Effect of pre-processing methods on bond strength between acrylic resin teeth and acrylic denture base resin

doi: 10.1111/j.1741‐2358.2011.00480.x
Effect of pre‐processing methods on bond strength between acrylic resin teeth and acrylic denture base resin Objectives: This study evaluated the effects of various pre‐processing methods on the bond strength between resin and denture teeth. Backgrounds: Debonding of acrylic resin teeth from denture base material is a problem for patients wearing complete dentures. Materials and Methods: Four experimental groups (n = 30) were investigated by subjecting tooth–resin bonding to tensile loading. Specimens were prepared and tested according to the methods of the International Standards Organization (ISO 22112:2005) using a special assembly. Four pre‐processing surface treatments of teeth were applied: (i) ST₁, no treatment applied (control); (ii) ST₂, wax solvent (Dewaks, Faber Kimya & Ilaç, Turkey); (iii) ST₃, boiling water followed by conditioning with methyl methacrylate (MMA) monomer (Meliodent, Bayer Dental, Germany); (iv) ST₄, boiling water followed by wax solvent agent and finally MMA monomer application. Bond strength test was performed using a universal testing machine. Results: All the strength values of the test groups were within clinically acceptable limits. The lowest values were from the ST₁ group and the highest values were in the ST₄ group. Conclusions: Wax elimination methods affected bonding strength. Application of wax solvent and MMA monomer to the ridge lap surfaces of the teeth gave the best results. In clinical practice, this application procedure may decrease the bonding failure of denture teeth.     

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.     

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.     

Bonding acrylic teeth to acrylic resin denture bases: a review

Partial or complete dentures are more commonly constructed for the elderly group of the population. Teeth debonding from the dentures can be frustrating to the patients as well as the dentist. Research has been carried out and is continuing to study the issue of bonding acrylic teeth to the denture base resin. The present review takes into account the majority of research papers published in the last five decades for determining the bond strength. Selection of more compatible combinations of denture base resins and acrylic teeth may reduce the number of prosthesis fractures and the resultant repairs.     

Effect of repeated microwave disinfections on bonding of different commercial teeth to resin denture base

doi: 10.1111/j.1741‐2358.2011.00516.x Effect of repeated microwave disinfections on bonding of different commercial teeth to resin denture base Objective: To verify the influence of repeated microwave disinfections on the shear bond strength of two commercial types of teeth to acrylic resin, when the ridge lap surfaces were unmodified, bur abraded, bur grooved or etched by monomer. Material and methods: Eighty specimens (n = 10) were adhered to the tooth ridge lap surface, polymerised in a water bath at 74°C for 9 h. Microwaved specimens were individually immersed in 150 ml of water and submitted to five simulated disinfections in a microwave oven calibrated at 650 W for 3 min. Control specimens were not microwave treated. Shear bond strength tests were performed in an Instron machine with a cross‐speed of 1 mm/min. The fracture load values were transformed into shear bond strength as a function of the bonding area (0.28 cm²). Data were submitted to anova and Tukey’s test (α = 0.05). Fractured areas were classified as adhesive, cohesive (resin or tooth) or mixed failures. Results: Repeated microwave disinfections increased the shear strength of the tooth/resin bond. Mechanical retention in microwaved and non‐microwaved procedures improved the shear bond strength. Conclusions: The different commercial types of teeth influenced shear bond strength values, with Biotone teeth showing the lower values.     

Fatigue resistance of acrylic resin denture base material reinforced with E-glass fibres

doi: 10.1111/j.1741‐2358.2011.00548.x
Fatigue resistance of acrylic resin denture base material reinforced with E‐glass fibres Objective: The purpose of the study was to determine the effect of different forms and concentrations (2.5, 3, 4, 5% by volume) of glass fibres (chopped strand mat, continuous and woven) on fatigue resistance of acrylic denture base resin. Material and Methods: The fatigue resistance was measured by applying repeated three‐point bending deflection to the specimens, the cycle frequency of 1.05 g and magnitude of deflection of 2.0 mm. The number of loading cycles needed to cause a fracture in the test specimen was considered the fatigue resistance of the specimen. Results: The results of this study revealed that the addition of three different glass fibre forms at all concentrations to acrylic resin did not produce a statistically significant increase in the fatigue resistance (p ≥ 0.05). This study also revealed that there were significant differences (p < 0.05) between glass fibres forms used concerning the effects on the fatigue resistance. Conclusion: This study showed that the woven glass fibres had a definite superiority over the chopped fibres and the continuous fibres in regard to the fatigue resistance of the acrylic denture base resin.     

