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ORIGINAL ARTICLE
Year : 2019  |  Volume : 22  |  Issue : 6  |  Page : 812-816

In vitro marginal and internal adaptation of metal-ceramic crowns with cobalt-chrome and titanium framework fabricated with CAD/CAM and casting technique


Department of Prosthodontics, Faculty of Dentistry, Ege University, Izmir, Turkey

Date of Acceptance28-Feb-2019
Date of Web Publication12-Jun-2019

Correspondence Address:
Dr. E Tamac
Department of Prosthetic Dentistry, Faculty of Dentistry, Ege University, Bornova-Izmir - 35100
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_570_18

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   Abstract 


Aim: The purpose of this study was to compare the marginal and internal fit of Co-Cr and titanium ceramic crowns fabricated with 2 different techniques: CAD/CAM milling and traditional casting (TC). Materials and Methods: Ten traditional casting of Co-Cr (TCC), 10 CAD/CAM milling of Co-Cr (MC), 10 traditional casting of titanium (TCT), 10 CAD/CAM milling of titanium ceramic crowns (MT) were fabricated. Silicone replicas were obtained to measure internal gap volume, marginal gap and internal adaptation that was evaluated at 3 regions: axial wall, axio-occlusal angle, and occlusal surface. Measurements were made with a X-ray micro computerized tomography (micro-CT) and analyzed with Bonferroni and Dunnet T3 post-hoc tests (α = 0.05). Results: One-way ANOVA revealed no statistically significant differences among the groups for measurements at the marginal gap (P > 0.05). At axial wall region the mean values of TCT group were higher than those of groups but only statistically not significant for TCC group (P < 0.05). TCC group statistically gives better results than MC group in axio-occlusal and occlusal regions (P < 0.05). The mean measurement of internal gap volume were 20.59 ± 0.83 mm3 for TCC, 22.73 ± 0.82 mm3 for MC, 22.83 ± 1.11 mm3 for TCT and 20.51 ± 1.16 mm3 for MT. Mean internal gap volume values MT group were smaller than those of groups but only statistically not significant for TCC group (P > 0.05). Conclusion: All groups performed similar marginal adaptation. The cement film thickness at axio-occlusal angle point and occlusal region were higher for MC crowns.

Keywords: CAD/CAM, casting, marginal and internal fit, titanium


How to cite this article:
Gurel K, Toksavul S, Toman M, Tamac E. In vitro marginal and internal adaptation of metal-ceramic crowns with cobalt-chrome and titanium framework fabricated with CAD/CAM and casting technique. Niger J Clin Pract 2019;22:812-6

How to cite this URL:
Gurel K, Toksavul S, Toman M, Tamac E. In vitro marginal and internal adaptation of metal-ceramic crowns with cobalt-chrome and titanium framework fabricated with CAD/CAM and casting technique. Niger J Clin Pract [serial online] 2019 [cited 2019 Jun 24];22:812-6. Available from: http://www.njcponline.com/text.asp?2019/22/6/812/260042




   Introduction Top


Base metal fused ceramic crowns are widely used due to their easy manifacturing and accuracies, high bonding strenght features and esthetical appearance of porcelain.[1] Because the restoration margins are often subgingivally placed, the metal should be biocompatible.

Titanium frameworks have been gaining popularity since 1990s as an alternative to base and noble metal alloys becaouse of its biocompatibility, low thermal conductivity, nominal density, and unique corrosion resistance.[2],[3]

Although many advantages of titanium; casting of titanium, bonding behaviour between titanium to porcelain, and titanium porcelain firing have some difficulties.[4] Molten titanium has an affinity to the dental investment and casting atmosphere which causes reactive oxygen rich layer called alpha-case layer.[5] With casting titanium, surface becomes chemically contaminated. Alpha-case layer is a crackable, frangible, and pore containing non homogeneous sheet. This reactive layer affects the bonding process of titanium framework to porcelain, and marginal accuracy.[6]

Furthermore several methods have been reported to solve titanium casting problems. Modified air pressure, burn-out tempreture, different investment materials, machined dublication and spark erosion have been recommended.[7] Veneering process of titanium is inconvenient due to over oxidation of titanium during firing. To prohibit oxidation, sandblasting, shot-peening, bonding agents, silicon coating, gold and nitride coating, sodium hydroxide anodization, electrical discharge machining, acid and caustic baths are used.[4],[8],[9],[10],[11],[12],[13]

At the end of the 20th century computer-aided design and computer-aided manifacturing (CAD/CAM) technology started to glamor the dental professionals to make copings simpler and faster.[14],[15] Titanium was one of the first metals in that technology as its biologic and mechanical features.[5] Beside conventional casting, spark erosion, and laser welding; milling titanium does not form a reactive surface layer.[16]

Long-term clinical success of restorations is generally influenced by the marginal and internal fit of restorations. An inaccurate marginal fit is responsible for cement solubility and plaque retention, periodontal disease and endodontic inflammation.[17] Several authors have investigated the marginal and internal fit of titanium ceramic crowns.[1],[3],[16],[18],[19] However, there is few information on the marginal and internal fit of titanium crowns. Therefore, the purpose of this study was to compare the marginal and internal fit of Co-Cr and titanium ceramic crowns fabricated with 2 different techniques: CAD/CAM milling and traditional casting (TC). The null hypothesis was there is no difference would be found on marginal-internal gap value and internal gap volume among the 4 groups.


