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PubMed1978

Wear of combinations of acrylic resin and porcelain, on an abrasion testing machine.

Wear tests of various combinations of acrylic resin and porcelain were made using a machine which was designed to test materials under conditions similar to those of masticatory function by simulating the loads, sliding distances, and contact times encountered in the human masticatory cycle. The results showed that the amount of wear of the two materials worn in combination depended on the nature of the surrounding medium and on the surface roughness of the opposing material. Acrylic resin showed good wear resistance provided no third party abrasive or opposing hard, rough surface was present. When a mild abrasive was incorporated in the system, the acrylic resin vs acrylic resin combination wore almost seven times more than porcelain vs porcelain. Clinical experience would suggest that this is a reasonably sound order of wear.

Acrylic Resins↗
PubMedDate not supplied

In vivo heat transfer capacities of autopolymerizing, heat-polymerizing, and injection-molded acrylic resins.

The aim of this pilot study was to measure the heat transfer capacities of heat-polymerizing, injection-molded, and autopolymerizing acrylic resins in vivo. Two volunteers used acrylic resin removable plates and consumed hot (69 degrees C) and cold drinks (6 degrees C). Differences between oral temperature and highest and lowest temperature readings were recorded. Temperature changes for the autopolymerizing acrylic resin were found to be significantly higher than the heat-polymerizing and injection-molded acrylic resins for both cold and hot drinks. Despite the disadvantages of autopolymerizing acrylic resins, their high heat transfer capacity may be an advantage.

Acrylic Resins↗
PubMedDate not supplied

Contact allergens in ultraviolet-cured acrylic resin systems.

Ultraviolet-cured acrylic resin systems expose the worker to an ultraviolet reactive prepolymer, multifunctional acrylate esters, and a photoinitiator system. Irritation occurs primarily with exposure to the acrylate compounds and increases with an increased number of acrylic double bonds, decreased viscosity, and the presence of hydrophilic groups. It is recommended that sensitive individuals handle these materials with nitrile gloves, but acrylics have been known to penetrate even this form of protection.

Acrylic Resins↗
PubMed1997

Reinforcement of acrylic resins for provisional fixed restorations. Part I: Mechanical properties.

Acrylic resins are commonly used in many dental applications; especially in the fabrication of provisional fixed partial dentures. Among noticed technical drawbacks associated with this material are unsatisfactory mechanical properties. Moreover, if acrylic resins are exposed to moist environment, water sorption results in further mechanical deterioration. In order to improve the mechanical properties, aluminum, magnesium, and zirconium oxide powders and pulverized E-glass particles were separately admixed with pre-polymerized acrylic resin beads prior to mixing with monomer liquid. Particle loading ratios were 1, 2 and 3 vol.% with respect to pre-polymerized beads. Poly(methyl methacrylate), poly(ethyl methacrylate) and poly(isobutyl methacrylate) were used as resin matrices. Furthermore, a metal primer agent was employed in order to form a strong interphase between admixed particles and polymer matrix phase. Samples were subjected to three-point transverse bending tests at a crosshead speed of 10 mm/min. It was concluded that (1) addition of particles generally increases the water sorbed by the composite resins systems, (2) however, two vol.% admixtures in a PMMA resin matrix showed significant improvements in the mechanical properties (p < 0.05), (3) among the oxide particles, zirconia exhibited the greatest improvements in modulus of elasticity, transverse strength, toughness and hardness, and (4) mechanical properties (transverse strength, 0.2% offset yield strength and modulus of elasticity) were linearly correlated to hardness numbers.

Acrylic Resins↗
PubMed1994

Development of a radiopaque, autopolymerizing dental acrylic resin.

PURPOSE: Current prosthetic acrylic resins are radiolucent and cannot be imaged using standard radiographic techniques. If accidentally impacted or ingested, delays in localizing or removing the foreign body may be life-threatening. The purpose of this study was to evaluate the influence of an experimental radiopaque additive, triphenyl bismuth (TPB), on polymethyl methacrylate resins formulated for dental use. We also investigated methods to improve TPB-containing resin microbeads and optimize processing variables for specimen fabrication in autopolymerizing resin systems. MATERIALS AND METHODS: Selfcured samples of experimental resins were prepared containing 0% to 27% TPB and were tested according to American National Standards Institute/American Dental Association and International Organization for Standardization performance standards. A control group and two commercial provisional crown and bridge resins were used for comparison. RESULTS: The standard of radiopacity (> or = aluminum radiopacity) is met at TPB levels of > or = 14.5%. The control resin had a greater transverse deflection compared with the TPB-resin groups, but deflection was within standard limits for all resins. Polishability, color stability, and solubility were unaffected by TPB, whereas sorption decreased, although not significantly, at higher TPB levels. Translucency decreased at 27% TPB, and specimens containing 0% to 20% TPB were transparent. A tendency to entrain air bubbles, because of the hydrophobicity of TPB, resulted in increased susceptibility to brittle failure at the higher TPB levels. Solubility slightly exceeded American Dental Association standards for all TPB-resins and the control. All other performance standards were acceptable for resins containing 0% to 20% TPB. CONCLUSIONS: At concentrations that provide a diagnostic level of radiopacity, TPB does not significantly alter required performance and processing properties. Thus, TPB is capable of commercially acceptable performance as a radiopacifying additive for dental acrylics.

