Restoring Aesthetics and Function With a Metal-Free Crown: Case Report

Like all things modern, aesthetic dentistry evolves to remain in step with the times. Methods, materials, and expectations each play a part in that evolution, changing over time to best suit the practice of dentistry. Perhaps the most dramatic change witnessed over the last several years has been in materials, which now provide more aesthetic options than ever before.
Patients and practitioners alike expect the most from the materials available today for use in techniques ranging from bleaching to full-mouth reconstruction. One thing, however, has remained true throughout the history of aesthetic dentistry: success depends as much on the restoration of function as it does on the restoration of appearance and form. Function is non-negotiable without it, the patient is no better off than when he or she walked into the office seeking dental care. A beautiful restoration that fails is like painting your house with watercolors: once that first rainstorm blows through, the beauty is lost, and youÌre left with a bigger problem than you had before.
As such, it is incumbent upon us as dental caregivers to do everything in our power to ensure functional success in all aesthetic restorations. One way we can maximize our chances is to pay close attention to occlusion, which plays a large role in determining functional and restorative success. Correct anatomical occlusion helps a restoration to withstand the functional load placed upon it, thereby eliminating one of the primary culprits in restorative failure.
A number of restorative materials are available to reconstruct our patientsÌ mouths. The metal-ceramic restoration has demonstrated the most predictable reliability when compared to several all-ceramic systems. As a result, companies are striving to improve the physical properties of all-ceramic materials with high zirconia content.1-5 The main goal is to provide us with a restorative material that can be used to support a variety of prosthetic requirements ranging from single-unit up to and including (perhaps) 5-unit bridges in all areas of the mouth.2
This article describes the use of a zirconium-based coping with stacked porcelain over the top to provide a sound, functioning restoration. Zirconium that is designed using the CAD/CAM process has demonstrated fracture strengths greater than 1,000 MPa, which indicates that they can be used for a number of clinical situations, including full-coverage crowns, fixed partial dentures, and implant abutments and crowns.

CASE REPORT

Figure 1. Gold crown is worn through on the MB cusp of the mandibular left second molar.

The patient was a young man who presented with a failed full-gold casting on the mandibular left second molar that had been placed more than 8 years ago. As can be seen in Figure 1, the gold crown had worn through on the MB cusp. Radiographically, all margins looked clinically intact with no evidence of decay. This author recommends that you always remove all old, failed castings, especially if you were not the clinician to place them, to verify that the underlying substrate is healthy and free from decay, which could compromise the longevity of the restoration. Because radiographs cannot reveal what is beneath metal, the substrate is suspect in such situations. If this was a new restoration the author had placed, and I was certain there was no clinical leakage, this would be an instance where a direct gold foil restoration would restore the worn cusp nicely.
The patient was very specific in requesting a tooth-colored aesthetic restoration.

Treatment Planning

After talking with the patient and understanding the desired end result, a treatment plan was developed. This case demonstrates the step-by-step protocol required to provide a sound, functional result, including the needed preparation design, impression taking, temporization made simple and easy, lab communication, seating and finishing, and then post-insertion follow-up.

Material Selection

Patient demand for aesthetics as well as function in dental restorations has accelerated in recent years. Many new all-ceramic systems have been introduced to the market. Ceramics address the demand for excellent aesthetics and offer biocompatibility. Yttrium-stabilized zirconium oxide is the toughest and strongest ceramic material available for use in dentistry today. Zirconia frameworks are available from several CAD/CAM systems such as VITA YZ (inVizion) milled on the Sirona inLab machine, Lava (3M ESPE), and Procera Zirconia (Nobel Biocare).  These systems use preparation and cementation procedures already familiar to dental professionals. In addition, new veneering porcelains are being engineered specifically for zirconia frameworks that match the coefficient of expansion.
The VITA inVizion restoration is milled on the Sirona inLab system from solid, homogenous blocks of inCeram 2000 YZ material and sintered in a Zyrcomat (Vident) furnace under optimal processing conditions. This combines the strength of yttrium-stabilized zirconium oxide with the highly aesthetic properties of the VITA VM9 fine-structure ceramic veneering material. The inVizion restoration results in enamel-like wear on the opposing dentition and is available in multiple-shaded substructures and a large variety of shades to be able to  replicate the shades of natural teeth more closely. InVizion restorations offer predictable, aesthetic options for CAD/CAM restorations to meet the ever-increasing demands from patients.

Preoperative Registration

A preoperative polyvinyl impression was taken with a plastic triple tray. We should always strive to make the temporizing stage very simple, easy, and predictable. A properly fitting temporary restoration is critical to the ultimate success of the case, as it maintains contact points, occlusal stability, and, most importantly, creates an ideal environment for a healthy soft-tissue response. In the past, suck-down stints, acrylic button, and alginates have been used, the latter being the least rigid and most likely to distort or even be destroyed if the patient does not bite into the proper position. Materials available for this purpose include Alginot (Kerr), Position Penta Quick (3M ESPE), and StatusBlue (Zenith Dental). In this case the impression was taken using StatusBlue, and it was set aside for the temporizing phase.
A preoperative shade was taken with the digital Vita Easyshade (Vident), so that upon fabrication of the restoration, as close to a perfect match as possible would be achieved.6

Preparation

Figure 2. The defective gold crown is prepared for removal.

Figure 3. Upon removal of the defective gold crown, recurrent decay was detected and a pin was identified that could not be retrieved.

Figure 4. After all caries was removed, lack of tooth structure required a buildup to ensure adequate retention of the final restoration.

Figure 5. The tooth preparation and sulcus are prepared for the impression.

