In this paper the relation of compressive strength of portland cement at 28 days with it's phases and fineness in completing of the Bogue's experimental formula have been contemplated. The laboratory results indicate that there is a direct relationship between phases and fineness of the cement with its compressive strength. In the proposed experimental formulas, the portion of each cement phase and its fineness has been given by coefficients. For any given value of the phases and fineness of cement, the compressive strength could be obtained with acceptable precision.        

One of the widely used cements for filling teeth and bones can be calcium zirconium aluminate cement Ca7ZrAl6O18, which of course can also be used as a refractory. The behavior and properties of this cement are more similar to tricalcium aluminate C3A cement. In this study, C7A3Z cement was synthesized by using commercial calcium carbonate, alumina and zirconia powders and after grinding for 4-6 hours and sintering at different temperatures of 1200-1400C for three hours. X-ray diffraction showed that C12A7, C3A, C7A3Z, CaZrO3, CaO phases exist at temperatures below 1400C, and at 1400C, almost cement only has calcium zirconium aluminate phase. The setting time of this cement was less than 5 minutes, which can be adjusted to longer times by adding citric acid. The hydrated phases of this cement included different phases of C3AH6, Al(OH)3, and similar phases, which obtained more information about their behavior using simultaneous thermal analysis (STA). The microstructure of the hydrated samples also led to the formation and growth of hydrated phases. The 3 and 7 days compressive strength of the samples was 48 and 40MPa, respectively.

Background: Cement space is necessary for seatabillity and fitness of cast crowns, but can affect crown's retention. In this study the interrelationship between them was investigated via die spacing.Materials and Method: For evaluating the effect of die spacing (cement space) on crown retention after cementation, 50 similar machined metallic dies were prepared and divided into five groups and coated with 0.2, 4, 6, 8 layers of paint-on standard die spacer, respectively. Cast crowns. Were fabricated on the dies using base metal alloys, and then cemented with zinc phosphate cement under a constant load of 5kg for 10 minutes. The samples were started in distilled water for 48 hours. Then the force required to remove each crown from the die was measured with instron.Results: Statistical analysis revealed a significant increase in the force required (crown retention) by adding layers of die spacer (p<0.05).Conclusion: Because retention didn't show any significant increase with more than 4 layers of die spacer, so optimum thickness of die spacer (or cement space produced) is suggested to be 4 layers equal to 40 microns.

Introduction: Microleakage is one of the most important factors in the failure of root canal treatment. Microhardness is one of the physical properties of bioceramics that can be affected by various environmental factors such as enviromental humidity. The aim of this study was to evaluation the effect of adding water to semi-setting cement on the microhardness and microleakage of CEM cement. Methods: 50 single-rooted teeth were selected. Teeth were cut from the CEJ region and the apical 3 mm of the root were trimmed and dentinal blocks with 5 mm height were prepared Peeso reamer size 2 was used to prepare the canal. The teeth were divided into two groups of 23 cases and two groups of 2 positive and negative controls. In the first group, CEM-cement prepared according to the manufacturer's instructions was placed in the canal. In the second group, after adding water to the semi-setting CEM cement mixture, the canal was filled with this cement. The samples were placed in 1% methylene blue for 3 days and then cut. Microleakage was recorded under a stereomicroscope. The microhardness of the samples was measured with Vickers device after mounting in acrylic resin. Statistical analysis was performed using SPSS19 software and Mann-Whitney Kruskal-Wallis and one-way ANOVA tests. Results: There was a statistically significant difference between the two groups in microleakage (P-Value <0. 008) and microhardness (P-Value <0. 001). Conclusion: According to the results of the present study, adding water to the semi-setting CEM cement not only does have a very bad clinical effect, but also may even increase sealling ability.

In this paper cement/carbon nanotube mechanical properties were predicted by micromechanical model. The effects of CNT properties such as internal, external diameters and its length as well as its volume percent on Young's modulus were investigated by this model. In addition, the effect of representative volume element (RVE) element shape (cylindrical, cubic and hexagonal) on Young's Modulus (E) was studied systematically. Finally, the predicted results were compared with cement /CNT experimental results. The predicted results showed that by increasing external CNT diameters, CNT Volume percent and its length, Young's Modulus (E) was increased. However, the internal diameter of CNT didn't have significant effect on E. These data indicated that hexagonal element shape resulted higher E rather than square and cylindrical RVE shape. Comparison of predicated E and experimental E showed that the proposed model could predict young modules with high accuracy. These results showed that micro mechanical modeling is a valuable method for predication of cement/CNT mechanical properties in nanoscale.

Objectives: The present study was carried out to investigate the relationship between different lunar phases and the occurrence of overdose attempted suicide. Method: The study was carried out for a period of three lunar years (Shaban 1416 to Shaban 1419) with patients admitted to the Intoxication Emergency Clinic at Imam Reza Hospital in Mashad. In this research,13422 cases of suicide attempts, which were recorded in the hospital files were studied. Admission dates which were originally recorded according to solar calendar, were later converted to lunar calender for the purpose of this study. Then, on the basis of lunar phases and the shape of the moon as observed from the earth, the days of lunar months were divided into four periods: the crescent-to-half moon period, the half moon-to-full moon period, the full moon to half-moon period, and the half moon-to-crescent period. The data collected for each period were analyzed through chi2. Findings: The result demonstrated that the highest numbers of overdose suicide attempts were made during the full moon period and the days around it. The frequency of attempts shows a significant difference in the above periods (P<0.05).

Skin injury caused by burns, surgery and other traumas may result in unpleasant psychological experiences and be reflected in behaviors. Extracellular matrix (ECM) is the largest component of natural skin which is gel-like and is produced by skin cells. ECM synthesis is a key factor for filling up skin wounds such as burns, leishmaniasis, chicken pox, acne, etc. ECM is composed of a variety of polysaccharides, water, and collagen proteins. Considering its weight, natural skin strength and its expandability are like steel, while it has high elasticity and compaction capacities. These characteristics are due to dual effects of main ECM molecules, which are secreted by fibroblasts and epidermal cells: 1) structural fiber proteins like: elastin, fibronectin and laminin which give strength and flexibility to ECM, and 2) proteoglycans such as dermatan sulfate and hyaluronic acid which are consisted of few glycosaminoglycan chains that branch out from a linear protein core. Proteoglycans are large and hydrated molecules which are resistant to external forces and protect underneath cells. In general, understanding the skin structure and wound healing phases can help us to design useful experiments and to conduct proper researches in this area.