Margin Design in the Most Overlooked Aesthetic Zone

Advancements in material technology now provide us many opportunities to improve a patient’s smile. No longer do we have to utilize metal ceramics in the aesthetic zone. As early as 1975 Rochette in France introduced bonding of ceramic materials to anterior teeth.1 Since that time newer metal-free restorations have been developed and demonstrated to be superior in mimicking natural tooth structure for a number of reasons.2-4
One such reason is the dynamics of light transmission. This principle greatly affects the natural appearance of restorations (Figure 1). As incidental light passes through enamel and into dentin it is diffused or scattered. This pattern, although not as intense, occurs with porcelain restorations. In other words, the incidental light passes through the enamel and is diffused in the dentin in a multitude of directions. With metal restorations, the incidental light is mostly directly reflected back away from the opacious metal. The end result is a less-than-natural appearance of the restoration. This is due to a difference in light transmission.

Figure 1. Light transmission patterns.	Figure 2. Incidental light.

Figure 3. Beauty of all-ceramic restorations.

In addition, the angle of incidental light can cause a shadowing with ceramo-metal restorations that detracts from a natural look (Figure 2). If the incidental light is concentrated from a lateral source, then the metal can cast a noticeable shadow on the opposite contact area. All-ceramic restorations diffuse light in a similar fashion to natural teeth. Therefore, all-ceramic restorations are the most aesthetic choice for the aesthetic zone (Figure 3).
The limits of the classic aesthetic zone depend on how wide someone smiles and shows teeth. The aesthetic zone can include maxillary and mandibular molars forward. Any combination of posterior and anterior teeth, both maxillary and mandibular, may be included.

Figure 4. Functional and aesthetic zones.

Sometimes the aesthetic and functional zones overlap (Figure 4). When this occurs, we usually try to find stronger restorations that can also be aesthetic. Some researchers suggest that there is little evidence to support that all-ceramic restorations are at a high risk of failure.5 Although many of the new substrate-supported systems have the ability to withstand maximum forces, our standard PFM system has the longest track record. With the incorporation of slight modifications, the PFM technique can give us restorations that are extremely aesthetic in addition to being strong.
It might be worth noting that the strongest restorations might not be the most desirable. Pascal Magne in his recent book Bonded Porcelain Restorations6 states that, “new restorative approaches should aim to create not the strongest restorations but rather a restoration that is compatible with the mechanical, biologic, and optical properties of underlying dental tissues.” If we accept this, then the concept of “aesthetic demands and functional risk” may very well be rewritten as new technologies and research merge.

Figure 5. 360º collar; a high noble gold-palladium alloy is shown.

Figure 6. Exposed facial gold margins.

Figure 7. Cut-back technique; a high noble gold-palladium alloy is shown.

Figure 8. Facial porcelain butt margins; a high noble gold-palladium alloy is shown.

One aspect of the PFM technique is the design of the gold and porcelain as they reach the gingival margin. Historically, a small (and sometimes not so small) gold collar was placed around the entire restoration (Figure 5). Certain early designs had the somewhat small gold collar on the facial aspect of the crown to be tucked slightly under the facial gingival tissue. This would often be aesthetically adequate for some finite period of time. However, eventually a small amount of recession would uncover this collar, and then unhappy patients would voice numerous opinions, mostly related to the notorious “dark band” around their crown (Figure 6).
Within recent years, cut-back techniques have been developed to hide any gold from being seen around the facial margin (Figure 7). In addition, newer and more easily utilized shoulder porcelains have been formulated. The new technologies include pressing porcelain to this metal-free margin. These improvements or advancements have made a tremendous impact on aesthetic dentistry.

Figure 9. Properly placed gold lingual collar.	Figure 10. Exposed lingual gold collar on anterior tooth.

Figure 11. Examples of unsightly lingual gold collars.

Figure 12. Facial and lingual porcelain butt margins.	Figure 13. Facial and lingual porcelain butt margins with knife-edge interproximal collars; a high noble gold-palladium alloy is shown.

Figure 14. Captek crown.

Figure 15. Deeply placed interproximal restorations.	Figure 16. Topography of contact areas.

