Effects of chemical disinfectants on the transverse strength of denture base acrylic resins

Effects of simulated long-term exposure to bottled, neutral pH electrolyzed oxidizing water on the properties of denture base resins

STATEMENT OF PROBLEM

Denture stomatitis can pose serious health risks, especially to older people. Chemical denture cleaning agents must be effective, yet not adversely affect the longevity of removable dentures. Ready-to-use (RTU) neutral pH electrolyzed oxidizing water (EOW) is an effective biocide against Candida albicans biofilms on denture resins, but the effects of daily disinfection with EOW on the physical and mechanical properties of resins have not been established.

PURPOSE

The purpose of this in vitro study was to investigate the effects of simulated long-term exposure to RTU EOW on the color, surface characteristics, and flexural strength of denture base resins.

MATERIAL AND METHODS

Heat-polymerized (HP), 3D printed (3D) and computer-aided design and computer-aided manufacture (CAD-CAM)-milled (CC) denture resin specimens (square: 20×20×3.3 mm; beam: 64×10×3.3 mm) were immersed in tap water (TW), RTU EOW (Neutral Anolyte ANK; Envirolyte; EOW), or a commercial denture cleaning tablet solution (Polident 3-Minute; Glaxo SmithKline; PD), mimicking a 5-minute once daily disinfection routine performed up to 3.0 years. Color and surface roughness were recorded (n=3, squares), and changes in color (∆E00) and surface roughness (∆Ra) were calculated. Flexural strength (n=12, beams) and surface hardness (n=18, beams) were measured with a universal testing machine. The fractured surfaces of specimens were examined by scanning electron microscopy and energy dispersive spectroscopy. Data were assessed by performing the Shapiro-Wilk or D'Agostino and Pearson normality tests. Two-way ANOVA or the Kruskal-Wallis test with a post hoc Tukey HSD or Dunn multiple comparisons (α=.05) was used for statistical analyses.

RESULTS

No significant changes were found in either color or surface roughness for HP, 3D, and CC resins after 1.5-year and 3.0-year immersion in any of the agents (P>.05). The surface hardness of 3D resins reduced by 14% with TW and by 23% with EOW and PD at 3.0 years. The flexural strengths of all 3 resins were unaffected by 3.0-year immersion (P>.05).

CONCLUSIONS

Simulated long-term immersion disinfection with RTU neutral pH EOW did not adversely affect the physical and mechanical properties of HP or CC denture resins.

Effects of disinfectants on physical properties of denture base resins: A systematic review and meta-analysis

STATEMENT OF PROBLEM

The disinfection of removable dental prostheses and orthodontic appliances is essential to preventing transmission of pathogens. However, whether different disinfection solutions and durations affect the physical properties of denture base resins is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to statistically analyze the influence of disinfectants on the physical properties of denture base resins.

MATERIAL AND METHODS

A systematic search in Medline, Embase, PubMed, and Cochrane Library databases was conducted to evaluate the effects of chemical disinfection on the physical properties of denture base resins such as surface morphology, roughness, hardness, and flexural strength. Of 1909 studies, 44 studies were included in the systematic review and 41 in the meta-analysis. Heterogeneity was analyzed by using I2 statistics. The influence of different disinfection solutions and durations on the physical properties was further analyzed, and the risk of bias evaluated. Statistical analyses were performed by using the RevMan 5.4 software program with the standardized mean differences (SMDs) and 95% confidence intervals (CIs).

RESULTS

Of the 44 included studies, 40 studies were assessed as having a low risk of bias, and 4 had an unclear risk of bias. Meta-analysis results showed that compared with the control, disinfection could not significantly affect surface roughness and hardness within 60 minutes of immersion in disinfectant solutions or flexural strength within 30 minutes (roughness: P=.79, I2=0%; flexural strength: P=.08, I2=0%; hardness: P=.05, I2=19%). In addition, the physical properties were not significantly affected when glutaraldehyde, chlorhexidine, and peracetic acid were repeatedly used for more than 30 minutes.

