimental groups. According to the mass fractions of reinforcing fillers， the experimental groups were divided into 2.5% reinforcing filler group， 5.0% reinforcing filler group， and 7.5% reinforcing filler group. The infrared spectrogram of composite resins in various groups were detected by the Fourier-transform infrared absorption spectrogram and the double bond conversion rates were calculated before and after light curing for 60 s. The curing depths of composite resin specimens in various groups after light curing for 20 s were calculated by cylindrical mould （height=10.0 mm， diameter=4.0 mm）. Three composite resin specimens in various groups were prepared and co-cultured with the dilute Streptococcus mutans solution. The plate colony counting method was used to determine the counts of attached bacteria on surface of the specimens and the antibacterial rates were calculated； live/dead bacteria staining method was used to observe the ratio of live bacteria/dead bacteria and morphology of composite resin speciments in various groups.The composite resin specimens were immersed in the artificial saliva for 1， 3， 5， and 7 d， and the mineralizations of surface of the composite resins were observed under scanning electron microscope （SEM）. The mouse fibroblast cells（L-929 cells） were incubated with the resin extract solution，and CCK-8 method was used to detect the relative growth rates （RGR） of the cells on the 1st， 2nd， and 3rd days and the cytotoxicity levels were evaluated. Results With the increasing of reinforcing filler proportion of the composite resins， the double bond conversion rates and curing depths of new type of the composite resins showed a decreasing trend， but all reached the clinical standard. Compared with control group， the double bond conversion rates of new type of the composite resins in 2.5% reinforcing filler group and 5.0% reinforcing filler group had no significant differences （P>0.05）， and the above index in 7.5% reinforcing filler group was decreased（P<0.05）. Compared with control group， the curing depths of the composite resins in experimental groups were increased （P<0.05 or P<0.01）， the counts of attached bacteria on surface of the speciments in experimental groups were significant increased （P<0.01）. When the proportion of reinforcing fillers reached 5.0%， the antibacterical rates of new type of the composite resins were higher than 90%. Compared with control group， the counts of live bacteria on surface of the composite resins in experimental groups were decreased with the increasing of proportion of the reinforcing fillers. The SEM results show that the mineralized nodules on surface of the composite resins in experimental groups could be observed， and the number of mineralized nodules was increased with the prolongation of time and the increasing of reinforcing fillers proportion. After treated for 7 d， the surface of the composite resins in 5.0% reinforcing filler group and 7.5% reinforcing filler group were almostly covered by mineralized nodules. The biosafety experiment results showed that the RGR of cells in various groups was above 75%，and the cytotoxicity level ≤1 grade. Conclusion The modified new type of composite resins meet the clinical standards， and it has antibacterial and remineralization properties， as well as high biosafety.

Key words: Composite resin, Dental caries, Secondary caries, Antibacterial property, Remineralization