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PubMed1990

Radiopaque acrylic resins containing miscible heavy-metal compounds.

Radiopacity is needed in order to facilitate diagnosis of polymeric appliances, which may be dislodged and become impacted in the upper respiratory or digestive tracts. In order for a stable, optically transparent, radiopaque material to be provided, heavy-metal compounds were investigated which we had previously shown to form homogeneous structures with methyl methacrylate-based systems. It was found that, when present in PMMA at 11 to 14%, several compounds of either bismuth or uranium or 35% of an organo-zirconium compound impart radiopacity equivalent to that of aluminum. A low level of cytotoxicity and lack of mutagenicity indicated that a high level of biocompatibility can be expected. Processing characteristics are somewhat altered, but formulations satisfactory for use in various dental devices were found.

Acrylic Resins↗
PubMed1992

Novel acrylic resins for dental applications.

A heat-cured resin based on a copolymer of bis-phenol-A glycidyl methacrylate (bis-GMA) and tetrahydrofurfuryl methacrylate (THFM) was investigated. Workable pastes were made by adding 90/10 w/w bis-GMA/THFM copolymer powder to a 70/30 w/w monomer of the same composition. The organic filler content was 60-64% w/w. Young's modulus, flexural strength, impact strength, hardness, water absorption and desorption, linear thermal expansion, polymerization shrinkage and glass transition temperature were determined. The materials studied showed high elastic modulus, hardness and glass transition temperature. A relatively low linear thermal expansion was obtained but poor impact strength and low flexural strength, indicating brittleness. Acceptable values were obtained for water absorption.

Acrylic Resins↗
PubMed2005

Dimensional change of heat-cured acrylic resin dentures with three different cooling regimes following a standard curing cycle.

The aim of the study was to compare dimensional changes in poly(methylmethacrylate) complete denture bases resulting from three different cooling regimens following a standard heating cycle. Changes in three separate dimensions were measured on ten dentures within each cooling regimen after curing, and before and after removing the denture from the cast using a computer imaging system. No consistent differences occurred as a result of removing the denture from the cast. The results indicated that there was greater change in dimension of dentures with the quenching cooling method than with either overnight cooling in the water bath or bench cooling. This was particularly evident after removal from the cast after curing (p<0.001). It is concluded that slow cooling results in less dimensional change.

Acrylic Resins↗
PubMedDate not supplied

The flexural strengths of denture base acrylic resins after relining with a visible-light-activated material.

PURPOSE: Previous studies disclosed the ability of a light-activated denture reline material to strengthen a particular denture base material. The present study investigated the ability of the reline material to strengthen denture base materials processed by other means. MATERIALS AND METHODS: Four denture base materials were tested for flexural strength at proportional limit (FSpl) with or without being relined. RESULTS: The reline material maintained the FSpl of the microwave-processed and the autopolymerizing denture base materials. It increased the FSpl of the heat-processed and the light-activated denture base materials. CONCLUSION: the light-cured reline material increased the flexural strengths of the heat-processed and the light-activated denture base materials and maintained those of the microwave-processed and the autopolymerizing denture base materials.

Acrylic Resins↗
PubMed1991

Surface treated polyethylene fibres as reinforcement for acrylic resins.

The use of poly(methyl methacrylate) as a bone and dental cement material over several decades has provided us with experience related to processing and performance. A recognized disadvantage of such cements is their mechanical behaviour, expressed by low crack propagation resistance, impact strength, fatigue resistance and reduced fracture toughness. Many attempts have been made to resolve these problems either by modifying the poly(methyl methacrylate) chemical structure via copolymerization or incorporating reinforcing additives. The latter is of great importance, because it can lead to the preparation of composite materials with considerably improved performance. Besides reinforcement, the incorporation of additives, such as fibres, results in better processing characteristics, e.g. lowers polymerization exotherm. In this work, poly(methyl methacrylate) reinforced with Tekmilon ultra high modulus polyethylene fibres was studied, focussing on the interfacial bonding between matrix and reinforcement. Some finishing agents were used to treat the fibres and their efficiency was mainly evaluated through the effect on the mechanical properties of the composite material prepared.

Acrylic Resins↗
PubMed1981

The validity of maxillomandibular records made with trial and processed acrylic resin bases.

