Base Composite Material Research Articles

Role of delayed light polymerization of a dual-cured composite base on marginal adaptation of class II posterior composite open-sandwich restoration

To determine the effect of delayed light polymerization of a dual-cured composite base material on the marginal adaptation of class II composite restoration. 35 extracted human molar teeth were used to prepare class II mesio-occlusal or disto-occlusal slot preparations with gingival margins at the CEJ. The teeth were restored using an open-sandwich technique with a 2mm base increment of dual-cured composite, and divided into 5 groups based on the mode of the polymerization of the dual-cured composite base: Group A - self-cured after placement (5 mins), Group B - light-cured immediately after placement, Group C - light-cured 30 seconds after placement, Group D - light-cured 60 seconds after placement, Group E - light-cured 120 seconds after placement. Then a top layer of a light-cured composite resin is placed to complete the restoration. The teeth were thermocycled and immersed in 1% aqueous solution of methylene blue for 24 hours. Sectioning of the teeth and scoring under stereomicroscope was done. Data will be statistically evaluated using the kruskal wallis 1-way ANOVA. Statistical analysis using kruskal wallis 1-way ANOVA showed that the dual-cured composite light polymerized 1 minute after placement exhibited the least microleakage. Delayed light polymerization of the dual-cured composite base reduced the microleakage in class II open-sandwich restorations.

Investigation of surface fatigue of thermally sprayed micro- and nanocrystalline cylinder wall coatings by means of cavitation testing

Abstract The future demands of diesel engines require new options for low-friction and wear-resistant materials in order to increase efficiency and achieve environmentally sound solutions. Efforts are made to improve the performance and reduce the weight of engine blocks by coating the aluminium cylinder bores using thermal-spray processes. Thus, along with other means, today nanocrystalline coatings are considered when looking for the desired combination of structural, productional, and topographical properties. Besides sufficient tribological properties it is important that the composite (base material and coating) allows for prolonged endurance under cyclic mechanical and thermal stresses. Prior to engine tests these coatings are characterised in the laboratory by means of bench tests for adhesive tensile strength, tribological properties and fatigue of the composite. Cavitation tests should reveal the tribological stability of these coatings and their ability to resist high-frequency cyclic impact stresses. The objective in this investigation is to describe the cavitation behaviour and the influence of voids such as pores or oxides.

Evaluation of the risk of batted-ball injury for slow-pitch softball pitchers

Over the past few years, there has been a significant change in the material used to construct softball bats. Since 2000, there has been a significant increase in the number of slow-pitch softball bats sold that are constructed entirely of composite-based materials. It is theorized that the introduction of these composite bats has resulted in an increase in batted-ball speed, which directly corresponds to a decrease in available pitcher reaction time and can lead to an increase in the risk of injury. To test this theory, a controlled field-test study was conducted using five different certified softball bat models and four experienced testers to quantify the performance of composite-based softball bats compared to a wooden softball bat. For the composite bats, the available pitcher reaction times varied from 0.390 to 0.365 s for a pitcher standing 15.24 m (50 ft) from the batter, while, for the wooden bat, the available pitcher reaction times varied from 0.452 to 0.419 s. This study demonstrates that composite-based slow-pitch softball bats perform at an unsafe level when the results are compared to published safety studies in the sports of softball and baseball, which advocate available pitcher reaction times of 0.409 to 0.420 s. In addition, possible mitigation methods are discussed that could make the sport of slow-pitch softball safer.

PRESSURE-ASSISTED SPINNING: A UNIQUE AND VERSATILE APPROACH FOR DIRECTLY FABRICATING MEMBRANES WITH MICRO- AND NANOFIBERS

Fibers are structurally interesting components most useful in a range of applications spanning the physical and life science areas of research. These membrane (scaffold) forming fibers have been explored in applications ranging from microfilteration to advanced biological investigations in tissue engineering to controlled and targeted drug delivery. One such robust fiber generation approach investigated for over a century, which has recently been exploited, is the well-established threading process referred to as electrospinning. In this technique, single- or multi-phase media are charged within a conducting needle and later exposed to an electric field which promotes the formation of a continuous micro- to nanosized fiber(s) which over a period of collection time has been reported for forming scaffolds and membranes. This process has been explored for a wide range of polymer composite-based materials and the technique has now reached the point where it has moved into industrial production. We report here as a first example a comparable fiber to membrane fabrication approach completely driven by the coupling of a coaxial needle system with a pressure. We refer to this novel methodology as pressure-assisted spinning (PAS) where the hazardous element of high voltage (as in the case of electrospinning) is nonexistent. Hence, our discovery introduces both a directly competing fiber, scaffold to membrane fabrication approach, which is versatile and has no associated hazards as those in electrospinning. Furthermore as our technique is nonelectric field driven, the media spun into fibers could have a high electrical conductivity, which in this case has no effect on the stability in processing near-uniform fibers/scaffolds to membranes. The fabricated fibers and membranes generated by means of this approach could directly be used for a plethora of applications spanning the engineering and biological areas of research.

