POLY METHYLMETHACRYLATE (PMMA) IN DENTURE BASE

Poly Methylmethacrylate (PMMA) in Denture base

Poly Methylmethacrylate (PMMA) in Denture Base

Introduction

Poly(methyl methacrylate) (PMMA) has been widely used as a biomaterial in dentistry, orthopedic retainers, bone replacement, and eyeballs. PMMA continues to be used as denture base materials because of its favorable characteristics, ease of processing, stability in the oral environment, ease in repair and superior esthetics. However, the primary problem of PMMA is its poor strength characteristics, low impact strength and fatigue resistance. Chen in his study, thus, suggests that there is a need to improve the performance of PMMA in denture base application. Several methods have been used to modify the properties of PMMA denture base materials. (Chen, 1997, 190-199) Approaches to strengthening the acrylic resin prosthesis have included modifying or reinforcing the resin by using filler and fiber, and graft copolymerization with high-impact resins.

Discussion

In a research done by John (2001), it was found that some effort has been made to increase the impact strength by the incorporation of a rubber phase in the PMMA, however, such materials have compromised flexural properties. Hydroxyapatite (HA) [Ca10(PO4)6(OH)2] was used in various biomedical fields such as dental material, bone substitute and hard tissue paste(Chen, 1997, 190-199). Hydroxyapatite (HA)-reinforced polymers have many potential clinical applications, e.g. bone cement, dental implants, coating of joint replacement prosthesis etc. The mechanical properties of PMMA/HA composites could be limited by the incompatibility between the PMMA and HA. Thus modification of PMMA/HA composites is required in order to achieve a high performance denture base materials with better mechanical properties. Polymeric compatibilizer and coupling agent can play a role to improve the interaction and adhesion between the organic PMMA matrix and inorganic HA particles. (John, 2001, 424-427)

From our previous work of John, it was found that the silane coupling agent [3-methacryloxypropyltrimethoxy silane (MPS)] can improve the mechanical and thermal properties of PMMA/HA significantly owing to the better adhesion. The use of heat-polymerized, permanent, acrylic resin denture bases has certain advantages owing to their strong and rigid behavior, in which, they should provide the retention and stability of the final denture. Water absorption of PMMA/HA composite is an important study for dentistry science. In oral environment, dental restorative materials are exposed to saliva containing water. Sometimes, the dental materials are exposed to exogenous substances such as acids, base, salts, alcohols, oxygen, during drinking or eating. (John, 2001, 424-427)

While Jagger argues that water absorption caused plasticization, lowering of the glass transition temperature (Tg) and may affect the mechanical properties of the polymeric denture based materials. Hydrolytic degradation of the hygroscopic filler may occur when subjected to water absorption. Excessive water uptake may lead to breakdown of the polymer itself, debonding of filler from matrix substance, chemical composition changes by leaching and lead to the ingress of microorganism. Besides, precipitation and swelling phenomena may produce voids and cracks, leaching the interface results in the loss of strength due to corrosion. All of these processes may lead to nucleation and growth of microcracks ...