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At least 145 records · Page 8Linked to original sources
PubMed1996

A comparison of microwave and dry-heat curing methods on the bond strength of silicone facial materials applied to acrylic resin.

PURPOSE: This study compared two curing methods (microwave irradiation and dry heat) on the tensile bond strength of silicone facial materials to cured acrylic resin. The facial materials studied were Mollomed, Silskin II, MDX4-4210, and A-2186. MATERIALS AND METHODS: The samples were processed with microwaves for 13 minutes at 90 W plus 2 minutes at 500 W and dry heat for 3 hours at 100 degrees C to cured acrylic resin. Facial materials 3-mm thick were processed between two half-dumbbells of acrylic resin. The bonding surfaces were treated with a primer. The samples were placed in tension until failure. RESULTS: The results showed that the bond strength was affected by the type of silicone material and not by the curing methods used. CONCLUSIONS: Mollomed had the highest bond strength of all materials tested. MDX4-4210 and A-2186 showed the lowest, and Silskin II had intermediate bond strength. Microwave irradiation has the potential of saving time, energy, and resources during the fabrication of facial prostheses, but further laboratory studies and clinical trials are indicated.

Acrylic Resins↗
PubMed2005

Effect of microwave treatments on dimensional accuracy of maxillary acrylic resin denture base.

Microwave energy has been used as an alternative method for disinfection and sterilization of dental prostheses. This study evaluated the influence of microwave treatment on dimensional accuracy along the posterior palatal border of maxillary acrylic resin denture bases processed by water-bath curing. Thirty maxillary acrylic bases (3-mm-thick) were made on cast models with Clássico acrylic resin using routine technique. After polymerization and cooling, the sets were deflasked and the bases were stored in water for 30 days. Thereafter, the specimens were assigned to 3 groups (n=10), as follows: group I (control) was not submitted to any disinfection cycle; group II was submitted to microwave disinfection for 3 min at 500 W; and in group III microwaving was done for 10 min at 604 W. The acrylic bases were fixed on their respective casts with instant adhesive (Super Bonder) and the base/cast sets were sectioned transversally in the posterior palatal zone. The existence of gaps between the casts and acrylic bases was assessed using a profile projector at 5 points. No statistically significant differences were observed between the control group and group II. However, group III differed statistically from the others (p<0.05). Treatment in microwave oven at 604 W for 10 min produced the greatest discrepancies in the adaptation of maxillary acrylic resin denture bases to the stone casts.

Acrylic Resins↗
PubMed2001

Microwave-cured acrylic resins and silicone-gypsum moulding technique.

This study evaluated the residual monomer (RM), Knoop hardness (KHN) and transverse strength (TS) of two microwave-cured acrylic resins (Acron MC(R) (A), GC Dent. Ind. Corp., Tokyo, Japan and Onda Cryl (O), AO Classico Ltda, São Paulo, Brazil) when processed with an all-type III gypsum moulding technique (G) or a silicone-gypsum moulding technique (S). One hundred and forty four specimens were fabricated and equally distributed into four groups (AG, AS, OG and OS). The TS tests were conducted after 48 h of water storage, and KHN values were obtained after 24, 48, 72 h and 30 days. The RM was determined every 24 or 48 h over a period of 288 h. The acrylic resins were prepared and processed according to the manufacturer's directions. Both AS and OS showed the highest means (P < 0.05) for RM (microg cm-2) only after 24 h (AS = 56.84 +/- 27.39/AG = 7.51 +/- 5.75/OS = 3.59 +/- 1.60/OG = 1.02 +/- 0.3), 48 h (AS = 28.99 +/- 9.35/AG = 2.65 +/- 2.17/OS = 2.37 +/- 0.84/OG = 0.68 +/- 0.49) and 72 h (AS = 15.98 +/- 9.01/AG = 1.40 +/- 0.57/OS = 1.87 +/- 0.52/OG = 0.75 +/- 0.44). Both AS and OS showed the highest means (P < 0.02) for KH after 24 h (AS = 18.69 +/- 2.3/AG = 17.79 +/- 0.7/OS = 18.41 +/- 1.0/OG = 16.04 +/- 0.6). After 48 h the mean values for OS and OG differed significantly (P < 0.03) (OS = 18.67 +/- 0.8/OG = 16.75 +/- 0.8). No differences of KHN were found among the groups during the storage periods. The TS values for A and O were not affected by either G or S (P > 0.05). Silicone-gypsum mould technique affected the RM and KHN of the resins in the first 2 and 5 days of analysis, respectively. The type of mould did not affect TS, and the acrylic resins differed from each other for all properties regardless of the type of mould.

