Written by Russell Beggs, DMD Sunday, 01 June 2003 00:00
Our goal as dentists is to conserve the dentition in the most functional and aesthetic way possible. In my office, virtually no restorative dentistry is performed using the same concepts or materials as we were taught 20 years ago. The understanding and integration of adhesion, sealing, and decay removal have profoundly altered the principles upon which our restorations are based. The integration of current principles promotes superior and easier dentistry.
This article discusses the restoration of teeth using current concepts and materials, including the concept of “arrowhead margins,” which maximize the aesthetics of exposed margins.
RESTORATIVE DENTISTRY: PAST AND PRESENT
In the typical case of a tooth with initial decay, the actual decay is frequently significantly greater than is revealed by radiographs, tactile sense, or visual assessment of unstained decay.1 Therefore, I stress the use of a well-researched caries detection stain to be sure that all decay has been found and removed.
If we look at the traditional concepts of restorative dentistry, the obvious decay was removed and an amalgam filling was placed. Numerous studies have shown that significant decay was frequently missed.1,2,3 Years later, when the amalgam or tooth had failed, a new tooth-colored filling was placed; again, decay may have remained. Later, when this tooth or restoration had failed, the common approach was a coronal restoration such as a crown. If a traditionally prepared crown is placed over the remaining tooth structure, a potentially less-than-optimal restoration will be rendered. With this type of restoration, stress forces are concentrated at the cervical aspect of the tooth. Have you noticed that this is where crowned teeth fail and wondered why?
A much better, more tooth-conservative restorative method is to identify and remove any remaining decay with a caries staining agent such as Caries Detector by Kuraray or Caries Finder by Danville Materials. At this point, the remaining healthy tooth structure should be restored with a bondable, sealable restorative material. In general, I prefer a dual-cured flowable composite such as Starfill 2B (Danville Materials); however, a layered light-cured or auto-cure composite with a compatible auto-cure bonding resin would be acceptable.
The ability to bond restorations such as metal, ceramic, or composite crowns with bond values in excess of 20 MPa means that retention form is no longer necessary. The additional surface irregularities and resistance form offer ample and adequate retention while conserving substantial tooth structure.
|Figure 1. A bonded crown (left) dissipates stress forces more effectively than a conventional crown (right), which concentrates stress forces just above the crestal bone level.|
A comparison of the stresses and areas available to dissipate stresses with flexure on a bonded versus a traditional crown are depicted in Figure 1. Note the concentration stresses in the traditional crown at just above the crestal bone level, whereas the stresses are spread out over a much greater area in the tooth-conservative bonded restoration. Also, note that in the bonded restoration, the margins are high, dry, and accessible for construction, finishing, and maintenance. For the typical tooth hollowed out by decay and sequential restorations, the ability to conserve the remaining tooth structure becomes far more significant when the concentrations of stress are evaluated.
EXPOSED MARGINS: THE ARROWHEAD MARGIN
|Figure 2. The arrowhead margin concept provides excellent aesthetics for exposed margins.|
Modern tooth-colored restorative materials such as indirect fiber-reinforced composite allow the use of exposed margins that can be aesthetically blended into tooth structure. In order to maximize the aesthetics of exposed margins, I recommend using an “arrowhead” type margin (Figure 2).
With this technique, a translucent material is used to form a prismatic-like structure (the “head” of the arrow) to diffuse the colors and translucencies of the adjacent restorative material and tooth structure. The marginal chameleon effect is best explained by the 3 diagrams depicted in Figures 3 through 5. The shaft of the arrow is meant to represent the direction of observation. The angle of the “arrowhead” is germane to the chameleon effect. As shown in Figure 3, if the angle is too narrow, the light gets trapped. If the angle is too wide (Figure 4), the light is superficially scattered. However, if the angle is just right, the light is reflected by both adjacent surfaces back toward the viewer (Figure 5). This will maximize the chameleon effect by blending adjacent colors. The restoration will also blend best when it is viewed from a more natural angle or the angle from which it was engineered to be viewed, such as in close interpersonal communication.
