Conventional Lost-wax Technique Research Articles

Evaluation of shear bond strength of feldspathic porcelain on various laser surface treated cobalt-chromium discs

Brief Background The aim of the study is to compare and evaluate shear bond strength of porcelain fused to metal substructure fabricated using conventional method, surface treated with different laser modalities and direct metal laser sintering. Material and Methods Forty samples made of Co-Cr were fabricated, divided into control (Group A) and three test groups (Group B, Group C, Group D) (n=10 each). Groups A, C, D samples were made by conventional lost wax technique and B by laser sintering. All the samples were sandblasted and group C and D were surface treated with Nd: YAG and Er: YAG lasers respectively. Further, samples were veneered using 2mm of porcelain. The samples were placed in a jig and held in a universal testing machine to test the bond strength between Co-Cr and porcelain. Samples were subjected to shear stress until the fracture occurred and the results were noted. Data analysis was done using one- way analysis of variance and Post-Hoc test. Result The mean shear bond strength was highest in group D (Er: YAG laser treated Co-Cr), then group B (Laser sintered Co-Cr), then group A (Sandblasted Co-Cr) and group C (Nd: YAG laser treated Co-Cr) which was the least. Conclusion All the groups showed significant difference in shear bond strength. Er: YAG laser surface treated Co- Cr had highest bond strength to porcelain, then laser sintered Co-Cr, followed by sandblasted Co-Cr and least Nd: YAG surface treated Co- Cr. Key Words Er:YAG Laser, Nd:YAG Laser, Conventional technique, Co-Cr alloy, DMLS, Porcelain, Shear bond strength.

The Dimensional Changes of Clasp Arm in Removable Partial Denture Frameworks Fabricated Through DMLS and Conventional Lost Wax Technique: An In Vitro Study

AIM: The aim of the present study is to evaluate the effect of CAD designing on the dimensions of the clasp arm. METHODOLOGY: A Kennedy Class III mod I cast was selected as the reference cast. Samples were divided into 2 groups, Group I with DMLS and Group II with Conventional lost wax technique. Three reference points were selected on the clasp arm and the vertical dimensions were measured in the digital design and compared it with the dimensions at the same points in the final framework. RESULTS: There was slight expansion in group 1 (p-value > 0.05) with mean of -0.035 and standard deviation 0.088. And there was decrease in dimensions in the clasp arm in group 2 (p-value < 0.05) with mean of 0.1741 and standard deviation 0.081. CONCLUSION: From the present study, it was concluded that the dimensions of the clasp arm of DMLS framework increased slightly, whereas the there was significant decrease in the clasp arm dimensions in the framework produced through conventional lost wax technique. Both the frameworks had clinically acceptable fit.

Accuracy of fit for cobaltchromium bar over two implants fabricated with different manufacturing techniques: an in-vitro study

ObjectiveThe purpose of the invitro research was to compare the fit of Cobalt Chromium customized bar fabricated with different manufacturing processes cast metal bar, milled bar and 3D printed bar using scanning electron microscope.Materials and methodsClear epoxy resin molds were prepared. In each mold two parallel implants with a 14 mm distance from each other were embedded. Thirty Co-Cr custom bars were constructed and were divided equally into three groups: Group (I) (Co-Cr conv), group (II) milled bar (Co-Cr milled), and group (III) printed bar (Co-Cr print). The marginal fit at implant-abutment interface was scanned using scanning electron microscope (SEM).ResultsThere was a significant difference between the three studied groups regarding marginal misfit the between implant and fabricated bars with p-value < 0.001. The highest value of micro-gap distance was found in Co-Cr conventional group (7.95 ± 2.21 μm) followed by Co-Cr 3D printed group (4.98 ± 1.73) and the lower value were found in Co-Cr milled (3.22 ± 0.75).ConclusionThe marginal fit of milled, 3D printed and conventional cast for Co-Cr alloy were within the clinically acceptable range of misfit. CAD/CAM milled Co-Cr bar revealed a superior internal fit at the implant-abutment interface. This was followed by selective laser melting (SLM) 3D printed bar and the least fit was shown for customized bar with the conventional lost wax technique.

