Towards the Development of a Biostable Dental Restorative System

Objectives: Current methacrylate (MA)-based dental resin-based restoratives (RBRs) are susceptible to hydrolysis, catalyzed by oral salivary, bacterial, and host immune system derived enzymes, limiting their service-lives in vivo. Currently, no alternative resin chemistry can match the functional properties and clinical workflow considerations of contemporary RBRs to address their limited-service lives. The objective of this work was to develop hydrolytically-stable monomers (HSMs), polymers (HSPs), and experimental restoratives that maintain or exceed the mechanical, safety, and workflow handling and compatibility standards of contemporary RBRs, while eliminating or retarding hydrolytic biodegradation.
Methods: Novel HSMs were synthesized as either (i) high molecular-weight with structurally “rigid” motifs or (ii) low molecular-weight with structurally “flowable” motifs for formulation as resins and cured HSPs that were initially compared to the properties of MA-based resin materials that included: degree of conversion, water contact angle and swelling, and surface hardness. Following initial properties assessment, HSMs, HSPs and MA-controls were incubated with reconstituted human saliva, simulated human salivary esterase (SHSE), and human neutrophils to evaluate hydrolytic stability. Finally, HSMs were formulated into both an experimental 3-step adhesive (EA) and bulk flowable restorative (EC) and evaluated for their mechanical properties compared to current commercial benchmarks, both dry and following long-term simulated oral enzymatic stress.
Results: HSPs based on HSMs achieved comparable physical properties to MA-based commercial equivalents, while displaying significantly improved biostability under all incubation challenges. Both the EC and EA matched the non-aged properties of MA-based commercial equivalent systems. Importantly, the EA system displayed significantly improved interfacial bond strength following long-tern immersion (1-year) in SHSE, while the commercial MA-based adhesive displayed compromised interfacial integrity after only 6 months.
Conclusions: The developed biostable restoratives could be used for improving the clinical service life of restorative materials while not compromising fundamental physical and mechanical properties of contemporary MA-based systems.