Acrylic Resins↗
PubMed2003

The effect of the addition of different fibres on the transverse and impact strength of acrylic resin denture base material.

The aim of the present study was to investigate the effect of the addition of different types of fibres on the transverse and impact strength of acrylic resin denture base material. The addition of glass fibres (strand) and polyethylene fibres produced a non significant increase in the modulus of elasticity, compared with the control of conventional heat-cured acrylic resin. The addition of glass fibres (woven and strand), polyethylene and carbon fibres to acrylic resin produced a non significant increase in the modulus of rupture. The addition of carbon, glass (strand) and polyethylene fibres produced a significant increase in the impact strength. Within the limitations of this study the addition of silk fibres did not produce an improvement in the mechanical properties.

Acrylic Resins↗
PubMed2003

Reducing the negative effects of chemical polishing in acrylic resins by use of an additional cycle of polymerization.

STATEMENT OF PROBLEM: The chemical polishing of dentures and orthodontic appliances is an efficient and time-saving technique. However, the process may adversely affect the physical properties of resin. PURPOSE: This study evaluated the effect of an additional polymerization cycle in a microwave or water bath on the physical properties of an autopolymerized acrylic resin submitted to chemical polishing. MATERIAL AND METHODS: Control groups comprised acrylic resin specimens submitted to mechanical (group 1) and chemical (group 2) polishing. Experimental groups comprised chemically polished specimens submitted to an additional cycle of polymerization in a microwave at 450 W for 3 minutes (group 3) or in a hot water bath at 65 degrees C for 1 hour (group 4). For the residual monomer test, 10 standardized half-disc specimens (30 x 3 mm) were fabricated for each of the test groups, and daily ultraviolet spectrophotometric (206 nm) analyses were assessed for 13 days (microg/cm(2)). For transverse strength and internal Knoop hardness (KH) tests, 10 (65 x 10 x 2.5 mm) and 5 (32 x 10 x 2.5 mm) specimens were fabricated for each test group, respectively. Internal Knoop hardness (kg/mm(2)) was assessed at depths of 100, 700, and 1500 microm. Transverse strength (MPa) was measured with a 3-point bending test in a universal testing machine with a 10-kg load cell at a crosshead speed of 5 mm/min. The data were analyzed with 1-way analysis of variance, and the means were compared with Student's t test and Tukey-Kramer intervals (P<.05). RESULTS: At the end of the first day of the test, all groups showed significantly different residual monomer levels (P<.05). The groups in order of decreasing residual monomer were: group 2 (1315.7 +/- 225.5 microg/cm(2)), group 3 (848.2 +/- 150.4 microg/cm(2)), group 4 (295.1 +/- 81.6 microg/cm(2)), and group 1 (136.6 +/- 45.5 microg/cm(2)). After 13 days of water storage, the lowest residual monomer levels were recorded for group 1 (4.6 +/- 1.6 microg/cm(2)). There were no significant differences among group 2 (11.3 +/- 3.1 microg/cm(2)), group 3 (9.6 +/- 1.5 microg/cm(2)), and group 4 (12.3 +/- 1.7 microg/cm(2)). Group 1 demonstrated the highest transverse strength (78.1 +/- 6.1 MPa); the other groups were not significantly different from each other. All groups exhibited lower KH values at the 100-microm depth than at 700- and 1500-microm depths. At the latter depths, group 4 specimens demonstrated the highest hardness values (18.0 +/- 0.5 and 18.8 +/- 0.7 kg/mm(2), respectively). CONCLUSION: Within the limitations of this study, additional polymerization with hot water reduced residual monomer content of chemically polished acrylic resins on the first day. Although additional polymerization increased the internal hardness of the material, however, it did not recover the transverse strength that was decreased by the chemical polishing.

