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CEREC Emax Crowns- Will's Process.

An article for patients, technically minded people, and other dentists that might be interested.

Dr. Will Kelly Dental Crown made in Gastonia

Above: Emax Lithium Disilicate Porcelain Crown. Designed on Sirona CEREC CAD/CAM unit, fitted and balanced to patients mouth before customizing esthetic characteristics and firing in a porcelain oven. The restoration was then bonded over the preparation--- the patient never left the dental office.

When I joined my father, Dr. Bill Kelly, in dental practice in 2004, we made some promises to each other about how we would practice dentistry. Dad had been in practice at that time for exactly thirty years, since the year I was born. With my career just getting started and my younger brother, Jim, in dental school Dad made a neat declaration:

"I'm not going to retire. I'm going to have fun doing this for a long time with you guys." One thing Dad decided to do was invest with me in as much state -of-the-art technology in our practice as we could. My job was to help implement it-- he wanted to enjoy trying it out and not finishing his career doing things "the old fashioned way". In 2004, we brought digital radiographs into our practice, digital record keeping, and I made digital photography the standard of care for the patient record. We invested in two different dental laser units, one to manage soft tissue and another to prepare teeth. I modernized our in-house lab to accommodate more challenging cosmetic and restorative cases . . . and we bought a CEREC machine.

CEREC is a computer based system that optically scans the tooth surface to get an impression of its shape, designs dental restorations (crowns, inlays, and onlays) and mills them out a high quality porcelain and resin ingots. The system was developed in Germany by the Siemens Corporation and has continued to evolve in the past two decades. Like all computer technology its evolution is exponential, it is here to stay, and is very good. Today Siemens has named its dental division Sirona, coincidentally its North America headquarters are within 12 miles of our practice (which is a very nice resource for training and support).

Our early experience with CEREC was good. We dedicated ourselves to travel and get properly trained as "Basic" and "Advanced" CEREC users. We had nice results in the first few years because we were very selective about choosing the appropriate cases and situations to use the technology. I was very happy to be able to share this investment within our larger group practice because it allowed us to be innovative and embrace the future of dentistry much earlier than other practices, but did not feel that we had to make the machine "produce", therefore we did not over use it.

The basic process for making a CEREC restoration is preparing a tooth like a traditional restoration, scanning a 3D image into the software, designing a crown, milling it from the material, polishing it and cementing it in the same day. The primary selling point of the technology is to provide the convenience of "same day" crowns without temporaries, impressions, labs, or waiting. To dentists, the technology is presented as an alternative to outsourcing to a dental laboratory and a service to convenience patients. For me, in 2011, CEREC has become so much more than that. I have created a process for making the crowns that I feel can have an equal or superior quality to a laboratory made crown, but that is also very customized because I have the ability to control the fit, bite and esthetic appearance of the restoration in the patients presence.

One thing that I fear as this technology becomes used more is that it will be misused and fall into the wrong hands. Behind the process there has to be a dentist. For all the steps that make CEREC restorations convenient and as amazing as the computer is at making a nearly perfect fitting restoration, there are some criteria for the dentistry that I "put my seal of approval on" that the machine can not always do for you. I think that is important for my patients to know that I am making a restoration for their behalf and that is very rare in dentistry. I do not let an assistant or a technician design my crowns on the software because I know that I will have a perfect crown in the end. One of the greatest steps forward in my use of CEREC was purchasing a porcelain oven and using Ivoclar Emax porcelain. Before having the ability to utilize this amazing dental material, I often chose to send many cases that I now make to a lab for a stronger and more appropriate material (I believe that weaker porcelains are used inappropriately in some situations some CEREC users.)

I would like to share a snap shot of my process for making a Emax crown with my CEREC machine in one visit.

One of the most important criteria for a crown in my practice is how it will fit into the patient's overall bite. Whenever appropriate, I like to assess and address, the patients overall bite before I change any thing in it. I spend a great deal of time with talented colleagues that also consider a stable bite one of the cornerstones of good dentistry-- most of them don't believe the CEREC can create this good occlusion--- I actually believe when making a few restorations at a time I have the very best control of occlusion.

Before I shape a tooth into a preparation, I equillibrate it (and other teeth if necessary) to define and design points and receiving areas in teeth. If it is useful I can get an image of the tooth and use these functional areas of their anatomy in the design of my final restoration.

After preparing the tooth into the shape that will go underneath the restoration, I scan in and design it in the computer. I typically find that the computer design proposal has reasonably attractive anatomy and a will probably feel pretty good when the patient bites into it, but has some flaws that need to be adjusted out. (For you dentists out there reading this: the main one I can think of is that it puts lots of contacts on inclines instead of anatomy perpendicular to the long axis of the tooth, like cusp tips and marginal ridges).

After designing a good scheme into the crown I select an ingot of porcelain that will look good to mill. When It is finished milling, Emax is in a "green" stage (un-vitrified it is blue or purple, it becomes tooth colored after exiting the firing oven.) In this stage I place the restoration into the patients mouth and work out final details in the fit and bite. I also address the esthetics and form at this time. One of my mentors, Dr. Todd Davis in Atlanta, mentioned that he thought CEREC crowns looked like "melting wax" or "ceramic marbles"--- not after I go in and shape them and make fine little additions of porcelain to create a very pleasing anatomical form and appearance. A major advantage of making all of the adjustments in this unfired stage is that any finite crazing that might occur while milling or adjusting the crown is mended in the firing process. By the way, fired EMAX is GOOD stuff, at 360 - 400 mPA strong they are twice as strong as the other CEREC crowns out there.

While the crown goes through a half hour firing process my patients watch Good Morning America, surf the web, read, sleep, or get some work done. I rarely have to make any adjustments to the crowns after they are fired and bonded.

I must say that I have a great relationship with my restorative laboratory--- they are masters and when cases are very challenging and large in scope, I trust and rely on their expertise. For the cases that I make with CEREC: I probably wouldn't do nearly as many crowns in my office today if I wasn't so pleased with the results of this specific process. Most importantly, I enjoy making things with my hands and patients really appreciate it. I really think my Dad made a good decision when he encouraged me to be innovative, I'm very thankful to him for making that possible so early in my career.

Dr. Will Kelly. 2011.

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