Social Security must change: means test hard but necessary.
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Age Factors↗
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[Development of visible-light cured FRP denture].
Acrylic denture may be fractured easily because it has a relatively poor resistance to stresses of impact, and the thick acrylic denture base also uncomforted to denture wearers. In this study, for improvement of the mechanical properties, the FRP is applied to the denture base, and try to make a thin denture base. Using the visible light-curing system, the laboratory fabrication time is saved dramatically. To develop the visible light-cured FRP denture base, with various combination of matrix resins and reinforcements, the physical properties of FRP plates were investigated first. From the results of the bending test, hardness test, and manipulation considering, the sateen weave's glasscloth was choose as the reinforcement of the prepreg. The matrix resin of Bis-GMA/UDMA/3G at 48/48/4 wt% was determined. The 3 plies glasscloth included FRP plate is 0.8 mm thickness has the maximum bending strength about 50 kgf/mm2, which is about 5 times larger than that of acrylic resin. Succeeding the study of above, the FRP denture base was fabricated by using the 0.8 mm thickness 3 plies included prepreg. This repreg is manufactured in sheet form beforehand, which is ease to manipulate at laboratory. By using the visible light curing system, it is only taken 10 min. to make a FRP denture base. The following procedures of fabricating a FRP denture is the same as metalplate denture. The visible-light cured FRP denture has some advantages such as accuracy of fit, ease of fabrication and manipulation, and only 0.8 mm thickness but has superior strength.
Bisphenol A-Glycidyl Methacrylate↗
[Development of denture base resin. 2. Manufacturing of visible-light cured prepreg and physical properties of FRP].
To develop the visible light-cured FRP denture base, we investigated the physical properties and the warp of FRP plate by using various combinations of matrix resin and reinforcement. From the results of the bending test, hardness test and manipulation processing, the matrix resin of Bis-GMA/UDMA/3 G at 48/48/4 wt% was determined. The sateen weave's glasscloth as the reinforcement of the prepreg was used. The maximum plies included FRP of 0.5 mm, 0.8 and 1.0 mm thickness have the same maximum bending strengths of 45 kgf/mm2, which is about 5 times larger than that of conventional acrylic resin. The warp of these FRP plates were not found.
Bisphenol A-Glycidyl Methacrylate↗
Physico-mechanical properties of a fast-set highly viscous GIC restorative.
UNLABELLED: The fast-setting reaction of 'fast-set' highly viscous glass-ionomer cements (GIC) may result in superior mechanical properties and good wear resistance as the material can theoretically achieve sufficient strength to resist masticatory loads within a shorter time. The aim of this study was to determine the hardness, strength (compressive and diametral tensile) and wear resistance of a 'fast-set' highly viscous GIC (Fuji IX GP Fast). Its regular set counterpart (Fuji IX GP) was used for comparison. The glass powders of the two cements were also characterized. Hardness testing [Vickers' hardness number (VHN)] was performed with a digital hardness tester (load=50 g; dwell time=30 s) and compressive/diametral tensile strength testing (MPa) was conducted based upon British Standards specification for GICs (BS6039, 1981). Wear testing was conducted using a reciprocal compression-sliding wear instrumentation at 20 MPa contact stress against SS304 counter-bodies with distilled water as lubricant. All specimens were immersed in distilled water at 37 degrees C and tested 24 h after start of mixing. Further mechanical tests (hardness and strength) were conducted with specimens stored for 1 week in distilled water at 37 degrees C. The glass powders were characterized using laser particle sizing, standard electron microscope (SEM) and energy dispressure X-ray (EDX) analysis. Results were analysed using multiple analysis of variance (manova) and independent samples t-test at significance level 0.05. No significant difference in hardness, compressive and diametral tensile strength was observed between Fuji IX GP and Fuji IX GP Fast at 1 day. There was also no significant difference in wear at all cyclic intervals. Although the difference in strength was not significant between the two cements at 1 week, Fuji IX GP Fast was significantly harder than Fuji IX GP. Particle size of both cements ranged from 0.3 to 200 microm. The mean particle sizes were, however, different and were 13.43 and 7.13 microm for Fuji IX GP and Fuji IX GP Fast, respectively. Fuji IX GP Fast offers no other advantage over Fuji IX GP with the exception of improved hardness. CLINICAL RELEVANCE: Besides being harder, the fast-set highly viscous GIC restorative offers no other physico-mechanical advantage over its regular set counterpart.
Dental Restoration Wear↗
Mechanical properties of two orthodontic adhesive materials polymerized with halogen and plasma curing.
