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.     

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.     

Glass fibre reinforced acrylic resin complete dentures: a 5-year clinical study

doi: 10.1111/j.1741‐2358.2010.00385.x Glass fibre reinforced acrylic resin complete dentures: a 5‐year clinical study Background and objectives: The aim of the study was to establish the wear resistance of the glass fiber reinforced complete dentures comparative to the traditional acrylic complete dentures. Materials and methods: Complete new dentures were made to replace old fractured ‘un’‐reinforced acrylic dentures. The total number of dentures was 30 and woven E‐glass fibre reinforcements were used in maxillary complete dentures. Unidirectional E‐glass fibre reinforcements were used as partial fibre reinforcements in mandibular complete dentures. Ten complete acrylic un‐reinforced dentures were used as control. The follow‐up period was 5 years and the recalls were made at 6 months. Results: After 5 years of wearing the new dentures, the control dentures suffered seven fractures. After 5 years all the mandibular reinforced dentures were in good shape. The maxillary complete reinforced dentures suffered four partial fractures. Fracture lines were restricted by the glass fibre net and the patients could still use their dentures. Conclusion: Pre‐impregnated E‐glass fibre nets and polymer pre‐impregnated E‐glass unidirectional fibres are useful in reinforcing acrylic resin complete dentures especially were heavy occlusal forces are involved. Glass fibre reinforcement will be applied on the tension side in both cases (total fibre reinforcement and partial fibre reinforcement). The reinforcement cannot replace the necessary linings and occlusal adjustments.     

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.     

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.     

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.     

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 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.     

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.     

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.     

Effectiveness of different cleaning agents on the adherence of Candida albicans to acrylic denture base resin

doi: 10.1111/j.1741‐2358.2010.00379.x
Effectiveness of different cleaning agents on the adherence of Candida albicans to acrylic denture base resin Objective:  To evaluate the ability of three alkaline peroxide‐type (Polident, Efferdent, Fittydent) and two mouth rinse cleaning agents (CloSYSII and Corsodyl) to inhibit Candida albicans on acrylic denture base resin. Background:  Appropriate routine cleaning of dentures is necessary to prevent denture stomatitis and maintenance of healthy supporting tissues. Materials and methods:  A total of 180 acrylic resin specimens (10 × 10 × 2 mm) were prepared and divided into six groups. Candida albicans was incubated on Sabouraud dextrose agar (SDA) at 37°C for 48 h. After dilution, a final yeast suspension of approximately 10 6 C. albicans per millimetre was prepared. Ten acrylic resin specimens for each group were placed in a sterile Petri dish covered with 20 ml of fungal suspension and incubated at 37°C for 90 min. Then, the specimens were immersed in 40 ml of the test solution at 37°C for 15, 30 and 60 min. Fungal cells adhering to acrylic resin surfaces were fixed in formaldehyde and counted microscopically. Results:  Mouth rinses showed the highest removal activity for all the treatment times and completely eliminated the adherence of C. albicans. Conclusions:  The use of mouth rinse may be a suitable method for cleaning dentures.     

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.     

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.     

Evaluation of the flexural strength and elastic modulus of resins used for temporary restorations reinforced with particulate glass fibre

doi: 10.1111/j.1741‐2358.2010.00410.x
Evaluation of the flexural strength and elastic modulus of resins used for temporary restorations reinforced with particulate glass fibre Objective: The flexural strength and the elastic modulus of acrylic resins, Dencor, Duralay and Trim Plus II, were evaluated with and without the addition of silanised glass fibre. Materials and methods: To evaluate the flexural strength and elastic modulus, 60 test specimens were fabricated with the addition of 10% ground silanised glass fibres for the experimental group, and 60 without the incorporation of fibres, for the control group, with 20 test specimens being made of each commercial brand of resin (Dencor, Duralay and Trim Plus II) for the control group and experimental group. After the test specimens had been completed, the flexural strength and elastic modulus tests were performed in a universal testing device, using the three‐point bending test. For the specimens without fibres the One‐Way Analysis of Variance and the complementary Tukey test were used, and for those with fibres it was not normal, so that the non‐parametric Mann‐Whitney test was applied. Results: For the flexural strength test, there was no statistical difference (p > 0.05) between each commercial brand of resin without fibres [Duralay 84.32(±8.54), Trim plus 85.39(±6.74), Dencor 96.70(±6.52)] and with fibres (Duralay 87.18, Trim plus 88.33, Dencor 98.10). However, for the elastic modulus, there was statistical difference (p > 0.01) between each commercial brand of resin without fibres [Duralay 2380.64 (±168.60), Trim plus 2740.37(±311.74), Dencor 2595.42(±261.22)] and with fibres (Duralay 3750.42, Trim plus 3188.80, Dencor 3400.75). Conclusion: The result showed that the incorporation of fibre did not interfere in the flexural strength values, but it increased the values for the elastic modulus.     

