Understanding How TiO2 Nanoparticles Improve the Performance of Dental Adhesives

Objectives: The strength of dental adhesives can be improved dramatically by adding as low as 0.1% mass fraction of titanium dioxide nanoparticles (TiO₂-NPs) functionalized with acrylic acid (AP25). The objective of this study is to explore the interactions of AP25 with the resin network and assess their photo-activities.  

Methods: TGA and FTIR were used to confirm the existence of C=C groups on AP25. Cross-linking capability of AP25 was examined by polymerizing with benzyl-methacrylate. UV-Vis and electron paramagnetic resonance (EPR) were used to evaluate the optical response and free radical production of AP25, respectively. AP25 was mixed at mass fraction 0%, 0.02%, 0.05%, 0.1%, 0.2% and 0.5% with two dental resins: 1) ethoxylated-bisphenol-A-dimethacrylate (EDMA), and 2) a mixture of pyromellitic-glycerol-dimethacrylate and hydroxyethyl-methacrylate (1:1 by mass). The resins were photo-polymerized under blue-light irradiation, and their degree of vinyl conversion (DC) was examined by transmission-near-infrared (n=5). One-way ANOVA with a 95% confidence interval was used to indicate significant differences.

Results: AP25 contained approximately 1% (by mass) of acrylic acid derivatives. The AP25’s C=C functionalities copolymerized with benzyl-methacrylate indicating that AP25 can: a) be incorporated into the polymer network, and b) provide additional cross-links and rigid, multi-functional junction points in the resins. The AP25 extended the optical response from ultraviolet (≈400 nm) to visible region (≈700 nm). Up to 22 % improvement in DC further authenticated this extended optical response. EPR showed that the AP25 generated more electrons than holes, and the hydroxyl groups in resins played an important role on free radicals’ release from AP25 to resins.  

Conclusions:  The improved performance of AP25-containing resins is a result of their multiple roles as co-initiator, reinforcing filler, and cross-linking agent. The knowledge gained from this study will benefit the future design of strong and durable dental adhesives.

Support: ADAF, CNST and NIST