Effect of microwave sterilization and water storage on the Vickers hardness of acrylic resin denture teeth

Microwave disinfection of facial silicone prostheses, part 2: Mechanical properties

STATEMENT OF PROBLEM

Part 1 of this 2-part study determined that microwave disinfection did not degrade the color stability of facial silicone prostheses. However, investigations on the effects of microwave disinfection on the mechanical properties of different silicone elastomers are lacking.

PURPOSE

The purpose of this in vitro study was to examine the mechanical properties of commonly used colored facial silicone elastomers before and after microwave disinfection over a simulated 1.5-year period.

MATERIAL AND METHODS

Six commonly used facial silicone elastomers: MDX4-4210, MDX4-4210/Type A, M511, A-2186, VST-50, and A-2000 were combined with functional intrinsic silicone pigments and opacifier (red, yellow, blue, and white). A total of 288 specimens were fabricated (n=12). Half of the specimens were tested for mechanical properties as the baseline, while the other specimens were tested after microwave disinfection. Microwave disinfection was performed with 660 W, 6 minutes of exposure time, and microwaved for 18 cycles to simulate 1.5 years of usage (one 6-minute exposure monthly). For mechanical property testing, all specimens were tested for tensile strength and percentage elongation (ASTM D412), tear strength (ASTM D624), and hardness (ASTM D2240). For each property, a 2-way ANOVA (silicone type and microwave disinfection factors) and Tukey multiple comparison test were performed using the R statistical software program (α=.05).

RESULTS

Following microwave disinfection, tensile strength and percentage elongation of A-2000 increased significantly (P<.05). MDX4-4210, MDX4-4210/Type A, and A-2000 showed significant increases in their hardness (P<.001). Tear strength also increased significantly for MDX4-4210 and VST-50 (P<.05). Among the materials tested (ranked from highest to lowest value,=not statistically significant different), for tensile strength, VST-50>A-2186=A-2000>MDX4-4210/Type A=M511=MDX4-4210 (P<.05). For percentage elongation, VST-50>MDX4-4210/Type A>A-2186>M511=A-2000=MDX4-4210=M511 (P<.05). For hardness, A-2000=A-2186>M511=VST-50>MDX4-4210>MDX4-4210/Type A (P<.05). For tear strength, VST-50>A-2186>A-2000>M511>MDX4-4210/Type A=MDX4-4210 (P<.05).

CONCLUSIONS

Overall, the mechanical properties of all the silicones tested were not adversely affected by microwave disinfection. VST-50 showed the best mechanical properties among the materials tested both before and after microwave disinfection. Microwave energy is a safe method of disinfecting the silicone elastomers tested in this study.

Comparison of Microhardness of Artificial Teeth with Different Contents After Waiting in Various Liquids

Objectives: This study aimed to assess the long-term microhardness of different artificial teeth after waiting in liquids of various pH values. Materials and Methods: Four different artificial teeth [conventional PMMA(Ivostar) as control group), double cross-linked PMMA(DCL), micro-filled composite resin(VivodentPE), nanohybrid composite resin(PhonaresiII)] were used for the study. After the samples fixed on acrylic blocks were immersed in distilled water at 37˚C for 24 hours, initial microhardness (T0) measurements were performed. Randomly selected samples from each group were immersed in liquids with different pH values (artificial saliva, kefir, orange juice, cola). Measurements repeated on the 7th day on the same samples were recorded as T1, and measurements repeated on the 14th day were recorded as T2. The data obtained were evaluated in the SPSS 22.0 program. Friedman and Kruskall Wallis tests were used to compare of the groups. Results: While the highest initial microhardness averages were found in the Phonares II group, the lowest average belongs to the Ivostar group. Microhardness findings of all materials measured at different times were obtained in the order of T0>T1>T2. When the data of samples aged in different liquids are compared, significant differences are observed (p0.05) Conclusions: A decrease in microhardness of materials that are immersed in liquids with different pH values for a long time was observed, and the microhardness of the materials exposed to these solutions is adversely affected.

An Enamel Based Biopolymer Prosthesis for Dental Treatment with the Proper Bond Strength and Hardness and Biosafety

Although dental prosthesis materials such as metal alloys, ceramics, and cured resin composite have long been utilized to restore teeth, their bond strength and hardness values are not well matched to human enamel. Prosthesis detachment and opposing enamel wear are major concerns in restorative dentistry. An experimental biopolymer, hybridized enamel, was synthesized and utilized as a dental prosthesis to compare hardness and tensile bond strength (TBS) with those of commercial materials. Vickers hardness (VHN) with a 100 g loading for 15 s at eight indentations on each specimen (n = 20) was measured. TBSs between prostheses and two types of resin luting agents (n = 10), Super-Bond C&B and All-Bond2 + Duo-Link, were tested. Fractured surfaces and the luting resin-prosthesis interface were examined under a stereomicroscope or a scanning electron microscope (SEM). Statistically significant differences in the TBS and hardness were revealed (p < 0.05). The experimental biopolymer provided a hardness value comparable with human enamel and the highest TBS for both luting agent types. The SEM micrograph demonstrated a honeycomb-like pattern interface between the experimental biopolymer and luting resin. These results suggest that this experimental biopolymer may be a better restorative material to protect from natural enamel loss from tooth reduction or attrition and prevent prosthesis detachment during mastication.

