Effect Of Microwave Disinfection Research Articles

Comparative Evaluation of Effect of Microwave Disinfection on Compressive and Diametral Tensile Strength of Various Type IV Dental Stones–An In Vitro Study

Comparative Evaluation of Effect of Microwave Disinfection on Compressive and Diametral Tensile Strength of Various Type IV Dental Stones–An In Vitro Study

The Effect of Microwave Disinfection on Denture Base Polymers, Liners and Teeth: A Basic Overview.

The aim of this paper was to overview the current scientific knowledge concerning the effect of microwave disinfection on denture related material properties. Cross-infection control in dentistry is a significant issue in everyday clinical practice due to the recent increase in some infectious diseases such as hepatitis B, C and AIDS and therefore numerous methods of disinfection have been used. The most widespread method of disinfection used in everyday practice is chemical, however, studies have suggested that chemical disinfectants alter the physical and mechanical properties of the acrylic resins and enable the growth and proliferation of certain bacteria. Therefore, microwaves were introduced as an easy to use-and-access, low cost, chemical free alternative. The question that arose was if and in what way the microwave irradiation affected the denture related material properties. Microwaving affects the denture resin bases, liners and teeth in different ways. The results showed that microwave disinfection could be a safe alternative for the disinfection of denture bases and liners compared to the chemical one, when the procedure is carried out in dry conditions, but could possibly cause dimensional changes of clinical significance on them when the irradiation takes place in wet environment. It also seems to have no detrimental effects of clinical importance on the flexural properties, impact strength and hardness of denture resins and the bond, flexural strength, porosity and hardness of denture liners. The effects of microwave disinfection on the hardness of denture teeth and teeth/denture bond strength are still controversial and no safe conclusions can be drawn.

Effect of microwave disinfection on compressive and tensile strengths of dental stones.

Background and aims Although microwave irradiation has been used for disinfection of dental stone casts, there are concerns regarding mechanical damage to casts during the process. The aim of this study was to evaluate the effect of microwave irradiation on the compressive strength (CS) and diametral tensile strength (DTS) of stone casts. Materials and methods In this in vitro study, 80 cylindrical type III and IV stone models (20 × 40 mm) were prepared and divided into 8 groups of 10. The DTS and CS of the specimens were measured by a mechanical testing machine at a crosshead speed of 0.5 cm/min after 7 times of frequent wetting, irradiating at an energy level of 600 W for 3 minutes and cooling. Data were analyzed by Student’s t-test. Results Microwave irradiation significantly increased DTS of type III and IV to 5.23 ± 0.64 and 8.17 ± 0.94, respectively (P < 0.01). Conclusion According to the results, microwave disinfection increases DTS of type III and IV stone casts without any effects on their CS.

Effect of Microwave Disinfection on Hardness of Acrylic Base Denture Lining Material

Effect of Microwave Disinfection on Hardness of Acrylic Base Denture Lining Material

Effect of microwave disinfection on mechanical properties of denture base acrylic resin

The microwave oven was used for sterilizing dentures contaminated with Candida albicans and other communicable diseases instead of disinfectant solutions. This study was carried out to evaluate the flexural properties, toughness, and impact strength of heat-cured acrylic resin sterilized by microwave oven either immersed in water or non-immersed for 5 and 15 min at full power. The results indicated that the microwave oven sterilization technique resulted in reduction of the load necessary to fracture the specimens, deformation at fracture, transverse strength, modulus of elasticity except disinfection at 5 min dry condition, toughness, and impact strength. This study concluded that the microwave oven is not acceptable for sterilization of dentures because of its weakening effects on the dentures that prone for fracture during clinical use. This method of sterilization increased the brittleness of acrylic resin specimens.

Growth of Candida species on complete dentures: effect of microwave disinfection

Microwave disinfection of complete dentures has been recommended to treat denture stomatitis in non-immune compromised patients. Oral candidiasis is a frequent manifestation of HIV infection. The objective of this study is to evaluate the effectiveness of microwave irradiation on the disinfection of complete dentures inoculated with American Type Culture Collection (ATCC) and HIV isolates of five species of Candida. Fifty dentures were made, sterilised and inoculated with the tested microorganisms (C. albicans, C. dubliniensis, C. krusei, C. glabrata and C. tropicalis). After incubation (37 degrees C/48 h), dentures were microwaved (650 W/3 min). Non-irradiated dentures were used as positive controls. Replicate aliquots of suspensions were plated at dilutions 10(-1) to 10(-4) and incubated (37 degrees C/48 h). Colony counts (cfu ml(-1)) were quantified. Dentures were also incubated at 37 degrees C for 7 days. Data were analysed with 2-way ANOVA and Tukey HSD tests (alpha = 0.05). Dentures contaminated with all Candida species showed sterilisation after microwave irradiation. All control dentures showed microbial growth on the plates. The cfu ml(-1) for C. glabrata was higher than those of C. albicans, C. dubliniensis and C. tropicalis whereas the cfu ml(-1) for C. krusei was lower. The cfu ml(-1) for clinical isolates was higher than those of ATCC yeast. Microwave irradiation for 3 min at 650 W resulted in sterilisation of all complete dentures.

