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PubMed1999

Flexural properties and surface finishing of acetal resin denture clasps.

PURPOSE: This study examined flexural properties of acetal resin to determine the appropriate design for an acetal resin removable partial denture clasp. The effectiveness of various acetal resin polishing procedures was also evaluated using scanning electron microscopy. MATERIALS AND METHODS: Loads of up to 1,500 g were applied to cylindrical acetal resin specimen lengths of 5, 10, and 15 mm, and the degree of deflection of the specimen tip was measured. Specimens were 2 mm and 1.5 mm in diameter with a round cross-section (R2 and R1.5, respectively), as well as 2 mm in diameter and half-round in cross-section. Half-round specimens were loaded with their flat surface vertical and then horizontal (HRV and HRH, respectively). Contour plots showing load and deflection for varying lengths of resin were developed for each cross-sectional type based on specimen length, and the stiffness was calculated. Additional acetal resin specimens underwent polishing techniques including tungsten carbide burs, aluminium oxide stones, abrasive impregnated rubber points, and "Polish-D." Polished specimens were examined with scanning electron microscopy to compare surface roughness. RESULTS: For the 5-mm-length specimens, the median stiffness values decreased in the following order: R2 > HRV > HRH > R1.5. The median stiffness values for the 10-mm and 15-mm lengths followed a similar trend. At each length, the R2 specimen was generally at least twice as stiff as other designs. Regarding polishing, the smoothest surface was seen on the specimen that was polished with the rubber point followed by "Polish-D." CONCLUSIONS: To have stiffness similar to a cast cobalt-chromium clasp 15 mm long and 1 mm in diameter, a suitable acetal resin clasp must be shorter (approximately 5 mm) with greater cross-sectional diameter (approximately 1.4 mm). To obtain a smooth surface, the acetal resin clasp should be polished with a rubber point followed by a material such as "Polish-D."

Chromium Alloys↗

PubMed2001

Effect of light source and time on the polymerization of resin cement through ceramic veneers.

PURPOSE: The purpose of this study was to evaluate the efficiency of 3 different light sources to polymerize a light curing resin cement beneath 3 types of porcelain veneer materials. MATERIALS AND METHODS: A conventional halogen light, a plasma arc light, and a high intensity halogen light were used to polymerize resin cement (Variolink II; Ivoclar North America Inc, Amherst, NY) through disks of veneer materials. Equal diameter and thickness disks of feldspathic porcelain (Ceramco II; Ceramco Inc, Burlington, NJ), pressable ceramic (IPS Empress; Ivoclar North America Inc), and aluminous porcelain (Vitadur Alpha; Vident Inc, Brea, CA) were used as an interface between the curing light tips and the light polymerized resin cement. The resin cement/veneer combinations were exposed to 4 different photopolymerization time protocols of 5 seconds, 10 seconds, 15 seconds, and 20 seconds for high intensity light units (Apollo 95E [Dental Medical Diagnostic Systems Inc, Westlake Village, CA] and Kreativ 2000 [Kreativ Inc, San Diego, CA]), and 20 seconds, 40 seconds, 60 seconds, and 80 seconds for conventional halogen light (Optilux; Demetron Research Inc, Danbury, CT). A surface hardness test (Knoop indenter) was used to determine the level of photopolymerization of the resin through the ceramic materials with each of the light sources. The data were analyzed by one-way analysis of variance and a post-hoc Scheffe test (p < .05). RESULTS: The data indicates that the Variolink II Knoop Hardness Number values vary with the light source, the veneer material, and the polymerization time. For a given light and veneer material, Knoop Hardness Number increases with longer polymerization times. The Kreativ light showed statistically significant differences (p < .05) between all test polymerization times. Use of this light required a polymerization time of greater than 20 seconds to reach maximum resin cement hardness. For samples polymerized with the Apollo light, there were statistically significant (p < .05) differences in surface hardness between samples polymerized at all times, except for the 15-second and 20-second times. Samples polymerized with the halogen light showed no statistically significant (p < .05) differences in hardness between polymerization times of 60 seconds and 80 seconds. CONCLUSIONS: High intensity curing lights achieve adequate polymerization of resin cements through veneers in a markedly shorter time period than the conventional halogen light. However, the data in this report indicate that a minimum exposure time of 15 seconds with the Kreativ light and 10 seconds with the Apollo 95E light should be used to polymerize the Variolink II resin, regardless of the composition of the veneer. Conventional halogen lights required a correspondingly greater polymerization time of 60 seconds.

