By Craig C. Callen, DDS
Spend a little time at your favorite crown and bridge dental laboratory the next chance you have and look closely at the models for the cases they are fabricating. You will gain a new appreciation for the problems they face trying to give dentists a quality product. One of the biggest hurdles they face with our preparations is that of inadequate occlusal or incisal clearance. Most dentists are way too conservative in their occlusal and incisal reduction. This leaves the lab trying to figure out how to fit 2 mm of porcelain in a 1 mm space and not have a case fail. Often you end up with a compromise that you may not know about until six months later when the patient shows up with two pieces of porcelain in hand that used to be your nice crown. The lab is literally stuck between a rock and a hard place on the case. Either they call you and have you re-prepare the case (not a pleasant call to make), or they give you a product that is less than what they are capable of producing. If you have to re-prepare, that means another appointment and numbing for the patient ... and lost time and profit for you.
How do we avoid this all-too-common problem? When I started placing primarily all porcelain restorations with our CAD/CAM system, occlusal clearance became paramount to the success of the case. When training to learn the system, we were shown a few tools to help attain adequate reduction, and we have picked up a few others along the way that we will discuss here.
1.) The crown and bridge preparation kit we have put together includes a diamond depth cutting bur, from www.occlusalbur.com. It looks kind of like a top hat. There is a stop located on the bur to prevent you from going deeper than the depth selected. The depths vary from 1 mm to 2.4 mm. This has been a great addition to our kit in that it not only ensures adequate reduction, but it has also reduced our preparation time as it cuts quickly and easily.
2.) Clearance tabs from Commonsense Dental Products (www.commonsensedental.com, 888-853-5773) called PrepCheck have been the second greatest tool we have to assure adequate reduction. These are boomerang-shaped tabs that have a marking powder on one end and come in differing depths. The shape makes it easier to place it between the posterior teeth, and the marking powder will leave a clear mark on the tooth where you need to adjust. We have the patient grind around a little to be sure we have clearance in excursive movements.
3.) Occlusal adjustment and football-shaped diamonds. These diamonds make a nice central groove in posterior teeth, allowing a little extra room for some nice anatomy to avoid getting those crowns that have chicken scratches for grooves. The football-shaped bur also works great to reduce the lingual of the maxillary anterior teeth as well as adjust the occlusion of restorations.
4.) Adequate lighting is a must for proper preparation. We use a combination of electric, fiber-optic handpieces, hand LED lamps, and a neat, handheld, fiber-optic light called Microlux from ADDENT INC. (www.addent.com) that can be positioned in the posterior area, making sure you have room around that maxillary second molar.
5.) For molar teeth that have had endodontic treatment, you can use the depth-cutting bur and cut an oblong hole in the central groove. It’s kind of a slot preparation. This serves a couple of functions. First of all, it gives the lab a huge amount of clearance for great anatomy and occlusion. Second, it acts as a nice solid seat to make sure the crown is solidly placed. Third, it gives added bulk and strength to an all-porcelain crown, and finally, it gives added surface area for retention of bonded porcelain teeth (this really helps with short teeth).
6.) As a last resort when all else has failed and the lab mounts the case and still wants more clearance, the technician will call and request to make a reduction coping with my permission. They make a plastic coping over the model, then reduce the preparation on the model to where they need it through the coping. Then they mark the reduced area in red. When seating the case, I will place the coping and reduce any tooth structure protruding from the hole in the coping. This procedure saves a lot of chair time and patient time by not having to reappoint to reduce one small spot.
If you want to treat your crown and bridge patients in an effective and predictable manner, occlusal and incisal clearance is critical. Using the tips and tools shown in this article, you should be able to improve both the quality and longevity of your restorations. You and your patient will be happy, and as a side benefit, your lab will feel better about producing quality restorations.
Dr. Craig C. Callen is a full-time dentist in the small rust belt city of Mansfield, Ohio. He graduated from Case Western Reserve School of Dentistry. Dr. Callen has written three books for dentists, “The Cutting Edge, I, II, & III,” is the associate editor for The Profitable Dentist newsletter, and has written numerous articles for national dental publications. He is a member of the American Dental Association, Academy of General Dentistry, and American Academy of Cosmetic Dentistry. Dr. Callen has lectured internationally on clinical and management topics in dentistry, and his latest seminar is titled, “The Multi-Million Dollar Blue Collar Dental Practice.” Dr. Callen has five children. You may contact him by email at firstname.lastname@example.org.
Are we clear?
By Craig C. Callen, DDS