Optical and mechanical properties of conventional, milled and 3D-printed denture teeth

OBJECTIVES

Investigate the effect of various liquids on the optical properties and Vickers hardness of conventional, milled and 3D-printed denture teeth.

METHODS

Six different types of denture teeth (Maxillary anteriors of three different conventional teeth, Vivodent DCL, SR Phonares II, Vita Physiodens; milled teeth, IvotionDent; and two different 3D-printed teeth, Asiga DentaTooth and NextDent C&B MFH) were investigated (total n = 336). The labial surface of each specimen was prepared to a dimension of 10 × 5 × 3mm. Specimens were immersed in artificial saliva, coffee, red wine and denture cleaner with artificial aging to simulate denture use of 12 and 24 months in vivo. Measurements of translucency parameter (TP), shade change (ΔE), surface roughness (Ra) and Vickers hardness (VHN) were conducted at baseline and after artificial aging while immersed in the liquids at each timeframe. Data were statistically analysed by ANOVA and post-hoc test (SPSS Ver 27). Surfaces of specimens were analysed under scanning electron microscopy (SEM).

RESULTS

Milled teeth had the highest overall translucency parameter (5.33 ± 0.76-7.3 ± 0.99). All materials had statistically significant change in translucency parameter and shade after 24 months simulated aging (p < 0.05), especially the milled and 3D-printed teeth (p < 0.01). Surface roughness of all materials were under plaque accumulation threshold Ra = 0.2 μm. At baseline, Vita Physiodens teeth (PMMA with microfillers) demonstrated the highest hardness (33.99 kgf/mm²±3.7), whereas both 3D-printed materials exhibited the lowest hardness (13.27 kgf/mm²±0.36-18.13 kgf/mm²±0.93). Artificial saliva, red wine and denture cleaner had a statistically significant impact (p < 0.05) on hardness of all materials (12.1 kgf/mm²±1.17-30.77 kgf/mm²±2.98).

CONCLUSIONS

Milled teeth exhibited the best optical properties (highest overall translucency parameter and lowest shade change). Milled teeth were also the only material that showed colour change (ΔE values) within clinically acceptable limits. Denture cleaner had the most impact on optical and mechanical properties of all materials. Surface roughness and hardness of 3D-printed teeth had the most change after artificial aging.

Effects of disinfection and sterilization on the dimensional changes and mechanical properties of 3D printed surgical guides for implant therapy - pilot study

Background

The purpose of this research was to investigate the effects of disinfection and three different sterilization methods on the dimensional changes and mechanical properties of three-dimensional (3D) printed surgical guide for implant therapy. The objective was to assess the effects of sterilization procedures in 3D printed drill guide templates with destructive and non-destructive material testing.

Methods

Fifteen identical drill guide templates were produced using a 3D printer. The surgical guides were classified into five groups: three controls, three disinfected (4% Gigasept®, 60 min), three plasma sterilized, three autoclave sterilized (+ 1 bar, 121 °C, 20 min), and three autoclave sterilized (+ 2 bar, 134 °C, 10 min).

The templates were digitalized with a Steinbichler SCAN ST 3D scanner. Length was measured under an SZX16 stereomicroscope. A scanning electron microscope was used to study the surface morphology of the drill templates. The hardness, and flexural and compressive strength were measured to assess any changes in the physical characteristics of the material caused by sterilization. The drill guide templates were also examined with a Dage XiDAT 6600 X-ray. During the X-ray examinations, the following parameters were used: 100 kV voltage, 128 AVG averaging, 0.8 W power. One-way analysis of variance (ANOVA) was used to detect the difference between groups.

Results

Evaluation of the hardness measurements of the various specimens shows that the hardness of the material was not changed by the plasma sterilization (p = 0.0680), steam sterilization on 121 °C (p = 0.6033) or disinfection process (p = 0.1399). The statistical analysis revealed significant difference in hardness strength of the autoclave sterilized (134 °C) specimens (p = 0.0002). There was no significant difference between the goups regarding the scanning electron microscopic and stereomicroscopic examinations. There was no significant difference regarding the X-ray visibility of the templates to the effect of the disinfection (p = 0.7844), plasma sterilization (p = 0.4091) and steam sterilization on 121 °C (p = 0.9277) and steam sterilization on 131 °C (p = 0.093). The effect of the sterilization was the same in case of both flexural and compressive strength of the material.

