Effect of disinfection and storage on the flexural strength of ocular prosthetic acrylic resins

doi: 10.1111/j.1741‐2358.2011.00570.x Effect of disinfection and storage on the flexural strength of ocular prosthetic acrylic resins Objective: To evaluate the influence of chemical disinfection and storage duration on the flexural strength of acrylic resins commonly used to make ocular prostheses. Methods: A total of 260 samples were manufactured with N1 resin and colourless resin. Both resins were thermopolymerised using a microwave oven. Samples were stored and periodically disinfected and were divided into groups: control (no disinfection) (I), neutral soap (II), Opti‐free (III), Efferdent (IV), 1% hypochlorite (V) or 4% chlorhexidine (VI). The flexural strength was measured before and after 60 and 120 days of storage. Data were analysed by anova and Tukey test (0.05). Results: The flexural strength of the N1 resin was higher than that for the colourless resin. There was a significant difference in the flexural strength before and after 60 and 120 days of storage with disinfection, regardless of the resin and disinfectant. Group I in the initial period exhibited greater flexural strength, with significant difference only in group VI after 120 days. Conclusion: It can be concluded that the flexural strength only changed after 120 days of storage for samples disinfected with chlorhexidine. However, all flexural strength values obtained herein were acceptable clinical limits for the acrylic resins.     

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

doi: 10.1111/j.1741‐2358.2011.00520.x 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.     

Influence of artificial accelerated ageing on the colour stability of paints used for ocular prosthesis iris painting

doi: 10.1111/j.1741‐2358.2010.00473.x
Influence of artificial accelerated ageing on the colour stability of paints used for ocular prosthesis iris painting Objectives: To evaluate the colour stability of paints used for ocular prosthesis iris painting submitted for accelerated artificial ageing (AAA). Materials and methods: Forty specimens of acrylic resin for sclera (16 × 2 mm) were made and separated into eight groups (n = 10) according to the type of paint (gouache, GP; oil, OP; acrylic AP; and composite resin for characterisation, CR) and the colours used (blue/brown). After drying (72 h), a new layer of colourless acrylic resin was applied and the initial colour readout was performed (Spectrophotometer PCB 6807). New colour readouts were performed after AAA, and ΔE was calculated. Results: Statistical analysis (two‐way anova –Bonferroni, p < 0.05) demonstrated that the brown colour showed lower ΔE means in comparison with the blue colour, with statistically significant difference for AP only. Blue colour showed no statistically significant difference with regard to the type of paint used. Brown AP showed lower ΔE than the other groups, with significant difference for OP and GP. GP showed greater alteration in ΔE for the brown colour, being statistically similar only to OP. Conclusions: Only the AP group for brown pigment shows clinically acceptable values for colour stability after AAA.     

Effect of the physical properties of acrylic resin of overnight immersion in sodium hypochlorite solution

doi:10.1111/j.1741‐2358.2009.00336.x
Effect of the physical properties of acrylic resin of overnight immersion in sodium hypochlorite solution Objectives: This study evaluated colour stability, surface roughness and flexural strength of microwave‐polymerised acrylic resin after overnight immersion in sodium hypochlorite, simulating 180 days use. Materials and methods: Forty disc‐shaped (15 mm × 4 mm) and 40 rectangular specimens (65 mm × 10 mm × 3 mm) were prepared from microwave‐polymerised acrylic resin. The specimens were immersed in 0.5, 1% sodium hypochlorite, Clorox/Calgon and distilled water. Colour measurements (ΔE) were determined by a portable colorimeter. A surface analyser was used to measure roughness (μm). The flexural strength (MPa) was measured using a three‐point bending test in a universal testing machine. Data were evaluated by one‐way anova , followed by Student–Newman–Keuls test (α = 0.05). Results: Statistical analysis found significantly higher colour changes (SNK, p < 0.001) for the 1% sodium hypochlorite, but mean ΔE value quantified by National Bureau of Standards was classified as slight. When comparing the surface roughness, no statistical significance was found among the solutions (anova , p = 0.637). The 1% sodium hypochlorite presented significantly lower flexural strength compared with the control group (SNK, p = 0.034). Conclusion: It was concluded that immersion in 1% sodium hypochlorite solutions for 8 h does influence the colour stability and flexural strength of microwave‐polymerised acrylic resin, during the simulated period of 180 days.     

