The search for high-quality, aesthetic, biocompatible, time-efficient dental restorations is one that dentists and patients share today. Dentists across America place an average of 25 crowns per month, most of them metal-based and taking two visits to accomplish. An estimated 1.2 billion amalgams will need to be replaced over the next 10 years, many of which will require full-coverage crowns.
Computer-aided design/computer-aided manufacture (CAD/CAM) technology is becoming pervasive in industry, and its application in dentistry offers tremendous opportunities to increase the level of customer service in our offices while becoming more productive and profitable in the process. Within about 1 hour, a clinician can fabricate and complete a metal-free, natural-looking full crown that displays excellent physical properties, marginal integrity, and biomechanics. CAD/CAM technology offers patients and doctors a viable alternative to traditional crown and bridge methodology. Advantages of this technique include:
• optimal customer service with enhanced referral potential via the one-visit aspect.
• elimination of unpleasant impressions.
• less pulpal trauma because of decreased bacterial contamination during temporary phase.
• complete control over the aesthetic result.
• complete control over morphology, fit, and occlusion.
• machined aspect of the restorative materials equates to biomechanical stability.
• cost savings with elimination of the second visit.
• maximum productivity on an hourly basis.
|Figure 1. Defective amalgam filling on tooth No. 29.|
A 42-year-old woman with a negative medical history presented with a defective amalgam restoration on tooth No. 29 (Figure 1). Overall periodontal health was adequate, with the exception of a localized inflammatory response at the gingival margin secondary to the proximal carious lesion as revealed by radiographs. Extensive stress fractures were observed during intraoral camera inspection. Functional patient concerns included the mercury aspect of the amalgam restoration, cracks observed, and long-term preservation of dentition. Avoiding temporaries and the inconvenience of a second visit for cementation also appealed to our patient because of her busy lifestyle.
|Figure 2. Paradigm MZ100 Blocks.|
The CAD/CAM system used for this case was the CEREC 3 system (Sirona Dental Systems, GmbH). Rapid anesthesia was achieved within 2 minutes using an intraosseous anesthesia technique (X-Tip, X-Tip Technologies, LLC). While waiting briefly for the anesthetic to take full effect, shade A2 was selected from six different colors and translucencies available in the 3M ESPE Paradigm MZ100 Block for CEREC line (Figure 2). Because the substrate color appeared to be of relatively low value, a block containing a higher refractive index was preferable to some of the more translucent blocks available, in order to obtain a more aesthetic result. The Paradigm MZ100 block material is made from 3M ESPE Z100 Restorative, which is a resin-reinforced ceramic composed of 85% zirconia-silica filler by weight, with an average particle size of 0.6 µm. The Paradigm material is processed under optimized laboratory conditions that have contributed to outstanding wear and mechanical properties. Laboratory studies have demonstrated wear characteristics nearly identical to that of enamel, preventing the kind of excessive wear to opposing dentition that many all-ceramic materials demonstrate.
The 3 P’s:
Prep, Powder, and Picture
|Figure 3. Prepared tooth with impression cord packed.|
A small, single-tooth rubber dam incorporating a circular flexible plastic frame (Instadam, Zirc) was placed on the tooth, and the defective amalgam was removed using a diamond inverted cone (Premier Dental Products Co). The subgingival nature of the carious lesion necessitated packing retraction cord dipped in a hemostatic agent. A bonded core buildup (Tetric Flow, Ivoclar) was placed using a type 4 self-etching primer system (Clearfil Linerbond 2V, Kuraray), and the tooth was prepared using a diamond chamfer bur (Axis Dental Corp) and a flame-tapered diamond finishing bur to remove unsupported enamel rods at the margins (Premier). A minimum of 1.5 to 2 mm occlusal clearance and 1 mm marginal thickness is required in order to provide the metal-free full crown enough material mass to withstand the biomechanical stresses experienced during function (Figure 3).
|Figure 4. CEREC design windows.|
In place of a traditional crown and bridge impression, the CEREC 3 system utilizes a highly accurate infrared camera to obtain an optical impression. The prepared tooth and adjacent teeth are isolated with cotton rolls and coated with an adhesive clear liquid coating brushed over and blown thin, followed by a highly reflective titanium dioxide powder, which enables the camera to accurately read the image in three dimensions. The camera is positioned over the teeth, and an image is captured by releasing a foot pedal located on the CEREC 3 acquisition unit. This image is accurate to within 25 mm, and is displayed on the flat-screen color monitor, with the entire impression process taking 2 minutes (Figure 4).
