Inhibition of denture plaque by TiO2 coating on denture base resins in the mouth

Effect of nano-ceramic coating on surface property and microbial adhesion to poly(methyl methacrylate)

To improve surface properties of poly(methyl methacrylate) (PMMA) using nano-ceramic coatings and assess microbial adherence after long-term use of a chemical cleanser. Thirty-six PMMA samples were fabricated, polished and coated with a nano-thin TiO₂ or mixed TiO₂ /ZrO₂ , with uncoated samples as controls. Six samples in each group (n = 12) were soaked in Polident denture cleaner 180 times for 30 min, while six were soaked in deionized water. Surface roughness of PMMA before and after being soaked in Polident was assessed. All samples were subsequently exposed to Candida albicans for 6 h and the adherent cells were determined by viable colony count. Two-way analysis of variance was performed for statistical analysis. No significant difference in surface roughness was noted between the uncoated and coated PMMA before soaking. After soaking, surface roughness of the uncoated PMMA increased from 0.164 to 0.532 μm (p < .05). No significant change was observed for TiO₂ -coated (0.105-0.143 μm) or TiO₂ /ZrO₂ -coated PMMA (0.104-0.141 μm). Attachment of C. albicans to PMMA soaked in water showed significantly less attachment to both TiO₂ -coated (1.4 × 10³ cfu/ml) and TiO₂ /ZrO₂ -coated PMMA (1.6 × 10³ cfu/ml) than to the uncoated PMMA (2.6 × 10³ cfu/ml). After soaking in Polident, the uncoated PMMA had significantly less C. albicans attachment than coated samples. Less attachment was noted on the TiO₂ /ZrO₂ -coated PMMA then the TiO₂ -coated samples (p < .05). Nano-ceramic TiO2₂ /ZrO₂ coating of PMMA denture base material alters surface properties thus reduces oral microbial adhesion. It represents a promising alternative to the chemical disinfection for PMMA denture materials.

The Use of Acrylate Polymers in Dentistry

The manuscript aimed to review the types of acrylate polymers used in dentistry, as well as their chemical, physical, mechanical, and biological properties. Regarding their consistency and purpose, dental acrylate polymers are divided into hard (brittle), which includes acrylates for the production of plate denture bases, obturator prostheses, epitheses and maxillofacial prostheses, their repairs and lining, and soft (flexible), which are used for lining denture bases in special indications. Concerning the composition and method of polymerization initiation, polymers for the production of denture bases are divided into four types: heat-, cold-, light-, and microwave-polymerized. CAD/CAM acrylate dentures are made from factory blocks of dental acrylates and show optimal mechanical and physical properties, undoubtedly better monomer polymerization and thus biocompatibility, and stability of the shape and colour of the base and dentures. Regardless of the number of advantages that these polymers have to offer, they also exhibit certain disadvantages. Technological development enables the enhancement of all acrylate properties to respond better to the demands of the profession. Special attention should be paid to improving the biological characteristics of acrylate polymers, due to reported adverse reactions of patients and dental staff to potentially toxic substances released during their preparation and use.

Antifungal and Surface Properties of Chitosan-Salts Modified PMMA Denture Base Material

Chitosan (CS) and its derivatives show antimicrobial properties. This is of interest in preventing and treating denture stomatitis, which can be caused by fungi. Therefore, the aim of this study was the development of a novel antifungal denture base material by modifying polymethyl methacrylate (PMMA) with CS-salt and characterizing its antifungal and surface properties in vitro. For this purpose, the antifungal effect of chitosan-hydrochloride (CS-HCl) or chitosan-glutamate (CS-G) as solutions in different concentrations was determined. To obtain modified PMMA resin specimens, the CS-salts were added to the PMMA before polymerization. The roughness of these specimens was measured by contact profilometry. For the evaluation of the antifungal properties of the CS-salt modified resins, a C. albicans biofilm assay on the specimens was performed. As solutions, both the CS-G and CS-HCl-salt had an antifungal effect and inhibited C. albicans growth in a dose-dependent manner. In contrast, CS-salt modified PMMA resins showed no significant reduced C. albicans biofilm formation. Furthermore, the addition of CS-salts to PMMA significantly increased the surface roughness of the specimens. This study shows that despite the antifungal effect of CS-salts in solution, a modification of PMMA resin with these CS-salts does not improve the antifungal properties of PMMA denture base material.

Comparison of adhesiveness of chewing gum to hard and soft denture base materials

PURPOSE

The purpose of this study was to compare the adhesiveness of chewing gum to hard and soft denture base materials to investigate food retention associated with the basal surface of the denture.

