Co-Cr Copings Research Articles

Comparative Evaluation of Retention and Vertical Marginal Accuracy of Co-Cr Copings Fabricated Using Three Different Techniques: An In Vitro Study.

This study was conducted to comparatively assess the retention and vertical marginal fit of cobalt-chromium copings fabricated by the conventional casting technique, 3D-printed resin pattern, and with direct metal laser sintering (DMLS) technique. Out of the total 60 test samples, 20 copings were obtained from inlay-casting wax and 20 from casting of 3D-printed resin patterns. In total, 20 copings were obtained from the laser sintering technique. All 60 test samples were then cemented serially on the prepared maxillary-extracted premolars and were evaluated for vertical marginal gap in 8 pre-established reference areas. Retention was evaluated using a universal testing machine. Results obtained for both marginal gap and retention were statistically analyzed, and the values fall within the clinically acceptable range. The DMLS technique proved precedence over the other two techniques used, as it exhibited maximum retention and marginal accuracy, which is an area of prime concern. The results from this study encourage further research with different pattern-forming materials and techniques and the need to identify the factors that facilitate better marginal fit and retention of cast restorations. This study has myriad of applications in clinical dentistry mainly in decision-making for casting procedure to provide better retention and marginal accuracy for fabrication of Co-Cr crowns. It also aims to aid the clinician to minimize errors by using different techniques for fabrication of wax pattern as well as the coping, keeping abreast with the recent technology to evaluate the accuracy of 3D-printed resin pattern over conventional wax pattern.

Comparison of the marginal accuracy of metal copings fabricated by 3D-printed resin and milled polymethyl methacrylate - An in vitro study.

Computer-aided design/computer-aided manufacturing (CAD/CAM) systems have gained popularity over the traditional laboratory procedures in dentistry. In the conventional metal casting technique by burnout of a pattern, instead of using a wax pattern (which has several disadvantages), milled polymethyl methacrylate (PMMA) and 3D-printed resin patterns can also be used. The objective of the study was to assess and compare the marginal accuracy of single-crown cobalt-chromium (Co-Cr) metal copings fabricated using milled PMMA and 3D-printed resin patterns. Digital designing was done for metal coping on a prepared typodont mandibular molar using 3Shape Dental Design software. Standard Tessellation Language document of CAD design was used to fabricate 3D-printed resin patterns (Sprintray 3D printer) and milled PMMA patterns (CAD/CAM milling machine CoriTEC). A total of ten Co-Cr copings were casted, of which five belonged to Group A: 3D-printed resin and the other five to Group B: milled PMMA. The copings were assessed for marginal fit at eight different points using a stereomicroscope. Statistical analysis was done using an independent t-test. The t-test revealed a significant difference between the mean marginal gap values of the two groups, with the marginal gap values for the 3D-printed resin group (82.21 ± 15.26 μm) being lesser than that of the milled PMMA group (106.75 ± 12.76 μm). The marginal accuracy of copings fabricated using 3D-printed resin patterns was superior to that of copings fabricated from milled PMMA patterns.

Marginal Misfit of 3D-Printed (Selective Laser Sintered), CAD-CAM and Lost Wax Technique Cobalt Chromium Copings with Shoulder and Chamfer Finish Lines: An In-Vitro Study.