EFFECT OF REPEATED FIRINGS ON METAL CERAMIC BOND STRENGTH OF CO-CR ALLOY FABRICATED BY DIRECT METAL LASER SINTERING AN IN-VITRO STUDY

Purpose: The bond strength of metal ceramic restorations places a key role for the longevity of the prosthesis which could be affected by the fabrication technique and the number of firings. The current research evaluates the effect of repeated firings on bond strength of metal ceramic systems with copings fabricated from two processing techniques, lost wax technique through induction casting and direct metal laser sintering. Materials and Methods: 21 metal ceramic bars will be fabricated using Direct Metal Laser Sintering (Group DMLS) and 21 using conventional lost wax technique (Group Cast). Each sample will have a dimension of 25x3x0.5mm respectively. In the center of each bar, a 1.1mm thickness of porcelain will be fused onto an 8x3mm rectangular area. Each group is further subdivided into 3 subgroups which are subjected to repeated firings (3, 5, 7) and the bond strength is measured with positioning of the samples on a Universal Testing Machine. Results: Group ANOVA and Post Hoc Tukeys test showed comparison of overall bond strength of ceramic samples fabricated using DMLS &amp; Casting subjected to different Firing was done and the difference in mean was statistically significant (p&lt;0.05). Conclusion: The DMLS group showed slight superior bond strength properties when compared with Cast group.

Clinical Applications of Polyetheretherketone in Removable Dental Prostheses: Accuracy, Characteristics, and Performance.

The high-performance thermoplastic polyetheretherketone (PEEK) has excellent mechanical properties, biocompatibility, chemical stability, and radiolucency. The present article comprehensively reviews various applications of PEEK in removable dental prostheses, including in removable partial dentures (RPDs) (frameworks and clasps), double-crown RPDs, and obturators. The clinical performance of PEEK in removable dental prostheses is shown to be satisfactory and promising based on the short-term clinical evidence and technical complications are scarce. Moreover, the accuracy of RPDs is a vital factor for their long-term success rate. PEEK in removable dental prostheses is fabricated using the conventional lost-wax technique and CAD/CAM milling, which produces a good fit. Furthermore, fused deposition modeling is considered to be one of the most practical additive techniques. PEEK in removable prostheses produced by this technique exhibits good results in terms of the framework fit. However, in light of the paucity of evidence regarding other additive techniques, these manufacturers cannot yet be endorsed. Surface roughness, bacterial retention, color stability, and wear resistance should also be considered when attempting to increase the survival rates of PEEK removable prostheses. In addition, pastes represent an effective method for PEEK polishing to obtain a reduced surface roughness, which facilitates lower bacterial retention. As compared to other composite materials, PEEK is less likely to become discolored or deteriorate due to wear abrasion.

Accuracy of Removable Partial Denture Frameworks Fabricated Using Conventional and Digital Technologies.

This study analyzed the fit accuracy of the removable partial denture (RPD) metal frameworks produced using digital and conventional manufacturing technologies. Mandibular RPD metal frameworks (N=15, n=3 per group) were fabricated on a representative clinical case. RPDs were fabricated using one of the following manufacturing procedures: a) conventional lost-wax casting technique (C-LW), b) conventional casting of milled sacrificial patterns (C-M), c) conventional casting of printed sacrificial patterns (C-P), d) selective laser melting (SLM), e) direct metal laser sintering (DMLS) technologies. The fit accuracy of RPD frameworks was analyzed by fabricating replicas with silicone registration material and measuring with a digital microscope. A total of 11 sites and 29 areas in the RPD metal frameworks were considered for the accuracy measurements (μm). Data were statistically analyzed using Wilcoxon signed rank and Friedman test (α=0.05). Before finishing and polishing, C-M method presented overall significantly better (P⟨.001) fit accuracy (118 μm) than those of other methods (195-265 μm). After finishing and polishing, C-M method showed overall significantly better (P⟨.033) fit accuracy (205.7 μm) than C-LW and SLM methods (285.7 μm; 249 μm) and comparable fit accuracy to that of C-P and DMLS methods. Accuracy at the minor and major connector areas of RPDs were affected from the manufacturing technologies. Clinical Implications: When accuracy of RPDs are considered, digital technologies tested presented similar results to those of conventional manufacturing method except for minor and major connector areas which necessitates further improvement.