A comparison was made of the accuracy of maxillomandibular records made with trial bases fabricated on casts with blocked-out undercuts and those made with final processed bases. The results of the study indicate that significantly greater occlusal discrepancies occurred after the final processing when trial bases were used to obtain jaw records. With processed final bases, the denture superstructures are attached to the same bases used for recording, transferring, and adjusting the occlusion of the dentures. Thus, the dimensional changes of processing and the uneven setting of the bases upon the unevenly resilient mucosa are incorporated into both records and dentures. When placed in the mouth the conditions during and after fabrication are similar and occlusal discrepancies are minimal. With the trial base technique, the imperfections of both bases and clinical records are transferred to the final denture bases, which also have processing inaccuracies and which settle differently when placed upon the resilient tissue support. The divergent conditions created by the use of two types of bases are reflected in occlusal discrepancies of the completed dentures.

Acrylic Resins↗
PubMedDate not supplied

Effect of 180-week water storage on the flexural properties of E-glass and silica fiber acrylic resin composite.

PURPOSE: The aim of this study was to determine the effect of long-term water immersion on the flexural properties of fiber-reinforced composite. MATERIALS AND METHODS: Continuous, woven, silanized E-glass fibers and woven silica fibers were used to reinforce heat-cured and autopolymerized denture base polymers. Fibers were oriented at a 45-degree angle to the long axis of the test specimens. Control specimens were unreinforced. Dry test specimens and those stored in water for up to 180 weeks were tested with a 3-point loading apparatus. RESULTS: Ultimate transverse strength and flexural modulus of unreinforced and fiber-reinforced composite test specimens decreased during water storage (P < 0.001, analysis of variance). Post hoc analysis revealed that after the storage of 4 weeks no statistically significant reduction occurred. CONCLUSION: The results of this study suggest that the ultimate transverse strength of the fiber-reinforced composite made from E-glass fibers is reduced by approximately 27% compared to the dry fiber-reinforced composite. The majority of the reduction occurred during 4 weeks of storage in water and remained approximately at that level for 180 weeks.

Acrylic Resins↗
PubMed2006

Residual monomer of reline acrylic resins. Effect of water-bath and microwave post-polymerization treatments.

OBJECTIVES: This study compared the residual monomer (RM) in four hard chair-side reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TRF and Ufi Gel hard-UGH) and one heat-polymerized denture base resin (Lucitone 550-L), which was processed using two polymerization cycles (short-LS and long-LL). It was also investigated the effect of two after polymerization treatments on this RM content. METHODS: Specimens (n=18) of each material were produced following the manufacturers' instructions and then divided into three groups. Group I specimens were left untreated (GI-control). Specimens of group II (GII) were given post-polymerization treatment by microwave irradiation. In group III (GIII), specimens were submitted to immersion in water at 55 degrees C (reline resins-10 min; denture base resin L-60 min). The RM was analyzed using high performance liquid chromatography (HPLC) and expressed as a percentage of RM. Data were analyzed by two-way ANOVA followed by Tukey's test (alpha=0.05). RESULTS: Comparing control specimens, statistical differences were found among all materials (p<0.05), and the results can be arranged as K (1.52%)>D (0.85%)>UGH (0.45%)>LL (0.24%)>TRF (0.14%)>LS (0.08%). Immersion in hot water (GIII) promoted a significant (p<0.05) reduction in the RM for all materials evaluated compared to control (GI), with the exception of LL specimens. Materials K, UGH and TRF exhibited significantly (p<0.05) lower values of RM after microwave irradiation (GII) than in the control specimens. SIGNIFICANCE: The reduction in RM promoted by water-bath and microwave post-polymerization treatments could improve the mechanical properties and biocompatibility of the relining and denture base materials.

Acrylic Resins↗
PubMedDate not supplied

Evaluation of the sustained release properties of Eudragit RS, RL and S (acrylic resins) microcapsules containing ketoprofen in beagle dogs.

Eudragit RS, RS-RL, RL and S microcapsules containing ketoprofen were prepared by the solvent evaporation process in oil phase. The sustained release effect of these microcapsules and Oruvail, the representative commercial product of ketoprofen, was evaluated by the pH shift dissolution method and in beagle dogs, respectively. The dissolution patterns of ketoprofen from Eudragit RS, RS-RL and RL microcapsules were independent of the pH of the dissolution medium, and its dissolution rate increased with increasing content of ketoprofen in microcapsules. But the dissolution pattern of ketoprofen from Eudragit S microcapsules and Oruvail was found to depend on the pH of the dissolution medium. The rank order of the dissolution rate of ketoprofen from Eudragit RS, RS-RL and RL microcapsules containing 30 and 40 per cent (w/w) ketoprofen was sufficiently clear as to enable prediction of the relative bioavailability of ketoprofen from these microcapsules. In vivo evaluation using beagle dogs, sustained release effects of Eudragit RL and Eudragit S microcapsules containing 30 per cent (w/w) ketoprofen and Eudragit RS-RL microcapsules containing 40 per cent (w/w) ketoprofen were almost the same as or slightly superior to that of Oruvail.