Aluminum Oxide↗

PubMed1986

Demonstration of contact sensitizers in resins and products based on phenol-formaldehyde.

12 phenol-formaldehyde resins were investigated with regard to the presence of 14 contact sensitizers by using high-pressure liquid chromatography. The allergens consisted of simple methylol phenols, dihydroxydiphenyl methanes, 4,4(1)-dihydroxy-(hydroxymethyl)-diphenyl methanes and 2,4(1)-dihydroxy-(hydroxymethyl)-diphenyl methanes. Four substances, 2,4-dimethylol phenol, 2,6-dimethylol phenol, 4,4(1)-dihydroxydiphenyl methane and 2,4(1)-dihydroxydiphenyl methane, were isolated from a resol resin and identified by mass-spectrometry and nuclear magnetic resonance spectrometry. The highest concentrations (up to 15% w/w) of allergens were noted for methylol phenols in resol resins based on phenol and formaldehyde. The corresponding novolak resins showed a high content of dihydroxydiphenyl methanes. There was great variation in concentration of the sensitizers between the resins. None of these sensitizers were demonstrated in the resin based on paratertiary-butyl phenol. Products based on phenol-formaldehyde resins were also investigated for the presence of allergens. Uncured impregnated paper for laminate production and uncured mineral wool contained the same concentrations of the sensitizers as some of the resins studied. The curing process decreased the content of all the allergens investigated in all products, but the sensitizers did not disappear, and they may thus be present in finished products.

Allergens↗

PubMed2006

Teaching of posterior composite resin restorations in undergraduate dental schools in Ireland and the United Kingdom.

PURPOSE: The aim of this study was to investigate the current teaching of posterior composite resin restorations to undergraduate dental students in Ireland and the United Kingdom (UK). The investigation was a follow-up to a survey undertaken in 1997. MATERIALS AND METHODS: A questionnaire was distributed by e-mail to the Heads of Departments of Restorative Dentistry/Units of Operative Dentistry in each of the 15 dental schools with undergraduate dental degree programmes in Ireland and the UK. The questionnaire sought information relating to the teaching of posterior composite resin restorations in each dental school. RESULTS: Fifteen completed questionnaires were returned (response rate = 100%). All schools (n = 15) taught the placement of composite resin restorations in occlusal cavities, 14 schools taught composite resin placement in two-surface occlusoproximal cavities and nine schools taught composite resin placement in three-surface occlusoproximal cavities. Respondents anticipated that the amount of preclinical teaching of posterior composite resin placement will increase twofold over the next 5 years, whilst the corresponding teaching of amalgam will fall to two-thirds its current level. Variation was found between dental schools in the teaching of the principles of cavity design, contraindications to placement, indications for lining and basing techniques, matrix and wedging techniques, and the use of curing lights. CONCLUSIONS: The amount of teaching of posterior composite resin restorations in undergraduate dental schools in Ireland and the UK has increased since the time of a previous survey in 1997. Composite resin may soon equal or overtake amalgam as the material of choice when restoring posterior cavities in Irish and UK dental schools. There was, however, much variation in the nature and extent of the teaching and the techniques taught.

Composite Resins↗

PubMed2002

Effect of resin-coating technique on dentin tensile bond strengths over 3 years.

PURPOSE: The resin-coating technique has been developed to protect prepared dentin and underlying pulp tissue. The purpose of this study was to evaluate the resin-coated dentin bond durability over a period of 3 years of a resin cement and to compare it with two representative resin cements. MATERIALS AND METHODS: Ten bovine dentin specimens were tested for tensile bond strengths with each of the following three materials: CLAPEARL DC with a resin-coating technique (CDRC), Panavia 21 (PA21), and Super Bond C&B (SBCB) at 1 day, 6 months, 1 year, and 3 years. Mean bond strengths were compared statistically by two-way analysis of variance and Fisher's PLSD test (p < .05). The mode of failure was classified by scanning electron microscope observation and analyzed using the Mann-Whitney U-test. RESULTS: The 3-year bond strengths of all resin cements were significantly lower than those at the other experimental periods except for 1 year (p < .05). There was no significant difference in mean bond strength between CDRC and SBCB (p > .05). Regarding the fracture modes, in the case of CDRC, an increase in adhesive failure at the resin-dentin interface was observed as the time period lengthened. Statistical differences were observed between SBCB and the other materials at 1 year (p < .05) and between PA21 and the other materials at 3 years (p < .05). CLINICAL SIGNIFICANCE: The mean tensile bond strengths of the three resin cements to dentin decreased at different rates during the study; the rate at which the bond decreases is likely to affect the long-term durability of restorations.