CONCLUSIONS

Most of the disinfectants did not reduce the physical properties of denture base resin within 30 minutes of immersion. Glutaraldehyde, chlorhexidine, and peracetic acid are recommended if longer immersion or repeated disinfection is required.

Effects of Denture Cleansers on the Flexural Strength of PMMA Denture Base Resin Modified with ZrO2 Nanoparticles

PURPOSE

The additions of zirconium oxide nanoparticles (nano-ZrO₂ ) to denture base materials have produced nanocomposites with satisfactory properties, although there is a lack of research investigating the effects of denture cleansers on these materials. This study aimed to evaluate the effect of denture cleansers on the flexural strength of denture base materials modified with nano-ZrO₂ .

MATERIALS AND METHODS

A total of 270 specimens were fabricated from pure and nano-ZrO₂ reinforced acrylic resins at 2.5% and 5%, resulting in 3 main groups. The groups were further divided into subgroups (n = 10) according to immersion solution (distilled water, Corega, sodium hypochlorite, and Renew) and immersion duration. Flexural strength was measured at baseline (T₀ ) in distilled water and after 180 and 365 days of immersion (T₁ and T₂ ) in denture cleansers. Data were collected and analyzed using repeated measure ANOVA and Bonferroni post hoc tests (α = 0.05).

RESULTS

The flexural strength of the nano-ZrO₂ modified denture base material decreased significantly after immersion in different denture cleansers at different immersion durations in comparison to baseline (T₀ ) (p < 0.001). Sodium hypochlorite showed the highest reduction in flexural strength followed by Corega, while Renew cleansing solution resulted in the least change.

CONCLUSION

Denture cleansers can significantly affect the flexural strength of nano-ZrO₂ modified denture base materials and thus should be used cautiously.

Effect of Disinfectants on Mechanical Properties of Orthodontic Acrylics

Objective

Infection control protocols in dentistry dictate that orthodontic acrylics have to be disinfected. No specific products for orthodontic acrylics are available. The objective of this study was to investigate the influence of chemical disinfectants on mechanical properties of orthodontic acrylics.

Materials and Methods

260 test specimens of two cold-curing orthodontic acrylics were manufactured. Three chemical disinfecting agents were tested: Impresept, D050 Instru-Gen, and Stammopur DR. Test specimens were stored in distilled water and divided into test groups. E-Modulus, flexural strength, macro hardness, micro hardness, average roughness, and colour change were measured.

Results

Disinfection agents showed no significant influence on E-modulus. Values ranged from 1783.80 ± 163.80 MPa (Forestacryl colourless) to 2474.00 ± 135.00 MPa (Orthocryl green) after storage in distilled water. Disinfection agents performed no significant influence on flexural strength. Values ranged from 18.64±1.59 N/mm² (Forestacryl colourless) to 25.64 ± 1.43 N/mm² (Orthocryl green) after storage in distilled water. Orthocryl colourless showed a reduction of the macro hardness after disinfection (Stammopur DR (p≤0.001), D050 Instru-Gen (p≤0.037)). Disinfection of Orthocryl green with D050 Instru-Gen (p<0.001) and Forestacryl colourless with Impresept (p≤0.001) led to a reduction of macro hardness. Micro hardness of Orthocryl colourless altered significantly after disinfection with D050 Instru-Gen (p≤0.001). Micro hardness of Forestacryl colourless increased (Impresept (p≤0.039)) and decreased (Stammopur DR (p≤0.006) Instru-Gen (p≤0.001)) after disinfection. Average roughness did not change significantly (Orthocryl colourless). Forestacryl colourless performed a significant change after disinfection with Stammopur DR (p≤0.05). This is also true for the disinfection of Orthocryl green and Forestacryl pink with Instru-Gen (p≤0.05). Disinfection performed no significant influence on colour change. ΔE-values were in a range of 1 to 2.