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.

ИЗУЧЕНИЕ ТОЧНОСТИ ПРИЛЕГАНИЯ МЕТАЛЛИЧЕСКИХ КАРКАСОВ НЕСЪЁМНЫХ ЗУБНЫХ ПРОТЕЗОВ В ЗАВИСИМОСТИ ОТ ИХ ПРОТЯЖЁННОСТИ

Objective: To carry out a comparative analysis of the accuracy of the adherence of tooth-supported cast and milled cobalt chrome alloy frameworks in the shoulder area depending on the length of the prostheses. Methods: For the clinical trial 314 patients who needed metal-ceramic fixed dental prostheses (FDPs) were recruited. Metal frameworks of prostheses were made with conventional lost-wax technique (CLW) and computer aided design and manufacturing (CAD/CAM). To assess the accuracy of the adhesion of the frameworks to the ledges of the prepared teeth stumps, the silicon film between the abutment teeth and inner surface of crowns was obtained, cut into 8 pieces and measured in the shoulder area. The marginal gaps were measured using ImageJ2 application from digital photos obtained with calibrated digital microscope (250×). The data obtained were analyzed using the non-parametric Kruskal-Wallis H-test and Mann- Whitney U-test. Results: The average values of the marginal gap in the CLW group ranged from 71.9±7.6 μm in single and double crowns to 117±3.7 μm in prostheses with a length of 7-8 units. With a corresponding increase in the length of the prostheses, the average values of the marginal gap in the CAD/CAM group were from 67.1±6.8 μm to 90.8±8.3 μm. Differences in marginal clearance parameters between all groups were statistically significant (p&lt;0.05), except for the group of single and paired crowns with milled caps. Conclusion: The values of the edge gap in all groups were within the acceptable range. However, CAD/CAM frameworks were significantly more accurate in long-length prostheses. Keywords: Teeth prep, CAD/CAM, accuracy of the fit, ledge, precision of the fit, marginal gap.

Lost-wax or laser sintering? Findings on marginal and internal adaptation of metallic copings

Marginal and internal adaptation are parameters of crucial importance to the success of prosthetic crowns. Automatized process creates an expectative of superior or equivalent results compared to restorations manufactured ​​by conventional lost-wax technique. The purpose of this study was to evaluate the marginal adaptation and internal adaptation (cement space) of metal-ceramic crown copings produced by lost-wax (LW) and direct metal laser sintering (DMLS) techniques. An artificial lower first molar was prepared for a full crown, duplicated in plaster and scanned. Twenty metal-ceramic crown copings were fabricated in cobalt-chromium by the two techniques (n=10). The copings were filled with low viscosity silicone and seated on the prepared tooth, resulting in a replica of the internal space. The pellicle formed was embedded in heavy body silicone, sectioned and captured by means of a stereomicroscope at 50x magnification, according to replica technique (RT). Shapiro-Wilk test followed by Holm-Sidak test were used for statistical analysis (α=.05). Marginal adaptation presented no difference between LW (101.5 ± 41.6) and DMLS (86.3 ± 39.9) groups (p=0.24). Conventional LW technique showed significantly lower occlusal (p&lt;0.008) and axial spaces (p&lt;0.03). Measurements of all regions showed numerically larger adaptation values than that defined during design​​ for DMLS group. Both the LW technique and the DMLS technique are within the clinically acceptable.

Retention Force of Removable Partial Dentures with CAD-CAM-Fabricated Telescopic Crowns.