Conclusions

Our findings indicate that plasma sterilization and steam sterilization at 121 °C were both suitable for sterilizing the tested 3D printed surgical guides.

Effect of surface treatment of prefabricated teeth on shear bond strength of orthodontic brackets

Objective:

The aim of this in vitro study was to evaluate and compare the effects of grinding, drilling, sandblasting, and ageing prefabricated teeth (PfT) on the shear bond strength (SBS) of orthodontic brackets, as well as the effects of surface treatments on the adhesive remnant index (ARI).

Methods:

One-hundred-ninety-two PfT were divided into four groups (n = 48): Group 1, no surface treatment was done; Group 2, grinding was performed with a cylindrical diamond bur; Group 3, two drillings were done with a spherical diamond bur; Group 4, sandblasting was performed with 50-µm aluminum oxide. Before the experiment, half of the samples stayed immersed in distilled water at 37^oC for 90 days. Brackets were bonded with Transbond XT and shear strength tests were carried out using a universal testing machine. SBS were compared by surface treatment and by ageing with two-way ANOVA, followed by Tukey’s test. ARI scores were compared between surface treatments with Kruskal-Wallis test followed by Dunn’s test.

Results:

Surface treatments on PfT enhanced SBS of brackets (p< 0.01), result not observed with ageing (p= 0.45). Groups II, III, and IV showed higher SBS and greater ARI than the Group 1 (p< 0.05). SBS was greater in the groups 3 and 4 (drilling, sandblasting) than in the Group 2 (grinding) (p< 0.05). SBS and ARI showed a positive correlation (Spearman’s R²= 0.57; p< 0.05).

Conclusion:

Surface treatment on PfT enhanced SBS of brackets, however ageing did not show any relevance. Sandblasting and drilling showed greater SBS than grinding. There was a positive correlation between SBS and ARI.

Evaluation of Surface Microhardness Following Chemical and Microwave Disinfection of Commercially Available Acrylic Resin Denture Teeth

INTRODUCTION

Denture disinfection is an indispensable procedure for preventing cross contamination and the maintenance of a healthy oral mucosa in patients rehabilitated with removable dental prosthesis. Nevertheless, they are known to cause changes in the physical and mechanical properties of denture base resins and acrylic resin denture teeth following immersion of a denture in a suitable chemical disinfectant solution or by undergoing microwave irradiation. One such mechanical property indicator for artificial tooth materials is hardness.

AIM

To assess the surface hardness of acrylic resin teeth of three different commercial brands (Ivoclar, Newace, Acryrock) following chemical (2% glutaraldehyde, 1% sodium hypochlorite) and microwave disinfections.

MATERIALS AND METHODS

Ten specimens of each of the three commercial brands were made for control and each simulated disinfection type and stored in distilled water at room temperature for 24 hours. After water storage, specimens were immersed in 2% glutaraldehyde and 1% sodium hypochlorite (one and three cycles) at room temperature for 10 minutes. Irradiation with microwave (one and three cycles) was done in domestic microwave for three minutes with the specimens immersed in 150 ml of distilled water. The specimens were stored in distilled water at room temperature for seven days after each disinfection cycle. Vickers hardness measurements were made using a hardness indenter under a load of 50 g force for 10 seconds. Data was subjected to repeated measure two-way ANOVA test and Tukey's test.

RESULTS

There were statistically significant differences for the variables disinfection, tooth, and cycle (p<0.05 for teeth & disinfectant interaction, p<0.05 cycle and disinfectant interaction). The mean surface hardness following one microwave disinfection cycle was lower than control, glutaraldehyde and sodium hypochlorite. Comparison among cycles revealed that microhardness was significantly decreased for three cycles of microwave disinfection.

CONCLUSION

It was concluded that there was no significant difference in microhardness when the teeth were subjected to chemical disinfection but three cycles of microwave disinfection produced decrease in the microhardness of different types of artificial teeth.

Effect of Disinfection on the Bond Strength between Denture Teeth and Microwave-Cured Acrylic Resin Denture Base

PURPOSE

Denture tooth debonding is a common complication for denture wearers; however, the effect of complete denture disinfection on bonding between denture teeth and acrylic resin remains unclear. The aim of this study was to evaluate the effect of disinfection methods on the bond strength between denture teeth and microwave-cured acrylic resin denture base.

