April 1, 2001
by Stephen Tsotsos, DDS
The fabrication of all-ceramic restorations in a single appointment via Cerec CAD/CIM* technology has been a clinical reality now for 15 years. Although conceptually sound from its inception relatively impotent computer processors and less-than user-friendly software originally relegated the Cerec concept to the “almost-rans” of hi-tech dental technologies. This unfortunately created a less than favourable reputation for this very appealing concept. Today, computer processors of blistering speed and Windows-based, ultra-user friendly software bring the Cerec concept to clinical reality for any dentist providing all-ceramic restorations.
The evolution of Cerec technology has indeed been fascinating. Cerec 1 (Fig. 1) was only intended for the fabrication of all-ceramic inlays. The resolution of the camera used to acquire the optical impression was limited; therefore, the final restoration’s marginal fit was not what many restorative dentists would consider clinically acceptable.1 Cerec 1’s single diamond milling wheel (Fig. 2) forced the Cerec dentist to prepare teeth in a very specific manner; this certainly did not appeal to many dentists considering Cerec technology. All in all, Cerec 1 was a fascinating novelty.
A quantum leap in hardware technology paved the way for a new rendition; Cerec 2 boasted faster processor speed, an optical impression camera of higher resolution and the addition of a diamond milling cylinder (Fig. 3). The Cerec 2 user was also the happy recipient of a steady flow of software upgrades enabling the design and fabrication of not only inlays but onlays, posterior crowns and finally, anterior crowns and veneers. The Cerec 2 user was able to produce single-appointment, single-tooth, all-ceramic restorations of any size or shape with the potential for exceptional margins.2 Unfortunately the learning curve proved to be not only long but also steep.
The most recent flavour of Cerec is the Windows-based Cerec 3. Relative to Cerec 2 software the Cerec 3 software redefines the oft-used phrase of user-friendliness. From a hardware perspective the replacement of the diamond milling wheel with a tapered diamond milling cylinder (Figs. 4 & 5) provides for a much smoother finish to the ceramic as well as the milling of secondary groove anatomy. Indeed, the innovative implementation of modern-day hardware and software has led to the creation of the Cerec 3.
Also of note is the recent creation of the CerecLink software package. CerecLink allows the Cerec 2 user to design restorations using Cerec 3 software. The Cerec 2 user therefore uses the Cerec 2 camera to acquire the optical impression, the CerecLink software loaded on a separate PC-based computer to design the proposed restoration and finally, the Cerec 2 milling chamber to fabricate the restoration.
CerecLink is a wonderful tool for the Cerec 2 user. It is interesting to note that with so many other technologies and products becoming obsolete subsequent to the introduction of the latest software or hardware upgrade Cerec 2 remains current with the introduction of CerecLink.
THE ADVANTAGES AND DISADVANTAGES OF CEREC TECHNOLOGY:
The advantages of Cerec technology for the fabrication of all-ceramic restorations are many:
1) The final restoration is completed in a single appointment. This provides exceptional service to our time-challenged patients.
2) There is no temporary restoration since we will complete our work in a single appointment. The cosmetically conscious patient certainly appreciates this convenience. No longer do we need to apologize to our uncompromising patient for aesthetically less than perfect temporary restorations.
3) The coefficient of wear of Vita Mark II ceramic used in the fabrication of Cerec restorations is very similar to natural enamel.3
4) Vita Mark II machinable ceramics are more resistance to fracture than ceramics produced in a commercial laboratory.4
5) With proper technique there is no post-operative sensitivity to Cerec restorations.5
1) As with any new technique or technology the clinician has much to learn. Many resources exist for both basic and advanced Cerec training. The newcomer to Cerec technology can shorten the learning curve through courses and practice on prepared models.
2) The use of monochromatic ceramic blocks in Cerec technology has been criticized by the misinformed cosmetic dentist. These blocks are highly translucent. Using dentin-coloured resin cements with enamel-coloured ceramic blocks creates a very natural effect. A new line of blocks from Vident aptly named ‘Esthetic Line’ are extremely translucent. The ceramic can also be customized with highly fluorescent pigments designed specifically for Vita Mark II ceramic blocks. The experienced Cerec user indeed can create many aesthetic effects.
3) Although the initial cost of Cerec technology is high one must realize that all-ceramic restorations created via Cerec technology eliminate a commercial laboratory fee.
THREE METHODS TO DIGITALLY DEAL WITH OCCLUSION:
There are three different software modes that can be used to design Cerec restorations. Extrapolation mode calculates the heights of cusp tips for the proposed restoration based on the heights of the cusp tips of adjacent teeth. This assumes that the heights of the marginal ridges of the teeth in the quadrant in question are relatively equal, that the Curve of Spee and the Curve of Wilson are relatively flat and that the tooth opposing our proposed restoration is not supra-erupted. Of course, if the above criteria are not met the clinician can make design changes to the heights of the cusp tips and the marginal ridges of the proposed restoration to accommodate the existing clinical situation.