Effect of thermal cycling and disinfection on colour stability of denture base acrylic resin

doi: 10.1111/j.1741‐2358.2012.00676.x Effect of thermal cycling and disinfection on colour stability of denture base acrylic resin Objectives: The purpose of this study was to investigate the effect of thermal cycling and disinfection on the colour change of denture base acrylic resin. Materials and Methods: Four different brands of acrylic resins were evaluated (Onda Cryl, QC 20, Classico and Lucitone). All brands were divided into four groups (n = 7) determined according to the disinfection procedure (microwave, Efferdent, 4% chlorhexidine or 1% hypochlorite). The treatments were conducted three times a week for 60 days. All specimens were thermal cycled between 5 and 55°C with 30‐s dwell times for 1000 cycles before and after disinfection. The specimens’ colour was measured with a spectrophotometer using the CIE L*a*b* system. The evaluations were conducted at baseline (B), after first thermal cycling (T₁), after disinfection (D) and after second thermal cycling (T₂). Colour differences (ΔE) were calculated between T₁ and B (T₁B), D and B (DB), and T₂ and B (T₂B) time‐points. Results: The samples submitted to disinfection by microwave and Efferdent exhibited the highest values of colour change. There were significant differences on colour change between the time‐points, except for the Lucitone acrylic resin. Conclusions: The thermal cycling and disinfection procedures significantly affected the colour stability of the samples. However, all values obtained for the acrylic resins are within acceptable clinical parameters.     

Bond strength of denture teeth to acrylic resin: effect of thermocycling and polymerisation methods

Background: Failure of bonding between acrylic resin teeth and denture base material is a considerable problem for patients who wear complete dentures. Objective: The purpose of this study was to evaluate the bond strength between acrylic resins and resin denture teeth with different thermocycling and polymerisation methods. Materials and methods: Microwave‐polymerised (Onda‐Cryl), heat‐polymerised (Clássico) and autopolymerising (Jet) acrylic resins and resin denture tooth (Biotone) were used. The acrylic resins were polymerised according to the following: (A) microwave – fast cycle, Onda‐Cryl; (B) microwave – long cycle, Onda‐Cryl; (C) microwave – manufacturer’s cycle, Onda‐Cryl; (T) water bath – long cycle, Clássico; and (Q) bench polymerisation cycle, Jet. Twenty specimens were prepared for each polymerisation method. Ten were thermocycled, and 10 did not receive thermocycling. For the purpose of the study, a shear test was used. Data were analysed with the Kruskal–Wallis test and Dunn’s multiple comparisons test (p = 0.05). Results: Cycles B, C and T were similar (p > 0.05), and had statistically higher bonding values than cycles A and Q (p < 0.05) for the thermocycled and non‐thermocycled groups. For all cycles, there were no statistically significant differences between thermocycled and non‐thermocycled groups (p > 0.05), except for cycle Q (p = 0.0038). Conclusion: Thermocycling decreased the bond strength, but not significantly for microwave and heat‐polymerised cycles. Regarding the bond strength of denture teeth to acrylic resin, the fast microwave polymerisation cycle should be avoided when polymerising Onda‐Cryl acrylic resin. In addition, Jet acrylic resin is not adequate for use in denture repair.     

Effect of monomer treatment and polymerisation methods on the bond strength of resin teeth to denture base material