Analysis of Variance↗
PubMed2002

Effect of commercial acrylic resins on dimensional accuracy of the maxillary denture base.

Denture base dimensional changes were found with commercial thermocured acrylic resins. Fifteen stone cast-wax base sets were packed for routine flasking. Clássico, Vipcril, and Meliodent Multicryl acrylic resins were prepared according to manufacturer instructions. After final acrylic resin pressing, the flasks were placed in strain clamps and submitted to polymerization cycles in heat-water following manufacturer instructions. The resin bases were fixed on casts with instant adhesive and the sets laterally sectioned in the corresponding regions to the distal of canines (A), mesial of first molars (B), and posterior palatal zone (C). The gap between the stone cast and resin base was verified with a measuring microscope at five reference positions for each type of cut. The data were submitted to ANOVA and Tukey's test and a significant statistical difference between the commercial acrylic resins was shown. The pattern of distortion verified in the posterior palatal region was confirmed in the C cut with significant statistical differences among the three acrylic resins. However, there were no significant statistical differences in A and B cuts.

Acrylic Resins↗
PubMed1980

Reactions to acrylic resin dental prostheses.

A review of the pertinent literature concerning acrylic resin and its relation to allergic reactions and chemical injury has been presented. The relation of acrylic resin prostheses and materials to oral reactions and lesions is discussed and possible causes and means of evaluation are proposed. Examples of mucosal infection and mucosal disease are presented (which may mimic acrylic resin allergy) along with examples of direct chemical injury of the oral mucosa as a result of autopolymerizing prosthetic techniques.

Acrylic Resins↗
PubMed1989

[New acrylic resins with very low residual monomer].

New experimental acrylic resins were prepared by polymerization of MMA in the presence of vinylidene fluoride/hexafluoropropylene copolymer. The amount of residual monomer in the resins prepared by visible light curing, cold curing, and heat curing, at various polymer/monomer ratios, was measured and compared with the usual MMA/PMMA resin. In the visible light cured resins containing 60 or 70 wt% of the fluoropolymer, the amount of residual monomer was less than 0.1%. In the cold cured resins, the amount of residual monomer was very low: 0.2% and 0.7% for the resins containing 70 and 60 wt% of the polymer, respectively. These values were comparable to the usual heat cured MMA/PMMA resins. In the heat cured resins, the amount of residual monomer was the lowest; less than 0.1%, even in the resin consisting of 50 wt% polymer. Thus, we prepared new acrylic resins with much less residual monomer than the usual MMA/PMMA resins.

Acrylic Resins↗
PubMedDate not supplied

Accuracy of the acrylic resin pattern for the implant-retained prosthesis.

An in vitro study was conducted to determine the accuracy of fit of the acrylic resin pattern for the implant-supported prosthesis to the implant abutments. A master model containing five Nobelpharma titanium implants was fabricated using Ivocap acrylic resin. Using this model, five standardized acrylic resin patterns were fabricated from the three test dental acrylic resins. The fabricated patterns remained on the master model for 24 hours before removal and subsequent measurement. To compute the accuracy of each pattern, three special measuring points were firmly attached to each gold cylinder prior to pattern fabrication and the x, y, and z coordinates of these measuring points were determined. Measurements were made prior to pattern fabrication, with the cylinders on their respective abutments and after pattern fabrication, when the pattern had been removed from the master model. The results of this study showed that there was a significant difference in accuracy between the test acrylic resins and that none of these materials was completely accurate.

Acrylic Resins↗
PubMedDate not supplied

Comparison of impact strength of acrylic resin reinforced with kevlar and polyethylene fibres.

The present study was done to evaluate the impact strengths of heat-activated acrylic resins reinforced with Kevlar fibres, polyethylene fibres and unreinforced heat activated acrylic resin. Each of three groups had 25 specimens. Brass rods of uniform length of 40 mm and diameter of 8 mm were used to prepare the moulds. A combination of long fibres (40 mm length) and short fibres (6 mm length) were used. The total amount of fibres incorporated was limited to 2% by weight of the resin matrix. Short and long fibres of equal weight were incorporated. The short fibres were mixed with polymer and monomer and packed into the mould, while, the long axis of the specimen, perpendicular to the applied force. The specimens were then processed. Impact strength testing was done on Hounsfield's impact testing machine. Kevlar fibre reinforced heat activated acrylic resin specimens recorded higher mean impact strength of 0.8464 Joules, while polyethylene fibres reinforced heat activated acrylic resin recorded mean impact strength of 0.7596 joules. The unreinforced heat activated acrylic resin recorded mean impact strength of 0.3440 Joules.