   Materıals and Methods Top


A hard thermosetting plastic analog of the left first mandibular molar (Frasaco GmbH Tettnang, Germany) was prepared with round-end diamond rotary cutting instrument (Komet Dental Gebr. Brasseler GmbH & Co. KG, Lemgo, Germany) with a circumferential deep chamfer margin (1.2 mm in width) was created and occlusal reduction of 1.5 to 2 mm was performed. The total convergence angle was 16°. Analog model based on a flat plane with the help of type 4 dental stone (Silky-Rock. Whip-Mix Corporation, Loisville, USA) before digitized the model. Analog model scanned (7series 3D scanners, Dental Wings Inc, Canada) to create cobalt-chronium (EOS Cobalt Chrome SP2; %61.8-65.8 Co, %23.7-25.7 Cr, %4.6-5.6 Mo, %4.9-5.9 W, %0.8-1.2 Si, %0.5 Fe, %0.1 Mn, EOS GmbH, Germany) master model with direct metal laser sintering (Eosint M 270; EOS GmbH, Germany).

Traditional casting of Co-Cr (Microlit Isı; %61.1 Co, %27,8 Cr, %8.5 W, MANI Schütz Dental Group, Germany) metal frameworks performed (n = 10) as a control group. CAD/CAM milling (DMG MORİ HSC 20 Linear DECKEL MAHO; Stuttgart, Germany) of Co-Cr alloy blocks (CopraBond K CoCr milling blank; %61 Co, %28 Cr, %8,5 W, %0,25 Mn, %0,5 Fe, %1,65 Si, %0,1 C, Whitepeaks Dental Systems, Wesel, Germany) performed as second group. Casting of titanium (Dentaurum Tritan; Ti min. %99, 5, bal Fe, O, H, N, C) metal frameworks (n = 10) and CAD/CAM milling (DMG MORİ HSC 20 Linear DECKEL MAHO; Stuttgart, Germany) of titanium metal frameworks (Copra Ti-5 milling blank; Whitepeaks Dental Systems, Wesel, Germany) were fabricated as third and fourth group of this study.

For the cast groups 2 coats of die spacer (Alpha die MF; MANI Schütz Dental Group, Germany) was applied starting from 0.8 mm occlusal to the margins. Two coats of die spacer was approximately 30 μm thickness. The cement thickness was set as 30 μm, starting from 0.8 mm occlusal to the margins for CAD/CAM milling groups according to a previous study.[17]

Wax patterns were invested with a phosphate based investment for traditional casting Co-Cr (AlphaCast MP; MANI Schütz Dental Group, Germany) and titanium (Rematitan Plus, Dentaurum; Ispringen, Germany) groups. After casting, residual investment on the crowns were eliminated by using airborne-particle abrasion with 250 μm aluminum oxide (Oxyker Duet; Manfredi, İtaly) at a pressure of 2 MPa.

All copings were checked by a low viscosity conditional elastomeric silicon (Speedex light-body, Coltene Whaledent, Switzerland) impression material on the master model for their marginal and internal fit. After eliminating the discrepancies on copings; veneering protocol performed according to the firing protocol and recommendations of the manufacturer.

Silicone replicas were obtained from all veneered crowns to measure the marginal and internal adaptation by using a light viscosity polyvinyl siloxane (Affinis Precious, Coltene Whaledent, Switzerland) impression material. Light viscosity polyvinyl siloxane material was mixed and applied inside the crowns with a finger pressure for 2 minutes. After 5 minutes the silicone material gently removed.

Scanning and measurements of marginal and internal adaptation of the crowns were made with a x-ray micro computerized tomography (SCANCO MEDİKAL μCT 50, Bruttiselen, Switzerland). Silicone replicas were inserted into the device tubes one by one and stabilized with packaging foam to be certain of replicas did not move during scanning.

The scanned specimens were raw images named as; tagged image file format. That two dimensional images sectioned silicone replicas from the central by sagitally and coronally to measure points shown in [Figure 1]. These points were separated into 4 regions as follows; (a) marginal gap = (points 1,2), (b) axial Wall = (point 3), (c) axio-occlusal angle = (point 4), and (d) occlusal surface = (points 5, 6, 7, 8, 9). The observer blinded to the method and made on each speciment 24, totally 960 measurements. All images converted from tagged image file format to three dimensional image format called STL to measure internal volumes of each silicone replicas.
Figure 1: Measurement areas and points of marginal and internal gaps

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Subsequently, each group region's measurement and group's internal gap volume were calculated and used for statistical analysis. All data sets were subjected to a Kolmogorov-Smirnov test to control the normalality of the distribution (α = 0.05). Data were analyzed with one-way Anova, Bonferroni post hoc test and dunnet T3 post hoc test (α = 0.05) by SPSS 21.0 (SPSS Inc., Chicago, IL, USA) for Windows.


