Introduction: METAL-ceramic restorations have been commonly used in dentistry. These restorations have both the esthetics of porcelain and the strength and durability of METAL. Noble ALLOYs and BASE-METAL ALLOYs are usually used for METAL-ceramic restorations. Applications of BASE-METAL ALLOYs has been developed because of economic considerations, mechanical properties and low density. Remelting of used ALLOYs is a common way in DENTAL labs to reduce the costs of fixed prostheses. Few studies have been performed on the effect of recasting ALLOYs on the METAL-ceramic bond strength. The purpose of this study was to evaluate the effect of commond ALLOY recasting on METALceramic bond strength.Materials & Methods: In this laboratory-experimental study, 23 waxed patterns in the size of 0.5´3´25 millimeter were cut with bisturi blade. Wax patterns were sprued, burned out and casted with commend ALLOY. The second group has the same method although they consisted of equal amount of fresh ALLOY and ALLOY remnants cast only once, the third and fourth group contained 50% fresh ALLOY and 50% used ALLOY of last group. After sandblasting, grinding and surface preparation, porcelain application was done with Noritake porcelain. samples fractured with 3-point bending test by Universal Testing machine at the speed of 0.5 mm per minute. Finally, the results were analyzed by ANOVA (p value=0.007).Results: The results indicate that the highest mean values of fracture strength of porcelain to METAL was in the first group (30.9 N) and then squencely in the group 3 (28.7 N), group 2 (26.8) and group 4 (24.3 N).There is a significant difference between group 1 and 2 (p value=0.03), group 1 and 4 (p value=0.001) and group 3 and 4 (p value= 0.02). There was no significant difference between group 1, 3 (p value=0.26), group 2 and 3 (p value=0.3) and group 2 and 4 (p value=0.18).Conclusion: Recasting of BASE METAL ALLOYs statistically decrease the bond strength of porcelain to METAL.

The purpose of this study was to compare the bond strength of etched bridge retainers to enamel, following the application of different surface treatments and adhesives.Sixty sound human extracted canines teeth were selected for this study. Cobalt Chromiun - bryllium retainers were made to adjust to the lingual surfaces of each tooth.Specimens were divided into three groups for their surface treatme!1t including: Sandblasting, Chemical etching and Heat treatment. Each group Was then divided into three subgroups BASEd on the use of each luting cemented: SBMP *, Dpo Cement ** of Enforce***.After treating the surface of both retainers and enamels, samples were bonded to the enamel surface of lingual side of the teeth. The shear bond-strength of the specimens were measured at a blade crosshead with the speed of 2mm/min after one week storage in 100% humidity at 37°C.The ANOVA and Duncan test were employed for any possible diference between groups.Results indicated that:1-The type of luting cement is not important after Air abrasion and Heat treatment.2- Using chemical treatment, the bond strength of SBMP and Duo cement shows a greater rise compare to Enforce (106.7kg).3- Bond strength of Enforce was found to be similar for all surface treatment methods.4- SBMP with Duo Cement, showed the greatest bond strength when chemical treatment was employed in comparison to the other treatment methods.5- The greatest bond strength was seen in SC group.6- There was an acceptable enamel bond strength associated with heat treatment.In Conclusion: Chemical treatment and SBMP is found to have the best result compare to the heat treatment and air abrasion technique.

Color matching and accurate shade selection are the challenging problems common to restorative dentistry. In ceramoMETAL restorations, the type of substructure ALLOY affects the final color of bonded porcelain. Nickel- chromium ALLOY is the most commonly used one that its Iranian product, namely Minalux, is similar to Verabond2.Purpose: The aim of this study was to assess and compare various color dimensions resulting from Minalux and Verabond2 ALLOYs. Materials and Methods: Nine disks, approximately 16 mm in diameter and 0.5 mm thickness, were cast from each ALLOY. Then, porcelain Vita VMK68 A2 was baked onto the entire test disks, following the manufacturer"s instruction. Color samples, at the same time and under the same conditions, was measured by Data color spectrophotometer in CIE Lab System and Munsel system under four light sources (A, C, D65 and TL81). Then MATLAB TOOL BOX Statistic 5.2 was used to determine mean and bilateral variance analysis.Results: It was indicated that the F value on hue, value and chroma was less than of the table value stated with 99% coefficient confidence, confirming Ho theory. In other words, there were not any significant differences between ceramoMETAL disks made of Minalux and Verabond2 in the three dimensions of color.Conclusion: Having desirable physical, mechanical and biological properties, Verabond2 can be replaced by Minalux ALLOY.

