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PubMed2006

Chemical study of triterpenoid resinous materials in archaeological findings by means of direct exposure electron ionisation mass spectrometry and gas chromatography/mass spectrometry.

A systematic study of standard triterpenes (alpha-amyrine, oleanolic acid, betulin, lupeol, betulinic acid and lupenone) and of raw resinous materials (frankincense resin, mastic resin and birch bark pitch) was performed using direct exposure electron ionisation mass spectrometry (DE-MS) and gas chromatography/mass spectrometry (GC/MS). DE-MS provides a mass spectral fingerprint of organic materials in a few minutes which highlights the compounds that are the main components in the sample. The application of principal component analysis (PCA) on DE-MS data in the mass ranges m/z 181-260 and m/z 331-500, corresponding to the fragmentation of triterpenoid molecules, enabled us to distinguish between different triterpenoid materials such as mastic resin, frankincense resin and birch bark pitch, and to graphically plot the resinous substances in three separate clusters, retaining 89% of the total variance. GC/MS analysis of the same materials has permitted us to elucidate in detail the molecular composition and to identify minor components and species that act as markers of the degradation undergone by the materials. The paper also reports the results for the organic residues contained in an Egyptian censer (5th-7th century AD) which was recovered in the excavation of the Necropolis of Antinoe (Egypt), and for the hafting material found on a Palaeolithic tool recovered at the site of Campitello (Arezzo, Tuscany), dating back to the Mid-Pleistocene period. Although DE-MS was found to be a fast analytical tool, it failed to give any information on the presence of less abundant compounds when applied to mixtures of different materials: only mastic resin was found in the residues from the Roman censer, whereas GC/MS analysis identified the presence of a vegetable oil from Brassicaceae seeds and Pinaceae resin. Birch bark pitch as a pure material was identified in the sample from the Palaeolithic flint flake using both procedures.

Archaeology↗

PubMed2006

In-vitro investigation on suitability of light-cured resins for interocclusal splints : part II: surface hardness.

OBJECTIVE: The aim of the present study was to determine the surface hardness of light- and auto-cured resins for the fabrication of occlusal splints employing Vickers hardness measurements. MATERIALS AND METHOD: In this study we used three auto-polymerized resins (Palapress, Orthocryl, Steady-Resin M) and four light-polymerized resins (Acrylight, Primosplint, Triad Tran- Sheet Colorless and Triad TranSheet Pink). The Vickers hardness measurement was carried out by means of a universal Durimet indenter applying a test load of 50 g for 30 seconds. The light-cured resins were polymerized in a Tagris Power light oven for 10 and 15 minutes each. Three separate test series were carried out (the hardness of plates under optimal conditions and of occlusal splints was measured, and the curing of light-polymerizing materials in layers of varying depth was evaluated). Data underwent statistical analysis via ANOVA and the Scheffé test. RESULTS: The microhardness determined in each case amounted to values between 10.4 HV 0.5 and 39.3 HV 0.5. The Vickers hardness determined for the plates that had been produced under optimal conditions demonstrated that their surface was significantly (p < 0.05) harder than that of cylinders and splints. The hardness values of the light-cured material Triad TranSheet Pink (39.3 HV 0.5) were significantly higher (p < 0.05) than those of all other resins. In all auto-polymerized resins, the surface hardness of the samples we examined (in the form of plates and splints) was significantly lower (p < 0.05) than that of the light-cured materials Triad TranSheet Pink and Colorless. CONCLUSION: The results we have obtained so far concerning surface hardness indicate that, in the fabrication of occlusal splints, light-cured resins may represent an alternative to auto-polymerizing materials.

Absorption↗

PubMed2007

HPLC analysis of components released from dental composites with different resin compositions using different extraction media.

