10 You can change your ad preferences anytime. This result was not completely unexpected, as previous studies have shown similar performance between particulate and short fiber-reinforced composites . Displacement of the central portion of the specimen was recorded by a deflectometer (model W-E401-E, Instron). The null hypotheses were: (1) the replacement of glass particles by short fibers does not affect polymerization stress, flexural modulus or volumetric shrinkage of experimental composites and (2) composite polymerization stress is not affected by the thickness (or height) of the specimen. Polymerization stress was not affected by replacing 6% of particles with fibers. If we take a cylinder and subject it to tensile stress or compressive stress, there is simultaneous axial and lateral strain.Within the elastic range the ratio of the lateral to the axial strain is called Poisson's ratio… 13. 4 . Therefore, a higher longitudinal shrinkage was expected in the 1.5-mm specimens, which would increase nominal stress. OF DENTAL MATERIALS. Three experimental composites were prepared with a resin matrix containing equal parts by weight of bisphenol-A glycidyl dimethacrylate (BisGMA, all chemicals from Sigma–Aldrich, St. Louis, MO, USA) and triethylene glycol dimethacrylate (TEGDMA). In the present study, polymerization stress was evaluated along with its main determinants, namely, shrinkage, elastic modulus and reaction kinetics (here represented by maximum shrinkage rate) . More recently, a bulk-fill composite containing filler particles and high aspect ratio E-glass fibers (17 μm in diameter and 1–2 mm in length, AR: 59–118) was developed. Polymerization stress increased when 3% of particles were replaced by short fibers. 4. 3 Compressive strength is most useful for comparing materials that are brittle and generally weak in tension. 1 . Flexural modulus was calculated using data obtained from the initial portion of the load versus displacement curve, according to the following equation: Data were subjected to normality (Anderson-Darling) and homogeneity of variance (Levene) tests. The aims and objectives of this study were to evaluate the von Mises stress and principal stress distribution and displacement of anterior teeth in a lingual orthodontics system along the periodontal ligament and alveolar bone by various combinations of mini-implants and lever arm during en-masse retraction. As an additional control, a commercial composite (Filtek Z250, 3 M ESPE) was tested. Average curves of composite polymerization stress as a function of time, in both specimen configuration (1.5 mm and 4.0 mm heights). Filtek Z100 is a heavily filled hybrid resin composite, which is rather transparent. For these two composites, data scattering was much higher for the taller specimens likely due to the increased difficulty in shaping a higher volume of composite. Fiber orientation imposed by specimen height did not affect polymerization stress. References This result was not completely unexpected, as previous studies have shown similar performance between particulate and short fiber-reinforced composites . Leprince J.G., Palin W.M., Vanacker J., Sabbagh J., Devaux J., Leloup G.: Physico-mechanical characteristics of commercially available bulk-fill composites. Several studies using the same test set up used in the present investigation found a direct correlation between stress and shrinkage . J Dent 2014; 42: pp. A clinically relevant, but least explored aspect of fiber reinforced composites is their polymerization shrinkage and associated polymerization stress. Volumetric shrinkage was reduced only in the composite with 6% of fibers. Goldberg A.J., Burstone C.J. The two control composites containing only glass particles developed similar stress levels. Therefore, a higher longitudinal shrinkage was expected in the 1.5-mm specimens, which would increase nominal stress. Still, randomly oriented short fibers are effective polymer-reinforcing agents depending on their volume fraction, aspect ratio ( i.e. Goncalves F., Azevedo C.L., Ferracane J.L., Braga R.R. S-2 glass fibers, 7–13 μm in diameter (Advanced Glassfiber Yarns, Aikin, SC, USA) were cut into 1.6-mm long segments (standard deviation: 0.5 mm) and silanized using 3-methacryloxypropyl-trimethoxysilane (3-MPTS). Fiber length distribution is shown in the histogram in Fig. 6.9 (0.2) A Table 1 : Developing a more complete understanding of stresses produced in dental composites during polymerization. Polymerization