Introduction: BASE METALs are being increasingly used in casting procedures in dentistry. Since recasting these ALLOYs in laboratory might have negative effects on marginal fitness, it seems necessary to study the effect of recasting procedures more carefully. The goal of this study was to study the effect of recasting BASE METALs on vertical marginal fitness of crowns with different marginal configurations with different percentages of ALLOYs.Material and Methods: In this study, two dies made up of brass with dimensions of prepared premolars and marginal configurations of shoulder bevel 450 and shoulder 1350 were prepared by CNC machine. Total of 30 copings were waxed and cast, 15 copings for each die. Copings were further subdivided in to three groups A, B and C. Group A consisted of 100% new ALLOY, group B consisted of combination of 50% new ALLOY and 50% old ALLOY, group C consisted of 100% recast ALLOY. After copings were seated, vertical distance from margin of the restoration to margin of the die was measured by metric microscope with Moticam camera at four points of buccal, lingual, mesial and distal. Data were analyzed by two- and one-way ANOVA and t- test.Results: Group A1 (135º shoulder finishing line cast with 100% new ALLOY): 156.11 micron. Group A2 (45o shoulder bevel finishing line cast with 100% new ALLOY): 99.74 micron. Group B1 (135o shoulder finishing line cast with 50% new ALLOY and 50% recast ALLOY): 273.38 micron. Group B2 (45o shoulder bevel finishing line cast with 50% new ALLOY and 50% recast ALLOY): 123.07 micron. Group C1 (135o shoulder finishing line cast with 100% recast ALLOY): 369.40 micron. Group C2 (45o shoulder bevel finishing line cast with 100% recast ALLOY): 106.97 micron. There were statistical differences between groups A, B and C in vertical gap when three different percentages of ALLOYs (100% new with average gap of 127.93 micron, 50% new+50% recast with average gap of 198.22 micron, 100% recast with average gap of 238.18 micron) were used (p value = 0.036). There were statistical differences in mean vertical gap distance between different preparations (shoulder bevel 45o, shoulder 135o) within each group (100% new, 50% new + 50% recast, 100% recast).Discussion: When three different percentages of ALLOYs were used (100% new ALLOY, 50% new + 50% old, 100% old), 100% new ALLOY showed the least mean vertical gap compared to other two groups. In shoulder 135o there were statically differences between group A and C only and in shoulder bevel preparation there were no statically differences between groups A, B and C. In group C (100% recast) there were significant differences between two preparations (shoulder bevel 45º and shoulder 135o). 

Background and Aim: Soldering is used in fixed prosthodontics, for different purposes such as connecting separate parts of the bridge, recontouring proximal and occlusal contacts and repairing casting voids. The aim of this study was to compare the flexural resistance of two rod and paste solders used in BASE METAL ALLOYs. Materials and Methods: Thirty rectangular specimens (1×4×30 mm) were made using super cast BASE ALLOY. The samples were sectioned into two equal parts and were placed in a soldering investment as pairs with 0.3 mm gaps between them. They were divided into 2 groups and soldered with rod solder in one group and paste solder in the other. The samples were subjected to a flexure test on a Universal Testing Machine. Statistically analysis was performed using F- and t-tests. Results: The minimum and maximum flexural resistance was 107.2N and 301.2N for the rod- and 62.8N and 109.3N for the paste solders, respectively. The mean flexural resistance was 196.5N in the rod solder group and 89.8N in the paste solder group. A significant difference in flexural resistance was observed between the two study groups (P=0.001). Conclusion: The results of this study indicated that flexural resistance of the rod solders was significantly higher than the paste solders.

Introduction: The Purpose of this inviro study was to evaluate the porcelain veneer to Ni-Cr Beryllium bond strength by different adhesives.Materials and Methods: 80 Casting models were molded; Each model had a cylindrical shape With two different diameters Larger diameter was used for adhesion the porcelain. After molding in self cured acrylic resin, the surface of samples was air abraded. Then specimens were divided into four groups of twenty. group C (Control): Aluminum foils were selected In mid part of each foil a 3.5mm diameter hole Was punched. Then they adapted on surface of model. Finally, Porcelain firing Was done. For experimental groups, 60 porcelain disks with 2mm thickness and 3.5mm diameter were made similar to P.E.M disks. But aluminum foils were put on refractory sheet. Surface treatment for porcelain disks was done with sandblasting and silane coupling agent.Group S: Firstly, SBMP adhesive was used in ALLOY surface. Then disks Were bonded with Duo Cement.Group P: Panavia 21 was used for porcelain ALLOY bonding.Group 0: firstly, One Coat Bond adhesive was used in ALLOY surfaces. Then disks were bonded with Duo Cement. breaking of samples was done by blade cross head with the speed of 2mm/min.ANOVA & Duncan and I tests with 99% significance level were used for data analysis. Results:Results: 1- Data mean for bond strength of groups C-P-S-O were respectively 25-19.5-15.5 and 13 MPa.2-In Comparison of group C bond strength with each of experimental groups, PFM showed greatest bond strength but had the least difference from group P.3- In Comparison of experimental groups, P had the greatest bond strength and showed a significant difference among with group O. While P and S had no significant differences.4- In Comparison among four groups, C had significant difference with all of experimental groups, while P showed significant difference from O. Conclusion: If facial surface of casting crown exposed porcelain, alumina air abraded as, has greatest bond strength with panavia 21 and then with (SBMP+ Duo Cement).

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).

Introduction: This study was evaluating the etched bridge to enamel bond strength by different types of chemical surface treatments with two adhesives.Materials and Method: 144 sound canines were selected. After cleaning and mounting with self cure acrylic resin in molds, rectangular plates with 9mm2 surface areas and 0.5 mm thickness and with one process in mid part of the each one, were created. Fitting surfaces of all samples, were sand blasted. The specimens were divided to four groups of 36 BASEd on type of chemical solutions. A): 50% V nitric acid-25%V hydrochloric acid- 25% V methanol. B): 18% V hydrochloric acid. C): 50% V, phosphoric acid, 25%V hydrochloric acid, 25% V, methanol. D): 3% w sulfuric acid, 1%w potassium permangenate. Then each of groups was divided to two groups of 18 BASEd on two types of adhesives. Scotch Bond Multipurpose (3M-CO) and One Coat Bond (Coltene). And finally were adhered by dual cure resin cement Duocement (Coltene). After 1000 thermal cycling, shear test was done by crosshead speed of 2mm/min.Statistical analysis were done by two way ANOVA with 95% significance level.Results:1- Two factors (acid and adhesive), had no interaction.2. Type of acid hadn’t significant effect on bond strength. So four types of acids were as the same in bond strength. 3. Type of adhesive had not significant effect on bond strength. Therefore, two types of adhesives were as the same in bond strength.Conclusion: For surface treatment of Maryland bridge retainers, acidic solution and adhesives (one component and multi steps) are the same. Therefore it is better that select simple method.