Immediate and Long-term Degree of Conversion of Experimental Antibacterial Adhesives

Objectives: Incorporation of metaloxide nanoparticles holds the promise of improving the properties and antibacterial characteristics of current polymer compositions. However, studies investigating the long-term impact of nanoparticles’ incorporation on the degree of conversion of dental adhesive resins are not available. The objective of this pilot study was to test the hypothesis that incorporation of antibacterial nanoparticles does not alter the degree of conversion of OptiBond Solo Plus immediately (NEW) and two years (OLD) after their incorporation in adhesive resin.
Methods: Four unaltered [Clearfil SE Protect (CSP), OptiBond Solo Plus (OSP), Adper Scotchbond (ASB), and Adper Single Bond Plus (SBP)] and six experimental adhesive resins containing nitrogen-doped TiO₂ nanoparticles (N_TiO₂, 5-30% [v/v], 5% increments) were placed on the diamond crystal of a heated Attenuated Total Reflectance unit (Golden Gate, Specac). Spectra of the adhesives were obtained at 37°C with a Fourier-transform infrared (FTIR) spectrometer (Nicolet IS50; 500-4,500 cm^-1; resolution 4 cm^-1, 10 internal scans per spectrum) before and after polymerization. Adhesive specimens (n=3/group) were polymerized (60s/specimen) using visible light irradiation (VALO, Ultradent Products, USA). Degree of conversion values (DC;%) were calculated from pre- and post-polymerization spectra using the two-frequency method and tangent-baseline technique. Time-dependent (NEW versus OLD) DC values were statistically analyzed using T-Test, whereas inter-group comparisons were statistically analyzed using General Linear Models and post-hoc Student-Newman-Keuls tests (a=0.05; SAS software).

Results: Mean DC values ranged from 57.77% (ASB_OLD) to 85.23% (30% N_TiO₂_NEW). No statistically significant changes in mean DC values were observed (p=0.1400) for experimental materials two years after nanoparticles incorporation. Mean DC values of experimental materials were significantly higher (p<0.001) when compared to ASB, CSP and SBP, independent of time (NEW or OLD), but not unaltered OSP.
Conclusions: Nanoparticles’ incorporation (5-30%, v/v) did not adversely impact the immediate (NEW) and long-term (OLD) DC values of experimental adhesive resins.