Background and Objectives: The aim was to compare the Misfit of 3D-Printed, Selective laser melting (SLM), milled (Computer aided design-Computer aided manufacture CAD-CAM) and Lost wax technique (LWT) fabricated Cobalt chromium (CoCr) alloy copings on shoulder (SH), radial shoulder (R-SH) and chamfer (CH) finish line configuration. Materials and Methods: Ninety resin, second maxillary premolar teeth were prepared for metal-ceramic crowns, equally divided into (n = 30) SH, R-SH and CH margin preparations. For each preparation design (SH, R-SH and CH), CoCr copings were prepared using SLM, CAD-CAM and LWT. This resulted in nine study groups with 10 CoCr copings each. The marginal misfit of specimens was assessed with a high-resolution digital microscope. Misfit was evaluated in vertical and horizontal dimensions in μm. Data were analyzed using ANOVA and a post hoc multiple comparisons test. Results: For vertical misfit, the highest was observed in SLM samples with chamfer margin (167.96 ± 24.1), and the least was shown by CAD-CAM samples with radial shoulder (58.8 ± 12.53). CAD-CAM and shoulder margins showed the least vertical misfit. For horizontal misfit, the maximum was observed in SLM samples with shoulder margin (137.94 ± 37.85) and the least by LWT samples with chamfer (89.38 ± 14.81). Chamfer margins and LWT samples showed the least horizontal misfit among the group samples. Fabrication technique and finish line design play a critical role in reducing the marginal misfit of CoCr copings. Conclusions: For vertical misfit, SLM copings showed poor outcomes compared to CAD-CAM specimens, however comparable outcomes to Cast specimens. SLM copings showed comparable horizontal misfit outcomes to CAD-CAM specimens and low misfit compared to Cast copings, respectively. Vertical misfit was low with shoulder margins, and horizontal misfit was better with chamfer marginal configuration.

EVALUATION OF MARGINAL FIT AND INTERAL FIT OF METAL COPINGS FABRICATED BY THREE DIFFERENT TECHNIQUES- AN IN VITRO STUDY

Statement of problem: An optimal marginal and internal fit plays an important role in the longevity of a restoration. Increased marginal gaps can cause bacterial and biofilm adherence. Also, poor internal fit can lead to decreased retention and resistance form. There are various techniques available for the fabrication of restorations. All these techniques have their own pros and cons. In regards to these problems, the present study was conducted to find out whether the manufacturing technique has any influence on the marginal and internal fit of copings. Aim: The aim of this study was to evaluate and compare the internal and marginal fit of Co-Cr copings fabricated by three different techniques namely, conventional lost wax technique, 3D resin printing technique and CAD/CAM milling technique. Materials and methods: A stainless steel master model and a custom tray were fabricated. Totally 30 impressions were made and poured with die stone to obtain 30 die specimens. The specimens were grouped into three groups. Group 1- conventional lost wax technique, group 2- 3D resin printing technique and group 3- CAD/CAM milling technique. Co-Cr copings were fabricated using the respective technique. For evaluating the internal fit, weighing technique was followed. The cross-sectional technique was followed to assess the marginal fit. Results: There was statistically significant difference between the different groups in terms of internal and marginal fit. The CAD/CAM milling technique showed better marginal and internal fit compared to the other two techniques. The 3D resin printing technique showed better results than the conventional technique but was not statistically significant. Conclusion: Within the limitations of this present study, the results drawn suggests the use of CAD/ CAM milling technique and the 3D resin printing technique for fabricating restorations in routine dental practice.

Comparison of Marginal Integrity and Surface Roughness of Selective Laser Melting, CAD-CAM and Digital Light Processing Manufactured Co-Cr Alloy Copings

The purpose of the present study was to evaluate the influence of fabrication techniques on the surface micro-roughness (Ra) and marginal misfit of cobalt chromium (CoCr) copings. A mandibular first molar was prepared for a metal ceramic crown. Forty metal copings were prepared and divided into groups (n = 10). Group 1, Casting-Lost wax technique (Cast-LWT), Group 2, CAD-CAM, Group 3, Selective laser melting (SLM), and Group 4, Digital light processing-Cast (DLP-Cast). Ra was measured using laser profilometry and marginal misfit was analyzed with Micro-CT. Analysis of variance (ANOVA), Tukey multiple comparison, and correlation coefficient tests were applied (p < 0.05). SLM technique showed the highest Ra (2.251 ± 0.310 μm) and the Cast-LWT group presented the lowest Ra (1.055 ± 0.184 μm). CAD-CAM copings showed statistically lower Ra compared with SLM samples (p = 0.028), but comparable Ra to DLP-Cast (p > 0.05). CoCr copings fabricated from the DLP-Cast technique demonstrated the highest marginal misfit (147.746 ± 30.306 μm) and the lowest misfit was established by SLM copings (27.193 ± 8.519 μm). The SLM technique displayed lower marginal misfit than DLP-Cast and CAD-CAM (p = 0.001), but comparable misfit to Cast-LWT copings. Ra influenced the marginal misfit in CAD-CAM, SLM, and DLP-Cast technique-fabricated copings. (p < 0.01). Marginal misfit and Ra of CoCr copings are contingent on the different fabrication techniques.