Components released from dental composite resins are essential factors in the assessment of biocompatibility of these materials. The effect of different extraction media on monomer release from composite resins based on different monomer types was evaluated. Three types of visible light cured composite resins were formulated based on the following monomers: triethylene glycol dimethacrylate (TEGDMA), bisphenol A glycerolate dimethacrylate (BisGMA), and urethane dimethacrylate (UDMA). Seventy-five composite resin discs were fabricated and light cured for 1 min in the absence of oxygen. Extraction media used were: distilled water, saline solution, artificial saliva, serum-free culture medium, and culture medium with 10% fetal calf serum. The analysis of extracts from the composite resins was carried out by High Performance Liquid Chromatography (HPLC). Quantifiable amounts of TEGDMA were released into the aqueous media. However, BisGMA and UDMA were not detectable in any of the extracts from the composite resins. Statistical analysis by one-way ANOVA followed by Tukey's test showed that there was a significant difference in TEGDMA release between culture media and other media (p < 0.05). From the results of this experiment it can be concluded that TEGDMA-based composite resins can release a high quantity of monomer into aqueous environments. The type of extraction medium may have a significant effect on monomer release from composite resins.

Biocompatible Materials↗

PubMed1976

The effect of oral doses of a polythiol resin on the excretion of methylmercury in mice treated with cysteine, D-penicillamine or phenobarbitone.

Mice dosed with methylmercury chloride (0.5 to 2.0 mg Hg/kg i.p.) labeled with the 203Hg isotope were given polythiol resin in their food (2% w/w). The effect of pretreatment with phenobarbitone, or co-administration of D-penicillamine or L-cysteine, was tested on the efficacy of the resin to accelerate the excretion of methylmercury. The effect of the polythiol resin in enhancing fecal excretion was dependent on the dose of methylmercury, it being significantly greater at doses of 1.0 and 2.0 than at 0.5 mg Hg/kg. In animals given the resin and phenobarbitone (0.1% w/w drinking water), fecal excretion was approx. 36% greater than in animals given resin alone. Penicillamine (2.5 mg/ml drinking water) actually retarted elimination of methylmercury in animals given the resin. Despite the enhanced efficacy of the resin plus phenobarbitone, the brain levels of methylmercury were not reduced beyond those seen in animals given resin alone. The mechanisms and implications of these effects are discussed.

Animals↗

PubMed1981

Flexure fatigue of 10 commonly used denture base resins.

The flexure fatigue properties of 10 denture base resins (four different types) were tested. Each specimen underwent two-way testing in a water bath maintained at 37 degrees +/- 1 degree C. A load of 3,650 gm was applied a 342 flexures per minute until the specimen broke. The resin types listed in order of increasing resistance to flexure fatigue are polymethylmethacrylate (PMM) pour resins, PMM thermosetting resins, vinyl resins, and a PMM grafted resin. Although small samples size and scatter of results limit broad application of this data, it is of some significance that the grafted resin Lucitone 199 tended to withstand repeated flexure when compared to the other resins.

Dental Stress Analysis↗

PubMed1989

Comparative bond strengths of light-cured, heat-cured, and autopolymerizing denture resins to denture teeth.

Standard and interpenetrating polymer network acrylic resin denture teeth were milled into cylinders 8 mm in diameter and processed against cylinders of the three different resins. The specimens were reduced by milling to a diameter of 6 mm in the region of the tooth-resin interface and thermocycled for 24 hours. Specimens were then subjected to tensile loading until fracture. Group means were compared by using the Duncan multiple range test at the 5% level of significance. The strongest bond occurred between the heat-cured resin and the standard acrylic resin teeth. Intermediate strength was achieved with the heat-cured resin to the IPN teeth and the autopolymerizing resin to both types of teeth. Lowest strength was measured with the light-cured resin to both types of teeth.

Acrylic Resins↗

PubMed1994

Physical and chemical properties of resin-reinforced calcium phosphate cements.

