Mechanical characterization and adhesive properties of a dental adhesive modified with a polymer antibiotic conjugate

This study is a follow up investigation on recent work by our group demonstrating synthesis, release and strong antibacterial character of resins modified with penicillin V (PV)-based polymer-antibiotic conjugates (PACs). Here, we aimed to evaluate the mechanical, bonding, and other relevant biomedical properties of a commercial adhesive resin modified with PV-PAC. Single Bond Plus (SB+) was modified with PAC containing 1.8 wt% conjugated PV. Adhesive resins were bonded to dentin from extracted human molars and restorative resin added. Beams of cross-sectional area of 0.9 ± 0.1 mm (Kutsch and Young, 2011) (n = 20) were obtained from the molars and tested for micro-tensile bond strength (μTBS) at 24 h and 4 months. For cohesive strength, hourglass beams (10 × 2 × 1 mm; n = 10) were assessed for ultimate tensile strength (UTS), beam-shaped specimens (25x2x2 mm; n = 10) evaluated for flexural strength and modulus (FS/FM) via three-point bending, and cylindrical specimens (3 × 2 mm; n = 10) assessed for ultimate compressive strength (UCS). For surface micro-hardness (MH), cylindrical specimens (3 × 2 mm; n = 6) were assessed before and after an EtOH challenge. The degree of conversion (DC) (5 × 1 mm; n = 6) was determined based on changes in absorbance ratio between peaks at ∼1637 cm^-1 and ∼1608 cm^-1 before and after curing of adhesive resins using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. To monitor water uptake and diffusion kinetics over a 28-day period, specimens (5 × 1mm) were desiccated, weighed and stored in deionized water. Control and PV-PAC modified adhesive resins demonstrated similar μTBS at 24 h and 4 months; both showing decrease in values after 4 months (p = 0.001 and 0.004). No significant differences between adhesive resins were shown in UTS, FS/FM or UCS (p<0.05). MH of PV-PAC adhesive resin was significantly reduced relative to the control (p<0.001). The DC values of the adhesive resins were not significantly different. While sorption and solubility were no different between materials, the diffusion coefficient of PV-PAC modified adhesive resin was higher than the control (p<0.001). We conclude that incorporation of PV-PAC with 1.8 wt% PV into an adhesive resin does not adversely affect its mechanical, bonding, and physical properties, thus providing a promising option for materials with long-term antibacterial character and on-demand release.