Fit of metal-ceramic crowns

Aim: To evaluate the influence of cobalt-chromium (Co-Cr) coping fabrication methods and ceramic application on the marginal and internal fit of metal-ceramic crowns. Methods: Co-Cr copings for metal-ceramic crowns were prepared by lost wax casting or CAD-CAM machining of sintered blocks. The fit was analyzed using the silicone replica technique at four assessment points: marginal gap (MG), axial wall (AW), axio-occlusal (AO) angle, and central occlusal (CO) wall. After the initial analysis, the copings were ceramic-veneered with the layering technique, and the fit was again determined. Data were statistically analyzed by paired and unpaired Student’s-t test (α=0.05). Results: Marginal and internal fit before ceramic application according to the coping manufacturing method showed significant differences only at CO (p < 0.001), with milled copings (137.98±16.71 μm) showing higher gap values than cast copings (112.86±8.57 μm). For cast copings, there were significant differences at MG (before 109.13±8.79 μm; after 102.78±7.18 μm) and CO (before 112.86±8.57 μm; after 104.07±10.63 μm) when comparing the fit before and after ceramic firing. For milled copings, there was significant difference only at AO (before 116.39±9.64 μm; after 108.54±9.26 μm). Conclusion: This study demonstrated that the coping fabrication method influenced the internal fit. Ceramic firing maintained or improved the fit of the metal-ceramic crowns. The marginal discrepancy of all restorations, before and after ceramic firing, can be considered clinically acceptable.

Effect of Material Selection and Different Fabrication Techniques on Marginal and Internal Fit of Metal Ceramic and All Ceramic Crowns (In vivo and In vitro study)

Purpose: Assess the effect of material selection as well as different fabrication techniques of metal ceramic (MC) and all ceramic crowns on their clinical outcomes, marginal and internal fit. Materials and methods: In vivo study(I); twenty- eight patients were provided with twenty-eight crowns restoring mandibular first molar tooth. Patients were distributed into 2 groups and 2 subgroups according to different materials and fabrication techniques: fourteen patients received MC crowns, group (I); seven patients received crowns with conventional casting of Co-Cr copings, subgroup (A) and seven patients received crowns with direct milling of Co-Cr copings, subgroup (B). Fourteen patients received IPS e.max press crowns, group (II); seven patients received crowns with conventional wax pattern, subgroup (A) and seven patients received crowns with 3D printing resin pattern, subgroup (B). The survival rate of these crowns was evaluated and statistically analyzed. In vitro study(II); one machined die was prepared to simulate crown preparation of mandibular first molar tooth. 60 crowns were constructed on die and divided into 2 groups (30 samples each) and 2 subgroups (15 samples each) according to different materials and fabrication techniques similar to in vivo study. Replica technique obtained to measure marginal and internal fit using Digital microscope. Results: The survival rate of MC and press crowns was 98% and 60% respectively. Press crowns and digital technique showed superior marginal and internal fit than MC crowns and conventional technique respectively. Conclusions: Material type and fabrication technique of MC and all ceramic crowns influence their clinical outcome, marginal and internal fit.