OBJECTIVES: The purpose of this study was to improve the handling and physical properties of a self-setting, water-based calcium phosphate cement by combining it with polymerizable resins and to study the setting reactions involved. METHODS: Dual-cured composite cements were prepared from a calcium phosphate cement powder and dental monomers that contain carboxylated hydrophilic resins or resin/water mixtures. The setting reaction of the calcium phosphate cement in the presence of the resins was evaluated by pH measurements, infrared spectroscopy, diametral tensile strength, x-ray diffraction analysis, and scanning electron microscopy. RESULTS: Carboxylated resins were chosen because they can form ionic bonds to the mineral filler, which was confirmed by appearance of an infrared absorbance peak at 1552 cm-1 within 24 h after mixing due to the formation of a carboxylate salt. Hydroxyapatite did not develop in composites prepared from resin and calcium phosphate cement. However, composites from calcium phosphate cement, resin and water showed approximately 40% hydroxyapatite. The resulting composite cements have moderately high DTS of 14-15 MPa and high pH. SIGNIFICANCE: Hydrophilic acidic resins allows mixing with water and/or allow rapid diffusion of water into the resinous cement so that the dissolution and reprecipitation processes required for the conversion of the calcium phosphate components to hydroxyapatite can occur. The characteristics of the resulting composite cements suggest that the materials may be useful in pulp capping and/or cavity lining.

Calcium Phosphates↗

PubMed1992

Allergic contact dermatitis from formaldehyde resins in permanent press clothing: an underdiagnosed cause of generalized dermatitis.

BACKGROUND AND METHODS: Formaldehyde resins have been used to impart wrinkle resistance to clothing fabrics since 1926. After several patients with positive patch tests to formaldehyde resins had been examined, a study was undertaken of the records of all patch tests performed at the University of Louisville Patch Test Clinic and the Allergy Section of the Skin and Cancer Clinic of New York University Medical Center from January 1988 through April 1990 to determine the prevalence of positive patch-test reactions to formaldehyde-based textile resins and the clinical and demographic patterns associated with textile resin allergy. RESULTS: Seventeen patients were identified at the two centers. Twelve were allergic to formaldehyde as well as to formaldehyde textile resins. Several clinical patterns were found, including accentuation of dermatitis in areas of tight clothing, primary occurrence in clothing-covered areas, and a chronic recalcitrant course. Ethylene urea melamine formaldehyde resin was the best screening agent with 14 definite positive reactions and one equivocal reaction. CONCLUSION: Formaldehyde textile resin allergy is more common than has been previously recognized. Patch testing with one or more formaldehyde textile resins is indicated in patients with a particular pattern of dermatitis.

Adult↗

PubMed2006

Evaluation of resin adhesion to zirconia ceramic using some organosilanes.

OBJECTIVES: This study evaluated and compared the effect of three trialkoxysilane coupling agents on the bond strength of a Bis-GMA-based unfilled resin and a dimethacrylate-based resin composite luting cement to a zirconia ceramics (Procera AllZircon, Nobel Biocare, Göteborg, Sweden). METHODS: Six square-shaped zirconia specimens were used for each test group, a total of 72 specimens. The specimens in each group were all assigned to air-borne alumina particle abrasion followed by tribochemical silica-coating and silanization with 1 vol% solutions of 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-isocyanatopropyltriethoxysilane in an ethanol-water mixture. The sample stubs were made of a Bis-GMA/MMA/DMAEMA resin or a commercial resin composite luting cement (RelyX ARC, 3M ESPE, Seefeld, Germany). They were bonded to the conditioned and silanized silica-coated zirconia specimens using polyethylene molds. All specimens were tested at dry and thermo-cycled (6000, 5-55 degrees C, 30 s) conditions. The shear bond strength of resin stubs to zirconia was measured in a universal testing machine (cross-head speed 1 mm/min). RESULTS: In dry conditions, the highest shear bond strength was 9.7 MPa (S.D. 3.3 MPa), and for thermo-cycled samples 7.4 MPa (S.D. 2.4 MPa) was obtained with RelyX ARC cement with 3-methacryloyloxypropyltrimethoxysilane. In general, thermo-cycling decreased the bond strengths significantly for the Bis-GMA resin (ANOVA, p < 0.005). The resin, cement and silanes differed significantly silanes (ANOVA, p < 0.005). All samples silanized with 3-isocyanatopropyltriethoxysilane de-bonded during thermo-cycling. De-bonding was dominantly due to adhesive failure. SIGNIFICANCE: Bonding of the experimental resin and commercial cement to silica-coated zirconia is effective with 3-methacryloyloxypropyltrimethoxysilane or 3-methacryloyloxypropyltrimethoxysilane, but not with 3-isocyanatopropyltriethoxysilane.

