Polymethyl Methacrylate Denture Base Material Research Articles

Cell death induced by eluates from hypoallergenic denture base acrylic resins in NIH-3T3 fibroblast cells

Background/purposeThe use of a hypoallergenic denture base material for dental patients is susceptible to trigger allergic reactions. The aim of this study was to compare the cytotoxicity at the cellular level of hypoallergenic denture base materials and polymethyl methacrylate denture base materials polymerized in different ways. Materials and methodsComparisons were done with the MTT (3-4,5-dimethylthiazol-2-yl)-2,5-dephenyltetrazolium bromide) results of eluates, which were derived from all test materials by immersing for 24 and 48 hours in various ratios of the test materials' weights to the volume of Dulbecco's modified Eagle's medium without supplements (0.2, 0.4, and 0.8 g/mL) and incubating NIH-3T3 cells for 24 and 48 hours (N = 9). Then the apoptotic effects of the materials were detected, using the TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay. ResultsThe 24-hour eluates of all materials exhibited strong cytotoxicity, and cytotoxicity increased with time but the difference was not statistically significant. In terms of cell death rates, the materials were ranked as follows: QC 20, Puran HC, Acron MC, Promysan Star. As a result of the apoptotic index of the materials, the ratio of necrotic cells was found from highest to lowest: QC 20, Puran HC, Acron MC, and Promysan Star. ConclusionIt was determined that the test materials have cytotoxic effects on fibroblasts, and polymethyl methacrylate-based test materials have a more necrotic effect on cells; however, other test materials induced apoptosis at a higher range.

Flexural properties of polyamide versus injection-molded polymethylmethacrylate denture base materials

Although polymethylmethacrylate is the most commonly used denture base resin, its limitation of compromised flexibility has promoted the use of nylon-based denture resins. Aims: The purpose of this study is to evaluate and compare flexural strength and flexural modulus of two commercially available nylon-based flexible denture base materials, Valplast and Lucitone FRS, and injection-molded SR Ivocap polymethylmethacrylate denture base resin. Materials and Methods: A total of 15 samples of each group (Group A, B, C [Valplast, Lucitone FRS, SR Ivocap]) were prepared. All the samples were subjected to three-point bending test on an Instron Universal Testing machine to test their flexural strength and flexural modulus. Results: The results were statistically analyzed using SPSS Version 12. The difference in flexural modulus and flexural strength of all the three groups was statistically significant, P Conclusion: The mean flexural modulus of Valplast was significantly lower than Lucitone FRS, indicating that Valplast is less rigid, more flexible than Lucitone FRS, and hence more useful in conditions where flexibility in denture base is desired. SR Ivocap displayed flexural strength comparable with Lucitone, but less than Valplast.

Mechanical Properties of Polyamide Versus Different PMMA Denture Base Materials

Polymethyl methacrylate (PMMA) resins are the most commonly used denture materials; however, they do not have a high flexural strength (FS). This study aimed to compare the mechanical properties of a polyamide-based, injection-molded denture material (Deflex) with another injection-molded PMMA base material (SR-Ivocap) and a conventional compression-molded PMMA (Meliodent). Flexural properties (deflection, bending strength, and bending modulus) of denture base materials were evaluated (n = 10). Specimens meeting International Standards Organization (ISO) specification number 20795-1 requirements were prepared (65 × 10 × 3 mm(3)). A three-point bending test was carried out on an Instron testing machine at a 5 mm/min crosshead speed. The Knoop hardness test was used to compare microhardness values. Data were analyzed using ANOVA, followed by REGWQ. The group results, standard deviations, and statistical differences (p < 0.01) for Deflex, SR-Ivocap, and Meliodent were (A) flexural strength (MPa: 78.3 ± 1.0,(a) 69.8 ± 1.4,(b) 81.1 ± 1(a)), (B) flexural modulus (GPa: 0.70 ± 0.13,(a) 0.85 ± 0.27,(a) 1.70 ± 0.23(b)), (C) Knoop Hardness (kg/cm(2) : 7.5 ± 1.0,(a) 13.5 ± 1.4,(b) 16.9 ± 1.0(c)). Different superscript letters indicate significant difference. All Meliodent specimens fractured during flexural testing, but no Deflex specimens did. While polyamide denture material produced good fracture resistance, its modulus is not yet sufficiently high to be equal to standard PMMA materials. Clinical Implications. Polyamide has some attractive advantages, but will require modification to produce consistently better properties than current PMMA materials.