Acid Etching, Dental↗

PubMed2005

Effect of light dispersion of LED curing lights on resin composite polymerization.

PURPOSE: This study evaluated the effect of light dispersion of halogen and LED curing lights on resin composite polymerization. MATERIALS AND METHODS: One halogen (Optilux 501, SDS/Kerr, Orange, CA, USA) and five light-emitting diode (LED) curing lights (SmartLite iQ, Dentsply Caulk, Milford, DE, USA; LEDemetron 1, SDS/Kerr; FLASHlite 1001, Discus Dental, Culver City, CA, USA; UltraLume LED 5, Ultradent Products, South Jordan, UT, USA; Allegro, Den-Mat, Santa Maria, CA, USA) were used in this study. Specimens (8 mm diameter by 2 mm thick) were made in polytetrafluoroethylene molds using hybrid (Z100, 3M ESPE, St. Paul, MN, USA) and microfill (A110, 3M ESPE) composite resins. The top surface was polymerized for 5 seconds with the curing light guide tip positioned at a distance of 1 and 5 mm. Degree of conversion (DC) of the composite specimens was analyzed on the bottom surface using micro-Fourier Transform Infrared (FTIR) spectroscopy (Perkin-Elmer FTIR Spectrometer, Wellesley, PA, USA) 10 minutes after light activation. DC at the bottom of the 2 mm specimen was expressed as a percentage of the mean maximum DC. Five specimens were created per curing light and composite type (n=5). Percent mean DC ratios and SDs were calculated for each light under each testing condition. Data were analyzed by analysis of variance (ANOVA)/Tukey's test (alpha = .05). A beam analyzer (LBA-700, Spiricon, Logan, UT, USA) was used to record the emitted light from the curing lights at 0 and 5 mm distances (n=5). A Top Hat factor was used to compare the quality of the emitted beam profile (LBA/PC, Spiricon). The divergence angle from vertical was also determined in the x- and y-axes (LBA/PC). Mean values and SDs were calculated for each light under each testing condition (0 and 5 mm, x- and y-axes) and analyzed by a two-way ANOVA/Tukey's test (alpha = .05). RESULTS: For DC ratios, significant differences were found based on curing light and curing distance (p < .05). At 1 mm, Optilux 501 and FLASHlite 1001 produced significantly higher DC ratios with the hybrid resin composite. No differences were found among lights with the microfill at 1 mm. At 5 mm, SmartLite iQ, FLASHlite 1001, LEDemetron 1, and UltraLume LED 5 produced significantly higher DC ratios with the hybrid resin composite, whereas LEDemetron 1 and SmartLite iQ produced significantly higher DC ratios with the microfill resin composite. The UltraLume LED 5, Allegro, and Optilux 501 had significant reductions in mean DC ratios at curing distances of 1 and 5 mm with both resin composite types. For dispersion of light, significant differences were found in Top Hat factor and divergence angle (p < .001). SmartLite iQ had overall the highest Top Hat factor and lowest divergence angle of tested lights. A linear regression analysis relating pooled DC with pooled Top Hat factors and divergence angles found a very good correlation (r2 = .86) between dispersion of light over distance and the ability to polymerize resin composite. CLINICAL SIGNIFICANCE: The latest generation of LED curing lights provides DC ratios similar to or better than the halogen curing light at a curing distance of 5 mm. Dispersion of light plays a significant role in the DC of resin composite. To maximize curing effectiveness, light guides should be maintained in close proximity to the surface of the light-activated restorative material.

Analysis of Variance↗

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↗

PubMed1995

Intragastric distribution of ion-exchange resins: a drug delivery system for the topical treatment of the gastric mucosa.