Adhesiveness↗

PubMed2006

Comparison of two methods for measuring the polymerization characteristics of flowable resin composites.

OBJECTIVES: The purpose of this study was to compare two methods for assessing the polymerization characteristics of flowable resin composites. METHODS: Two different flowable resin composites and a hybrid resin composite control were investigated. In order to measure the volumetric shrinkage (DeltaV), each material was placed into a mould and extruded into a water-filled dilatometer. The specimens were then light irradiated for 30s using a curing unit with the power density adjusted to either 100 or 600mW/cm(2). For the speckle contrast measurement, each resin composite was condensed into a glass tube and irradiated. The laser-speckle field was recorded in a digital frame. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function of time were obtained. RESULTS: The average DeltaV values of the resins after 180s ranged from approximately 3.3 to 4.4% for the flowable composites and from approximately 1.8 to 2.3% for the hybrid composite control. The overall magnitude of the speckle contrasts decreased soon after the initial light exposure commenced and gradually increased thereafter. The speckle contrast measurements revealed changes in the pastes due to the polymerization of the flowable resins that were greater than those obtained with the water-filled dilatometer. SIGNIFICANCE: These data suggest that the polymerization characteristics of flowable resins can be measured successfully using two different methods. Moreover, our findings are of clinical relevance, as the data obtained under laboratory conditions might give an indication of the suitability of flowable resin composites for specific clinical applications.

Analysis of Variance↗

PubMed2004

Microhardness of acid-treated and resin infiltrated human dentine.

OBJECTIVE: The aim is to determine if superficial or deep dentine microhardness (MH) is affected by different chemical dentine pre-treatments performed for resin bonding. METHODS: Dentine discs of superficial (SD) and deep dentine (DD) were obtained by transversally sectioning the crowns of human third molars. Knoop MH was measured after different treatments: (1) polished up to 4000 grit, (2) polished and etched (37% ortophosphoric acid for 15 s), (3) resin (Single Bond -SB-) infiltrated dentine after acid etching, (4) polished, etched and treated with 5% NaOCl for 2 min, (5) resin infiltrated (SB) after etching and NaOCl treatment. For resin infiltrated surfaces care was taken in order to remove the excess adhesive layer, and obtain infiltrated dentine, by measuring thickness of the sample before resin infiltration and polishing after resin infiltration until obtaining the initial thickness of the sample. Indentations (n=20) were performed on moist surfaces with a standard Knoop MH tester (20 g, 5 s). Data were expressed in Knoop Hardness Numbers (KHN) and analysed by ANOVA and multiple comparisons (P<0.05). RESULTS: Dentine KHN decreased on both SD and DD after acid etching. NaOCl treatment after acid etching did not affect MH on SD, but KHN of DD was lowered. Resin infiltration increased KHN but did not recover the initial MH values in both SD and DD. CONCLUSIONS: Treating dentine with either H3PO4 or NaOCl caused marked reduction of its surface hardness and subsequent resin infiltration was not capable to restore it.

Acid Etching, Dental↗

PubMed2005

Retention of a resin-modified glass ionomer adhesive in non-carious cervical lesions. A 6-year follow-up.

OBJECTIVES: The purpose of this study was to evaluate the clinical retention of a new resin-modified glass ionomer cement based adhesive combined with a hybrid resin composite or a poly-acid modified resin composite in non-carious cervical lesions during a 6-year period. METHODS: The resin-modified glass ionomer adhesive (Fuji Bond LC), was placed in 73 cervical lesions, 36 with a universal hybrid resin composite (Tetric Ceram) and 37 with a poly-acid modified resin composite (Hytac). Fifty-one in lesions with sclerotic dentin and 22 in non-sclerotic ones. Of the sclerotic lesions 38 were slightly roughened with a diamond bur before conditioning. The restorations were evaluated with slightly modified USPHS criteria every six months during a 6-year period. RESULTS: All except six restorations were evaluated during the 6 years. Twelve (17.9%) were lost, four Tetric Ceram (11.8%) and eight Hytac (24.2%) (p<0.05). Four were found in non-sclerotic lesions (20.0%) and eight in sclerotic lesions (17.0%). The differences between the sclerotic and non-sclerotic and the roughened and non-roughened lesions were not significant. CONCLUSIONS: The resin-modified glass adhesive showed a superior clinical retention combined with the resin composite material, with an annual failure rate of 2%.

