Biocompatibility and bond degradation of poly-acrylic acid coated copper iodide-adhesives
Introduction
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 [1]. Agents with anti-bacterial and anti-proteolytic properties such as benzalkonium chloride [2], glutaraldehyde [3], chlorhexidine digluconate [4], and methacryloyloxydodecyl pyridinium bromide (MDPB) [5] have been proposed.
Nanoparticles with antibacterial properties, such as silver [6] and copper [7], have received considerable attention when incorporated into adhesive materials [8] since bacteria are less likely to acquire resistance against metal nano-particles than to other conventional narrow-target antibiotics [9]. 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 [9]. Recently, adhesive materials containing poly-acrylic acid coated copper iodide (PAA-CuI) particles have demonstrated strong long-term antibacterial properties and reduced collagen degradation [10], [11]. 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.
Section snippets
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.
Micro-tensile bond strength
A significant effect of ‘treatment’ and ‘time’ (p < 0.001), but no effect of their interaction (p = 0.063) was demonstrated. No significant variations were observed after 6 months for any of the groups relative to their 24 h values. Except for Protect, all other control adhesives demonstrated significant bond degradation after 1 year (p = 0.027, p < 0.001 and p = 0.027 for XTR, Solo and XP, respectively) (Fig. 1). Neither XTR or Solo with PAA-CuI degraded after 1 year regardless of the concentration,
Discussion
This study provides original information on the effects of PAA-CuI modified adhesives on bond degradation, tensile strength, and biocompatibility as per evaluation of the cytotoxicity and ion release. No degradation was observed for any adhesive after 6 months. Six months has previously been reported as insufficient time to detect the effects of hydrolytic degradation [17]. After 1 year, however, all the control groups, except Protect, showed significant degradation with self-etch adhesives
Conclusion
Within the limitations of this study, it can be concluded that incorporation of PAA-CuI particles was able to prevent bond degradation after 1 year for XTR, Solo, but not XP. No bond degradation was observed for any of the adhesives after 6 months. The UTS remained unaffected for all adhesives regardless of the concentration of PAA-CuI particles. Cell viability was not affected with the incorporation of 0.1 and 0.5 mg/ml PAA-CuI to XTR or 0.1 to Solo, but it was reduced when incorporating 0.5
Acknowledgements
This work was supported by a Small Technology Transfer Research (STTR) grant [grant number 1R41 DE026085-01] from the National Institute of Dental and Craniofacial Research, NIH, Bethesda, MD to Dr. Walter Renné (CuRE Innovations, LLC). The authors wish to thank Mr. Peter Bush for his invaluable assistance with SEM, EDX and XRF analysis. This paper is based on the thesis dissertation submitted in partial fulfillment of the requirements for the degree of Master of Oral Sciences in the Graduate
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