Abdollah Maleki1 , Alireza Karimpour2, Masumeh Mokhtarpour3, Solmaz Maleki Dizaj 4, 5
1Faculty of mechanical engineering, Amirkabir University of Technology, Tehran, Iran.
2Matin-Plast Company, Azarshahr, East Azerbaijan, Iran.
3Faculty of Chemistry, Tabriz University, Tabriz, Iran.
4Dental and Periodontal Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.
5Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran.
Abstract
Fillers have a key part in manufacture of desired composites and the decrease of final processing costs. Inorganic fillers are broadly used to advance the mechanical possessions of polymer based composites. The properties can be modified by altering the volume fraction, shape, and size of filler particles. Nanotechnology permits the production of nano-sized filler particles that can improve the clinical performance of esthetic restorative materials. Dental Poly(methyl methacrylate) (PMMA) composite resins including nanofiller have revealed to substantially progress in their performance. In the current paper we reviewed the effect of nano-fillers on mechanical properties of dental PMMA based composites using internet database mainly PubMed. The search results showed the increasing rate for the use of nanofillers in dental composite production processes.
Keywords: Nano-fillers, Mechanical properties, Dental composites, PMMA.
Introduction
Nanofillers are the fillers in nanometric size range that show different properties from traditional fillers [1-3]. In the use of traditional fillers in composite production, large particles are minified by pinning; however, for fillers such a minifying not accrued due to the small nanometric particle size [1].
Poly(methyl methacrylate) (PMMA) is the most commonly applied polymer for dental uses. Its outstanding properties such as low price, optical possessions, biocompatibility, nontoxic, good stability in the oral cavity, and simple processing convert PMMA to useful dental polymer [4, 5]. PMMA also does not need any high price devices. Besides, this polymer is odorless, tasteless and does not cause irritation of tissues. Despite its advantages, the mechanical properties of pure PMMA denture base do not meet the essential level for denture fabrication so far. Reinforcing PMMA with nanofillers can more efficiently progress the mechanical possessions of the composites [6]. In the current paper we reviewed the effect of nano-fillers on mechanical properties of dental Poly(methyl methacrylate) based composites using internet database mainly PubMed.
PMMA
Poly(methyl methacrylate) (PMMA) is the most commonly used polymer for dental applications. Its ideal possessions such as low price, optical properties, biocompatibility, nontoxicity, good stability in the oral cavity, and simple processing convert PMMA to useful dental polymer. PMMA also does not need any high price devices. As well, this polymer is odorless, tasteless and does not cause irritation of tissues [6].
Despite its advantages, the mechanical properties of pure PMMA denture base do not meet the essential level for denture fabrication so far. In the composite production process PMMA shows poor strength, low resistance impact, low flexural strength, insufficient ductility, crazing, susceptibility to distortion,10 tendency to aging, insufficient surface hardness, and poor antibacterial property, that all of these resulted in breakage of dental composite [4, 7].
To solve denture fracture issues, some methods have been presented in order to advance the mechanical properties of PMMA dentures. These methods are; addition of crosslinking agents or incorporation of fillers commonly include fibers, nanoparticles and whiskers [4].
Micro-fillers in dental PMMA based composites
Addition of micro-fillers into dental PMMA based composites can improve stability of composites. Al2O3 as the main inorganic filler have been used in this regards. Some studies established that incorporation of Al2O3 micro-fillers into PMMA denture base resulted in improvements in flexural strength, wear resistance, and hardness [8]. The reports showed that Al2O3 in small particle size can proficiently improve the impact strength. The experimental outcomes exhibited about 24 % increase in flexural strength, and 76.3% decrease in wear volume loss of the composites [9]. In a study by Vojdani et al. assessed the effects of adding Al2O3 particles (3 μm in mean), on the flexural strength, surface hardness, and roughness of PMMA denture base. Their results showed that the addition of 2.5 wt. % Al2O3 caused in 6.4 % growth in flexural strength, 15 % increase in hardness and showed no adversely influence on the surface roughness of the composites [8].
In a work by Antunes et al the effect of particle volume fraction and size on the wear loss of polyester resin have been tested. They found that the composite reinforced with silica, with average size of 6 μm, exhibited the highest wear resistance. Their results also showed that the abrasion resistance of the composite improved with declining volume fraction of the filler particles. The authors supposed that PMMA denture base incorporated with Al2O3 micro-fillers possessed high fracture toughness and flexural properties [10]. In another work, the investigators reported the consequence of Al2O3 micro powder addition on the flexural strength of PMMA denture base. Their results revealed that the flexural strength of the composite increased more than 30% after incorporation of 10% Al2O3.18 The other tests have also shown increased effect of Al2O3 micro-particles on the thermal conductivity and tensile strength of the composites [11].
Nano-fillers in dental PMMA based composites
Reinforcing polymers with nano-fillers can more efficiently progress the mechanical possessions of the composites compare to microparticles [1, 4, 12].
The addition of SiO2 nanoparticles increased the fracture toughness, microhardness, and modulus of epoxy in a work by Zhang et al.28 SiC nanoparticles also showed the improved effect on the wear resistance.29 TiO2 (20 nm) improved the possessions of epoxy resin [13].
The reports also showed that incorporation of Al2O3 nanoparticles improved the mechanical properties of polymers. In a work spherical and whisker Al2O3 nanoparticles improved the mechanical properties of the PMMA composites. and in particular, whisker Al2O3 nanoparticles had more improvement effect [4]. According to reports by Foroutan et al adding Al2O3 nanoparticles had improved effect on the flexural and tensile strength of dental composites.24 Another group also reported that the application of Al2O3 and ZnO nanofillers enlarged the hardness of dental amalgam [14].
Safi examined some mechanical properties of PMMA dental composite after adding Al2O3, TiO2 and SiO2 nanofillers. The obtained data presented more thermally and mechanically stability for the nano-composite than the neat PMMA composite. The results of a work by Saboktakin et al. on mechanical properties of PMMA dental composite indicated that the addition of Al2O3 nanoparticles increased the storage moduli [4].
Kundie et al tested the effect of adding of Al2O3 micro- and nano-particles to PMMA denture base resin composite samples. Their FTIR results showed that Al2O3 micro- and nanoparticles treated by the silane coupling agent. Their obtained data also showed the increased fracture toughness in both micro- and nanoparticles. The results also showed that the flexural modulus improved with increasing filler content, whereas the flexural strength reduced with increasing filler loading [4].
Conclusion
In the current paper we reviewed the effect of nano-fillers on mechanical properties of dental PMMA based composites using internet database mainly PubMed. The search results showed the increasing rate for the use of nanofillers in dental composite production processes.
References