METHODS

Test specimens were fabricated using acrylic resin[Re], cobalt-chromium alloy[Co], zirconia[Zr], silicone soft relining material[SS], and acrylic soft relining material[AS]. Samples were set on a top-and-bottom pair lifting platform equipped with a digital force gauge. The experimenter chewed 3.0 g of chewing gum for 5 min. After surface saliva was wiped off, the chewing gum was placed on the lower test fragment and compressed until the distance between the upper and lower test fragments decreased to 1 mm. The upper test fragment was pulled at a crosshead speed of 100 mm/min. Adhesiveness was measured under dry conditions, and under wet conditions with inter-positioned artificial saliva.

RESULTS

Under dry conditions, the adhesive strength was 17.04 ± 1.99 N for Re, 12.88 ± 2.20 N for Co, 3.80 ± 1.03 N for Zr, 5.76 ± 1.41 N for SS, and 12.54 ± 2.44 N for AS. Under wet conditions, the adhesive strength was 5.26 ± 1.64 N for Re, 0.96 ± 0.21 N for Co, 3.32 ± 0.40 N for Zr, 5.20 ± 1.35 N for SS, and 6.78 ± 1.97 N for AS.

CONCLUSIONS

Among the hard denture base materials, zirconia recorded low adhesiveness and Re recorded high adhesiveness under both wet and dry conditions. The adhesiveness of Co was low under wet conditions but high under dry conditions. Among the soft denture base materials, SS under dry conditions recorded lower adhesiveness than that of AS. The adhesiveness of SS was low under both wet and dry conditions.

Protein-repellent and antibacterial effects of a novel polymethyl methacrylate resin

OBJECTIVES

Heat-cured resins are commonly used in orthodontics; however, there is a high incidence of caries, periodontal diseases and denture-induced stomatitis. The objectives of this study were to: (1) develop a new bioactive polymethyl methacrylate (PMMA) resin containing 2-methacryloyloxyethyl phosphorylcholine (MPC) and quaternary ammonium dimethylaminohexadecyl methacrylate (DMAHDM), and (2) investigate the effects on mechanical properties, protein-repellency and antibacterial properties.

METHODS

MPC and DMAHDM were mixed into a commercial acrylic resin (Nature Cryl™ MC). Mechanical properties were measured in three-point flexure. Surface roughness was assessed using atomic force microscopy (AFM). Protein adsorption onto the PMMA resin was measured using a micro bicinchoninic acid (BCA) method. A human saliva microcosm model was used to investigate the live/dead staining and metabolic activity of the biofilms.

RESULTS

Incorporation of 3% MPC and 1.5% DMAHDM into PMMA resin achieved protein repellent and antibacterial capabilities, without compromising the mechanical properties. PMMA resin with 3% MPC + 1.5% DMAHDM had protein adsorption that was 1/6 that of a commercial control (p < 0.05). The PMMA resin with 3% MPC + 1.5% DMAHDM had much greater reduction in biofilm growth than using MPC or DMAHDM alone (p < 0.05).

CONCLUSIONS

A bioactive PMMA resin with a combination of strong protein-repellent and antibacterial capabilities was developed for the first time. The new resin greatly reduced the biofilm growth and metabolic activity, without compromising its mechanical properties.

SIGNIFICANCE

Novel PMMA resin is promising for applications in orthodontic retainers and orthodontic appliances to reduce biofilm activity and protein adsorption around the resin.

Antibacterial, Hydrophilic Effect and Mechanical Properties of Orthodontic Resin Coated with UV-Responsive Photocatalyst

Photocatalysts have multiple applications in air purifiers, paints, and self-cleaning coatings for medical devices such as catheters, as well as in the elimination of xenobiotics. In this study, a coating of a UV-responsive photocatalyst, titanium dioxide (TiO₂), was applied to an orthodontic resin. The antibacterial activity on oral bacteria as well as hydrophilic properties and mechanical properties of the TiO₂-coated resin were investigated. ultraviolet A (UVA) (352 nm) light was used as the light source. Antibacterial activity was examined with or without irradiation. Measurements of early colonizers and cariogenic bacterial count, i.e., colony forming units (CFU), were performed after irradiation for different time durations. Hydrophilic properties were evaluated by water contact angle measurements. While, for the assessment of mechanical properties, flexural strength was measured by the three-point bending test. In the coat(+)light(+) samples the CFU were markedly decreased compared to the control samples. Water contact angle of the coat(+)light(+) samples was decreased after irradiation. The flexural strength of the specimen irradiated for long time showed a higher value than the required standard value, indicating that the effect of irradiation was weak. We suggest that coating with the ultraviolet responsive photocatalyst TiO₂ is useful for the development of orthodontic resin with antimicrobial properties.