Strategies to Improve Biocompatibility of Dental Materials

Curr Oral Health Rep (2014) 1:222–231 DOI 10.1007/s40496-014-0028-5 DENTAL RESTORATIVE MATERIALS (F OZER, SECTION EDITOR) Strategies to Improve Biocompatibility of Dental Materials Gottfried Schmalz Published online: 11 September 2014 # Springer International Publishing AG 2014 Abstract Adverse reactions to dental materials occur and public interest in this topic has increased during recent decades. Thus, improving the biocompatibility of dental materials is necessary and must be based on several strategies. First, a strategy for improving the administrative and technical conditions for material certification processes should be included, such as the development of in vitro tests with enhanced predictability of the generated data for use in the clinic. Second, research on material/tissue interactions must be enhanced and include mechanistic approaches, as this strategy leads to the development of new and more biocompatible materials. Research into patients and their individual exposure situation is a strategy directed at better defining risk groups. Finally, improvement of education will also lead to improved biocompatibility of dental materials. Keywords Biocompatibility . Composite resins . Cytotoxicity . Dental materials . Medical device legislation . MTA . Risk Assessment . Surface chemistry Introduction Adverse reactions to dental materials occur in patients and dental personnel [1••]. Local reactions take place at the exposure site, e.g., dental pulp and pulp inflammation after pulp capping with adhesives and resin-based composites has been described [2–5], which was related to substances released G. Schmalz (*) Department for Operative Dentistry and Periodontology, University of Regensburg, 93053 Regensburg, Germany e-mail: G. Schmalz School of Dental Medicine – ZMK Bern, University of Bern, Freiburgstrasse 7, 3010 Bern, Switzerland from the applied materials. Also, inhibition of biomineralization after pulp capping with adhesives was observed [6] and can also be related to eluted substances from dental materials such as acrylic monomers [7, 8••]. In other cases, pulp inflammation has been related to bacteria under restorative materials such as resin-based composites [9, 10], and bacterial growth was found to be promoted by such materials [11]. Recurrent caries, a bacteria-mediated process, has been reported to be one of the most important reasons for restoration failures, especially with resin-based composites [12]. In these cases, bacteria-mediated adverse effects can be considered to be indirectly caused by the dental material. Systemic reactions occur in tissues and organs distant from the exposure site and have mainly been discussed for amalgam [1••] in the past, but nowadays are also discussed regarding resin-based composites in respect to the content of bisphenol-A and its possible health effects [13]. Recently, the biologic effect of materials on the environment, e.g., mercury or bisphenol-A, have been under discussion [13–15]. Allergic reactions to resin-based composites and metals, such as nickel, palladium, cobalt, or gold, have been observed in patients and in dental personnel [1••, 16, 17••]. Clinically observed adverse reactions cover a broad spectrum of different clinical entities and are based on different mechanisms. Furthermore, these reactions are observed with a large number of different dental materials. This complex situation makes it plausible that (1) strategies to improve biocompatibility of dental materials are necessary; and (2) not one but several strategies for biocompatibility improvement of dental materials need to be pursued in parallel. Definitions and Aims A strategy can be defined as a human attempt to achieve desirable ends or aims with the available means [18]. In this Curr Oral Health Rep (2014) 1:222–231 context, the aim is to have biocompatible materials and devices available. What does this mean? In 1987, biocompatibility was defined as the ability of a material to perform with an appropriate host response when applied as intended [19]. Later, this definition was considered to be too general. In 2008, Williams proposed that biocompatibility can be regarded as the ability of a biomaterial to perform its desired function with respect to a medical therapy without eliciting any clinically significant adverse effects in the recipient of that therapy, generating the most appropriate beneficial cellular or tissue response to that specific situation, and optimizing the clinically relevant performance of the therapy [19]. This definition covers different concepts of material/tissue interaction. The biotolerant/inert material concept is aimed at materials that do not harm tissues (see below) [19]. Further to this, the above definition covers bioactive materials, which are not meant to substantially degrade but are designed to stimulate biological effects, such as dentin bridge formation after pulp capping with MTA (mineral trioxide aggregate) or related materials [20, 21•]. Finally, the above definition includes materials used as scaffolds in tissue engineering for assisting in tissue regeneration. These materials must degrade, which is a further challenge in respect to the release of toxic moieties or of particles [19]. The term biocompatibility is closely related to the term safety; in this context, safety is defined as freedom from unacceptable risks [22]. Both of the terms biocompatibility and safety refer to the risk concept. In daily life, the term risk is well-known, but it is used mainly intuitively and is not related to the actual risk [23]. In science and within certification processes (see below), risk is defined as the combination of the severity of an adverse effect and the frequency of it occurring [22]. This realistically means that the strategic aim can only be to minimize adverse effects under the given clinical therapeutic situation, because freedom from any adverse effect occurring is virtually impossible. Improvement of Biocompatibility by Consumer Protection The aim of this strategy is to prevent damage for the patient, dental personnel, and environment that may potentially be derived from new materials or to test for new risks for known materials (for instance, bisphenol-A in resin-based composites). Thus, biocompatibility of dental materials on the market is improved through a preclinical certification process by eliminating the entrance of problematic materials into the market place. Such certification processes are legally regulated worldwide and dental materials are classified as Medical Devices (used in dentistry). New materials must pass this certification 223 process before they are allowed to be marketed [1••]. Here, an important aspect is biocompatibility. The basis for biocompatibility evaluation is a Clinical Risk Assessment, which evaluates potential risks related to the material properties, due to the exposed tissue and the duration of exposure, mainly according to internationally r (...truncated)