MATERIALS AND METHODS

Three commercial brands of denture teeth (Trilux, Biolux, Vipi Dent Plus) and one microwave-cured acrylic resin denture base were tested. Each brand of denture teeth was divided into seven groups (n = 6; estimated by partial Eta squared). The specimenss of groups H and Cl were immersed in 1% sodium hypochlorite and 4% chlorhexidine digluconate for 7 days, respectively. In group Br, the specimens were subjected to toothbrush simulation under 200 g of force for 20,000 cycles. In groups Br-H and Br-Cl, the specimens were brushed and further disinfected with 1% sodium hypochlorite and 4% chlorhexidine digluconate, respectively. In control groups 1 (Co1) and 2 (Co2), the specimens were stored in distilled water for 50 ± 2 hours and 7 days, respectively. Shear bond strength testing was performed at the resin/tooth interface in a universal testing machine at a 1 mm/min crosshead speed. The failure pattern was quantified and classified into adhesive, cohesive, or mixed. Data were analyzed using two-way ANOVA and Tukey HSD test (α = 0.05).

RESULTS

Disinfection with 1% sodium hypochlorite (p = 0.031), brushing (p < 0.0001), and association of brushing with either 1% sodium hypochlorite (p < 0.0001) or 4% chlorhexidine digluconate (p = 0.01) reduced the bond strength between denture teeth and microwave-cured acrylic resin denture base. All commercial brands of denture teeth presented a similar bond strength (p > 0.05). The failure pattern was predominantly adhesive independent of the disinfection method and denture tooth brand.

CONCLUSIONS

Disinfection with sodium hypochlorite, brushing, and the association of mechanical and chemical methods reduced the bond strength between denture tooth and microwave-cured acrylic resin denture base.

Surface properties of multilayered, acrylic resin artificial teeth after immersion in staining beverages

Objective

To evaluate the effect of staining beverages (coffee, orange juice, and red wine) on the Vickers hardness and surface roughness of the base (BL) and enamel (EL) layers of improved artificial teeth (Vivodent and Trilux).

Material and Methods

Specimens (n=8) were stored in distilled water at 37°C for 24 h and then submitted to the tests. Afterwards, specimens were immersed in one of the staining solutions or distilled water (control) at 37°C, and the tests were also performed after 15 and 30 days of immersion. Data were analyzed using 3-way ANOVA and Tukey’s test (α=0.05).

Results

Vivodent teeth exhibited a continuous decrease (p<0.0005) in hardness of both layers for up to 30 days of immersion in all solutions. For Trilux teeth, similar results were found for the EL (p<0.004), and the BL showed a decrease in hardness after 15 days of immersion (p<0.01). At the end of 30 days, this reduction was not observed for coffee and water (p>0.15), but red wine and orange juice continuously reduced hardness values (p<0.0004). Red wine caused the most significant hardness changes, followed by orange juice, coffee, and water (p<0.006). No significant differences in roughness were observed for both layers of the teeth during the immersion period, despite the beverage (p>0.06).

Conclusions

Hardness of the two brands of acrylic teeth was reduced by all staining beverages, mainly for red wine. Roughness of both layers of the teeth was not affected by long-term immersion in the beverages.

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.

Synthesis of a resin monomer-soluble polyrotaxane crosslinker containing cleavable end groups

A resin monomer-soluble polyrotaxane (PRX) crosslinker with cleavable end groups was synthesized to develop degradable photosetting composite resins. The PRX containing 50 α-cyclodextrins (α-CDs) with disulfide end groups was initially modified with n-butylamine to obtain a resin monomer-soluble PRX. The PRX containing 13 n-butyl groups per α-CD molecule was completely soluble in conventional resin monomers such as 2-hydroxyethyl methacrylate (HEMA) and urethane dimethacrylate (UDMA). The synthesized n-butyl-containing PRX was further modified with 2-aminoethyl methacrylate to provide crosslinkable acrylic groups onto PRX. The prepared resin monomer-soluble PRX crosslinker was successfully polymerized with a mixture of HEMA and UDMA to provide photosetting plastic. It was confirmed that the Vickers hardness of the prepared plastic was greatly decreased after treatment with dithiothreitol. This indicates that the resin monomer-soluble PRX crosslinker can be applied to design degradable photosetting plastics potentially used in the industrial or biomedical field.

Photosensitization of in vitro biofilms formed on denture base resin

STATEMENT OF PROBLEM

Proper sterilization or disinfection of removable prostheses and surgical guides has been problematic in dental practice because of the absence of simple and low-cost techniques that do not cause damage to acrylic resins.

PURPOSE

The purpose of this study was to study the effect of photodynamic therapy against Streptococcus mutans, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans biofilms formed on acrylic resin specimens.