EFFECT OF RECASTING CO-CR ALLOYS ON THE MARGINAL FIT OF CROWN WITH SHOULDER MARGIN - AN INVITRO STUDY

Introduction: Marginal adaptation is one of the most important and weakest links in the success of cast restorations. There is some indication that the quality of marginal adaptation may be as important to gingival health as marginal location.01
 Aims and Objectives: To evaluate the marginal integrity and occlusal discrepancy of base metal alloy copings by recasting method using conventional casting technique.
 Methodology: The 30 test samples were grouped into 3groups as Group I: 10 samples will be prepared using 100% new co-cr alloy.Group II: 10 samples will be prepared using 50% new alloy and 50% reused alloy.Group III:10 samples will be prepared using 25% new alloy and 75% reused alloy. The patterns obtained were casted with an induction casting machine and Co-Cr copings, the vertical gap and internal gap/occlusal discrepancy of all the 30 Co-Cr cast copings are obtained, with the use of stereo microscope.
 Results: Paired t test and tukey Kramer tests were conducted to determine p value. The p value for marginal integrity was found to be less than 0.01 which indicates that there is a significant difference between groups on buccal,lingual,mesial and distal surfaces . p value for occlusal discrepancy was found to be greater than 0.01 indicating that there is no significant difference between groups on occlusal mesial surfaces while distal side it is less than 0.01 which is significant.
 Summary and Conclusion: The patterns were prepared with inlay casting wax on the custom-made stainless steel die. 30 of the patterns were invested with a metal ring during investment. The vertical marginal gaps of three groups cast copings obtained by conventional casting were statistically significant to each other with higher value in group 2 followed by group 3 and group 1.

Comparison of Retention and Seating of Implant-Supported Hard and Soft Metal Copings.

Objectives:Implant-supported restorations are generally used for the replacement of the lost teeth. Stability against masticatory forces and proper retention are critical for optimal durability of restorations. The aim of this experimental study was to compare the retention of cobalt-chromium (Co-Cr) copings made by different techniques.Materials and Methods:Twenty-four solid abutment analogs were mounted and scanned with a desktop scanner. They were divided into two groups (n=12) and received metal copings fabricated by either soft or hard Co-Cr alloy. Soft Ceramill Sintron Co-Cr patterns were milled and sintered. Hard Co-Cr blocks were milled in a milling machine. The copings were sandblasted, polished, adjusted, and placed on the respective abutments. The frequency of adjustments was recorded for each abutment. The copings were cemented with zinc phosphate cement and underwent tensile test by a universal testing machine. The Mann-Whitney test and t-test were used to compare the two groups (α=0.05).Results:There was no significant difference in retention of copings between the experimental groups. The mean retentive force was 559.58±115.66 N and 557.13 ±130.48 N for the soft and hard metal groups, respectively (P=0.96). Considering the non-normal distribution of adjustment frequency data, the Mann-Whitney test showed that the frequency of adjustments was significantly higher in the hard metal group than the soft metal group (9.5 versus 0.1667; P<0.001).Conclusion:Although hard metal copings required more adjustments, retention of soft and hard Co-Cr copings was not significantly different.

Comparison of Marginal and Internal Fit of Different CAD/CAM Copings

This study compared the internal and marginal gap between CAD/CAM copings to determine the clinical acceptability. Hundred dental stone duplications of a metal major maxillary molar die were fabricated and separated into five. All copings were produced by milling and laser sintering method in the form of twenty groups. At x 180 magnification, marginal and internal gaps of each coping were measured at 75 points, and a total of 7500 measurements were performed for six regions on digital photographs taken with video microscope. Data were analyzed using one-way analysis of variance (ANOVA) and post hoc test (Tukey and Bonferroni). The internal and marginal gaps of the milling group were significantly larger than the laser sintering group (P All copings were presented clinically acceptable marginal and internal accuracy. Milling and laser sintering systems are suitable for manufacturing of copings.

Comparative Evaluation of the Marginal Adaptation of Cast Ni-Cr Copings, Direct Metal Laser Sintering Co-Cr Copings, and Computer-aided Design and Computer-aided Manufacturing Zr Copings: An In-vitro Study.