Conclusions

Some orthodontic acrylics disinfection caused significant changes of determined parameters. Changes were specific for the applied disinfectant and tested orthodontic acrylic. Further studies should verify the impact of long-term disinfection intervals. Thus, from manufacturers of orthodontic acrylics recommendations for appropriate disinfectants would be desirable.

Effects of nonaldehyde immersion disinfection on the mechanical properties of flexible denture materials

STATEMENT OF PROBLEM

Variation in the baseline mechanical properties of polyamide thermoplastic polymers used in the fabrication of prosthetic dental appliances and the effects of nonaldehyde disinfectants on the mechanical properties of these polymers are unclear.

PURPOSE

The purpose of this in vitro study was to compare the flexural and impact strengths of 2 flexible denture materials (Valplast and Sunflex) and evaluate the effect of 24-hour immersion in nonaldehyde disinfectant (Perform) on their flexural and impact strengths.

MATERIAL AND METHODS

Of 48 specimens of Valplast and Sunflex, half were immersed in nonaldehyde disinfectant solution containing the active ingredient 2% peroxymonosulfate for 24 hours. Flexural and impact strengths were measured using a universal testing machine. The Student t test with Bonferroni correction was used (α=.008).

RESULTS

For the Valplast group, the mean ±standard deviation flexural strength was 27.8 ±0.57 MPa, and the impact strength was 3.5 ±0.98 kJ/m². For the Sunflex group, the mean flexural strength was 57.4 ±4.09 MPa, and the impact strength was 6.0 ±3.11 kJ/m². Sunflex showed greater flexural strength (P≤.001) and impact strength (P=.001) than Valplast. A significant increase in the impact strength (P≤.001) but not in the flexural strength of Valplast was observed after exposure to the disinfectant solution. Immersion disinfection had no significant effect on the strength of Sunflex.

CONCLUSIONS

The flexural and impact strengths of Sunflex were significantly greater than those of Valplast. Immersion disinfection with peroxymonosulfate had no significant effect on Sunflex but increased the impact strength of Valplast.

Impact of Denture Cleansing Solution Immersion on Some Properties of Different Denture Base Materials: An In Vitro Study

PURPOSE

To evaluate the effect of several denture cleansing solutions on the color stability, surface roughness, and flexural strength of three denture base materials.

MATERIALS AND METHODS

Twenty-seven specimens were prepared using heat-polymerized (HP) denture base material, 27 using autopolymerized (AP) denture base material, and 27 using visible-light-polymerized (VLP) denture base, creating a total of 81 specimens. The specimens were randomly divided into three groups (n = 27): the distilled water group (DWG), Corega group (CG), and Renew group (RG). Color changes (ΔE), surface roughness (Ra, nm), and flexural strength (MPa) of each specimen were measured using a spectrophotometer, an optical profilometer, and a universal testing machine, respectively. The results were statistically analyzed using a one-way ANOVA and a post hoc Tukey's test (α = 0.05).

RESULTS

The only statistically significant color change detected was in the VLP resin treated with Corega and Renew. There was a significant increase in the surface roughness of all denture resin groups after immersion in Corega. Immersion in Renew significantly increased surface roughness only in the HP and AP specimens. The only significant reduction in flexural strength was detected in the HP resin after immersion in Corega (p < 0.05).

CONCLUSIONS

Within the limitations of this study, it can be concluded that Corega has a significantly greater negative impact than distilled water on the flexural strength of HP resin base materials. Renew significantly increased the surface roughness of AP and HP, while Corega increased the surface roughness of all resin materials.

