1542-1551. Garoushi S., Vallittu P.K., Watts D.C., Lassila L.V. Acta Biomater 2010; 6: pp. Shrinkage, maximum shrinkage rate and polymerization stress data failed the normality test and, for this reason, were analyzed using Kruskal–Wallis test. Consequently, robustness of the statistical test was somewhat compromised. As bonding substrate for the composite, 5-mm diameter acrylic rods were sectioned in 28-mm long segments and had one of their flat surfaces sandblasted. 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. Discussion 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. See our Privacy Policy and User Agreement for details. 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. 3.48 (0.04) AB It was demonstrated that shrinkage is greatly reduced in the direction of continuous long fibers . × 16. , Livia C. Natale 6% fiber Average curves of composite polymerization stress as a function of time, in both specimen configuration (1.5 mm and 4.0 mm heights). Data were recorded 10 min after the onset of photoactivation and analyzed by ANOVA/Tukey test (FM only) and Kruskal–Wallis (alpha: 5%). Macromol Symp 1999; 147: pp. A finite element analysis (FEA) study verified that for a low-modulus substrate, high nominal stress values were associated with high shrinkage and low modulus values. J Esthet Dent 2000; 12: pp. Fig. 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. Flexural modulus was reduced for both fiber levels. 2 Author information: (1)Faculty of Mechanical Engineering, Technion, Haifa, 32000, Israel. 2.6 (0.6) AB Replacing 6% of particles by fibers did not increase PS significantly. shearing. 3 shows the average curves for polymerization stress development over time, evidencing the higher stresses developed by the fiber-reinforced materials. 1 645-652. Dent Mater 2015; 31: pp. , length/diameter) and the interfacial strength between fiber and resin matrix . 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 . While maximum polymer reinforcement is obtained with oriented continuous fibers, these materials are not easily molded into complex shapes . 3 shows the average curves for polymerization stress development over time, evidencing the higher stresses developed by the fiber-reinforced materials. Acrylic rods were used as bonding substrate in the polymerization stress test based upon a previous investigation showing that stress data from a high compliance system presented a stronger correlation with in vitro tests evaluating the quality of bonded interfaces, in comparison with the use of a low compliance system . Dental Materials. Lower shrinkage values were also reported with short-fiber composites using the strain gage method, when the fibers are partially oriented parallel to the gage surface . A clinically relevant, but least explored aspect of fiber reinforced composites is their polymerization shrinkage and associated polymerization stress. In order to explain these results, it is important to have in mind that the force recorded by the load cell in the polymerization stress test is not governed only by composite shrinkage and modulus, but also (and no less important) by the interaction between the tested material and the bonding substrate. The control group was left intact. LVDT readings were converted to volumetric shrinkage values using input values of composite mass and density. Replacing 3% (by volume) of the filler particles by glass fibers significantly increased polymerization stress of experimental composites (regardless of specimen height). 385-393. 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 . Flexural modulus was calculated based on the load versus displacement curve obtained in three-point bending testing. A clinically relevant, but least explored aspect of fiber reinforced composites is their polymerization shrinkage and associated polymerization stress. In order to explain these results, it is important to have in mind that the force recorded by the load cell in the polymerization stress test is not governed only by composite shrinkage and modulus, but also (and no less important) by the interaction between the tested material and the bonding substrate. The two composites with reinforcing phase constituted only by silanized particles reached similar polymerization stress levels. The principal aim of Dental Materials is to promote rapid communication of scientific information between academia, industry, and the dental practitioner. Materials and methods 55. Garoushi S., Vallittu P.K., Lassila L.V. The composite was inserted between both rods and shaped into a cylinder following their external circumference. 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. 14. 1.9 (0.6) BC Photoactivation was conducted with the tip of the light guide placed underneath the glass slide. Polymerization stress of experimental composites containing random short glass fibers Fronza B.M., Rueggeberg F.A., Braga R.R., Mogilevych B., Soares L.E.S., Martin A.A., et. Materials and Methods: Eighty samples (2.5×10×65 mm 3 ) were fabricated and divided into five groups. 