Oral Health Group
Feature

CAD/CAM Is Here to Stay

July 1, 2006
by Tom Hedge, DDS


Computers have had a major impact in all industries. They have continued to get smaller, faster and less expensive. This allows improved efficiencies and better and more cost effective production of products.

Computers are playing an increasing role in dentistry. In the beginning, they helped us manage our practice, keeping track of our appointment book, collecting money, and billing insurance. Today computers are involved in almost every aspect of dentistry. Computers present treatment by storing and playing multimedia presentations on dentistry (CAESY). Computers help us store organize, and present our digital images of patients conditions (ImageFX). Computers will measure shades, and give us hue, chroma, and value readings of teeth and restorations (Vita Easyshade and Cynovad’s Shade Scan). Computers will send automated appointment reminders and birthday greetings via e mail, and text messaging to our patients (Smilereminder). Computers will measure muscle EMG’s of the muscles of mastication, joint sounds and vibration, and track mandibular motion to help us treat TMJ problems and occlusal disease (Myotronics and Bioresearch). Computers will measure occlusal contacts with an evaluation of timing and intensity (Tek Scan). It is clear that computers are invaluable to our business.

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Let’s focus on what computers are doing to help us provide indirect restorations for our patients. There are two main categories of applications, one for the dentist and one for the laboratory. The laboratory applications are many. Procera is a process where the stone die is scanned and the information sent by modem for coping milling. This Alumina or Zirconia coping is returned to the laboratory for veneering porcelain.

Cercon utilizes a process where the laboratory pours a stone model and waxes the restoration. The waxed restoration is then scanned, and milled in Zirconia. The material is in a softer state when it is milled and is later scintered, or infused with glass in an oven (Fig. 1). Veneering porcelain is then added over a stained or unstained framework to get the desired value (Fig. 2). This process does not require the laboratory to send out the restoration to a major milling centre. Cercon applications are shown in Figure 3. Lava is a true CAD/CAM process where the die is scanned, The restoration is designed in software (Fig. 4) and the restoration is milled (Fig. 5) in Zirconia.

The next step is scintering to make it hard and strong. It is then returned to the laboratory for veneering porcelain (Fig. 6). CEREC InLab is a similar process, except the restoration is scanned and milled in house and not sent to a milling center.

The second category where CAD/CAM impacts the dental office is the indirect immediate delivery model pioneered by CEREC (Fig. 7). This technology has come a long way over the past 17 years, and it is here to stay. Early systems milled inlays only and fits were not as good as laboratory fabricated units. Today, the marginal fit is every bit as good as a laboratory produced unit. Contacts can be right on the money with no adjustment (This requires some experience).

Occlusion can also be near perfect when tried via two methods. The first is referred to as “Correlation”, where the existing tooth morphology is captured and “memorized” by the three dimensional camera. The final restoration duplicates this with extreme accuracy. In fact, it is so accurate, that the morphology of an existing crown under a removable partial denture with a rest seat and clasps can be duplicated to the degree of precision that the RPD will actually fit over the new crown. This is just about impossible with a laboratory procedure.

The second technique is referred to as “Database” with the opposing occlusion captured with a bite registration. This can be a difficult concept to visualize in an article. No pre-operative images are necessary. Prepare the tooth to completion. Inject bite registration material over the preparation and let it set. Powder this and capture an image to the computer. Remove the registration, powder the preparation, and capture the image of the preparation to the computer.

CEREC has a database of “perfect” teeth and will insert this morphology and fit it to the opposing occlusion. You can also choose where the contacts will be on the adjacent teeth. This mode is great for teeth that are less than ideal prior to preparation.

The two biggest criticisms for CEREC have been fit and esthetics. Fit is just not an issue. Numerous studies have validated what I have observed clinically. The fit is great and is certainly as good as pressed ceramics. Is it as pretty as pressed ceramics? It can be as good as you want it to be. A monochromatic block straight out of the milling unit will not look good initially (Fig. 8). Try in will look opaque and may not match well.

After cementation and polish, it will take on a greatly improved appearance. The Cerec crown on the first bicuspid in Figure 9 was polished only. Using a Trilux block with three layers of opacity/translucency will greatly improve the aesthetics of a crown made with Cerec. This will cost you an extra seven dollars for a Trilux block over a standard block. I predominantly use Trilux blocks. The quadrant of onlays and inlays in Figures 10-12 were completed in two hours.

Taking esthetics to the next level involves staining and glazing. This will cost you the initial cost of the oven (two to four thousand dollars) and about fifteen minutes per procedure. This extra investment takes your restoration to a level of laboratory produced units.

Henry Schein will be selling the D4D, late this year. The D4D is a chairside CAD/CAM unit like CEREC. The two major differences between the two are the front and back ends, the acquisition unit and the milling unit. Cerec uses an infrared camera. One image is usually sufficient to fabricate a single crown. The preparation must be powdered first for the Cerec camera to “see” the preparation. This is done by spraying a fine coating of zinc oxide. The Cerec camera has a shutter speed of 1/8 of a second and must be held still so as to not distort the image. Acquisition of images with Cerec is very simple and predictable.

The D4D utilizes a laser scanner to capture the image. No powdering is necessary. However, it is recommended that four to five images be utilized to stitch together an image. The D4D laser has a shutter speed of 1/30 of a second and a steady hand may be less critical.

The back end difference is the milling unit. The Cerec unit is the size of a large microwave oven. It weighs around 40 pounds. It has two milling burs of different shapes. The block is moved in both the “y” (in and out) and “z” (up and down) direction. Average milling time for a single unit crown is around 15 minutes.

The D4D unit is two to three times as big and is approximately 30% wider and 25% taller (both machines have the same depth) and weighs 200 pounds. It too has two milling burs, but the move along a single axis. The block is what is rotated. There are two sets of burs which have varying tool diameters that are utilized to mill a restoration. There is a course set and a fine set.

The machine changes them automatically during the milling process, using the larger tool diameter for the removal of the initial 50%- 70% of material and a smaller tool for the remaining portion of the restoration, usually reserved for the intaglio and milling of anatomy. D4D technologies reports that the milling time is markedly faster because of the bur changing system.

Both of these units seem to have their pluses and minuses. Time will tell, but there is no doubt that CAD/CAM is here to stay.

Dr. Tom Hedge established the Dental Health Center in West Chester, OH, in 1988. His lecture series, Dental Diamonds, covers a gamut of topics from CEREC 3D, to digital photography, the internet, and customer service.

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