The aim of this study was to compare the retention forces after artificial aging of telescopic crowns fabricated either by a conventional lost-wax technique or by computer-aided design/computer-aided manufacturing (CAD-CAM) technology. Two types of telescopic crowns (0°) were fabricated conventionally using high-noble (group A) and non-precious metal (group B). CAD-CAM fabricated telescopic crowns (0°) were made of non-precious metal (group C). Retention forces were assessed before and after artificial aging and after axial and non-axial loading. Initially [I.] and after artificial aging [IV.], specimens of group C (I. 16.2 N; IV. 13.6 N) exhibited the highest retention forces. The retention forces in groups B (I. 12.5 N; IV. 4.6 N) and A (I. 9.6 N; IV. 2.9 N) were found to be lower than those of group C. The retention force differences between the groups were statistically significant (p < 0.001) at all measurement times [I. vs. IV.]. Different fabricated telescopic crowns with approximately identical designs and materials exhibited different retention forces and different long-term retentive behavior. An optimized CAD-CAM process with individually defined design parameters ensured telescopic crowns with a better fit. These findings might influence prospective clinical decision-making.

The Fit Accuracy of Removable Partial Denture Metal Frameworks Using Conventional and 3D Printed Techniques: An In Vitro Study

To evaluate the accuracy of removable partial denture (RPD) metal frameworks fabricated by the conventional lost-wax (CLW) technique and those made by the selective laser melting (SLM). A dentoform of a mandibular Kennedy class III, modification 1 dental arch were surveyed, and rest seats were prepared on the abutment teeth. The dentoform was then duplicated into a metal die which was used as a reference model. Thirty RPD metal frameworks were fabricated by two techniques; fifteen for each technique. Polyvinyl siloxane (PVS) impression material was painted on the intaglio surface of the rests of each framework which is then seated on the reference die. PVS specimens that represent the gap under the rest were measured in four zones: buccal, lingual, marginal and central by a single examiner using a digital microscope at 50x in micrometers. Comparison between the two techniques for each abutment tooth revealed that the CLW technique had better fit in one tooth, while the SLM technique showed a better fit in two teeth. Regarding the edentulous span length within the SLM technique, the long edentulous span had a significantly better fit. When comparing the four measured rest zones, it was found that in the CLW technique group, the marginal zone had the highest fit accuracy while the lingual zone showed the lowest fit accuracy. In the SLM group, the central zone had the best fit and the buccal zone had the worst fit. RPD frameworks fabricated using the SLM technique showed better fit accuracy than those made by the CLW technique, however, the difference was not statistically significant. SLM is a promising technique for the fabrication of RPD frameworks in routine clinical practice.

Comparison of bond strength and fracture toughness of metal–ceramic restorations fabricated by conventional lost-wax technique and selective laser sintering

Introduction: Porcelain fused to metal is the most common restoration. The success of the prosthesis greatly depends on the mechanical bonding between the metal alloy and the ceramic. Newer techniques such as selective laser sintering (SLS) and computer-aided design are fast replacing the lost-wax technique due to ease of fabrication. This study was carried out to ascertain the best possible technique to ensure success. Materials and Methods: Forty strips of cobalt–chromium (Co–Cr) metal were fabricated and divided into two groups (lost-wax technique vs. SLS technology), which were then bonded with ceramic and compared for bond strength and fracture toughness. Results: SLS group showed higher bond strength than conventional lost-wax technique (CAST) group but lowered fracture toughness. This difference was also found to be statistically significant. Conclusion: The lost-wax technique is a time-tested method that needs not be abandoned until successful evolution of emerging technologies is firmly established.

