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PubMed2006

[The study of adhesion of Candida albicans to the selected acrylic resins].

The study has been performed on 3 acrylic resins used to fabricate removable dentures. Aim of the study was to detect possible differences in Candida albicans' adhesion within particular materials. Polished and non-polished samples were made, than these samples were sunk in precipitates containing Candida albicans material. Adhesion of Candida albicans to the surface of the materials occured within a concentration of 10. After 24 hours of incubation differences were found concerning the number of the plate cultures. Most of all plate cultures were observed on Lucitone 199, fewer on Zhermacryl, the poorest one was found on Palaxpress resin. Considerable number of plate cultures occured on non-polished samples relating to polished ones. After 48 hours of incubation further development of Candida albicans took place, with differences concerning various materials.

Acrylic Resins↗
PubMed2006

Flexural properties of glass fibre reinforced acrylic resin polymers.

BACKGROUND: In recent years, glass fibres have been used to strengthen denture base resins. A major difficulty in using reinforcing fibres with multiphase acrylic resins, such as powder liquid resins, is inadequate impregnation of the fibres with the resin. METHODS: This investigation examined the reinforcing effect of glass fibres on the fracture resistance and flexural strength of acrylic denture base resins. Eighty identical specimens were formed in specially designed moulds in accordance with the manufacturer's recommendations. The four experimental groups were prepared and these consisted of conventional acrylic resin and the same resin reinforced with glass fibres. Ten specimens were fabricated in a standardized fashion for each experimental group. Flexural strength was tested using a 3-point universal testing machine. RESULTS: In this study, statistically significant differences were found in the flexural strength of the specimens (P < 0.05). The injection-moulded, fibre-reinforced group had significantly lower flexural strength than the injection-moulded group (P < 0.001), strength than the microwave-moulded, fibre-reinforced group (P < 0.001), and the microwave-moulded, fibre-reinforced group had lower flexural strength than the microwave-moulded group. The fracture resistance was significantly higher in the injection-moulded, fibre-reinforced group than in the injection-moulded group (P < 0.05), and the fracture resistance was significantly higher in the microwave-moulded, fibre-reinforced group than in the microwave-moulded group. CONCLUSION: Within the limitations of this study, the flexural strength of heat-polymerized PMMA denture resin was improved after reinforcement with glass fibres. It may be possible to apply these results to distal extension partial and complete denture bases.

Acrylic Resins↗
PubMed2003

Influence of number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin.

Simultaneous irradiation of multiple flasks may have deleterious effects on the polymerization of microwave cured-acrylic resins. This study evaluated the effect of the number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin. Samples were made of Acron MC(R) (AMC, GC Dent. Ind. Corp.) processed at 500 W. The following associations of the number and position of the flasks were tested: one simple flask centrally placed on the turning plate (I, control); two flasks, one in the centre (IIa) and the other peripherally placed in the plate (IIb); two flasks centrally, one above (IIIa) and the other below (IIIb). The processing time varied according to the number of flasks: 3 or 4.5 min for one or two flasks, respectively. For monomer release, each specimen (n = 12) was put in an assay glass tube containing 6 mL of deionized water that was changed daily. Monomer levels were obtained by spectrophotometry at 206 nm. For hardness test (n = 10), 12 indentations were made in the surface of each specimen. Immersing the polished specimens in permanent ink and counting the porous in a stereo light microscope verified the porosity. Monomer release was significant before 24 h: GI = 263.1(153.3)a, GIIa = 236.9(180.2)a, GIIb = 441.5(446.2)a, GIIIa = 1216.6(857.9)b. Tukey test showed no statistically significant differences among the groups for porosity and hardness. Monomer release was affected by the position of the flask (P < 0.05).

Acrylic Resins↗
PubMed2002

Effect of intrinsic pigmentation on the flexural strength of a microwave-cured acrylic resin.