Shear bond strength between different materials bonded with two resin cements

doi: 10.1111/j.1741‐2358.2011.00565.x
Shear bond strength between different materials bonded with two resin cements Background: The aim of this study was to compare the shear bond strength between Ni–Cr alloy specimens bonded to air‐abraded Ni–Cr, bur‐abraded Ni–Cr, etched ceramic and etched enamel substrates using the resin cements RelyX ARC or Enforce. Materials and methods: Ni–Cr specimens were made and sandblasted with Al₂O₃ airborne‐particles. Disc‐shaped patterns were made for each of the four experimental substrates: Ni–Cr treated with Al₂O₃ airborne‐particles, Ni–Cr treated with diamond bur abrasion, etched enamel and etched ceramic. Results: Significant differences in shear bond strength were found between the different materials and luting agents evaluated. The Ni–Cr alloy cylinders bonded to Ni–Cr surfaces sandblasted with 50 μm Al₂O₃ particles and bonded with Enforce achieved the highest bond strength when compared with other substrates (28.9 MPa, p < 0.05). Bur‐abraded metal discs had lowest values, regardless the cement used (2.9 and 6.9 MPa for RelyX and Enforce, respectively). Etched enamel and etched ceramic had similar shear bond strengths within cement groups and performed better when RelyX was used. Conclusions: Bonding Ni–Cr to Ni–Cr and ceramic may result in similar and higher bond strength when compared to Ni–Cr/enamel bonding. For metal/metal bonding, higher shear bond strength was achieved with resin cement Enforce, and for metal/ceramic and metal/enamel bonding, RelyX had higher results.     

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.     

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.     

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.     

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.     

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.     

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.     

In vitro antiseptic properties of an ammonium compound combined with denture base acrylic resin

Background: Denture base acrylic resin is easily colonised by oral endogenous bacteria and Candida spp., and eventually by extra‐oral species such as Staphylococcus spp., Pseudomonadaceae or members of Enterobacteriaceae. This microbial reservoir can be responsive for denture related stomatitis and aspiration pneumonia, a life‐threatening infection especially in geriatric patients. However, the oral and denture hygiene of dependant elderly individuals is extremely poor. Objective: This in vitro study aimed to determine the per cent of a quaternary ammonium compound heat‐polymerised in acrylic resin necessary to obtain denture base displaying antiseptic properties. Design: Acrylic resin discs containing 2–50% ammonium polymer (Poly 202063A; 0% control) were soaked in artificial saliva for 4 weeks. Resin discs were incubated for 24 hours with Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa [37°C, brain–heart infusion (BHI) broth and phosphate‐buffered saline (PBS) buffer] and Candida albicans (30°C, Schaedler broth), in 15 ml (168 discs) and 600 μl (168 discs) of inoculum. Microbial growth was verified at t 0 hours and t 24 hours. Data were recorded as the mean of three colony forming unit (CFU) numerations. The borderline of antimicrobial effect was determined at 0.1% viable cells. Results: In 600 μl of PBS inoculum, resin specimens had a bactericidal effect (E. coli and S. aureus: 2%; P. aeruginosa: 10%) and a fungicidal effect (C. albicans: 50%). Long‐term stability and toxicity in vivo studies are now required. Conclusion: A 2% quaternary ammonium compound polymerised with a denture acrylic resin displayed antiseptic properties after a 4‐week soaking period in artificial saliva. Such antiseptic denture base could help geriatric patients to improve their oral health.     

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.     

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.     

