Oral Health Group
Feature

Conservative Preparation for Bonded Porcelain Laminate Veneers

April 1, 2007
by Ross W. Nash, DDS


Ceramic veneers that can be glazed on the outer surface and etched on the internal surfaces for micro-mechanical retention provide us with materials that are more durable, stain resistant and enamel-like in appearance than previous composite resin alternatives. They can be fabricate by a ceramist and bonded to place with composite resin by the dentist. Stacked porcelain (powder/ liquid) either feldspathic or synthetic such as that used for porcelain fused to metal crowns can be used. A number of porcelain materials designed specifically for veneering procedures have been developed. Only 0.3 to 0.5mm of thickness is needed for these materials, so conservative preparation is possible.

Pressed ceramics for veneering applications as well as for full crowns, inlays and onlays have also been developed. These materials are made through the lost wax technique similar to cast metals. They exhibit excellent fit and high strength. I have found that most technicians I have worked with want at least a millimeter of thickness for pressed ceramics, so a more aggressive preparation is needed compared to the stacked porcelain alternatives. I have found that, when I have the room after necessary preparation, I tend to prescribe these materials because of the fit and strength qualities. But I prefer stacked porcelain for most elective porcelain veneer cases because it allows me to conserve more natural tooth structure.

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The reason that thin layers of porcelain can be used with great success in these veneering processes is because of something called “the lamination effect.” Ceramic materials are inherently brittle in nature. But when a ceramic is laminated to an underlying strong material, it becomes quite strong itself.

An example of this phenomenon is that of a piece of floor tile. A strong man can break a piece of floor tile in his hands. However, after being laminated to the floor, a floor tile rarely breaks. The tile is strengthened by lamination. This is why porcelain fused to metal works so well. The porcelain is laminated to the metal substrate providing it with the strength to work in highly stressed areas such as molars. Now that we can laminate a ceramic material to the tooth structure itself through the bonding process, the tooth becomes the supporting structure and the ceramic is strengthened.

One of the disadvantages of ceramic veneers is that ceramics, bonded correctly, are removed by cutting them off with a diamond bur in a high speed handpiece, unlike a cemented restoration that can more easily be removed. My experience tells me that removal of a bonded ceramic will invariably result in removal of more natural tooth structure. My clinical history tells me that even though ceramic veneers are lasting a long time (ten to fifteen years or more), like any other restorative material, they cannot be considered “permanent.” Unless placed in the twilight of a patient’s life, it is likely that replacement will be needed or desired sometime in the future. If aggressive tooth reduction has already been performed, the patient’s options will be limited. It is likely that better, more durable and more conservative materials will be developed, so I feel compelled to be as conservative as I can for the patients benefit.

Elective Porcelain laminates can be used for a variety of clinical situations. New surfaces for the teeth fabricated from porcelain can correct for undesirable color, defective areas such as in mottled enamel, diastemas, rotated teeth, moderate crowding, broken or worn incisal edges and deficient enamel or dentin, to name a few.

CLINICAL EXAMPLES

Case 1

The patient in Fig. 1 wanted a central diastema closed and lighter and more well aligned surfaces created for her maxillary anterior teeth. It was decide to prepare veneers for her central and lateral incisors, her canines and here premolar teeth. 0.5mm of facial reduction and 1.0mm of incisal reduction using a tapered diamond bur was accomplished for her six maxillary anterior teeth. 0.5mm of facial reduction was accomplished for the premolars with no occlusal preparation. Shallow horizontal facial grooves were prepared in the premolars to be used as seating grooves. A subtle chamfer margin was prepared at the height of the tissue. All line angles were rounded and smooth.

Full arch impressions were taken with a polyvinal siloxane impression material and stone models were poured in the dental laboratory. Platinum foil matrix material was swedged to the dies and stacked porcelain laminates were fabricated. The internal surfaces were etched with hydrofluoric acid to for micromechanical retention. The internal surfaces of the thin veneers can be seen in Fig. 2.

