Single crowns with CAD/CAM-fabricated copings from titanium: 6-year clinical results Jeremias Hey, DMD,a Florian Beuer, DMD, PhD,b Tobias Bensel, DMD,c and Arne F. Boeckler, DMD, PhDd University School of Dental Medicine, Martin Luther University, Halle, Germany; Munich Dental School, Ludwig Maximilian University, Munich, Germany Statement of problem. Computer-aided design/computer-aided manufacturing (CAD/CAM) titanium ceramic restorations were developed with the potential for replacing expensive, high noble metal ceramic restorations. However, little information exists about the clinical performance of CAD/CAM titanium ceramic single crowns. Purpose. The purpose of this study was to evaluate CAD/CAM titanium ceramic single crowns after 6 years in function. Material and methods. A total of 41 crowns were fabricated for 21 patients. The titanium copings were CAD/CAM milled (Everest CAD/CAM system), with an even thickness of 0.5 mm and veneered with low-fusing porcelain (Vita Titanium Porcelain) in the powder-build-up technique. All the crowns were cemented with zinc phosphate. The participants were recalled at 12, 24, 36, 48, 60, and 72 months after cementation to document any mechanical and biologic complications and to measure the periodontal parameters, such as probing depth, bleeding on probing, and the plaque index. The success and survival rates were calculated according to the Kaplan-Meier analysis. Results. After 6 years of clinical service, 12 mechanical complications and 1 biologic complication were found, which resulted in a success rate of 67.8%. The cumulative survival rate of the crowns was 91.3% after 6 years. At the end of the follow-up period, the probing depth was 3.21 mm, the percentile of surface with bleeding on probing was 25, and the plaque index was 0.37. No secondary caries or decementation was detected during the 6-year observation period. Conclusions. The clinical performance of the CAD/CAM titanium-ceramic crowns after 6 years was poor because of veneering porcelain problems. Recent CAD software with tools to design proper copings might improve the clinical success. (J Prosthet Dent 2014;-:---)

Clinical Implications The computer-aided design/computer-aided manufacturing-fabricated titanium-ceramic crowns evaluated showed poor clinical performance during the observation period. The presented treatment approach cannot be considered as an acceptable clinical alternative to metal ceramics with high-gold alloys.

Titanium dental restorations have desirable properties, for example, good corrosion resistance, low specific gravity, good mechanical properties, high

biocompatibility, and low cost.1 The increased cost of noble metal alloys and the long-term clinical success of restorations with precious metal

alloys have led to the development of alternative materials for dental restorations.2-6 Unfortunately, several problems have been reported with the

Presented at the International Association for Dental Research 90th General Session and Exhibition, Ignuaçu Falls, Brazil, June 2012. a

Assistant Professor, Department of Prosthetic Dentistry, University School of Dental Medicine, Martin Luther University. Assistant Professor, Department of Prosthodontics, Munich Dental School, Ludwig Maximilian University. c Resident, Department of Prosthetic Dentistry, University School of Dental Medicine, Martin Luther University. d Assistant Professor, Department of Prosthetic Dentistry, University School of Dental Medicine, Martin Luther University. b

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Volume casting and veneering process of titanium.7,8 The difficulty of the casting process is caused by the high melting temperature of titanium.9 Molten titanium has a high affinity for investment materials and reacts with the ingredients. The result is a marginal layer that is brittle and impure. This reactive “a-case layer” reduces the bond strength between the veneering porcelain and the titanium substructure, and affects the marginal accuracy.10 Several methods have been developed to solve the problems of titanium casting. Modified air pressure and burn-out temperature have been used to improve the quality of casting titanium, and different investment materials have been tested.11-15 As alternative methods, machined duplication and spark erosion have been suggested.16 The difficulty of the veneering process is due to the excessive oxidation of titanium during porcelain firing. This oxidation results in the formation of a darkened layer, which makes predictable esthetics challenging and impairs the bond between the porcelain systems and the titanium. To prevent spontaneous oxidation, some manufacturers recommend the use of titanium-ceramic bonders.17 Veneered titanium-ceramic crowns. manufactured with copy milling, spark erosion, and low-fusing porcelain, have been applied in several clinical studies with consistent results.18-23 At the end of the last century, computer-aided design/computer-aided manufacturing (CAD/CAM) technology started to influence the manufacturing of dental restorations and has made the titanium coping fabrication process simpler and faster.24 Titanium was one of the first metals to be used for dental CAD/CAM frameworks because of its biologic and mechanical properties. Compared with copy milling, spark erosion, and laser welding, milling titanium produces excellent fitting and avoids the a-case layer.25,26 Titanium-ceramic restorations represent a treatment option. Although the bond strength between titanium and the veneering porcelain was improved