Most clinicians are now comfortable with porcelain butt margins, as well as the resin cements used to stabilize these restorations. The remaining collar covering three fourths of the clinical crown was made out of a band of gold (Figure 8). Often these collars were designed for the convenience of the technician to hold the substrate. Currently these lingual gold collars can be made 1 mm or less and placed under the gingival sulcus to fabricate a maximum aesthetic result (Figure 9).
The most overlooked aesthetic zone is the lingual aspect of the maxillary molars, premolars, and sometimes the canines and incisors. Anyone with a wide open mouth upon laughing, or who has a small child or grandchild, knows what I am talking about. “Mom, Dad, Grand-ma, or Grandpa, what is that dark thing in your mouth?” (Figures 10 and 11).
By utilizing a porcelain butt margin on the lingual as well as the facial we are virtually eliminating any aesthetic drawback (Figure 12). The remaining margin interproximally is designed for a gold knife-edged margin. This gold knife-edged margin is the most predictable and easy to finish interproximally (Figure 13).
The most aesthetic and healthy of all PFMs for the soft tissue are those utilizing facial and lingual porcelain butt margins, along with a gold knife-edged interproximal margin made from Captek gold (Figure 14). Research has documented the bacteriostatic nature of Captek gold. Captek may be the best choice for patients with a periodontal history, due to noted reduction of plaque on the gold margin surface.7 There is no other restoration that maximizes strength, aesthetics, and gingival health. Should the aesthetic zone and functional zone overlap, consider this product as an excellent choice.
In addition, it must be remembered that many of the premolars and molars have extensive amalgam restorations placed deep into the interproximal tissues (Figure 15). Often, biologic width issues can be a concern. The gold knife-edge margin is the most controllable of all margins in the interproximal region.
Some clinicians advocate a 360° porcelain butt margin around all teeth. The key to predictable margins is the ability to control the finishing of all 360° of margin around the tooth. Anterior teeth have interproximal margins that can be reached and highly polished. However, as we move from premolars to molars, the facial-lingual dimension in-creases (Figure 16). This, in addition to being covered with more interproximal gingival tissue, diminishes the ability of the clinician to control the environment around the margins. Also, some of the root surfaces are concave, which eliminates or greatly diminishes the chance of properly finishing the margin.
There will always be circumstances where 360° porcelain butt margins will be ideal on all teeth. Care should be given in selecting marginal preparation design due to the decreasing ability to finish margins as we go from an-terior to posterior.

CONCLUSION

In focusing our concerns on the aesthetic nature of contemporary restorations, we often limit our focus to the facial aspect of teeth. If we can comprehend all the visual possibilities, new areas of focus will appear. The lingual aspect of most maxillary teeth falls into this new focus. By incorporating both the facial and lingual zones of aesthetics we will be generating a higher level of aesthetics for the patients we treat.

References

1. Rochette AL. A ceramic restoration bonded by etched enamel and resin for fractured incisors. J Prosthet Dent. 1975;33:287-293.
2. Krasteva K. A technique for aesthetic, natural-looking anterior metal-free restorations. Dent Today. Oct 2001;20:82-89.
3. Roberts J, Roberts M. Achieving optimal aesthetics using contemporary porcelain materials: a case report. Pract Proced Aesthet Dent. 2004;16:495-502.
4. Little DA. Illustrating predictable anterior and posterior esthetic results: two case studies. Compend Contin Educ Dent. 2002;23(3 suppl 1):17-23.
5. El-Mowafy O, Brochu JF. Longevity and clinical performance of IPS-Empress ceramic restorations: a literature review. J Can Dent Assoc. 2002;68:233-237.
6. Magne P, Belser U. Bonded Porcelain Restorations in the Anterior Dentition: A Biomimetic Approach. Carol Stream, Ill: Quintessence; 2002:52.
7. Goodson JM, Shoher I, Imber S, et al. Reduced dental plaque accumulation on composite gold alloy margins. J Periodontal Res. 2001;36:252-259.

Dr. Wynne maintains a private practice in Raleigh, NC, focusing on aesthetic and restorative dentistry. He graduated from the University of North Carolina School of Dentistry, Chapel Hill, NC, in 1971. He has recently become a member of the Academy of Pankey Scholars. He is a member of the American Academy of Cosmetic Dentistry and a longtime member of The American Academy of Dental Practice Administration. He has completed Level I and II of the Ultimate Esthetic Continuum at Americus in New York City. His past lecturing has been with the Ultimate Esthetic Continuum in New York City, the Esthetic Epitome in Charlotte, NC, and various educational study groups. He has published numerous articles on aesthetic dentistry, occlusion, and eating disorders. He can be reached at (919) 851-8383, wpdw@nc.rr.com, or by visiting billwynnedds.com.