The veneers were bonded to place by acid etching the prepared tooth surfaces for fifteen seconds with 37% phosphoric acid gel, followed by placement of a dentin and enamel bonding agent. The internal etched surfaces of the porcelain laminates were treated with silane for thirty seconds and dried before a light cured composite luting agent was applied. After placement on the prepared teeth, the composite cement was light cured for twenty seconds on the facial and lingual surfaces. The excess composite was removed with a carbide finishing bur used in a high speed handpiece. The occlusion was adjusted with finishing diamonds and the adjusted surfaces were polished.

The finished result is shown in Fig. 3. We were able to create the esthetic result the patient desired with minimal tooth reduction.

Case 2

In this case, the patient was missing her maxillary lateral incisors and the canine teeth had been moved into the spaces through orthodontic treatment. The patient desired to have porcelain veneers placed to simulate lateral incisors in the proper location and improve the surface characteristics of her maxillary anterior teeth.

With only minimal preparation (Fig. 4), we were able to use stacked porcelain veneers to accomplish these goals. The veneers are shown on the working model from the incisal view in Fig. 5. The final result with all eight veneers bonded to place can be seen in Fig. 6.

Case 3

Sometimes conditions exist where a new surface is desired on both facial and lingual areas of the teeth. Conventional crowns can be used to accomplish this, however aggressive tooth reduction is necessary. 360 degree laminates can be used in some instances to provide a similar result with much less tooth reduction.

In Fig. 7, you can see maxillary anterior teeth prepared for stacked porcelain laminates with 0.5mm of facial reduction and 1.0mm of incisal reduction. The lingual areas have also been prepared at 0.5mm as can be seen in Fig. 8. One of the thin 360 degree laminate veneers can be seen over the working die in Fig. 9. The internal etched surfaces can be seen in Fig. 10. This restoration was fabricated on a refractory die rather than on a platinum foil matrix. Note that the 360 degree laminate or “mini-crown” is very thin, but when it is bonded to place, the lamination effect will allow for enough strength for function.

The final result is show from the facial view in Fig. 11 with the 360 degree laminates bonded to place. The incise view can be seen in Fig. 12.

In the same case, it was desired to resurface the first premolar In Fig. 13. A 360 degree laminate shown over the working die can be seen in Fig. 14. The thin laminate is shown in Fig. 15 after it was bonded to place. Note the standard porcelain veneer for the second premolar.

Case 4

For mandibular incisors, my preference is to use only 0.3mm of axial reduction as show in figure 16. 1.0mm of incisal clearance is desired so that the porcelain laminate can overlap this area. The internal etched surfaces of the thin stacked porcelain veneers are shown in Fig. 17. They are shown bonded to place in Fig. 18.

CONCLUSION

Porcelain laminate veneers can be used to solve a number of clinical problems. It is not always necessary to remove large amounts of natural tooth structure to accomplish par
tial or full coverage. The lamination process allows us to use thin layers of porcelain to resurface natural tooth structure in some cases. While pressed ceramics can be used to provide high strength, well fitting restorations, most ceramists desire at least 1.0mm of axial reduction or clearance to achieve the esthetics desired. Stacked porcelain laminates can be fabricated at as little as 0.3mm of thickness and provide excellent esthetics. Lamination from the bonding process enhances the strength of these restorations much like that in conventional porcelain fused to metal. It is often possible to conserve more natural tooth structure by using stacked porcelain laminates. The tooth itself becomes the supporting structure.

Ross W. Nash, DDS is co-founder and president of the Nash Institute in Charlotte, N.C. where he provides continuing dental education for dentists and team members. Dr. Nash maintains a private practice in Cornelius, N.C. He is an editorial advisor and regular writer for several dental publications and has authored a chapter in a dental textbook on esthetic dentistry. An international lecturer on subjects in esthetic and cosmetic dentistry, he is a Fellow in the American Academy of Cosmetic Dentistry and Diplomat for the American Board for Aesthetic Dentistry. He has been a clinical instructor at the Medical College of Georgia School of Dentistry. Dr. Nash is a consultant to numerous dental products manufacturers. For information on courses at the Nash Institute call Max Maxwell toll free at 1-888-442-0242 or 1-704-442-6996. He can be contacted by calling 1-704-364-5272 or emailing at rosswnash dds@aol.com. His website is www. NashInstitute.com.

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