   Results Top


The mean marginal, internal adaptation measurements and internal gap volume calculations for each groups with 95% confidence are presented in [Table 1] and [Table 2]. No statistically significant differences were found among the 4 groups for measurement at the marginal gap (P = 0.196). Statistically significant differences were found among the 4 groups at the axial wall (P = 0.001), axio-occlusal (P < 0.001), occlusal surface region (P < 0.001) and internal gap volume (P < 0.001). At axial wall region the mean values of Cast Ti group were higher than those of groups but only statistically not significant for Cast Co-Cr group (P = 0.075). At axio-occlusal region and occlusal surface region the mean values of Milling Co-Cr group were higher than those of groups statistically significant. At internal gap volume the mean values of Milling Ti group were smaller than those of groups but only statistically not significant for Cast Co-Cr group.
Table 1: Mean and standard deviation of marginal and internal adaptation measurements (μm) of all groups

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Table 2: Mean and standard of internal volume calculations (mm3) of all groups

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   Discussion Top


The null hypothesis that there is no difference would be found on marginal-internal fit and internal gap volume among the 4 groups was rejected except marginal gap region. Marginal and internal fit is one of the major point while determining longivity of the crown. Inadequacies of the crown reasons both cement solubility and plaque retention.

In this study Co-Cr die was used as an abutment for measurement of discrepancies. The advantages of the Co-Cr die are; standardized preparation, prevention of ingestion of the die during the fabrication, and measurement of the copings.[16],[20],[21],[22] Circumferential deep chamfer preparation was chosen in the present study as it exhibits better marginal adaptation.[18],[23]

Measurement under a microscope after sectioning the embedded specimens called replica technique and measurement by direct visualization are two promised methods of measuring marginal and internal gaps.[18],[19],[24] In the current study, antecetent method was combined with a 3D micro CT system. Micro CT is able to scan replicas with delicate, innovative method that ensure high-resolution observation of the marginal and the internal gap between preparation side and the restoration. Micro CT allows 2D and 3D measurements with micron sections from any angle or position without any damage to the specimens.[25]

There is no standard sentiments on marginal accuracy between researchers. McLean and von Fraunhofer[26] reported that crown margin gap can be furthest 120 μm for clinical acceptance. Several authors reported that up to 120 μm marginal discrepancies can be clinically acceptable for titanium ceramic crowns.[3],[27],[28] In the present study two different metal alloys two different techniques were used and veneered. The mean measurement of marginal gap were 103.20 ± 14.76 μm for TCC, 113.36 ± 19.10 μm for MC, 104.66 ± 20.63 μm for TCT and 95.75 ± 16.11 μm for MT. The measurement of the marginal discrepancy of the crowns were within the clinical acceptance limits. All groups act similar marginal behaviour as before veneering procedure all copings checked with a low viscosity conditional elastomeric silicone.

Tamac et al.[17] reported that; there is no statistically difference between Co-Cr casting and Co-Cr milling at the axial wall region. Another author reported that; there is a statistically difference between Ti casting and Ti milling at the axial wall.[18] Both two studies correspond to present study.

During milling process, design program, and bur diameter should be in a harmony for adequate crowns. Örtorp et al.[29] explain that harmony as “drill compensation”. Although there is a harmony between the design program and milling process, the 1 mm diameter burs can not produce the desired precision in axio-occlusal and occlusal regions. The same author mentions that, the vibration generated during the milling process adversely affects the sensitvity of the copings. In the present study CC group gives better results than the MC group of axio-occlusal and occlusal regions statistically.

Only few authors have mentioned the internal gap volume over lithium disilicate crowns.[30],[31] There is no published research that had used present study methodology for measuring internal gap volume. The mean measurement of internal gap volume were 20.59 ± 0.83 mm3 for TCC, 22.73 ± 0.82 mm3 for MC, 22.83 ± 1.11 mm3 for TCT and 20.51 ± 1.16 mm3 for MT.

Another important point that needs to be explained is that MT group is statistically different according to the MC group in both axio-occlusal and occlusal regions and internal gap volume. During milling process, CoCr alloys are harder than Ti alloys and cause burs to break down more quickly. CoCr alloys produce more craters on the surface than titanium alloys when drilled in milling equipment. In this case, harmonization is negatively affected. The different formation of thermal conductivity between the two alloys leads to the formation of high radial gradients in CoCr alloys in cutter burs.[32],[33]


   Conclusıon Top


Within the limitation of this in vitro investigation, the following conclusions are suggested;

  1. All copings fabricated with TCC, MC, TCT, and MT exhibited similar marginal gap within the clinical acceptance range
  2. Mean axio-occlusal angle point and occlusal region MC group exhibited significantly higher values statistically
  3. Mean internal gap volume values MT group were smaller than those of groups but only statistically not significant for TCC group.


Acknowledgements

The authors thank to Timur KOSE for the evaluation of statistical analysis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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