Evaluation of the tensile bond strengths of heat cure acrylic and Valplast with silicone self cure soft liner

Soft lining materials have a key role in modern prosthodontics because of their capability of restoring health of inflamed and distorted mucosa. Gradual changes of oral tissues require that complete or partial dentures be relined to improve their adaptation to the supporting tissue. This study aimed to evaluate the tensile bond strength of heat cure acrylic and Valplast denture base materials to silicone self-cure soft lining material stored in artificial saliva. Materials and method: Two types of self cured silicone soft lining material (one with prime the other without prime or adhesive) applied to polymethylmet hacrylate and injection-molded nylon denture base materials for tensile bond strength testing using Instron machine. Results: The comparison between all test groups after (48) hours immersion in artificial saliva were highly significantly different from each other except for the comparison between groups PSP and VSP in which their means were non-significant. After (12) weeks, the comparison between all test groups were highly significantly different from each other when compared statistically. Conclusion: This study indicated that prime (adhesive) increase the bond strength of the silicone soft lining materials

Effect of 180 Days of Water Storage on the Transverse Strength of Acetal Resin Denture Base Material

Acetal resin has been used as an alternative denture base and clasp material since 1986. The manufacturers claim that acetal resin has superior physical properties when compared to conventional denture base acrylic resins. Limited information is available about transverse strengths of acetal resin. The purpose of this investigation was to compare transverse strengths of pink and white acetal resins to transverse strengths of conventional heat-polymerized polymethylmethacrylate (PMMA) resin in increasing durations of water storage. A transverse strength test was performed in accordance with International Standards Organization (ISO) specification No 1567. Twenty 65 x 10 x 2.5 mm(3) specimens of each resin were prepared; five specimens of each resin group were subjected to three-point bending test after 50 hours, 30 days, 60 days, and 180 days of water storage in distilled water at 37 degrees C. Experimental groups' transverse strengths were compared by three-way ANOVA and Duncan's multiple range tests. Transverse strength of PMMA denture base material was found to be in accordance with the requirements of ISO specification No 1567. Transverse strengths of white and pink acetal resin could not be calculated in this study, as white and pink acetal resin specimens did not break at the maximum applied force in the three-point bending test. Flexural strength of acetal resin was found to be within the ISO specification limits. As the water storage time increased, the deflection values of PMMA showed no significant difference (p > 0.05). Both the white and pink acetal resin showed significant increase in deflection as the water storage time was increased from 50 hours to 180 days (p < 0.05). The results of this study indicated that transverse strength values of PMMA were within the ISO specification limit. Water storage time (50 hours, 30, 60, and 180 days) had no statistically significant effect on the transverse strength and deflection of PMMA. Acetal resin suffered from permanent deformation, but did not break in the three-point bending test. Acetal resin showed significant increase in deflection as the water storage time was increased from 50 hours to 180 days. All materials tested demonstrated deflection values in compliance with ISO specification No 1567.

The evaluation of flexural strength and impact strength of heat-polymerized polymethyl methacrylate denture base resin reinforced with glass and nylon fibers: An in vitro study

With the advent of newer denture base materials, fiber reinforcement in polymethyl methacrylate (PMMA) acrylic resin by various fibers to improve the strength properties of PMMA denture base materials is common nowadays. So it has become imperative to evaluate which fiber suits best to improve both flexural and impact strengths of the denture base resin and to know up to what extent the fiber-reinforced PMMA denture base resin fulfills the strength requirement of an ideal denture base material. This study compared the resistance-to-fracture properties of a commercially available heat-polymerizing PMMA denture base resin with those of the same material reinforced by glass and nylon fibers. The fibers were randomly oriented and used in concentration of 2% by weight. The 20 test specimens of similar dimensions were prepared for each of the 4 experimental groups, viz., conventional PMMA denture base resin; and the same resin reinforced with monomer-treated glass fibers, silane-treated glass fibers, and monomer-treated nylon fibers. A total of 10 test specimens from each study group were subjected to three-point bend test on a Universal Instron testing machine, and the remaining 10 test specimens were tested for impact strength by Charpy's pendulum impact strength tester. From the literature, it was found that the flexural and impact strengths of heat-polymerized PMMA denture base resin reinforced with fibers are significantly more than those of the conventional heat-polymerized PMMA denture base resin.