Influence of surface treatments on the flexural strength of denture base repair

doi: 10.1111/j.1741‐2358.2011.00454.x Influence of surface treatments on the flexural strength of denture base repair Objective: The purpose of this study was to evaluate the flexural strength of repairs made with autopolymerising acrylic resin after different treatments of joint surfaces. Material and Methods: Fifty rectangular specimens were made with heat‐polymerised acrylic resin and 40 were repaired with autopolymerising acrylic resin following joint surface treatments: group 1 (intact specimens), group 2 (chemical treatment: wetting with methyl‐methacrylate for 180 s), group 3 (abraded with silicon carbide paper), group 4 (abraded and wetting with methyl‐methacrylate for 180 s) and group 5 (without surface treatment). The flexural strength was measured by a three‐point bending test using a universal testing machine with a 100 Kgf load cell in the centre of repair at 5 mm/min cross‐head speed. All data were analysed using one‐way anova and Tukey HSD test for multiple comparisons (p < 0.05). Results: Among repaired specimens, groups 2 and 4 had 66.53 ± 3.4 and 69.38 ± 1.8 MPa mean values and were similar. These groups had superior flexural strength than groups 3 and 5 that were similar and had 54.11 ± 3.4 and 51.24 ± 2.8 MPa mean values, respectively. Group 1 had a mean value of 108.30 ± 2.8 MPa being the highest result. Conclusion: It can be concluded that the treatment of the joint surfaces with methyl‐methacrylate increases the flexural strength of denture base repairs, although the strength is still lower than that observed for the intact denture base resin. Abrasion with sandpaper was not able to influence the flexural strength of repaired denture bases.     

Effect of flask closure method and post‐pressing time on the upper denture base adaptation

doi:10.1111/j.1741‐2358.2009.00307.x
Effect of flask closure method and post‐pressing time on the upper denture base adaptation Objectives: The purpose of this study was to evaluate the effect of flask‐closure methods, post‐pressing times and acrylic resins on denture base adaptation. Materials and methods: The resins were flasked using a hydraulic press and closed with the traditional clamp or RS system. Conventional heat‐cure resin was polymerised immediately or at 6 h post‐pressing at 74°C for 9 h. Rapid cycle heat‐cure resin was polymerised in boiling water for 20 min. After cooling, the bases were deflasked and the sets of cast‐base transversally sectioned in the regions distal to the canine, mesial to the first molar and in the posterior palatal zone. The adaptation was measured with an optical microscope (0.0005 mm) at five reference points for each section. Data were analysed using anova and Tukey’s test (α = 0.05). Results: Traditional clamp and immediate post‐pressing time improved base adaptation for conventional heat‐cure resin. Both post‐pressing times showed most accurate base adaptation for conventional heat‐cure resin when the traditional clamp was used. Immediate post‐pressing time improved base adaptation for conventional heat‐cure resin and the 6‐h delay in time was significant for the rapid cycle heat‐cure resin. Conclusions: Traditional clamp and immediate post‐pressing time improved base adaptation for conventional heat‐cure resin.     

Evaluation of the occlusion vertical dimension of complete dentures after microwave disinfection

doi: 10.1111/j.1741‐2358.2011.00567.x Evaluation of the occlusion vertical dimension of complete dentures after microwave disinfection Objectives: An increase in occlusal vertical dimension (OVD) after microwave disinfection may result in the need for adjustments in the complete dentures. This in vitro study evaluated the increase in OVD of maxillary complete dentures submitted to microwave disinfection protocols. Material and methods: Thirty sets of complete dentures were evaluated as follows: Group 1–15 sets had the maxillary complete dentures submitted to microwave disinfection (650 W/3 min), once a week, for 4 weeks. Group 2–15 sets had the maxillary complete dentures submitted to microwave disinfection (650 W/3 min), three times a week, for 4 weeks. The vertical dimension was measured with a micrometre (in mm) before disinfection protocols (baseline readings) and after each week of disinfection. Data were analysed using Wilcoxon and Friedman tests (α = 0.05). Results: For Group 1, no significant difference was found between the increases in OVD and zero, and no significant difference was found between the weeks. For Group 2, the increases in OVD were significantly greater than zero, and the Friedman test showed that weeks 3 and 4 had significantly greater changes than week 1 and that week 4 had significantly greater change than week 2. Conclusion: Microwave disinfection only promoted significant increase in OVD in Group 2, in which the values increased progressively.