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. : Contraction stress related to composite inorganic content. Flexural modulus data were normal and homoscesdastic; therefore, they were analyzed using one-way ANOVA/Tukey test. Average curves of composite polymerization shrinkage as a function of time. Dent Mater 2010; 26: pp. It is particularly important to highlight that among experimental composites, the material with lowest shrinkage did not present the lowest polymerization stress, as flexural modulus also plays an important role in stress development. A finite element analysis (FEA) study verified that for a low-modulus substrate, high nominal stress values were associated with high shrinkage and low modulus values. The commercial composite presented the lowest shrinkage among the tested materials, only similar to the composite with 6% of fibers. 835-841. Still, investigating their polymerization stress behavior is important in order to access, for example, a possible risk of internal gap formation and the post-operative sensitivity. 10/30/2013. Filtek Z250 984-992. This apparent increase in transverse modulus would restrict the projection of the acrylic rod periphery towards the composite and increase the bending of the bonded interface, reducing the force recorded by the load cell. 23. Statistical analysis used shrinkage values recorded 10 min after the beginning of photoactivation. Filtek Z100 is a heavily filled hybrid resin composite, which is rather transparent. 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. : The effect of length and concentration of glass fibers on the mechanical properties of an injection- and a compression-molded denture base polymer. Fiber length distribution is shown in the histogram in Fig. Further investigations must be undertaken in order to verify if the results reported here correlate with the quality of tooth-composite bonded interfaces. Therefore, some of the longer fibers were forced to assume an orientation perpendicular to the specimen rotational axis, somewhat altering the materialś isotropic character. It was demonstrated that shrinkage is greatly reduced in the direction of continuous long fibers . 697-703. Also, the experimental control and the composite with 3% of fibers showed similar shrinkage, but the latter developed higher stresses. According to manufacturer’s information, each unit delivered an irradiance of 1,200 mW/cm 2 . Volumetric shrinkage was reduced only in the composite with 6% of fibers. The two control composites containing only glass particles developed similar stress levels. 1 . The proportional limit C. Polymerization stress was not affected by replacing 6% of particles with fibers. 1.61 (0.33) B b is the specimen's width, and 3 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. PS was not affected by specimen height for any of the tested materials. 4 A single 20-s exposure was used to cure the specimen (Radii-cal, SDI). For instance, when the experimental composites are compared, the results seem conflicting, as the control showed higher shrinkage, but similar polymerization stress than the composite containing 6% of fibers. 0% fiber Maximum shrinkage rate was statistically similar among experimental materials. Stress values from high compliance systems are usually lower than those obtained in more rigid ( i.e ., low compliance) systems due to the relatively low elastic modulus of the bonding substrate. Three experimental composites were prepared, each containing similar mass fractions of BisGMA and TEGDMA and 60 vol% of fillers, being 0%, 3% or 6% constituted by 1.6-mm long glass fibers and the remaining by 1 μm glass particles. 1 . Dent Mater 25: 331-338. The glass slide was clamped to a glass column, which was then filled with mercury. Data were subjected to normality (Anderson-Darling) and homogeneity of variance (Levene) tests. 216-226. An LVDT probe (linear variable differential transducer) was positioned touching the mercury surface. Total Cards. × Dental Materials, 2016-09-01, Volume 32, Issue 9, Pages 1079-1084, Copyright © 2016 The Academy of Dental Materials. 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. High-aspect ratio fiber-reinforced composites are not suitable for restoring the entire cavity due to their poor polishing, and a “cap” of particle-filled composite must be applied as the last increment. Dental materials are subjected to many cycles of repeated stress during mastication. Acknowledgements Anne C.E. : Development and clinical applications of a light-polymerized fiber-reinforced composite. Therefore, a higher longitudinal shrinkage was expected in the 1.5-mm specimens, which would increase nominal stress. Filtek Z100, Aelite Flo and Flow-it show inferior shrinkage/contraction stress properties, compared to the materials on the regression line. Elastic limit is the maximum stress that a material will withstand without permanent deformation. PS ( n = 5) was tested in a high compliance system, using two specimen heights (1.5 mm and 4.0 mm). 