MATERIAL AND METHODS

The specimens were sterilized in ethylene oxide gas and submitted to in vitro biofilm growth. The photodynamic therapy consisted of the application of 0.05% methylene blue (P+) conjugated to irradiation with a light-emitting-diode of 630 nm and 150 mW (L+). The specimens were randomly divided into groups (n=5): negative control (P-L-); stained and irradiated at 10 J/cm(2) (P+L+ 10); stained and irradiated at 30 J/cm(2) (P+L+ 30); stained and not irradiated (P+L-); not stained and irradiated at 10 J/cm(2) (P-L+ 10); not stained and irradiated at 30 J/cm(2) (P-L+ 30); and gold standard (GS), sterilized. Afterward, the specimens were submitted to contact with culture medium agar for 10 minutes in petri plates, which were incubated for 48 hours at 37°C. The number of colony-forming units was obtained, and the data were expressed according to scores (1=0; 2=1-10; 3=11-100; 4=101-1000) and analyzed by the Friedman and Dunn tests (α=.05).

RESULTS

Streptococcus mutans was sensitized by (P+L-); P aeruginosa and C albicans were also sensitized by the dye but showed a slight microbial reduction with (P+L+ 30), as did S aureus (P>.05); E coli presented an initial score of 3 and achieved a bacterial reduction to score 2 with (P+L+ 30) (P=.039).

CONCLUSIONS

Photodynamic therapy was effective in reducing E coli counts on biofilms formed on acrylic resin specimens. The inhibition of microorganism growth tended to be directly proportional to the amount of energy provided by the light-emitting diode.

Comparison of denture microwave disinfection and conventional antifungal therapy in the treatment of denture stomatitis: a randomized clinical study

OBJECTIVE

The aim of this study was to compare the effectiveness of denture microwave disinfection and antifungal therapy on treatment of denture stomatitis.

STUDY DESIGN

Sixty denture wearers with denture stomatitis (3 groups; n = 20 each), were treated with nystatin or denture microwave disinfection (1 or 3 times/wk) for 14 days. Mycologic samples from palates and dentures were quantified and identified with the use of Chromagar, and clinical photographs of palates were taken. Microbiologic and clinical data were analyzed with the use of a series of statistical tests (α = .05).

RESULTS

Both treatments similarly reduced clinical signs of denture stomatitis and growth on palates and dentures at days 14 and 30 (P > .05). At sequential appointments, the predominant species (P < .01) isolated was C. albicans (range 98%-53%), followed by C. glabrata (range 22%-12%) and C. tropicalis (range 25%-7%).

CONCLUSIONS

Microwave disinfection, at once per week for 2 treatments, was as effective as topical antifungal therapy for treating denture stomatitis.

Effect of chemical and microwave disinfection on the surface microhardness of acrylic resin denture teeth

PURPOSE

The purpose of this study was to evaluate the effect of simulated disinfections (2% glutaraldehyde, 1% sodium hypochlorite, and microwave energy) on the surface hardness of Trilux, Biocler, Biotone, New Ace, and Magister commercial artificial teeth.

MATERIALS AND METHODS

Specimens (n = 10) were made with the teeth included individually in circular blocks of acrylic resin, leaving the labial surface exposed. Cycles of simulated chemical disinfection were accomplished with the specimens immersed in the solutions at room temperature for 10 minutes, followed by tap water washing for 30 seconds and storage in distilled water at room temperature for 7 days until the next disinfection. Simulated disinfection by microwave energy was carried out in a domestic oven with 1300 W at a potency of 50% for 3 minutes with the specimens individually immersed in 150 ml of distilled water. Control (no disinfection) and the experimental groups (first and third disinfection cycles) were submitted to Knoop hardness measurements with indentations at the center of the labial tooth surface. Data were submitted to repeated measure two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

Biocler, Magister, and Trilux showed lower surface microhardness when submitted to microwave. Lower microhardness for Biotone was promoted by hypochlorite, while no significant difference was shown for New Ace. The third disinfection cycle significantly decreased the tooth surface hardness only for microwave.

CONCLUSIONS

Different disinfection methods promoted different effects on the microhardness of different types of artificial teeth. Surface microhardness of the teeth was less affected by the simulated chemical disinfections when compared to microwaved specimens.

Effect of experimental Ricinus communis solution for denture cleaning on the properties of acrylic resin teeth

This study evaluated Knoop hardness, surface roughness and color alteration of artificial teeth for dentures after immersion in water, 1% sodium hypochlorite and an experimental solution of 2% Ricinus communis (RC). Thirty specimens of Vipi, Biolux and Trilux were analyzed. Tests of Knoop hardness, surface roughness and color alteration were conducted immediately after specimen preparation (T0) and after two immersion protocols for 15 days (ΔT(15)) and 183 days (ΔT(183)). Data variation (ΔT) were subjected to ANOVA and Tukey's test (p<0.05). At ΔT(15), Vipi presented hardness increase and Biolux presented the highest variation (p=0.01). RC caused the highest increase in hardness (p=0) and the lowest increase (p=0.005) in roughness. Biolux presented the lowest color alteration (p =0). At ΔT(183), Trilux underwent the highest hardness variation (p=0). Biolux presented an increase in roughness (p=0). There was no significant differences in color alteration among the artificial teeth (p=0.06) and among solutions (p=0.08) after 183 days of immersion. All solutions (distilled water, 1% sodium hypochlorite and 2% RC) caused alterations on the analyzed properties. Both immersion protocols caused alterations on the analyzed properties.

