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PubMed1998

Bond strength of acrylic resin to cobalt-chromium alloy treated with the Silicoater MD and Kevloc systems.

BACKGROUND: An optimum bond strength at the resin-metal interface of a prosthesis is essential to the success of that prosthesis. Silicoater MD and Kevloc are two systems used to increase bond strength at the resin-metal interface. This study investigated the effect that surface pretreatment and chemical shelf life had on the bond strength of silicoated samples and compared the shear bond strength of the two systems. METHODS: Test samples consisted of autocure denture resin attached to cylinders of chrome cobalt that had been treated either with the Silicoater MD or the Kevloc bonding system. The shear strength of the resin-metal interface was tested using a universal testing machine. The following variables were tested: various silicoating pretreatments; shelf-life period of the silanating chemicals; the method of silicoating. The shear strength of repairs using the Kevloc system were also tested. RESULTS: Surface pretreatment using aluminium oxide and sandblasting significantly enhanced the shear bond strength. The shelf life of the chemicals used in the silicoating process did not affect the bond strength over a six-week testing period. Samples treated with the Kevloc system showed significantly higher bond-strength values (17.3 +/- 1.7 MPa) and less variability than samples treated with the Silicoater MD system (11 +/- 3.6 MPa). In addition, all the samples repaired with the Kevloc system had bond strengths comparable to the original Kevloc-treated samples. CONCLUSION: The Kevloc system has the potential to provide a more optimal resin-metal bonding system, a stronger and more consistent bond and a simpler laboratory technique.

Acrylic Resins↗
PubMed2004

Comparison of the dimensional accuracy of injection-molded denture base materials to that of conventional pressure-pack acrylic resin.

PURPOSE: This study compared the linear dimensional changes of 3 injection-molded denture base materials to that of conventionally processed polymethylmethacrylate (PMMA) resin. MATERIALS AND METHODS: An impression of an aluminum maxillary edentulous arch was made with a condensation silicone impression material (Denture Elasticon) to fabricate a gypsum master cast that was replicated as a silicone mold. A maxillary complete denture with acrylic teeth was waxed to full contour on the master cast and replicated to make 40 wax dentures. ERA attachments cast in metal (Rexillium) with indices milled into the centers were waxed into 3 positions in each denture for recording dimensional measurements of the wax denture. Ten dentures were allocated to each of 4 groups; Group 1 was processed using conventionally processed PMMA (Microlon), Group 2 used injection-molded PMMA (SR-lvocap), Group 3 employed injection-molded nylon (Valplast), and Group 4 used injection-molded styrene (Northern). All processed specimens were stored at room temperature (25 degrees C, ambient humidity) for 1 week (while still on the master cast) before anteroposterior and cross-arch measurements were made using the ERA reference points with a digital caliper. After separation from the master cast and following water storage at 37 degrees C for 7 days additional measurements were made. RESULTS: An analysis of the results showed that the effect of processing was not the same for the 3 dimensions studied, regardless of which dimension was considered (p < 0.0001). The pattern of dimensional changes associated with the material type was not the same between the wax and processing stages as it was for the change between the processing and decasting stages (p < 0.0001). CONCLUSIONS: Processing the denture base materials produced unequal deformation in different dimensions (anterior-posterior and cross-arch). Each material tested also responded differently to the processing stages.

Acrylic Resins↗
PubMed1989

The use of microwave energy for processing acrylic resins.

Test strips of five different resins were processed with (1) microwaves by using a kitchen-type microwave oven, and (2) a conventional water bath. The strips were tested for hardness, porosity, and transverse strength. The results showed no significant difference between resin strips cured by either method. Maxillary dentures were waxed on stone casts of an aluminum model in another study. The dentures were processed with the same five resins, half by using microwave energy and the remainder with the water bath. The adaptation of the processed dentures to the aluminum cast was measured with feeler gauges. The results showed no statistically significant differences between dentures cured by either method. These studies demonstrated that the important physical characteristics of microwave-cured resin are approximately the same as resin cured in a conventional water bath. Curing dentures by microwave energy has the advantages of reduced curing time, ease, and cleanliness.

Acrylic Resins↗
PubMed2004

Evaluation of gloss changes of two denture acrylic resin materials in four different beverages.

OBJECTIVES: The primary disadvantages of the materials which are used in construction of complete and removable partial dentures is that their esthetic, physical and mechanical properties change rapidly with time in the oral environment. For esthetics, color stability is one of the criteria that needs careful attention. Color may provide important information on the serviceability of these materials. Color change affects the gloss of these materials. The objective of the present study was to determine the gloss changes resulting from the testing process in four different beverages in one heat-polymerized denture base resin and one cold-polymerized denture base repair resin. METHODS: Thirty-six samples were fabricated for each material. Each sample had a smooth polished and a rough unpolished surface. The gloss measurements were made with a glossmeter before testing. Four different beverages (tea, coffee, cola and cherry juice) were used for testing. Two angles of illumination (20 and 60 degrees) were used for the gloss measurements. The samples were immersed in water, tea, coffee, cola and cherry juice solutions. The gloss of the samples was measured again with the glossmeter at the end of the 45th day and 135th day of testing. The arithmetic mean and standard deviation of each of the samples were calculated and compared with each other statistically by using the Wilcoxon test (within times) (p < or = 0.05 significant), the Kruskal-Wallis analysis of variance (p < or = 0.05 significant) and the Mann-Whitney U-test with Bonforoni correction (when the difference between the samples was significant) (p < or = 0.05 significant). RESULTS: The results of this study revealed that gloss changes occurred after testing in heat-polymerized denture base resin and cold-polymerized denture base repair resin. The significance of the gloss changes exhibited by each sample, kept for different lengths of time in the same solution, were compared using the Wilcoxon test. The results were statistically significant (p < or = 0.05). According to the Kruskal-Wallis analysis of variance, the difference between measurements for angles of illumination was statistically significant (p < or = 0.05). Also according to the Mann-Whitney U-test, the difference between two polished surfaces or two unpolished surfaces was statistically insignificant (p > 0.05), but the difference between smooth polished and rough unpolished surfaces was statistically significant (p < or = 0.05). SIGNIFICANCE: It was found that either the gloss of heat-polymerized denture base resin or the gloss of cold-polymerized denture base repair resin was affected by tested agents, and the four beverages demonstrated noticeable gloss changes. Cherry juice demonstrated the least change, while tea exhibited the greatest change.

