Dr. Gregg A. Helvey describes a little-known crown technique that conserves tooth structure and minimizes invasiveness.
By Gregg A. Helvey, DDS
A paradigm is a philosophy of a scientific discipline comprised of theories, rules, and generalizations that form a conceptual framework within which scientific research is performed. For example, the four-volume treatise published by G.V. Black in 1908 set the standards for operative dentistry in his time and remained dominant for many years later. The standards set by Black have had an amazing run for the last hundred years. In fact, many of his principles are still taught in dental schools today.
Changes in the way procedures are clinically performed will usually occur as scientific improvements are presented. A significant change in the method in which a procedure is executed would be considered a change to that paradigm, which is referred to as a paradigm shift.
In particular, the introduction of adhesive dentistry opened the door to a paradigm shift in the way the traditional crown preparation is performed. As restorative and cementing materials have improved, the preparation techniques have mostly remained the same. Adhesive dentistry has changed so many of our standard restorative techniques because retention is not derived by mechanical means. The non-retentive adhesively retained all-ceramic crown preparation, also known as a “tabletop” restoration, simply replaces a defective occlusal table. The resistance and retention form of the crown preparation are not provided. In fact, these important traditional crown preparation requirements are substituted with a wide band of enamel that provides retention strictly through adhesive means.
There are a number of reasons why teeth are restored with a full crown. In the traditional crown preparation, the resistance and retention form are created by the preparation angle of the axial walls. This means removal of all the enamel on all sides of the tooth. In many cases, this enamel is structurally intact but removed for the purposes of retention and resistance to dislodgement. The reduction is also required for the fabrication of a traditional style crown. If a tooth requires major structural enhancement, a full crown may not be the only choice of treatment.
An example of a paradigm shift would be if a clinician were able to restore 100% of the structural integrity of a tooth by only having to replace the occlusal table with a non-retentive adhesively retained ceramic restoration that provided the esthetic and functional occlusal requirements. A paradigm shift in the crown preparation would then be to remove only the defective parts of the tooth and replace them with a high-strength ceramic material that was adhesively retained to a large amount of intact enamel. This paradigm shift would conserve tooth structure and minimize the invasiveness of the procedure.
A patient presented with the chief complaint of pain upon chewing with thermal sensitivity associated with tooth No. 29, the lower right second bicuspid. Clinically, the tooth presented with a distal-occlusal restoration that was more than two-thirds the width of the tooth and a fracture line on the mesial marginal ridge (Fig. 1). A radiograph revealed the restoration to be very deep. Using transillumination from the facial aspect, the fracture appeared to be beyond the dentin-enamel junction. Bite stick analysis confirmed a diagnosis of cracked tooth syndrome.
Fig. 1 — Preoperative view shows the existing restoration and the fractured mesial marginal ridge.
An adhesive-retained CAD/CAM ceramic restoration would be used to restore the tooth, so a preoperative digital picture was taken. After removal of the existing restoration, axial-pulpal line angle fractures were present in both the facial and lingual cusps. Using a #330 carbide bur, depth cuts of 2 mm were placed in the two cusps. A horizontal cut was then used to remove these cusps. This exposed the widest band of enamel at the super-bulge area of the tooth. A flat-end tapered diamond bur was used to create a flow between both sides of the tooth so there would not be any abrupt changes in the topography of the occlusal surface (Fig. 2).
Fig. 2 — “Tabletop” prepared tooth with intact facial and lingual axial walls.
The preparation did not include reduction of the axial walls. All surfaces were smoothed with a 12-fluted finishing bur and the non-retentive adhesively retained “tabletop” preparation was completed. The prepared tooth was then scanned. The restoration was designed and then milled using a lithium metasilicate ceramic block. After milling, the restoration was tried in to confirm the fit and occlusion. After polishing and staining the occlusal surface, the restoration was placed in a two-stage porcelain furnace to facilitate the growth of crystals (crystallization) with a gradual temperature rise to 1,650° F. This heating cycle converted the restoration from a lithium metasilicate form to a disilicate form. At the completion of the crystallization cycle and time allowed to cool, the bonding surface of the ceramic restoration was treated with phosphoric acid, rinsed with water, and dried. Clearfil Ceramic Primer was then applied and dried. The restoration was inserted using a sixth generation bonding adhesive system (Figs. 3 and 4).
Fig. 3 — Facial view of the “tabletop” restoration in place.
Fig. 4 — Lingual view of the “tabletop” restoration in place.
The tooth had now been restored with a new occlusal surface adhesively connecting the facial and lingual sides of the tooth without destroying the intact axial walls. Although this technique is not a totally new concept (the author has been using it successfully for more than 10 years), it is not a widely published technique. Further information can be found in the following articles: “Non-retentive, adhesively retained posterior restorations” by G.A. Helvey and “Posterior, all-porcelain, adhesively retained restorations” by E.M. Bakeman and J.C. Kois.
Dr. Gregg Helvey is part of an elite group of dentists who are also skilled ceramists. This combination of experience as both a dentist and a laboratory technician has aided in the development of unique restorative and laboratory procedures, many of which have been published in peer-reviewed journals. He currently serves on the editorial board of Inside Dentistry, Compendium of Continuing Education in Dentistry, and Inside Dental Technology. In addition to his position as adjunct associate professor at Virginia Commonwealth University School of Dentistry, Dr. Helvey teaches in the AEGD residency program emphasizing all-ceramic restorations. He received his dental degree from Georgetown University in 1976, and received his Mastership in the Academy of General Dentistry in 1997. Dr. Helvey lectures nationally and internationally and maintains a private practice in Middleburg, Va.