The effect of long-term disinfection procedures on hardness property of resin denture teeth

OBJECTIVE

The aim of the study was to evaluate the effect of long-term disinfection procedures on the Vickers hardness (VHN) of acrylic resin denture teeth.

MATERIAL AND METHODS

Five acrylic resin denture teeth (Vipi Dent Plus-V, Trilux-T, Biolux-B, Postaris-P and Artiplus-A) and one composite resin denture teeth (SR-Orthosit-O) were embedded in heat-polymerised acrylic resin within polyvinylchloride tubes. Specimens were stored in distilled water at 37°C for 48 h. Measurements of hardness were taken after the following disinfection procedures: immersion for 7 days in 4% chlorhexidine gluconate or in 1% sodium hypochlorite (CIm and HIm group, respectively) and seven daily cycles of microwave sterilisation at 650 W for 6 min (MwS group). In the WIm group, specimens were maintained in water during the time used to perform the disinfection procedures (7 days). Data were analysed with anova followed by the Bonferroni procedure (α = 0.01).

RESULTS

Microwave disinfection decreased the hardness of all acrylic resin denture teeth (p < 0.001). Immersion for 7 days in 4% chlorhexidine gluconate or distilled water had significant effect on the hardness of the acrylic resin denture teeth A (p < 0.01), and 1% sodium hypochlorite on teeth T (p < 0.01). All disinfection procedures decrease the hardness of the composite resin denture teeth (p < 0.01). Teeth O exhibited the highest and teeth V the lowest hardness values in the control group (p < 0.01).

CONCLUSIONS

Disinfection procedures changed the hardness of resin denture teeth.

Evidence-based guidelines for the care and maintenance of complete dentures: a publication of the American College of Prosthodontists

The current rates of edentulism have been estimated to be between 7% and 69% of the adult population internationally. In the United States, while the incidence of edentulism continues to decline, rapid population growth coupled with current economic conditions suggest that edentulism and conventional denture use will continue at current or higher numbers. Unfortunately, evidence-based guidelines for the care and maintenance of removable complete denture prostheses do not exist. In 2009, the American College of Prosthodontists (ACP) formed a task force to establish evidence-based guidelines for the care and maintenance of complete dentures. The task force comprised members of the ACP, the Academy of General Dentistry, American Dental Association (ADA) Council on Scientific Affairs, the American Dental Hygienists' Association, the National Association of Dental Laboratories, and representatives from GlaxoSmithKline Consumer Healthcare. The review process included the assessment of over 300 abstracts and selection of over 100 articles meeting inclusion criteria of this review. The task force reviewed synopses of the literature and formulated 15 evidence-based guidelines for denture care and maintenance. These guidelines were reviewed by clinical experts from the participating organizations and were published in February 2011 issue of The Journal of the American Dental Association for widespread distribution to the dental community. These guidelines reflect the views of the task force.

A conventional microwave oven for denture cleaning: a critical review

INTRODUCTION

Denture cleaning should be quick and easy to perform, especially in long-term care facilities. The lack of proper oral hygiene can put older adults at higher risk from opportunistic oral infections, particularly fungal. As an alternative to regular brushing, the use of a microwave oven has been suggested for cleaning and disinfecting dentures.

OBJECTIVES

To synthesise and discuss the advantages and disadvantages of the use of a conventional microwave oven for cleaning and disinfecting complete dentures.

METHODS

A brief literature search focused on papers dealing with microwave therapy for denture cleaning through PubMed Central, Cochrane Database of Systematic Reviews, Google Scholar, Ovid MEDLINE(R) In-Process, and Scifinder Scholar.

RESULTS

One hundred and sixty-seven manuscripts published in English with full text were found, and 28 were accepted and discussed in the light of the advantages and disadvantages of the use of conventional microwave oven for cleaning and disinfecting complete dentures.

CONCLUSIONS

There was no standardisation for microwave use for denture cleaning. Manual cleaning still seemed to be the optimal method for controlling fungal infection and denture stomatitis. However, such a daily routine appeared to be underused, particularly in long-term care facilities.