Effects of Denture Cleansers on Heat-Polymerized Acrylic Resin: A Five-Year-Simulated Period of Use

This study evaluated color stability, surface roughness and flexural strength of acrylic resin after immersion in alkaline peroxide and alkaline hypochlorite solutions, simulating a five-year-period of use. Sixty disc-shaped (16 x 4 mm) and 60 rectangular specimens (65 x 10 x 3.3 mm) were prepared from heat-polymerized acrylic resin (Lucitone 550) and assigned to 3 groups (n = 20) of immersion (20 min): C1: distilled water; AP: warm water and one alkaline peroxide tablet; SH: 0.5% NaOCl solution. Color data (∆E) were determined by a colorimeter and also quantified according to the National Bureau of Standards units. A rugosimeter was used to measure roughness (μm) and the flexural strength (MPa) was measured using a universal testing machine. Data were evaluated by Kruskal-Wallis followed by Dunn tests (color stability and surface roughness) and by one-way ANOVA and Bonferroni test (flexural strength). For all tests was considered α = 0.05. AP {0.79 (0.66;1.42)} caused color alteration significantly higher than C1 {0.45 (0.37;0.57)} and SH {0.34 (0.25;0.42)}. The mean ∆Ε values quantified by NBS were classified as "trace" for C1 (0.43) and SH (0.31) and "slight" for AP (0.96). SH {-0.015 (-0.023;0.003)} caused significantly higher ΔRa than the C1 {0.000 (-0.004;0.010)} and AP {0.000 (-0.009;0.008)} groups. There was no statistically significant difference among the solutions for flexural strength (C1: 84.62 ± 16.00, AP: 85.63 ± 12.99, SH: 84.22 ± 14.72). It was concluded that immersion in alkaline peroxide and NaOCl solutions simulating a five-year of 20 min daily soaking did not cause clinically significant adverse effects on the heat-polymerized acrylic resin.

Effects of fluconazole, chlorhexidine gluconate, and silver-zinc zeolite on flexural strength of heat-cured polymethyl methacrylate resin

Aim:

We evaluated the effect of incorporating Fluconazole, Chlorhexidine Gluconate, and Silver-Zinc Zeolite as bioactive materials (10% of mass) on the flexural strength of commercially available heat-cured polymethyl methacrylate (PMMA; Travelon).

Materials and Methods:

The following four groups were compared; Group 1: Control group with pure PMMA, Group 2: Antibacterial drug group with chlorhexidine gluconate in powder form + PMMA, Group 3: Antifungal drug group with fluconazole in powder form + PMMA, Group 4: Antimicrobial agent group with silver zinc zeolite in powder form + PMMA. After processing, the specimens were subjected for flexural strength testing using three-point bending test in a universal testing machine.

Results:

A significant (P < 0.0001) decrease in flexural strength following incorporation of Fluconazole, Chlorhexidine Gluconate, and Silver-Zinc Zeolite to heat polymerized acrylic resin was observed when compared with the control group. The decrease in mean flexural strength was minimal in the fluconazole group.

Conclusion:

Although the addition of a bioactive material to PMMA acrylic is desirable, it is not practical as it reduces flexural strength of the acrylic base.

Influence of a new denture cleaning technique based on photolysis of H(2)O(2) the mechanical properties and color change of acrylic denture base resin

The purpose of this study was to evaluate the influence of a disinfection technique based on photolysis of H2O2 on the mechanical properties and color change of acrylic denture base resin. Resin specimens were immersed in 1 M H2O2 irradiated with light-emitting diode (LED) light at 400 nm for 1 week. The immersion duration of 1 week (168 h) corresponded to performing approximately 500 times of 20-min cleaning. Hydroxyl radicals are potent oxidants and they were generated via the photolysis of H2O2. Oxidative damage caused by these radicals included reduced flexural strength and altered color for the acrylic resin. Nonetheless, the degraded flexural strength and altered color of acrylic resin after 500 times of cleaning in the disinfection system would be within clinically acceptable levels.

Effect of green tea extract and mouthwash without alcohol on Candida albicans biofilm on acrylic resin

OBJECTIVE

To evaluate the effect of aqueous extract of green tea and the oral antiseptic without alcohol, on Candida albicans biofilm formation to heat-curing acrylic resin plates.