OBJECTIVES: The aim of this study is to compare the efficiency of two polymerization techniques (halogen curing--Astralis 7 and plasma curing--Flipo), with two orthodontic adhesive materials (Enlight, a composite resin, and Fuji Ortho LC, a glass ionomer cement). METHODS: The efficiency of the polymerization techniques was shown by two mechanical tests. The hardness test was carried out on the exposed and non-exposed surfaces using 10 x 4 x 3-mm samples, polymerized either by halogen curing (40 seconds) or by plasma curing (5 seconds). The three-point bending tests were carried out on 2 x 2 x 25-mm samples polymerized as above. The samples were kept 1 hr at room temperature, then for 24 hrs in distilled water at 37 degrees C. RESULTS: Whatever the polymerization technique used, the results are similar for hardness and flexion, with the exception of the hardness tests carried out after polymerization with the Flipo light on the surface not directly exposed. CONCLUSION: In orthodontic practice, both polymerization techniques can be used. But a multi-bracket session can be long, and the reduction of time spent in the chair obtained by using plasma lamps seems to make this technique preferable.
Acrylic Resins↗
Impact test for hardness of compressed powder compacts.
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Hardness↗
The chemical and pharmaceutical equivalence of sulphadoxine/pyrimethamine tablets sold on the Tanzanian market.
This study investigated chemical and pharmaceutical equivalence of 11 brands of pyrimethamine-sulphadoxine combination tablets sold on the Tanzanian market. Physical and chemical tests were performed for all the 11 brands. These tests included hardness test, friability, disintegration, dissolution, weight uniformity and assay for the active components. All the brands passed all the quality specifications of the United States Pharmacopoeia (USP) and British Pharmacopoeia (BP) in terms of hardness, friability, disintegration, assay and dissolution test, except for three brands that failed the hardness, disintegration or friability tests. One brand failed both the hardness and disintegration test; one failed the hardness test, whereas another one failed the friability test. The percentage content of pyrimethamine in the brands was in the range of 91.04-100.20% whereas that of sulphadoxine ranged from 91.53% to 99.88%. There were no major differences between the different brands of tablets containing pyrimethamine and sulphadoxine and the innovator product (Fansidar), and all brands were physically and chemically equivalent. The results indicate that the post-market surveillance and registration process in Tanzania is having an impact on product quality as there was no brand which could be considered of very poor quality. Impurity profiling of all the locally produced brands indicated that they all contained the same sulphadoxine impurity, which was absent in the innovator product, suggesting a common source of generic raw material.
Antimalarials↗
Hardness of heat-polymerized acrylic resins after disinfection and long-term water immersion.
STATEMENT OF THE PROBLEM: In selecting a disinfectant for dental prostheses, compatibility between the disinfectant and the type of denture base material must be considered to avoid adverse effects on the hardness of the acrylic resin. PURPOSE: This study investigated the hardness of 2 denture base resins after disinfection and long-term water immersion. MATERIAL AND METHODS: Thirty-two disk-shaped specimens (13 mm in diameter and 8 mm thick) were fabricated from each resin (Lucitone 550 and QC-20), polished, stored in water at 37 degrees C for 48 hours, and submitted to hardness tests (Vickers hardness number [VHN]) before disinfection. Disinfection methods included scrubbing with 4% chlorhexidine gluconate for 1 minute, immersion for 10 minutes in 1 of the tested disinfectant solutions (n=8) (3.78% sodium perborate, 4% chlorhexidine gluconate, or 1% sodium hypochorite), and immersion in water for 3 minutes. The disinfection procedures were repeated 4 times, and 12 hardness measurements were made on each specimen. Control specimens (not disinfected) were stored in water for 56 minutes. Hardness tests (VHN) were also performed after 15, 30, 60, 90, and 120 days of storage in water. Statistical analyses of data were conducted with a repeated measures 3-way analysis of variance (ANOVA) and Tukey post-hoc test (alpha=.05). RESULTS: Mean values +/- SD for Lucitone 550 (16.52 +/- 0.94 VHN) and QC-20 (9.61 +/- 0.62 VHN) demonstrated a significant (P <.05) decrease in hardness after disinfection, regardless of material and disinfectant solutions used (Lucitone 550: 15.25 +/- 0.74; QC-20: 8.09 +/- 0.39). However, this effect was reversed after 15 days of storage in water. Both materials exhibited a continuous increase (P <.05) in hardness values for up to 60 days of water storage, after which no significant change was observed. CONCLUSION: Within the limitations of this in vitro study, QC-20 and Lucitone 550 specimens exhibited significantly lower hardness values after disinfection regardless of the disinfectant solution used.