Background: The fracture between acrylic denture base material and artificial teeth is a common clinical occurrence in dental prosthodontic practice. Objective: To evaluate the bond strength between acrylic resins and resin denture teeth when submitted by two protocols of monomer liquid application on the tooth surface and using different polymerisation methods. Material and methods: Microwave‐polymerised (Onda‐Cryl), heat‐polymerised (Clássico) and autopolymerising (Jet) acrylic resins and a brand of resin denture teeth (Biotone) were used. The acrylic resins were polymerised according to the cycles: (A) microwave – fast cycle, Onda‐Cryl; (B) microwave – long cycle, Onda‐Cryl; (C) microwave – manufacturer’s cycle, Onda‐Cryl; (T) water bath – long cycle, Clássico and (Q) bench polymerisation cycle, Jet. Thirty specimens were prepared for each polymerisation method; 10 were packed with acrylic resin after 60 s of monomer liquid application on the tooth surface, 10 after 180 s and 10 without any monomer liquid application. For the purpose of the study, a shear test was used. anova and Tukey tests were performed to identify significant differences (α = 0.05). Results: The highest bond strength values were found for monomer surface treatments, regardless of the polymerisation cycles. The highest significant values were found for cycles B (15.4 ± 1.8 MPa), C (11.9 ± 4.9 MPa) and T (15.4 ± 2.6 MPa) for non‐treated and 60 s methylmethacrylate treated groups. Comparing the monomer liquid treatment, they did not differ significantly (p > 0.05), except for cycle A (p < 0.05). Conclusion: Chemical treatment using monomer on the tooth surface prior to the acrylic resin packing improved the bond strength between resin denture tooth and acrylic resin, regardless of monomer liquid treatment protocols. The microwavable resin, polymerised by fast cycle and autopolymerising resin should be avoided for processing denture and denture repairs, respectively.     

Weight loss and changes in surface roughness of denture base and reline materials after simulated toothbrushing in vitro

doi: 10.1111/j.1741‐2358.2010.00422.x
Weight loss and changes in surface roughness of denture base and reline materials after simulated toothbrushing in vitro Objective: To evaluate the weight loss and the surface roughness of acrylic resins after simulated brushing tests. Material and methods: Ten specimens of each material (Tokuyama Rebase II‐TR, New Truliner‐NT, Ufi Gel Hard‐UH and Lucitone 550‐L) were made. The wear loss (mg) by weight and the surface roughness (Ra μm) of each specimen was determined before and after brushing. The specimens were placed on the brushing machine and a total of 20 000 brushing cycles was performed. The results of weight loss and roughness values were submitted to the anova followed by the Tukey’s test (p = 0.05). Results: The mean weight loss of material L was statistically higher (p < 0.001) than that of the relines TR, UH and NT. No significant differences were found among the roughness values of resins TR, UH and L (p > 0.05). Only for L, toothbrushing increased the surface roughness. After toothbrushing, there was no significant difference between the roughness values of materials L and NT. The highest mean weight loss during the simulated toothbrushing tests was observed for L. Before the toothbrushing tests, the NT exhibited the highest mean roughness. Conclusion: Brushing resulted in increase in roughness only for resin L.     

Effect of toothbrushing, chemical disinfection and thermocycling procedures on the surface microroughness of denture base acrylic resins

doi: 10.1111/j.1741‐2358.2011.00582.x Effect of toothbrushing, chemical disinfection and thermocycling procedures on the surface microroughness of denture base acrylic resins Objective: This study verified the surface microroughness of denture acrylic resins submitted to toothbrushing, chemical disinfection and thermocycling procedures. Material and methods: Samples were prepared according to conventional, microwaved and boiled resins and submitted to microroughness measurements before and after procedures using a profilometer (Ra). Data were subjected to anova and Tukey’s test (5%). Results: Before thermocycling, a difference was found among treatments for microwaved and boiled resins, with greater values for toothbrushing and lower values for Efferdent and hypochlorite; control was intermediate. Differences among resins were observed for treatments, with higher values for boiled resin and lower values for conventional and microwaved resins. After thermocycling, differences were found for microwaved resin, with a higher value for toothbrushing and a lower value for Efferdent and hypochlorite; control was intermediate. Tooth‐brushed boiled resin presented higher values and hypochlorite lower values; control and Efferdent were intermediates. Differences among resins were seen for treatments, with higher values for boiled resin and lower values for conventional and microwaved resins. Boiled resin presented differences for toothbrushing and hypochlorite, before and after thermocycling procedures were compared. Conclusions: For microwaved and boiled resins, toothbrushing and chemical disinfection promoted different levels of surface microroughness when associated or not with thermocycling.     