BACKGROUND

Candida is associated with oral candidiasis in poorly cleaned dentures.

MATERIAL AND METHODS

Standardised specimens of heat-cured (Conv; n = 30) or microwave-cured acrylic resin (Mw; n = 30) were obtained and divided into six groups (n = 10): G1 = Conv resin and green tea aqueous extract, G2 = Conv resin and mouthwash, G3 = control of Conv resin, G4 = Mw resin and green tea aqueous extract, G5 = Mw resin and mouthwash and G6 = control of Mw-cured resin. The specimens were contaminated with 10 ml of Sabouraud dextrose broth inoculated with 0.1 ml of standard suspension containing 1 × 10(6) cells/ml of C. albicans and incubated for 24 h at 37°C. After this period, they were immersed in the aqueous extract or in mouthwash for 15 min. The control groups were treated with sterile distilled water. Aliquots of 0.1 ml were plated on Sabouraud dextrose agar and incubated at 37°C for 24 h. The numbers of colony-forming units per test specimen (CFU/TS) were calculated, and the results statistically analysed by two-way anova and Tukey's tests (5%).

RESULTS

Statistically significant difference was observed for the aqueous extract groups (G1; 33.65%) and mouthwash (G2; 17.06%), when compared to control (G3; 100%), for Conv resin. For the Mw resin, there was significant difference between mouthwash (G5; 43.16%) and control (G6; 100%).

CONCLUSION

The aqueous extract of green tea and mouthwash led to a reduction in the number of viable fungal cells in biofilm formed on acrylic resin.

Color Stability, Surface Roughness and Flexural Strength of an Acrylic Resin Submitted to Simulated Overnight Immersion in Denture Cleansers

This study evaluated color stability, surface roughness and flexural strength of acrylic resin specimens after immersion in alkaline peroxide and alkaline hypochlorite, simulating a period of one and a half year of use of overnight immersion. Sixty disc-shaped (16X4 mm) and 80 rectangular specimens (65X10X3.3 mm) were prepared from heat-polymerized acrylic resin (Lucitone 550) and distributed into 4 groups (n=20): C1: without immersion, C2: 8 h immersion in distilled water; AP: 8 h immersion in alkaline peroxide effervescent tablet; SH: 8 h immersion in 0.5% NaOCl solution. Properties were evaluated at baseline and after the immersion. Color data were also calculated according the National Bureau of Standards (NBS). Results were analyzed statistically by ANOVA and Tukey's HSD test (α=0.05). AP (2.34 ± 0.41) caused color alteration significantly higher than C2 (0.39 ± 0.30) and SH (1.73 ± 0.52). The mean ΔE values were classified as indicial for C2 (0.36 ± 0.29) and noticeable for AP (2.12 ± 0.39) and SH (1.59 ± 0.48). SH (0.0195 ± 0.0150) caused significantly higher ΔRa (p=0.000) than the C2 (0.0005 ± 0.0115) and PA (0.0005 ± 0.0157) groups. There was no statistically significant difference (p=0.063) among the solutions for flexural strength (C1: 105.43 ± 14.93, C2: 100.30 ± 12.43, PA: 97.61 ± 11.09, SH: 95.23 ± 10.18). In conclusion, overnight immersion in denture cleansing solutions simulating a year and a half of use did not alter the flexural strength of acrylic resin but caused noticeable color alterations, higher for alkaline peroxide. The 0.5% NaOCl solution caused increase in surface roughness.