Measurement of interfacial porosity at the acrylic resin/denture tooth interface

PURPOSE

Small pores of almost uniform shape and size are common in polymeric materials; however, significant porosity can weaken a denture base resin and promote staining, harboring of organisms such as Candida albicans, and bond failures between the artificial tooth and denture base resin. The aim of this study was to investigate the porosity at the interface of one artificial tooth acrylic resin (Trilux, copolymer of polymethyl methacrylate, ethylene glycol dimethacrylate, and color pigments) and three denture base resins: Acron MC (microwave-polymerized), Lucitone 550 (heat-polymerized), and QC-20 (heat-polymerized).

MATERIALS AND METHODS

Ten specimens of each denture base resin with artificial tooth were processed. After polymerization, specimens were polished and observed under a microscope at 80x magnification. The area of each pore present between artificial tooth and denture base resin was measured using computer software, and the total area of pores per surface was calculated in millimeter square. The Kruskal-Wallis test was performed to compare porosity data (alpha= 0.05).

RESULTS

Porosity analysis revealed the average number of pores (n), area range (S, mm(2)), and diameter range (d, mum) for Acron MC (n = 23, S = 0.001 to 0.0056, d = 35 to 267), Lucitone 550 (n = 13, S = 0.001 to 0.005, d = 35 to 79), and QC-20 (n = 19, S = 0.001 to 0.014, d = 35 to 133). The analyses showed that there were no statistically significant differences among the groups (p= 0.7904).

CONCLUSIONS

Within the limitations of this in vitro study, it was concluded that the denture base resins evaluated did not affect porosity formation at the artificial tooth/denture base resin interface.

Denture disinfection by microwave irradiation: a randomized clinical study

OBJECTIVE

This study evaluated the clinical effectiveness of two exposure times of microwave irradiation on the disinfection of complete dentures.

METHODS

Biofilm samples were collected from dentures of 30 patients, who were randomly divided into two experimental groups of 15 subjects each: Group 1-patients had their maxillary denture microwaved for 3 min (650W); Group 2-patients had their maxillary denture microwaved for 2 min (650W). Denture biofilm samples were taken with swabs, before (left side surfaces) and after (right side surfaces) microwave irradiation. All microbial material was plated on selective media for Candida spp., Staphylococcus spp., mutans streptococci and a non-selective media. After incubation (48 h/37 degrees C), the number of colony-forming units (cfu/mL) was counted. Microorganisms which grew on selective media were identified using biochemical methods. The data were statistically analyzed by Kruskal-Wallis test, followed by Dunn's post-test (alpha=0.05).

RESULTS

Microwave irradiation for 3 min (Group 1) resulted in sterilization of all dentures evaluated. After microwave irradiation for 2 min (Group 2), a significant decrease in Candida spp. (P=0.0062), Staphylococcus spp. (P=0.0178), mutans streptococci (P=0.0047) and non-identified species (P<0.0001) was achieved in comparison with the cfu/mL obtained before irradiation. The colonies grown after 2 min of microwave irradiation were identified as Candida albicans, non-aureus Staphylococci and Streptococcus mutans.

CONCLUSION

Microwave irradiation for 3 min may be a potential treatment to prevent cross-contamination.

Effect of different exposure times on microwave irradiation on the disinfection of a hard chairside reline resin

PURPOSE

This study evaluated the effectiveness of different exposure times of microwave irradiation on the disinfection of a hard chairside reline resin.

MATERIALS AND METHODS

Sterile specimens were individually inoculated with one of the tested microorganisms (Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and Bacillus subtilis) and incubated for 24 hours at 37 degrees C. For each microorganism, 10 specimens were not microwaved (control), and 50 specimens were microwaved. Control specimens were individually immersed in sterile saline, and replicate aliquots of serial dilutions were plated on selective media appropriate for each organism. Irradiated specimens were immersed in water and microwaved at 650 W for 1, 2, 3, 4, or 5 minutes before serial dilutions and platings. After 48 hours of incubation, colonies on plates were counted. Irradiated specimens were also incubated for 7 days. Some specimens were prepared for scanning electron microscopic (SEM) analysis.

RESULTS

Specimens irradiated for 3, 4, and 5 minutes showed sterilization. After 2 minutes of irradiation, specimens inoculated with C. albicans were sterilized, whereas those inoculated with bacteria were disinfected. One minute of irradiation resulted in growth of all microorganisms. SEM examination indicated alteration in cell morphology of sterilized specimens. The effectiveness of microwave irradiation was improved as the exposure time increased.

CONCLUSION

This study suggests that 3 minutes of microwave irradiation can be used for acrylic resin sterilization, thus preventing cross-contamination.

Compositional characteristics and hardness of acrylic and composite resin artificial teeth

STATEMENT OF PROBLEM

New types of artificial teeth are commercially available; however, evidence-based information regarding composition and properties is lacking.

PURPOSE

The purpose of this study was to qualify the compositional characteristics and hardness of new commercially available types of acrylic resin and composite resin artificial teeth.