Acrylic Resins↗
PubMedDate not supplied

Effect of the addition of poly(methyl methacrylate) beads on some properties of acrylic resin.

PURPOSE: There have been numerous attempts to improve the mechanical properties of acrylic resin. However, the fracture of dentures is still an unresolved problem. The potential advantage of self-reinforcement should be improved mechanical properties over the amorphous random polymer. This study investigated the addition of poly(methyl methacrylate) (PMMA) beads in a variety of percentages on a range of mechanical properties of PMMA denture base acrylic resin. MATERIALS AND METHODS: The transverse and impact strengths and hardness of acrylic resin specimens stored in water for periods of 1 week and 6 months prior to testing were investigated. RESULTS: The results showed that for specimens stored for 1 week, the addition of up to 25% beads produced a significant increase in the modulus of elasticity. Addition of 5% beads produced a slight but nonsignificant increase in the modulus of rupture, although additions of increasing percentages produced a decrease in the modulus of rupture. The impact strength was increased for 5% to 25% beads and decreased for 40% beads. The hardness showed only small changes. For specimens stored in water for 6 months, the modulus of rupture decreased with increasing percentages of beads. The addition of beads up to 10% significantly increased the modulus of elasticity. There was no significant increase in impact strength but a significant increase in hardness for 5% beads. CONCLUSION: The addition of PMMA beads to acrylic resin did not produce a substantial improvement in the mechanical properties and cannot be recommended as a method of reinforcement in its present form.

Acrylic Resins↗
PubMed1993

Effects of thermocycling and occlusal force on the margins of provisional acrylic resin crowns.

Transitional acrylic crowns were examined for changes in axial contour and increases in marginal gap width after simultaneous thermocycling and occlusal loading. Two groups of 10 crowns--one with a shoulder finish line and another with a chamfer finish line--were treated with 3400 thermocycles and 50,000 load cycles simultaneously within an artificial oral environment chamber in an MTS Dental Materials Testing System. The marginal gaps were increased for both groups after treatment. However, the group of crowns with the shoulder finish lines demonstrated a smaller gap width (x = 90 microns) after treatment than the crowns with chamfer finish lines (x = 210 microns). A statistical comparison identified a significant difference in gap width between groups (p < 0.01). Changes in the axial profile of the groups were similar, but one crown with a chamfer finish line exhibited a cracked margin.

Acrylic Resins↗
PubMedDate not supplied

An investigation of heat transfer to the implant-bone interface related to exothermic heat generation during setting of autopolymerizing acrylic resins applied directly to an implant abutment.

Excessive heat generation at the implant-bone interface may cause bone damage and compromise osseointegration. Autopolymerizing acrylic resins are commonly used intraorally to join impression copings and suprastructure components for soldering. The effect of heat generation at the implant surface related to the exothermic setting reaction of autopolymerizing acrylic resins applied to an attached abutment was examined in vitro. Two brands of autopolymerizing acrylic resin, Duralay and GC Pattern Resin, were compared. Acrylic resin was applied to a titanium alloy abutment connected to a titanium alloy cylindric implant in varying controlled volumes, with both bulk application and brush paint-on techniques. The implant was embedded in an acrylic resin mandible in a 37 degrees C water bath. Temperature changes were recorded via embedded thermocouples at the cervical and apical of the implant surface. Analysis of variance for repeated measures was used to compare treatment groups. A mean maximum increase in temperature of 4 to 5 degrees C was seen at the implant cervical for both materials, with a maximum temperature increase of 6 degrees C. No difference between Duralay and GC Pattern Resin was seen, except for bulk application to medium-sized copper bands at the implant cervical (P < .05). No difference between the bulk and brush techniques was seen for all options, except for GC, where bulk application to medium-sized copper bands produced higher temperatures than the brush technique (P < .05). Spray coolant reduced temperatures for bulk application of both Duralay and GC (P < .05).

Acrylic Resins↗
PubMed1975

Minor connector designs for anterior acrylic resin bases: a preliminary study.

The effect of nine different designs on the strength of acrylic resin attachment to the partial denture framework in anterior endentulous spaces was tested. Thirty metal frameworks, incorporating nine different designs and a control, were fabricated. Acrylic resin was processed to these frameworks, and the resin was subjected to a shear force. The framework designs offering strong retention for acrylic resin bases allowed the use of a greater bulk of acrylic resin projecting through openings in the metal retention design.

Acrylic Resins↗
PubMed1990

Post embedding immunoelectron microscopy of human breast cancer: a comparison of three acrylic resins.