Comparison of physical and mechanical properties of microwave-polymerized acrylic resin after disinfection in sodium hypochlorite solutions

This study evaluated the color stability, surface roughness and flexural strength of a microwave-polymerized acrylic resin after immersion in sodium hypochlorite (NaOCl), simulating 20 min of disinfection daily during 180 days. Forty disk-shaped (15 x 4 mm) and 40 rectangular (65 x 10 x 3 mm) specimens were prepared with a microwave-polymerized acrylic resin (Onda-Cryl). Specimens were immersed in either 0.5% NaOCl, 1% NaOCl, Clorox/Calgon and distilled water (control). Color measurements were determined by a portable colorimeter. Three parallel lines, separated by 1.0 mm, were registered on each specimen before and after immersion procedures to analyze the surface roughness. The flexural strength was measured using a 3-point bending test in a universal testing machine with a 50 kgf load cell and a crosshead speed of 1 mm/min. Data were analyzed statistically by ANOVA and Tukey's test (?=0.05). There was no statistically significant differences (p>0.05) among the solutions for color, surface roughness and flexural strength. It may be concluded that immersion in NaOCl solutions simulating short-term daily use during 180 days did not influence the color stability, surface roughness and flexural strength of a microwave-polymerized acrylic resin.

Efficacy of denture disinfection methods in controlling Candida albicans colonization in vitro

OBJECTIVE

The aim of this study was to rank 10 denture disinfection methods according to their efficacy in reducing Candida albicans (C. albicans) colonization on soft denture relining material.

MATERIAL AND METHODS

Circular specimens (diameter 8 mm) were made of soft denture relining material (Mucopren E, Kettenbach) and thermally aged. Specimens were incubated with C. albicans (strain 1386, DSMZ) followed by 1 of 10 disinfection procedures (6 soaks, 2 microwave irradiation regimes, 1 effervescent commercial cleansing product, and denture left dry overnight). Incubation with phosphate buffered saline (PBS) served as a control. Adhering fungi were quantified using a bioluminometric assay in combination with an automated plate reader for cell quantification. Scanning electron micrographs (SEMs) were made for validation.

RESULTS

Low median luminescence intensities indicated the presence of a few viable fungi after the soaking of specimens in sodium hypochlorite (10 relative luminescence units (rlu)), microwave irradiation immersed in water (8 rlu), and application of effervescent cleansing tabs (22 rlu). No statistically significant difference (p>0.05) to control PBS (200 rlu) was found after immersion in hydrogen peroxide (172 rlu), glutaraldehyde (103 rlu), household vinegar (196 rlu), Listerine coolmint (194 rlu), Plax (222 rlu), dry microwave irradiation (221 rlu) and specimens left dry overnight (165 rlu). SEM displayed C. albicans monolayers with different morphologic forms on each surface investigated.

CONCLUSIONS

Only soaking in sodium hypochlorite (1%; 10 min), microwave irradiation immersed in water (800 W; 6 min), and application of effervescent cleansing tabs (Blend-a-dent tabs; 10 min) proved to be effective against C. albicans colonization on soft denture relining material.

In-vivo evaluation of the bacterial contamination and disinfection of acrylic baseplates of removable orthodontic appliances

INTRODUCTION

This randomized clinical trial assessed, by using microbial culture and scanning electron microscopy (SEM), the contamination by mutans streptococci (MS) colonies/biofilms on acrylic baseplates of removable orthodontic appliances and evaluated the efficacy of antimicrobial sprays (Periogard [Colgate-Palmolive Ind. Brasileira, Osasco, SP, Brazil], Cepacol [Merrell Lepetit Farmacêutica e Industrial Ltda, Santo Amaro, SP, Brazil], and sterile tap water [control]) on their disinfection.

METHODS

Seventeen children were randomly enrolled in a 3-stage changeover system with a 1-week interval between each stage. All solutions were used in all stages by a different group of children. The acrylic baseplates were worn full time except at meals. At the end of each week of the trial, the baseplates were submitted to a randomized disinfection protocol and were sent for microbiologic analysis. New baseplates were constructed, and the same sequence of procedures was repeated 2 more times. Acrylic baseplates representing each test solution were examined by SEM. The Friedman test assessed differences at the 5% significance level among the solutions for MS biofilm formation on acrylic surface.

