Biocompatibility of Dental Polymers

The use of polymers has revolutionized the biomedical industry ever since their discovery. Dental polymers, commonly known as “Dental Resins,” were first used in dentistry in 1839, and since then they are widely used especially in restorative dentistry for both cosmetic and functional purposes. A variety of different polymer materials – vinyl acrylics, epoxy resins, polyether, polysulfide, silicone, polycarbonates, polyacrylic acid, polystyrene, polyethylene, polyvinyl acetate – are used in dentistry. Typical applications of polymers in dentistry are impression materials, relining materials, temporary crown materials, denture base materials, obturation materials (endodontic treatment), and filling materials (composites, cements, adhesives). Many prostheses and implants made from polymers have been in use for the last three decades and there is a continuous search for more biologically inert and stronger polymer dental materials. Biocompatibility of dental polymers is an important clinical issue. The dental polymers that is to be used in the oral cavity should be harmless to all oral tissues—gingiva, mucosa, pulp, and bone. Furthermore, it should contain no toxic, leachable, or diffusible substance that can be absorbed into the circulatory system, causing systemic toxic responses, including teratogenic or carcinogenic effects. The material also should be free of agents that could elicit sensitization or an allergic response in a sensitized patient. Rarely, unintended side effects of dental polymers may occur as a result of toxic, irritative, or allergic reactions. These reactions may be local and/or systemic. Local reactions involve the gingiva, mucosal tissues, pulp, and hard tooth tissues, including excessive wear on opposing teeth from restorative materials. Systemic reactions are expressed generally as allergic skin reactions. The quantity of unconverted resinous monomers that remain after polymerization determines the cytotoxic effects of polymeric dental materials, such as light-cured methacrylate polymers. These monomers may alter the lipid layer of the cell membrane, which affects membrane permeability. They may also undergo hydrolysis, producing a water-soluble cytotoxic substance, methacrylic acid. Some monomers may also displace water in dentin and they are capable of diffusing rapidly through the dentin. Furthermore, they may reduce the rate of cellular proliferation and result in apoptosis, possibly as a response to DNA damage. Additionally, because the oral cavity is highly vascularized, the effect of dental polymers on vascular function can be relevant to clinical practice. Several experimental studies provided evidence for the marked vasodilating effect of dental polymers, which might impair pulpal healing by promoting hemorrhage. In accordance with existing standards, all dental polymers should pass primary tests (screening to indicate cellular response), secondary tests (evaluating tissue responses), and usage tests in animals before being evaluated clinically in humans. After a material has successfully passed the primary and secondary tests, it should be tested in humans to evaluate its performance and the favorable or unfavorable reactions that may present under normal clinical conditions. The aim of the current paper is to provide an overview of the current literature on toxicology of dental polymers and to give implications for possible improvements concerning their biocompatibility.