Acrylic Resins↗
The effect of powder-liquid ratio and the mixing method on the surface hardness of phosphate-bonded investment materials.
In this experimental study the surface-hardness changes of three phosphate-bonded investments were observed in relation to: a) the ratio of liquid-powder, b) the way of the mixing, in 3 hours and 24 hours after mixing. The Vickers hardness test was used for testing the surface hardness of the specimens (ISOMA SA, Bienne, Swiss, hardness testing apparatus). This study indicated that the surface hardness of the specimens increased after mechanical mixing, and also that it was higher in 24 hours than in 3 hours. Also, as more water was included in the mixing liquid, as lower became the surface hardness of the materials. Finally, it was observed that one material appeared to have the greatest fluctuations of surface hardness: Maruvest MI.
Dental Casting Investment↗
Effect of the polishing technique at low or high speed on the micro-hardness of dental amalgam.
Dental cavities were prepared and restored with amalgam, using three different silver alloys. The surface of the restorations was finished 24 hours after condensation, with a rotatory instrument using a low- or high-speed handpiece. The specimens were then submitted to metallographic polishing and one of the margins of the amalgam restoration were then submitted to Vickers' micro-hardness test. Another micro-hardness test was accomplished 168 hours after condensation and the two sets of micro-hardness values were compared. No significant statistical differences were detected between the micro-hardness values obtained with low or high speed in the polishing technique.
Dental Amalgam↗
A safety study in vitro for the effects of an in-office bleaching system on the integrity of enamel and dentine.
OBJECTIVE: The aim of this study was to investigate safety concerns with bleaching procedures by studying the effects of a high concentration hydrogen peroxide (HP) in-surgery bleaching product on enamel and dentine. METHOD: Flat enamel and dentine samples embedded in epoxy resin were prepared from human third molar teeth. Erosion of enamel: groups of enamel samples were treated with 35% HP then citric acid (CA) or brushing with toothpaste or CA alone and water alone. Enamel Loss was measured using a profilometer. Abrasion/erosion of dentine: groups of dentine specimens were treated as follows: Group 1--brushed with water for 30 min. Group 2--brushed with 35% HP for 30 min. Group 3--power bleached for 30 min and then Group 4--brushed with toothpaste for 1 minute. Group 5--water soaked for 30 min followed by brushing with toothpaste for 1 min. Group 6--orange juice soaked for 30 min followed by brushing with toothpaste for 1 min. Treatment effects were measured using a profilometer. Hardness tests: enamel and dentine specimens were hardness tested using a Wallace indenter prior to and post bleaching. Scanning Electron Microscopy: enamel and dentine specimens were taped and the exposed tissue treated with 35% HP and then studied under scanning electronmicroscopy (SEM). RESULTS: Enamel erosion: bleaching enamel samples had no measurable effect on enamel. Pre-bleaching had no significant effect on subsequent CA erosion or brushing. Abrasion/erosion of dentine: no significant differences were found between treatments 1-5 with little change from baseline detected. Orange juice (Group 6) produced considerable and significantly more erosion than other treatments. Hardness tests: there were no significant changes in hardness values for enamel and dentine. SEM: there was no evidence of any topographical changes to either enamel or dentine. CONCLUSION: Using one of the highest concentrations of HP for tooth bleaching procedures and maximum likely peroxide exposure, there was no evidence of deleterious effects on enamel or dentine. It must be assumed that studies which reported adverse effects on enamel and or dentine of bleaches reflect not the bleach itself but the pH of the formulation used.
Beverages↗
Permeability of the root canal wall and occlusion of dentinal tubules by Ag(NH3)2F: a comparison of combined use with pulsed Nd:YAG laser or iontophoresis.
OBJECTIVE: We used SEM-EDX and the Vickers hardness test to compare the penetration and hardness of silver resulting from use of either (i) pulsed Nd:YAG laser or (ii) iontophoresis, after root canal wall shaping using the standard method of coating with 38% Ag(NH3)2F solution. SUMMARY BACKGROUND DATA: There have not been any reports of penetration and hardness following the application of Ag(NH3)2F solution together with laser or iontophoresis. METHODS: We used 21 extracted human single-rooted teeth randomly divided into three groups. Group 1 was coated with Ag(NH3)2F, Group 2 was irradiated with a Nd:YAG laser after coating with Ag(NH3)2F solution, and Group 3 was iontophoresised after coating. Then we observed the permeability of silver through the root canal wall using SEM-EDX. RESULTS: The results show that iontophoresis after coating with Ag(NH3)2F solution (Group 3) resulted in the greatest and deepest penetration of silver into the root canal wall. There was no significant difference between teeth in Groups 1 and 2. For the hardness test, the 21 teeth were tested using SEM-EDX test, 7 untreated teeth were used as a control. The results show that Group 2 (laser treatment) teeth were the hardest. CONCLUSION: We therefore propose that root canals should be treated using irradiation with an Nd:YAG laser that has been coated with Ag(NH3)2F solution and that this method provides better results than either iontophoresis after coating, or coating alone.
