Cristina Bettencourt Neves

Biodegradation of acrylic based resins: A review

OBJECTIVES The development of different types of materials with application in dentistry is an area of intense growth and research, due to its importance in oral health. Among the different materials there are the acrylic based resins that have been extensively used either in restorations or in dentures. The objective of this manuscript was to review the acrylic based resins biodegradation phenomena. Specific attention was given to the causes and consequences of materials degradation under the oral environment. DATA AND SOURCES Information from scientific full papers, reviews or abstracts published from 1963 to date were included in the review. Published material was searched in dental literature using general and specialist databases, like the PubMED database. STUDY SELECTION Published studies regarding the description of biodegradation mechanisms, in vitro and in vivo release experiments and cell based studies conducted on acrylic based resins or their components were evaluated. Studies related to the effect of biodegradation on the physical and mechanical properties of the materials were also analyzed. CONCLUSIONS Different factors such as saliva characteristics, chewing or thermal and chemical dietary changes may be responsible for the biodegradation of acrylic based resins. Release of potential toxic compounds from the material and change on their physical and mechanical properties are the major consequences of biodegradation. Increasing concern arises from potential toxic effects of biodegradation products under clinical application thus justifying an intensive research in this area.

Ethanol Postpolymerization Treatment for Improving the Biocompatibility of Acrylic Reline Resins

Objective. To evaluate the effect of postpolymerization treatment based on ethanol-aqueous solutions on the residual monomer (RM) content, flexural strength, microhardness, and cytotoxicity of hard chairside reline resins (Kooliner, Ufi Gel Hard). Methods. After polymerization, specimens were immersed in water, 20%, 50%, or 70% ethanol solutions at 23°C or 55°C for 10 minutes. Controls were left untreated. HPLC was used for the determination of RM content. Specimens were submitted to Vickers microhardness and 3-point loading flexural strength tests. Cytotoxicity of resin eluates was determined on human fibroblasts by assessing cellular mitochondrial function and lactate dehydrogenase release. Results. Higher concentrations of ethanol promoted lower RM content at 55°C in both materials. The mechanical properties were maintained after 50% and 20% ethanol treatments in Kooliner and Ufi Gel Hard, respectively. Specimens submitted to those treatments showed significant reduction on cytotoxicity compared to immersion in hot water, the treatment of choice in the recent literature. Significance. Immersion of relined dentures in specific ethanol solutions at 55°C for 10 minutes can be considered an effective postpolymerization treatment contributing to increase materials biocompatibility. The proposed protocol is expeditious and easy to achieve with simple equipment in a dental office.

Incorporation of tocopherol acetate-containing particles in acrylic bone cement

Acrylic bone cement (BC) is used in orthopaedic surgery to anchor cemented prostheses to bone. Association of antioxidant molecules to BC may suppress reactive species injury which contributes to implant failure. Tocopherol acetate (ATA)-loaded polymethylmethacrylate (PMMA) particles (ATA(PMMA)) were prepared by single emulsion solvent evaporation technique and were incorporated into BC. An encapsulation efficiency of 84% (w/w) was obtained and drug release studies showed distinct ATA release profiles and mechanisms before and after particle incorporation into BC. Experimental data, analysed using first-order, Higuchi and Korsmeyer-Peppas models revealed that ATA was released from particles by a Fickian diffusion mechanism while a non-Fickian transport was observed upon particle incorporation in BC. There were no changes in the mechanical properties of BC specimens containing ATA(PMMA) particles, in contrast to what was observed when ATA was loaded directly into BC. Overall, ATA(PMMA) particles are potential carriers for the incorporation of an antioxidant drug into BC.