[Denture base preparation for removable partial denture].
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Denture Bases↗
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Completely clear acrylic denture bases for complete or partial dentures.
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Acrylic Resins↗
Flexural properties of denture base polymers.
Heat-polymerized denture base materials with the cross-linking agent 1,4-BDMA and with different amounts of the cross-linking agent EGDMA have similar flexural properties. At the relatively low loading rate of 2 N/minute all the heat-polymerized denture base materials investigated have better flexural properties than the autopolymerized pour- and dough-type materials. The autopolymerized materials with the cross-linking agent 1,4-BDMA have flexural properties intermediate to the heat-polymerized and the autopolymerized resins with the cross-linking agent EGDMA. The various autopolymerized resins behave differently, probably due to varying amounts of pendant methacrylate groups. Due to so-called solvent crazing, denture base polymers have poorer flexural properties when tested in water than in air.
Chemical Phenomena↗
In vitro evaluation of the influence of repairing condition of denture base resin on the bonding of autopolymerizing resins.
STATEMENT OF PROBLEM: Bonding failures of repair resin to denture base resin occurs when denture base resin is wet, however, little is known of how water relates to failures. PURPOSE: This study evaluated the influence of water absorbed in denture base resin on the bond strength and resistance to cyclic thermal stresses of autopolymerizing resins bonded to denture base resin. MATERIAL AND METHODS: Denture base resin disks (n = 180; 12 mm diameter and 3 mm thick) were fabricated from heat-polymerized acrylic resin (Lucitone 199). The disks were divided into groups (n = 60) with 3 conditions of water content: (1) complete water saturation (control), (2) superficial desiccation by blowing air on the specimen, or (3) complete desiccation. Each denture base specimen received 1 of 3 surface treatments (n = 20) including: (1) no treatment, (2) airborne-particle abrasion, or (3) methylene chloride application. An autopolymerizing repair resin (Repair Material, n = 10) or reline resin (Tokuso Rebase Normal set, n = 10) was applied to the bonding area (5 mm diameter) and polymerized at 37 degrees C for 10 minutes. The resistance to cyclic thermal stress was determined after subjecting the specimens to 50,000 thermal cycles between 4 degrees C and 60 degrees C water baths with a 1-minute dwell time (n = 5 per group). Bond strength (MPa) was measured by shear bond testing at a 1.0 mm/min crosshead speed until the applied resin debonded from denture base resin. Data were statistically analyzed by 3-way analysis of variance and multiple comparisons among the groups were performed with Bonferroni test (alpha = .05). RESULTS: The mean bond strengths of repair resin to airborne-particle-abraded denture base specimens were not significantly influenced by either thermal cycling or water content. The mean bond strengths of reline resin significantly decreased after thermal cycling (P < .0001) regardless of the conditions of surface treatment and water content. For methylene chloride treated specimens, bond strengths of both repair and reline resins to completely water saturated specimens were significantly higher than those of completely desiccated specimens (P = .0048 for repair resin, P < .0001 for reline resin) after thermal cycling. CONCLUSIONS: Bond strengths of autopolymerizing resin to denture base resin were not significantly influenced by water content of denture base resin but were significantly influenced by resin type, thermal cycling, and surface treatment.
Absorption↗
[Experimental studies on the influences of occlusal loading conditions and supporting design on stabilization of the base in free-end denture base].
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Dental Stress Analysis↗
Effect of denture base surface pretreatment on microleakage of a silicone-based resilient liner.
