Evaluation of the flexural resistance and stress contraction of a silorane-based composite submitted to different protocols of polymerization

Abstract

When introduced to the market, silorane-based materials promised less contraction compared to other materials. The purpose of this study was to evaluate the contraction stress, flexural strength, and elastic modulus of the Filtek Silorane composite with different photoactivation protocols. Filtek Silorane and Filtek Z350 composites were inserted in a circular photoelastic resin matrix and subjected to photoactivation at 650 mW cm 2 for 40 s (protocol I), 325 mW cm 2 for 80 s (protocol II), 100 mW cm 2 for 260 s (protocol III), 100 mW cm 2 for 5 s + 1 min delay +650 mW cm 2 for 39.5 s (protocol IV), or 100 mW cm 2 for 5 s + 3 min delay +650 mW cm 2 for 39.5 s (protocol V). Five samples were prepared for each resin with each photoactivation protocol. To determine contraction stress, fringes were analyzed in a polariscope. For flexural strength analyses, 25 specimens (10 × 2 × 2 mm) of each resin with each photoactivation protocol were submitted to the 3-point bending test in a universal testing machine. Data were submitted to ANOVA and post hoc Tukey's tests (α = 0.05). Filtek Silorane showed higher contraction stress results than Filtek Z350 for protocols II (16.4 ± 3.88 vs. 5.9 ± 1.64 MPa), IV (17 ± 2.67 vs. 8.8 ± 1.30 MPa), and V (16.3 ± 3.33 vs. 5.1 ± 1.95 MPa). Both resins showed similar flexural strength values, but the elastic modulus of Filtek Silorane was significantly higher with all photoactivation protocols. Pulse-delay photoactivation was effective for Filtek Z350, but not Filtek Silorane, because the elastic modulus and contraction stress were reduced for Filtek Z350 without any change in flexural strength.

A simple characterization methodology for the identification of the visco-elastic behavior of thermoset adhesives during cure

“…Then, during the following steps (Fig. 6b, c) the viscous relaxation lasts longer and continues during (12)…”

“…From the previous equations (Eqs. 12,14,16) and the load variations measured at some characteristic points defined in Fig. 4, it is possible to calculate the force evolution over time.…”

“…In the confined conditions of a bonded assembly, this volume reduction may be restrained by the presence of the substrate. As the mechanical stiffness of the adhesive increases, this shrinkage might initiate the development of residual stresses and may lead to early failure especially during subsequent thermal cycling conditions or mechanical loadings [12,14,18,25,27]. In order to predict these residual stresses and to prevent adhesive related failures, the mechanical behavior of adhesives must be well understood especially during curing in order to model and predict their mechanical response all along the process.…”

Influence of glass-fiber reinforcement on the flexural strength of different resin composites

“…In specimens in which fiber reinforcement was not used, there were no differences in flexural strength between X-tra fil and Filtek Z350 XT composite. Filtek Z350 XT exhibited high flexural strength despite an inhomogeneous distribution of filler particles [20,30], while X-tra fil inherently contained a greater proportion of fillers. Filtek Z350 XT Flow demonstrated lower flexural strength, probably due to a lower filler content.…”

“…The load was applied perpendicular to the long axis of the specimen at a crosshead speed of 0.5 mm/min until fracture. The flexural strength (FS [MPa]) was calculated using the equation FS = 3 F max L/2WH 2 [20], in which F max is the maximum load in newtons, L is the distance between the support points (8 mm), and W and H are the specimen width and thickness in mm.…”