Surface roughness of denture base and reline materials after disinfection by immersion in chlorhexidine or microwave irradiation

doi: 10.1111/j.1741‐2358.2011.00484.x
Surface roughness of denture base and reline materials after disinfection by immersion in chlorhexidine or microwave irradiation Background: This study evaluated the effect of disinfection by immersion and microwave irradiation on the roughness of one denture base resin (Lucitone‐L) and five relining materials, three hard (Tokuyama Rebase II‐TR, New Truliner‐NT, Ufigel Hard‐UH) and two resilient (Trusoft‐T, Sofreliner‐S). Methods: Fifty specimens were made and divided into groups: CL2 specimens were brushed with 4% chlorhexidine (1 min), immersed in the same solution (10 min) and immersed in water (3 min); MW2 specimens were immersed in water and microwave irradiated (650W; 6 min); CL2 and MW2 specimens were disinfected twice; CL7 and MW7 specimens were submitted to seven cycles using chlorhexidine or microwave irradiation, respectively; W specimens were not disinfected and remained in water (37°C; 7 days). Results: Results were statistically analysed (p = 0.05) and revealed that, at baseline, the highest mean value was observed for T (p < 0.001). Material NT showed increase in roughness after the first (p = 0.003), second (p = 0.001), seventh (p = 0.000) cycles of microwave disinfection and after 7 days of immersion in water (p = 0.033). Conclusions: Resilient liner S presented significant increase in roughness after the second cycle of disinfection with chlorhexidine (p = 0.003). Material T exhibited significantly decreased roughness in group W (p = 0.010), while microwaving produced severe alterations on its surface.     

The effect of immersion cleansers on gloss,colour and sorption of acetal denture base material

doi: 10.1111/j.1741‐2358.2012.00657.x The effect of immersion cleansers on gloss, colour and sorption of acetal denture base material Objective: To study the effect of peroxide and hypochlorite cleansers on gloss, colour and sorption of acetal denture resins. Materials and methods: Pink acetal and thermoplastic acrylic resins were evaluated. Thirty‐five specimens 39 × 39 × 1.8 mm of each resin were prepared. Each group of specimens (n = 7) was then immersed into cleansers for 100 days. Group I immersed in tap water, Group II in Corega Extradent for 5 min, Group III in Corega Extradent for 8 h, Group IV in NitrAdine? Seniors for 15 min and Group V in NaOCl 5.25%. Gloss, colour and weight measurements were taken initially and after 100 days. Data subjected to two‐way anova and Tukey’s test at α = 0.05. Results: Acrylic resin showed reductions of glossiness from ?5 to ?15 and acetal from ?0.2 to ?6. Colour changes (ΔΕ*) ranged from 2.64 to 7.64 for acrylic and 2.77 to 26.54 for acetal resin. Sorption for acrylic ranged from 11.64 to 17.06 μg/mm³ and 9.18 to 24.79 μg/mm³ for acetal resin. The results of (ΔΕ*) and sorption showed an interaction between denture resins and cleansers. Conclusions: The gloss of acetal resin was less affected by water, peroxides and NaOCl 5.25% compared with acrylic resin. Acetal resin showed clinically acceptable (ΔΕ*) whereas acrylic resin unacceptable ones for water and peroxide solutions. The immersion of acetal resin in NaOCl 5.25% showed clinically unacceptable (ΔΕ*) and higher sorption and should be avoided or should be managed with care.     

Microbiological analysis of conjunctival secretion in anophthalmic cavity,contralateral eye and ocular prosthesis of patients with maxillofacial abnormalities

The purpose of this study was to identify and analyse the micro‐organisms present in the conjunctival secretion in anophthalmic cavities of wearers of ocular prostheses, as well as on the prostheses used by them, correlating them with the microbiota of the contralateral eye. Nine patients with maxillofacial abnormalities, wearers of an acrylic resin ocular prosthesis participated in the study. Collections of conjunctival secretions and biofilm were performed on the prosthesis, anophthalmic cavity and contralateral eye for the mycological and bacterial analyses. The data were submitted to statistical analysis, performing a Kendall correlation test to identify the correlation between the collection site and the identified micro‐organism (P < 0·05). It was verified that the most prevalent micro‐organisms were the Staphylococcus aureus and Staphylococcus epidermidis, independent of the collection site, and that negative cultures for fungi were encountered in 85·2% of collections, independent of the region. It was not possible to establish a correlation among the types of micro‐organisms and the collection sites.

Significance and Impact of the Study

Some evidence suggests that the surface roughness of ocular prostheses can influence interactions with micro‐organisms, with greater prejudicial consequences, such as the establishment of biofilms, which could lead to infections. Thus, it becomes extremely important to identify the micro‐organisms present on the acrylic surfaces of ocular prostheses, as well as the microbiota of the anophthalmic cavity and contralateral eye of wearers of the same, so that subsequent control measures promote the homeostatic maintenance of the ocular region.     