Previous studies by this group on freeze-dried oral dosage forms containing finely-divided ion-exchange resins revealed prolonged gastric residence and uniform distribution within the stomach. The present study was carried out to ascertain whether this was due to freeze-drying, properties of the radiolabelled ionic exchange resin, or the small dosing volume used. 99mTc-labelled cholestyramine resin was administered in two dosage forms, a freeze-dried tablet which dissolved in the oral cavity (orally dissolving tablet; ODT) and a 1.5 mL aqueous suspension. Two resin particle sizes (20-40 and 90-125 microns) were studied. Oesophageal transit and intragastric distribution and residence were followed by gamma scintigraphy. In a second study, in six subjects, gastric emptying of the water-soluble fraction of the ODT and 1.5 mL of water, was measured using 99mTc diethylenetriaminepentaacetic acid. Oesophageal transit of a water-soluble marker and resin in suspension was rapid, but the transit of the resin in the ODTs was significantly prolonged. Regardless of particle size or dosage form, the resin was evenly distributed throughout the stomach with 20-25% remaining for 5.5 h. In contrast, the water-soluble marker cleared from the stomach rapidly from both dosage forms. We suggest that oral dose forms containing finely-divided ion-exchange resins may form a useful system for topical treatment of the gastric mucosa, for example in targeting to Helicobacter pylori infection.

Adult↗

PubMed2006

Caries-preventive effect of a one-time application of composite resin and glass ionomer sealants after 5 years.

The aim of the present trial was to (1) compare the caries-preventive effect of glass ionomer sealants, placed according to the atraumatic restorative treatment (ART) procedure, with composite resin sealants over time and (2) investigate the caries-preventive effect after complete disappearance of sealant material. Forty-six boys and 57 girls, mean age 7.8 years, were randomly divided into two treatment groups in a parallel-group study design. A light-polymerized composite resin sealant material and a high-viscosity glass ionomer were each placed in 180 fully erupted first molars in their respective treatment groups. Evaluation took place annually for 5 years by calibrated examiners. After 5 years, 86% composite resin and 88% glass ionomer sealants did not survive. Three categories of re-exposure periods for caries development in pits and fissures after complete loss of sealants were distinguished: 0-1, 1-2 and 2-3 years. In the 2- to 3-year group, 13 and 3% of pits and fissures previously sealed with composite resin and glass ionomer, respectively, were diagnosed as having developed a dentine lesion. The relative risks (95% CI) of dentine lesion development in surfaces sealed with glass ionomer compared to those sealed with composite resin after 3, 4 and 5 years were 0.22 (0.06-0.82), 0.32 (0.14-0.73) and 0.28 (0.13-0.61), respectively. The relative risks of dentine lesion development in pits and fissures previously sealed with glass ionomer compared with composite resin over re-exposure periods of 1-2 and 2-3 years were 0.26 (0.14-0.48) and 0.25 (0.09-0.68), respectively. We conclude that the caries-preventive effect of high-viscosity glass ionomer sealants, placed using the ART procedure, was between 3.1 and 4.5 times higher than that of composite resin sealants after 3-5 years. Furthermore, high-viscosity (ART) glass ionomer sealants appear to have a four times higher chance of preventing caries development in re-exposed pits and fissures of occlusal surfaces in first molars than light-cured composite resin sealant material over a 1- to 3-year period. A well-designed clinical trial using different types of oral health personnel should be implemented to confirm these initial results.

Cariostatic Agents↗

PubMed1992

Morphological aspects of the resin-dentin interdiffusion zone with different dentin adhesive systems.

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the inter-diffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

Acid Etching, Dental↗

PubMed1995

Resin restorations for anterior teeth--1995.

Resin restorations for anterior teeth, properly planned and well placed, should be expected to serve many years. Small resin restorations in anterior teeth may even be lifetime restorations. Class III, IV and V resin restorations with large facial display are best when hybrid resin is placed internally and microfill resin is placed facially. Restorations without significant facial display are best treated with hybrid resin alone. Although new, more refined resin systems will come, the current state of the art for anterior resin restorations is excellent and certainly the best it has ever been.

Composite Resins↗

PubMed2003

Clinical evaluation of packable and conventional hybrid resin-based composites for posterior restorations in permanent teeth: results at 12 months.

