Making Difficult Cases Easier With Supragingival Dentistry: Porcelain Onlays and Veneers

INTRODUCTION
Recently, I was in a very popular chat room for dentists and became engaged in a heated debate with some colleagues who presented themselves as very progressive clinicians and educators, fully versed in modern adhesive dentistry. The debate started when I suggested that supragingival onlays are excellent substitutes for full-coverage crowns in many cases, often making crowns not the most conservative nor best restorative choice. The other chat room participants felt that porcelain onlays are only for simple cases, defending their position that full crowns are needed most of the time for badly damaged teeth. This shows the controversy that currently exists regarding certain restorative choices among dental colleagues.

The purpose of this article is to present a rationale for supragingival restorative dentistry as a viable substitute for traditional full crowns both in the anterior and the posterior areas. This minimally invasive concept of restorative treatment is especially useful with badly damaged teeth, often making difficult cases easier.

Indirect Restorations: When and Which One?
First of all, indirect restorations should be reserved for cases in which the tooth is too badly damaged to be restored with a more minimally invasive direct composite restoration. The literature shows long-term evidence that direct composite restorations compare well with much more expensive and more invasive indirect porcelain or composite inlays.^1,2 Thus indirect onlays, veneers, or full crowns should be reserved for cases with severely damaged teeth by caries, secondary caries on failing restorations, or fractures. Truly, with today’s adhesives and much improved composites, it is becoming increasingly difficult to determine exactly when it is desirable or appropriate to go indirect. Almost any tooth could be repaired with a direct composite restoration, including a direct composite crown, similar to the direct amalgam crown of old. Doing an indirect restoration is desirable mostly for convenience, because freehanding a very large restoration that includes cusp tips, grooves, and marginal ridges, would be very time consuming and imperfect.

Supragingival Restorative Dentistry
Subgingival dentistry is difficult, unpredictable, and often unhealthy periodontally for our patients in the long term. Implementing supragingival dentistry can improve the health of our patients, and also make restorative work easier and more predictable. As we all understand, adhesive dentistry depends on excellent isolation since any contamination during the cementation steps can lead to early failure, secondary caries, or postoperative sensitivity. For more than a decade, the author has been teaching about the importance of supragingival dentistry and its many benefits. This includes how, by using certain modern translucent all-ceramic materials, invisible (or nearly invisible) margins can be predictably and consistently achieved using this restorative technique. In addition, a supragingival approach to restorative work removes the need for a challenging subgingival margin preparation with the usual need for a double-cord technique, a higher percentage of impression problems, and the usual clinical challenges associated with achieving proper isolation and the cementation protocol.

In the author’s opinion, to achieve supragingival margins in badly decayed or broken down teeth, a new approach to preparation is needed. There are 5 supragingival restorative principles that, when implemented properly, can provide predictable results in even the most broken down teeth.

Simple and self-explanatory, the principles are as follows:

1. Careful removal of caries and old restorations to protect and preserve enamel and tooth structure close to the margins.
2. No proximal boxes because proximal boxes are unnecessary for mechanical retention, with box preparation often leading to subgingival margins.
3. Enamel preservation at the margins and reinforcement with adhesives and composite.
4. Margin elevation and buildups to repair subgingival margins and any weakened tooth structure.
5. Proper use of translucent restorative materials.

All of these restorative principles ultimately allow for supragingival restorative margins and thus easier and more predictable impression and resin cementation protocols. (Note: Future articles are planned that will cover the 5 supragingival restorative principles in more detail.)

Differences Between Full Crowns and Partial Coverage Onlays or Veneers
Full-coverage crowns of any material, and partial-coverage onlays and veneers, can be used for the same purpose in order to replace/restore large areas of tooth structure previously damaged by caries and/or fractures. Both types of restorations—full-coverage crowns and partial-coverage bonded onlay and veneers—start in the same way; removing the damaged part of the tooth, followed by creating sufficient occlusal or incisal space for the material thickness. However, the similarities end there, since full-coverage crowns require axial wall reduction for mechanical retention and resistance.³ This usually requires cutting healthy tooth to create space for the axial wall of the crown needed for retention.