Background and purposeMarginal adaptation is critical for the long-term longevity and clinical success of dental restorations. Improper marginal adaptation may lead to oral fluids, resulting in microleakage and cement dissolution. The present in vitro study aimed to evaluate the marginal adaptation of nickel-chrome (Ni-Cr) copings, cobalt-chrome (Co-Cr) coping, and zirconium (Zr) copings, produced with different manufacturing procedures.Material and methodsA total of 45 copings were fabricated on a standardized metal die by using a two-stage putty impression and poured with die stone. They were divided into three groups of 15 each: A, B, and C. For group A, Ni-Cr copings were fabricated by conventional casting procedures; for group B, Co-Cr copings by direct metal laser sintering (DMLS); and for group C, zirconium copings by computer-aided design and computer-aided manufacturing (CAD/CAM) systems. Four areas around the tooth surface, namely, the mid-mesial, buccal, distal, and lingual surfaces, were digitally analyzed for marginal adaptation under the scanning electron microscope.ResultsThe mean marginal gap for group A on the mid mesial, buccal, distal, and lingual surfaces was 79.67, 83.27, 90.67, and 89.13 µm, respectively. The mean marginal gap for group B on the mid-mesial, buccal, distal, and lingual surfaces was 38.13, 46.20, 45.73, and 42.20 µm, respectively. The mean marginal gap for group C on the mid mesial, buccal, distal, and lingual surfaces was 36.73, 31.73, 29.00, and 30.53 µm, respectively.ConclusionThe marginal adaptation of CAD/CAM Zr copings is more accurate when compared to the DMLS Co-Cr and Cast Ni-Cr copings on a standard master die.

Effect of finish line design and metal alloy on the marginal and internal gaps of selective laser melting printed copings

Statement of problemSelective laser melting (SLM) technology has been introduced for printing metal dental restorations from Co-Cr base alloys or Au-Pt high noble alloys. However, information regarding the fit of restorations fabricated by using this technique is limited. PurposeThe purpose of this in vitro study was to determine the effect of 3 different finish line designs on the marginal and internal gaps of metal copings made from a base (Co-Cr), high noble (Au-Pd-Ag), and noble alloy (Co-Pd) by using the SLM technology. Material and methodsThree Ivorine right maxillary central incisors were prepared with a chamfer, deep chamfer, or shoulder finish line. The preparations were scanned by using a TRIOS scanner, and a total of 90 dies were printed using DPR 10 Resin (30×3 finish line designs). Ten SLM copings were fabricated for each margin design and metal alloy combination for a total of 90 copings (10×3 finish line designs×3 alloys). Copings were cemented onto dies using an autopolymerizing composite-resin luting material. All coping-die assemblies were sectioned buccolingually by using a low-speed diamond saw, and images were obtained by using an inverted bright field metallurgical microscope at ×100 magnification. Marginal and internal gaps were measured at 5 locations: buccal margin, midfacial, incisal, midlingual, and lingual margin. After gap measurements, representative specimens were embedded in autopolymerizing resin and prepared for metallographic examination. A 2-way multivariate analysis of variance (MANOVA) was conducted to determine the overall significance, followed by ANOVA for each dependent variable (α=.05). ResultsThe results indicated that alloy type and finish line had a significant influence on marginal gap of copings (P<.001). Relative to the internal gap, alloy type had a significant effect (P<.001), but the type of finish line had no statistically significant influence (P=.337). No statistically significant interactions occurred. Base alloys were printed with almost no observable porosity, whereas noble and high noble alloys exhibited hot tears and porosity. ConclusionsThefinish line type did not influence the internal gap between copings and dies, whereas the alloy type influenced the marginal gap between copings and dies. SLM-fabricated Co-Cr copings on teeth prepared with a deep chamfer finish line demonstrated the lowest marginal gap.

Comparative evaluation of marginal fit and axial wall adaptability of copings fabricated by metal laser sintering and lost-wax technique: An in vitro study.

