August 1, 2010
by Dr. Jeffrey Caso, DDS and Dr. Peter Gardell, DDS
Every day, the restorative dentist is faced with a great many challenges. Patient demands, esthetic concerns, parafunctional habits, pain management and a plethora of other obstacles need to be identified and addressed so that we can reliably do our jobs. Recently, Cad Cam dentistry has evolved to a level that allows us to effectively deal with any of these challenges. It then allows us to deliver a highly esthetic, functional and long lasting restoration to our patients in a single visit.
To do this efficiently, we need to adapt to a new way of visualizing the end result. Gone are the days of stone models that can be held in our hands and manipulated. Replacing this mainstay of our dental training is a virtual model displayed on our computer monitor. By the very nature of this virtual model a shift in our thinking needs to take place for us to become comfortable working with it. Soon after getting involved with and becoming a true believer in Cad Cam dentistry, the realization that something was missing began to emerge. The ability to mark a stone model with a pencil or trim the base flat and symmetrical is not possible. Simple things like visualizing alignment, proportions, incisal embrasures and tooth length became difficult, if not impossible.
Research has been done which focused on what made a beautiful smile in the eyes of dentists and patients. The most significant finding was that the midline cant had the greatest influence on ones perception of what looks good and normal. The midlines could be misaligned, this pertained to both the facial midline and the midline of the dentition and the patient would not notice. The centrals could be different in their mesiodistal width by what the dentist would consider a significant amount and the patient would not notice. The gingival architecture could be asymmetrical in both its height and the profile of the soft tissue and the patient would not notice. It was even possible to get away with a combination of these factors. However, when a midline cant was thrown into the equation, then all of the separate factors suddenly became more noticeable. Unfortunately, with the cad cam system available we shrink our field of view down to the point where many of the landmarks we usually rely on are not seen. It opens up the possibility of the dentist to fall short of their esthetic goals.
It became clear that what was necessary was a stable reference point or better yet, a series of reference lines. These lines are important for many reasons. They would allow a proposed restoration to be aligned properly in the arch form in every angulation. They would allow one to visually compare the proposed restoration to the contralateral tooth. They would prevent a restoration that is canted to the right or left resulting in an unpleasant result. They would act as a reference to develop a series of restorations which take the golden proportions into account. They would allow for the proper development of the gingival embrasures. By adding other visual aids such as circles, the designer would be able to match and form consistent incisal embrasures as well. To address all of these needs, Dental Cad Products developed The Anterior Overlay.
It was important to us to make this overlay simple to use and to not add an appreciable set up time to the design phase of a restoration. We chose the low tech solution of applying the overlay to the computer monitor and manipulating the virtual model to fit the overlay. This is done by using the zoom feature and both right and left mouse buttons. This approach led to an easy to use design aid which works equally well for both complex anterior rehabilitations involving multiple teeth or the single tooth restoration.
The overlay has been designed to be an aid but not a replacement for proper design education. We recommend for those interested in improving their efficiency and the execution of Cad Cam restorations to pursue further continuing education.
Single central via Replication
The following is a demonstration of the overlay in use. The patient presented with a fractured porcelain jacket. The tooth was asymptomatic and radiographically no pathology or fractures were noted. Unfortunately, the patient did not have the fractured segment. In addition, she had an important business meeting and wanted the tooth restored as soon as possible.
The first step is to decide the appropriate method to use to restore the fractured tooth. The available options with the Cerec system are Correlation, Database and Replication.
Correlation is usually the most efficient manner to restore an anterior tooth but in this case it would require mocking up the broken tooth. This can be done quickly but is an extra labor intensive and time consuming step. The patient also did not have time to wait for diagnostic casts and a wax up to be done.
Database is a way that the restoration can be done and the overlay greatly eases the design process but as can be seen, the patient had some anatomy that would take time to mimic in the design process. If both centrals were to be restored, then database would be very efficient. However, the design of a single central could present some challenges.
Replication was the method chosen for this same day restoration. There was an existing contralateral tooth with nice unique anatomy. Replication allows the cad cam dentist to create a mirror image of the existing dentition is an efficient streamlined manner.