RESULTS

Cepacol and Periogard reduced the formation of MS colonies/biofilms, and both solutions differed statistically from sterile tap water (P <.001). However, Periogard was significantly more effective against MS than Cepacol (P <.001). When MS colonies/biofilms were detected on acrylic surfaces under stereomicroscopy, this was confirmed with SEM.

CONCLUSIONS

Acrylic baseplates of removable orthodontic appliances worn by children were contaminated by MS colonies/biofilms in all cases after 1 week. Although Cepacol had better results than sterile tap water, spraying with Periogard showed significantly greater efficacy in reducing MS colonies/biofilms on acrylic surfaces.

Bond strength of hard chairside reline resins to a rapid polymerizing denture base resin before and after thermal cycling

PURPOSE

This study assessed the shear bond strength of 4 hard chairside reline resins (Kooliner, Tokuso Rebase Fast, Duraliner II, Ufi Gel Hard) to a rapid polymerizing denture base resin (QC-20) processed using 2 polymerization cycles (A or B), before and after thermal cycling.

MATERIALS AND METHODS

Cylinders (3.5 mm x 5.0 mm) of the reline resins were bonded to cylinders of QC-20 polymerized using cycle A (boiling water-20 minutes) or B (boiling water; remove heat-20 minutes; boiling water-20 minutes). For each reline resin/polymerization cycle combination, 10 specimens (groups CAt e CBt) were thermally cycled (5 and 55 degrees C; dwell time 30 seconds; 2,000 cycles); the other 10 were tested without thermal cycling (groups CAwt ad CBwt). Shear bond tests (0.5 mm/min) were performed on the specimens and the failure mode was assessed. Data were analyzed by 3-way ANOVA and Newman-Keuls post-hoc test (alpha=.05).

RESULTS

QC-20 resin demonstrated the lowest bond strengths among the reline materials (P<.05) and mainly failed cohesively. Overall, the bond strength of the hard chairside reline resins were similar (10.09+/-1.40 to 15.17+/-1.73 MPa) and most of the failures were adhesive/cohesive (mixed mode). However, Ufi Gel Hard bonded to QC-20 polymerized using cycle A and not thermally cycled showed the highest bond strength (P<.001). When Tokuso Rebase Fast and Duraliner II were bonded to QC-20 resin polymerized using cycle A, the bond strength was increased (P=.043) after thermal cycling.

CONCLUSIONS

QC-20 displayed the lowest bond strength values in all groups. In general, the bond strengths of the hard chairside reline resins were comparable and not affected by polymerization cycle of QC-20 resin and thermal cycling.

Contemporary Methods of Labeling Dental Prostheses?A Review of the Literature

Forensic identification (ID) based on an assessment of the dentition is commonplace. However, despite an increase in the oral health of Western populations, there are still many millions of individuals who are edentulous and whom have been treated with completed dentures. In the United Kingdom alone over 300,000 patients are rendered edentulous each year. In order to facilitate the ID of such individuals a number of forensic and governmental organizations have recommended that dentures be labeled. A number of labeling systems exist which can be broadly separated into inclusion systems, marking systems, and novel methods. Each of the commonly described systems are demonstrated with an assessment of their strengths and weaknesses. It is recommended that an inclusion denture marker, preferably metallic, should be used in order to withstand the most common postmortem assaults.

Effect of Disinfectants on the Hardness and Roughness of Reline Acrylic Resins

PURPOSE

Potential effects on hardness and roughness of a necessary and effective disinfecting regimen (1% sodium hypocholorite and 4% chlorhexidine) were investigated for two hard chairside reline resins versus a heat-polymerizing denture base acrylic resin.

