Background and Aim: Metal ceramic restorations are widely used in crowns. The marginal fitness of these artificial crowns is prone to alteration during the firing cycle of PORCELAIN. Gold electroformed metal-ceramic restorations have been introduced as alternatives to conventional metal-ceramic restorations. However little is known about the relationship between procelain firing procedures and marginal adaptation of this type of crown. The aim of the present study was to evaluate the influence of firing procedures on the marginal adaptation of electroformed metal-ceramic crown restoration.Materials & Methods: One steel die was prepared for maxillary molar crowns with deep chamfer finishing line design. Ten standardized gold electroformed copings were fabricated. Marginal discrepancy was measured at four sites along the circumferential margin of each coping (Midbuccal - Midpalatal - Midmesial - Middistal) using SEM (Mag: X400) prior to and after PORCELAIN firing procedure. Data among the 2 different groups (before PORCELAIN firing) were statistically analyzed using the paired t-test (a=0.05) analysis.Results: The marginal discrepancy of the postfiring procedures (21.45±2.27 mm) were significantly greater than those of the prefiring procedures (18.23±1.96 mm) (p<0.002).Conclusion: The PORCELAIN-firing procedures influenced the marginal distortion of electroformed metal-ceramic crown restorations, but the marginal discrepancies for all copings and examined design are clinically acceptable (less than 100 mm).

Background and Aim: Discoloration is a major concern with regard to the use of toothcolored restorations. Type of restorative material and surface treatment are believed to play a role in this regard. This study sought to compare the color change of glazed and polished DENTAL PORCELAIN after 30 days of immersion in chlorhexidine (CHX). Materials and Methods: In this in vitro, experimental study, 20 discs with 10 mm diameter and 2 mm thickness were fabricated of A1 shade of Noritake PORCELAIN using a gypsum mold. All samples had one opaque layer. They were then randomly divided into two groups of 10. Glaze powder was added to PORCELAIN in group 1, and group 2 was polished using a polishing kit. The CIE L*a*b color parameters of samples were then measured using a spectrophotometer. All samples were immersed in 0. 02% chlorhexidine solution for 30 days and color parameters were then measured again. Change in each color parameter was compared between the two groups (polished and glazed) using t-test. Results: After 30 days of immersion in CHX, Δ E was 0. 76± 0. 16 in the glazed and 0. 89± 0. 16 in the polished group. The difference in this regard between the two groups was not significant (P=0. 092). Conclusion: Both polishing and glazing confer optimal color stability to DENTAL PORCELAIN.

Background and Aim: Surface roughness of DENTAL restorations can reduce the biological properties and wear the opposite. The goal of this investigation was comparing these process effects on the surface roughness of PORCELAIN.Materials and Methods: In this experimental study, 20 Noritake PORCELAIN disks of 1 cm diameter and 2-2.5 mm thickness with non-percious metal base were fabricated. All samples were finished with medium grit silicone disk and then randomly divided into four groups (n=5). In the first group, the samples were self-glazed. In the second group, the samples were polished (EVE Polisher Kit). In the third group, after self-glazing with a coarse grit stone, the self glaze layer was omitted, then reglazed. The fourth group was similar to the third group, but in the end stage a polishing kit was used. Samples were evaluated with Profilometer and then with SEM. As a result of normal distribution of the data, One-Way analysis of variance (ANOVA) was used for statistical analysis. The mean roughness for the glazed group was 1.06±0.0547; the polished group, 0.92±0.1304; the reglazed group, 1.22±1304; and the polished after glaze group 1.14±0.1342.Results: The polished and polished after glaze groups had a round shape in 100%, but the glazed and reglazed groups had a sharp shape in 60%.Conclusion: The polished surface is less rough compared to the glazed surface and in the polish after glaze group, the surface of the PORCELAIN is less rough compared to the reglaze group.

Statement of Problem: DENTAL PORCELAIN is one of the best materials ever used in dentistry. Excellent tissue compatibility, esthetics, very low solubility in oral fluids, high compressive strength, and the lowest bacterial plaque accumulation on the glazed PORCELAIN are some of its advantages. PORCELAIN brittleness due to its low tensile strength, impact strength and the occlusal attrition of opposing teeth enamel are some of its disadvantages. The most important mechanical properties of DENTAL PORCELAINs are their flexural strength that is the ability of a PORCELAIN to resist fracture when loaded from above. Different ways have been proposed to eliminate PORCELAIN brittleness and develop its flexural strength, among which baking PORCELAIN on a metal framework is more commonly used.Purpose: Considering that restoration and replacement of teeth by PORCELAIN fused to metal restorations is still the most commonly used technique, the aim of the present study was to measure the flexural strength of a PORCELAIN bonded to metal powder, D4 Dentin, and to compare it with Vita Dentin powder.Materials and Methods: In this experimental study, a stainless steel box, 25×5×2mm was made according to ISO 6872: 1995 (E) Standard and filled with D4 Dentin powder and Vita Dentin (VMK 68N) and baked in Vita furnace. Then 10 blocks of D4 Dentin and 10 of Vita Dentin were made. Samples were placed on the three point bending test machine and force was applied the middle of each block. To analyze the data, t- student test and co-variance analysis were used.Results: Mean flexural strength of D4 Dentin was 53.40 1.35 MPa and that of Vita Dentin was 53.86 7.38 MPa. The difference was not statistically significant.Conclusion: According to ISO 6872: 1995 (E) standard, the flexural strength of all D4 Dentin samples were greater than 50 Mpa.