STATEMENT OF PROBLEM: Microleakage between resilient liner and denture base resins is a significant clinical problem, often responsible for debonding of the resilient liner from the denture base resin. PURPOSE: This study investigated the effect of 2 surface treatments, airborne-particle abrasion (APA) and wetting with methyl methacrylate monomer (MMA), on microleakage between a silicone-based resilient liner and denture base resin using a gamma camera imaging technique. MATERIAL AND METHODS: Thirty-three specimens, each having 2 plates measuring 40 x 40 x 2 mm, were prepared by packing and processing an acrylic denture base resin (QC-20) into square plates following manufacturer's instructions. Specimens were divided into 3 groups (n=11) as APA-, MMA-, and control-treatment groups. For the APA group, the inner surfaces of both plates were airborne-particle abraded with 250-microm Al 2 O 3 particles and, for the MMA group, surfaces were treated with monomer (QC-20). Control specimens were not surface treated. Following application of an adhesive (Ufi Gel P-specific), a silicone lining material (Ufi Gel P) was prepared and applied to the inner surfaces of all 33 specimens. Eleven size-matched polymethyl methacrylate (PMMA) specimen blocks (40 x 40 x 6 mm) were prepared to calculate the level of residual radioactivity for the denture base itself, the entire outer surface count (OSC). All specimens and PMMA blocks were immersed in a radioactive solution (thallium-201 chloride) for 24 hours. Specimen activities (gamma-ray cts/sec, representing thallium-201 concentration) were then measured using a high-resolution gamma camera. The amount of OSC-subtracted total specimen counts was a direct indicator of the quantity of inward diffusing tracer. The subtracted values were analyzed using a 1-way analysis of variance (ANOVA) and Bonferroni multiple comparison tests (alpha=.05). RESULTS: OSC levels averaged 754 +/- 110 gamma-ray cts/sec. OSC-subtracted APA, control, and MMA values were 5,546 +/- 1,534, 3,392 +/- 738, and 1,405 +/- 392 gamma-ray cts/sec, respectively. All 3 groups were significantly different ( P <.05) from each other. Surface wetting with MMA showed the lowest microleakage values among all specimen groups. CONCLUSION: In terms of microleakage, surface treatment with MMA monomer preceding the adhesive application demonstrated lower values than adhesive application alone. APA pretreatment resulted in 4 times the microleakage found in MMA-treated specimens, and 1.5 times the microleakage of the untreated control. None of the surface pretreatments completely prevented microleakage. Microleakage between the silicone-based resilient liner and denture base resin can be quantitatively determined using the gamma camera imaging technique.
Acrylic Resins↗
Shear bond strength of denture reline polymers to denture base polymers.
PURPOSE: This study was undertaken to characterize the shear bond strength established between four denture base polymers and four denture reline polymers. MATERIALS AND METHODS: Cylindric columns of denture reline polymers were bonded to columns of denture base polymers. Specimens were immersed in water for 4 months and then thermocycled. The strength at which the bond failed under shear stress was recorded. RESULTS: Significant differences in bond strength existed among the specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P < .05). A light-activated denture base polymer (Triad) bonded adequately with a light-activated reline polymer (Triad) but less well with the other reline polymers tested. The bond strength established between some denture base polymers and a different light-activated reline polymer (Rebaron LC) was relatively low. CONCLUSION: The type of denture base polymer and denture reline polymer affected the shear bond strength between them.
Acrylic Resins↗
Impact testing of denture base polymers.
Acrylic resin has been the denture base material of choice since its initial production in 1936, due to its aesthetic properties and ease of processing. It would be desirable, however, to have a material which is also unbreakable under clinical conditions. A wide range of materials has been suggested for use as denture base materials. The impact resistance of a polysulphone denture base polymer has been compared with that of a linear poly(methyl methacrylate) and four rubber-methacrylate denture base polymers. When tested under oral conditions, the polysulphone material had an impact resistance about twice as high as the best rubber-methacrylate and about four times as high as ordinary poly(methyl methacrylate).
Acrylic Resins↗
Longitudinal study on forces transmitted from denture base to retainers of lower distal-extension removable partial dentures with conus crown telescopic system.
The purpose of this study was to perform longitudinal measurement of forces transmitted from the denture base to retainers of lower distal-extension removable partial dentures with a conus crown telescopic system. The experimental denture was embedded with a force-detecting unit which could detect a change in lateral and vertical forces transmitted from denture base to retainers at the same time. Forces were measured during chewing of food on several separate occasions from the insertion of new dentures to about 3 months after. Max.ver (maximal mean value of vertical force) and Max.lat (maximal mean value of lateral force) were calculated from the peak level of all strokes of chewing of food at the minimum of the interocclusal distance. The results are summarized as follows: (i) There were no significant changes of Max.ver and Max.lat; (ii) There were no significant differences of Max.ver between subjects the value of which was about 20 N; (iii) There were significant differences of Max.lat between subjects the value of which was less than 15 N.
Bite Force↗
Some mechanical properties of a highly cross-linked, microwave-polymerized, injection-molded denture base polymer.
