Thermoset polymethacrylate-based materials for dental applications

Poly(methyl methacrylate) (PMMA) is widely used worldwide for artificial teeth and the fabrication of denture bases. Compared to metallic denture base materials, PMMA exhibits beneficial properties, such as aesthetic value, lighter weight, ease of manipulation, and cost-effectiveness. On the other hand, prostheses based on PMMA are susceptible to fracture due to poor mechanical properties (flexural and impact strengths) and tend to degrade over time due to water sorption. To improve the mechanical attributes of the PMMA resins for dental applications, various techniques have been investigated and varying results have been obtained. One method is to fabricate PMMA based biocomposites (e.g., polyamides, epoxy resins) or adding a rubber based copolymer (e.g., butadiene styrene) to PMMA to enhance its impact strength. Alternative methods include the use of metal wires or different types of fibers to strengthen PMMA based dentures. However, metal incorporation negatively affects the aesthetics, and tends to generate stress concentration zones which weaken the dentures instead of strengthening them.The addition of carbon/graphite fibers (CFs) into PMMA resins has been shown to substantially enhance the flexural and impact strengths of acrylic resin-based dentures. However, their gray color negatively affects their esthetic value. Therefore, they are not commonly used as a means of reinforcing dentures. Ultra-high molecular weight polyethylene (UHMWPE) fibers have a naturally white appearance and they have been shown to strengthen PMMA based dentures by increasing the impact strength and Young’s modulus. However, in order to create a bond between the fibers and PMMA resin, these fibers need to undergo special pretreatment (e.g., plasma treatment) before they can be used. Despite substantially enhancing the tensile strength and toughness of PMMA based dentures, aramid fibers (AFs) are not commonly used for denture reinforcement as they possess a yellow color and are difficult to incorporate into PMMA resins.Encouraging results have been achieved by the incorporation of glass fibers (GFs) into PMMA resins for denture strengthening. The beneficial effect of the addition of GFs on the mechanical properties of acrylic resins has been documented in several research studies. GFs possess excellent esthetics, in addition to having excellent mechanical properties. As a result, they are currently the prime focus of research aimed at reinforcing acrylic dentures. Additionally, GFs easily bond with PMMA resins after treatment with a suitable silane coupling agent, such as trimethoxysilylpropylmethacrylate silane.Apart from the obvious benefits of fiber reinforcement on PMMA dentures, their clinical use is still limited due to their high cost and the difficult technique necessary for their incorporation into PMMA, especially when short and randomly oriented GFs are used which tend to “clump” within the denture and negatively affect the strength of the prosthesis. This issue can be overcome by using woven or multidirectional fibers in the form of a mesh or network. The aim of this chapter is to highlight the benefits of PMMA and the advancements in PMMA based materials for dental application.