Adult↗

PubMed2005

Improved and selective platinum recovery from spent alpha-alumina supported catalysts using pretreated anionic ion exchange resin.

Improved and selective recovery of platinum from a spent dehydrogenation platinum alpha-alumina supported catalyst using a strong basic ion exchange resin is reported. Platinum and other precious metal group (PMG) complexes are leached using concentrated hydrochloric acid along with about 0.20 vol.% nitric acid as an oxidizing agent from de-coked and crushed spent catalyst. Effects of hydrochloric acid concentration, time, and temperature in leaching stage are investigated. The strong basic anionic resin is treated by sodium hydroxide solution to replace chloride anion by hydroxyl group ion. The supernatant of the leaching process is passed through a fixed column of hydroxylated strong base anionic resin. The treated resin on which the platinum complex is adsorbed is dried and burned in an oxidizing atmosphere at 750-800 degrees C. The recovered gray metallic powder is mainly platinum. Results compared with those obtained from untreated anionic resin show that adsorption of platinum complexes onto the treated anionic resin is more selective and the yield of separation is considerably improved. The breakthrough curves of the pretreated anion exchanger and that of untreated exchange resin reveals that the capacity of the hyroxilated resin is decreased by about 14%. These breakthrough curves can be used for calculation of height of a practical exchange plate (HPEP) for design purposes.

Aluminum Oxide↗

PubMed2003

In vitro deformation of acetyl resin and metal alloy removable partial denture direct retainers.

STATEMENT OF THE PROBLEM: Acetyl resin removable partial denture (RPD) direct retainers may provide an esthetic alternative to conventional metal direct retainers. The effect of repeated stress on acetyl resin direct retainers is unknown. PURPOSE: This study compared deformation of acetyl resin and metal alloy RPD direct retainers after repeated dislodgments over a test die. MATERIAL AND METHODS: Ten acetyl resin (Thermoflex) and 10 metal alloy (Ticonium Premium 100) RPD direct retainers, fabricated to manufacturers' specifications, were dislodged over a stainless steel die by means of a laboratory test apparatus for a simulated 3-year period (5000 cycles). Occlusal and facial digital images made before and after cycling were measured (mm) for direct retainer deformation by using computer-imaging software (Scion Image 1.62). Student t tests (alpha=.05) were performed for statistical comparisons. RESULTS: A significant difference in deformation between acetyl resin and metal alloy direct retainers occurred in the occlusal view (P=.045), but not in the facial view (P=.832). Average deformation varied but was greatest in the occlusal view: 0.09 +/- 0.8 mm for acetyl resin direct retainers compared with 0.01 +/- 0.9 mm for metal alloy direct retainers. Average facial view deformations revealed no significant differences: 0.039 +/- 0.6 mm for metal alloy and 0.033 +/- 0.7 mm for acetyl resin direct retainers. CONCLUSION: Within the limitations of this in vitro study, significantly greater deformation resulted with acetyl resin compared with metal alloy direct retainers after 3 years of simulated use.

Dental Alloys↗

PubMed2004

The effect of polymerization cycles on porosity of microwave-processed denture base resin.