PURPOSE: The impact strength and the flexural properties of denture base materials are of importance in predicting their clinical performance upon sudden loading. This study compares the impact and transverse strengths and the flexural modulus of three denture base polymers. MATERIALS AND METHODS: The investigation included a relatively new microwave-polymerized polyurethane-based denture material processed by an injection-molding technique, a conventional microwave-polymerized denture material, and a heat-polymerized compression-molded poly(methyl methacrylate) (PMMA) denture material. Impact strength was determined using a Charpy-type impact tester. The transverse strength and the flexural modulus were assessed with a three-point bending test. The results were subjected to statistical analysis using a one-way analysis of variance and the Scheffé test for comparison. RESULTS: The impact strength of the microwave-polymerized injection-molded polymer was 6.3 kl/m2, while its flexural strength was 66.2 MPa. These values were lower than those shown by the two compression-molded PMMA-based polymers. The differences were statistically significant. The flexural modulus of the new denture material was 2,832 MPa, which was higher than the conventional heat-polymerized polymer but was comparable to the other microwave-polymerized PMMA-based polymer. The difference in the flexural modulus was statistically significant. CONCLUSION: In terms of the impact and flexural strengths, the new microwave-polymerized, injection-molded, polyurethane-based polymer offered no advantage over the existing heat- and microwave-polymerized PMMA-based denture base polymers. However, it has a rigidity comparable to that of the microwave-polymerized PMMA polymer.
Acrylic Resins↗
A reliable method for securing anterior denture teeth in denture bases.
STATEMENT OF PROBLEM: Bond failures continue to occur between resin denture teeth and the denture base. PURPOSE: This qualitative study examined a denture tooth modification to determine whether the joint produced between the denture tooth and the denture base resin was stronger than the materials from which it was composed. MATERIAL AND METHODS: Modified and unmodified resin denture teeth were processed to a denture base and stressed until fracture occurred. The fragments were saved, labeled, examined, and evaluated. RESULTS: The unmodified resin denture teeth, which were displaced from the denture, exhibited no evidence of a bond to the denture base. The modified resin denture teeth fractured before separation could occur. CONCLUSION: Within the limitations of this study, the cingulum ledge lock modification produced a mechanical union of the resin denture teeth tested to the denture base material tested that was stronger than the materials from which the lock was composed.
Acrylic Resins↗
Leaching and cytotoxicity of formaldehyde and methyl methacrylate from acrylic resin denture base materials.
Acrylic resin dentures have the potential to elicit irritation, inflammation, and an allergic response of the oral mucosa. Studies of substances leachable from acrylic resins, their cytotoxicity to cultured cells, and means of reducing their leaching were systematically conducted. Under in vivo and in vitro conditions, formaldehyde and methyl methacrylate were significantly leached into human saliva and saliva-substitute buffer, especially from autopolymerized resins. Both leachable substances showed cytotoxic potentials in the range of their leaching concentrations. Formaldehyde was cytotoxic at lower concentrations than methyl methacrylate. Preleaching in water reduced subsequent leaching of both formaldehyde and methyl methacrylate, and the amount of reduction depended on an increase in the preleaching temperatures. Immersion of acrylic resin dentures in hot water (50 degrees C) before insertion is recommended, especially for autopolymerized resins used either for rebasing or as denture base materials, to minimize the risk of adverse reactions in patients who wear acrylic resin dentures.
Cell Count↗
The static strength and modulus of fiber reinforced denture base polymer.
OBJECTIVES: Partial fiber reinforcements have been employed to strengthen dentures both during repair and in the manufacturing process. The reinforcing fibers can be evenly distributed in the denture base polymer or alternatively fiber-rich phase in the denture base polymer can form a separate structure. The aim of this study was to determinate static three-point flexural strength and modulus of denture base polymer that had been reinforced with different fiber reinforcements. METHODS: The test specimens (3 x 5 x 50 mm) were made of auto-polymerized denture base polymer and reinforced with different fiber reinforcements. The test groups were: (A) no fibers; (B) non-impregnated polyethylene fibers; (C) light-polymerized monomer impregnated glass fibers; (D) porous polymer preimpregnated glass fibers and (E) light-polymerized monomer-polymer impregnated glass fibers. The fibers were oriented parallel to the long axis of the specimen and embedded into the denture base resin on the compression side (n=7) or tension side (n=7). Dry specimens were tested with three-point static flexural strength test set-up at crosshead speed of 5 mm/min. RESULTS: The statistical analysis by two-way analysis of variance showed that the brand and the location of the fiber reinforcements significantly influenced the flexural strength (p<0.0001). However, the location of the fiber reinforcements did not influence the flexural modulus (p<0.722). SIGNIFICANCE: The results suggest that impregnated and preimpregnated fibers reinforce denture base polymer more than non-impregnated fibers. Fiber reinforcements placed on the tensile side resulted in considerably higher flexural strength and flexural modulus values compared with same quantity of fibers placed on the compression side.