Acrylic Resins↗
PubMed1995

Thyroid carcinoma metastasized to the sternum: resection of the sternum and reconstruction with acrylic resin.

Recently we resected and reconstructed the sternum in two female patients with thyroid carcinoma metastatic to the sternum. Histological diagnosis of the metastatic lesion was follicular carcinoma in the first case and papillary carcinoma in the second case. Reconstruction of the sternum was accomplished by using an acrylic resin plate alone in the first case and an acrylic resin plate sandwiched between layers of Marlex mesh (Marlex sandwich procedure) in the second case. In the first case the acrylic resin plate was directly fixed to the ribs with metallic wires, most of which snapped off later, and a small amount of exudate accumulated around the plate for a short period of time. In contrast, the postoperative course in the second case was uneventful and the Marlex sandwich procedure seemed superior in the chest wall reconstruction following resection of the sternum.

Acrylic Resins↗
PubMed2005

Influence of chemical and mechanical polishing on water sorption and solubility of denture base acrylic resins.

Influence of polishing methods on water sorption and solubility of denture base acrylic resins was studied. Eighty samples were divided into groups: Classico (CL), and QC 20 (QC) - hot water bath cured; Acron MC (AC), and Onda Cryl (ON) - microwave cured; and submitted to mechanical polishing (MP) - pumice slurry, chalk powder, soft brush and felt cone in a bench vise; or chemical polishing (CP) - heated monomer fluid in a chemical polisher. The first desiccation process was followed by storage in distilled water at 37 +/- 1 degrees C for 1 h, 1 day, 1, 2, 3 and 4 weeks. Concluding each period, water sorption was measured. After the fourth week, a second desiccation process was done to calculate solubility. Data were submitted to analysis of variance, followed by Tukey test (p<or=0.05). Means of water sorption (%) and solubility (%), respectively, were: CL-MP: 1.92 and 0.02; CL-CP: 1.98 and 0.52; QC-MP: 2.31 and -0.05; QC-CP: 2.32 and 0.25; AC-MP: 2.45 and -0.07; AC-CP: 2.43 and 0.41; ON-MP: 2.32 and -0.06; ON-CP: 2.34 and 0.27. Mechanical polishing promoted significantly lower solubility of acrylic resins; initially, water sorption values were higher for chemically polished samples, however, after 4 weeks all groups were similar.

Absorption↗
PubMed1990

Monopoly coating on acrylic resin surfaces: a bacteriologic study.

In an open bulb of a buccal flange obturator, it is almost impossible to polish the inner surface of the bulb. Because it cannot be cleaned easily, oral and nasal secretions lead to odors. To obtain a smoother surface, it is suggested that monopoly be painted on the unpolished surface of the open bulb. In this study, the effect of a monopoly coating on bacteria retention and washability of acrylic resin surfaces was investigated. Coated and uncoated acrylic resin samples were prepared and both were contaminated with Escherichia coli. After standard washing, the remaining viable E. coli colonies were counted. The statistical results showed that the difference in the number of E. coli colonies between coated and uncoated groups was highly significant (p less than 0.001). It was suggested that monopoly should be applied to the acrylic resin surfaces where mechanical polishing cannot be done.

Acrylic Resins↗
PubMed1994

Assessing shade differences in acrylic resin denture and natural teeth.

Four experiments in this study assess shade differences in acrylic resin denture and natural teeth. The first two examine the perceptual errors made by experienced dentists in their use of a manufacturer-provided shade guide for acrylic resin denture teeth. In the first of four experiments, dentists examine whether the numbering of a selected shade guide corresponds to the arrangement of the tabs from light to dark. In the second experiment, a visual discrimination task determines whether dentists can distinguish shade guide tabs from one another. The results from these two experiments revealed that the numbered progression of the shade tabs does not correspond to a light-to-dark order, that dentists have difficulty discriminating between several shade tabs, and that the shade tabs can be rearranged on an empirical basis. The third experiment demonstrated how the shade of natural teeth varies by age, gender, and complexion. The Biotone shade guide, rearranged in the manner suggested by the second experiment, was used to make these assessments. The fourth experiment examined whether the shades used for complete dentures were similar to shades found in natural teeth. The results from the last two experiments showed that shade selection can be facilitated by use of a rearranged set of shade guide tabs. The results also reveal that natural teeth significantly and clinically darken with age; however, selections made for denture teeth tend to be relatively constant in color, despite the age of the patient. Differences for gender and complexion do not appear to be clinically significant.