Combined Modality Therapy↗
[Mechanical properties of titanium casting obtained using short-time cast procedure].
The purpose of this study was to investigate the mechanical properties of titanium casting obtained using short-time cast procedure. A commercial phosphate-bonded investment for titanium casting were used. And dumbbell-shaped specimens with phi 2 mm x 14 mm parallel portion were cast according to manufacture instruction and by way of three different short-time cast procedures. Then, micro vickers hardness test and tensile test were performed with these specimens. In the hardness test, the micro vickers hardness of 50 approximately 250 microns deep location from specimen surface was ranged from 192.8 to 259.0 Hv; there were significant difference among both the location factor and the casting procedure factor by the two-way ANOVA (p < 0.05). In the tensile test, tensile strength, yield strength, elastic modulus and elongation were obtained: these tensile properties of short-time cast procedures were not significantly different from those of manufacture instruction. These results indicated that the short-time cast procedure for titanium casting was available in the point of mechanical properties. It was, however, not obvious that how the short-time cast procedures effected the dimensional accuracy of titanium casting. Therefore, further investigation was needed for the practical usage of this method.
Dental Casting Technique↗
Bonding of photo and dual-cure adhesives to root canal dentin.
This study evaluated the regional tensile bond strength of a dual-cure resin composite core material to root canal dentin using photo and dual-cure adhesives and different modes of polymerization. Nineteen extracted premolars were decoronated and their root canals prepared to a depth of 8 mm and a width of 1.4 mm using Para Post drills. For the microtensile bond strength (microTBS) test, 15 roots were randomly divided into five groups and their canal walls treated with a dual-cure self-etching primer (Clearfil Liner Bond 2V Primer, Kuraray Medical Co, Japan). Adhesive resin (Clearfil Liner Bond 2V Bond A) was applied to two of the groups and light cured for 20 seconds. A dual-cure adhesive resin (Clearfil Liner Bond 2V Bond A+B, Kuraray Medical Co, Japan) was applied to the remaining three groups, one of which was light cured. The post spaces of all the groups were filled with a dual-cure resin composite (DC Core) and three were light cured for 60 seconds from a coronal direction. Chemical-cure resin composite was placed on the outer surfaces of the roots, which were then stored in water for 24 hours. They were serially sliced perpendicular to the bonded interface into eight 0.6 mm-thick slabs, then transversely sectioned into beams approximately 8 x 0.6 x 0.6 mm for the microTBS test. All of the failure modes were observed under SEM and analyzed using the Kruskal-Wallis Rank test. For Knoop hardness testing, four specimens were prepared in a similar manner, two were light-cured and the other two chemically-cured. The specimens were longitudinally sectioned into two pieces, and three indentations were made at 100 microm intervals from a coronal to an apical direction in the eight halves. Data were divided into two groups (coronal/apical halves of post space) and analyzed using two-way ANOVA and Scheffe's test (p<0.05). For each curing strategy, there were no significant differences in microTBS and Knoop hardness between the coronal and apical regions (p>0.05). Light exposure of both the adhesive resin and resin composite resulted in significantly higher microTBS than chemical-cure alone (p<0.05). Light exposure also significantly increased Knoop hardness at both the coronal and apical regions (p<0.05). When the bonding resin and dual-cure resin composite were chemically-cured, failures occurred cohesively within the resin. Photo-initiated polymerization of the adhesive resin and dual-cure resin composite was necessary to achieve good bonding to root canal dentin, which was not dependent upon region.
Analysis of Variance↗
Effects of different disinfectants on physical properties of four temporary soft denture-liner materials.
