Background and Aim: Over there past few years, the use of fiber reinforced composites has increased in dentistry. The type of fiber used for reinforcement plays an important role in the structural strength of composites. This in vitro study compares the fracture resistance of posterior reinforced composite inlay bridges with two different fiber types.Materials & Methods: This experimental, in vitro study was performed on 20 FRC bridges which replaced maxillary second premolars. The abutment teeth were prepared with proximal box design and the samples were divided in to two groups of 10 (n=10). For the first group polyethylene fiber reinforced composites (Fiber span/ NSI/ Australia) were used directly. In second group pre impregnated glass fiber (INTERLIG/ Angelus/ Brazil) were applied the same. After thermo cycling process (5000 cycles, 5°c / 55°c, dwell time 30s, interval 2s) fracture testing was performed in a universal testing machine (Zwick/ Roell/ Germany, 1 mm/ min) applying direct vertical force to the center of the pontic. The One Sample Kolmogorov Smirnov Test showed a normal distribution. Data analysis was done using independent sample T-test.Results: The mean fracture strength and the standard deviation of the FRC Inlay Bridge was 469 ± 247 N for polyethylene fiber group and 541 ± 206 N for glass fiber group. The result of Independent Sample Test was not statistically significant (P=0.491). The most failure mode observed, was crack and fracture on the surface of FPDs in distal part of the pontics. Frameworks remained with no damage in all samples. There was no stateside difference between two groups of FPDs.Conclusion: Direct application of each fiber reinforced composite (glass or polyethylene fiber) with the same architecture (Braided) of fibers is comparable in posterior region of maxilla so the structural design of the fiber is more important than the fiber type itself, in fracture resistance of FPDs.

In this study, the effect of hygrothermal conditioning on the moisture diffusion properties of the fabric composite (glass fiber/epoxy resin) was investigated. The water uptake of the specimens conditioned in humid environment at different relative humidities (0, 60 and 96 % r.h) at constant temperature (60°C) was evaluated by weight gain measurements. The moisture diffusion properties of the fabric composite (glass fiber/epoxy resin) were determined using standard weight gain method. The weight gain experiments were performed to determine the equilibrium moisture content Mm of the fabric composite as a function of relative humidity (r.h). The measured weight gain is then fit to the solution to the diffusion equation (Fick’s law) to determine the diffusivity D. The comparison carried out between the values obtained of the characteristic parameters (D and Mm) of the kinetics of water absorption by the hygrothermal test of conditioning carried out into the laboratory and those given by Loos and Springer confirms the following principal remarks clearly: the diffusion coefficient D and the maximum weight gain Mm depend not only on the nature of material but also of the environmental conditions (hygrothermal conditioning). The maximum concentration of water (matrix+interface) obtained from calculations based on measured values, where a homogeneous diffusion phenomenon is assumed inside the material (Df=0), shows clearly that the presence of fibers in a polymeric matrix reduces the water up-take of the matrix by about 4 times.

Background and Aim: The aim of this study was to evaluate the effect of glass-fiber on the flexural strength of composite resins.Methods & Materials: The study was done experimentally in which flexural strength of glass - fiber reinforced composite resins were assessed with a three-point load test on 22 samples. 11 samples of composite resin blocks and 11 samples of composite resins reinforced with glass- fiber were prepared in a mold of 25x6x2mm and stored in 100% of moisture for one month, until they were ready for testing in an Instron Universal Testing Machine using a crosshead speed of 1 mm/min. Student t test was used for statistical analysis.Result: Flexural strength in the first group was 22.39±3.38 MPa and in second group was 29.74±2.36 MPa. According to t test analysis, the difference between the two groups was statistically significant. (P<0.01).Conclusion: The results of this study suggest that the flexural strength of the fiber-reinforced composite made from glass - fibers was more than composite resin.