Evaluation of the fit of metal copings fabricated using stereolithography

Statement of problemRapid prototyping, including stereolithography (SLA), is a more recent technique for fabricating metal frameworks than the conventional lost-wax technique. However, investigations of the marginal discrepancies and internal spacing of cobalt-chromium (Co-Cr) metal copings fabricated using SLA are lacking. PurposeThe purpose of this in vitro study was to evaluate the clinical acceptability of the marginal discrepancies and internal spacing of Co-Cr metal copings fabricated using the SLA technique. Material and methodsA resin tooth of a maxillary right first premolar was prepared with a deep chamfer margin for a metal–ceramic crown. Titanium master dies were milled after scanning the prepared tooth (n=45). In conventional lost wax group (group LW), the conventional lost-wax technique was used to fabricate Co-Cr metal copings (n=15). In milling group (group MC), a computer-aided design (CAD) system was used to design the metal copings, which were milled from Co-Cr alloy (n=15). The CAD system was also used to design the metal copings in a 3D-printed group (group SL), and Co-Cr metal copings were cast from resin patterns fabricated using the SLA device (n=15). Marginal discrepancies and internal spaces were measured using an optical microscope at ×100 magnification at 11 reference points. The values were analyzed statistically with 1-way analysis of variance (α=.05). ResultsThe mean (±SD) overall space was 63.2 ±16.6 μm for group LW, 70.2 ±15.5 μm for group SL, and 130.3 ±13.8 μm for group MC. The overall spaces differed significantly between group MC and the other 2 groups (P<.05). The marginal discrepancy and internal spaces were significantly larger in group MC than in groups LW and SL. (P<.05). Occlusal spaces differed significantly among the 3 study groups (P<.05). ConclusionsCo-Cr metal copings fabricated using an SLA technique showed clinically acceptable marginal discrepancies and internal spaces. These spaces did not differ significantly from those obtained with the conventional lost-wax technique.

Marginal accuracy of computer-aided design- and computer-aided manufacturing-fabricated full-arch zirconia restoration.

ObjectiveThis study evaluated marginal accuracy of full-arch zirconia restoration fabricated from two digital computer-aided design and computer-aided manufacturing (CAD-CAM) systems (Trios-3 and CS3500) in comparison to conventional cast metal restoration.Materials and methodsA stainless steel model comprising two canine and two molar abutments was used as a master model for full-arch reconstruction. The canine and molar abutments were machined in a cylindrical shape with 5° taper and chamfer margin. The CAD-CAM systems based on the digital approach were used to construct the full-arch zirconia restoration. The conventional cast metal restoration was fabricated according to a conventional lost-wax technique using nickel–chromium alloys. Ten restorations were fabricated from each system. The marginal accuracy of each restoration was determined at four locations for each abutment. An analysis of variance (ANOVA) and Tukey’s honest significant difference (HSD) multiple comparisons were used to determine statistically significant difference at 95% confidence interval.ResultsThe mean values of marginal accuracy of restorations fabricated from conventional casting, Trios-3, and CS3500 were 48.59±4.16 μm, 53.50±5.66 μm, and 56.47±5.52 μm, respectively. ANOVA indicated significant difference in marginal fit of restorations among various systems. The marginal discrepancy of zirconia restoration fabricated from the CS3500 system demonstrated significantly larger gap than that fabricated from the 3Shape system (p<0.05). Tukey’s HSD multiple comparisons indicated that the zirconia restoration fabricated from either CS3500 or Trios-3 demonstrated a significantly larger marginal gap than the conventional cast metal restoration (p<0.05).ConclusionFull-arch zirconia restoration fabricated from the Trios-3 illustrated better marginal fits than that from the CS3500, although, both were slightly less accurate than the conventional cast restoration. However, the marginal discrepancies of restoration produced by both CAD-CAM systems were within the clinically acceptable range and satisfactorily precise to be suggested for construction full-arch zirconia restoration.

Comparative evaluation of the dimensional accuracy of cast partial denture frameworks fabricated by conventional technique and light-cure wax technique: An in vitro study