STATEMENT OF PROBLEM: Although most of the physical properties of denture base resin polymerized by microwave energy have been shown to be similar to resins polymerized by the conventional heat polymerization method, the presence of porosity is a problem. PURPOSE: This study evaluated the effect of different microwave polymerization cycles on the porosity of a denture base resin designed for microwave polymerization. MATERIAL AND METHODS: Thirty-two rectangular resin specimens (65 x 40 x 5 mm) were divided into 3 experimental groups (A, B, and C; Onda-Cryl, microwave-polymerized resin) and 1 control group (T; Clássico, heat-polymerized resin), according to the following polymerization cycles: (A) 500 W for 3 minutes, (B) 90 W for 13 minutes+500 W for 90 seconds, (C) 320 W for 3 minutes+0 W for 4 minutes+720 W for 3 minutes, and (T) 74 degrees C for 9 hours. Porosity was calculated by measurement of the specimen volume before and after its immersion in water. Data were analyzed using 1-way analysis of variance (alpha=.05). RESULTS: The mean values and SDs of the percent mean porosity were: A=1.05%+/-0.28%, B=0.91%+/-0.15%, C=0.88%+/-0.23%, T=0.93%+/-0.23%. No significant differences were found in mean porosity among the groups evaluated. CONCLUSION: Within the limitations of this study, a denture base resin specifically designed for microwave polymerization tested was not affected by different polymerization cycles. Porosity was similar to the conventional heat-polymerized denture base resin tested.

Acrylic Resins↗

PubMed2005

Effect of microwave sterilization and water storage on the Vickers hardness of acrylic resin denture teeth.

STATEMENT OF PROBLEM: Acrylic resin denture teeth soften upon immersion in water, and the heating generated during microwave sterilization may enhance this process. PURPOSE: Six brands of acrylic resin denture teeth were investigated with respect to the effect of microwave sterilization and water immersion on Vickers hardness (VHN). MATERIAL AND METHODS: The acrylic resin denture teeth (Dentron [D], Vipi Dent Plus [V], Postaris [P], Biolux [B], Trilux [T], and Artiplus [A]) were embedded in heat-polymerized acrylic resin within polyvinylchloride tubes. For each brand, the occlusal surfaces of 32 identical acrylic resin denture posterior teeth were ground flat with 1500-grit silicon carbide paper and polished on a wet polishing wheel with a slurry of tin oxide. Hardness tests were performed after polishing (control group, C), after polishing followed by 2 cycles of microwave sterilization at 650 W for 6 minutes (MwS group), after polishing followed by 90-day immersion in water (90-day Wim group), and after polishing followed by 90-day storage in water and 2 cycles of microwave sterilization (90-day Wim + MwS group). For each specimen, 8 hardness measurements were made and the mean was calculated. Data were analyzed with a 2-way analysis of variance followed by the Bonferroni procedure to determine any significance between pairs of mean values (alpha=.01). RESULTS: Microwave sterilization of specimens significantly decreased (P <.001) the hardness of the acrylic resin denture tooth specimens P (17.8 to 16.6 VHN), V (18.3 to 15.8 VHN), T (17.4 to 15.3 VHN), B (16.8 to 15.7 VHN), and A (17.3 to 15.7 VHN). For all acrylic resin denture teeth, no significant differences in hardness were found between the groups MwS, 90-day Wim, and 90-day Wim + MwS, with the exception of the 90-day Wim + MwS tooth A specimens (14.4 VHN), which demonstrated significant lower mean values (P <.001) than the 90-day Wim (15.8 VHN) and MwS (15.7 VHN) specimens. CONCLUSIONS: For specimens immersed in water for 90 days, 2 cycles of microwave sterilization had no effect on the hardness of most of the acrylic resin denture teeth.

Acrylic Resins↗

PubMed2005

An in vitro comparison of retentive force and deformation of acetal resin and cobalt-chromium clasps.

