abbas fallahtafti

The masking ability of dental ceramics has an important role in the final color of all-ceramic restorations. The masking ability of super-high translucent zirconia is not clearly determined. This study aimed to evaluate the masking ability of two super high translucent zirconia (Zolid fx and DD cubeX2) in comparison to lithium disilicate reinforced glass ceramic (IPS e.max CAD LT).

In this experimental study, 30 ceramic discs with 1 mm thickness and 10 mm diameter in two groups of super-high translucent zirconia (Zolid fx and DD cubex2) and one group of lithium disilicate reinforced glass ceramic (IPS e.max CAD LT) were fabricated (n=10). To determine the masking ability value (ΔE), a spectrophotometer was used to measure the color parameters of each sample (L*, a *, b*) in black and white backgrounds. One-way ANOVA and Tukey Post Hoc statistical tests were used to analyze the data. The level of significance was considered at 0.05.

The mean of ΔE in the three groups of IPS e.max CAD LT, Zolid fx, and DD Cubex2 were 8.37±0.47, 9.87±0.25, and 9.11±0.78 respectively. Significant differences were found in the ΔE values in the three groups (P<0.001).

The masking abilities of two super high translucent zirconia Zolid fx and DD CubeX2 were lower than IPS e.max CAD LT. This ability was lower in Zolid fx than in DD cubeX2.

graphene is a two-dimensional nanostructure consist of a single layer of SP2 carbon atoms that arranged by covalent bonds in a hexagonal bee web. The reinforcement by GO is due to functional groups that lead to strong interaction, dispersion and stress distribution. Due to lower mechanical properties and strength of PEMA than PMMA, we evaluate effect of GO on mechanical properties of PEMA.

In this invitro-exprimental study, flexural strength, elastic modulus, Knoop micro hardness and SEM examination of 30 acrylic sample with dimensions 2(width)×2(height)×2(length) in 3 groups was evaluated.

The maximum mean Knoop micro hardness was related to 0.25%wt GO and the lowest value was related to 0.5%wt GO groups. The mean flexural strength and modulus of elasticity of the control group were higher.

GO can increase micro hardness of PEMA in low value, thus the use of GO can be recommended to improve mechanical properties of PEMA. GO did not increase elastic modulus and flexural strength.

The opacity of dental ceramics has important role in final appearance of all ceramic restorations. opacity of super high translucent zirconia is not clearly determined.The aim of this study was evaluating the opacity of two super high translucent zirconia (zolid fx and DD cubeX2) and lithium disilicate reinforced glass ceramic(IPS e.max CAD LT).

In this experimental study, 30 ceramic discs with 1 mm thickness and 10 mm diameter in two groups of super high translucent zirconia (zolid fx and DD cubex2) and one group of lithium disilicate reinforced glass ceramic (IPS e.max CAD LT) were fabricated(n=10). For determining the contrast ratio (CR), spectrophotometer was used to measure Y parameters of each sample in black and white backgrounds. One-way ANOVA and Tukey Post Hoc statistical tests were used to analyze the data. Level of significancy was 0.05.

The mean of CR in the three groups of IPS e.max CAD LT ، zolid fx and DD Cubex2 were 0.97 ± 0.002, 0.96 ± 0.004 and 0.96 ± 0.005 respectively. Significant differences were not found in the CR values of three groups (P = 0.2).

Regarding the limitation of this study, Opacity of three ceramic were similar.

The purpose of this study was to compare dimensional changes of two types of auto polymerizing acrylic resin patterns (APARPs) in three different storing environments.
60 acrylic post and core patterns were made of two types of Duralay acrylic resins (Aria dent, Iran and Reliance, Dental Mfg. Co, USA) using a canine model. Then coronal, apical diameter and coronoapical length of patterns were measured. Afterwards, they were divided into two categories of 30 for each type of Duralay acrylic resin type. Each category was divided into three groups of ten randomly to immerse in three storage environments (Deconex®53plus Borer ChemieAG, Switzerland), Unident ® Impre(USF Healthcare S.A, Sweitzerland) and water. After one hour, three mentioned values were measured again. Data were analyzed by SPSS20 using t-test, paired t-test and ANOVA.
Results showed that there were no statistically difference (p value> 0.05) about all dimensions of auto polymerizing acrylic post and core patterns except apical diameter and coronoapical length of Dental Mfg. Co, USA in Deconex®53 plus.
The best environment to store Duralay APARPs with minimal changes was water and for disinfection, Deconex®53plus and Unident ® Imprecan showed acceptable properties with both of Duralay types.