Acrylic Resins↗
PubMed1989

Applicability of using acrylic resins in post-embedding ultrastructural immunolabelling of human neutrophil granule proteins.

In this study, quantitative assessments were carried out, (1) by light microscopy during tissue preparation for electron microscopy and (2) by electron microscopy after on-grid immunogold staining, to determine the suitability of using LR White and Lowicryl K4M thin sections to identify lactoferrin and elastase in the granules of human neutrophil leucocytes. Quantitative assessment of the effect of fixation, dehydration and embedding on the preservation of antigenicity during tissue preparation for electron microscopy, using light microscopic peroxidase anti-peroxidase immunocytochemistry, enabled the selection of preparation conditions that adequately preserved both antigenicity and ultrastructure. OsO4 post-fixation, following primary aldehyde fixation, improved the retention of antigenicity during dehydration and embedding and the preservation of fine structure. Partial rather than complete dehydration retained more of the antigenicity. The efficiency, sensitivity and resolution of immunolabelling and the ultrastructure and quality of sections achieved after embedding in LR White were superior to those obtained after embedding in Lowicryl K4M. Consequently room temperature embedding in LR White following double fixation and partial dehydration is a better and more reliable preparation technique than low-temperature embedding in Lowicryl K4M following single fixation and partial dehydration for localizing lactoferrin and elastase to the specific and primary granules respectively in human neutrophilic granulocytes by the on-grid immunogold staining method.

Acrylic Resins↗
PubMed1986

Clinical effects of glazing denture acrylic resin bases using an ultraviolet curing method.

Control of denture plaque accumulation is essential to obtain and maintain a healthy oral mucosa in denture wearers. The present study was designed to study the effect on denture plaque accumulation and denture stomatitis of coating the fitting denture surface by a glaze. Twenty-one subjects wearing complete dentures participated in the study. Glazing of the denture surface was performed using a Perma Cure System. Plaque accumulation was studied clinically and using a semiquantitative microbiologic technique. Plaque accumulation on the glazed and the non-glazed halves of the fitting denture surface was compared after 1 wk. There was significantly less plaque on the glazed half of the denture (P less than 0.001), and the calculated number of CFU of bacteria/cm2 was significantly lower from the test area of the glazed half than from the test area of the non-glazed half of the denture (P less than 0.001). When the patients were re-examined 1 month after the entire fitting denture surface had been glazed plaque scores, yeast scores and number of CFU of bacteria/cm2 were not significantly different from those observed before glazing. There was a reduction of the erythema of the palatal mucosa in 14/19 patients with denture-induced stomatitis. The study indicates that coating of the fitting denture surface by a glaze may be a means to improve denture cleanliness; however, the present glazing system should be further developed to produce a more uniform glazing.

Acrylic Resins↗
PubMed2006

The effect of cyclic drying on dimensional changes of acrylic resin maxillary complete dentures.

Poly(methyl methacrylate) dentures may exhibit dimensional changes when drying. Drying has been shown to destroy Candida albicans. This study investigates the effect of simulating overnight cyclic drying on dimensional changes of four complete denture base materials. Denture specimens used in this study had been prepared for a previous study. All dentures had been kept hydrated at room temperature for 2 years. The materials used were, group 1, conventionally packed and cured Trevalon, group 2 was injection moulded and conventionally cured (Trevalon Success), group 3 (Acron MC) and group 4 was Microbase, which is injection moulded and microwave cured. The measurements of the inter-molar and inter-premolar width, and anterior posterior dimension between the premolars and molars were recorded after 8 h drying and then after four cycles of dehydration and rehydration. The dentures were more dimensionally stable in the anterior posterior than the cross arch dimension. There was a statistically significant (P < 0.02) increase in the intermolar width for Trevalon, Trevalon Success and Acron after 8 h drying and after four cycles. There was a statistically significantly difference between Microbase and the other materials after 8 h drying and there was a significant difference between the injection moulded groups in the interpremolar width (Trevalon Success versus Acron, Trevalon Success versus Microbase) after cyclic drying. Although statistically significant dimensional changes were observed for all materials these were small and were considered not to be clinically significant. Microbase was the least dimensionally stable material during air-drying.

Acrylic Resins↗
PubMedDate not supplied

Effect of water storage on the flexural properties of E-glass and silica fiber acrylic resin composite.

