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Objectives. The present study aimed to assess the effect of ferrule location on fracture resistance of maxillary premolars. Materials and Methods. A total of 72 extracted human maxillary premolars were selected and randomly assigned to six groups (n = 12 in each) considering ferrule location: circumferential ferrule (CF), without ferrule (WF), buccal ferrule (BF), lingual ferrule (LF), mesial ferrule (MF), and buccal–lingual ferrule (BLF). Cast posts were cemented into the prepared post spaces. Following conventional impression, Ni–Cr crowns were cemented to the specimens. After thermocycling (5,000 cycles, 5–55°C), the specimens were loaded at 45° in a universal testing machine until fracture. Data were analyzed with one-way ANOVA, Kolmogorov–Smirnov, and Tamhane tests. Results. The maximum and minimum mean fracture resistance were related to the CF (1,143.84 N) and WF (514.89 N) groups, respectively, (P=0.039). Fracture resistance in the BF (933.67 N) and BLF (874.01 N) groups was significantly higher than in the MF group (617.54 N) (P=0.001). There was no significant difference between the MF, LF (722.89 N), and WF groups in terms of fracture resistance (P>0.05). Conclusion. Teeth with CF showed maximum fracture resistance. The location of the ferrule effects on the fracture resistance of maxillary premolars and also the mode of failure.

Background and Aim: Bacterial colonization occurs following contamination of impression materials with blood and saliva. However, not all disinfecting agents are compatible with the impression materials and may cause changes in the resultant casts. The purpose of this study was to assess the impact of various immersion time of addi-tion silicon impressions in different disinfecting solutions on the surface hardness and detail reproduction of gypsum casts. Materials and Methods: In this in vitro experiment, 84 addition silicone impressions were divided into seven groups (n=12). One group served as the control and the other groups were disinfected with 1% sodium hypochlorite, 2.4% glutaraldehyde, and 5% povidone-iodine for 5 and 30 minutes. Impressions were poured with type IV dental stone. The Knoop hardness value (KHN) was measured by microhardness tester. Surface detail reproduction, casts were inspected under a light microscope at X10 magnification. The surface hardness data was analyzed using two way ANOVA, Tuk-ey`s test, Dunnett`s, One way ANOVA and t-test. The detail reproduction results were analyzed using the Kruskal-Wallis test. Results: Immersion in povidone-iodine for 5 minutes and in sodium hypochlorite and glutaraldehyde for 30 minutes significantly lowered the KHN of resultant casts (P=0.001). No other significant differences were noted (P>0.05). No significant difference was found in detail reproduction between groups (P>0.05). Conclusion: Increasing the immersion time of impressions in povidone-iodine increased the hardness of casts. Thus, 5% povidone-iodine is a more suitable disinfecting solution for longer immersion time given that other properties of the casts are not affected.

Background and Aims: Constant dynamic and static activities are considered as the main cause of musculoskeletal problems among dentists. The aim of this study was to evaluate the musculoskeletal problems and related factors among dentists in specialized clinics and dental schools in Tehran in 2014 using the REBA method. Materials and Methods: In this cross-sectional study, the dentists from clinics of dental schools in Tehran were selected as individual targets. Nordic anddemopghrphic questionnaire were completed through interview from dentists. In order to assess the musculoskeletal disorders, REBA method (Rapid Entire Body Assessment) was used. In this method, positions and postures of the dentists during their work was observed and recorded. Data was analyzed using Regression Logestic test. Results: The obtained results showed that among 100 dentist, 6% were in the very high risk (15-11) for musculoskeletal problems and 17% and 25% were in high-risk (10-8) and average risk (7-4), respectively. Based on the findings from Nordic questionnaire, the most skeletal- muscle travail were related to the neck (60%), lumbar (58%) and rear (46%) consequently. It seemed that factors such as gender, body mass index (BMI), height, specialty, body posture during the work (standing or sitting), smoking and using the direct or indirect vision, had an impact on the musculoskeletal disorders. Conclusion: Findings from the final scoring of REBA showed that a high percentage of dentists were struggling with skeletal- muscle problems and they were in moderate to high range of risk for these type of disorders.

Background and Aims: Preserving intact coronal and radicular tooth structure is considered to be crucial for the optimal biomechanical behavior of restored teeth .The ferrule effect has been extensively studied and still remains controversial from many perspectives. The purpose of this study was to summarize the results of different issues related to the ferrule effect and published in journals listed in Pub Med. Materials and Methods: The search was conducted from 1985-2014 from Pub Med and scientific dentistry internal journals using the following key words: Ferrule, Ferrule effect, Literature review, Fracture resistance, Fatigue, Finite element analysis. Results: The finding showed that the presence of 1.5-2 mm high and 1mm thickness ferrule had a positive effect on the fracture resistance of endodontically treated teeth. Conclusion: The presence of ferrule effect is essential for successful endodontic treatment. If a ferrule can performed, the teeth will have poor prognosis for survival.

Introduction: Color match between the restoration and the patient’s natural teeth has always been a source of concern in esthetic dentistry. One of the reasons for a lack of color match between the restoration and the natural teeth is the type of the alloy used in the metallic structure of the restoration. The aim of this study was to assess and compare the effect of 4 alloys on the color of the overlying porcelain: Degobond 4 from the high noble group, Begopal from the high-palladium group, and Super Cast and Minalux from the nickel-chromium base metal group. Materials and Methods: In this in vitro study, twenty disks, measuring 2 mm in thickness and 10 mm in diameter, were prepared (5 samples from each alloy). Then Vita 3DMaster 3M2 porcelain was placed on the samples. In addition, 5 control samples, measuring 2 mm in thickness, were prepared from the porcelain. A spectrophotometer was used to determine sample colors, which were evaluated based on CIELAB system. Data was analyzed with one-way ANOVA and Tukey test (α = 0.05). Results: The four alloys in this study exhibited significant differences in a* and b* values from the control group (p value < 0.001). The alloy groups did not exhibit any significant differences from each other in a* and b* values (p value > 0.05). There were significant differences in L* values between Supercast and Begopal (p value = 0.009) and between Begopal and the control (p value = 0.013) groups. There were no significant differences in ∆E between the alloys. Conclusion: The type of the alloy has an effect on the final color of porcelain; however, this color difference is clinically acceptable. Key words: Alloys, Color, Metal ceramic restorations, Spectrophotometry.

Tooth/implant supported fixed prostheses may present biomechanical design problems, as the implant is rigidly anchored within the alveolus, whereas the tooth is attached by the periodontal ligament to the bone allowing movement. Many clinicians prefer tooth/implant supported fixed prosthesis designs with rigid connectors. However, there are some doubts about the effect of attachment placement in different prosthesis designs. The purpose of this study was to examine the stresses accumulated around the implant and natural teeth under occlusal forces using three dimensional finite element analysis (3D FEA).In this study, different connection designs of tooth/implant fixed prosthesis in distal extension situations were investigated by 3D FEA. Three models with various connection designs were studied; in the first model an implant rigidly connected to an abutment, in the second and third models an implant connected to abutment tooth with nonrigid connector in the distal part of the tooth and mesial part of the implant. In each model, a screw type implant (5×11mm) and a mandibular second premolar were used. The stress values of these models loaded with vertical forces (250N) were analyzed.There was no difference in stress distribution around the bone support of the implant. Maximum stress values were observed at the crestal bone of the implant. In all models, tooth movement was higher than implant movement.There is no difference in using a rigid connector, non rigid connector in the distal surface of the tooth or in the mesial surface of an implant.