19. Compressive stress (S C), Shear stress (S S), Tensile stress (S T). Three experimental composites were prepared, each containing similar mass fractions of BisGMA and TEGDMA and 60 vol% of fillers, being 0%, 3% or 6% constituted by 1.6-mm long glass fibers and the remaining by 1 μm glass particles. 10. C is the load (in N) corresponding to the displacement d (in mm), Several studies using the same test set up used in the present investigation found a direct correlation between stress and shrinkage . Karacaer O., Polat T.N., Tezvergil A., Lassila L.V., Vallittu P.K. h It can occur in fixed partial dentures or cantilever structures. Group Photoactivation was conducted with the tip of the light guide placed underneath the glass slide. Fig. Polymerization shrinkage (vol%) Polymerization stress increased when 3% of particles were replaced by short fibers. On the other hand, in 4.0-mm specimens fibers would have enough clearance to be randomly oriented resulting in a more isotropic behavior of the composite. 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. Results 6. R Danso et al published “ Development of an oxirane/acrylate interpenetrating polymer network (IPN) resin system” in Dental Materials, October, 2018. : The effect of carbon fiber orientation on the fatigue resistance and bending properties of two denture resins. Polymerization stress increased when 3% of particles were replaced by short fibers. 22. The replacement of 3% of filler particles with glass fibers significantly increased stress ( H = 25.26, p < 0.01), while the composite with 6% of fibers presented stress levels similar to the experimental control. 3.22 (0.11) BC The rods were attached to the opposite fixtures of a universal testing machine (Instron 5565, Canton, MA, USA) and positioned at pre-set distances of 1.5 mm or 4.0 mm. Though mechanically these materials did not stand out amidst particle-only materials , in one of them fibers were responsible for its “packable” viscosity . The replacement of 6% of the particles by glass fibers resulted in a statistically significant reduction in volumetric shrinkage ( H = 10.38, p < 0.05). 1720-1727. 36-42. 20. BACKGROUND: Stress shielding considerations suggest that the dental implant material's compliance should be matched to that of the host bone. Koplin C, Jaeger R, Hahn P (2009) A material model for internal stress of dental composites caused by the curing process. Therefore, a fraction of the shrinkage force is responsible for causing elongation of the rods situated between the extensometer fixation clamps and, as a consequence, is not recorded by the load cell . PS ( n = 5) was tested in a high compliance system, using two specimen heights (1.5 mm and 4.0 mm). Korabi R(1), Shemtov-Yona K(1), Rittel D(1). As bonding substrate for the composite, 5-mm diameter acrylic rods were sectioned in 28-mm long segments and had one of their flat surfaces sandblasted. • A shear stress tends to resist the sliding of one portion of a body over another. 1.5 mm For instance, when the experimental composites are compared, the results seem conflicting, as the control showed higher shrinkage, but similar polymerization stress than the composite containing 6% of fibers. Silane content on the fibers was 6%, as determined by thermogravimetric analysis. 21. LVDT readings were converted to volumetric shrinkage values using input values of composite mass and density. 2.4 Dent Mater 2010; 26: pp. Therefore, a fraction of the shrinkage force is responsible for causing elongation of the rods situated between the extensometer fixation clamps and, as a consequence, is not recorded by the load cell . p > 0.05). : Critical issues in achieving desirable mechanical properties for short fiber composites. The replacement of 3% of filler particles with glass fibers significantly increased stress ( H = 25.26, p < 0.01), while the composite with 6% of fibers presented stress levels similar to the experimental control. Indeed, the use of alternative or modified resin monomers and photo-initiators, as well as improved filler particles, has increasingly contributing to less shrinkage … Shrinkage was reduced only for the composite with 6% of fibers, while shrinkage rate was not affected. 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. Fig. To evaluate flexural strength of a dental material, bar- shaped specimen with dimension of 25 mm in length X 2 mm in width X 2 mm in height is generally used (ISO 9917 – 212). Composite formulation This deficiency is considered to be a major short coming especially with the wide spread use of ceramics in dentistry, the elastic–plastic mechanical properties of these materials is of considerable interest. A spherical indenter was used to test the materials with nanometer and micro-Newton displacement and force … : Packable composites: overview and technical considerations. Dent Mater 2008; 24: pp. 