MATERIAL AND METHODS

Twelve brands of 3 types (2 conventional acrylic resins, 3 cross-linked acrylic resins, and 7 composite resins) of artificial teeth were examined. The filler geometry and composition were observed using scanning electron microscopy and energy disperse x-ray analysis, respectively. Vickers hardness was determined for each layer of the polished cross-sectioned teeth. The inorganic content of the enamel layer was determined by thermogravimetric analysis with an ash method. The swelling behavior of the artificial teeth after 12 hours of methyl methacrylate immersion was observed to determine the cross-linking structure. The data were statistically analyzed using 1-way analysis of variance and Tukey's multiple comparison (alpha=.05).

RESULTS

Examined teeth were composed of 2, 3, or 4 layers of resin. Different sizes and shapes of filler were found but were composed only of silicon oxide. Vickers hardness ranged from 17.4 to 47.0 kgf/mm(2). The inorganic content ranged from 0 to 42.8 mass%. The enamel layer of all teeth, except for 3 products, produced negligible swelling, and the base layer of all the teeth, except for 2 products, produced obvious swelling. A significant linear correlation was observed between hardness and inorganic content.

CONCLUSIONS

Within the limitations of this study, differences in size, shape, distribution, and content of the silica filler and the cross-linking nature of the resin matrix were found among the commercial brands of artificial teeth evaluated.

Influence of microwave disinfection on the dimensional stability of intact and relined acrylic resin denture bases

STATEMENT OF PROBLEM

Microwave irradiation has been suggested as a method to disinfect denture bases. However, the effect of microwave heating on the dimensional stability of the relined denture bases is unknown.

PURPOSE

The purpose of this study was to evaluate the dimensional stability of intact and relined acrylic resin denture bases after microwave disinfection.

MATERIAL AND METHODS

A standard brass cast simulating an edentulous maxillary arch was machined and used to fabricate 2- and 4-mm-thick denture bases (n=200), which were processed with heat-polymerized acrylic resin (Lucitone 550). The 2-mm thick-specimens (n=160) were relined with 2 mm of autopolymerizing resin (Tokuso Rebase Fast, Ufi Gel Hard, Kooliner, or New Truliner). Distances between 5 removable pins on the standard brass cast were measured with a Nikon optical comparator, and the area (mm) formed by the distance between 5 pins was calculated and served as baseline. During fabrication, the pins were transferred to the intaglio surface of the specimens. Differences between the baseline area and those subsequently determined for the specimens were used to calculate the percent dimensional changes. The intact and relined denture bases were divided into 4 groups (n=10) and evaluated after: polymerization (control group P); 1 cycle of microwave disinfection (MW); daily microwave disinfection for 7 days (control group MW7); water storage for 7 days (WS7). Microwave irradiation was performed for 6 minutes at 650 W. Data were analyzed using 2-way ANOVA followed by Tukey's test (alpha=.05).

RESULTS

Intact specimens and those relined with Kooliner and New Truliner showed increased shrinkage after 1 (P=.05, .018, and .001, respectively) and 7 (P <.001, .003, and <.001, respectively) cycles of microwave disinfection. With the exception of specimens relined with Kooliner, intact specimens showed greater shrinkage than the relined specimens after 7 cycles of microwave disinfection.

CONCLUSIONS

Microwave disinfection produced increased shrinkage of intact specimens and those relined with New Truliner and Kooliner.

Candida albicans inactivation and cell membrane integrity damage by microwave irradiation

In indicating the microwave irradiation for disinfecting dentures it is necessary to see how this procedure influences Candida albicans integrity and viability. The aim of this study was to evaluate the ability of microwaves to inactivate C. albicans and damage cell membrane integrity. Two 200-ml C. albicans (ATCC 10231) suspensions were obtained. A sterile denture was placed in a beaker containing the Experimental (ES) or the Control suspension (CS). ES was microwaved at 650 W for 6 min. Suspensions were optically counted using methylene blue dye uptake as indicative of membrane-damaged cells; spread on Agar Sabouraud dextrose (ASD) for viability assay; or spectrophotometrically measured at 550 nm. Cell-free solutions were submitted to content analyses of protein (Bradford and Pyrogallol red methods); Ca++ (Cresolftaleine complexone method); DNA (spectrophotometer measurements at 260 nm) and K+ (selective electrode technique). Data were analysed by Student's t- or Wilcoxon z-tests (alpha = 0.05). All ES cells demonstrated cell membrane damage. Viable cells were non-existent in the ES ASD plates. No significant difference in optical density between ES and CS was observed (P=0.272). ES cells released significantly high protein (P<0.001, Bradford; P=0.005, Pyrogallol red), K+ (P<0.001), Ca++ (P=0.012) and DNA (P=0.046) contents. Microwaves inactivated C. albicans and damaged cell membrane integrity.