|Figures 3 through 5. The correct angle of the arrowhead maximizes the chameleon effect.|
|Figure 6. To achieve an arrowhead margin in this case, a wedge of restorative material is removed and replaced with a translucent material.||Figure 7. The unbonded margins appear white, opaque, and unaesthetic at try-in.|
|Figure 8. After bonding, the arrowhead margin blends with the tooth in an aesthetic manner.|
To illustrate the clinical use of the arrowhead margin technique, Figure 6 shows how a wedge of material is removed during construction and replaced with a translucent material such as Herculite Incisal (Kerr). Be aware that refraction of light at the unbonded margin makes the margin look white and opaque and unaesthetic during try-in (Figure 7). However, as soon as the restoration is bonded, the margin will camouflage into the tooth beautifully (Figure 8).
COMBINING A TRADITIONAL MATERIAL WITH MODERN CONCEPTS
|Figure 9. Tooth preparation for a bonded 3/4 gold crown.|
As exciting as modern tooth-colored restorative materials are, gold remains an excellent material that can benefit from modern concepts of tooth conservation and aesthetics, such as a gold 3/4 crown. Using current techniques, the margins are accessible and easy to finish remarkably well. As shown earlier, the objective is to remove all decay and unsupported enamel and enough tooth structure to achieve appropriate resistance form (Figure 9). Anesthesia is seldom needed during seating if there is minimal exposed dentin.
|Figure 10. The surface of the gold to be bonded is tin-plated (before tin-plating on left; after tin-plating on right).||Figure 11. The margins are finished with a carbide bur and a rubber polishing wheel.|
|Figure 12. Excellent margins can be achieved when combining bonding with traditional gold material.|
The cast gold 3/4 crown is first microetched for a few seconds with 50 µm AL2O1. The etched gold is then easily tin-plated in a few seconds with a tin plater (Danville Engineering or Kuraray). Note the difference in color before and after tin-plating in Figure 10. Seating is accomplished by preparing the tooth structure for bonding. Microetch (sandblast) and etch with 37% phosphoric acid (Star-etch by Danville Materials) for 20 seconds. Wash, dry gently (if significant dentin is exposed or if sensitivity is manifested, I then apply Microprime [Danville Materials] for 30 seconds and dry gently), apply Photo Bond with Activator (Kuraray) to both the tooth and the tin-plated gold, and gently air-dry. I prefer using a dual-cured composite for luting such as Starfill 2B (Danville Materials) or Panavia 21 (Kuraray). (I would use the same bonding sequence for an indirect resin restoration.) Excess material in the gel state is removed with floss and a scaler. I like to finish the margins with a 7902 carbide (Figure 11) and a rubber polishing wheel using brief, gentle contact to minimize heat. The seating process takes only a few minutes to deliver an outstanding margin (Figure 12).
In the 20 years since I graduated from dental school, the materials and concepts of restorative dentistry have changed profoundly, to the point where very few restorations are performed in my office as they were originally taught. A conceptual understanding of the opportunities available for predictable decay removal, conservation and support of existing tooth structure, and aesthetic margins provides the enlightened dentist clinical options for providing patients with superior restorations.
The author wishes to acknowledge and thank Dr. Raymond Bertolotti for his guidance and his many contributions to the advancement of clinical dentistry.
1. Kidd EA, Joyston-Bechal S, Smith MM, et al. The use of a caries detector dye in cavity preparation. Br Dent J. 1989;167:132-134.
2. Anderson MH, Charbeneau GT. A comparison of digital and optical criteria for detecting carious dentin. J Prosthet Dent. 1985;53:643-646.
3. Fusayama T. New Concepts in Operative Dentistry: Differentiating Two Layers of Carious Dentin and Using an Adhesive Resin. Chicago, Ill: Quintessence Publishing Co; 1981.
Disclosure: Dr. Beggs is a researcher with Danville Materials and is involved in developing new and innovative products. He is a stockholder in the company.
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