Correlation mode allows for the duplication of the contours and occlusal anatomy of a tooth. This is particularly handy when replacing an occlusally-correct original crown. Duplicating the contours and anatomy of a tooth that retains a removable partial denture permits the fabrication and insert of a restoration that fits the clasp assembly including any rest preparations. This is all accomplished in a single appointment; the patient no longer needs to go without the partial denture. Correlation can also be used quite effectively to duplicate a diagnostic wax-up of any tooth in question.
Function mode provides occlusal information concerning the opposing tooth by using a functionally-generated path technique. Function mode also allows us to register occlusal data from a tooth or a diagnostic wax-up of the tooth to ensure that our proposed restoration design will meet the necessary occlusal criteria.
THE SINGLE APPOINTMENT, ALL-CERAMIC, ANTERIOR RESTORATION
The most challenging yet most gratifying restoration for the Cerec user is the anterior restoration. In this particular case (Figs. 6-10) the patient asked for a cosmetic improvement over the maxillary anterior porcelain-fused-to-metal crowns she had done approximately 18 years ago. All teeth were vital. The benefits versus risks and costs were discussed concerning restoring also teeth #’s 13 and 23. A decision was made to use composite resin to develop cusp tips to these teeth. A change in shape and length relative to the existing crowns was discussed as well as a change to the base shade. The patient expressed the desire to have fairly white teeth without the heavy characterization of the original crowns.
The analysis of study models and pre-operative digital images proved that minor changes to length and contour would be of tremendous benefit to the overall aesthetics. This was confirmed in the diagnostic wax-up.
The ‘Esthetic Line’ of ceramic blocks with a base shade of Vitapan 3D-Master 1M1 was chosen for all four planned restorations. Consideration was given to Correlation mode using resin mock-ups done directly on the existing crowns. The intent was to correlate the optical impressions of the prepared teeth to the optical impressions of the resin mock-ups (Figs. 11 & 12).
After milling all units the ceramic was refined with fine sintered diamonds in a lab handpiece. A try-in verified the marginal integrity and the aesthetics from a contour standpoint. All units were then customized (Figs. 13-15) using the Vita Akzent kit and a Vita Vacumat 30 porcelain oven. Staining and glazing can be carried out quite quickly; only a few colours are usually required and our ‘canvas’ is quite small. The stain and glaze cycle of the Vacumat 30 oven is only eight minutes. An additional two minutes is required for the restoration to cool. In this particular case only three shades were used: Niagara (Akz 17) which is blue for a natural translucency; Inca Gold (Akz 04) which is a yellowish-brown shade for cervical areas and Redwood (Akz 12) which is a mauve used sparingly for added translucent effects.
The final images (Figs. 16-22) verify that our initial goals of increased length and improved contour along with whiter, less characterized teeth have been achieved.
The experienced Cerec user has the ability to produce single-appointment, multiple, anterior and posterior single-tooth all-ceramic restorations of any size or shape with excellent marginal integrity. These restorations not only exhibit excellent resistance to fracture and a very favourable coefficient of wear but are also very pleasing aesthetically.OH
Dr. Tsotsos is a member of the Ontario Dental Association, the Toronto Crown & Bridge Study Club, The International Society of Computerized Dentistry and the Canadian Academy of Computerized Dentistry where he serves as Treasurer. He has a solo practice restricted to restorative dentistry in Toronto, Ontario.
Oral Health welcomes this original article.
1.W. Mormann, J. Shug Grinding Precision and Accuracy of Fit of Cerec 2 CAD-CAM Inlays. CAD-CIM in Aesthetic Dentistry, Cerec 10 Year Anniversary Symposium by Quintessence (1996): 335-345.
2.J. Runge, K-H. Kunzelman, R. Hickel, R. Perry, G. Kugel Marginal Accuracy of CAD/CAM Crowns Compared to Conventional Ceramic Crowns
3.al-Hiyasat AS, Saunders WP, Sharkey SW, Smith GM, Gilmour WH Investigation of Human Enamel Wear Against Four Dental Ceramics And Gold J Dent 1998 Jul-Aug;26(5-6):487-95
4.Tinschert J.; Zwez D.; Marx R.; Anusavice KJ. Structural reliability of alumina-, feldspar-, leucite-, mica-, and zirconia-based ceramics. J Dent 2000 Sept. 1;28(7):529-535
5.CRA Report: Sensitivity Newsletter, November, 1999.
* Computer Aided Design/Computer Integrated Manufacture
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