Evaluation of Vickers hardness of different types of acrylic denture base resins with and without glass fibre reinforcement

doi: 10.1111/j.1741‐2358.2010.00435.x
Evaluation of Vickers hardness of different types of acrylic denture base resins with and without glass fibre reinforcement Objective: To evaluate the Vickers hardness of different acrylic resins for denture bases with and without the addition of glass fibres. Background: It has been suggested that different polymerisation methods, as well as the addition of glass fibre (FV) might improve the hardness of acrylic. Materials and methods: Five types of acrylic resin were tested: Vipi Wave (VW), microwave polymerisation; Vipi Flash (VF), auto‐polymerisation; Lucitone (LT), QC20 (QC) and Vipi Cril (VC), conventional heat‐polymerisation, all with or without glass fibre reinforcement (GFR) and distributed into 10 groups (n = 12). Specimens were then submitted to Vickers hardness testing with a 25‐g load for 30 s. All data were submitted to anova and Tukey’s HSD test. Results: A significant statistical difference was observed with regard to the polymerisation method and the GFR (p < 0.05). Without the GFR, the acrylic resin VC presented the highest hardness values, and VF and LT presented the lowest. In the presence of GFR, VC resin still presented the highest Vickers hardness values, and VF and QC presented the lowest. Conclusions: The acrylic resin VC and VW presented higher hardness values than VF and QC resins. Moreover, GFR increased the Vickers hardness of resins VW, VC and LT.     

In situ evaluation of surface roughness and micromorphology of temporary soft denture liner materials at different time intervals

Objective

To perform an in situ evaluation of surface roughness and micromorphology of two soft liner materials for dentures at different time intervals.

Background

The surface roughness of materials may influence the adhesion of micro‐organisms and inflammation of the mucosal tissues. The in situ evaluation of surface roughness and the micromorphology of soft liner materials over the course of time may present results different from those of in vitro studies, considering the constant presence of saliva and food, the changes in temperature and the pH level in the oral cavity.

Materials and methods

Forty‐eight rectangular specimens of each of the two soft liner materials were fabricated: a silicone‐based material (Mucopren Soft) and an acrylic resin‐based material (Trusoft). The specimens were placed in the dentures of 12 participants (n = 12), and the materials were evaluated for surface roughness and micromorphology at different time intervals: 0, 7, 30 and 60 days. Roughness (Ra) was evaluated by means of a roughness tester. Surface micromorphology was evaluated by scanning electron microscopy.

Results

Analysis of variance for randomised block design and Tukey's test showed that surface roughness values were lower in the groups using the silicone‐based material at all the time intervals (P < .0001). The average surface roughness was higher at time interval 0 than at the other intervals, for both materials (P < .0001). The surface micromorphology showed that the silicone material presented a more regular and smoother surface than the acrylic resin‐based material.

Conclusion

The surface roughness of acrylic resin‐based and silicone‐based denture soft liner materials decreased after 7 days of evaluation, leading to a smoother surface over time. The silicone‐based material showed lower roughness values and a smoother surface than the acrylic resin‐based material, thereby making it preferred when selecting more appropriate material, due its tendency to promote less biofilm build‐up.     

Evaluation of Candida albicans adhesion and biofilm formation on a denture base acrylic resin containing silver nanoparticles

Aim: This study firstly evaluated the activity of a silver nanoparticle (AgNPs) solution against Candida albicans and then the effect of incorporation of AgNPs into a denture base acrylic resin on the material’s hydrophobicity, C. albicans adhesion and biofilm formation. Methods and Results: The AgNPs solution was synthesized by chemical reduction and characterized. Minimum inhibitory (MIC) and minimum fungicidal (MFC) concentrations for planktonic cells and sessile cells (MFCs) of the AgNPs solution against C. albicans were determined. Specimens (n = 360) of silver‐incorporated acrylic resin at concentrations of 1000, 750, 500, 250 and 30 ppm were also prepared and stored in PBS for 0, 7, 90 and 180 days. Control was acrylic resin without AgNPs (0 ppm). After the storage periods, contact angles were measured and the specimens were used for C. albicans adherence (37°C; 90 min; n = 9) and biofilm formation (37°C; 48 h; n = 9) by XTT reduction assay. MIC, MFC and MFCs values were 3·98, 15·63 and 1000 ppm, respectively. Incorporation of AgNPs reduced the hydrophobicity of the resin. No effect on adherence and biofilm formation was observed. At 90 and 180 days of storage, there was significant increase in adherence and biofilm formation. Conclusions: Although the AgNPs solution had antifungal activity, no effect on C. albicans adherence and biofilm formation was observed after its incorporation into a denture base resin. Significance and Impact of the Study: The synthesized AgNPs solution is a promising antifungal agent, warranting investigations of more efficient methods of incorporation into denture base resins.     