A pitcher injury risk assessment study analyzing composite, titanium, aluminum and wood softball bat performance

Over the past few years, there has been a significant increase in the performance of softball bats from the Olympics down to the recreational level. It is theorized that the introduction of composite-based material bats has been the largest contributor to the increase in batted-ball performance, which directly corresponds to a decrease in available pitcher reaction time that can lead to an increase in injury potential. To test this theory, a controlled field-test study comparing all of the different bat model types currently available was conducted. The performance of ten bat model types; two composite-based, two titanium-based, two aluminum-based multi-wall, two aluminum-based single-wall and two wood-based bats were measured using 1686 N/0.64 cm (379 lbs/0.25”) compression softballs in order to calculate available pitcher reaction times when using a specific bat model type. Over 1000 Batted-ball velocity measurements were analyzed using two calibrated radar devices and five experienced test subjects. The results of this study indicate that when titanium-based or composite-based softball bat performance results are compared to published safety studies in the sports of softball and baseball, available pitcher reaction times are unsafe, which can lead to a higher injury risk potential. The significance of this research is to provide experimental field-test data on the possible safety risks to pitchers that can be used to reduce the injury potential and promote safety awareness in the sport of softball.

Effects of Material Composition and Microstructural Features on Dry Sliding Wear Behaviour of Fe–TiC Composite and a Cobalt-Based Stellite

This investigation deals with the influence of hardfacing En31 steel separately with Fe–TiC composite and commercial cobalt base (stellite 6) material on their sliding wear behaviour at 2.94 m/s speed and varying applied pressures. Wear response of the samples was substantiated through the scanning electron microscopic studies of the wear surfaces, subsurface regions and debris particles. The hardfaced samples revealed superior wear performance than that of the substrate. Further, the steel hardfaced with cobalt-based stellite offered higher wear resistance over the one overlayed with Fe–TiC composite. The applied pressure controlled the wear behaviour (rate) in a complex manner and its influence was dependent on material composition/microconstituents and test conditions. The friction coefficient got reduced with pressure except in the case of the Fe–TiC composite overlay beyond 2 MPa. The hardfaced samples were noted to be better suited for more severe conditions. Microcracking was quite frequently observed on wear surfaces of the hardfaced material especially under mild wear conditions. Sticking of fine debris particles on to the specimen surface was also observed.

Effect of different luting materials on the marginal adaptation of Class I ceramic inlay restorations in vitro

Objectives: The aim of this in vitro study was to assess the marginal adaptation of prefabricated Class I ceramic inlay restorations placed with various luting materials. Methods: Forty-two standardized occlusal cavities were prepared in extracted human molars with diamond burs exactly corresponding to the dimensions of prefabricated glass ceramic inlays. The prepared teeth were randomly assigned to seven groups of six teeth each and restored using (1) the composite resin Tetric Ceram in increment technique [Group I] or (2) ceramic inlays (Cerana) luted with: the composite based materials Dual Cement [Gr. II] and Panavia 21 [Gr. III], the compomer material Dyract Cem [Gr. IV], Dyract Cem with additional use of Prime & Bond 2.1 [Gr. V], the silicophosphate cement Trans-Lit [Gr. VI], or the ethylcyanoacrylate Cyano-Veneer [Gr. VII]. Marginal adaptation was evaluated by SEM-analyses before and after thermal cycling (2500 cycles; 5–55 °C) and mechanical loading (100 N; 500,000 cycles) using replica models. Kruskal–Wallis H-test and Mann–Whitney U-test were used for statistical analyses. Results: Group I (increment technique) as well as Groups II–V (inlay technique) revealed high percentages of perfect marginal adaptation in over 95% of the analyzed margins, both before and after thermo-mechanical loading. Statistical significant differences could not be detected within these groups. All inlays luted with silicophosphate cement (Group VI) and four of six inlays applied with Cyano-Veneer (Group VII) fractured under occlusal load. Significance: A stable bonding to the enamel and to the ceramic inlay was achievable with the composite luting resins Dual Cement and Panavia 21 as well as with the compomer based luting material Dyract Cem but not with the use of the silicophosphate cement Trans-Lit or the ethylcyanoacrylate Cyano-Veneer.

Color stability of provisional resin restorative materials

Statement of problem. Use of temporary crowns and fixed partial dentures is especially relevant when the treatment plan requires restorations for long interim periods, and the in-service discoloration of provisional restorative materials is a major drawback. Purpose. This study evaluated the discoloration effect of coffee and tea on some materials that are commonly used in the fabrication of provisional restorations. Material And Methods. Six commercially available provisional resins (Jet, Caulk TBR, Protemp Garant, Luxatemp Solar, Provipont DC and SR-Ivocron-PE) were evaluated after 1 day, 7 days, and 30 days of immersion in various staining solutions. Color measurements were obtained by using a Dr Lange Micro Color tristimulus colorimeter and color differences (ΔE*) were estimated. Results. The 2 chemically activated resins (Jet and Caulk TBR) and the heat-cured resin (SR-Ivocron PE) exhibited the least color changes, whereas the Provipont-DC resin was the least color stable. After immersion for 30 days, the combination with the coffee solution resulted in unacceptable discoloration for all the tested materials. Conclusions. Provisional restorative materials, staining solutions, and immersion time were significant factors that affected color stability. After immersion for 7 days, all materials showed observable color changes. The composite-based materials, especially light-curing composites, were the least color stable. The coffee solution exhibited more staining capacity than the tea solution. (J Prosthet Dent 1998;80:533-9.)