BACKGROUND: Packable resin-based composites and simplified resin bonding systems are marketed to offer many advantages over conventional posterior hybrid composites and total-etch bonding systems. The authors conducted a study to evaluate the initial clinical performances of a packable and a conventional hybrid resin-based composite used with a simplified bonding system. METHODS: A total of 57 Class I and 45 Class II restorations were placed in the permanent teeth of 65 adult patients. The carious lesions were restored with either packable resin-based composite (SureFil, Dentsply DeTrey GmbH, Konstanz, Germany) or conventional hybrid resin-based composite (SpectrumTPH, Dentsply DeTrey GmbH), using a resin adhesive (Non-Rinse Conditioner and Prime & Bond NT, both manufactured by Dentsply DeTrey GmbH). The authors evaluated the restorations using U.S. Public Health Service-Ryge modified criteria (in which Alfa is the highest rating) and by using color transparencies and die stone replicas. RESULTS: Three SureFil restorations failed before their baseline evaluation. There were no failures among the 78 SpectrumTPH restorations evaluated at 12 months. For both resin-based composites, Alfa ratings were 90 percent or higher for marginal discoloration, anatomical form, surface texture and surface staining. Lower percentages of restorations were rated Alfa for color match, marginal integrity and gingival health. Occasional mild postoperative sensitivity was reported for four SureFil restorations and one SpectrumTPH restoration. The mean occlusal wear rate was 38 micrometers for the larger SureFil restorations and 25 microm for the smaller SpectrumTPH restorations. CONCLUSIONS: The 12-month clinical performances of the two restorative materials were satisfactory and not significantly different for each of the parameters evaluated. CLINICAL IMPLICATIONS: A packable and a conventional hybrid resin-based composite placed with a simplified bonding system in posterior permanent teeth showed satisfactory and similar results after 12 months.

Adolescent↗

PubMed1989

[Basic studies on cutting of composite resin cores].

Filler contents, Knoop hardness, characteristics of cutting and surface texture of eight commercial composite resin cores were investigated. Two posterior composite resins and two silver alloys were used as controls. No differences were found in filler contents and Knoop hardness between the composite resin cores and posterior composite resins. In the composite resins, Knoop hardness was correlated to the filler content. The characteristics of cutting with a diamond point varied largely among materials. The composite resin cores were divided by deterioration of the characteristics of cutting into two groups. The degree of surface roughness of composite resins polished with a finishing diamond point was larger than that of the silver alloys. SEM examination revealed little differences in the composite resin surfaces cut with a diamond point but large differences in surfaces polished with a finishing diamond.

Composite Resins↗

PubMed1989

[Adaptation of acrylic resin dentures polymerized using various activation modes].

The purpose of this in vitro study was to compare the dimensional accuracy of maxillary dentures made using a conventional heat-activated PMMA resin, a pour resin, a visible light-activated resin, and a microwave-activated acrylic resin. Two simple methods for measuring dimensional accuracy were used: (1) weight of impression material entrapped between the base and master die and (2) measurement of the posterior border gap at five locations. The volume of space between the denture base and the master die was determined by (1) computation and (2) estimation. Statistical analysis (Bartlett, ANOVA and Tukey's Tests) supported the following conclusions: (1) all groups showed a processing contraction, most apparent from buccal flange to buccal flange, (2) the poorest fitting group was processed in a brass flask and a water bath at a temperature which rose from 70 to 100 degrees C, using a heat activated resin (Acron), (3) the visible light activated resin (Triad) produced dentures of intermediate accuracy, as did Acupac 20 when either heat or microwave activated, (4) the two best fitting groups were prepared from a chemically activated resin system using pressure at low heat (PER form), and the resin developed for microwave activation (Acron MC).

Acrylic Resins↗

PubMed1999

Microhardness evaluations of resin-dentin bonding areas by nano-indentation.

