Nanoparticles in Prosthetic Materials: A Literature Review.

The commonly used prosthodontic materials are resins, ceramics, metals and silicones. A comprehensive review of literature was completed about the incorporation of nanomaterials in prosthetic dentistry using PubMed and Google Scholar databases. This was supplemented with a manual search of selected journals. English language articles in peer- reviewed journals were selected. Current literature reveals that incorporation of nanomaterials has significantly improved the properties of the prosthetic materials within the clinically acceptable ranges. There appears to be a need for a standardization for these in vitro studies carried out to evaluate their physical, mechanical and antimicrobial properties. Copyright:

INTRODUCTION

In the evolution of these prosthetic materials in dentistry, there had been lots of modifications such as incorporation of additives, surface modifications, structural variations were done to improve the mechanical, physical, and biological properties. Recently, incorporation of nanoparticles has provided a considerable improvement in the properties.

PubMed and Google scholar databases were accessed to search for pertinent peer-reviewed articles written in English published between 2000-2020. Keywords entered were “nanoparticles synthesis”; “incorporation of nanoparticles”, “nanoparticles in dental materials”; either individually or in combination. The hand search of the Journal of Prosthetic Dentistry, International Journal of Biomaterials, International Journal of Dental Research and Journal of Prosthodontics were performed for the period from 2000-2020. The abstracts were reviewed and articles were sorted based on the following inclusion and exclusion criteria. Articles published in English peer-reviewed journals, describing an original research, synthesis of nanoparticles, investigating the physical, mechanical and antimicrobial properties of denture base resins and maxillofacial silicone elastomers were included. Technical reports, abstracts, personal communications related articles were excluded.

A total of 465 articles were identified through the PubMed and Google scholar searches. Abstracts were reviewed to confirm the articles met the inclusion criteria. A total of 48 articles published between 2000-2020 were identified and read in their entirety. Forty-six articles were selected of literature reviews and invitro studies. Three studies evaluated the physical and mechanical impact of zirconia nanoparticles on these resins and three studies evaluated the antimicrobial effects of zirconia nanoparticles on maxillofacial silicone elastomers. Three studies investigated the physical impacts of titanium dioxide nanoparticles on resins and one study evaluated the antimicrobial properties of titanium dioxide nanoparticles on silicone elastomers. Twelve studies evaluated the improvement in mechanical and antimicrobial properties of resins after the incorporation of silver nanoparticles. Thirteen studies evaluated the improvement of physical, mechanical and antimicrobial properties of resins after incorporation of other nanoparticles. Five studies evaluated the impact of silica nanoparticles on maxillofacial silicone elastomers for the improvement of physical, mechanical and optical properties. Eight studies evaluated the physical, mechanical and antimicrobial properties of silicone elastomers after the incorporation of titanium dioxide nanoparticles into them

NANOPARTICLES

The concept of nanoparticles was first introduced in 1980's with particle size less than 100nm1. These nanoparticles are classified as – organic nanoparticles such as Poly Lactic-co-Glycolic Acid (PLGA) and chitosan; non – organic nanoparticles such as bioactive glass and mesoporous calcium silicate; metal nanoparticles of silver, silica and gold and metal oxide nanoparticles like zinc oxide, titanium oxide and magnesium oxide. titanium oxide, and magnesium oxide. Nanoparticles are synthesised by three methods namely– top down, bottom up and molecular self assembly approach.[2]

DISCUSSION

Polymethymethacrylate (PMMA) resins

The resins are into prosthodontic purposes for more than 70 years for their biocompatibility, optical properties and aesthetics. Low fatigue resistance and microbial adhesion are mainly seen in long term polymethylmethaacrylate (PMMA) wearers. Researchers have shown much interest in incorporation of nanoparticles like zirconium oxide (ZrO). Titanium dioxide (TiO2) etc for improving the properties of PMMA. showed improvement in their mechanical properties.[3]

PMMA resins and soft liners with nano-zirconia particles

Nano-zirconia has been evaluated with PMMA and has shown significant improvement in flexural and impact strength.

Mohammed Gad et al,[3] in 2016, and Leao et al,[4] in 2020, investigated nano-zirconia (1.5%) on PMMA and concluded an increase in flexural, transverse and impact strength, reduction in wear, and also shown good antifungal and antibacterial properties.

PMMA resins and soft denture liners with titanium dioxide nanoparticles

Addition of 3wt% of TiO2 showed positive results against oral bacterial species as proven, where SuW., et al,[5] in 2009 evaluated the antibacterial properties of resin materials with nano-titania particles and concluded about 99.99% growth inhibition rate of E. coli species. Shrikavad., et al[6], in 2014, Alrahlah., et al,[7] in 2018 investigated nano-titania particles in three different concentrations of 0.5, 1, and 2 (wt%) into polymethacrylate and liners and concluded increase in tensile strength and good antifungal properties.

PMMA resins and soft denture liners with silver nanoparticles

Pal., et al.,[8] in 2007, Casemiro., et al.,[9] in 2008, Chladek., et al[10], in 2012, Hamedi Rad et al[11] in 2014, Ghafari et al.,[12] in 2014, Köroğlu A et al.,[13] in 2016, Yin et al.,[14] 2020 investigated the antimicrobial properties in different shapes and concentrations of Ag nanoparticles and concluded significant decrease in microbial count and reduction in hardness, tensile bond strength of resins and liners.

Vimbela et al.,[15] in 2017, investigated the antimicrobial properties, with four different concentrations of Ag nanoparticles 1, 2, 3and 5 (wt%) and proved significant reduction of C. albicans at 5wt% in resins and liners. Habibzadeh., et al.,[16] in 2020 investigated three different silver concentrations of 0.3, 0.8 and 1.6 (wt%), in PMMA where 0.8 and 1.6 (wt%) showed reduction in flexural strength and elastic modulus of resins.