This study investigated the effect of intrinsic pigmentation on the transverse strength of a microwave-cured acrylic resin. Forty transverse strength specimens were fabricated according to ADA specification #12 and divided into 5 groups. No fibers were added to group I (GI, control group); acrylic stain (AS) was added to GII and GIII in concentrations of 0.5 and 1.5% w/w, respectively; acrylic fibers (AF) were added to groups GIV and GV in concentrations of 0.5 and 1.5% w/w, respectively. All specimens were irradiated in a microwave oven with a cycle of 3 min at 360 W, followed by 4 min resting, then 3 min at 810 W. Flasks were bench-cooled for 30 min at room temperature, followed by immersion in cold tap water for 30 min. After storage in distilled water at 37 degrees C for 48 h, all specimens were tested for flexural strength in a testing machine (EMIC-DL 500) at a crosshead speed of 0.5 cm/min. Mean and standard deviation (MPa) for the flexural strength test were: GI = 86.0 +/- 7.9; GII = 86.0 +/- 9.8; GIII = 86.6 +/- 7.7; GIV = 84.9 +/- 5.3; GV = 84.9 +/- 5.2. No statistical differences were detected among the groups (ANOVA, p > 0.05). The addition of the acrylic fibers or the acrylic stain did not affect the transverse strength of the microwave-cured acrylic resin.

Acrylic Resins↗
PubMed2004

Does plasma irradiation improve shear bond strength of acrylic resin to cobalt-chromium alloy?

OBJECTIVES: Plasma treatment leads to surface modification such as the improved wettability of dental materials. Studies have suggested that plasma treatment may bring about an improvement in the shear bond strength between cobalt-chromium alloy and self-curing acrylic resin. METHODS: Forty-eight cobalt-chromium alloy specimens were randomly divided into four groups (each of the groups consisted of 12 specimens); air abrasion, adhesive primer, adhesive primer after air abrasion, or after plasma irradiation. A self-curing acrylic resin, 2 mm thick and 3.6 mm in diameter, was processed on all specimens before storage in distilled water at 37 degrees C for 24 h. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data was statistically analyzed using Scheffé's test. RESULTS: Adhesive primer clearly increased the shear bond strength compared with air abrasion (p < 0.05). The synergy of air abrasion and adhesive primer greatly increased the shear bond strength, showing a five-fold increase over air abrasion, or one and a half-fold over adhesive primer. A similar tendency in increase was observed in the adhesive primer after plasma treatment, but to a lower degree. Adhesive primer after plasma treatment showed half the shear bond strength of the treatment of adhesive primer after air abrasion (p < 0.05). Moreover, adhesive primer after plasma treatment showed a lower shear bond strength than adhesive primer alone although the difference was not statistically significant. SIGNIFICANCE: Plasma treatment does not improve adhesion between cobalt-chromium alloy and self-curing acrylic resin.

Acrylic Resins↗
PubMed2001

The effect of the addition of surface treated chopped and continuous poly (methyl methacrylate) fibres on some properties of acrylic resin.

Poly (methyl methacrylate), the material most commonly used in the construction of dentures, is not without limitations particularly in terms of mechanical strength, such as flexural and fatigue strength. The Dental Practice Board for England statistics show that many dentures fail as a result of fracture. This study investigated the self-reinforcement of acrylic resin through the addition of surface treated poly (methyl methacrylate) fibres in chopped and continuous form. The effect of the addition of fibres on transverse and impact strengths was investigated. The addition of surface treated chopped or continuous fibres to acrylic resin did not improve the transverse or impact strengths. The addition of surface treated poly (methyl methacrylate), in the present form, to acrylic resin cannot be recommended as a method of reinforcement.

Acrylic Resins↗
PubMed1998

[Synthesis and application of novel acrylic resin as enteric coating].

The pH sensitive two- and three-component acrylic resins were synthesized by radical solution copolymerization of methyl methacrylate (MMA), methacrylic acid (MAA) and/or butyl acrylate (BA) and their acid values were measured by acid-base titration. The dissolution of naproxen pellets coated with the synthesized resins in dissolution medium of different pH value was studied. The results show that the acrylic resin with different acid value can be prepared by adjusting the monomer ratios (MMA:MAA or MMA:MAA:BA). The smaller the acid value of the resin is, the higher pH sensitive value it has. The release of naproxen from pellets coated with these resins is greatly influenced by the pH value of the dissolution medium and the pH sensitive value of the coating resin. The three-component resins are plastic and can be used as coating material without adding plastisizers.

