How To: Prepare atypical crowns with KOMET USA's extended-length diamonds

Today's HOT How To features a technique demonstrating the use of KOMET USA's S6856XL.FG.021 extended-length diamonds to help ease crown preparations when gingival recession is present. Case presentations are performed by Christine M. Yonker, DDS, and Sergio Rubinstein, DDS, from Oral Rehabilitation Center in Skokie, Ill.

Problem solving, innovating and adapting instrumentation and technique to meet the challenges of each new case are among the hallmarks that distinguish a great dentist from a good dentist. All dentists, however, will agree that they are happiest when procedures are completed as expected and the need to solve problems doesn’t arise. Having the appropriate instruments and materials on hand for each individual case reduces the need to over-modify or potentially misuse traditionally used items for purposes that  weren’t originally intended.

An example of this is as simple as the rotary instruments used with dental handpieces. In dental school students learn about diamond and carbide burs-the types of rotary instruments best employed for particular purposes and the configurations and sizes that best create ideal preparations in typical cases. Then, the first atypical patient presents with limited interocclusal distance, and the dentist is unable to precisely position the bur parallel to the second molar, especially on the distal. This is when the dentist’s creativity is called upon. Sometimes one bur is used to cut a portion of the shank of another bur, which is then placed back into the handpiece and used for the tooth preparation. Using the shortened bur typically provides a satisfactory result.

In another scenario, however, a patient presents with moderate bone loss due to periodontal disease and requires a crown on a canine or central incisor. As tooth preparation begins, even after completing incisal reduction, we find we cannot reach our margin with the correct handpiece angulation or without the handpiece hitting either the edge of the tooth being prepared or the adjacent teeth. Again, the dentist’s creativity is summoned.

Either the handpiece must be angled in such a way, often awkwardly, to likely produce an undercut, or the bur must be pulled from the chuck in the head of the handpiece as far as feasible so the friction grip still retains the bur and operation can continue. The dentist simply hopes, however, that the bur stays in the handpiece while preparation continues.

These aren’t new issues in dentistry, and longer burs have been developed, but in practice, we need to determine whether the extended-length burs are actually long enough to avoid problematic situations.

Longer diamond burs
Developed to address crown preparation requirements in cases presenting gingival recession, the KOMET® S6856XL.FG.021 diamond features a 12 mm working length. This extra-long, perio-length diamond allows the operator to maintain ideal position and angle of the handpiece and avoid interference with adjacent teeth, thus permitting the precise preparation and refinement of optimal crown margins at the proper angle in patients who have longer, exposed crown lengths.

The KOMET® S6856XL.FG.021 diamond is a new addition to KOMET USA’s S-Diamonds®, which efficiently remove tooth structure during crown preparation procedures. KOMET S-Diamonds feature a diamond understructure on their working portions, which incorporate staggered plane surfaces to optimize material reduction, ensure maximal debris removal, facilitate cooling, and save operator time. Less loading of the KOMET S-Diamonds cutting surfaces enhance patient comfort.
KOMET S-Diamonds are offered in a variety of configurations and lengths to accommodate individual crown preparation designs, including tapered chamfer, long chamfer, modified taper, modified taper shoulder, modified cylinder, modified parallel shoulder, modified tapered chamfer, modified parallel chamfer and parallel chamfer.

An egg-shape diamond for occlusal/lingual reduction and a round diamond also are available, as are kits containing a selection of KOMET S-Diamonds for modified tapered-chamfer preparations, tapered-chamfer preparations and modified tapered-shoulder preparations.

Case presentations
The following cases demonstrate a variety of clinical applications of a diamond bur with increased length. The first case exemplifies insufficient length of diamond cutting surface relative to the length of the tooth. The second and third cases illustrate how adjacent teeth can interfere with the head of the handpiece, thereby preventing access to the margin of the prepared tooth.

Case 1
The patient doesn’t like the appearance of her existing crowns and veneers due to recession that has occurred over time. The treatment plan includes replacing the older, unesthetic crowns from tooth No. 6 to tooth  No. 11. To improve the appearance of the new crowns, the margins must be prepared slightly subgingivally (Fig. 1).

Once the crowns are removed and the preparations are refined, we find that the cutting surface of the regular-length diamond is inadequate in length relative to the length of the canine (Fig. 2).
By changing burs and using the KOMET® 12 mm long diamond bur, the margin can be prepared subgingivally while providing sufficient length of cutting surface to accommodate the entire length of the tooth (Fig. 3).

The greater length allows the entire tooth to be prepared uniformly and produces a nice, clean margin in the desired subgingival location (Figs. 4-6).

The occlusal view demonstrates the margins on the canine are just as precise as the preparations on the shorter teeth as a result of having a longer length diamond bur (Fig. 7).

Case 2
This patient had a crown removed from tooth No. 11. Notice the apical position of the existing margin on tooth No. 11 as compared to tooth No. 10. The length of tooth No. 10 also is greater than that of an average, healthy lateral incisor. For a standard diamond bur to access the margin for refinement, the handpiece would have to approach the tooth from the distal. Because patients don’t have removable cheeks, a longer bur is needed to prevent the handpiece head from interfering with the incisal edge of the adjacent lateral incisor (Fig. 8).

The longer bur allows more freedom of movement while re-preparing and smoothing this tooth (Figs.  9-10) .

Case 3
This case is similar to Case 2. In this instance, a lower canine with an existing veneer requires replacement due to a transverse fracture in the porcelain (Fig. 11). Again, the standard–length diamond has limited capability to properly prepare this tooth because the incisal edge of the adjacent tooth interferes with handpiece positioning and movement. The bur is simply not long enough to reach the margin (Fig. 12).

In this case, the KOMET “perio-length” diamond bur produces enough clearance to permit access to the margin without the adjacent tooth restricting the path of the handpiece head (Fig. 13). 

A clean margin lays the foundation for a predictable outcome in the final porcelain restoration (Fig. 14).

About the Authors
Dr. Christine M. Yonker received her dental degree from Indiana University School of Dentistry. She was an active participant in periodontal research that explored the inflammation that occurs on a cellular level. Dr. Yonker is in private practice and continues to work on publications for dental journals on a multitude of topics.

Dr. Sergio Rubinstein completed his Periodontal-Prosthesis program at the University of Illinois College of Dentistry where he became an Assistant Professor for 12 years. He invented a device to prosthetically correct misaligned implants and lectures on a national and international level. Patients are referred to Dr. Rubinstein to manage and treat the most simple to the most complex cases, especially when it relates to function and esthetics.