PMMA resins and soft denture liners with other nanoparticles

Tuan Rahim., et al.,[17] in 2011 conducted a study with silica dioxide nanoparticles and concluded that addition of metal nanoparticles increases the surface hydrophobicity.

Xie., et al.,[18] Lipovsky., et al.,[19] in 2011, Kamonshantikul., et al.,[20] in 2017 has investigated the antibacterial properties and polymerization shrinkage of PMMA of zinc oxide nanoparticles in 3 and 10 mm concentrations and proved 100% inhibition of microbial growth and resulted in clinically significant decrease in polymerization shrinkage.

Jiankongkho., et al.,[21] in 2018 investigated carbon and silica nanoparticles in different concentrations of 0.25, 0.5, 1, 5, 10 and 15 (w%) into PMMA and 1w% of nanosilica particles showed increase in flexural strength, fracture toughness and clinically acceptable young's modulus.

Lee., et al.,[22] in 2018 has investigated the antifungal activity of tissue conditioners with chitosan and concluded that chitosan and quaternized chitosan nanoformulations did not affect the viability of human gingival epithelial cell/fibroblasts.

Vikram., et al.,[23] in 2020, Homsiang., et al.,[29] in 2020, has investigated the flexural strength of PMMA resins with zinc oxide nanoparticles in different concentrations of 0, 0.4, 0.6, 0.8, 1.2, and 1.4% concluded an increase in flexural strength.

Homsiang., et al.,[24] in 2020, has investigated antifungal properties with varying concentrations of 0, 5, 10, 15 wt% zinc oxide nanoparticles and 15wt% Zinc oxide nanoparticles provided antifungal effects upto 14 days without any adverse effects

MAXILLOFACIAL SILICONE ELASTOMERS

Maxillofacial materials are used to replace missing facial parts which have been lost through disease or trauma[2526]. They are usually comprised poly (dimethylsiloxane) elastomers. Although these materials are widely used, they are far from ideal. In order to improve their shortcomings such as low color stability, antimicrobial adhesion and mechanical properties, and nanoparticles were incorporated and resulted in increase in tensile strength, tear strength, and percentage elongation of the maxillofacial silicone material which provided a clinical advantage to the marginal integrity of a facial prosthesis.

Silicone elastomers with silica nanoparticles

Han., et al.,[27] in 2008 has investigated the nanooxides of Ti, Zn, and Ce (nonsurface treated) at 2%–2.5% concentrations into A-2186 silicone elastomers and showed improvement in their mechanical properties.

Sara M. Zayed et al.,[28] in 2014 has evaluated the effect of surface-treated silicon dioxide and concluded in improvement of mechanical properties of silicone elastomers when 1.5 wt% of nanosilica was added they showed decrease in percentage of elongation and 3 wt% of nanosilica showed increase in tensile strength, tear strength when incorporated in them, Fatalla., et al.,[29] in 2015 has concluded 5% silanated silicon dioxide nanoparticles reduced the tear strength, tensile strength, and hardness values.

Cevik and Eraslan.,[30] in 2016 and Tukamachi., et al.,[31] in 2017 evaluated the mechanical properties of A-2000 and A-2006 silicone elastomers by incorporating the nanotitania, fumed silica, and silanized silica in three different concentrations of 4, 5, and 6 (wt%) of nanosilica particles, where 5 wt% nanosilica particles showed highest mean values indicating improvement in all properties with slight color changes in the elastomer materials.

Silicone elastomers with silver and titanium dioxide nanoparticles

The most popular medical grade silicone material is A-2186 which despite of long clinical use suffers durability and infection control issues. Recent studies suggest that AgNPs may be a good antifungal agent. AgNPs have fungicidal activity against C. albicans at lower concentrations.

Nguyen et al.[32] in 2013 have investigated nanotitania and zinc oxide nanoparticles and concluded that these did not improve the mechanical properties of these elastomers. However, TiO2 nanoparticles decreased the tear strength and zinc oxide nanoparticles did not influence the mechanical properties.

Wang et al.[33] in 2014 has investigated TiO2 nanoparticles in MDX4-4210 commercially available maxillofacial silicone elastomer in varying concentrations of 2, 4, and 6 (w%) after artificial aging and concluded 2 wt% of these nanoparticles significantly increased the physical properties of these elastomers.

Nobrega et al.[34] in 2016 incorporated TiO2 nanoparticles in two different concentrations of 1 and 2% and showed significant reduction in hardness of the silicone elastomer study groups.

Meran et al.[35] in 2017 has investigated the biocompatibility and antifungal properties of 5 mg/L Ag and 50 mg/L silver nitrate nanoparticles and concluded that Ag coated silicone elastomers showed good antifungal activities without any adverse reactions on human dermal fibroblast cells in vitro.

Bishal et al.[36] in 2018 investigated silicone elastomers with functional intrinsic pigments with a nanolayer of TiO2 using atomic layer deposition was exposed to artificial aging at 450 kJ/m2 for 120 h and concluded that TiO2 nanocoating was shown to be effective in reducing color degradation. Sonnahalli et al.,[37] in 2020 has evaluated the physical properties such as hardness, tear strength, and tensile strength in Teksil 25 (S25) silicone elastomer by incorporating 20 ppm of Ag nanoparticles and concluded a decrease in hardness.

CONCLUSION

The existing literature reveals advances in the field of nanotechnology are set to reform the prosthodontic practice. Future utilization of advancements of nanotechnology will facilitate the improvement in prosthetic materials. More research in the field of nanomaterials, improves the properties of prosthetic materials and this leads to the patient satisfaction and improved quality of the life.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.