Acrylic Resins↗
Effect of cooling procedure on final denture base adaptation.
Well-fitted dentures prevent hyperplasic lesions, provide chewing efficiency and promote patient's comfort. Several factors may affect final adaptation of dentures, as the type of the acrylic resin, the flask cooling procedure and the water uptake. This investigation evaluated the effect of water storage and two different cooling procedures [bench cooling (BC) for 2 h; running water (RW) at 20 degrees C for 45 min] on the final adaptation of denture bases. A heat-cured acrylic resin (CL, Clássico, Clássico Artigos Odontológicos) and two microwave-cured acrylic resins [Acron MC, (AC) GC Dent. Ind. Corp.; Onda Cryl (OC), Clássico Artigos Odontológicos] were used to make the bases. Adaptation was assessed by measuring the weight of an intervening layer of silicone impression material between the base and the master die. Data was submitted to ANOVA and Tukey's test (0.05). The following means were found: (BC) CL=0.72 +/- 0.03 a; AC=0.70 +/- 0.03 b; OC=0.76 +/- 0.04 c//(RW) CL= 1.00 +/- 0.11 a; AC=1.00 +/- 0.12 a; OC=0.95 +/- 0.10 a. Different labels join groups that are not statistically different (P > 0.05). Comparisons are made among groups submitted to the same cooling procedure (BC or RW). The conclusions are: interaction of type of material and cooling procedure had a statistically significant effect on the final adaptation of the denture bases (P < 0.05); water storage was not detected as a source of variance (P > 0.05) on the final adaptation.
Acrylic Resins↗
The swelling phenomenon of acrylic resin polymer teeth at the interface with denture base polymers.
PURPOSE: This study examined the interface between acrylic resin polymer teeth and denture base polymers. MATERIAL AND METHODS: An autopolymerized denture base polymer was cured either at 30 degrees C, 50 degrees C, or 70 degrees C, and a heat-cured denture base polymer was cured at 100 degrees C in contact with acrylic resin polymer teeth. The specimens were ground wet and polished to a thickness of 0.21 mm for the examination of the interface with a light microscope. The surface of the specimens was then treated with the solvent tetrahydrofuran, and the specimens were examined with a scanning electron microscope (SEM). RESULTS: As a result of grinding, the inner parts of the beads at the interface of the teeth were exposed to the denture base polymer. The inner part in these polymer beads of the polymer teeth swelled to a depth of 3 microns when the autopolymerized polymer was cured at 30 degrees C. When cured at 70 degrees C, the thickness of the swelled layer was 21 microns (p < 0.001). Microscopically, the interface between the heat-cured denture base polymer and the polymer teeth appeared diffuse in the region of the interpenetrating polymer networks (IPN) and the matrix. The IPN appeared as a separate zone in the outer parts of the beads of the teeth, both with the light microscope and with the SEM. CONCLUSIONS: The results suggest that by increasing the polymerization temperature, the monomers of the denture base polymers diffused more effectively into acrylic resin polymer teeth. This increases the bond strength between the polymer teeth and the denture base polymer.
Acrylic Resins↗
Comparison of the fracture resistance of six denture base acrylic resins.
Fracture strength of denture base resins is of great concern, and many approaches have been used to strengthen acrylic resin dentures. Fracture resistance of six commercially available acrylic resin denture base materials were compared, through impact and transverse strength tests. Three rapid heat-polymerised resins (QC 20, Meliodent and Trevalon), two high-impact strength resins (Trevalon Hi and Lucitone 199) and a strengthened injection-moulded acrylic resin (SR Ivocap plus) were included in the study. Twenty acrylic resin test specimens were fabricated from each resin. For impact strength test, ten notched specimens were tested in a Charpy-type impact tester. The other ten specimens were used for transverse strength tests, deflection and modulus of elasticity values were also determined, which were assessed with three-point bending tests using an Universal Testing Machine. Impact test values showed significant differences among acrylic resins (F= 4.817 p = 0.0). SR Ivocap resin showed the highest impact strength values, followed by Trevalon Hi and Lucitone 199. The transverse strength test values were not significant when six acrylic resins were compared (F= 1.705 p = 0.151). High-impact resins can be recommended to increase the impact strength of denture base. If the cause of fracture is mechanical or anatomical, strengthened acrylic resins and conventional acrylic resins have similar fracture resistance.
