L-Arginine-Modified Composites: Effects on Physical and Mechanical Properties

Objectives: Inspired by the modulatory effects of arginine-containing dental adhesives on multi-species biofilms, we intend to investigate the antibacterial properties of restorative composites containing L-arginine. Nevertheless, before pursuing this goal, we evaluated some of the compulsory properties of a commercial composite modified by a high concentration of L-Arginine. We hypothesized that addition of 10% L-Arginine would critically affect the degree of conversion (DC), water sorption (WS), solubility (SL) and flexural strength (FS) of a commercial composite.
Methods: Ten-% L-Arginine (Sigma-Aldrich) was incorporated to a commercial composite (IPS Empress Direct, shade A4, Ivoclar/Vivadent) using an orbital mixer (SpeedMixer, FlackTek) Control group consisted of same commercial composite without L-Arginine-addition. For all experiments, composite specimens were polymerized using a LED-curing unit (Bluephase, Ivoclar/Vivadent) for 20s. The DC (%) of each adhesive blend was measured using an ATR-FTIR approach (Spectrum-Two, PerkinElmer) (n=3/group). Disc-like specimens (4x1mm thick) were prepared for WS and SL measurements (mg/mm³), which were obtained using a standardized protocol (n=5/group) based on ISO-4049. For assessment of the FS (MPa), bar-like specimens (2x2x12.5mm length) were prepared for three-point bending tests (EZ-LX, Shimadzu) and performed on a standing of 10-mm support span (n=8/group). The variables DC, WS, SL and FS were analyzed separately by ANOVA and Tukey tests (a=0.05).
Results: The DC% was 44 ± 0.5% for control and 43 ± 1.0% for L-arginine-modified composite. Differences in DC% were not significant. The WS and SL values were significantly higher (p<0.05) for L-arginine-modified composite (WS=26 ± 3.2mg/mm³; SL=3.5 ± 2.1mg/mm³) compared to control (WS=19.4 ± 4.2mg/mm³; SL=1.0 ± 0.9mg/mm³). The mean FS of L-arginine-modified composite (FS=103.3 ± 9.7MPa) was lower compared to control (FS=110.5 ± 8.5MPa), but such difference was not significant (p=0.085).
Conclusions: Our hypothesis should be partially accepted. Addition of 10% L-Arginine exerted a critical effect only on the WS and SL of tested composite.