in the last decade, it still seems to be critical.27 Titanium has a low coefficient of thermal expansion. The quantity of alkali oxide metals is increased, and the fraction of aluminum oxide and leucite is decreased in veneering porcelain for titanium compared to conventional metal ceramic restorations. Therefore, a low firing temperature and a low coefficient of thermal expansion can be reached in veneering porcelain for titanium. The flexural strength of the veneering porcelain is increased by high fractions of leucite and aluminum oxide. In addition, a higher inclusion of water in the ceramic is caused by an increased amount of alkali oxide metals.27 However, the authors identified no clinical studies that describe the general performance of CAD/CAM titanium ceramic crowns manufactured with the concept presented in this study. Therefore, the purpose of the prospective clinical study was to evaluate the success, survival rate, and clinical parameters of CAD/CAM titanium ceramic single crowns after 6 years in function. The hypothesis was that titaniumceramic crowns manufactured with the proposed concept will provide clinical results comparable with those reported for cast titanium after 6 years.

MATERIAL AND METHODS This prospective clinical trial was designed according to the recommendations of the CONSORT (Consolidated Standards of Reporting Trials) for improving the quality of clinical trials. The requirements of the Helsinki Declaration were fulfilled and were approved by the ethical committee of the University of Halle-Wittenberg (05032004). Twenty-one participants (8 men, 13 women; mean (SD) age 49.4  12.8 years [age range, 26-67 years]) recruited from patients who attended the Department of Prosthodontics of the Martin-Luther-University Halle-Wittenberg. The prospective tooth to be crowned was required to be periodontally healthy, vital or with a root canal treatment that was adequate

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(no clinical sign or symptom, no apical radiolucency), correctly positioned in the dental arch; and with a sufficient amount of coronal tooth structure to allow a ferrule design of at least 2 mm in height in dentin. Furthermore, normal occlusal function, a healthy temporomandibular joint, and a favorable interocclusal relationship were required. Individuals with untreated temporomandibular disorders or untreated systemic or infectious diseases were excluded from the study. Pregnant women also were excluded from the study. Self-reported pregnancy was stated in the clinical history. Forty-one crowns were fabricated and delivered (12 anterior, 29 posterior). Preparation was performed according to the guidelines for conventional metal ceramic crowns modified for CAD/CAM restorations: a 360-degree, 1.2-mm chamfer preparation, a 6- to 10-degree preparation angle, and an occlusal reduction of 1.2 to 2 mm with rounded edges. All impressions were made with a combination of heavy- and light-body polyether (Impregum [heavy body] and Permadyme [light body]; 3M ESPE). Definitive casts were fabricated with scannable Type-IV gypsum (Everest Rock; KaVo Dental GmbH). Casts were digitized by using a white-light projector scanner with a coded-light charge-coupled device camera (Everest Scan; KaVo Dental GmbH). The detection of the preparation margin was performed automatically (Everest Scan Software and Everest Design Sherpa; KaVo Dental GmbH). A CAD software (Everest CAD; KaVo Dental GmbH) was used to design the copings. The CAM data were transferred to the 5-axis milling unit (Everest Engine; KaVo Dental GmbH). The copings were milled from grade-2 titanium blanks (Everest T-Blank; KaVo Dental GmbH) with a uniform thickness of 0.5 mm. All copings were veneered with low-fusing porcelain (VITA Titanium Porcelain; VITA Zahnfabrik GmbH) according to the firing protocol and recommendations of the manufacturer. To increase the adhesive bond strength between

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RESULTS Three participants with a total of 4 crowns (1 anterior, 3 posterior) missed the 4-, 5-, and 6-year follow-up because of medical conditions or address changes, and were withdrawn from the study. During the period of investigation, mechanical complications accounted for 10 cohesive and 2 adhesive porcelain fractures that resulted