Acrylic Resins↗
PubMed2005

HPLC determination of residual monomers released from heat-cured acrylic resins.

HPLC was used to examine the leachability of three non-phthalic and four phthalic post-polymerized residual monomers from three commercially available heat-cured acrylic resins. Specimens of equal dimensions were constructed from each brand of material by following the standardized procedure and were stored under three different conditions, namely, distilled water, artificial saliva, and a binary mixture of ethanol/water. The resulting liquids provided samples for analysis by HPLC. Three different experiments were performed for each brand of acrylic and each storage condition in order to examine the effects of parameters, particularly time and temperature. The results obtained from this study suggest that a wide spectrum of residues diffuse out of the three examined acrylic resin materials. The non-phthalic compounds were leached at high concentrations, whereas all the phthalates examined exhibited different degrees of elusion commensurate with the storage condition, brand of material, and type of experiment. It seems that a significant quantity of non-phthalic and phthalic residues diffuse out of the acrylic resin materials examined. The main component extracted was methyl methacrylate, the level of which seems to be time-dependent and decreases for a period of up to 5 days when resins are stored in distilled water at room temperature.

Journal Article↗
PubMedDate not supplied

An examination of the stress distribution in a soft-lined acrylic resin mandibular complete denture by finite element analysis.

PURPOSE: The aim of this study was to calculate the effect of a soft liner on stress distribution within a mandibular complete denture. Although patients have welcomed soft-lined complete dentures, early fracture is one of the main reasons for failure. To minimize and prevent prosthesis fracture, the understanding of the stress distribution within a prosthesis is important. MATERIALS AND METHODS: A 3-dimensional finite element model of a mandibular complete denture for a severely reduced residual alveolar ridge was constructed. The stress was calculated with linear static finite element analysis. The stress distribution in the soft-lined acrylic resin mandibular complete denture was compared with that of a conventional acrylic resin denture. The resulting stresses were displayed in terms of von Mises equivalent stress and the major principal stresses according to 5 different loading conditions: vertical loads in premolar, molar, and incisor regions; and oblique loads in premolar and molar regions. RESULTS: Oblique loads produced higher levels of stress in the labial notch regions than vertical loads, where tension was the primary mode of stress. Significantly reduced levels of von Mises stress were calculated in soft-liner layers under all loading conditions. Acrylic resin denture base portions, however, exhibited higher levels of von Mises stress in soft-lined complete dentures. CONCLUSION: Three-dimensional finite element analysis gave a realistic explanation of denture fractures and patient response to mandibular complete dentures with and without soft linings. Control of excess lateral occlusal contact might be helpful to reduce the probability of a fracture in soft-lined mandibular complete dentures.

Acrylic Resins↗
PubMed2003

The effect of the addition of poly (methyl methacrylate) fibres on the transverse strength of repaired heat-cured acrylic resin.

The aim of the present study was to investigate the effect of addition of an experimental poly (methyl methacrylate) (PMMA) fibre in linear form, 0.75 mm in diameter on the transverse strength of repaired heat-cured poly (methyl methacrylate) denture base material. Specimens of heat-cured PMMA were repaired with an autopolymerizing acrylic resin and an autopolymerizing acrylic resin together with the addition of untreated and surface-treated PMMA fibres in different arrangements. The transverse bend test was carried out using a LIoyd's Instrument Material Testing Machine. From the results, it can be concluded that the box incorporated into the repair joint produced a significant decrease in the moduli of elasticity and rupture which may be due to stress concentration effects. The addition of one layer of untreated PMMA fibres significantly decreased the modulus of rupture. The addition of two layers of untreated fibres produced a slight but statistically non-significant increase in the modulus of rupture. The addition of surface-treated (with butadiene styrene latex emulsion) fibres into the repair complex gave no improvement compared with the addition of untreated fibres in terms of transverse strength. There was an insignificant decrease in the modulus of rupture compared with the untreated fibres.

Acrylic Resins↗