BACKGROUND: Removable partial dentures are an economical way of replacing lost structures, especially in cases where FPD or implants are not possible. Metal alloys by the conventional lost-wax technique are the most common way of fabricating such dentures which can be done by using either conventional casting wax or light-cure wax. PURPOSE: The objective of this study is to evaluate and compare the dimensional accuracy of cast partial denture frameworks fabricated using conventional casting wax and light-cure wax. MATERIALS AND METHODS: This in vitro studied was carried out in the Department of Prosthodontics and Crown and Bridges, and Department of Oral Pathology and Microbiology, KAHE's KLE VK Institute of Dental Sciences, Belagavi. A total of 30 samples were included in the study divided into two groups as follows: Group 1: cast partial denture frameworks fabricated using conventional casting wax and Group 2: cast partial denture frameworks fabricated using light-cure wax. A partially edentulous Kennedy's Class III Mod 1 metal die was created, which was then duplicated using a silicone duplicating material to form a master mold. 15 refractory (phosphate bonded investment) and 15 stone (Type III gypsum) casts were poured according to the manufacturer's instructions onto which conventional casting wax and light-cure wax was adapted, respectively, followed by subsequent investing and casting using cobalt–chromium alloy. The final frameworks were finished and polished and checked for dimensional accuracy by assessing the dimensional fit and the linear dimensional change. The dimensional fit was evaluated by measuring the gap between the palatal major connector and the palatal portion of the metal die at five different points: at midline, at 5 mm, and at 10 mm on either side of the midline, by interposing pattern resin between the two and checking thickness under a stereomicroscope. The linear dimensional change was assessed by calculating the difference of the distance between two specific points on the die and the frameworks. The data were subjected to independent t-test (P RESULTS: The dimensional fit of the Group 1 frameworks using conventional casting wax was 748.25 μm and Group 2 using light-cure wax was 794.02 μm. The result was statistically insignificant. The linear dimensional changes observed for Group 1 and Group 2 were 0.78 mm and 0.63 mm, respectively. The result was statistically insignificant. CONCLUSION: There was no significant difference between the dimensional accuracies of the cast partial denture frameworks fabricated using conventional casting wax and light-cure wax. Hence, the light-cure wax fabrication method can be considered as an alternative for the cast partial denture framework fabrication, as it is simple and much less time-consuming.

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.

Comparison of porcelain bond strength of different metal frameworks prepared by using conventional and recently introduced fabrication methods

Statement of problemMost studies evaluating dental laser sintering systems have focused on the marginal accuracy of the restorations. However, the bond strength at the metal-ceramic interface is another important factor that affects the survival of restorations, and currently, few studies focus on this aspect. PurposeThe purpose of this in vitro study was to compare the porcelain bond strength of cobalt-chromium (Co-Cr) metal frameworks prepared by using the conventional lost-wax technique, milling, direct metal laser sintering (DMLS), and laser cusing, a direct process powder-bed system. Material and methodsA total of 96 metal frameworks (n=24 in each group) were prepared by using conventional lost-wax (group C), milling (group M), DMLS (group LS), and direct process powder-bed (group LC) methods according to International Organization for Standardization standard ISO 9693-1. After porcelain application, a 3-point bend test was applied to each specimen by using a universal testing machine. Data were statistically analyzed using 1-way ANOVA and Tukey honest significant difference tests (α=.05). Failure types at the metal-ceramic interfaces were examined using stereomicroscopy. Additionally, 1 specimen from each group was prepared for scanning electron microscopy analysis to evaluate the surface topography of metal frameworks. ResultsThe mean bond strength was 38.08 ±3.82 MPa for group C, 39.29 ±3.51 MPa for group M, 40.73 ±3.58 MPa for group LS, and 41.24 ±3.75 MPa for group LC. Statistically significant differences were observed among the 4 groups (P=.016). All groups, except for LS, exhibited adhesive and mixed type bond failure. ConclusionsBoth of the laser sintering methods were found to be successful in terms of metal-ceramic bond strength.

Marginal fit of all-ceramic crowns fabricated using two extraoral CAD/CAM systems in comparison with the conventional technique.

ObjectiveThe purpose of this study was to determine the effect of two extraoral computer-aided design (CAD) and computer-aided manufacturing (CAM) systems, in comparison with conventional techniques, on the marginal fit of monolithic CAD/CAM lithium disilicate ceramic crowns.Study designThis is an in vitro interventional study.Place and duration of studyThe study was carried out at the Department of Prosthodontics, School of Dentistry, Prince Sattam Bin Abdul-Aziz University, Saudi Arabia, from December 2015 to April 2016.MethodologyA marginal gap of 60 lithium disilicate crowns was evaluated by scanning electron microscopy. In total, 20 pressable lithium disilicate (IPS e.max Press [Ivoclar Vivadent]) ceramic crowns were fabricated using the conventional lost-wax technique as a control group. The experimental all-ceramic crowns were produced based on a scan stone model and milled using two extraoral CAD/CAM systems: the Cerec group was fabricated using the Cerec CAD/CAM system, and the Trios group was fabricated using Trios CAD and milled using Wieland Zenotec CAM. One-way analysis of variance (ANOVA) and the Scheffe post hoc test were used for statistical comparison of the groups (α=0.05).ResultsThe mean (±standard deviation) of the marginal gap of each group was as follows: the Control group was 91.15 (±15.35) µm, the Cerec group was 111.07 (±6.33) µm, and the Trios group was 60.17 (±11.09) µm. One-way ANOVA and the Scheffe post hoc test showed a statistically significant difference in the marginal gap between all groups.ConclusionIt can be concluded from the current study that all-ceramic crowns, fabricated using the CAD/CAM system, show a marginal accuracy that is acceptable in clinical environments. The Trios CAD group displayed the smallest marginal gap.

