Journal of Dental Medicine

Statement of Problem: Nowadays economical issues on high gold alloys have changed the practice of metal-ceramic restorations toward base-metal alloys. Minalux is one of the base-metal alloys produced in Iran. Marginal fitness is of high importance to be evaluated in dental alloys.
Purpose: The aim of the present study was to compare the marginal adaptation of two base-metal alloys, Minalux (Mavadkaran Co. Iran) and VeraBond2 (Aibadent Co. USA ) during firing cycles of porcelain.

 Materials and Methods: In an experimental study 24 standard brass dies, with 135° chamfer finishing line were fabricated by Computer Numeric Controlled (CNC) milling machine. The samples were randomly divided in two groups, A and B, 12 in each. Following wax-up, the samples were equally cast with two mentioned alloys. In each group, there were 4 controlled samples, which proceeded to firing cycle without veneering porcelain. Scanning electron microscope (SEM) measurements of marginal gap from buccal and lingual aspects were performed after 4 stages of casting, degassing, porcelain application and glazing. The data were analyzed using Four-way ANOVA and multiple comparative test based on Tukey criteria.

 Results: The findings of this study revealed that there was no significant difference in the marginal gap of Minalux (31.10±7.8u.m) and VeraBond2 (30.27±6.96u.m) with confidence level at 0.95 (P=0.43). For both alloys the greatest gap was observed after degassing stage (P<0.05). Porcelain and porcelain veneering proximity caused significant changes in the marginal gap of Minalux castings (P<0.05), however, such changes did not occur in VeraBond2 (PO.05).
Conclusion: Based on the findings of this study, the marginal gaps of two base metal alloys, Minalux and VeraBond2, were proved to be identical and that of the Minalux alloy existed in the range of acceptable clinical application. It was also concluded that Minalux dental alloys could provide proper marginal adaptation.

Background and Aim: An important criterion for success assessment of implant-supported prostheses is marginal fit. Vertical and horizontal discrepancy can result in loosening of the prosthetic screw, crestal bone resorption, peri-implantitis and loss of osseointegration. Despite careful attention to waxing, investing, and casting, marginal discrepancies are inevitable. The aim of this study was to evaluate the marginal gap and overhang in three casting methods with two different alloys in ITI implants.

Materials and Methods: In this experimental in vitro study 48 analog abutments were randomly divided into six groups as follows: 1) burn out cap + BegoStar, 2) impression cap + BegoStar, 3) conventional wax up + BegoStar, 4) burn out cap + Verabond2, 5) impression cap + Verabond2, 6) conventional wax up + Verabond2. Waxing was done in 0.7 mm thickness verified by a digital gauge and a putty index was made for all groups. Reamer was used for correction of the finish line after casting in all groups. Castings were seated on analog abutments and embedded in acrylic resin. Specimens were sectioned by isomet instrument and polished and cleaned by ultrasonic cleaner for 10 min. The marginal gap and overextended margins of castings were examined under a  Scanning Electron Microscope (SEM) (X200). The mean gap and margin overextension were calculated for each group. Data were analyzed by multivariate analysis and Bonferroni post-hoc test with p<0.05 as the level of significance.

Results: No significant difference in gap size was observed among the three casting methods with two alloys (P=0.056). The marginal gap was not different in the studied casting methods (P=0.092). Gold alloy crowns showed lower marginal gaps compared to base metal alloy crowns (P<0.001). No significant difference in overhang size was observed among casting methods with two alloys (P=0.093). Base metal alloy crowns showed less overhang compared to gold alloy crowns (P<0.001). There was a significant correlation between overhang and use of impression cap in base metal alloys (P<0.001).

Conclusion: Based on the results of this study, vertical discrepancy of frameworks made with gold alloy were less than those made with base metal alloy. Base metal alloy demonstrated less overhang. Conventional wax up or using burn out caps produced less horizontal discrepancy.

Background and Aims: Since a large marginal opening allows more plaque accumulation, gingival sulcular fluid flow and bone loss, microleakage, recurrent caries and periodontal disease, marginal fit is of great importance in fixed restorations. The aim of this study was to compare the marginal fit of zirconium-based all ceramic (Cercon) frameworks, made by two different approaches (Direct and Wax-up scanning).

Materials and Methods: An abutment analog, with 5.5 mm width and height, was selected as an experimental model. Twenty all ceramic cores were made for this model (10 specimens per each group). In the first group (Direct), experimental models were scanned directly using Computer Aided Design/Computer Aided Manufacturing (CAD/CAM). The core was then designed with the aid of a computer and machined. In the second group (Wax-up or CAM) a wax-up pattern was made on the experimental model and then scanned and milled from Cercon blocks. The marginal discrepancy of each specimen was recorded using a stereomicroscope (SZX9, Olympus, Japan) and digital camera (Mode TK, C1380E, JVC, Japan) and then measured by Adobe Photoshop CS software. The data were analyzed using T-test.

Results: Mean marginal discrepancy of Direct group (85.2±3.95 µm) was significantly less than that of Wax-up group (120.2±6.91 µm).

Conclusion: Improved marginal fit of zirconia ceramics was found with the direct model scanning compared with that of Wax-up scanning using CAD/CAM.

  Background and Aims: Marginal fit is one of the key factors in the success of fixed restoration. The aim of this study was to evaluate the fitness of feldespatic crowns made from additional silicon impression and gypsum cast by CAD/CAM.

  Materials and Methods: 10 intact extracted upper premolar teeth were used for this experimental study. After preparation of the mounted teeth with radial shoulder finish line, 2 Vita Mark II feldespatic CAD/CAM machined crowns were fabricated for each tooth (one from scanning the additional silicone impression of the prepared tooth and the other one from the plaster model). Marginal gap of each crown was measured using SEM in two points on the mesial and 2 points on the buccal surface. Data were analyzed using Paired t-test with SPSS version 17 software (P<0.05).

  Results: The mean of marginal gaps in crowns fabricated from additional silicone and model plaster were (155.13±37.11) and (130.18±12.35), respectively. However, no significant difference emerged between marginal gaps of the two methods (P=0.055). Also, the mean of marginal gaps in crowns fabricated from additional silicone and model plaster was higher in mesial (157.82±44.41) compared to buccal (127.50±24.26) region (P=0.003).

  Conclusion: Marginal fit was not significantly differen ce between crown s made of the plaster casts and silicone molds and both methods showed the same results .