Purpose:The present study aims to compare and evaluate the marginal fit and axial wall adaptability of Co-Cr copings fabricated by metal laser sintering (MLS) and lost-wax (LW) techniques using a stereomicroscope.Materials and Methods:A stainless steel master die assembly was fabricated simulating a prepared crown; 40 replicas of master die were fabricated in gypsum type IV and randomly divided in two equal groups. Group A coping was fabrication by LW technique and the Group B coping fabrication by MLS technique. The copings were seated on their respective gypsum dies and marginal fit was measured using stereomicroscope and image analysis software. For evaluation of axial wall adaptability, the coping and die assembly were embedded in autopolymerizing acrylic resin and sectioned vertically. The discrepancies between the dies and copings were measured along the axial wall on each halves. The data were subjected to statistical analysis using unpaired t-test.Results:The mean values of marginal fit for copings in Group B (MLS) were lower (24.6 μm) than the copings in Group A (LW) (39.53 μm), and the difference was statistically significant (P < 0.05). The mean axial wall discrepancy value was lower for Group B (31.03 μm) as compared with Group A (54.49 μm) and the difference was statistically significant (P < 0.05).Conclusions:The copings fabricated by MLS technique had better marginal fit and axial wall adaptability in comparison with copings fabricated by the LW technique. However, the values of marginal fit of copings fabricated that the two techniques were within the clinically acceptable limit (<50 μm).

Comparative Evaluation of Marginal Accuracy of Metal Copings Fabricated using Direct Metal Laser Sintering, Computer-Aided Milling, Ringless Casting, and Traditional Casting Techniques: An In vitro Study.

Purpose:The purpose of the study is to determine the amount of marginal discrepancy produced by Co-Cr copings fabricated using various fabrication methods which include direct metal laser sintering (DMLS), computer-aided milling, traditional casting, and ringless casting and compare the values obtained between each fabrication technique and to evaluate if the fabrication technique can produce prosthesis that is within the standards of clinical acceptance of marginal discrepancy.Materials and Methods:Ten metal copings were fabricated by DMLS, computer-aided milling, traditional casting, and ringless casting. Marginal gap at the buccal, lingual, mesial, and distal areas was measured using silicone replica technique. A digital microscope was used to measure the silicone layer. Statistical analysis was done using one-way ANOVA test and post hoc Bonferroni test to test the difference between the fabrication method and categories of measured points, respectively.Results:The values indicate that the marginal gap was least for the copings fabricated using ringless casting followed by traditional casting and DMLS. The widest gap was seen in copings fabricated using computer-aided milling. Analysis of results showed statistically significant difference between copings fabricated using computer-aided milling and traditional casting (P = 0.029 and 0.043 – mesial and distal, respectively) and computer-aided milling and ringless casting (P = 0.002 and 0.001 – mesial and distal, respectively).Conclusion:Even though the marginal gap was found to vary with the fabrication method, all measurements of marginal gap of all groups were well within the standard clinical acceptance of 120 μ.

In Vitro Comparison of Marginal Fit of All Metal, Porcelain Fused to Metal and All Ceramic Crowns

PURPOSE: To compare the marginal fit of all metal, porcelain fused to metal and all ceramic crowns fabricated using different materials and techniques commercially available. MATERIALS AND METHODS: 80 freshly extracted human mandibular first premolars were divided into 8 groups of 10 each which received Nickel-Chromium (Ni-Cr) all metal (AM) crowns, Cobalt-Chromium (Co-Cr) AM crowns, Ni-Cr three-quarter crowns, Co-Cr three quarter crowns, porcelain fused to metal (PFM) crowns with Ni-Cr copings, PFM crowns with Co-Cr copings, pressed all ceramic (AC) crowns and CAD/CAM fabricated AC crowns respectively. Crowns were cemented and specimen were sectioned buccolingually. The marginal gap was evaluated under a stereomicroscope. Lesser marginal gap indicated a better marginal fit. RESULTS: The mean marginal gap was maximum for Group 8 (222.3 μm) and least for Group 1 (85.5 μm). The mean marginal gaps for ‘all metal crowns’ and ‘metal ceramic crowns’ showed significantly lesser marginal gaps (p&lt;0.05) for Ni-Cr Groups than Co-Cr Groups. When only ‘all ceramic crowns’ were compared, significantly lesser marginal gap was found for pressed AC crowns (148.6 μm) than CAD/CAM fabricated AC crowns (222.3 μm). CONCLUSION: Marginal fit of AM crowns were significantly better than PFM crowns and AC crowns. Ni-Cr group always showed better marginal fit than Co-Cr group. A better marginal fit of pressed AC crowns was seen than CAD/CAM fabricated AC crowns. Chamfer finish line showed a significantly better marginal fit than shoulder finish line.

