Statement of Problem: In a previous study it was reported that a durable resin-ceramic tensile bond could be obtained by an appropriate silane application without the need for HF acid etching the ceramic surface. Evaluation of the appropriate application of silane by other test methods seems to be necessary.Purpose: The purpose of this study was to compare the interfacial fracture toughness of smooth and roughened ceramic surfaces bonded with a luting resin.Materials and Methods: Ceramic discs of 10 mm in diameter and 2 mm in thickness were prepared.Four different surface preparations (n=10) were carried out consisting of (1) ceramic surface polished to a 1µm finish, (2) gritblasted with 50µm alumina, (3) etched with 10% HF for 2 min, and (4) gritblasted and etched. The ceramic discs were then embedded in PMMA resin. For the adhesive area, the discs were masked with Teflon tapes. A circular hole with diameter of 3 mm and chevron-shaped with a 90° angle was punched into a piece of Teflon tape. The exposed ceramic surfaces were treated by an optimised silane treatment followed by an unfilled resin and then a luting resin cylinder of 4mm in diameter and 11 mm in length was built. Specimens were stored in two different storage conditions: (A): Distilled water at 37°C for 24 hours and (B): Distilled water at 37°C for 30 days. The interfacial fracture toughness (GIC) was measured at a cross-head speed of 1 mm/min. The mode of failure was examined under a stereo-zoom microscope and fracture surfaces were examined under Scanning Electron Microscope.Results: The mean interfacial fracture toughness values were; Group A: 1) 317.1±114.8, 2) 304.5±109.2, 3) 364.5±169.8, and 4) 379.4±127.8 J/m2±SD. Group B: 1) 255.6±134.4, 2) 648.0±185.1, 3) 629.3±182.6 and 4) 639.9 ±489.0 J/m2±SD. One way Analysis of Variance showed that there was no statistically significant difference in the mean interfacial fracture toughness for groups A1-A4 (P>0.05). However, the mean interfacial fracture toughness for group B1 was significantly different from that for groups B2, B3 and B4 (P<0.05). Independent-ٍٍٍSamples T-Test results showed that there was a significant increase in the GIC mean value for groups B2 and B3 after 30 days water storage (P<0.05). The modes of failure were predominantly interfacial or cohesive within the resin.Conclusions: The fracture toughness test method used in this study would be appropriate for analysis of the adhesive zone of resin-ceramic systems. From the results, it can be concluded that micro-mechanical retention by gritblasting the ceramic surfaces could be sufficient with no need for HF acid etching the ceramic surfaces when an appropriate silane application procedure is used.

Background and Aim: Compomers are placed between composite resins and glass ionomers cements regarding their surface and mechanical properties. Compoglass is a trademark of compomers that is bonded to tooth surface using Syntac single component. The aim of this study was to investigate the effects of tooth surface conditioning on fracture resistance of compoglass restorations prior to Syntac agent application.Materials and Methods: In an experimental study, thirty intact maxillary premolar teeth were chosen and divided into three groups of ten each. MOD cavities were prepared and restored with compoglass as follows: Group 1: Restoring the teeth without conditioning the cavity surfaces prior to Syntac application.Group 2: Conditioning the cavity surfaces with phosphoric acid prior to Syntac application.Group 3: Conditioning the cavity surfaces with polyacrylic acid prior to Syntac application. All the samples were tested under compressive loading and the findings were statistically analyzed using ANOVA test.Results: The mean values obtained from groups 1, 2 and 3 were 1585.70, 1465.20 and 1535.60, respectively. No statistically significant differences were found in fracture resistance between tested groups.Conclusion: Conditioning tooth surfaces with phosphoric acid and polyacrylic acid prior to Syntac application had no effect on increasing the fracture resistance of compoglass restored teeth.