Acrylic Resins↗
PubMed1978

Spherical powder for retaining thermosetting acrylic resin veneers.

1. Nine different sizes of spherical powder were prepared, and their effectiveness as retentive devices was evaluated against those available commercially. 2. Smaller-diameter spherical powder (No. 5) gave the best results of all retaining devices tested. 3. The physical properties of the resins play an important role in the retentive strength with No. 5 retention beads. The retentive strength was reduced when brittle resin was used. 4. The retentive strength of the resin veneer was greatly affected by the angle of stress at the incisal resin. The retentive strength increased as the angle between the longitudinal axis of the specimen and the direction of stress decreased.

Acrylic Resins↗
PubMed2004

Dimensional accuracy of acrylic resin maxillary denture base polymerized by a new injection pressing method.

The purpose of this study was to confirm the dimensional accuracy of a newly developed injection pressing method for resin polymerization by making use of the internal electric resistance of resin to determine the optimal timing for resin injection. A new injection pressing polymerization pot with a built-in system to measure the internal electric resistance of resin was used for resin polymerization. Fluid-type resin was injected into the mold of a maxillary complete denture base under nine different conditions: three different timings for resin injection according to the electric resistance of resin dough (early stage: 11 Mohms; intermediate stage: 16 Mohms; final stage: 21 Mohms) and three different motor powers for resin injection (2000 N, 4000 N, and 6000 N). In the best polymerization condition (injected during the early stage of resin dough under a motor power of 6000 N), the adaptation of the denture base showed a statistically significant improvement compared with the conventional pouring method.

Acrylic Resins↗
PubMed1992

A new acrylic resin formulation: a useful tool for histological, ultrastructural, and immunocytochemical investigations.

We describe a new formulation for a hydrophilic resin, mostly composed of glycol methacrylate and hydroxypropyl methacrylate and here referred to as bioacryl, that allows the performance of morphological and immunohistochemical investigations at both light and electron microscopic levels. Immunolocalizations performed on bioacryl-embedded tissues are characterized by high specificity with virtually absent background staining. Finally, the new resin yields satisfactory fine-structural preservation, resulting in ultrastructural images of better quality than those obtained with Lowicryl K4M.

Acrylic Resins↗
PubMed1987

Dimensional stability of dentures processed in boilable acrylic resins: a comparative study.

An investigation was conducted to evaluate and compare the dimensional stability of three fast boilable denture resins with a conventional and a high-impact denture resin processed with a long-curing cycle. Although the boilable denture resins have been introduced to the dental profession and offer merits such as faster processing, saving time for the dentist, patient, and technician, reduction of energy costs, and dramatic increase in denture laboratory production without adding personnel or purchasing new equipment, the relevant dental literature is sparse. The results of this investigation indicate that all five denture resins produced dentures that shrink. Also measurements between certain teeth showed shrinkages. Linear shrinkages of denture bases and teeth distances were less than 1%. Flange-to-flange and molar-to-molar changes were less than 0.5 mm and 0.2 mm respectively. Maxillary complete dentures processed in boilable resins presented less distortion in the midpalatal area across the posterior section than dentures processed in the conventional heat-cured resin. Although linear changes reported in this investigation were thought to be clinically insignificant, clinical studies should be conducted to establish correlation with laboratory findings.

Acrylic Resins↗
PubMedDate not supplied

In vitro study of the adherence of Candida albicans to acrylic resins: relationship to surface energy.

PURPOSE: This study aimed to determine whether small variations in the composition of the polymethylmethacrylate (PMMA) of widely used dentures produce differences in the degree of Candida albicans adherence and to relate any differences found to the surface energy of the resins, which appears to play a major role in the initial phases of microorganism adhesion. MATERIALS AND METHODS: A reference strain of C albicans (18.804 ATCC) and 11 different PMMAs (Vacalon, Inkotherm 85, Veracril, Probase Cold, Inkotherm Press, Inkotherm 85 T, Ruthinium, Vertex, SR Ivocap, Idoacryl, Lucitone) were used. Fifty specimens (15 x 10 x 1 mm) of each type were prepared. C albicans adhesion was determined by microorganism count under fluorescent optical microscope, and the surface energy of the resins was calculated by the contact angle method. P < .05 was regarded as significant. RESULTS: C albicans adhesion on the resins ranged from 7.12 cells/mm2 to 330.8 cells/mm2, with statistically significant (P > .05) differences in some cases. Despite small variations in the composition of the resins, their surface energy values were very similar (38.78 to 41.2 mJ/m2), and no relationship was found between C albicans adhesion and surface energy. CONCLUSION: The adhesion of C albicans to different resins varied in vitro, possibly as a result of the action of residual postpolymerization products. According to these results, variations in surface energy that result from differences in the composition of the different PMMA resins appear to have no influence on the adhesion of C albicans or, therefore, on the onset of denture stomatitis.

Acrylic Resins↗