Correlation between factors associated with the removable partial dentures use and Candida spp. in saliva

doi: 10.1111/j.1741‐2358.2010.00390.x
Correlation between factors associated with the removable partial dentures use and Candida spp. in saliva Objectives: To correlate the presence and number of Candida spp. in the saliva of wearers of removable partial dentures retained with precision attachments with the proportion of metal/acrylic resin present in the dentures. Methods: Saliva samples from 40 removable partial denture wearers (test) and one paired sample of individuals, non‐wearers of any type of removable denture (control) were collected, seeded, and the colony forming units of Candida counted and identified. The metal/acrylic resin proportion of each denture was quantified, using silicone plates pressed over each denture. Results: Candida spp. was found in the saliva of 80% of the individuals in the test group and 65% of the control, with C. albicans being the most prevalent species. The test group presented with the highest number of colony forming units of Candida per ml of saliva, and there was weak correlation between this number and the metal and resin area of the denture (Pearson’s coefficient of correlation). Greater prevalence and a higher number of colony forming units of Candida per ml of saliva occurred in removable partial denture wearers (p = 0.04) with a weak positive correlation between the metal and resin area and the number of colony forming units of Candida per ml of saliva. However, this correlation was more significant for the area of resin.     

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.     

Evaluation of stain removal and inhibition properties of eight denture cleansers: an in vitro study

Gerodontology 2012; doi: 10.1111/j.1741‐2358.2011.00522.x
Evaluation of stain removal and inhibition properties of eight denture cleansers: an in vitro study Objectives: To determine the ability of eight denture cleansers to remove and inhibit tea‐stain build‐up on acrylic resin. Materials and methods: In the stain removal study, Perspex^® (cast heat polymerised resin) specimens previously soaked in saliva were stained using multiple exposures of chlorhexidine and tea solutions. Specimens were exposed for 1 min to one of the eight denture cleansers for five cycles, washed and dried and their optical density read on a uv/vis spectrophotometer at 295 nm. In the stain inhibition study, clear specimens were exposed to saliva followed by cleansers then tea solution, for five cycles. The build‐up of stain at each cycle was measured, and differences in optical densities from baseline were calculated. Results: All denture cleansers were significantly more effective than water in removing stain (p < 0.05). There were significant differences in cleaning ability between cleansers (p < 0.001), Dentural^® and Kleenite^® were particularly effective. The stain inhibition experiment showed that most cleansers were significantly more effective than water in inhibiting stain (p < 0.05). There were significant differences in inhibition ability between cleansers (p < 0.01). Kleenite^® and Equate were particularly effective. Conclusions: All denture cleansers had a capacity to remove stain and most had an inhibitory effect on staining. Kleenite^® was particularly effective in controlling stain formation.     

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.     

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.     

Survival analysis of mandibular complete dentures with acrylic‐based resilient liners

doi: 10.1111/j.1741‐2358.2012.00658.x Survival analysis of mandibular complete dentures with acrylic‐based resilient liners Objective: The purpose of this long‐term randomised controlled trial was to compare the longevity of dentures constructed using a conventional acrylic resin (CAR) to that of dentures constructed using an acrylic‐based resilient liner (ARL). Materials and methods: The follow‐up study was essentially carried out by annual telephone calls to each of the 67 participants. The Kaplan–Meier method and life‐table analysis were used for univariate analyses. The Cox proportional‐hazards test was used as a final model for statistically adjusting predictor variables such as sex, clinician type, mandibular denture type and age at denture delivery. Results: The denture type was likely to affect the survival time of the dentures, while the sex and clinician type were not. The group using acrylic‐based resilient denture liners had twice the risk of having shorter denture‐survival times than those using conventional acrylic resin dentures. Younger participants were likely to have a reduced risk of having shorter denture‐survival times than older participants. Conclusion: We conclude that mandibular complete dentures constructed using ARL are twice as likely as dentures constructed using CAR to have shorter denture survival times, mainly because of material deterioration.