In contrast, minimally invasive supragingival onlays and veneers do not need the axial wall preparation, as they depend on adhesion for retention, so there is no need for this additional tooth removal.⁴ Lack of trust in adhesion keeps many dentists preparing teeth for full crowns with the traditional and long-taught mechanical retentive features that were developed long before modern adhesive dentistry was introduced. On the other hand, many industries outside of dentistry have developed a great trust in adhesion. As an example, think about what has happened in the field aerospace engineering. Manufacturers are building amazing high-tech aircraft (such as the Boeing 787 Dreamliner, and military jets like the Northrup Grumman B-2 Spirit, and the Lockheed-Martin F-22 Raptor) that depend upon reliable and durable adhesive bonding to hold crucial components together under extreme stress and high-performance flying conditions. Clinical studies showing excellent longevity for bonded onlays and veneers abound, with most failures being attributed to fractures and secondary caries.^5-7 It is more difficult to find clinical data of failures due to problems related to adhesive retention. Understanding the limited value of anecdotal evidence, the author reports that he has bonded several thousand onlays and veneers during the past 20 years and reports less than 10 restorations that have failed due to retention failure. In the author’s experience, adhesion works!

Porcelain Veneers As Substitute to Full Crowns in the Anterior Region
It is worth clarifying that porcelain veneers can be used as aesthetic facings to achieve ideal smiles, and also for restorations that can repair badly damaged or endontically treated anterior teeth. In many cases, anterior teeth are found to be damaged by decay or fractures, so both the full-crown procedure and the supragingival minimally invasive veneer procedure start the same way, by removing the part of the tooth damaged by caries, old restorations, and/or fractures. After that initial similarity, both procedures change dramatically.

After removing the damaged part of the tooth, the choice of a full traditional crown will require the removal of the remaining enamel and some dentin from the facial and lingual of the tooth to create the traditional form of a crown preparation with its mechanical retentive/resistance form. Often subgingival margins are placed to hide the opacious materials used for a crown, making this restoration less predictable and unhealthy for the gingiva.⁸ The preparation for veneers, on the other hand, begins in the same way, by removing the bad part of the tooth; however, because these restorations do not require the traditional mechanical retention, usually the lingual part of the tooth can be fully preserved. Furthermore, if done using supragingival minimally invasive techniques, after the removal of the decay, any damaged tooth structure can be repaired with composite and then traditional veneer preparation can be performed with most of the facial enamel also being preserved. Preserving enamel is crucial for to maintain proper tooth stiffness.

The scientific literature supports the idea that bonded restorations reinforce teeth and can be used predictably to bring badly damaged teeth to a state similar to the original.^2,9 It is usually perceived that crowns are easier but, in fact, experienced clinicians have realized that veneer preparation and cementation is usually faster and easier than full-crown techniques, if the correct clinical techniques are implemented (as being taught at the Los Angeles Institute of Clinical Dentistry and other top-notch teaching institutions).

CASE REPORTS
Clinical Cases 1 and 2: Managing Badly Damaged Anterior Teeth
In Case 1, the clinician decided to employ a traditional full-crown preparation approach to treatment. (Note: This case, shared by Erick Gutierrez, DMD, of Pasadena, Calif, was not the author’s patient.) The patient presented with badly damaged anterior central incisiors (Figure 1). First, any old restorative materials and caries were removed (Figure 2). Next, the teeth were built up with composite resin and then prepared for traditional crowns with subgingival margins (Figures 3 and 4).

CASE 1 Figure 1. Both maxillary central incisors presented with severe damage from caries. Figure 2. Both central incisors after caries removal. Figure 3. After buildups and final crown preparations. Observe the large amount of remaining dentin and enamel that had been removed. Figure 4. Radiograph showing severe caries damage on right maxillary lateral; also note the missing tooth structure at the mesial-incisal.

For Case 2 (Figure 5), a minimally invasive supragingival technique was used to repair a broken-down anterior lateral incisor. After careful removal of the caries and old restorative materials (Figure 6), direct composite resin (CLEARFIL MAJESTY SE Classic [Kuraray]) was placed (Figures 7 and 8). Then, a supragingival minimally invasive veneer preparation was accomplished.

