Effect of sealer coating on mechanical and physical properties of permanent soft lining materials

doi: 10.1111/j.1741‐2358.2011.00487.x
Effect of sealer coating on mechanical and physical properties of permanent soft lining materials Objective: To evaluate the long‐term effects of sealer coating on tensile bond strength and surface roughness of soft liners. Background: Failure of the bond between resilient liners and denture base significantly compromise the dentures’ longevity. In addition, surface roughness contributes to bacterial adherence on prosthetic materials, increasing the risk of oral infections. Methods: Specimens were manufactured from four reliners [Mucopren Soft (MS), Dentuflex (DF); Soft Comfort Denso (SC) and Ufi Gel SC (USC)], distributed into 10 groups (n = 10), according to material and coating treatment. Tensile bond strength was performed after one year of ageing, while surface roughness was evaluated at 0, 1, 3, 6 and 12 ageing months. Bond strength data were submitted to two‐way anova and Tukey‐HSD tests, while roughness data were submitted to mixed model analysis for repeated measurements (p ≤ 0.05). Results: MS and DF without sealer coating presented the highest tensile bond strength. After coating, DF and SC presented increased tensile bond strength. No surface roughness difference was observed in the non‐coated groups over time, acrylic‐based reliners presented higher roughness. Among coated groups, only SC presented increased surface roughness. Acrylic‐based materials presented reduced roughness at three months. Conclusion: Surface coating was effective for acrylic reliners in maintaining their initial properties. However, sealer coating should be re‐applied every 3 months.     

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.     

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.     

Effect of thermocycling on hardness, absorption, solubility and colour change of soft liners

doi: 10.1111/j.1741‐2358.2010.00447.x
Effect of thermocycling on hardness, absorption, solubility and colour change of soft liners Objective: The effect of artificial ageing on the hardness, absorption, solubility, and colour of soft denture liners was investigated. Materials and methods: Liner materials based on acrylic resin (Trusoft) or silicone (Dentusil, Ufi Gel P, and Ufi Gel SC) were tested before and after 2000 thermal cycles. A total of 20 specimens of each material were tested. Half of the specimens were used for hardness and colour evaluation, and the remainder for absorption and solubility tests. The hardness evaluation was carried out using a Shore A durometer, while absorption and solubility tests were performed by storing samples in a desiccator and weighing daily until reaching constant mass (W1). After thermocycling, the samples were again weighed (W2) and dried (W3). Colour was measured using a spectrophotometer. Statistical analysis was performed using GraphPad InStat at the p < 0.05 level. Results: Thermocycling significantly affected the hardness of the specimens. The Trusoft material exhibited the highest absorption (1.48 ± 0.48), solubility (1.26 ± 0.28), and colour change (3.92 ± 0.33), significantly different from the other materials. There were no significant differences among the silicones in terms of absorption, solubility, and colour change, except for the colour of Dentusil, which changed (0.83 ± 0.11). Conclusion: It can be concluded that silicone liners performed significantly better compared to acrylic resin.     

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 reline material and denture base surface treatment on the impact strength of a denture base acrylic resin

doi:10.1111/j.1741‐2358.2009.00292.x
Effect of reline material and denture base surface treatment on the impact strength of a denture base acrylic resin Objective: In this study, the effect of relining and surface treatment on the impact strength (IS) of a heat‐polymerising denture base acrylic resin (Lucitone 550‐L) was evaluated. Materials and methods: Rectangular bars of L were made (60 × 6 × 2 mm) and relined (2 mm) with the relining resins Ufi Gel Hard (UH) and Tokuso Rebase Fast (TR). Specimens relined with L and intact L, TR and UH specimens were also made (60 × 6 × 4 mm), for comparison. Before relining, the L surface was left untreated or wetted with methyl methacrylate monomer and/or the bonding agents (BA) supplied by manufacturers of the reline resins. V‐notches were machined at the midpoint of the length of all specimens. The notches were made either across the width (Nw) or across the thickness of the specimens (Nth). The Charpy impact test was performed using a 0.5‐J pendulum, which had been specially designed and constructed. Data were analysed separately for each notch position using one‐way analysis of variance and Tukey honestly significant difference post‐hoc test (p = 0.05). Results: The IS of L was similar to that of L/L. For the Nw notch, treating the denture base L with TR BA and relining with TR reline material produced the highest IS. Conclusion: The IS of specimens made from heat polymerising acrylic resin Lucitone 550 was increased after relining using the hard chairside reline resin TR with its proprietary BA.     