The suitability of three acrylic resins for the immunoelectron microscopical localization of cell surface and cytoskeletal antigens in surgically excised, immersion fixed human breast cancer, using an immunogold system, has been assessed. Good localization of milk fat globule membrane was achieved with LR White, LR Gold and Lowicryl K11M, although the embedding schedule for LR White had to be modified. The best results were achieved with Lowicryl K11M. Only scanty labelling of actin and cytokeratin was seen in LR White embedded tissue, whereas there was clear localization in LR Gold and Lowicryl K11M embedded samples. Tubulin and alpha-actinin was detected at low level in tissues in the low temperature embedding resins, but not in LR White embedded samples. The morphology of the latter was poorer, and there was greater variability in ultrastructure and labelling. Of the two low temperature embedding resins, Lowicryl K11M gave slightly better results. However, the advantages could be outweighed by the problem incurred in achieving the low temperatures, and by poorer handling properties than LR Gold.

Acrylic Resins↗
PubMed1984

The transverse strength of acrylic resin strips and of repaired acrylic samples.

A method was developed for measuring the transverse strength of repaired acrylic samples at a single butt joint. The strength was determined for samples prepared from two types of heat polymerizing resins and two types of repair resins. The temperature elevation during curing of the repair resins was determined. Cross-linking of the resins was evaluated by immersion of samples in solvents. The appearance of the bead microstructure after various treatments was considered to indicate relaxation at the sample surface. Repaired samples of the heat polymerizing resin which exhibited relaxation after immersion in monomer, had a lower strength than samples prepared from the resin for which relaxation was not observed, although both resins were cross-linked to a similar extent. The application of pressure during curing increased the strength of the samples repaired with the rapid curing, cross-linked, repair resin. The strength of the samples repaired with the uncross-linked, slow curing, repair resin was affected by pressure only if the insertion of the repair resin between the sample parts was delayed after mixing. Variations in the powder to liquid ratio of the uncross-linked repair resin did not affect the sample strength. Wetting of the sample parts with monomer before repair, and variations in the curing temperature did not affect the sample strength for the investigated resin combinations.

Acrylic Resins↗
PubMedDate not supplied

Monitoring the polymerization process of acrylic resins.

Four groups of autopolymerizing acrylic resins used for various purposes in current dental practice were investigated by monitoring their temperature changes during the polymerization process. Resins were compared in terms of characteristic parameters (such as the time interval needed to reach mechanical stability and the maximum temperature generated during the polymerization process) and interpretations were made of such temporal temperature profiles.

Acrylic Resins↗
PubMedDate not supplied

Effect of chemical disinfectants and repair materials on the transverse strength of repaired heat-polymerized acrylic resin.

PURPOSE: The purpose of this study was to evaluate both the effects of immersion in different chemical disinfectant solutions and the type of repair material on the transverse strength of repaired heat-polymerized acrylic resin. MATERIALS AND METHODS: A total of 110 rectangular specimens (65 x 10 x 3 mm) of heat-polymerized acrylic resin (Triplex) were fabricated. After polymerization, the specimens were polished, then stored in distilled water at 37 degrees C for 1 week. The specimens were divided into 11 groups (n = 10) coded A to K. Specimens of Group A remained intact (control). The specimens of Groups C to F and Groups H to K were immersed in the following chemical disinfectant solutions (1%, 2.5%, and 5.25% sodium hypochlorite and 2% glutaraldehyde, respectively) for 10 minutes. The specimens of all groups except those of Group A were sectioned in the middle to create 10 mm gaps and repaired with the same resin (Groups B to F) and autopolymerizing acrylic resin (Groups G to K). The specimens of Groups C to F and Groups H to K were again immersed in the disinfectant solutions in the same sequence. The transverse strength (N/mm(2)) was tested for failure in a universal testing machine, at a crosshead speed of 5 mm/min. Two-way analysis of variance (ANOVA) was performed to evaluate the effects of both the disinfectant solutions and repair materials on the transverse strength of repaired specimens. All data were statistically analyzed using one-way analysis of variance followed by Tukey's test at 95% confidence level. RESULTS: The repaired specimens treated with/without disinfectant solutions showed similar (p > 0.05) transverse strength values. No differences (p > 0.05) were detected among the repaired specimens either with heat-polymerized or autopolymerizing acrylic resins. The intact specimens showed transverse strength values (86.9 +/- 11.8) significantly higher (p < 0.05) than the values of the repaired specimens. CONCLUSIONS: Among the repaired specimens, transverse strength was not affected after immersion in the disinfectants for the immersion period tested (10 min). The repair material, either heat-polymerized or autopolymerizing acrylic resin, had no effect on the transverse strength of the repaired acrylic resin specimens.

Acrylic Resins↗