Background and Aim: Considering flexural strength of fiber-reinforced composites (FRC) and also the role of conservative cavities in protecting sound tissue of abutments, the aim of this study was to evaluate the fracture resistance of these bridges by handmade samples in vitro.Materials and Methods: In this experimental in vitro study, 44 sound newly extracted teeth were used to make 22 fixed inlay bridges including 11 three unit anterior upper inlay bridges substituting clinical model of upper central and 11 three unit posterior lower inlay bridges substituting clinical model of lower first molar.Specimens were prepared with FRC and mounted with artificial PDL in acryl. Cases were exposed to final load by using Universal Testing Machine (Instron 1195) with the speed of 1 mm/min. Statistical analysis was performed by Kolmogorov- Smirnov, independent sample T and Kaplan-Meier tests with p<0.05 as the level of significance.Results: Based on the statistical tests, the 95% confidence interval of mean was 450-562 N in anterior and 1473- 1761 N in posterior area. Fracture strength was high in the studied groups. Fractures in both groups occurred on composite facing, and the framework remained intact. The highest percentage of fracture in posterior teeth was in the middle of pontic towards the distal connector and in the anterior teeth in the lateral connector, between central pontic and lateral abutment. Using the independent sample T test a significant statistical difference was observed between two groups (P<0.001). The fracture resistance of anterior samples was lower than the posterior ones.Conclusion: Based on the results of this study regarding the high fracture resistance in both areas FRC inlay bridges could be recommended for upper anterior and lower posterior teeth in clinical dentistry certainly more studies are needed to ascertain this treatment option.

Investigating the behavior of fiber/polymer composite structures and the effect of various factors on their mechanical properties is vital in defining the design, manufacturing and troubleshooting process. In this paper, the changes in the mechanical behavior of the E-glass fiber/polyester composite structure under the influence of thermal preloading on the glass fiber fabric have been studied. For this purpose, in addition to performing mechanical tests, scanning electron microscopy (SEM) has been used to investigate the manner and nature of glass fiber breakage as well as the cross-sectional area of fiber fracture. Also, the changes in the state of the bonding agent on the surface of the glass fibers used in the woven fabric, in the initial conditions of as received fabric and also in its secondary conditions after applying thermal preload by placing it in an oven at 350 °C temperature was studied. In this regard, the Attenuated Total Reflectance (ATR) infrared spectroscopic analysis method was used. The results indicate a significant decrease in the mechanical properties of the manufactured composite, as a result of applying thermal preloading on plain fabric made of E-class glass fibers, before the impregnation stage with unsaturated polyester resin.

In this study, behavior of pin-loaded glass fiber reinforced with polyethylene laminated composites with different stacking sequence and different dimensions has been observed experimentally and stress analysis was performed using ANSYS software. The aim is to investigate stresses, failure strength and failure mode of composite laminates containing a pin loaded hole, when the material exhibits linear elastic behavior. The logical methodology for modeling the joint problem uses the two major steps: failure analysis and stress analysis. Failure analysis is done experimentally and stress analysis is done by using ANSYS software. To investigate and verify to the analytical predictions of mechanical behavior, and to observe the failure characteristics of the pin-loaded composites, a series of experiments were performed with eight different material configurations, in all, over 36 specimens. The edge distance-to-hole diameter ratios and width-tohole diameter ratios of plates were changed. For this part of study, layered composite materials were manufactured in our Institute. The stress distribution around the hole in pin-loaded glass-fiber with polyethylene laminate was performed, and in addition, ANSYS was performed to compare effects of different boundary conditions used to simulate the pin load on stress distributions around the hole.

This paper presents an experimental investigation using graphene nanoplatelets (GnPs) to enhance the bending performance of E-glass fiber/epoxy composites. Each specimen was prepared with two layers of E-glass chopped strand mat via the hand lay-up technique and using various contents of GnPs in the matrix (0. 1, 0. 2, 0. 3, 0. 4 and 0. 5 wt%). Mechanical and ultrasonic stirring methods were employed to disperse the GnPs in the matrix. The obtained results demonstrated that the highest increases of 23% and 26% in the flexural strength and modulus, respectively, were observed for the composite containing 0. 4 wt% GnPs. With the incorporation of 0. 1 wt% GnPs, the flexural failure strain of the composite was enhanced by 16% compared to the control composite. The evaluation of the fractured surfaces clearly demonstrated that the interface between the glass fiber and polymeric matrix was improved when GnPs were added into the matrix.