Effect of addition of titanium dioxide nanoparticles on the antimicrobial properties, surface roughness and surface hardness of polymethyl methacrylate: A Systematic Review.

Polymethyl Methacrylate (PMMA) denture-base resins have poor surface properties that facilitates microbial adhesion causing denture stomatitis. This systematic review aims to evaluate the effect of different sizes and percentages of titanium dioxide nanoparticles (TiO2NP) on the antimicrobial property, surface roughness and surface hardness of PMMA denture base resin.  A systematic search of English peer-reviewed articles, clinical trial registries, grey literature databases and other online sources was performed using the PRISMA-S Guidelines for and studies. Qualitative data synthesis was performed to analyse sample dimensions, acrylic used, treatments of nanoparticles, methods used for testing and effect of size and percentage of nanoparticle. Risk of bias assessment was done using modified Cochrane risk of bias tool. Out of 1376 articles, 15 were included. TiO NP of size less than 30 nm was most frequently used. Both antimicrobial property and surface hardness improved irrespective of the size of the added TiO NP. Three studies reported increase in the surface roughness with less than 50 nm TiO NP.  3% TiO NP was most frequently used. On increasing the percentage, three studies reported an increase in antimicrobial property, while two studies found no change. With TiO NP greater than or equal to 3%, six studies reported an increase in surface hardness, while two reported increase in surface roughness. Large methodological variations were observed across studies. All studies except one were of moderate quality.   On addition of TiO NP to heat polymerized PMMA, the antimicrobial property and surface hardness improved irrespective of the size of the TiO NP, however, addition of nanoparticles less than 50 nm increased the surface roughness. Increasing the percentage of TiO NP increased the surface hardness but did not always increase the antimicrobial property. Addition of 3% TiO NP provided optimum results with regards to antimicrobial effect and surface hardness, but increase in the surface roughness.