The purpose of this experiment was to determine the hardness values of the hybrid layer and its surroundings through the continuous use of a microhardness measuring device. Black's Class V cavities were prepared in nine dog teeth. The cavities were divided into four groups according to the dentin adhesive system applied. The adhesive systems were: "Bond One System", "Liner Bond II sigma System", "One Step System", and "Single Bond System". The treated teeth were observed at seven days post-application. Specimens were cross-sectioned perpendicularly or horizontally to the resin-dentin interface and embedded in epoxy resin. Their surfaces were polished. The microhardness of the resin-dentin bonding area was measured with a nano-indentation tester. The hardness values at a point of 10 microns distant from the interface in the direction of the dentin differed between systems. It appeared that this was influenced by the presence of the decalcified dentin not impregnated by resin, differences in the chemistry forming the hybrid layer, and the composition of the bonding resin. The hardness of the dentin-bonding interface and its surroundings was determined, and these areas were observed using SEM. Three layers were confirmed the healthy dentin layer, the composite resin layer, and the hybrid layer, (in which decalcified dentin impregnated by resin and that not impregnated by resin are considered to be mix). In the hybrid layer, no impression was found by SEM although the hardness in the bonding interface was significantly different. These layers appear to be more elastic and softer than the healthy dentin.

Animals↗

PubMed2002

Wear resistance of hybrid composite resin for crown material by the two-body sliding test.

Comparative studies on two-body sliding wear resistance were performed between a hybrid composite resin and conventional light-curing composite veneering materials. This study investigated the wear resistance of hybrid composite resins compared with three composite resin veneering materials for 12%Au-Ag-Pd alloy, the wear resistance of four restorative materials opposed to hybrid composite resin, and the influence of surface characteristics on hybrid composite resins. Hybrid composite resin without heat-curing, which was compared with other composite resin materials exhibited inferior wear resistance, but hybrid composite resin mechanically polished after heat-curing exhibited the most superior wear resistance.

Analysis of Variance↗

PubMedDate not supplied

The effect of chopped poly(methyl methacrylate) fibers on some properties of acrylic resin denture base material.

PURPOSE: The fracture of acrylic resin dentures remains an unresolved problem. Over the years, various approaches to strengthening acrylic resin have been suggested, including modifying or reinforcing the resin. The aim of this study was to investigate the effect of chopped poly(methyl methacrylate) (PMMA) fibers on some properties of acrylic resin denture base material. MATERIALS AND METHODS: PMMA in the form of fibers 0.75 mm in diameter and 5 mm in length was added to acrylic resin denture base material in various percentages to form a composite material. The influence on doughing and manipulation times and transverse strength was examined. The results were subjected to statistical analysis using a one-way analysis of variance and, where appropriate, the Scheffé test. RESULTS: The results showed that the doughing time was decreased by the addition of fibers, with the manipulation and setting times showing inconsistent changes. There was a significant difference between the materials in terms of the transverse strength. When the amount of PMMA fibers in the acrylic resin was increased, there was a decrease in the modulus of rupture and a decrease in the modulus of elasticity. The differences were shown to be statistically significant in some groups. CONCLUSION: The doughing time was decreased by the addition of fibers, while the manipulation and setting times showed inconsistent changes. The incorporation of chopped, randomly oriented PMMA fibers into acrylic resin had no advantage over the unmodified polymer in terms of strength and cannot be recommended as a reinforcing agent for acrylic resin denture base material.

Acrylic Resins↗

PubMed1999

Protective effects of resin impregnation on demineralization of enamel.

PURPOSE: To determine if resin penetrated into the enamel etch pattern, in the absence of a polymerized outer surface film, could reduce the degree of demineralization of enamel subjected to a simulated caries challenge, and to evaluate whether the addition of fluoride to the resin would enhance reductions in demineralization. MATERIALS AND METHODS: Enamel surfaces of extracted human incisors were acid-etched. One-half of the etched area was treated with an unfilled bonding resin, while the other one-half was left untreated as a control. In another group, this same procedure was followed except the unfilled bonding resin contained fluoride. The applied resin was aggressively air thinned to ensure oxygen inhibition throughout the external surface film thickness. The thinned film was visible light-cured and the area was wiped with an ethanol swab to remove the inhibited layer. The specimens were exposed to a buffer solution of pH = 4.7 for 4 days, and were sectioned and examined by polarized light microscopy and microradiography. RESULTS: In each of the two test groups, the demineralization of the resin-treated side was significantly lower than the control side (P < 0.015). Under the conditions of this study, the experimental fluoride resin did not produce statistically significant reductions in demineralization compared with the non-fluoride resin.

Acid Etching, Dental↗