A promising approach to improve the poor antibacterial properties of dental composite resins has been the addition of metal oxide nanoparticles into the resin matrix. This systematic review aimed to determine whether the addition of zinc oxide nanoparticles (ZnO-NPs) improves the antibacterial properties of direct dental composite resins. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered with the PROSPERO database: CRD42019131383. A systematic literature search was conducted using the following databases: Medline (Ovid), the Cochrane Library, SCOPUS, CINAHL, Web of Science, Trove, Google Scholar, World Cat, and OpenGrey. The initial search retrieved 3178 results, which were then screened against inclusion and exclusion criteria, resulting in a total of four studies that were eligible for qualitative synthesis within this review. All the included studies were in vitro non-randomized post-test design experimental studies. A lack of congruity in the results obtained from these studies that used different tests to evaluate antibacterial activity was evident. Although some studies demonstrated a significant improvement of antibacterial properties in composites containing at least 1% ZnO-NPs (wt %), they are unlikely to present any clear clinical advantage due to the short lifetime of observed antibacterial properties.
Carbon black conductive filler material, 2–40% by weight was added to specially designed polyurethane polymer to prepare shape memory polymer nanocomposites. The synthesised polyurethane (PU) has exhibited a high glass transition temperature of 85°C compared to the reported values in published literatures. The polymer was characterised for its chemical, electrical, thermal and mechanical properties. The stiffness, load-bearing capacity and electrical conductivity were observed to improve with increased carbon loading. It was found to be capable of responding to thermal as well as electrical stimuli. The shape recovery efficiency was found to be 94% for thermal and 98% for electrical stimuli which is among the highest for PU reported so far.
Electro-active shape memory polymer nanocomposite from polyurethane matrix with carbon black fillers was synthesized and characterised for its electrical properties. The polyurethane matrix possesses high transition temperature, which enables it to be a candidate for high temperature applications. The carbon nanoparticle content was varied with conductivity measured at each instance, and a percolation threshold value of 6% was observed experimentally. The conductivity phenomenon was studied using Monte Carlo simulation approach on a pseudo random model of the system, developed using constrained optimization by linear approximations algorithm in visual C language platform. The probability of three dimensional network formations of carbon particles was evaluated for varying filler loading and percolation threshold of 6.2% was obtained from the model. The conductive networks formed have resulted in multiple electron paths, generating volumetric heating of the system while connected with a known power supply. This joule heating was used as stimuli for activating the shape memory behaviour by passage of electric current. High shape recovery efficiency (>95%) observed with faster recovery time (25 s), along with high transition temperature (85°) can help to qualify the system for space applications.
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