To create a good adhesion between porcelain veneers and zirconia restorations has been important issues is the prosthesis. The aim of this study was to identify an effective way to prepare the zirconia surface infrastructure to increase its shear bond strength to the porcelain veneer.
75 samples of zirconia (Y-TZP) cylinders (diameter of 7 mm and a thickness of 3 mm) were fabricated. Based on the surface treatment, specimens were randomly divided into 3 groups: control, air abrasion and Er-YAG laser. After surface treatment, the specimen surfaces were examined by SEM. Using a metal mold, the porcelain was veneered on the zirconia surface and then fired. After thermocycling, the shear bond strength of porcelain to zirconia was measured and then the failure mode of each specimen was analyzed using a stereo-microscope. Data were analyzed by one-way ANOVA and Tukey test.
Significant differences were observed between the mean shear bond strength of different groups (P=0.001). The greatest amount of shear bond strength was observed in the group (S) and the lowest bond strength in the control group. Analysis of failure modes showed no statistically significant difference in the type of failure among study groups. The adhesive failure was predominating failure at the intersection of porcelain veneers.
The highest shear bond strength between zirconia and porcelain was achieved by sandblasting the zirconia surfaces compare with that of Er_YAG application.

Statement of Problem: Recent clinical results for Zirconia all-ceramic restorations have revealed that the fracture rate 6-15% of the Zirconia framework is so low and the core of Zirconia has high stability. However, chipping-off fractures of porcelain are the most common reason for failures of Zirconia in the fixed partial dentures.
The purpose of this study was to compare the shear bond strength (SBS) of porcelain in the porcelain fused to metal and all-ceramic crowns with Zirconia core.
Two groups were selected: porcelain fused to metal (PFM) and porcelain fused to Zirconia (PFZ) (n = 30).In the PFM group, a wax model (10 × 10 × 10mm)was used to cast metal base (Ni_Cr alloy). In the PFZ group, an acrylic cubic model (10 × 10 × 10mm) was made as Zirconia model for scanning.15 cubic Zirconia samples were milled by CAD-CAM. The procedure of porcelain veneering was conducted by the conventional layering technique up to 2 mm thickness (2.5 × 2.5 × 2 mm). All specimens were stored in water for 48 hrs. Thermal cycling was conducted for 20000 cycles between 55°C and 5ºC alternatively for 30s.All samples were mounted in acrylic resin and the SBS test was performed, using a universal testing machine. The analysis of data was performed at a significance level of 0.05 using Kolmogorov-Smirnov and Mann-Whitney U-test.
Mean of SBS in PFM and PFZ was 24.57 and 20.88, respectively. The results of Mann-Whitney test showed that there was no statistically significant difference between the two groups of porcelain fused to metal and Zirconia in item shear bond strength (p = 0.455).
There was no significant difference between the two groups of PFM and PFZ in the item SBS.

The toxicity of the methyl methacrylate monomer is an ongoing concern in dentistry. Therefore, those who are involved with this substance need to be cognizant of how to work with it..
This study aimed to evaluate the level of working knowledge about methyl methacrylate among undergraduate prosthodontics students at Shahid Sadoughi university in 2014..
In this descriptive cross-sectional study, the knowledge level of 54 undergraduate prosthodontics students, who had passed the last 2 years of their education, was assessed via a 13-question survey related to methyl methacrylate. Each correct answer was assigned 2 points, and the total sum of right answers was used to measure the knowledge level of each participant. In order to analyze the study data, SPSS16 was used to apply an ANOVA test, t-test, and Pearson correlation coefficient..
The mean level of individuals’ knowledge in regard to working with methyl methacrylate was 14.74 ± 5.03, with a domain variance of 0 to 22. A significant relationship was observed between age-related knowledge level mean and education level (P = 0.001), though no relationship was confirmed in regard to knowledge mean and gender (P The study results demonstrated that undergraduate prosthodontics students in their last two years of study had an average knowledge of working with methyl methacrylate. Therefore, health education should focus more on working with dentistry substances, in order to enhance the knowledge level of the targeted students..

Inappropriate transfer of pressure during final impression making in fabrication of complete denture can result in ridge resorption. This study aimed to assess the effect of vent size and spacer thickness on pressure produced during maxillary edentulous impression making by different impression materials in vitro.
This experimental study was carried out using a maxillary edentulous model, two types of impression materials (regular body addition silicone and zinc oxide eugenol) and two types of trays with spacer thicknesses of 0 and 1.5 mm and each thickness with four vent sizes of 0, 0.5, 1 and 2 mm. Totally eight types of trays for each impression material (80 samples) were used. Impressions were made and transferred pressure in the first molar area of edentulous ridge and mid-palatal raphe was measured (g/mm2) by two load cells. Data were analyzed using two-way ANOVA, post hoc Tukey’s test and t-test.
As the vent size or thickness of spacer increased, the mean pressure on maxillary edentulous ridge decreased from 59.0±2.22 to 36.8±2.50 and 98.5±5.85 to 42.8±2.11 g/mm² in ridge area and 35.0±1.66 to 19.4±1.74 and 52.1±3.80 to 22.3±1.25 g/mm² in mid-palatal raphe for regular body addition silicone and zinc oxide eugenol, respectively. Comparison between groups indicated that there were significant differences in the magnitude of pressure in use of the two materials and areas with different vent sizes and thicknesses of spacer (P Impression pressure changes significantly by change in tray design or impression material. For making impressions of an edentulous maxilla, using a tray with a 1.0 mm or larger venthole or 1.5 mm spacer thickness is recommended. Key Words: Dental Impression Materials, Dental Impression Technique, Dentures, Maxilla