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Success Rate

titanium and the veneering porcelain, a titanium-ceramic bonder was applied (Vita Bonder; VITA Zahnfabrik GmbH). Twenty crowns were produced with a buccal porcelain butt margin (up to and including the second premolar). The other 21 crowns were made with a metal margin. After the evaluation of the proximal contacts, the marginal fit was checked with a light-body silicone material (Fit Checker; GC Europe), then the occlusal contacts were evaluated and adapted if necessary. All surfaces were polished meticulously (Polishing Kit for Ceramics; Komet Dental Brasseler and Diamond Polishing Paste; Bredent Medical GmbH); if more than 1 mm2 was involved, then an additional glaze firing was carried out. The crowns were cemented with zinc phosphate cement (Harvard Cement; Harvard Dental International GmbH). After cementation, the probing depth, bleeding on probing, and plaque index of the restored teeth were measured. The participants were recalled annually after cementation, and the restorations were examined for technical and biologic complications. A crown was categorized as a success if it was free of any mechanical complications and categorized as survival if it was not replaced but functioning in place with or without mechanical complications. Details about materials and methods were described in a previous publication.28 Statistical analyses were performed with PAWS Statistics 18. The level of significance was set to 5% (P.05, Mann-Whitney U-test).

DISCUSSION The present study revealed a low clinical success rate for ceramic veneered crowns with a CAD/CAM fabricated substructure. Compared with the 3-year results of this study, the cumulative success rate with regard to mechanical complications decreased

4

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Table I.

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Results of periodontal examinations

Parameter

Baseline (n[41)

12 Mo (n[37)

24 Mo (n[37)

36 Mo (n[36)

48 Mo (n[36)

60 Mo (n[35)

72 Mo (n[35)

Mean probing depth, mm

2.20

2.22

2.74

2.93

3.03

3.05

3.21

Percentage of surface with bleeding on probing

17.1

Mean plaque index

0

from 82.3% to 67.8% after 6 years (Fig. 1). The cumulative survival rate with regard to function decreased from 94.9% after 3 years to 91.3% after 6 years.28 Two of the 37 crowns were replaced because of mechanical or biologic complications. One endodontically treated tooth was extracted because of recurrent apical periodontitis. Secondary caries and loss of retention were not detected during the 6-year observation period. This indicates that the marginal accuracy and internal fit of the titanium copings, even with earlier versions of the CAD software, were acceptable.26 The mean probing depths were maintained at 3.21 mm; 25% of surfaces showed bleeding on probing at the end of the observation period. The measured periodontal indices remained within clinically acceptable limits. Similar results were reported in earlier studies that investigated ceramic crowns manufactured by alternative methods (copy milling, spark erosion, and low-fusing porcelain).22 However, this indicates that the effect of CAD/CAM titanium ceramic crowns on periodontal tissues is minimal and comparable with other restorations.29 The low cumulative survival rate can be explained by the sample size and the inclusion criteria. Fractures on the veneering porcelain were detected in 27% of the investigated titanium ceramic crowns. Ten cohesive and 2 adhesive fractures were investigated during the observation period. Titanium oxidizes during the porcelain firing process. The oxide layer leads to limitations in the quality of titaniumceramic bonding and esthetics. The bond strength between titanium and

25.7 0.35

29.1 0.35

29.2 0.31

ceramics increases with the use of a titanium-ceramic bonder.30 A titaniumceramic bonder consists of kibbled glass powder, which seals or dissolves existing oxides on the titanium surface.17 At 882 C, titanium undergoes a phase transformation, during which bulking occurs in combination with intense embrittlement and contamination. This is in addition to the a-case layer and spontaneous oxidation.31 To avoid this phase transformation, the firing process of the veneering porcelain must not exceed 882 C.27 Difficulties in matching the thermal expansion of the veneering porcelain to the titanium might have decreased the mechanical strength of titaniumceramic.32,33 The high amount of porcelain fractures may be related to the uniform thickness of the substructures. Optimized substructure designs improved the clinical performance of veneered dental restorations.34,35 To avoid stress cracking, manufacturers recommend cooling fins, which provide consistent cooling after the veneering firings. These cooling fins can compensate for the low heat conductivity of titanium. Cooling fins have not been implemented because available CAD programs offer the possibility of smart substructure design. Therefore, the titanium-ceramic concept might not give the same consistency as porcelain fused to conventional highgold alloys.36,37

CONCLUSION The clinical performances of the CAD/CAM titanium-ceramic crowns with a nonanatomic coping design for 6 years were poor.

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28.6 0.39

29.8 0.35

25 0.37

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Corresponding author: Dr Jeremias Hey Große Steinstrasse 19 University, Halle, Germany 06108 Halle GERMANY E-mail: [email protected] Acknowledgment The authors are grateful for the partial support of this study by KaVo Dental GmbH, Biberach, Germany. Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.

CAM-fabricated copings from titanium: 6-year clinical results.

Computer-aided design/computer-aided manufacturing (CAD/CAM) titanium ceramic restorations were developed with the potential for replacing expensive, ...
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