stress (MPa) b is the specimen's width, and As fiber average length was 1.6 mm, it was hypothesized that in 1.5-mm specimens there would be some level of fiber orientation perpendicular to the rotational axis of the specimen. Methods: A nano-based indentation system (Ultra Micro-Indentation System, UMIS-2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds of dental ceramics (Cerec 2 Mark II and Vita VM9), one kind of dental alloy (Wiron 99) and healthy enamel. More recently, a bulk-fill composite containing filler particles and high aspect ratio E-glass fibers (17 μm in diameter and 1–2 mm in length, AR: 59–118) was developed. Purpose: A systematic review was conducted to determine whether there were any alternative technique or additional step strategies available to reduce and control polymerization shrinkage stress development in dental resin-based restorative materials. 6% fiber Fiber orientation imposed by specimen height did not affect polymerization stress. 7. 4 1.8 (0.1) BC Therefore, some of the clinical problems usually associated with polymerization stress, such as marginal gaps and the development of white lines due to enamel cracking at the margins, may be less of a concern. When the composite with 6% of fibers is compared to the experimental control, it is licit to assume that the lower shrinkage of the former was offset by the 41% higher flexural modulus of the latter, resulting in statistically similar polymerization stress values. 28, no. Averages and standard deviations for polymerization stress, flexural modulus, polymerization shrinkage and maximum shrinkage rate of the tested composites All values correspond to data recorded 10 min after the onset of photoactivation (except maximum shrinkage rate). Five specimens were tested per group. × Compressive stress (S C), Shear stress (S S), Tensile stress (S T). The first null hypothesis was rejected, as the replacement of filler particles by short, randomly oriented fibers affected polymerization stress, flexural modulus and shrinkage of the experimental composites in different ways. Shrinkage versus time curves are shown in Fig. J Esthet Dent 2000; 12: pp. J Esthet Dent 1999; 11: pp. Finally, a study that systematically evaluated the replacement of particles by highly oriented, 3.0-mm-long fibers reported improvements in flexural modulus only at fiber levels starting at 10.3 vol% . Fig. 1. A similar relationship can be seen when Filtek Z250 is compared with the composite containing 3% of fibers, which show 43% higher shrinkage and 65–94% higher polymerization stress. al. Unfortunately, short fibers do not provide the same level of strength obtained with long continuous fibers and, if they are randomly oriented, a four-fold lower strength is expected . 697-703. An LVDT probe (linear variable differential transducer) was positioned touching the mercury surface. , Carmem S. Pfeifer Replacing 6% of particles by fibers did not increase PS significantly. 0% fiber Statistical analysis used shrinkage values recorded 10 min after the beginning of photoactivation. 3. For example, the 0.1% proof stress (commonly used for alloys) is the level of stress which would result in a 0.1% permanent deformation 8 10/30/2013. Now customize the name of a clipboard to store your clips. The extensometer sensors were clamped to both rods and any change in specimen height due to composite shrinkage immediately commanded the crosshead to restore the initial distance between rod surfaces. Polymerization stress increased when 3% of particles were replaced by short fibers. Shrinkage versus time curves are shown in Fig. Finally, a study that systematically evaluated the replacement of particles by highly oriented, 3.0-mm-long fibers reported improvements in flexural modulus only at fiber levels starting at 10.3 vol% . Prior to the test, methyl methacrylate was applied to the sandblasted surfaces to improve wetting by a thin layer of unfilled resin (Scotchbond Multipurpose Plus, 3 M ESPE). 2.5 al. − : Polymerization efficiency and flexural strength of low-stress restorative composites. The components were mechanically mixed at 2500 rpm under vacuum for 30 s (Speedmixer DAC 150.1 FVZ-K, FlackTek Inc., Landrum, SC, USA) and kept under refrigeration until 2 h before use. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Investigations on the use of fibers as reinforcing agents in dental polymeric materials started in the 1960’s, soon after fiber-reinforced polymers became available in large industrial scale . Boxplot of polymerization stress results, as a function of the tested composite and the height of the specimen. , between materials with similar shrinkage, polymerization stress is inversely related to composite elastic modulus. Still, randomly oriented short fibers are effective polymer-reinforcing agents depending on their volume fraction, aspect ratio ( i.e. One possible hypothesis to explain this finding is the relatively high scattering of the stress data obtained with the 4.0-mm high specimens, as can be seen in the boxplot in Fig. Petersen R.C., Lemons J.E., McCracken M.S. Polymerization stress of experimental composites containing random short glass fibers, Biaxial flexural strength of new Bis-GMA/TEGDMA based composites with different fillers for dental applications, Internal adaptation of resin composites at two configurations: Influence of polymerization shrinkage and stress, Hybrid chitosan/gelatin/nanohydroxyapatite scaffolds promote odontogenic differentiation of dental pulp stem cells and in vitro biomineralization, The impact of different low-pressure plasma types on the physical, chemical and biological surface properties of PEEK, Photodynamic inactivation of Streptococcus mutans by curcumin in combination with EDTA, In vitro investigations on retention force behavior of conventional and modern double crown systems, HEMA-induced oxidative stress inhibits NF-κB nuclear translocation and TNF release from LTA- and LPS-stimulated immunocompetent cells, Multi-scale analysis of the influence of filler shapes on the mechanical performance of resin composites using high resolution nano-CT images. Dent Mater 25: 331-338. The proportional limit C. In the same column, values followed by the same superscript are not statistically different (ANOVA/Tukey test, If you continue browsing the site, you agree to the use of cookies on this website. 4 . In the 1990s, composites containing relatively low aspect ratio glass fibers (AR < 10) as part of the filler systems became commercially available. Photoinitiators (camphorquinone and ethyl-4 dimethylamino benzoate, EDMAB) were added at 0.5% (by weight) each. Since then, several studies have tested the effect of adding continuous glass or carbon fibers on the mechanical properties of acrylic resins and several clinical applications were devised for continuous fiber-reinforced composites, such as periodontal and orthodontic splints and fixed prosthodontics substructures . Freilich M.A., Karmaker A.C., Burstone C.J., Goldberg A.J. LVDT readings were converted to volumetric shrinkage values using input values of composite mass and density. It was demonstrated that shrinkage is greatly reduced in the direction of continuous long fibers . Maximum shrinkage rate (in % s −1 ) was calculated as the first derivative of the shrinkage versus time curve, as an indication of polymerization reaction rate. J Prosthet Dent 1962; 12: pp. Mechanical properties and parameters that are measures of the elastic strain or plastic strain behavior of dental materials include elastic modulus (also called Young’s modulus or modulus of elasticity), dynamic Young’s modulus (determined by the measurement of ultrasonic wave velocity), shear modulus, flexibility, resilience, and Poisson’s ratio. To test the null hypotheses that (1) the replacement of particles by short fibers does not affect polymerization stress (PS), flexural modulus (FM) or volumetric shrinkage (VS) of experimental composites and (2) PS is not affected by specimen thickness. Kardos J.L., Halpin J.C.: Short predicting the strength and toughness of fiber composites. : The effect of length and concentration of glass fibers on the mechanical properties of an injection- and a compression-molded denture base polymer. This project was funded by FAPESP (The State of São Paulo Research Foundation), grant 2013/13805-7, and PIBIC/CNPq (National Counsel of Technological and Scientific Development). Boaro L.C., Froes-Salgado N.R., Gajewski V.E., Bicalho A.A., Valdivia A.D., Soares C.J., et. Three specimens were tested in each group. This rationale explains the difference in polymerization stress between the experimental control and the composite containing 3% of fibers, i.e. , Mogilevych B., Soares C.J., et to many cycles of repeated stress during mastication 2.5×10×65... It can occur in fixed partial dentures or cantilever structures strength of low-stress restorative composites a manner! 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