MATERIALS AND METHODS

Two standard hard chairside reliners (Kooliner and Duraliner II), one heat-treated chairside reliner (Duraliner II +10 minutes in water at 55 degrees C), and one standard denture base material (Lucitone 550) were exposed to two disinfecting solutions (1% sodium hypochlorite; 4% chlorhexidine gluconate), and tested for two surface properties [Vickers hardness number (VHN, kg/mm(2)); Roughness (Ra, microm)] for different times and conditions (1 hour after production, after 48 hours at 37 +/- 2 degrees C in water, after two disinfection cycles, after 7 days in disinfection solutions, after 7 days in water only). For each experimental condition, eight specimens were made from each material. Data were analyzed by analysis of variance followed by Tukey's test, and Student's t-test (p= 0.05).

RESULTS

For Kooliner (from 6.2 +/- 0.3 to 6.5 +/- 0.5 VHN) and Lucitone 550 (from 16.5 +/- 0.4 to 18.4 +/- 1.7 VHN), no significant changes in hardness were observed either after the disinfection or after 7 days of immersion, regardless of the disinfectant solution used. For Duraliner II (from 4.0 +/- 0.1 to 4.2 +/- 0.1 VHN), with and without heat treatment, a small but significant increase in hardness was observed for the specimens immersed in the disinfectant solutions for 7 days (from 4.3 +/- 0.2 to 4.8 +/- 0.5 VHN). All materials showed no significant change in roughness (Kooliner: from 0.13 +/- 0.05 to 0.48 +/- 0.24 microm; Duraliner II, with and without heat treatment: from 0.15 +/- 0.04 to 0.29 +/- 0.07 microm; Lucitone 550: from 0.44 +/- 0.19 to 0.49 +/- 0.15 microm) after disinfection and after storage in water for 7 days.

CONCLUSIONS

The disinfectant solutions, 1% sodium hypochlorite and 4% chlorhexidine gluconate, caused no apparent damage on hardness and roughness of the materials evaluated.

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.

Hardness of heat-polymerized acrylic resins after disinfection and long-term water immersion

STATEMENT OF THE PROBLEM

In selecting a disinfectant for dental prostheses, compatibility between the disinfectant and the type of denture base material must be considered to avoid adverse effects on the hardness of the acrylic resin.

PURPOSE

This study investigated the hardness of 2 denture base resins after disinfection and long-term water immersion.

MATERIAL AND METHODS

Thirty-two disk-shaped specimens (13 mm in diameter and 8 mm thick) were fabricated from each resin (Lucitone 550 and QC-20), polished, stored in water at 37 degrees C for 48 hours, and submitted to hardness tests (Vickers hardness number [VHN]) before disinfection. Disinfection methods included scrubbing with 4% chlorhexidine gluconate for 1 minute, immersion for 10 minutes in 1 of the tested disinfectant solutions (n=8) (3.78% sodium perborate, 4% chlorhexidine gluconate, or 1% sodium hypochorite), and immersion in water for 3 minutes. The disinfection procedures were repeated 4 times, and 12 hardness measurements were made on each specimen. Control specimens (not disinfected) were stored in water for 56 minutes. Hardness tests (VHN) were also performed after 15, 30, 60, 90, and 120 days of storage in water. Statistical analyses of data were conducted with a repeated measures 3-way analysis of variance (ANOVA) and Tukey post-hoc test (alpha=.05).

RESULTS

Mean values +/- SD for Lucitone 550 (16.52 +/- 0.94 VHN) and QC-20 (9.61 +/- 0.62 VHN) demonstrated a significant (P <.05) decrease in hardness after disinfection, regardless of material and disinfectant solutions used (Lucitone 550: 15.25 +/- 0.74; QC-20: 8.09 +/- 0.39). However, this effect was reversed after 15 days of storage in water. Both materials exhibited a continuous increase (P <.05) in hardness values for up to 60 days of water storage, after which no significant change was observed.

CONCLUSION

Within the limitations of this in vitro study, QC-20 and Lucitone 550 specimens exhibited significantly lower hardness values after disinfection regardless of the disinfectant solution used.