Utilizing Lab-based CAD/CAM Technology for Metal-free Ceramic Restorations

Significant research of late has been directed toward the application of computer-aided design/computer-aided manufacturing (CAD/CAM) technology in the fabrication of ceramic restorations. This article presents 2 case reports in which this technology was used to fabricate aesthetic and functional restorations.

Figure 1. The CEREC inLab system.
Figure 2. The tooth preparation is secured in the scanning platform.
Figure 3. Data is captured with a noncontact laser.


Figure 4. A prefabricated VITA block is placed in the milling chamber.
Figure 5. Two milling diamonds create the restoration coping to precise specifications.
Figure 6. Restoration coping, postmilling process.


TECHNOLOGY AND MATERIALS

Although CAD/CAM systems may seem to be new to the dental marketplace, they have actually been under development for quite some time. For the 2 cases described in this article, the CEREC inLab System (Sirona, Inc) was used. This system has been on the market for less than 2 years, but the ceramic materials and CAD/CAM equipment used to create CEREC inLab restorations are based on 2 proven technologies. The first is the CEREC 3, Sironas chairside CAD/CAM system, which has had over 17 years of clinical use since the first restoration was placed in 1985.1-3 A number of long-term clinical studies have documented the effectiveness of these restorations.1,3 In addition, the ceramic materials used with the CEREC inLab system are the VITA In-Ceram line (Vident), which has a documented clinical track record of success at 6 years in vivo.4-6 

The CEREC inLab CAD/CAM system scans, designs, and mills well-fitting and strong all-ceramic crown copings and 3-unit bridge frameworks. The system consists of a single piece of equipment that is connected to a computer with a software design program (Figure 1). The compact unit is able to perform the optical scanning of the tooth preparation die as well as milling of the ceramic coping. Because the restoration design is created on the computer software program, wax models of restorations are not required for copying. The preparation die is optically scanned to capture the data to the computer, and the restoration copings are designed by using the systems proprietary software program. The computer then directs the 2 milling diamonds to create the copings from the computer design. 

The 3 distinct materials in the In-Ceram line of restorative materials used with this system are designed to satisfy strength and aesthetic considerations for any location in the mouth. Spinell has the highest translucency, which is particularly useful for the anterior region. Alumina is characterized as having a high level of translucency and 525 MPa of flexural strength for anterior crowns and bridges and posterior crowns. Zirconia provides moderate translucency and 750 MPa of flexural strength for maximum strength for posterior crowns and bridges milled out of a single block. These materials are suitable aesthetic alternatives to PFMs, as well as meeting the functional needs of the patient.

Figure 7. Various shades of infiltration glass allow the lab technician to sel
ect the ideal match for each use.
Figure 8. Porcelain buildup with Vitadur Alpha porcelain. Figures 9. The end result is an aesthetically pleasing restoration.

 

Figures 10 and 11. Case Report No. 1: Preoperative view.

 

 

 
Figures 12 and 13. Preparation of
the resin core.

 

Figures 14 and 15. Cementation with 3M ESPE RelyX ARC.
Figure 16. Case Report No. 2: Preoperative view.

 


TECHNIQUE

As outlined in the following 2 cases, the tooth preparation for CEREC inLab restorations requires adequate reduction to ensure optimal strength of the ceramic material, not to enable accurate optical scanning of the preparation. Dentists can continue to use their existing ceramic preparation techniques because the system works well with both chamfer and shoulder margins. Margins can be placed at or above the free gingival margin, rather than subgingivally, because there is no opaque or metallic margin to conceal. 

The final impression is sent to the dental laboratory, where it can be poured in either die stone or epoxy. The tooth preparation die is separated from the cast and secured in the scanning platform (Figure 2). The platform is mounted in the CEREC inLab unit and then optically scanned with a noncontact laser to capture the data to the computer (Figure 3). A digital image of the die is then displayed on the computer monitor, and the laboratory technician designs the coping by using the software program. The marginal integrity and coping thickness can be monitored and controlled through the application of the software program. A prefabricated block of ceramic is placed in the milling chamber, and the computer software directs the 2 milling diamonds to create the restoration coping to the precise specifications designed (Figures 4 and 5). When the restoration coping is removed from the milling chamber, it is a chalky white color (Figure 6). At this point it is in a pre-sintered, softer state, enabling it to be easily adjusted with rubber points and wheels. At first glance, the opaque color of the milled coping may be considered problematic for excellent aesthetic results; however, the aesthetics of these restorations begins at the core, with various shades of infiltration glass that allow the laboratory technician to select the ideal match for each case and provide the optimum foundation for porcelain buildup (Figure 7). The infiltration glass is fired in an oven at 1140C, where the glass melts and, by capillary action, fills the interstitial spaces between the grains of the partially sintered block material, maximizing the strength of the coping. 