OBJECTIVE: The purpose of this study was to evaluate the effects of some commonly used disinfectants on physical properties of four temporary soft denture-liner materials. METHOD AND MATERIALS: Soft-liner materials, including three plasticized acrylic resin-liners (Tempo, Immediate, Flexacryl Soft) and one silicone-based material (Ufi Gel P) were studied. Specimens prepared with the soft-liner materials were tested after the application of disinfectants (5% Deconex and 3.5% Savlex for 10 minutes; 2% sodium hypochlorite and 5.25% sodium hypochlorite for 5 minutes) and were compared with the control group (not disinfected; immersed in distilled water). Five specimens of each material were tested and data collected on days 4, 7, 11, and 15. The hardness values were determined using the Shore A hardness test. RESULTS: Water sorption test results showed that the disinfectants had statistically significant effects on water sorption values (except days 7 and 15 for Flexacryl Soft and days 4, 7, and 11 for Ufi Gel P). Water solubility and hardness test results also showed statistically significant effects on the materials by the disinfectants. CONCLUSION: Disinfectants significantly affected the physical properties of water sorption, water solubility, and hardness of the soft-liner materials.
Absorption↗
[Determination of copper alloy hardness, in original form and after casting as a function of casting techniques].
It was evaluated the Vickers hardness of five high-copper casting alloys, in their original package form and after casting, according to the casting method used. That way, ten ingots, supplied by the manufacturers of each alloy, were included in self-curing acrylic resin, polished, numerated and submitted to Vickers hardness test at load of 200 g during 30 seconds. Afterwards the numerated ingots were removed from the acrylic resin and five of those were cast in an electrical casting machine and the other five in a centrifugal casting machine with an air/gas torch. The specimens obtained were included in self-curing acrylic resin, polished and submitted to Vickers hardness test. As a result it was verified that there is a variation of hardness among the alloys tested, and the use of the electrical casting machine produced lower hardness values than those produced when used the centrifugal casting machine with an air/gas torch. Also, there is a decrease of hardness of the cast alloys when they are tested in their original form and after casting.
Copper↗
Hardness measured with traditional Vickers and Martens hardness methods.
OBJECTIVE: To determine the differences, if any, between hardness measured with traditional Vickers and Martens hardness test methods on denture teeth under 2, 10 and 50 N loads. METHOD: Hardness of acrylic resin (VIV), composite resin (ORT) and porcelain (POR) denture tooth materials was measured using a traditional Vickers hardness (HV) method and Martens hardness (HM) method at 2, 10 and 50N test loads. Vickers hardness was also calculated from the force-indentation depth curves (HVfid) that were recorded during Martens hardness. Indentation creep of the three test materials was also determined during Martens hardness testing. RESULTS: HM values were the same irrespective of the test force used. However, HV values were different for the three test forces. ANOVA using Tukey's test of the HM data showed that the hardness of POR was significantly higher than VIV or ORT (P<0.001). Moreover, ORT had a significantly higher hardness than VIV (P<0.001). The statistical analysis of HVfid data showed similar results. ANOVA of the HV data showed the hardness of VIV to be significantly higher than ORT (P<0.001) under 2, 10 and 50 N test load. The HV values for POR under 2 and 10 N test load could not be calculated because of inability to measure the indentation diagonals. Under the 50 N load, the hardness of POR was significantly higher than VIV and ORT. POR had a significantly lower creep value than any other material tested while VIV showed a statistically significantly higher creep than ORT. SIGNIFICANCE: This study confirms that the visco-elastic recovery of the materials has a very significant effect on the outcome of the hardness tests of denture teeth and the Martens hardness test method has obvious advantages when testing dental materials.
Acrylic Resins↗
Hardness and compressive strength of indirect composite resins: effects of immersion in distilled water.
The aim of this study was to evaluate the effect of ageing in distilled water on the hardness and compressive strength of a direct composite resin Z100, a feldspatic porcelain (Noritake) and three indirect composites (Artglass, Solidex and Targis). For the Vickers hardness tests, five disk-shaped specimens (2 x 4 mm) of each material were prepared according to the manufacturers' instructions. The hardness tests were conducted using a Vickers diamond indentor. Compressive strength measurements were recorded on cylindrical specimens with a diameter of 6 mm and a length of 12 mm. The compression tests were carried out with a constant cross-head speed of 0.5 mm min(-1) on a mechanical test machine. For each material, 10 specimens were tested after 7 days of dry storage at 37 +/- 1 degrees C and 10 specimens were tested after water storage at 37 +/- 1 degrees C for 180 days. Noritake porcelain specimens showed higher hardness values than the composites. Among the composite materials, Z100 promoted the highest VHN values, regardless of the ageing periods. The results showed that Solidex and Z100 had the highest compressive strength values. Ageing in water reduced the hardness for all composites, but had no long-term effect on the compressive strength.
Composite Resins↗