Journal of Dental Medicine

It has been shown that noble alloys require metal collar to resist distortion when subjected to repeat firing cycle of porcelain. Metal collar is undesirable due to esthetic concerns. Since base metal alloys have superior physical properties, it seems that metal collar would not be necessary for obtaining better marginal adaptation of base metal crowns. The Purpose of this study was to evaluate the effect of metal collar on marginal distortion of base metal- ceramic crowns, Twenty base metal copings were constructed and divided into two groups with and without collars. After surface preparation, porcelain was applied onto the surface of specimens. Marginal gap was measured by scanning electron microscope during three stages of crown fabrication: before degassing, after degassing and after glazing. The mean measurements in collarless group were 21.4±13.4, 2I.4±14.9 and 21.9±11.9 u_m, respectively, and in-group with collar 24.7±11.4, 24.0±! 1.5 and 26.6±11.7 urn, respectively. Two- way ANOVA revealed no significant difference in the mean values between two groups and among different stages of crown fabrication. The results of this study showed that base metal alloys did not distort during crown fabrication and metal collar had no effect on the amount of marginal opening (gap).

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: The need for recrimping precrimped stainless steel crowns by the dentist in clinic is controversial. This study aimed to evaluate the rate of marginal circumference and marginal thickness change of precrimped stainless steel crowns after recrimping.

Materials and Methods: In this experimental study, 30 primary photos were taken from margins of 30 S.S.Cs (3M, Ni-Cr) related to tooth 85 with a digital camera fixed at a determined distance. Margins of crowns were crimped by 114 and 137 pliers with a controlled force (0.2 N) and then 30 secondary photos were taken in the same conditions. The circumference of crown margins in primary (group A) and secondary (group B) photos were assessed by a digitizer system. Comparing the circumferences of crown margins in primary and secondary photos showed a significant decrease after crimping. Thickness of 30 random points on the crown margins of a crown similar to mentioned cases was measured by SEM (×150). Then similar procedures including taking a primary photo, crimping and taking a secondary photo was done for the sample crown. After significant reduction in margin circumference, thickness of 30 other random points on the crown margin were measured by SEM. Data were analyzed by paired sample t-test with p<0.05 as the limit of significance.

Results: The mean marginal circumference of precrimped stainless steel crowns was reduced by 7.3% which was significant (P<0.001). On the other hand the mean marginal thickness of sample stainless steel crown showed 18µ increase.

Conclusion: According to the results of this study, marginal circumference of precrimped stainless steel crowns (3M, Ni-Cr) showed a significant decrease after crimping. It is concluded that crimping the stainless steel crowns even for precrimped ones seems necessary.

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 Aim: It is well recognized that implant treatment is common worldwide, but the approach to success is not predictable because of bone loss that occurs around the implants. Also there are many factors affecting crestal bone loss around the implants that one of them is the surgical protocol of implant installation. The purpose of this investigation was to evaluate the amount of crestal bone loss around the Replace implants installed according to submerged and non- submerged treatment protocol.

Materials and Methods: In this study, 11 patients received 34 implants. In each patient (unilateral or bilateral mandible), one of the implants was placed with submerged procedure and in the other one non- submerged procedure was used. In a period of 3 months a temporary partial denture that covered the implants was used. After 3 months the submerged fixture was exposed, impression was performed and fixed prosthesis was fabricated. Loss of crestal bone at each implant was measured. These measurements have been done at surgical times, over a period of 3 months after implant installation and 6 months after the delivery of the fixed prosthesis. The measurement was done with digital subtraction radiography. Data was analyzed by Wilcoxon Signed Ranks test.

Results: Three months after implant placement, submerged groups showed statistically more crestal bone loss (0.65±0.71) than non-submerged (0.41±0.53) group (p=0.02). After 6 months the mean value of crestal bone loss in submerged group was 0.21±0.40 mm and in non submerged group was 0.29±0.49 mm. This data indicated no statistically significant difference between the two groups of implants (p>0.05).

Conclusion: Our results are in accordance with previously published studies and confirm that the value of crestal bone loss in submerged and non-submerged groups after 3 and 6 months were similar and in acceptable limit.