Introduction: The increasing trend of research concerning bonds between Metal, PORCELAIN, … and DENTAL tissue of enamel and dentine, to determine which bonding agent has a higher quality in particular conditions has been going on. Objective: This research was carried out to compare three types of bonding agents Panavia Ex, Mirage bond Flc and Optibond in shear bond strengths PORCELAIN and tissue of enamel. Materials and Methods: In 60 samples of human teeth which were divided in three groups of A, B and C (each group consisting of 20 samples) PORCELAIN was bonded to enamel with these three bonding agents, then they were put under the Instron machine with shear force of 0.5 cm/min On the PORCELAIN near the bonding place. According to the separation time of PORCELAIN from enamel the bond strength power was obtained. Results: After calculating the average figures and variance analyzing (Anova) and also using Scheffe, Duncan, Tukey Hsd Test, these results with were reported in groups A, B and C respectively: Panavia Ex 4.39 Mpa, Mirage Bond Flc 10.41 Mpa and optibond with the most shear strength of 15.90 Mpa Conclusion: Regarding to the result of this research, optibond material was found to have a higher shear bond strength, comparing with the two other substances. Therefore it can be used to bond Inlay، Only and PORCELAIN crown to the tissue of enamel.

Introduction: Soldering has several applications in prosthodontic treatments; however, the effect of soldering on PORCELAIN to metal bond strength has not been adequately studied. This study was designed to assess the bond strength of PORCELAIN to metal, and the mode of failure at the soldered and non-soldered areas of cubic specimens. Materials & Methods: In this in vitro, experimental study, 40 PORCELAIN-metal specimens were fabricated under similar conditions and divided into two groups (n=20). In the test group, a hole was created at the center of the frame and was then soldered and veneered with PORCELAIN. The second group was considered as a control group. The bond strength was measured at the center of the specimen using the 3-point bending test in a universal testing machine with a crosshead speed of 0. 5 mm/min. The mean force required for debonding was determined. Photographs of the specimens were digitalized by a scanner and magnified on a computer screen with x10. 5 magnification. Next, each image was divided into 100 squares (1×1 mm). The mode of failure was determined for each specimen. The two groups were compared using independent t-test (p-value˂ 0. 05). Results: The mean PORCELAIN-metal bond strength was 36. 6± 7. 3 N for the soldered and 37. 4± 4. 6 N for the non-soldered group with no significant difference between them (P>0. 05). The mode of failure was cohesive in all specimens in both groups with no significant difference between them (P>0. 05). Conclusion: Within the limitations of this study, the soldered and non-soldered specimens showed no significant difference regarding the PORCELAIN-metal bond strength.

Background and Aim: Adhesion of S.mutans to the DENTAL PORCELAIN surface is may lead to development of gingival inflammation and secondary caries. Surface roughness is considered to be a factor affecting the bacterial adhesion to the PORCELAIN. The purpose of this study was to evaluate the effect of four different surface treatment methods on the adhesion of S.mutans to DENTAL PORCELAINs.Materials and Methods: Sixty specimens (10×3 mm) of Noritake PORCELAIN were fabricated. Specimens were divided into 4 groups (n=15) that were treated with one of the following four surface finishing techniques: 1.glazing 2.overglazing 3.polishing (with Kenda kit) 4.nonglazed (without any surface treatment). The samples were exposed to bacterial suspension (1×106 cell/ml) with standard code of S.mutans PTCC1643, and were cultured in blood agar. The level of adhesion of the S.mutans on specimens was assessed and the specimen’s surface roughness were determined with SEM. Data was analyzed with one-way Kruskal-Wallis and Mann-whitney test and the correlation between the level of adhesion and specimens surface roughness was evaluated by pearson test.Results: The average bacterial adhesion in each group was as follows: Glazed group (35±20.92), Overglazed group (28±6.73), Polished group (103±22.1), Nonglazed group(115±16.2). There difference in 4 groups was statistically significant p<0.05). The average surface roughness in each group was found to be as follows: Glazed group (0.67±0.004), Overglazed group (0.48±0.003), Nonglazed (0.89±0.005), and Polished (1.7±0.004). Statistically significant differences were seen between all groups. (p<0.0001) There was a positive correlation between the adhesion of S. mutans and surface roughness. (p=0.0001).Conclusion: This in vitro study indicates that the samples in the Overglazed group had the lowest bacterial adhesion whereas the Nonglazed group had the maximum bacterial adhesion. Furthermore, the Glazed surfaces show less adhesion than the Polished surfaces.

Background and Aims: Poor adhesion between PORCELAIN and some of the DENTAL alloys is one of the most challenges to select the desirable alloy in DENTAL restorations. Therefore, the aim of this study was to evaluate the bond strength of PORCELAIN to some of the commercial alloys. This can help in selection of desirable alloy. Materials and Methods: The shear bond strength of PORCELAIN to the three of the most widely used nickel-base DENTAL alloys commercially named as: Verabond, Damcast and Noritake were evaluated according to standard ASTM E4. The results were analyzed based on the statistical method of independent t with the meaningful level of P<0. 05. Then, the bonding interface of the fired samples was evaluated using SEM equipped with EDX analyzer and X-ray diffractometry. Results: The average bonding strength of PORCELAIN to each of the above mentioned alloys were determined as: 27. 54± 5. 48, 22. 46± 4. 99 and 26. 18± 4. 27 MPa, respectively. Due to the existence of Be and Al in the chemical composition of Verabond and Damcast and their higher appetencies to form the different surface oxides in preference to Cr2O3, not only the bond strength of PORCELAIN to two these alloys was increased about 20 percent (compared with the Noritake), but also the color of their PORCELAIN was not changed. Conclusion: To replace the replacing of deleterious elements from the chemical composition of DENTAL alloys. The added new elements should control through the oxide layer and the formation of Cr2O3 in PORCELAIN-alloy interfaces for adequate bond strength.