Flexural properties of repaired heat‐polymerising acrylic resin after wetting with monomer and acetone

doi:10.1111/j.1741‐2358.2009.00321.x
Flexural properties of repaired heat‐polymerising acrylic resin after wetting with monomer and acetone Objectives: Repair strength can be improved by treating fractured surfaces of a denture. Background: This study investigated flexural properties of heat‐polymerised acrylic resin specimens repaired with auto‐polymerising and visible light curing (VLC) resins after the repair surfaces were wetted with monomers or acetone. Materials and Methods: Fifty‐four specimens (65 × 10 × 2.5 mm) were prepared and 48 of them were sectioned to simulate denture fracture. Butt‐joint designed repair surfaces were wetted with heat‐, auto‐polymerising monomers and acetone for 180 s and repaired with auto‐polymerising and VLC resins. After repairs, specimens were subjected to three‐point bending test and flexural strength, strain, fracture load, modulus of elasticity and deflection values were recorded. Data were analysed with Student t and LSD tests (p ≤ 0.05). Results: Overall flexural strength, strain, fracture load and deflection values of specimens repaired with VLC resin were significantly higher than the specimens repaired with auto‐polymerising resin for all types of wetting agent (p < 0.05). Within the wetting agents, heat‐ and auto‐polymerising monomers produced the best mechanical properties, while wetting with acetone did not provide superior effect over both monomers. Conclusion: In clinical use, wetting the repair surfaces may result in stronger repairs. The use of bonding agent in VLC resin repairs in combination with wetting agent results in improved flexural properties.     

The occurrence of porosity in reline acrylic resins. Effect of microwave disinfection

Background: Microwave energy has proved to be an effective method for disinfecting acrylic dentures. However, the effect of microwave heating on the porosity of autopolymerising denture reline resins has not been investigated. Objective: The purpose of the study was to determine the effect of microwave disinfection on the porosity of autopolymerised denture reline materials (Kooliner‐K, New Truliner‐NT, Tokuso Rebase Fast‐TR and Ufi Gel Hard‐UGH) and a conventional heat‐polymerised denture base resin (Lucitone 550‐L). Material and methods: Specimens (10 mm × 20 mm × 1 mm) were obtained from the impression surface of the palatal mucosa in a single person and divided into four groups (n = 5). The porosity was evaluated after polymerisation (C1), after two cycles of microwave disinfection (MW2), after seven cycles of microwave disinfection (MW7) and after 7 days storage in water at 37°C (C2). Specimens from group MW7 were exposed to microwave disinfection daily being stored in water at 37°C between exposures. All the replicas were sputter coated with gold and micrographs/digital images were taken of each replica using scanning electron microscopy at magnification × 100. The SEM micrographs were then examined using an image analyser to determine the number of pores. Comparison between materials and groups were made using Kruskal–Wallis tests. Results: MW7 resulted in a significant increase in the number from the pores of material K, but decreased in number in reline material TR and UGH reline resin. The number of pores in materials NT and L remained unaffected following microwave disinfection. Conclusion: Differences in the porosity amongst the materials and for different experimental conditions were observed following microwave disinfection.     