Design and Fabrication
Designing a full crown on the CEREC 3 system is quick and easy to accomplish within 5 minutes with step-by-step assistance from the new and updated Windows-based CEREC 3 software. The clinician is led through each step of the design process, and does not require knowledge of computer operation. Overall morphology and dimensions can be checked in all aspects and changed easily.
|Figure 5. Milling chamber with diamond cylinder and taper burs.|
Once the crown design is complete, the chosen block is placed into the milling chamber (Figure 5). An initial calibration process takes place, then the milling begins. Diamond cylinder and diamond cone burs mounted on rotating motors precisely carve the crown to completion within approximately 12 minutes. Studies have shown that a significantly higher number of crowns can be milled with the Paradigm MZ100 Block before burs need to be changed, versus porcelain blocks traditionally used with the CEREC system.
|Figure 6. Try-in of milled crown.|
Interproximal contacts were adjusted and polished with polishing discs (Sof-Lex, 3M ESPE) until the crown could be fully seated (Figure 6). Marginal integrity was verified and occlusal contact was checked and adjusted with an occlusal cone diamond (Diatech). Once the try-in sequence was completed, intricate occlusal supplemental anatomy was quickly placed using a flame-tapered diamond. The exterior surfaces of the restoration were smoothed and polished to a high shine with the Sof-Lex system and diamond polishing paste.
Creating a final aesthetic result that rivals a laboratory-fabricated crown requires some modification of the monochrome block. The Paradigm MZ100 material offers advantages over all-ceramic systems that may require the use of time-consuming oven-fired staining and glazing techniques. The MZ100 block can be easily enhanced through the use of the 3M ESPE TM Sinfony Magic Set, which consists of a wide variety of chroma-rich resin tints. Direct color enhancement puts the final aesthetic result in the hands of the clinician, eliminating the need for written lab prescriptions and photographs that can be misinterpreted.
|Figure 7. Resin tinted crown.|
Before applying the resin tints, the internal crown surface was micro air abraded (Danville Engineering) and silanated. Using a fine sable-hair brush on the internal surfaces of the crown, a red-orange modifier color was placed at the cervical 2 mm, dark brown was applied to the occlusal, and blue was brushed near the incisal aspect. These internal tints were brushed thin to ensure fit, then light cured to facilitate swift aesthetic modification in less than 3 minutes from start to finish (Figure 7).
|Figure 8. Crown bonded in place.|
The prepared tooth and core buildup was micro air abraded to help ensure maximum bond strength. The tooth was completely etched with 32% phosphoric acid gel, rinsed, and isolated. 3M ESPE Single Bond Dental Adhesive was then applied to the entire bonding surface (tooth + core): two coats were brushed on, lightly air dried, then light cured for 10 seconds. This technique ensured excellent bond to both the core buildup and to the small remaining dentin area. The crown was bonded into place (Figure 8) using an A3 shade resin cement system (RelyX ARC resin cement, 3M ESPE). This system sets to a rubber-like consistency within 3 minutes, allowing swift and complete cleanup with an explorer.
|Figure 9. Restoration at 3 weeks postoperative.||Figure 10. Aesthetic results rival that of a commercial lab.|
This one-visit/1-hour CEREC crown technique was completed within 53 minutes from the time anesthesia was administered to completion of the case. Three-week postoperative examination demonstrated the superb aesthetic results of this technique, rivaling that of a commercial laboratory (Figure 9). After the periodontal tissue healed, the buccal crown margin was observed to be 1 mm supragingival, rendering a nearly indistinguishable transition from tooth structure to crown (Figure 10).
Our patients can benefit from revolutionary developments in computer technology and materials science utilized in CAD/CAM. Happy, satisfied patients lead to greater case acceptance and increased referral of those who want the kinds of services you enjoy providing. Highly aesthetic results can be efficiently achieved in full-crown fabrication within a time frame that satisfies both patients and clinicians. Lower laboratory fees and elimination of costly nonproductive second visits reduce expenses while productivity and profitability are maximized utilizing the CAD/CAM method described.
1. Saliger G. Designing a CEREC Crown: CAD/CAM in Aesthetic Dentistry. Ten-year Symposium. Chicago, Ill: Quintessence; 1996;427-440.
2. Voiers DW. Form, function, and aesthetics in a single visit with CAD/CAM restorations. Signature. 1999;7:1011.
3. Hehn S. The evolution of a chairside CAD/CAM system for dental restorations. Compend Contin Educ Dent. 2001;22(suppl 6):4-6.
4. Rusin RP. Properties and applications of a new composite block for CAD/CAM. Compend Contin Educ Dent. 2001;22(suppl 6):35-41.
5. Voiers DW. Optimal esthetics in single-visit, computer-aided all-ceramic restorations. Contemp Esthet Restor Pract. 1999;3:60-68.
6. Dias WRL, Pereira PNR, Sift EJ. Maximizing esthetic results in posterior restorations using composite opaquers. J Esthet Restor Dent. 2001;13:219-227.
7. Ross S: One-visit makeovers. Contemp Esthet Restor Pract. 2001;5:42-53.
8. Kunzelmann K-H, Manhart J, Mehl A, et al. The effect of CEREC CAD/CAM materials on the wear of human enamel. J Dent Res. 2001;80(AADR Abstracts, No. 574).
Dr. Voiers practices comprehensive restorative and reconstructive dentistry in Avon Lake, Ohio. He lectures throughout the country on CAD/CAM dentistry. As director of Computerized Restorative Dentistry at the Great Lakes Education Center in Southfield, Mich, Dr. Voiers teaches dentists hands-on methods for integrating CEREC into their practices. He can be contacted at (440) 933-3270.