Statement of Problem: Evaluation of fracture properties is a basic principle for true assessment of brittle materials’ properties. Resin–based composite materials are being used extensively in today’s dentistry. Fracture toughness is considered an important parameter for providing useful information about material’s nature, properties and its resistance to fracture. Purpose: The purpose of this study was to evaluate the fracture toughness of a resin composite produced in the country and to compare it with that of other standard materials. Materials and Methods: Four types of resin composite materials were used as follow to prepare 60 specimens (n=15 for each group), A) Tetric Ceram (Ivoclar–Vivadent); B) Brilliant (Coltene-Whaledent); C) SpectrumTPH (Dentsply); and D) Ideal Macoo (Ideal Macoo, Iran). Specimens of 5 mm diameter (± 0.1 mm) and 2 mm depth (±0.1 mm) were prepared in a central notch (90° notch angle) PTFE mold. Then specimens were light cured with two applications of overlapping exposures for a total of 120 s and were stored in distilled water at 37ºC for 48 hours, A cylindrical roller of 3 mm diameter was seated inside the V sections and fracture was accomplished in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed by one–way ANOVA and post-hoc paired Tukey HSD test with P<0.05 as the limit of significance. Results: The mean KIC and torque to fracture (T) values for each material tested were; A) 3.08±0.42, 16.99±2.34, B) 2.88±0.63, 16.04±1.98; C) 3.40±0.53, 18.75±2.93 and D) 2.87±0.46, 15.78±2.57 MN/m3/2±SD and N/mm±SD, respectively. Group C showed significantly the highest mean KIC and T values among groups tested which was significantly higher than that of group B and D (P<0.05). The mean KIC and T values for groups A, B, and D were not significantly different (P>0.05). Conclusion: From evaluating the fracture properties of materials tested in this study it was concluded that the mean fracture toughness value for SpectrumTPH (Dentsply) was significantly higher than that of Ideal Macoo resin composite material (Ideal Macoo, Iran). The F.T value for Ideal Macoo was considered acceptable as it was not significantly different from that of other resin composite materials tested.  

In this research, the effect of temperature on the mean size of fracture surface features, as well as the relation between fracture surface morphologies and ductility of a La-based BMG as a relatively brittle alloy, was systematically investigated. After producing the alloy, three-point bending experiments, over a wide range of temperatures, were conducted on the samples; then the fracture surfaces were analyzed using scanning electron microscopy. The results demonstrated that the width of stable crack growth region (Δ W) was increased upon ductility (δ p). Conversely, the mean size of the features on both stable (Ds) and fast (Df) crack growth regions and also, shear offset width (Δ L) were found to decrease with increasing ductility. In this case, the shear band instability was reduced, and the plastic strain could be more homogeneously distributed on the shear bands. The similarity of Δ L and Ds values suggested that the formation of vein pattern was caused by steak-slip behavior and multiple-step sliding inside the shear band through the fluid meniscus instability mechanism. Furthermore, the results obtained from correlation between ductility and fracture surface morphologies in the BMG indicated that the size of features was reduced with increasing ductility.

Introduction: Following increasing people’s demand for having aesthetic, functional and simultaneous benefits of composite and amalgam restorations, combined restoration of composite-amalgam has been introduced. The aim of this study was to evaluate the effect of there methods of surface treatment on composite-amalgam fracture strength. Materials & Methods:  In this experimental invitro study, on thirty uniform and sound human maxillary premolar teeth mesiobuccal class II cavities were prepared so that in all specimens the thickness of buccal reminder enamel was one millimeter. They were divided randomly into three groups of ten and filled with amalgam. After 24h in each tooth, thin mesiobuccal enamel was removed and amalgam surface were veneered with Tetric Ceram composite by one of the three following methods. In A and B groups after etching with phosphoric acid, Scotchbond Multi-purpose and One Coat Bond were applied respectively. In group C after sandblasting and acid etching, margin bond unfilled resin was applied for adhesion of composite to amalgam. Finally for fracture strength measurement, the specimens were loaded under Instron testing machine at a crosshead speed of 1mm/min with 45° angles. Fracture areas were also considered from stand point of CEJ location and type of debonding (adhesive – cohesive – mixed). Data were analyzed with One Way ANOVA and Duncan tests. Results: Mean fracture strengths in three methods were significantly different (P=0.02). Group C had the highest and group B had the lowest fracture strength. In all three groups, the most common type of debonding was adhesive and above to the CEJ. Conclusion: The highest mean value of fracture strength was obtained in group with amalgam sandblasting followed by application of unfilled resin which did not differ significantly with Scotchbond Multi-purpose group. However it differed significantly with One Coat Bond group.