Colour change of soft denture liners after storage in coffee and coke

doi:10.1111/j.1741‐2358.2009.00356.x
Colour change of soft denture liners after storage in coffee and coke This study was to evaluate the colour change of soft denture liners after thermocycling and storage in coffee and coke. Four liners, two silicone‐based (Sofreliner S and Reline GS) and two acrylic resin‐based (Soft Confort and Dentuflex), were evaluated in this study. Ten samples were obtained for each group. After 2000 cycles of thermocycling with baths of 5°C and 55°C, five samples were stored in coffee and the remaining samples in coke. The colour alteration was evaluated in a reflection spectrophotometer before and after thermocycling, and after 1, 3, 24, 48 and 96 h of storage in coffee and coke. Data were submitted to anova and Tukey’s HSD test (α = 0.05). Thermocycling and storage period represented a higher statistically significant influence for the resin liners than for the silicone materials. Coke did not influence the colour stability of the materials during storage. However, the coffee solution generated statistically significant colour alteration in the material Soft Confort. In the comparison between the coffee and coke solutions, there was no statistically significant difference for colour alteration only for the material Dentuflex. The silicone liners presented better colour stability following thermocycling and storage independent of the solution. The coffee solution was a statistically significant factor for colour alteration of the material Soft Confort.     

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.     

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.     

Flexural and bond strengths of relined denture polymers assessed by four‐point bending tests and Weibull analysis

doi: 10.1111/j.1741‐2358.2011.00515.x Flexural and bond strengths of relined denture polymers assessed by four‐point bending tests and Weibull analysis Objectives: The aim of this study was to (1) investigate the flexural strengths of three denture resins i.e. heat, photopolymerised and microwaved and how it was affected by relining with auto‐ and visible light–polymerised hard reliners, (2) investigate the bond strengths between denture resins and hard reliners and (3) interpret the results of both tests by utilising Weibull analysis. Materials and methods: Specimens (65 × 10 × 2.5 mm) from denture resins, relined and bonded combinations were tested using a four‐point bending test in a universal testing machine and a crosshead speed of 5 mm/min. Ten specimens for each bulk resin and denture resin–reliner combination for a total of 150 were tested. Results: Statistical analysis indicated significant differences between bulk materials (p < 0.001) and between reliners (p < 0.001) for flexural and bond strength tests. Conclusion: It was concluded that (1) the four‐point flexural strength was different between the denture base materials, (2) flexure strength between bulk and relined or between relined with autopolymerised and photopolymerised bases was different, (3) flexural strength among relined denture bases was different and (4) bond strengths among relined denture bases were different.     

The influence of double flask investing on tooth displacement in dentures processed by microwave irradiation

doi: 10.1111/j.1741‐2358.2011.00587.x The influence of double flask investing on tooth displacement in dentures processed by microwave irradiation Objective: This study evaluated the influence of the bimaxillary flask (BMF) and two different investing materials on first molar inclination in dentures processed by microwave irradiation. Background: The BMF may minimise tooth displacement, saving time and improving occlusion. Methods and materials: Forty pairs of dentures were randomised into four groups: stone wall in monomaxillary flask; silicone wall in BMF; stone wall in BMF; acrylic resin retentions and silicone in BMF. Dentures were processed by microwave irradiation. Two referential points were established on tooth surface. A microscope and a digital pachymeter were used to measure the distance between these points, and the angles α (right maxillary molar), β (left maxillary molar), α′ (right mandibular molar) and β′ (left mandibular molar) were calculated by the law of cosines. Data were submitted to Kruskal–Wallis (5% significance). Results: No difference was observed among the groups (p > 0.05). In the intra‐group analysis, α was significantly different for groups I, II and III; α′, for groups II and IV; β, for all groups; β′, for groups III and IV. Conclusion: First molar inclination was similar for monomaxillary and BMFs. The use of stone or silicone as investing materials presented the same effect on tooth inclination.     

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.     

Effect of thermocycling on the flexural and impact strength of urethane-based and high-impact denture base resins

doi: 10.1111/j.1741‐2358.2011.00474.x
Effect of thermocycling on the flexural and impact strength of urethane‐based and high‐impact denture base resins Objective: Mechanical properties of the acrylic resins used for denture fabrication may be influenced by water and temperature. Thus, the aim of this study was to evaluate the effect of thermocycling on the flexural and impact strength of a high‐impact (Lucitone 199) and a urethane‐based denture material (Eclipse). Materials and methods: Flexural strength (64 × 10 × 3.3 mm) and impact strength (60 × 6 × 4 mm) specimens were made following the manufacturers’ instructions and assigned to two groups (n = 10): control (C) – not thermocycled – and T – thermocycled (5000 cycles between 5 and 55°C). Specimens were submitted to three‐point bending and Charpy impact tests. Results: Flexural strength (MPa) and impact strength (kJ/m²) data were analysed with two‐way anova (p = 0.05). The flexural strength of material Eclipse (C, 136.5; T, 130.7) was significantly higher than that of resin Lucitone 550 (C, 99.4; T, 90.1). Material Eclipse exhibited significantly higher impact strength (C, 6.9; T, 5.3) than the resin Lucitone 550 (C, 3.5; T, 3.0). For both materials, a significant decrease in flexural and impact strengths was observed when the specimens were thermocycled. Conclusion: Flexural and impact strengths were higher for Eclipse than for Lucitone 550, in both groups. Thermocycling decreased the flexural and impact strengths of Eclipse and Lucitone 550.     