Particle fracture in metal-matrix composite friction joints

The influence of welding parameters, reinforcing particle chemistry and shape, matrix condition and silver interlayers on particle fracture during similar and dissimilar friction welding of aluminium-based metal-matrix composite (MMC) base material was investigated. Two composite base materials were examined, one containing Al2O3 particles and the other containing 72 wt% Al2O3–7 wt % Fe2O3–17 wt % SiO2–3 wt % TiO2 particles. The different material combinations comprised MMC/MMC, MMC/alloy 6061, MMC/AISI 304 stainless steel and MMC/1020 mild steel joints. Particle fracture was confined to a narrow region immediately adjacent to the dissimilar joint interface. The calculated normal pressure for fracture of Al2O3 particles ranges from 0.56–17.58 MPa and is in agreement with an experimentally measured pressure of 1.06 MPa found during sliding wear testing of aluminium-based composite base material. Because the lowest normal pressure applied during friction joining was 30 MPa, particle fracture occurs very early in the joining operation (immediately following contact between the two substrates). The application of a silver interlayer during dissimilar MMC/AISI 304 stainless steel joining decreased the particle fracture tendency. It is suggested that the presence of a silver interlayer decreased the coefficient of friction and lowered the stresses applied at the contact region. The particle fracture tendency was markedly increased when the MMC material contained blocky alumina particles. However, there was negligible particle fracture when the MMC base material contained spherical 72 wt % Al2O3–7 wt % Fe2O3–17 wt % SiO2–3 wt % TiO2 particles.

New Composite Packaging

This paper describes some of the benefits of electronic packages manufactured from silicon carbide reinforced aluminium composites. The housings which were analysed and tested consisted of iron‐nickel alloy sidewalls soldered to composite bases. The metal matrix composite bases were produced using Lanxide's PRIMEX™ pressureless metal infiltration process. Hermeticity test results on the base to sidewall seals are presented along with comparative electrical performance of the composite versus conventional base materials. Analysis of the thermal, mechanical and weight performance of this approach is also provided.

Properties of an iron-copper composite-base rolled material sintered for a short time

Properties of an iron-copper composite-base rolled material sintered for a short time

Radiopaque denture base materials technic dentures.

AbstractTechnic dentures were made using composite base materials containing 30,40, and 50 weight % of a silance‐treated, readiopaque, powdered glass as the reinforcing filler and poly (methyl methacrylate) as the matrix. Dentures containing no glass were included for comparison. Molar‐to‐molar dimensional changes, effects of silance treatment fo the procelain teeth and handling and finishing characteristics were determined.Dentures containing glass had less dimensional change during curing and subsequent water storage than those without glass. Thick upper dentrues exhibited the least change and thin lowers, the most. The Differences in the magnitudes of the changes would not be clinically noticeable.Silance treatment fo the procelain teeth in thick upper dentures resulted in breakage of theposterior teeth in almost all instances. posterior teeth also freactured in thick upper dentures containing 40 and 50% of the silance‐treated glass even though the teeth were not treatedwith silance.Mixing and molding properties of the composite materials, while acceptabgle, were slightly inferior to thematerial containing ono glass. Finiching characteristics were definitelyinferior in that it was more difficult and time‐consuming to attain the fial surfaces and these surfaces were not as smooth as smooth as those in dentures without glass.

Physical properties of a radiopaque denture base material.

AbstractPhysical properties were determied for radiopaque composite denture base materials consisting of poly (methyl methacrylate) as thematrix and 30, 40, and 50% by weight fo a singlane‐treated barum fluoride‐containing glass powder as the reinforcing filler. Specimens without glass were include for comparision.All of the materials met the requirements of Amerrican ental Association Specification No. 12 for Denture Base Polymer except that t6he material containing 50% glass had less deflection than the minimum required at the 5000‐gm load in transverse testing.There was little or no difference among thematerials with respect to hardness, in denation resistance, water sorption, color stability, and resistance to drop impact.Addition of glass of the 30% level decreased the transevers strenght while 50% means with no glass. In general, the addition of glass increased the time to reach only slight effect on densities, and Young's, bulk, shear, and flexural moduli, had only slight effect on solubility and decreased the cold‐cure repairability and the coefficient of linear thermal expanision.The solubility of the glass power was aboutfour times that of powdered porcelain teeth after 24 hr, and totaled 0.55% afeter 5 days.