Acrylic Resins↗
Effect of five woven fiber reinforcements on the impact and transverse strength of a denture base resin.
STATEMENT OF PROBLEM: Fracture strength of denture base resins is of great concern, and many approaches have been used to strengthen acrylic resin dentures. PURPOSE: This study measured the effect of 5 fiber strengtheners on the fracture resistance of denture base acrylic resin material. Impact strength, transverse strength, deflection, and elasticity modulus values of a heat-polymerized denture base resin (Trevalon), reinforced with glass, carbon, thin Kevlar, thick Kevlar, and polyethylene fibers in woven form were studied. MATERIAL AND METHODS: One hundred acrylic resin test specimens reinforced with woven fibers were fabricated. The control group consisted of 20 specimens with no fiber reinforcement. For the impact strength test, a Charpy-type impact tester was used. Transverse strength was assessed with a 3-point bending test by using a screw-driven mechanical testing machine. Ten specimens were used for each test. RESULTS: The highest impact test values were produced by polyethylene-reinforced group, and the lowest values were obtained from specimens containing no fibers. There were significant differences among the test groups, but no significant differences in transverse strength were found. The lowest transverse strength values were obtained for specimens strengthened with polyethylene fibers, which also insignificantly decreased transverse strength of the acrylic resin. CONCLUSION: The impact strength of denture base acrylic resins was increased with fibers in woven form. Tested fibers did not have a significant effect on the transverse strengths.
Analysis of Variance↗
Comparison of bond strengths of three denture base resins to treated nickel-chromium-beryllium alloy.
PURPOSE: In-vitro bond strengths of 3 denture base resins (Trutone, Lucitone 199, and Triad) to a nickel-chromium-beryllium removable partial denture alloy (Ticonium) were tested with 3 surface pretreatments: sandblast, acid etch, and Rocatec (silica blasting), with or without primers (Dentsply, CR inlay cement, and Super Bond). MATERIAL AND METHODS: Lucitone 199 denture base resin bonded to the nonprimed sandblasted alloy specimen served as the control group. Alloy specimens were prepared, surface treated, and primed or not primed with primer. The treated specimens were then packed and processed with the denture base resin. Bonded specimens were stored in the distilled water at 37 degrees C for 24 hours, and then debonded in tension. The force at which the bond failed was noted, and bond strength was calculated in megapascals (MPa). Five replications for each condition (180 specimens total) were tested. RESULTS: Significant differences in bond strength were observed with primer, the most important factor, followed by pretreatment and denture base resin. Without primer for all 3 denture base resins, the Met-Etch and Rocatec treated group showed significantly higher bond strengths than the sandblasted groups. For Trutone denture base resin, nonprimed treated groups produced significantly higher bond strength than those for the other 2 denture base resin, nonprimed treated groups produced significantly higher bond strength than those for the other 2 denture base resins. The control group had zero bond strength. For Dentsply primer, the Rocatec treated group bonded to Lucitone 199 resin produced the highest bond strength value (14.8 +/- 1.8 MPa). For CR inlay cement, the Met-Etch and Rocatec treated groups for Lucitone denture base resin demonstrated the highest bond strength (19.3 +/- 4.8 MPa, and 19.3 +/- 1.8 MPa, respectively). For super Bond primer, the Met-Etch treated group for Trutone resin demonstrated the highest bond strength (19.8 +/- 6.2 MPa). CONCLUSIONS: Without primer, the control had the lowest bond strength (0 MPa), and the Trutone groups showed the highest bond strength (11.7 +/- 4.1 MPa). Met-Etch and Rocatec treated groups produced higher bond strengths than the sandblasted groups. The primed specimens demonstrated significantly higher bond strengths than nonprimed specimens, except for Trutone resin, for which primed specimens produced lower bond strengths than the nonprimed specimens.
Acid Etching, Dental↗