Now, compare the amount of natural tooth preserved with the veneer using supragingival margins in Case 2 with the lack of tooth conservation seen in the final crown preparations in Case 1 (Figures 3 and 7). Of course, restoring a tooth in this modern fashion requires a paradigm shift, as the restorative margins of the veneer will be cemented in part on the composite resin restorations and not all on natural tooth, as traditionally done.

CASE 2 Figure 5. Observe the large amount of tooth removed due to caries, but also the large amount of enamel and dentin preserved. Figure 6. After tooth was repaired with direct composite resin. Figure 7. After supragingival veneer preparation. Figure 8. Finished restoration (Layered Noritake Feldesphatic Veneer) immediately after cementation.

Supragingival Minimally Invasive Onlays Can Make Difficult Cases Easier
As previously described, both crowns and onlays start the same way: by removing the bad part of the tooth and ensuring that there is enough occlusal/incisal space for the restorative material. After the above is done, full-crown preparations require extensive additional tooth removal for axial reduction, because they depend on mechanical retention. The required 3 to 4 mm of (minimal) axial wall height, along with the need for an adequate ferrule on natural tooth structure, often force the placement of subgingival margins, the use of double-cord techniques, and all the potential clinical challenges and possible long-term problems for the patient.¹⁰ On the other hand, with the supragingival approach, after the removal of any previously placed and damaged restorative materials, caries removal, and incisal edge reduction, no additional axial reduction was needed for bonded onlays. Instead, enamel preservation is the goal. This is the case because retention is fully achieved not by wall or boxes, but by bonding adhesion.¹¹ When caries or old restorations are in fact subgingival, margin elevation techniques can be performed.⁴ While most clinicians have the perception that onlays and veneers are more difficult, this is often due to lack of experience and the use of incorrect techniques.¹²

Clinical Cases 3 and 4: Badly Damaged Posterior Teeth
Case 3 was a badly decayed tooth that would be best treated using an indirect restoration (Figure 9). Similar to a crown preparation, caries removal was the first step (Figure 10). Because this was an onlay preparation using supragingival techniques with the goal of enamel preservation, the weakened enamel was reinforced with adhesive (CLEARFIL SE Protect [Kuraray]) and composite resin (CLEARFIL MAJESTY Flow [Kuraray]). Instead of completely preparing the tooth, observe the lingual portion of the tooth and the 1.5 mm of occlusal reduction achieved for the proper thickness of the restorative material chosen for this case (Figure 11). No further removal of tooth for axial wall, boxes, and/or offsets was needed for mechanical retention. Again, the restoration depends on adhesion for retention. This all-ceramic restoration (e.max HT [Ivoclar Vivadent]) was cemented using CLEARFIL ESTHETIC CEMENT (Kuraray) and CLEARFIL SE Protect (Figure 12). In this case, if the axial wall had been reduced for a full-crown preparation, this tooth would have resulted in deep (2.0 to 3.0 mm) subgingival margins to gain the minimal axial wall height required for traditional resistance/retention form, the use of a double-cord technique, and impression and cementation technique challenges with less predictable results.

CASE 3 Figure 9. Posterior second molar with severe caries and total loss of distal ridge and DL cusp. Figure 10. After caries removal and an indirect pulp cap. Imagine if this were to have been prepared for a full crown: it would have resulted in margins at 2.0 to 3.0 mm subgingival on half of the tooth to achieve minimal axial wall height required for resistance/retention with a traditional full-crown preparation. Figure 11. Finished onlay preparation; the entire margin is supragingival. Figure 12. Finished onlay preparation with all supragingival margins.

Case 3 serves to demonstrate that using supragingival minimally invasive techniques made this restoration easier to do for the clinician.

In Case 4 (Figure 13), the patient presented with an old failing amalgam restoration and recurrent caries in a posterior first molar. After the initial removal of the old filling material (Figure 14), it clearly appeared to me that it would have been a difficult case if it were to be done using a traditional full-crown technique. Figure 15 shows the finished onlay preparation. Surprisingly, the margin ended up all supragingival and, furthermore, we were able to maintain its entire periphery in enamel. This was achieved via thoughtful and judicious removal of tooth structure, and with enamel preservation utmost in mind.

