Retentive strength of implant-supported base metal copings over short metal abutments using different luting agents and surface treatments.

PURPOSE: To evaluate the effect of surface treatments on retention of implant-supported restorations over short abutments. MATERIALS AND METHODS: One hundred twenty metal copings were made on Straumann solid abutments (3 mm length). The copings were divided into 2 groups: control and air abraded (50 µm Al2O3). The copings were luted using Fleck's, Poly F, Panavia F, and Fuji Plus. In resin cements groups, 2 subgroups were studied base on the application of Alloy Primer (n = 10). After conditioning in saliva and 5000 thermal cycles, retentive strengths of specimens were measured. Data were analyzed by 1-way ANOVA and Tukey honestly significant difference tests (α = 0.05). RESULTS: Panavia F 2.0 combined with Alloy Primer showed the most retentive values. In control and air abraded groups, there was no significant difference between the studied luting agents. Alloy Primer significantly increased the retention of copings luted with Panavia F 2.0. CONCLUSION: Within the limitations of this study, the retentive strength of metal copings over short implant abutments was not improved by airborne-particle abrasion. However, Alloy primer enhanced the retention of metal copings that were luted using Panavia F 2.0.

Effect of sintering temperature on translucency parameter of zirconia blocks.

Background: The main drawbacks of zirconia are its high refractive index and opacity. This study aimed to assess the effect of sintering temperature on the translucency of Ivoclar e. max ZirCAD (IEZ), and White Peaks Symphony (WPS) zirconia blocks. Materials and Methods: In this in vitro experimental study, 30 IEZ and 30 WPS zirconia blocks measuring 10 mm × 10 mm × 1 mm were prepared and underwent sintering in three subgroups at 1440°C, 1500°C, and 1530°C. The specimens were then photographed against a black and a white background with a standard digital camera. The L*, a*, and b* color parameters were measured using Adobe Photoshop software, and translucency was calculated. Data were analyzed using one-way ANOVA and Tukey's test (P < 0.05). Results: In both the IEZ and WPS groups, the maximum and minimum translucency parameters were recorded in 1530°C and 1440°C subgroups, respectively. The difference in the mean translucency was significant among the three subgroups of each zirconia group (P < 0.001). The mean translucency of WPS zirconia was significantly higher than that of IEZ zirconia (P < 0.01), and maximum difference was noted at 1500°C sintering temperature. Conclusion: Increasing the sintering temperature from 1440°C to 1530°C can significantly increase the translucency of IEZ and WPS zirconia blocks, and can be considered to improve the quality of zirconia restorations.

The Effect of Autoclave Sterilization on Resistance to Cyclic Fatigue of Hero Endodontic File #642 (6%) at Two Artificial Curvature.

STATEMENT OF THE PROBLEM: File fracture can interfere with cleaning and shaping of the canal and compromise periradicular healing. Autoclave sterilization may prone the files to fracture. PURPOSE: The purpose of the present study was to determine the effect of autoclave sterilization on the cyclic fatigue resistance of Hero642 rotary instrument in two curvatures of 45 and 60 degrees. MATERIALS AND METHOD: For this experimental in-vitro study, 90 Nickel-Titanium HERO 642 rotary files #30 with 0.06 taper were selected. They were divided into two groups (curvature of 45 and 60 degree) of 45 files. Each group was then subdivided into 3 subgroups; group I: no sterilization, group II: 5 cycles of sterilization and group III: 10 cycles of sterilization. Files were used in artificial canals until fracture. The cyclic fatigue was measured as the number of cycles before fracture. The data was statically analyzed by Student's t-test and two-way analysis of variance. RESULTS: There was a significant difference in cyclic fatigue of two curvature of 45 and 60 degrees (p= 0.001). However, sterilization process has no significant effect on cyclic fatigue of HERO files (p= 0.557). CONCLUSION: Sterilization had no effect on the cyclic fatigue of HERO 642 files when used in curvature of 45 or 60 degrees.

Retentiveness of implant-supported metal copings using different luting agents.

BACKGROUND: With regard to potential retrievability of cement-retained implant restorations, the retentive strength of the luting agents is critical. The aim of this study was to evaluate the retention values of implant-supported metal copings using different luting agents. MATERIALS AND METHODS: Twenty ITI implant analogs and solid abutments of 5.5-mm height were embedded vertically in autopolymerizing acrylic resin blocks. Metal copings with a loop on the occlusal surface were fabricated using base metal alloy (Rexillium III). The copings were luted using eight cements with different retention mechanisms (Panavia F2.0, Fuji Plus, Fleck's, Poly F, Fuji I, Temp Bond, GC-free eugenol, and TempSpan) under static load of 5 kg (n=10). All specimens were incubated at 37°C for 24 hours, conditioned in artificial saliva for 7 days and thermocycled for 5000 cycles (5-55°C). The dislodging force was measured using a universal testing machine at a crosshead speed of 5 mm/min. Statistical analyses were performed using Kruskal-Wallis (α=0.05) and Mann-Whitney tests with Bonferroni correction (α=0.001). RESULTS: Fuji Plus and TempSpan had the highest and the least mean retentive strength, respectively (320.97±161.47, 3.39±2.33). There was no significant difference between Fuji Plus, Fleck's, Ploy F, and Panavia F2.0. These cements were superior to provisional cements and Fuji I (P<0.001) which showed statistically same retentive strength. CONCLUSION: Within the conditions of this study, the resin modified glass ionomer, zinc phosphate, zinc polycarboxylate, and Panavia F2.0 had statistically the same retentive quality and are recommended for definitive cementation of single implant-supported restorations. The provisional cements and glass ionomer may allow retrievability of these restorations.

The effect of three irrigants on the coronal leakage of the root canals system irrigants.

INTRODUCTION: The production of smear layer during canal instrumentation is thought to increase coronal microleakage even after canal obturation. Previous studies have shown that the type of irrigant does not necessarily affect the seal of the obturation. Our study aimed to evaluate the effect of three irrigation solutions (MTAD, citric acid and EDTA/NaOCl) on the coronal microleakage of root canals. MATERIALS AND METHODS: Fifty five intact single rooted teeth were instrumented and randomly divided into three experimental groups (15 teeth each) and two control groups (5 teeth each). Final irrigation was carried out with MTAD in group I, citric acid in group II, and EDTA/NaOCl in group III. EDTA/NaOCl was used for the negative control group and saline irrigation was carried out in the positive control group. After lateral compaction with gutta-percha, the access cavities of the experimental specimens were restored with temporary restorative material. Temporary cement was not used in the positive control group. In the negative control group, access cavities and foramen apices were sealed with glass ionomer. Microleakage of samples was measured using the dye penetration technique. Data were analyzed with ANOVA and Tukey test to determine statistical differences between groups. RESULTS: MTAD, citric acid and EDTA/NaOCl all had less microleakage compared to normal saline. However, no difference was detected between the experimental groups. CONCLUSION: In this study, all three groups demonstrated effective seal with gutta-percha obturation. This is likely to be due to various factors including their ability to remove smear layer.