Effect of rigid rod polymer filler on mechanical properties of poly-methyl methacrylate denture base material

Objectives The aim of this study was to evaluate the mechanical properties of denture base material with rigid rod polymer (RRP) particulate fillers. Methods Specimens were fabricated from autopolymerized polymethylmethacrylate denture base resin (Palapress Heraus-Kulzer) and RRP particles were used as fillers (Parmax Mississippi Polymer Technologies, Inc.). Five groups were tested: 0 wt% RRP, 10 wt% RRP, 20 wt% RRP, 30 wt% RRP, and 100 wt% RRP. Specimens were stored dry at room temperature for 2 days or in water at 37 °C for 44 days before testing until failure at a three point bending test (ISO 1567) for measuring flexural properties. The surface microhardness, water sorption, and solubility were also measured. Existence of interpenetrating polymer network (IPN) between filler and denture resin was examined using solvent treatment and scanning electron microscopy (SEM). Results Specimens with RRP filler revealed higher flexural modulus, but the flexural strength decreased. Specimens with 30% RRP filler showed flexural strength of 67.4 MPa, whereas specimens without fillers gave strength of 93.9 MPa. The 100% RRP group revealed the highest flexural strength (305 MPa). Flexural strength of water-stored test specimens decreased in most groups when compared to dry specimens. Microhardness increased as a function of RRP filler. SEM micrographs revealed no IPN-network on the surface of RRP fillers. Addition of RRP fillers decreased the water sorption, whereas solubility was not affected. Significance This study revealed that although RRP polymer has good mechanical properties, addition of RRP to denture base resin as fillers did not increase mechanical properties. This was explained by lack of IPN-formation between RRP fillers and polymer matrix.

Effect of test method on the bond strength of a silicone resilient denture lining material

The purpose of this study was to compare the peel, tensile, and shear bond strength values of a commonly used heat-cured denture soft-lining material (Molloplast-B) bonded to a polymethyl methacrylate denture base material. A further purpose was to evaluate the effect of liner thickness and deformation rate on the bond strength. Results showed that recorded failure and the mode of specimen failure are affected by the type of the test method. The highest tensile and shear strengths were obtained by specimens having the lowest liner thickness. The deformation rate had a significant effect on Molloplast-B tensile and shear strengths. Bond strength results must be interpreted with caution. Cohesive failure of soft lining material during testing provides information regarding the material itself instead of an accurate measure of bond strength.

The nature of the interface between polymethyl methacrylate denture base materials and soft lining materials

Four of the commonly used resilient denture lining materials were investigated. They were of different chemical composition, physical forms and processing cycles. Scanning electron microscope examinations of the interface between the liners and the regular acrylic resin base material were carried out in an attempt to assess the bonding of these materials to the denture base, and to evaluate the reliability of their use. The physical and mechanical bonding properties of the resilient lining materials to acrylics were studied, which included tensile, shear, peel and compression tests to measure the efficacy of the joint between the acrylic and the lining materials and its resistance to various external damaging loads. The effect of water on the liner/denture base interface and on the liner's bonding properties to acrylics was also investigated, and the validity of roughening the tissue surface of the denture base prior to processing the liner was assessed. The findings point to the advisability of using the acrylic type of soft liners whenever resilient liners are indicated. Roughening the fitting surface of the denture base to which the resilient lining materials are to be applied has a weakening effect on the bond between the lining and the denture base. Long-term exposure of the liners to water has a destructive effect. The infusion of the water into the material leads to swelling and stresses build up at the denture base interface and these tend to promote distortion and reduction in bonding.

Effect of the curing cycle on some properties of a poly methylmethacrylate denture base material : JAGGER R. G. J. Oral Rehabil. 5 (1978) 151–157

Effect of the curing cycle on some properties of a poly methylmethacrylate denture base material : JAGGER R. G. J. Oral Rehabil. 5 (1978) 151–157

Effect of the curing cycle on some properties of a polymethylmethacrylate denture base material

The properties of a denture base material may be modified by altering both the temperature and the time of heating during the curing cycle. In this study a polymethylmethacrylate denture base containing no crosslinking agent was polymerised using four different curing cycles. The structure of the materials so obtained was investigated by an acid etching technique. The materials were characterized with respect to degree of cure, strength and water sorption. It was concluded that: 1. No correlation was observed between the curing cycles and polymer structure. 2. The curing cycle of 7 h at 70 degrees C plus 1 h at 100 degrees C produced best indentation strength and tensile strength. 3. A correlation was observed between residual monomer, indentation resistance, tensile strength and water sorption. This suggested that residual monomer concentration is the most important parameter in the determination of the properties of the material investigated in this study.

A characterization of polymethylmethacrylate bone cement

Polymethylmethacrylate cement is characterized in terms of chemical composition, handling characteristics, and physical properties; the dough time, setting time, handling time, and temperature rise were found to be most affected by environmental temperature and kneading of the dough mass. As the set material ages, the residual monomer content gradually decreases and the strength increases. A volume shrinkage of up to 5 per cent was observed. The porosity, which is increased by rapid mixing, may reach 10 per cent. The mechanical properties of the cement approximate those of polymethylmethacrylate denture base material. Some variability encountered in the handling qualities of the cement could be attributed only to the variability of different batches.