The overlay helps guide the practitioner to place the proposal in the proper arch form. The components of the overlay lay down a series of reference marks and lines that the practitioner can use to orient the replication shell of the contralateral tooth
Since this is a replication case, the tooth can be prepared immediately after the anesthesia has taken effect. The preferred method preparation design is a 3/4 crown to maintain the cingulum but in this case we are replacing an existing all ceramic restoration so the full coverage prep is refined. All existing decay is removed and margins are checked for clarity. The beauty of the all ceramic restoration is the ability of leaving supra gingival margins for easy imaging and bonding. Since this was a replacement of an existing restoration the margin was slightly sub gingival. Any of the retraction methods the paractitioner is comfortable with may be used that facilitates this. Cord, an Axis ceramic gingival shaping bur, retraction paste such as Expansyl, electrosurgery, and or diode laser are the most popular methods utilized. In this case a diode laser was used to expose the margin and make it easy to image. When taking the images it is a good idea to capture as much of the anatomy of the tooth you want to replicate. Take the image from the occlusal and roll the camera to capture as much of the facial surface as possible. You are limited in changing the angulation of the camera up to 20 degrees so sometimes multiple images will be required to allow for this. Imagable bite material is placed on the prepared tooth and the patient is instructed to bite down for three minutes. The patient then is asked to open; the dentition is sprayed with imaging powder and the antagonist images are taken. The antagonist is removed; powder reapplied to give a complete uniform coat and the preparation images are taken. If the practitioner switches the camera orientation during the imaging it is important to have the red box image or white circle images taken from the same direction. Otherwise problems with stitching will occur
The software will take you through the steps of design, Trim model, Trim antagonist, Marginate, Correct insertion angle. It is a timesaving step to not only check the line of draw for the preparation but also check the models relationship to the position markers on the Cerec screen. Rotating the virtual model of the preparation so the buccal of the preparation aligns with the buccal marker will allow the
software to place the replication shell in a better position. There will always be a need to adjust the shell to get it in a position the practitioner is happy with.
In replication you will be asked to outline the tooth structure you want to replicate. If you took roll pictures of the tooth structures it will be possible to capture the surface down to the gingival. This will give a bigger shell that makes it easier to design the proposal. You want to make sure you outline all the unique anatomy you want to reproduce in the new tooth. Mesial and distal line angles are extremely important.
After you are satisfied with the gathering of the information you move forward by clicking the green arrow and the shell is displayed. Many times the proposal will have to be manipulated with the position and rotate tools to get it in the desired position. The application of the overlay helps to guide you. By rotating the virtual model to view from the occlusal you can evaluate the incisal edge position of the proposal. The rotate and position tools allow you to position the shell to the proper relationship with the adjoining teeth. In this case we pick the lingual surface of the lateral incisors to be out reference marks. The central vertical line is the midline and the horizontal blue lines are perpendicular to this. Buccal position, Embrasures, angulation and rotation can all be evaluated easier through the use of the overlay. Once you are happy with the incisal view the virtual model can be rotated so you view the proposal from the buccal position. Once again the position, angulation, embrasures and length can be evaluated and adjusted through the use of the overlay. Once you are satisfied with the position of the shell you can have the software render the proposal by clicking the green arrow. The proposal can be refined through the use of all the tools in the Cerec software you are familiar with. If any significant changes are required such as widening the proposal it is quicker to red arrow back to the construction line screen. There will be a message saying the restoration will be deleted. It is OK to say yes to this. No information will be lost. This allows for proportionate enlarging or shrinking of the restoration in all directions. The position can be changed with the rotate and position tools in this screen. With the Cerec design you want to do the large movements first and then mark finer adjustments until you get to a point where the proposal is to your satisfaction. The restoration can then be sent to the milling chamber to be fabricated
The excuse many practitioners used in the past was that they didn’t want to do cutbacks to get esthetic restoration. Too much time and effort to get a restoration that the patient would accept. The block manufacturers have been great in bringing many esthetic blocks, and developing newer materials for us to use to mimic nature. A easy and quick stain and glaze process is all it takes to get some beautiful restorations in a single visit. Even the dreaded single incisor restoration can be accomplished with proper planning and execution.
The Anterior Overlay is helping to give the clinician confidence in his design abilities so that he can routinely perform beautiful anterior rehabilitations, chairside with his Cad Cam system. Using the Anterior Overlay to overcome the pitfalls of designing restorations virtually will help to propel Cad Cam dentistry into the total system it was intended to be and really can be. There are indeed simple solutions to high tech problems and Dental Cad Product’s Anterior Overlay is one of the most innovative.
It is unmistakable that the forward momentum in Cad Cam dentistry is picking up rapidly. The 25 th anniversary of CEREC is upon us and the days of thinking that Cad Cam dentistry is a posterior, single tooth system are over.
For other applications of the Anterior Overlay please go and watch the online videos at DentalCadProducts.com OH
Dr. Jeffrey Caso and Dr. Peter Gardell are both adjunct faculty members of CerecDoctors.com, clinical mentors in the Cad Cam department at the Scottsdale Center of Dentistry, and Beta Testers for the Cerec software.
Oral Health welcomes this original article.