However human oral cavity consist a mass of microorganisms, some alteration such as application the complete removable denture with poor oral hygiene in edentulous patients may cause overgrowth of several opportunistic microorganisms resulted denture stomatitis. The aim of present study was to compare the dominant oral micro-flora between edentulous denture users with dentate elderly. In current analytical, cross-sectional study, 30 edentulous patients with complete removable denture and 30 dentate subjects, who admitted for non-prosthetic treatments, were randomly selected in Yazd dentistry department. Their oral cavity samples were obtained using sterile cotton-tip swabs, for direct smear analyzing and cultivation on the selective fungal as well as bacterial media. Isolated predominant bacteria and fungi were enumerated and identified by microbiological differential diagnosis tests. Data were analyzed with SPSS software with T test and differences were considered statistically significant when p<0.05. The non-aureus staphylococcus and alpha-hemolytic streptococci showed the highest positive culture among the isolated microorganisms in both groups, whereas beta hemolytic streptococci showed the least percent of isolated microorganism in both groups. The higher density of non-aureus Staphylococci, α-hemolitic Streptococci, Gram negative cocobasillus, non-pathogenic Neisseria, Candida and Corynebacterium were recovered from oral samples of denture users in compare with dentate subjects (P= 0.0001). There was also seen a statistical significant correlation between the number of isolated microorganisms and the duration of denture utilization in denture users (P=0.013). Results of the present study showed that complete denture can be act as a predisposal factor in overgrowing of several oral micro-flora particularly Candida, non-aureus Staphylococci, α-hemolytic streptococci, gram negative cocobacillus, non-pathogenic Neisseria, and Corynebacterium, which emphasized the users denture hygine.

Impression materials are in contact with blood and saliva, may act as a source of microbial cross-infection in dentistry. The aim of this study was to compare the stability of C. albicans, S. mutants and S. aureus in foreign and Iranian Zinc Oxide Eugenols (ZOE) used for impression in complete prosthesis.

In current lab-trial study with 38 samples, in 3 groups (each group included 12 maxillary edentulous typodent) were contaminated with C. albicans, S. aureus, S. mutans in 0.5 McFarland standard suspensions on reciprocal shaker. They divided into 2 groups, which impressed with Cavex ZOE and Golchai ZOE. Impressions were removed after 5 minutes and after 1 hour, circular discs in 5 mm diameter was cut from the first molar tooth by a sterile cutter, used for viable microbial cell counting. Each disc was separately transferred in a sterile microtube containing 1ml of sterile PBS Finally 100 µl of PBS was spread. After incubation for 2–3 days, bacterial and fungal colonies were enumerated on each plate, and the relative colony-forming units were calculated as the left microorganisms on impression materials.Data were analyzed with SPSS 17 software using Mann-Whitney and kruskal-wallis analytic tests.

There was seen a statistically significant differences between 2 impression materials for stability of every tested organisms (P<0.05). S. mutants in comparison with other 2 microorganisms showed the most stability in all 2 impression materials.

Every 3 microorganisms showed that minimum stability on Iranian Golchei ZOE . So this impression material is better for prevention of cross-contamination.

Microbial contamination of removable denture and their contact with saliva and oral tissues can cause microbial cross-contamination among dental clinic personnel, dental laboratories and patients. These microorganisms can cause unpredictable infections especially systemic, pneumonia and even cardiac infections in elderly and immunosupressed patients. The aim of this study was to identify the microorganisms on the surface of removable prostheses ready for delivery (new dentures) in Yazd dental laboratories Fifty five new removable complete dentures were randomly selected from 5 Yazd dental laboratories. All dentures were washed by 100ml of sterile normal saline, centrifuged and precipitants were used for culture on the specific microbial media. Finally, the isolated aerobic, anaerobic microbial colonies and isolated fungi were identified according to diagnostic tests. Bacterial contaminations were seen in all prostheses whereas 58.2% showed fungal contaminations. Staphylococcus, nonpathogenic Neisseria spp, Corynebacteria, Acenitobacteria, E. coli, and Entrobacter spp were the common isolated bacteria in the current study. Saprophyte fungi such as Aspergillus, penicillium, mucor and yeasts especially Candida species were the most isolated fungi from dental prostheses in the present study. Results of the present study showed bacterial and fungal contamination even on newly made prostheses. It seems that control and prevention of cross-contamination should be taken more seriously in dental practices and laboratories.