PURPOSE: The aim of this study was to determine the effect of water on the flexural properties of fiber-reinforced denture base polymers. MATERIALS AND METHODS: Continuous woven silanized electrical glass, or E-glass, fibers and woven silica fibers were used to reinforce heat-cured and autopolymerized denture base polymers. Fibers were oriented at a 45-degree angle to the long axis of the test specimens. Control specimens were unreinforced. Dry test specimens and those stored in water for up to 48 weeks were tested with a three-point loading apparatus. The surfaces of the fibers of the test specimens stored dry or 48 weeks in water were analyzed with a scanning electron microscope to evaluate the degree of adhesion between fibers and polymer matrix. RESULTS: The ultimate transverse strength of unreinforced and reinforced denture base polymers decreased during 48 weeks' storage in water (P < 0.05, one-way analysis of variance, n = 5), and most of this reduction occurred during the first 4 weeks of storage in water. The flexural modulus of the unreinforced test specimens decreased significantly (P < 0.001), whereas there was less, if any, change in the flexural modulus of the fiber-reinforced test specimens. Scanning electron microscopic examination revealed no differences in adhesion of E-glass fibers to the polymer matrix when the specimens stored in water were compared with those stored by. Reduced adhesion between the silica fibers and matrix was observed after 48 weeks' storage in water. CONCLUSION: The results of this study suggest that the ultimate transverse strength of the E-glass fiber-reinforced test specimens decreased 14% and that of the silica fiber-reinforced test specimens decreased 36% after 48 weeks of storage in water.

Acrylic Resins↗
PubMed2001

A comparison of palatal adaptation in acrylic resin denture bases using conventional and anchored polymerization techniques.

PURPOSE: The study investigated the effects of palatal depth and a resin anchoring system on the adaptation of denture base resin to the master cast after compression molding and heat polymerization. MATERIALS AND METHODS: Forty-eight virtually identical polymethyl methacrylate dentures were fabricated on master casts with either a deep or shallow palatal vault. One half of the master casts of each palate type were altered by the addition of anchoring holes along the posterior land area, as well as perpendicularly in the midsaggital area. Anchoring holes were made with a #8 round bur to a depth of 5 mm. Twenty-four hours after polymerization, the bases on their casts were sectioned at the posterior border and evaluated for degree of adaptation using a traveling microscope. Maladaptation at the interface of the denture base and master cast was measured at predetermined mediolateral locations. A split-plot analysis of variance (alpha = 0.05) was performed followed by a post-hoc Dunn Multiple Comparison Test. RESULTS: In general, depth of the palatal vault did not significantly influence denture palatal discrepancy (p =.0780), but the use of the anchoring system significantly reduced mean gap distances (p =.000). At lateral and midpalate locations, gap distances between the denture bases and their casts were reduced from approximately 0.3 mm to approximately 0.1 mm when the anchoring system was used. CONCLUSIONS: Mean gap distances for steep palate dentures were significantly less than shallow palate dentures at vestibule and lateral palate locations, and anchoring holes placed in an edentulous master cast along the posterior land area and at the midline significantly improved the adaptation of denture bases.

Acrylic Resins↗
PubMed2004

Morphology and properties of denture acrylic resins cured by microwave energy and conventional water bath.

OBJECTIVES: This study examined the influence of microwave energy levels on the morphology and properties of an impact resistant denture material poly(methyl methacrylate) with a thickness of 10 mm. METHODS: A microwave flask containing two resin blocks was processed at 80, 160, 240, and 560 W for 15, 10, 7, and 2 min, separately. Each Flask was then turned over, and cured for an additional 2 min at 560 W. The process using conventional methods was carried out at 70 degrees C for 9 h. The blocks were tested for hardness, porosity, flexural properties, solubility, and molecular weight. The morphology of the specimens after staining with osmium tetroxide was examined by transmission electron microscope. RESULTS: The changes in temperature with time were recorded during microwave heating at 80, 160, and 240 W, respectively. A significantly large difference in the curing temperature was observed when comparing these two processing methods. There was little difference in the mean values of surface hardness and the weight percent of the insoluble parts. The mean domain size and the volume fraction of the rubber phase favor of the water-bath method. However, the porosity in the water-bath-cured specimens was much less than that in the microwave-cured specimens. Thus, the conventionally cured specimens showed better flexural strength and flexural modulus than the microwave-cured specimens. SIGNIFICANCE: This study has shown that microwave energy can efficiently polymerize denture base polymer. Highly statistical differences in morphology and flexural properties favor of the water-bath method. Choice of a suitable microwave power and polymerization time is important in order to reduce porosity to a minimum level and increase the domain size and volume of the rubber phase.

Acrylic Resins↗