Acrylic Resins↗
PubMed1989

The effectiveness of two disinfectants on denture base acrylic resin with an organic load.

This study compared the biocidal effectiveness of chlorine dioxide and 5.25% sodium hypochlorite (diluted 1:10) on acrylic resin strips inoculated with Staphylococcus aureus, Candida albicans, or Escherichia coli in the presence of an organic load. Sterile acrylic resin strips were immersed in a solution containing 10% horse serum and 10(5) to 10(7) organisms/ml for each type of organism, then disinfected in chlorine dioxide, sodium hypochlorite, or 0.9 sterile saline for 30 seconds or 1, 2, or 4 minutes. After disinfection, the strips were neutralized and incubated for 72 hours. The results showed a difference between the ability of chlorine dioxide and sodium hypochlorite to kill the test organisms on acrylic resin strips when organic matter is present. Chlorine dioxide achieved complete disinfection of all three organisms within 2 minutes. Sodium hypochlorite achieved complete disinfection of all three organisms within 4 minutes.

Bacteria↗
PubMed1990

Evaluation of analytical techniques for measurement of denture-base acrylic resin glass-transition temperature.

The glass-transition temperature of a range of acrylic resin materials used in prosthetic dentistry was determined. The techniques used to make the measurement included: thermal mechanical analysis, dynamic mechanical thermal analysis, and differential scanning calorimetry. It was found that the measuring techniques used yielded very similar results, and as a consequence it was concluded that: familiarity and easy availability of thermal mechanical analysis lead to the recommendation that this technique should be employed as the standard glass-transition evaluation technique for denture-base acrylic resins.

Acrylic Resins↗
PubMed1999

Composite veneered acrylic resin provisional restorations for complete veneer crowns.

Restorations that are remade to improve esthetics, teeth with pronounced gingival-to-incisal color contrast, or high-value translucent teeth can limit the capability of shaded acrylic resin provisional restorations to satisfy the esthetic demands of certain patients. This article describes a procedure to incorporate a composite veneer in an acrylic resin provisional restoration. Improved optical properties of microfilled composite are combined with the excellent marginal seal and contour of acrylic resin. Precise control of color, translucency, and surface texture provide excellent interim esthetics and a better guide for the definitive prosthesis.

Acrylic Resins↗
PubMed1993

Flow injection analysis of formaldehyde leached from denture-base acrylic resins.

Formaldehyde is responsible for allergic inflammation in acrylic denture wearers and the quantitation of formaldehyde is necessary to study its leaching from denture-base materials. Flow injection analysis was developed to quantify the formaldehyde leached from acrylic resins. Different resins were immersed in aqueous solvents at 37 degrees C and the immersion solutions were directly injected into the flow system, in which formaldehyde was converted on-line to a fluorescent derivative and its fluorescence was detected. Under the optimized conditions, the leached formaldehyde could be quantified in a short time (within 4 min) with high sensitivity (pmol levels per injection) and high specificity (no fluorescent response to the other leachables). In leaching experiments, significant amounts of formaldehyde were leached from autopolymerized resins, but not from heat- and microwave-polymerized resins.

Acrylic Resins↗
PubMed1993

Clear acrylic resin T-bar used in denture identification.

A preformed, T-shaped, clear acrylic resin bar can be utilized as a vehicle for identification of an existing removable dental prosthesis. A printed label attached to the T-bar makes a convenient vehicle for embedding the label in the prosthesis with light-cured acrylic resin. The resultant finished surface of the T-bar assembly provides a protective cover and an exceptionally clear window for viewing the label. The procedure is time-effective and relatively easy.

Acrylic Resins↗