Background and Aims: When composite resin polymerizes, shrinkage stresses tend to produce gaps at the tooth/ restoration interfaces. Surface sealants may reduce or avoid problems related to the marginal interface. The aim of this study was to evaluate the effect of two different surface sealants (Fortify and Optiguard) on the microleakage of class V resin composite restorations.Materials and Methods: Twenty three sound noncarious molars were collected. Totally, 45 Class V cavities with the occlusal margins in enamel and cervical margins in cementum were prepared in both buccal and lingual surfaces. The specimens were randomly assigned in three groups (15 cavities in each group) and then restored with a resin composite. After the finishing and polishing procedures, the restorations in each group were covered with a specific surface sealant, except for the control samples, which were not sealed. After placing restorations, the specimens were thermocycled and then immersed in a 50% silver nitrate solution (tracer agent) for four hours, sectioned longitudinally and analyzed for leakage using a stereomicroscope in a blind manner. The marginal microleakage was evaluated at the occlusal and cervical interfaces and compared among the three groups using the Kruskall-Wallis and the Mann-Whitney U tests.Results: Microleakage was found in all groups at both occlusal and cervical margins. Significantly greater leakage was observed at the cervical margins compared to the enamel margins of the material groups (P=0.005).There was no statistically significant difference among the groups at occlusal margins (P=0.66). In the cervical region, Fortify showed improved results and statistically presented the lowest degree of microleakage (P=0.003).Conclusion: The used sealant materials presented different rates of effectiveness and Fortify decreased marginal microleakage significantly.

The API X65 steel (with a minimum yield strength of 65ksi equivalent to 448MPa) is one of the most common types of pipe steels in the transportation of natural gas in Iran. By studying the ductile and brittle fracture areas at the fracture surface of this steel, we can show the quality of this type of steel. In the present study, macroscopic fracture surface characteristics in three-point bending test specimen are studied (based on the geometry and standard notch of drop-weight tear test specimen). Test specimens were machined from an actual steel pipe of API X65 grade with an external diameter of 1219 mm (48 inches) and wall thickness of 14. 3 mm. Due to the quasi-static test conditions and speed of the machine’ s jaw (0. 1 mm/s), the test was carried out on base metal specimens with machine chevron notch of 15, 10, and 5. 1 mm depth, respectively, that was controlled with changing location. By applying the test load, cracking initiated from the notch root in each specimen and continued without crack specimen (ligament). At the end of the test, test specimens were cooled by liquid nitrogen and were broken in a brittle manner. In this paper, after investigation of the failure mode and the crack expansion in the standard specimen, investigation of macroscopic fracture surface characteristics was conducted by optical microscopy. By observing the fracture surface, different features such as thickness variation, shear regions (ductile fracture), cleavage fracture, shear lips, inverse fracture, and brittle fracture were studied. Having above 85% shear area, the ductile fracture of specimen was confirmed.

Functionalized nanostructures such as, boehmite, salicylate alumoxane (Sal-A) and p -hydroxybenzoate alumoxane (PHB-A), were studied in varying amounts with respect to curing behavior, thermal stability, hardness and fracture surface morphology of their corresponding epoxy-based nanocomposites, emphasizing on the dispersabilities of the nanostructures in the epoxy matrix and the potential mechanisms of the interactions between various species. TG–DTA, Vickers hardness test and SEM were used to characterize the composite specimens. Addition of nanostructures into the epoxy matrix accelerated the curing process. The experimental tests proved that Sal-A acted most effectively as a co-curing agent through the autocatalytic curing process of the epoxy resin and also produced the highest values of Vickers hardness in its corresponding nanocomposites. The presence of the nanostructures also lowered the heat of reaction in curing process with an exception of PHB-A containing nanocomposites. Thermal stability of the nanocomposites was improved due to existence of the functionalized nanostructures. Mechanisms are proposed for the possible interactions between various species, constructing the three types of nanocomposites, divided into positive and negative types. The functional groups on the surfaces of the nanostructures not only facilitated chemical interactions with the polymer matrix but also improved their dispersion in the epoxy matrix. Dispersability tendency of the nanostructures in the epoxy matrix was of the order: boehmite<PHB-A<Sal-A. Extent of agglomeration of the nanostructures in the epoxy matrix depended on the types of the functional groups on their surfaces and consequently, their interactions with the epoxy matrix and hardener.