There is a range of shades available for the veneering porcelain. Vitadur Alpha porcelain allows the lab technician to select from a comprehensive selection of shades, a majority from VITAs VITAPAN 3D-Master shade system (which includes bleaching shades) and original VITA Classical shades (Figure 8). This unique combination allows lab technicians to create vitality that replicates natural tooth enamel while matching any tooth shade, with no dark lines at the supragingival margin. The end result is an aesthetically pleasing, strong restoration that demonstrates a consistently accurate fit (Figure 9).

CASE REPORT NO. 1
A 55-year-old woman in good general health presented with a prior composite core on tooth No. 5 that required a crown (Figures 10 and 11). The adjacent tooth (No. 4) had a prior PFM crown that did not present any exposed metal, and the patient requested that no metal be exposed on the crown for tooth No. 5. A CEREC inLab Zirconia crown was chosen, as it would provide high strength while avoiding the use of a metal substructure. Pretreatment photos were taken and shade was determined before initiating treatment. The existing composite resin core was prepared for the all-ceramic crown, with care taken to ensure adequate axial (1.2 to 1.5 mm) and occlusal (2 mm) reduction (Figures 12 and 13). Gingival retraction cord was placed and a final impression using polyvinylsiloxane material was made. A temporary crown was fabricated and cemented before dismissing the patient. Because of the high-strength core of the finished restoration, it may be delivered by using either a conventional cementation technique with a resin-modified glass ionomer cement, or an adhesive cementation technique with a composite resin luting agent. The crown was cemented with RelyX ARC (3M ESPE) (Figures 14 and 15).


Figure 17. Teeth prepared with chamfer margins.  

Figure 18. Ideal strength is achieved with VITA In-Ceram Zirconia blocks.


Figures 19 and 20. Final cementation of restorations.


CASE REPORT NO. 2
A 35-year-old woman in good general health presented with multiple missing teeth and defective restorations (Figure 16). After a complete oral examination and treatment plan, a CEREC inLab crown and fixed partial denture were chosen to satisfy the patients aesthetic and functional demands to restore teeth Nos. 11 through 14 as the initial step in rehabilitating her dentition. The mandibular arch was to be restored at a later time per the patients desire to complete her treatment in stages. The teeth were prepared with chamfer margins circumferentially with a minimum of 1.2 mm axial reduction (Figure 17). Final impressions and mounting indexes were made to mount the case on a semi-adjustable articulator. Temporary restorations were delivered and the case sent to the dental laboratory for fabrication. The dies were mounted in the CEREC inLab unit, scanned, and the copings designed on the computer. In-Ceram Zirconia blocks were used to mill the copings to maximize the strength of the restorations (Figure 18). The milled copings were infiltrated and veneered with porcelain to achieve the final contours and aesthetics desired. The final restorations were cemented and the occlusion refined (Figures 19 and 20).

SUMMARY
This article describes 2 clinical cases using technology and materials that give the laboratory technician complete control over the timing, fit, and color of the restoration, while the dentist can rely on the consistent dependability of the technology and the aesthetic quality of the material.

Acknowledgment

Dental laboratory work is courtesy of Tom Nieting of Renstrom Dental Studio, St. Paul, Minn.

References
1. Martin N, Jedynakiewicz NM. Clinical performance of CEREC ceramic inlays: a systematic review. Dent Mater. 1999;15:54-61. 
2. Sjogren G, Molin M, van Dijken J. A 5-year clinical evaluation of ceramic inlays (CEREC) cemented with a dual-cured or chemically cured resin composite luting agent. Acta Odontol Scand. 1998;56:263-267. 
3. Fasbinder DJ, Lampe K, Dennison JB, et al. Three-year clinical performance of CAD/CIM generated ceramic onlays. J Dent Res. 2001;80(Abstract 1883). 
4. Probster L. Four-year clinical study of glass-infiltrated, sintered alumina crowns. J Oral Rehab. 1996;23:147-151.
 5. Scotti R, Catapano S, DElia A. A clinical evaluation of In-Ceram crowns. Int J Prosthodont. 1995;8:320-323. 
6. Segal BS. Retrospective assessment of 546 all-ceramic anterior and posterior crowns in a general practice. J Prosthodont Dent. 2001;85:544-550.


Dr. Fasbinder is the director of the Advanced Education in General Dentistry Program and clinical professor in the Department of Cariology, Restorative Sciences and Endodontics, University of Michigan School of Dentistry. His research interests and endeavors have been in the area of applied laboratory and clinical evaluation and development of aesthetic materials and techniques. He also maintains a part-time private practice through the Dental Faculty Associates at the University of Michigan School of Dentistry. He has been involved with research using CAD/CAM technology since 1993. Most recently, Dr. Fasbindes research has focused on clinical applications of the CEREC system. Projects are ongoing to evaluate and document clinical longevity of large adhesive ceramic onlays and inlays. Additional current clinical research projects are aimed at evaluation of newer polymer materials for use with the CEREC system. Dr. Fasbinder can be reached at djfas@ umich.edu.



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