The Effect of Microwave Disinfection on Tensile Strength of Dental Gypsum

The Effect of Microwave Disinfection on Tensile Strength of Dental Gypsum

Effect of microwave disinfection on physical and mechanical properties of acrylic resins

This study evaluated the effect of microwave energy on the hardness, impact strength and flexural strength of the Clássico, Onda-Cryl and QC-20 acrylic resins. Aluminum die were embedded in metallic or plastic flasks with type III dental stone, in accordance with the traditional packing technique. A mixing powder/liquid ratio was used according to the manufacturer's instructions. After polymerization in water batch at 74 degrees C for 9 h, boiling water for 20 min or microwave energy at 900 W for 10 min, the specimens were deflasked after flask cooling at room temperature, and submitted to finishing. Specimens non-disinfected and disinfected by microwave irradiation were submitted to hardness, impact and flexural strength tests. Each specimen was immersed in distilled water and disinfected in a microwave oven calibrated to 650 W for 3 min. Knoop hardness test was performed with 25 g load for 10 s, impact test was carried out using the Charpy system with 40 kpcm, and 3-point bending test with a crosshead speed of 0.5 mm/min until fracture. Data were submitted to statistical analysis by ANOVA and Tukey's test (alpha=0.05). Disinfection by microwave energy decreased the hardness of Clássico and Onda-Cryl acrylic resins, but no effect was observed on the impact and flexural strength of all tested resins.

Effect of microwave disinfection on denture base adaptation and resin surface roughness

This study evaluated the effect of disinfection methods [chemical disinfection (immersion in 100 ppm chloride solution) or microwave disinfection (690 W for 6 min)] on the internal adaptation of denture bases and resin surface roughness. For the adaptation test, 18 maxillary denture bases were obtained from stone casts duplicated from a metallic master model and submitted to the following treatments: 1) control (no disinfection), 2) chemical disinfection or 3) microwave disinfection. Disinfection procedures were performed twice (T1, T2) with a 7-day interval between them. Internal adaptation was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between the resin base and the master model. For surface roughness measurement, 60 rectangular (5x10x40 mm) resin specimens were either mechanically or chemically polished and then submitted to the disinfection treatments. Surface roughness (Ra) was recorded after polishing (T0) and after T1 and T2. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni correction at 5% significance level. Bases submitted to microwave disinfection had gradual increase of misfit, while bases immersed in chloride solution did not differ from the control group. Surface roughness increased in the mechanical polishing groups with microwave disinfection and decreased in the chemical polishing groups.

Effect of microwave disinfection on the hardness and adhesion of two resilient liners

Microwave irradiation has been suggested for denture disinfection. However, the effect of this procedure on the hardness and bond strength between resilient liners and denture base acrylic resin is not known. This study evaluated the effect of water storage time and microwave disinfection on the hardness and peel bond strength of 2 silicone resilient lining materials to a heat-polymerized acrylic resin. Acrylic resin (Lucitone 199) specimens (75 x 10 x 3 mm) were stored in water at 37 degrees C (2 or 30 days) before bonding (n = 160). The resilient lining materials (GC Reline Extra Soft and Dentusil) were bonded to the denture base and divided into the following 4 groups (n = 10): Tests performed immediately after bonding (control); specimens immersed in water (200 mL) and irradiated twice, with 650 W for 6 minutes; specimens irradiated daily for 7 total cycles of disinfection; specimens immersed in water (37 degrees C) for 7 days. Specimens were submitted to a 180-degree peel test (at a crosshead speed of 10 mm/min) and the failure values (MPa) and mode of failure were recorded. Pretreatment and posttreatment hardness measurements (Shore A) of the resilient materials were also performed. Three-way analysis of variance, followed by the Tukey HSD test, was performed (alpha = .05). The analysis revealed that, for all conditions, the mean failure strengths of GC Reline Extra Soft (0.95-1.19 MPa) were significantly higher ( P < .001) than those of Dentusil (0.45-0.50 MPa). The adhesion of the liners was not adversely affected by water storage time of Lucitone 199 or microwave disinfection. All peel test failures were cohesive. There was a small but significant difference ( P < .001) between the pretreatment (34.33 Shore A) and posttreatment (38.69 Shore A) hardness measurements. Microwave disinfection did not compromise the hardness of either resilient liners or their adhesion to the denture base resin Lucitone 199.

Microwave disinfection of soft contact lenses.

We evaluated the effectiveness and convenience of microwave irradiation as a method of disinfecting soft contact lenses. Soft contact lenses from each of the four Food and Drug Administration (FDA) categories were placed in sterile vials and immersed in 2 ml of saline which had been contaminated with one of three common species of bacteria. The contaminated lens vials were placed in a standard 600 W microwave oven and exposed to microwave irradiation times ranging from 30 to 180 s. Significant reductions in bacteria colony counts were found after 30 s of microwave irradiation. Few of the bacteria survived 60 s of microwave exposure and none survived 90 s. Our findings indicate that microwave disinfection can be an effective and rapid means of killing bacteria on soft lenses and in the storage solution. However, further studies are necessary to determine the minimum exposure time required, the effect of microwave disinfection on other microorganisms, and the effect of microwave irradiation on contact lens polymers and lens dimensions.