Effect of adding TiO2 nanoparticles on the SEM morphology and mechanical properties of conventional heat-cured acrylic resin

Nanocurcumin Release from Self-Cured Acrylic Resins; Effects on Antimicrobial Action and Flexural Strength

The placement of orthodontic appliances into the oral area can lead to infection, inflammatory and gingival collapse. Using an antimicrobial and anti-inflammatory material in the matrix of orthodontic appliance may help to reduce these issues. This study aimed to assess the release pattern, the antimicrobial action and the flexural strength of self-cured acrylic resins after adding different weight percentages of curcumin nanoparticles (nanocurcumin). In this in-vitro study, 60 acrylic resin samples were divided into five groups (n = 12) based on the weight percentage of curcumin nanoparticles added to the acrylic powder (0 for control, 0.5, 1, 2.5, and 5%). Then, the dissolution apparatus was used for the release assessment of nanocurcumin form the resins. For antimicrobial action assessment, the disk diffusion method was used and a three-point bending test was performed with a speed of 5 mm/min to determine the flexural strength. Data were analyzed using one-way analysis of variance (ANOVA) and Post-Hoc Tukey tests (with p < 0.05 as significant level). The microscopic images showed the homogeny distribution of nanocuricumin in self-cured acrylic resins in varied concentrations. The release pattern showed a two-step release pattern for all concentrations of nanocurcumin. The one-way ANOVA outcomes indicated that adding curcumin nanoparticles to self-cured resin increased the diameter of the inhibition zones for the groups against Streptococcus mutans (S. mutans) significantly (p < 0.0001). Additionally, as the weight percentage of curcumin nanoparticles increased, the flexural strength decreased (p < 0.0001). However, all strength values were higher than the standard value (50 MPa). No significant difference was detected between the control group and the group with 0.5 percent (p = 0.57). Considering the proper release pattern and the potent antimicrobial activity of curcumin nanoparticles, then the preparing self-cured resins containing curcumin nanoparticles can be beneficial for antimicrobial aims without damaging the flexural strength to use in orthodontic removable applications.

Incorporation of Treated Woven Carbon Fiber to Methacrylate Resin for Heat-Cured Acrylic Denture Composite

This research has studied the addition effect of woven carbon fiber treated with NaOH and coated by β- TCP to the conventional polymethyl methacrylate (PMMA). Two stages are involved in the preparation of heat-cured acrylic denture composite. The first chemical treatment of woven carbon fiber (WCF) surface by different concentrations of NaOH (0.10, 0.15, and 0.20 M) and coating carbon fiber with β-TCP by various weight fractions (0.08, 0.10, and 0.12 wi) were carried out. The second stage includes the reinforcement of denture base material by treated and coated WCF. The functional groups of the WCF surface before and after alkali treatment were studied by FTIR. The morphology of the WCF surface before and after alkali treatment was observed by FESEM, the diameter of pores on the untreated and treated fibers, and the adhesion of β-TCP powder to the fiber was also observed. Mechanical tests include: impact strength (I.S.) and flexural strength (F.S) were calculated using a three-point bending test with a universal test machine and a Charpy impact test machine, respectively. From the result, reinforcing PMMA with treated and coated WCF improves the mechanical properties (impact and flexural strength).

Evaluation of microhardness in two types of denture bases after using sodium hypochlorite and NatureDent disinfecting agents