Marginal and internal fit of cobalt-chromium copings fabricated using the conventional and the direct metal laser sintering techniques: A comparative in vitro study.

Background and Objectives:This in vitro study seeks to evaluate and compare the marginal and internal fit of cobalt-chromium copings fabricated using the conventional and direct metal laser sintering (DMLS) techniques.Methods:A master model of a prepared molar tooth was made using cobalt-chromium alloy. Silicone impression of the master model was made and thirty standardized working models were then produced; twenty working models for conventional lost-wax technique and ten working models for DMLS technique. A total of twenty metal copings were fabricated using two different production techniques: conventional lost-wax method and DMLS; ten samples in each group. The conventional and DMLS copings were cemented to the working models using glass ionomer cement. Marginal gap of the copings were measured at predetermined four points. The die with the cemented copings are standardized-sectioned with a heavy duty lathe. Then, each sectioned samples were analyzed for the internal gap between the die and the metal coping using a metallurgical microscope. Digital photographs were taken at ×50 magnification and analyzed using measurement software. Statistical analysis was done by unpaired t-test and analysis of variance (ANOVA).Results:The results of this study reveal that no significant difference was present in the marginal gap of conventional and DMLS copings (P > 0.05) by means of ANOVA. The mean values of internal gap of DMLS copings were significantly greater than that of conventional copings (P < 0.05).Conclusions:Within the limitations of this in vitro study, it was concluded that the internal fit of conventional copings was superior to that of the DMLS copings. Marginal fit of the copings fabricated by two different techniques had no significant difference.

Influence of porcelain firing and cementation on the marginal adaptation of metal-ceramic restorations prepared by different methods

Statement of problemMarginal adaptation plays an important role in the survival of metal-ceramic restorations. Porcelain firings and cementation may affect the adaptation of restorations. Moreover, conventional casting procedures and casting imperfections may cause deteriorations in the marginal adaptation of metal-ceramic restorations. PurposeThe purpose of this in vitro study was to compare the marginal adaptation after fabrication of the framework, porcelain application, and cementation of metal-ceramic restorations prepared by using the conventional lost-wax technique, milling, direct metal laser sintering (DMLS), and LaserCUSING, a direct process powder-bed system. Alterations in the marginal adaptation of the metal frameworks during the fabrication stages and the precision of fabrication methods were evaluated. Material and methodsForty-eight metal dies simulating prepared premolar and molar abutment teeth were fabricated to investigate marginal adaptation. They were divided into 4 groups (n=12) according to the fabrication method used (group C serving as the control group: lost-wax method; group M: milling method; group LS: DMLS method; group DP: direct process powder-bed method). Sixty marginal discrepancy measurements were recorded separately on each abutment tooth after fabrication of the framework, porcelain application, and cementation by using a stereomicroscope. Thereafter, each group was divided into 3 subgroups according to the measurements recorded in each fabrication stage: subgroup F (framework), subgroup P (porcelain application), and subgroup C (cementation). Data were statistically analyzed with univariate analysis of variance (followed by 1-way ANOVA and Tamhane T2 test (α=.05). ResultsThe lowest marginal discrepancy values were observed in restorations prepared by using the direct process powder-bed method, and this was significantly different (P<.001) from the other methods. The highest marginal discrepancy values were recorded after the cementation procedure in all groups. ConclusionsThe results showed that the direct process powder-bed method is quite successful in terms of marginal adaptation. The marginal discrepancy increased after porcelain application and cementation.