CASE 4 Figure 13. Severely damaged tooth with old, large apparently subgingival amalgam. Figure 14. After amalgam removal. This tooth would appear to have subgingival caries and would traditionally be considered better suited for a crown.   Figure 15. Finished onlay preparation showing how with careful caries removal we can often achieve supragingival or at least equi-gingival margins; easy to manage from here.

CLOSING COMMENTS
Indirect restorations should only be used for teeth damaged to an extent that direct restorations are no longer indicated. Unlike the general beliefs, partial coverage bonded onlays and veneers are not just for the simple cases, and crowns for the other most complicated cases. In fact, supragingival minimally invasive bonded onlays and veneers are ideal for difficult cases, often simplifying those cases when proper supragingival restorative techniques are implemented.

References

1. Pallesen U, Qvist V. Composite resin fillings and inlays. An 11-year evaluation. Clin Oral Investig. 2003;7:71-79.
2. Shor A, Nicholls JI, Phillips KM, et al. Fatigue load of teeth restored with bonded direct composite and indirect ceramic inlays in MOD class II cavity preparations. Int J Prosthodont. 2003;16:64-69.
3. Shillingburg HT, Hobo S, Whitsett LD, et al. Principles of tooth preparations. In: Shillingburg HT, Hobo S, Whitsett LD, et al, eds. Fundamentals of Fixed Prosthodontics. 3rd ed. Chicago, IL: Quintessence Publishing; 1997:119.
4. Ruiz JL. Supragingival dentistry using metal-free restorations. Dent Today. 2008;27:104-109.
5. Swift EJ Jr, Friedman MJ. Critical appraisal. Porcelain veneer outcomes, part I. J Esthet Restor Dent. 2006;18:54-57.
6. Krämer N, Frankenberger R. Clinical performance of bonded leucite-reinforced glass ceramic inlays and onlays after eight years. Dent Mater. 2005;21:262-271.
7. Ruiz JL, Christensen GJ, Sameni A, et al. Clinical performance of bonded ceramic and resin-based composite inlays and onlays using a self-etch bonding system—a 51-month report. Inside Dentistry. 2007;3:62-65.
8. Reitemeier B, Hänsel K, Walter MH, et al. Effect of posterior crown margin placement on gingival health. J Prosthet Dent. 2002;87:167-172.
9. Magne P, Douglas WH. Cumulative effects of successive restorative procedures on anterior crown flexure: intact versus veneered incisors. Quintessence Int. 2000;31:5-18.
10. Christensen GJ. The state of fixed prosthodontic impressions: room for improvement. J Am Dent Assoc. 2005;136:343-346.
11. Ruiz JL, Christensen GJ. Rationale for the utilization of bonded nonmetal onlays as an alternative to PFM crowns. Dent Today. 2006;25:80-83.
12. Ruiz JL, Christensen GJ. Myths vs. realities: State-of-the-art indirect posterior tooth-colored restorations. Journal of Cosmetic Dentistry. 2011;27:63-72.

Additional Learning Resources
To receive a video explaining the 4 principles of supragingival restorative techniques, visit the Web site located at: ruizdentalseminars.com/4supra-gingivalprinciples.

Dr. Ruiz is director of the Los Angeles Institute of Clinical Dentistry, an associate instructor at Dr. Gordon Christensen’s PCC in Utah, and an independent evaluator of dental products for CR Foundation. He is course director of numerous continuing education courses at University of Southern California, and is an honorary clinical professor at Warwick University in England. He has been practicing in the Studio District of Los Angeles for more than 20 years, focusing on treating complex cosmetic, rehabilitation, and implant cases. He has published several clinical and research papers on adhesive dentistry, occlusion, and aesthetic dentistry. He can be reached at (818) 558-4332 or via e-mail at ruiz@drruiz.com.

Disclosure: Dr. Ruiz reports no disclosures.