STATEMENT OF PROBLEM: The use of metal clasps on anterior teeth may cause esthetic problems. Recently, acetal resins have been used as an alternative tooth-colored denture clasp material to improve esthetics. However, there are few studies to support acetal resin use. PURPOSE: The purpose of this in vitro study was to compare the retentive force and deformation of acetal resin and cobalt-chromium clasps after 36 months of simulated clinical use. MATERIAL AND METHODS: Forty clasps each of acetal resin (1.2 or 2.0 mm thick) and cobalt-chromium (Dentorium)(1.2 mm thick) were fabricated using half-round standard prefabricated clasp patterns. The groups were further subdivided (n=10) into the type of tooth (premolar or molar metal model) and undercut (0.25 mm or 0.50 mm). The retentive force of the clasps was measured in distilled water by a specially designed insertion-removal testing apparatus with intervals corresponding to 0, 6, 12, 18, 24, 30, and 36 months of simulated clinical use of a removable partial denture. The distance between the clasp tips (mm) was measured with a microscope before and after the insertion-removal testing procedure. Comparison of the mean values of the retentive force (gram force) of the clasps and the distance (mm) between the clasp tips was conducted with 3-way analysis of variance and a Least Significant Difference (LSD) multiple range test (alpha=.05). RESULTS: The mean values of tensile load required to dislodge acetal resin clasps with 1.2-mm thickness (111.6 g or 0.11 N) and with 2.0-mm thickness (178.4 g or 1.75 N) was significantly lower than that to dislodge Co-Cr clasps (694.1 g or 6.81 N) (P<.001). The retentive force needed to dislodge all 3 types of clasps was significantly lower for the molar than premolar models and also lower for the models with 0.25-mm undercuts than for those with 0.50-mm undercuts (P<.001). After 36 months of simulated clinical use, there was evidence of deformation in the cobalt-chromium clasps but no deformation noted for the acetal resin clasps. The retentive force of cobalt-chromium clasps (297.4 g or 2.91 N) after deformation remained significantly higher (P<.001) than the retentive force of acetal resin clasps that were 1.2 mm (110.7 g or 1.08 N) and 2.0 mm thick (177.5 g or 1.74 N), respectively. CONCLUSION: Within the limitations of this study, the results suggest that both thicknesses of acetal resin clasps evaluated required less force for insertion and removal than Co-Cr clasps over a simulated 36-month period.

Analysis of Variance↗

PubMed2006

Influence of ceramic surface conditioning and resin cements on microtensile bond strength to a glass ceramic.

STATEMENT OF PROBLEM: It is not clear how different glass ceramic surface pretreatments influence the bonding capacity of various luting agents to these surfaces. PURPOSE: The purpose of this study was to evaluate the microtensile bond strength (microTBS) of 3 resin cements to a lithia disilicate-based ceramic submitted to 2 surface conditioning treatments. MATERIAL AND METHODS: Eighteen 5 x 6 x 8-mm ceramic (IPS Empress 2) blocks were fabricated according to manufacturer's instructions and duplicated in composite resin (Tetric Ceram). Ceramic blocks were polished and divided into 2 groups (n=9/treatment): no conditioning (no-conditioning/control), or 5% hydrofluoric acid etching for 20 seconds and silanization for 1 minute (HF + SIL). Ceramic blocks were cemented to the composite resin blocks with 1 self-adhesive universal resin cement (RelyX Unicem) or 1 of 2 resin-based luting agents (Multilink or Panavia F), according to the manufacturer's instructions. The composite resin-ceramic blocks were stored in humidity at 37 degrees C for 7 days and serially sectioned to produce 25 beam specimens per group with a 1.0-mm(2) cross-sectional area. Specimens were thermal cycled (5000 cycles, 5 degrees C-55 degrees C) and tested in tension at 1 mm/min. Microtensile bond strength data (MPa) were analyzed by 2-way analysis of variance and Tukey multiple comparisons tests (alpha=.05). Fractured specimens were examined with a stereomicroscope (x40) and classified as adhesive, mixed, or cohesive. RESULTS: The surface conditioning factor was significant (HF+SIL > no-conditioning) (P<.0001). Considering the unconditioned groups, the microTBS of RelyX Unicem was significantly higher (9.6 +/- 1.9) than that of Multilink (6.2 +/- 1.2) and Panavia F (7.4 +/- 1.9). Previous etching and silanization yielded statistically higher microTBS values for RelyX Unicem (18.8 +/- 3.5) and Multilink (17.4 +/- 3.0) when compared to Panavia F (15.7 +/- 3.8). Spontaneous debonding after thermal cycling was detected when luting agents were applied to untreated ceramic surfaces. CONCLUSION: Etching and silanization treatments appear to be crucial for resin bonding to a lithia disilicate-based ceramic, regardless of the resin cement used.

Ceramics↗