Relining of prosthesis with auto‐polymerizing hard denture reline resins: effect of post‐polymerization treatment on flexural strength

Background: It has been suggested that microwave irradiation and prosthesis immersion in hot water after its polymerization may improve mechanical and viscoelastic properties of acrylic resins. Purpose: This study was proposed to verify the influence of microwave post‐polymerization (PP) treatment over the flexural strength of thermo‐polymerizing acrylic resin specimens (QC‐20) relined or not with two different composition hard chairside auto‐polymerizing reliners [Kooliner (K) and New Truliner (NT)]. Materials and Methods: For this study, 50 specimens of 64 × 10 × 3.3 mm were polymerized and distributed into five groups. G1 (control) specimens without relining and PP; G2 specimens relined with K, without PP; G3 specimens relined with NT, without PP; G4 specimens relined with K, with PP (microwave irradiation with 650 W for 5 min); G5 specimens relined with NT, with PP. Tests were performed on a universal testing machine Instron 4411 with compression speed of 5 mm/min. Results: Specimens of K without PP did not show statistically different results (p < 0.05) when compared with control. However, when submitted to PP these specimens showed a significant increase in flexural strength. Specimens of NT showed the lowest flexural strength of all groups, with or without PP when compared with control and K groups. Conclusion: Microwave PP (650 W for 5 min) proved to be an effective method of improving the flexural strength of K relined prosthesis. However, it did not seem to affect NT specimens.     

Effect of repeated cycles of chemical disinfection on the roughness and hardness of hard reline acrylic resins

doi:10.1111/j.1741‐2358.2009.00282.x
Effect of repeated cycles of chemical disinfection on the roughness and hardness of hard reline acrylic resins Objective: The aim of this study was to assess the effect of repeated cycles of five chemical disinfectant solutions on the roughness and hardness of three hard chairside reliners. Methods: A total of 180 circular specimens (30 mm × 6 mm) were fabricated using three hard chairside reliners (Jet; n = 60, Kooliner; n = 60, Tokuyama Rebase II Fast; n = 60), which were immersed in deionised water (control), and five disinfectant solutions (1%, 2%, 5.25% sodium hypochlorite; 2% glutaraldehyde; 4% chlorhexidine gluconate). They were tested for Knoop hardness (KHN) and surface roughness (μm), before and after 30 simulated disinfecting cycles. Data was analysed by the factorial scheme (6 × 2), two‐way analysis of variance (anova ), followed by Tukey’s test. Results: For Jet (from 18.74 to 13.86 KHN), Kooliner (from 14.09 to 8.72 KHN), Tokuyama (from 12.57 to 8.28 KHN) a significant decrease in hardness was observed irrespective of the solution used on all materials. For Jet (from 0.09 to 0.11 μm) there was a statistically significant increase in roughness. Kooliner (from 0.36 to 0.26 μm) presented a statistically significant decrease in roughness and Tokuyama (from 0.15 to 0.11 μm) presented no statistically significant difference after 30 days. Conclusions: This study showed that all disinfectant solutions promoted a statistically significant decrease in hardness, whereas with roughness, the materials tested showed a statistically significant increase, except for Tokuyama. Although statistically significant values were registered, these results could not be considered clinically significant.     

Evaluation of the efficacy of chemical disinfectants for disinfection of heat‐polymerised acrylic resin

doi: 10.1111/j.1741‐2358.2010.00400.x
Evaluation of the efficacy of chemical disinfectants for disinfection of heat‐polymerised acrylic resin Objective: This study evaluated the efficacy of disinfectants on the internal aspect of heat‐polymerised acrylic resin contaminated with microbial strains. Background: Dentures absorb oral fluids and become contaminated by different microorganisms. Methods: Two hundred and fifty rectangular specimens were made of heat‐polymerised acrylic resin, and then divided into five groups corresponding to the microbial strains (Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, S. mutans and Enterococcus faecalis). After contamination, the specimens were immersed in 1 and 2% sodium hypochlorite and 2% glutaraldehyde for periods of 5, 10 and 15 min. The specimens were placed into tubes containing different broths and incubated at 35°C and then visually analysed. Turbidity in the medium indicated microbial growth. The Fisher’s exact test was used in the analysis of the results. Results: The strain E. faecalis was the most resistant to the disinfectant solutions, and among them, glutaraldehyde was more effective than 2 and 1% hypochlorite for disinfection for 5 min; in the 10‐min period there were no differences between the disinfectants. In 15 min of immersion, 1% hypochlorite and glutaraldehyde were more effective than 2% hypochlorite. Conclusions: Disinfection for 10 min with 1% hypochlorite and glutaraldehyde is effective in disinfecting the internal aspect of heat‐polymerised acrylic resin.