Surface changes in denture soft liners with and without sealer coating following abrasion with mechanical brushing

Gerodontology 2010; doi: 10.1111/j.1741‐2358.2010.00375.x Surface changes in denture soft liners with and without sealer coating following abrasion with mechanical brushing Aim: To evaluate the surface alterations of soft liners with or without sealer coating following abrasion with mechanical brushing. Methods: Thirty specimens were made of a methacrylate‐ (Coe‐Soft) and a siloxane‐based material (Ufi‐Gel SC), and 15 received two coatings of surface sealer. The specimens were submitted to a mechanical brushing‐dentifrice assay under 200 g of force at 250 cycles/min. Mechanical brushing was simulated for a period of 1 (1250 cycles) and 6 months (5000 cycles). Surface roughness (Ra parameter) was measured, and scanning electron microscopy (SEM) images were obtained. Ra data were analysed by anova for repeated measures and Bonferroni’s test (alpha = 0.05). Results: Ra increased from baseline to 6 months regardless of sealer coating. At baseline, only Coe‐Soft without sealer had a higher Ra than the other groups. After 1 month, the Ra of Coe‐Soft with sealer was three‐fold higher than the Ra at baseline; the other groups showed no significant increase of Ra. SEM images showed degradation of the soft liners over time, except for the Ufi‐Gel SC with sealer, which displayed minimum alteration of surface texture. Conclusion: Sealer coating reduced the surface degradation of the tested soft liners, but the protective effect was more pronounced for the siloxane‐based material.     

Fracture resistance of maxillary complete dentures subjected to long-term water immersion

doi: 10.1111/j.1741‐2358.2012.00616.x Fracture resistance of maxillary complete dentures subjected to long‐term water immersion Objective: This study investigated the fracture resistance of maxillary acrylic resin complete dentures subjected to long‐term water immersion. Materials and Methods: Maxillary acrylic resin complete dentures were fabricated from five denture base resins. Half of the dentures were stored in water for 50 h, and the other half were kept in water for 180 days before testing. Ten specimens were fabricated per group. The flexural load at the proportional limit (FL‐PL) of the dentures was tested. Results: A two‐way anova revealed a significant difference in FL‐PL because of the denture base material variable. There were no significant differences in FL‐PL because of the effect of water immersion and the interaction between the effect of water immersion and the denture base material. The FL‐PLs of the dentures fabricated with the two conventional heat‐processed resins, the pour‐type autopolymerizing resin and the microwave energy‐processed resin were not significantly different from each other; they were significantly higher than the light‐activated resin in regard to their FL‐PL. Conclusion: The FL‐PLs of the maxillary acrylic resin complete dentures did not change after long‐tern water immersion, and the FL‐PL of the denture fabricated from the light‐activated resin was lower than those of the other materials.     

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 microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin

doi:10.1111/j.1741‐2358.2009.00333.x
Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth.     

Effect of the addition of silanated silica on the mechanical properties of microwave heat-cured acrylic resin

doi: 10.1111/j.1741‐2358.2011.00604.x
Effect of the addition of silanated silica on the mechanical properties of microwave heat‐cured acrylic resin Objectives: The purpose of this study was to evaluate fthe flexural strength and Vickers hardness of a microwave energy heat‐cured acrylic resin by adding different concentrations of silane surface‐treated nanoparticle silica. Methods: Acrylic resin specimens with dimensions of 65 × 10 × 2.5 mm were formed and divided into five experimental groups (n = 10) according to the silica concentration added to the acrylic resin mass (weight %) prior to polymerisation : G1, without silica; G2, 0.1% silica; G3, 0.5% silica; G4, 1.0% silica; and G5, 5.0% silica. The specimens were submitted to a three‐point flexural strength test and to the Vickers hardness test (HVN). The data obtained were statistically analysed by anova and the Tukey test (α = 0.05). Results: Regarding flexural strength, G5 differed from the other experimental groups (G1, G2, G3 and G4) presenting the lowest mean, while G4 presented a significantly higher mean, with the exception of group G3. Regarding Vickers hardness, a decrease in values was observed, in which G1 presented the highest hardness compared with the other experimental groups. Conclusion: Incorporating surface‐treated silica resulted in direct benefits in the flexural strength of the acrylic resin activated by microwave energy; however, similar results were not achieved for hardness.     

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.     

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.