Background and Aims: Marginal adaptation is important for the long-term success of full-coverage restorations. Preparation design is one of the important factors influencing the marginal integrity. Therefore, the purpose of this study was to compare the effect of radial shoulder and chamfer finish line designs on the marginal adaptation of all-ceramic Cercon restorations.
Materials and Methods: This in vitro study was done using single blind experimental technique. One stainless steel die with 7 mm height and 5 mm diameter was prepared by milling machine. The preparation design consisted of half radial shoulder with 1mm depth and half chamfer with 0.8mm depth. All walls had a convergence angle of 10º. Ten stone dies and ten ZrO2 copings of Cercon (Cercon Smart Ceramics, DeguDent, Hanau, Germany) were made and after cementation were ground at buccolingual direction. Then marginal gap of each sample was measured by scanning electron microscopy. Data were then analyzed using t-test.
Result: The mean marginal gap for radial shoulder was 98.4µ and for chamfer was 39.7µ. The difference was statistically significant (P=0.002).
Conclusion: The marginal gap of chamfer preparation is less than that of radial shoulder.

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: The most effective preventing tooth decay method is fluoride compounds applications. Some studies suggested that APF gels caused changes on the superficial physical properties of composite. Therefore, the purpose of this study was to evaluate the marginal microleakage of class V composite restorations before and after AFP gel application.

  Materials and Methods: The class V cavities in buccal surfaces of 45 molar teeth were made in such a way that occlusal margin was placed in enamel and cervical margin in cement. In group 1, at first fluoride-therapy and then cavity preparation and restoration by composite resin was done. In group 2, at first the class V cavities were prepared and restored, then fluoride-therapy was carried out. In group 3, cavities were prepared and restored with no fluoride-therapy. The dye penetration rate in occlusal and cervical margins was examined by stereomicroscope. Data were statistically analyzed using Kruskal-Wallis and Mann-Whitney test.

  Results: There was no statistically significant difference between groups ( P=0.975).

  Conclusion: Fluoride-therapy using AFP gel before and after class V composite restorations, had no significant effect on the microleakage of dentin and enamel margins.

  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 .

Background and Aims: Marginal accuracy is a crucial factor influencing the clinical long-term reliability of implant-supported fixed dental prostheses (FDPs). The aim of this in vitro study was to evaluate the marginal fit of three-unit zirconia bridge frameworks fabricated using two different computer-aided design (CAD)/
computer-aided manufacturing (CAM) systems (AmannGirrbach and Zirkonzahn).

Materials and Methods: The master model of 3-unit FDP was made of two implant abutments (AmannGirrbach and Zirkonzahn) from canine to second premolar. Twelve frameworks were manufactured using each fabricating system from semi-sintered zirconia blanks, which had to be sintered for final density after milling. After manufacturing, the absolute marginal discrepancy in each abutment were determined by means of Video Measurement System (VMS). The data were analyzed, using independent and paired t test (P=0.05).

Results: For the premolar abutment, the absolute marginal discrepancy of frameworks fabricated by AmannGirrbach system was significantly greater than those of the other system (P=0.005). There was no significant difference between the marginal discrepancy of canine and premolar abutments (P>0.05).

Conclusion: Within the limitations of this study, it could be concluded that the marginal fit of zirconia FDPs was significantly dependent on the CAD/CAM system used, but the abutment size was not an effective factor.

Resin-based composite restorative materials  have a substantial share in dental treatments. Their esthetic has made them patients’ first choice as restorative materials. Marginal leakage is one of their problems which leads to recurrent caries and post-operative hypersensitivity. Our aim was to evaluate the theoretical and clinical methods that have been proposed in the dental literature. Around 50 articles from Pubmed, SCOPUS and google scholar were selected and categorized in 4 groups based on the selected keywords. All the studies discussed in this paper have emphasized that there is no way to eliminate the microleakage but it can be reduced by means of some approaches. On the other hand, due to the multifactorial nature and difference of oral environment and laboratory conditions, there isn’t any certain way to define precisely. It seems that there is an absolute need for more research in this field to make the relation of theoretical results and clinical findings possible.