Poly-acrylic acid coated copper iodide (PAA-CuI) adhesives delayed degradation of resin- adhesive bonds.
Incorporation of PAA-CuI particles did not affect the tensile strength of any of the adhesives.
No changes in cell viability were observed for XTR with 0.1 mg/ml or Solo with 0.1 and 0.5 mg/ml.
Cell viability values decreased for XTR with 0.5 mg/ml and XP with 0.1 and 0.5 mg/ml.
XP demonstrated the highest copper release with a similar pattern of release shown for all adhesives.
To investigate the effect of poly-acrylic acid (PAA) copper iodide (CuI) adhesives on bond degradation, tensile strength, and biocompatibility.
PAA-CuI particles were incorporated into Optibond XTR, Optibond Solo and XP Bond in 0.1 and 0.5 mg/ml. Clearfil SE Protect, an MDPB-containing adhesive, was used as control. The adhesives were applied to human dentin, polymerized and restored with composite in 2 mm-increments. Resin–dentin beams (0.9 ± 0.1 mm 2 ) were evaluated for micro-tensile bond strength after 24 h, 6 months and 1 year. Hourglass specimens (10 × 2 × 1 mm) were evaluated for ultimate tensile strength (UTS). Cell metabolic function of human gingival fibroblast cells exposed to adhesive discs (8 × 1 mm) was assessed with MTT assay. Copper release from adhesive discs (5 × 1 mm) was evaluated with UV–vis spectrophotometer after immersion in 0.9% NaCl for 1, 3, 5, 7, 10, 14, 21 and 30 days. SEM, EDX and XRF were conducted for microstructure characterization.
XTR and Solo did not show degradation when modified with PAA-CuI regardless of the concentration. The UTS for adhesives containing PAA-CuI remained unaltered relative to the controls. The percent viable cells were reduced for Solo 0.5 mg/ml and XP 0.1 or 0.5 mg/ml PAA-CuI. XP demonstrated the highest ion release. For all groups, the highest release was observed at days 1 and 14.
PAA-CuI particles prevented the bond degradation of XTR and Solo after 1 year without an effect on the UTS for any adhesive. Cell viability was affected for some adhesives. A similar pattern of copper release was demonstrated for all adhesives.
Despite significant progress to improve the survival of composite restorations, their long-term durability remains a concern. Bacterial proliferation due to marginal breakdown, and hydrolysis of both resin-based polymers by salivary esterases and demineralized collagen by endogenous proteases have been extensively investigated in the last few decades . Agents with anti-bacterial and anti-proteolytic properties such as benzalkonium chloride , glutaraldehyde , chlorhexidine digluconate , and methacryloyloxydodecyl pyridinium bromide (MDPB) have been proposed.
Nanoparticles with antibacterial properties, such as silver and copper , have received considerable attention when incorporated into adhesive materials since bacteria are less likely to acquire resistance against metal nano-particles than to other conventional narrow-target antibiotics . This is presumably because metals are known to act on a broad range of microbial targets, and several mutations would have to occur for microorganisms to resist their antibacterial activity . Recently, adhesive materials containing poly-acrylic acid coated copper iodide (PAA-CuI) particles have demonstrated strong long-term antibacterial properties and reduced collagen degradation . We speculate that, in addition to their strong antibacterial properties, PAA-CuI-adhesives may help delay bond degradation. The biocompatibility of PAA-CuI containing materials, however, is still of concern since biodegradation of dental materials with the consequent byproduct release into the oral environment, might then initiate local and systemic biological responses. To date, the amount of copper released into the oral environment remains unknown.
Therefore, the purpose of this study was to evaluate adhesives containing PAA-CuI particles for their ability to delay bond degradation. Their effect on the adhesives’ mechanical properties, cytotoxicity and copper release was also investigated. Scanning electron microscopy (SEM), X-ray diffraction analysis (EDX) and X-ray fluorescence (XRF) were conducted for microstructure characterization. Specific aims included evaluation of the PAA-CuI adhesives for bond strength after 24 h, 6 months and 1 year of storage, ultimate tensile strength (UTS), cell viability with MTT assay and copper release.
Materials and methods
Three commercially available adhesives, XP Bond (XP, Dentsply, York, PA, USA), Optibond Solo Plus (Solo, Kerr, Orange, CA, USA) and Optibond XTR (XTR, Kerr), were modified with 0.1 and 0.5 mg/ml PAA-CuI particles. Clearfil SE Protect (Protect, Kuraray America, New York, NY, USA) containing MDPB, a known antibacterial agent, was used as positive control.
Preparation of the PAA-CuI adhesive resins
Both synthesis of PAA-CuI particles and generation of PAA-CuI adhesives was conducted according to Sabatini et al. . Briefly, 10 mg of PAA-CuI powder was admixed with 1 ml of one of three adhesives, XP, Solo and XTR, to yield a concentrated solution (10 mg/ml). To ensure uniform dissolution of the particles, a probe tip sonicator (Sonic Dismebrator 100, Fisher Scientific, Waltham, MA, USA) was used for 15 s under dark conditions in an iced-water bath. Immediately after, 10 or 50 μl of the concentrated solution was micro-pipetted into amber vials containing either 990 or 950 μl, respectively of the appropriate stock adhesive to yield a final working concentration of 0.1 or 0.5 mg/ml of PAA-CuI adhesive. The following study groups were evaluated: 1) XP; 2) XP-0.1 CuI; 3) XP-0.5 CuI; 4) Solo; 5) Solo-0.1 CuI; 6) Solo-0.5 CuI; 7) XTR; 8) XTR-0.1 CuI; 9) XTR-0.5 CuI and 10) Protect. All procedures were performed at controlled room temperature (23 ± 2 °C) and humidity conditions.
Micro-tensile bond strength (μTBS)
Thirty recently extracted, healthy human molars, obtained under a protocol approved by the State University of New York’s institutional review board (IRB ID No. 00000133), were used to obtain dentin substrate. The teeth were equally and randomly assigned to ten groups. A flat, transversely cut surface of occlusal superficial dentin was obtained using a water-cooled lab trimmer (Whip Mix, Louisville, KY, USA), and a standardized smear layer created with 320-, 400- and 600-grit silicon carbide abrasive paper (SiC paper, Buehler, Lake Bluff, IL, USA). All materials were applied and polymerized following manufacturer’s recommendations ( Table 1 ) with LED light-curing unit (VALO, Ultradent, South Jordan, UT, USA) with a power density of 1400 mW/cm 2 . Resin composite (Filtek Z100, 3M ESPE, Saint Paul, MN, USA) was applied in increments less than 2 mm to the bonded surface and polymerized for 40 s. After distilled water (DW) storage at 37 °C for 24 h, sixty resin–dentin beams (0.9 ± 0.1 mm 2 ) per group were obtained according to the non-trimming technique , and incubated in DW for μTBS evaluation after 24 h, 6 months or 1 year (n = 20). Individual beams were mounted on a stabilizing jig with cyanoacrylate (Zapit, Dental Ventures of America, Corona, CA, USA) and stressed to failure with a universal testing machine (Bisco, Schaumburg, IL, USA) at a cross-head speed of 1 mm/min. The load required to fracture the specimen was expressed in megapascals (MPa).