Background. Chemical agents, in combination with mechanical methods, play an important role in reducing microbial plaque on denture surfaces. However, these methods might change the mechanical behavior of acrylic resins, including microhardness and surface roughness. This in vitro study investigated the effect of two disinfectants, i.e., water and sodium hypochlorite, on the microhardness of conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins. Methods. Sixty acrylic resin specimens were divided into two groups, and the samples in each group were randomly assigned to three subgroups (n=10). Heat-cured specimens and 1 wt% TiO₂ acrylic resin were prepared and immersed in three solutions: water, a solution prepared with NatureDent pills, and 1% sodium hypochlorite for 30, 60, and 90 days. Microhardness tests were performed on each sample at each immersion stage. The data were analyzed using descriptive statistical methods, three-way and one-way ANOVA, repeated-measures t test, and Tukey HSD tests using SPSS 17. P values<0.05 were considered significant. Results. All three independent parameters, including resin, solution, and time, significantly affected microhardness (P<0.05). The microhardness of both specimen types, i.e., conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins, immersed for 30, 60, and 90 days, was the highest and lowest in water and hypochlorite solutions, respectively. Regarding 90 days, the microhardness values of conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins were 17.050±0.094 and 19.953±0.053 in water, 15.675±0.069 and 18.965±0.037 in hypochlorite, and 16.713±0.122 and 19.39±20.113 in NatureDent solutions, respectively. Conclusion. Disinfecting two types of acrylic resin specimens decreased their microhardness as a function of immersion time for up to 90 days in the three solutions. However, the magnitude of hardness lost was less for TiO₂ nanoparticles-reinforced acrylic resin.

Incorporation of Chitosan Nanoparticles into a Cold-Cure Ortho-Dontic Acrylic Resin: Effects on Mechanical Properties

Improvement of the antibacterial properties of acrylic resins, used in the construction of removable orthodontic appliances, is an important strategy to reduce the incidence of caries and oral diseases in orthodontic treatments. The addition of antimicrobial agents to acrylic resins is one of the effective methods to enhance the antimicrobial properties of these materials. However, one main concern is that modification of acrylic resin has negative effects on its mechanical properties. Recently, chitosan nanoparticles (NPs), as biocompatible and biodegradable polysaccharides with remarkable antimicrobial properties, have been used in different areas of dentistry and medicine. This study aimed to investigate the effects of adding chitosan NPs on the mechanical properties of a cold-cure orthodontic acrylic resin. The chitosan NPs were added to the acrylic resin in various weight percentages: 0% (control), 0.5%, 1%, 2%, and 4%. The flexural strength, compressive strength, Vickers microhardness, and impact strength measurements were performed for all five groups. The results showed that adding up to 1% (w/w) chitosan NPs to an acrylic resin had no significant negative effects on its flexural strength and compressive strength, while it decreased these parameters at weight percentages of 2% and 4% (w/w). The results also revealed that modification of acrylic resin with chitosan NPs up to 4% had no significant negative effects on the microhardness and impact strength of acrylic resin. In conclusion, the addition of chitosan NPs up to 1% (w/w) had no significant negative effects on the mechanical properties of cold-cure acrylic resin.

Preparation and Characterisation of Poly(methyl metacrylate)-Titanium Dioxide Nanocomposites for Denture Bases

Introduction of titanium dioxide nanoparticles (TiO₂ NPs) to poly(methyl methacrylate) (PMMA) aims to improve the mechanical, microbiological and tribological properties of dental prosthesis bases. The aim of the research was to assess the polymerisation time and the change in the colour of the new biomaterial. Samples with the 1 wt% and 2 wt% content of TiO₂ additionally modified by ultrasounds were created. The effectiveness of ultrasounds was assessed by comparing the average size of conglomerates in a liquid acrylic resin monomer by means of a dynamic light scattering (DLS) analysis. The biomaterial structure was assessed by the energy-dispersive X-ray spectroscopy (EDS) analysis. The colour change was analysed by means of a colorimetric test and provided in the CIE (Commission internationale de l’éclairage) L*a*b* and RGB (Red Green Blue) colour palette. It was observed during the DLS test that the ultrasonic homogenisation process caused an increase in the suspension heterogeneity. The EDS analysis confirmed the presence of nanoparticles sized below 100 nm, which constitutes a ground for calling the new biomaterial a nanocomposite. The addition of TiO₂ NPs as well as the ultrasounds result in the reduction of the average PMMA polymerisation time. The obtained data reveal that the addition of both 1 wt% and 2 wt% causes a considerable change in the PMMA colour: its whitening. To summarise, the reduced polymerisation time of the new biomaterial fully enables performance of standard procedures related to creation of dental prosthesis bases. Due to the considerable change in the colour, the clinical application is limited to performance of repairs or relining of the prosthesis, where the new material is located in an unaesthetic zone.