To Evaluate the Marginal Fit of Metal Copings Fabricated by Conventional Casting Procedure and Direct Metal Laser Sintering Technology – an In Vitro Study

Abstract Purpose: The purpose of this in vitro study was to evaluate marginal fit of cobalt- chromium (Co-Cr) copings fabricated by direct metal laser sintering system (DMLS) and conventional lost-wax technique (LW). Materials and method: Forty tooth preparations were carried out over extracted mandibular molars. They were divided into two groups A and B of 20 each. For group A Co-Cr copings were fabricated by direct metal laser sintering (DMLS) and for group B by lost wax technique (LW). Glass –ionomer cement (GIC) was used to tack the copings over their preparations. Marginal fit was then evaluated directly under the stereomicroscope. Results: The mean marginal gap of group A was 27.9 ± 2.4 μm and group B was 40.4 ±6 μm. Statistical analysis using t - test showed highly significant difference (P&gt;.05) between the marginal mean of the DMLS (group A) compared to LW (group B). Conclusion: The DMLS copings demonstrated superior marginal fit compared to that of conventional Co-Cr casted copings.

Evaluation of marginal and internal gaps of Ni-Cr and Co-Cr alloy copings manufactured by microstereolithography.

PURPOSEThe purpose of this study was to evaluate the marginal and internal gaps of Ni-Cr and Co-Cr copings, fabricated using the dental µ-SLA system.MATERIALS AND METHODSTen study dies were made using a two-step silicone impression with a dental stone (type IV) from the master die of a tooth. Ni-Cr (NC group) and Co-Cr (CC group) alloy copings were designed using a dental scanner, CAD software, resin coping, and casting process. In addition, 10 Ni-Cr alloy copings were manufactured using the lost-wax technique (LW group). The marginal and internal gaps in the 3 groups were measured using a digital microscope (160 ×) with the silicone replica technique, and the obtained data were analyzed using the non-parametric Kruskal-Wallis H test. Post-hoc comparisons were performed using Bonferroni-corrected Mann-Whitney U tests (α=.05).RESULTSThe mean (±standard deviation) values of the marginal, chamfer, axial wall, and occlusal gaps in the 3 groups were as follows: 81.5±73.8, 98.1±76.1, 87.1±44.8, and 146.8±78.7 µm in the LW group; 76.8±48.0, 141.7±57.1, 80.7±47.5, and 194.69±63.8 µm in the NC group; and 124.2±52.0, 199.5±71.0, 67.1±37.6, and 244.5±58.9 µm in the CC group.CONCLUSIONThe marginal gap in the LW and NC groups were clinically acceptable. Further improvement is needed for CC group to be used clinical practice.