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). × Shrinkage, maximum shrinkage rate and polymerization stress data failed the normality test and, for this reason, were analyzed using Kruskal–Wallis test. Compressive strength is most useful for comparing materials that are brittle and generally weak in tension. We are also interested in the wear of natural teeth opposing dental restorations. The decrease in mercury column height due to composite shrinkage was monitored for 60 min, at the rate of 0.1 s −1 . 3.60 (0.06) A However, the available literature shows that random short fibers may have different effects on post-gel shrinkage depending on the composite fiber content, testing method and the choice of controls . In the same column, values followed by the same superscript are not statistically different (ANOVA/Tukey test, Dental Materials, 2016-09-01, Volume 32, Issue 9, Pages 1079-1084, Copyright © 2016 The Academy of Dental Materials Description. A feedback system consisting of an extensometer (model 2630-101, Instron, resolution: 0.1 μm) was used to keep specimen height constant throughout the test. 2.25 (0.03) C giving way to tooth fracture; hence, the use of this material Stress von Mises N/(mm2) 20 18 16 14 12 10 8 6 4 2 0 M1 M2 M4 Z Y X Z Y X Z Y X Z Y X Z Y M3 M5 Figure 6: von Mises stress accumulation of restorative materials. 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. Posts about stress written by JC40. 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). Level. Three specimens were tested in each group. Thermal properties Specific Heat Thermal conductivity Thermal Diffusivity Coefficient of thermal expansion 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 . Boaro L.C., Goncalves F., Braga R.R. Materials subjected to such a stress undergo material fatigue, which means they fracture at a stress lower than the value required for a single load application. 688-694. Dent Mater 1992; 8: pp. 704-709. Flexural modulus (GPa) Physical and mechanical properties of dental material, Impression materials, introduction, classification and requirements, Investments and refrectory dies in dentistry, Rheological properties of dental materials, No public clipboards found for this slide, Stress & Strain Properies of dental materials. Dent Mater 2006; 22: pp. Composite volumetric shrinkage was measured in a mercury dilatometer (ADA Health Foundation, Gaithersburg, MD, USA). : Monomer conversion, microhardness, internal marginal adaptation, and shrinkage stress of bulk-fill resin composites. : Short glass fiber reinforced restorative composite resin with semi-inter penetrating polymer network matrix. Online submission and editorial system now available at here to register for free access to Dental Materials online.. While maximum polymer reinforcement is obtained with oriented continuous fibers, these materials are not easily molded into complex shapes . This result was not completely unexpected, as previous studies have shown similar performance between particulate and short fiber-reinforced composites . Dent Mater 2008; 24: pp. PS was not affected by specimen height for any of the tested materials. Ferracane J.L. Also, a systematic review of studies reporting the flexural properties of unidirectional or woven fiber-reinforced composites found no significant effect of fiber reinforcement on flexural modulus, in comparison to unreinforced controls . 12. FM was tested in three-point bending ( n = 10). For instance, novel resin-based dental materials may present the SDR™ chemistry (i.e., stress decreasing resin), which has optimized both the organic matrix and filler phase of the material (Ilie and Hickel, 2011, Zorzin et al., 2015). 2.3 Polymerization stress (MPa) Methods: Eighteen commercially available resin-composites were investigated. An applied load or force B. 2. 14. Five specimens were tested per group. Fig. 3.19 (0.38) A The elastic limit B. Pure Appl Chem 1985; 57: pp. 610-616. It is important to mention that reaction kinetics (expressed by the maximum shrinkage rate) was not affected by the replacement of particles by fibers and, therefore, differences in polymerization stress results cannot be attributed to this variable. 993-1000. Goncalves F., Pfeifer C.C., Stansbury J.W., Newman S.M., Braga R.R. On the other hand, in 4.0-mm specimens fibers would have enough clearance to be randomly oriented resulting in a more isotropic behavior of the composite. Fig. As an additional control, a commercial composite (Filtek Z250, 3 M ESPE) was tested. Polymerization stress was not significantly affected by specimen height. 1,200 mW/cm 2 the sliding of one portion of the specimen was by!, microhardness, internal marginal adaptation, and shrinkage Measuring system by Proto-tech, C.C.... 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