Marginal and internal adaptation of milled cobalt-chromium copings

Statement of problemThe application of computer-aided design and computer-aided manufacturing (CAD/CAM) systems to produce complete coverage restorations with different materials continues to increase. To date, insufficient information is available regarding the adaptation of recently introduced milled cobalt-chromium (Co-Cr) copings for metal ceramic restorations. PurposeThe purpose of this in vitro study was to evaluate the marginal and internal fit of milled Co-Cr copings produced by CAD/CAM with 2 different marginal preparation designs. Material and methodsFour master dies were developed from 2 ivorine central incisors and 2 ivorine maxillary molars, 1 of each prepared with a 0.8-mm chamfer and a 1.2-mm rounded shoulder. These 4 groups of teeth were replicated with polyvinyl siloxane and used as templates to fabricate epoxy dies (n=10) for each of the 4 groups; a total of 40 epoxy resin dies. Cobalt-chromium copings of standard thickness (0.4 mm) were fabricated for each die with CAD/CAM technology. Next, the working dies were scanned with a 5-axis laser scanner to produce a 3-dimensional model. A thin layer of low-viscosity polyvinyl siloxane material was placed inside each coping and seated on the die until the material set. Copings were removed from the dies, leaving the polyvinyl siloxane intact, and these silicone-coated dies were scanned. The software superimposed the 2 scans, and the marginal openings and internal fit were measured at multiple locations. The marginal opening was determined at 4 locations: mid-buccal (mB), mid-lingual (mL), mid-mesial (mM), and mid-distal (mD), and the mean of these 4 measurement locations was referred to as the group variable “edge.” The internal occlusal adaptation was measured at the midpoint from buccal to lingual and mesial to distal locations and referred to as mid-occlusal (mO). Means and standard deviations for edge (marginal adaptation) and mO were calculated for each of the 4 groups. A 2-sample t test was performed to detect differences among groups. A regression analysis was done to evaluate the interaction between the variables mO and edge (α=.05). ResultsSignificantly smaller mean marginal openings (P=.017) were observed overall for the chamfer marginal design (anterior chamfer: 61 ±41 μm; posterior chamfer: 52 ±27 μm) compared with the shoulder design (anterior shoulder 103 ±49 μm, posterior shoulder 113 ±110 μm). The anterior chamfer had a statistically significant (P=.055) smaller mean marginal opening (61 ±41 μm) than the anterior shoulder (103 ±49 μm). No statistically significant differences (P=.119) were found between the posterior chamfer and posterior shoulder. The internal adaptation at the mO location was not significantly different among all 4 groups (P>.05). However, a regression analysis demonstrated a strong correlation (R=.842; P<.001) between the occlusal seat (mO) and marginal opening, with the smaller mean marginal opening of the chamfer design coinciding with the smaller occlusal seat values (61μm; mO: 182 μm) anterior chamfer; (52 μm; mO: 172 μm) posterior chamfer versus (103 μm; mO: 235 μm) anterior shoulder; (113 μm; mO: 242 μm) posterior shoulder. ConclusionsThe milled Co-Cr copings produced with a CAD/CAM system in this study demonstrated clinically acceptable marginal fit in the range of 52 to 113 μm before ceramic application.

Evaluation and comparison of the marginal adaptation of two different substructure materials.

PURPOSEIn this study, we aimed to evaluate the amount of marginal gap with two different substructure materials using identical margin preparations.MATERIALS AND METHODSTwenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables.RESULTSAccording to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, 24.47 ± 5.82 µm before and 35.11 ± 6.52 µm after cementation; in the laser-sintered Co-Cr structure, it was, on average, 60.45 ± 8.87 µm before and 69.33 ± 9.03 µm after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface.CONCLUSIONMarginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.

Influence of the accuracy of abutment tooth preparation on the marginal adaptation of Co-Cr alloy copings fabricated with a selective laser sintering technology

Purpose: The purpose of present study is to examine the correlation between the accuracy of abutment preparation and the marginal adaptation of metal coping. With this view, this study compared the correlations regard to the three different manufacturing methods of selective laser sintering technique, milling and casting. Materials and methods: Two master models were made in a different way. First model with deep chamfer margin was prepared directly by a general clinician and the second model was designed by 3-D designing software program with the same abutment preparation principle and produced by computer aided manufacturing. 12 Co-Cr alloy copings were produced respectively with three different method; SLS system, CAD/CAM milling and conventional lost wax technique from each master model. The total 72 copings fully sit on the master model were stereoscopically evaluated at 40 points along the entire circumferential margin. Results: Significant differences in the absolute marginal discrepancies of CoCr copings from SLS system (P=.0231) and casting method (P<.0001) were shown between hand preparation model and computer designed model. However, no significant difference was found between the two model groups from milling method (P=.9962). Conclusion: Within the limitation of this study, the effect of the accuracy of abutment preparation on the marginal adaptation of Co-Cr coping is statistically significant in SLS system and casting group. The copings produced by SLS system exhibited the lowest marginal discrepancies among all groups, and the marginal gap of this method group was influenced by the accuracy of the abutment preparation. (J Korean Acad Prosthodont 2015;53:337-44)