Figure 6. The final impression.

The preparation was initiated by using a GW 557 carbide bur (SS White) to placea stress-breaking section through the facial aspect of the crown to the lingual just shy of the lingual margin (Figure 2). This will allow you to take a small, flathead screwdriver, place it in the slot, and gently rotate it in the mesial-distal direction.  You will find that the crown will atraumatically loosen and come off. Upon removal of the full casting, we identified clinical recurrent decay and a pin that could not be retrieved (Figure 3). Also, a very small amount of amalgam was left, which was removed. We next applied caries finder solution (Kuraray) to be sure all clinical decay was removed. Upon all caries removal, the clinical core design was less than ideal to maximize clinical retention, so we were required to build up the tooth to provide the ideal retentive form. After total-etching the tooth for 10 to 15 seconds and rinsing, we applied Gluma Comfort Bond and Desensitizer (Heraeus Kulzer), light cured, then applied Luxa-Core (Zenith Dental), and light cured for 20 seconds (Figure 4).
In order to eliminate or minimize tooth chatter during preparation, which can result in micro fractures, new burs should be used each time. In this case we used GWU carbide burs (SS White). There will always be a difference in opinion as to whether diamonds are better than carbides for tooth preparation, but I feel that the major difference comes down to personal preference. In my opinion, the GWU carbides operate in a slightly different manner, mostly due to the blade design. The blade design seems to allow it to cut through various substrates in a fairly smooth manner while not getting clogged.
The GWU 856-016 carbide bur was used to circumferentially prepare the tooth for the full-coverage restoration, ensuring that no unsupported enamel rods remained.
The main preparation parameters are as follows: you want to ensure 3 planes of reduction starting with 1.5-mm reduction at the gingival level, which ensures the needed space for the technician to design an ideal soft-tissue emergence profile; 1.5-mm midbody reduction will allow the ceramist to create the midbody chroma as needed; and the 1.5-mm to 2.0-mm cusp tip reduction with the lingual angulations will allow the ceramist ideally to place the cusp tips in the proper arch form while maximizing aesthetics.
Following all preparation, caries-indicating solution was applied to ensure that no caries remained. A polyvinyl siloxane bite registration using Memoreg 2 (Heraeus Kulzer) was then taken to ensure that the case could be properly mounted for good centric occlusion.

We must properly manage the soft-tissue interface prior to taking a final impression. We read about the use of retraction cord, electrosurgery, and even the use of lasers. I used a method with a 00 cord (Ultradent Products) followed by Expasyl (Kerr). The clay-like aluminous chloride-impregnated material, when expressed into the sulcus, provided both adequate hemostasis and sulcular expansion. This means we can see the preparation 360° and there is no sulcular moisture, which is key to obtaining an accurate final impression7,8 (Figure 5).
A vinyl polysiloxane light-body impression material (Flexitime [Heraeus Kulzer]) was used to accurately define and impress the preparation, and a vinyl polysiloxane heavy-body tray material (Flexitime) was loaded into a metal impression triple tray. The impression was taken and inspected for clarity after 3 minutes (Figure 6). It is the author's choice not to use plastic triple trays due to possible flexing upon biting into the tray.

Temporization

Figure 7. The temporary restoration is seated.

Performing indirect restorative dentistry is challenging. Aside from the clinical skills required to prepare a case properly, there is also the time-consuming provisional stage. As we all know, a properly fitting provisional is important to the ultimate success of the case. It not only maintains contact points and occlusal stability, but also creates an ideal soft-tissue response environment by providing a detailed marginal fit.
While we have used fabrication methods such as vacuum-form stints and heated acrylic buttons, using alginate in conjunction with plastic disposable trays has been the most popular. However, alginates are a relatively unstable means for creating and replicating provisionals if the patient does not bite down on the impression matrix containing the self-curing resin in perfect accordance with the originally recorded bite.
I have been using a heavy-body PVS tray material for making preoperative  temporization matrices for years because of its stability and predictability.
Vinyl polysiloxanes have recently started to become more popular for this application because they are dimensionally stable and a reliable means of creating temporary restorations, but companies are now starting to create alginate replacement materials such as Position Penta Quick, Alginot, and Status-Blue. Creating a temporary restoration occurs at the end of a focused session of completing the needed prosthetic steps, and we would all like nothing better than to be able to make temporaries in a quick, simple, predictable manner.
As was mentioned above, if you take your preoperative bite and load a self-cure resin into the tray (eg, Fill-In [Kerr], Integrity [DENTSPLY], Luxatemp [Zenith Dental], or Protemp 3 Garant [3M ESPE]), once set (2 minutes) you will have your finished temporary restoration, which is trimmed with disks (OptiDisc [Kerr] or  Sof-Lex [3M ESPE]), and then seated with a noneugenol temporary cement (Figure 7).

Laboratory Fabrication

The relationship between the dentist and the laboratory technician is critical in determining restoration success. A team approach is the best method for providing the patient with restorative excellence, and open lines of communication greatly enhance the work environment.
Recognizing that the quality of communication between the clinician and technician is a crucial factor in the indirect restorative process, a detailed prescription was sent to the laboratory. The prescription identified the chroma and value, indicating a rich chroma in the central fossa and high value or brightness up the cusp incline. In addition, intraoral photographs were sent along with the prescription to assist the technician in matching characterizations.

RESTORATION VERIFICATION

Figure 8. The final restoration is seated.

When the completed restoration arrives from the laboratory, the author always checks for color, fit, contact points, and overall aesthetic appearance.

CEMENTATION

Attention to detail is essential; a lab-manufactured restoration may have great aesthetics, sound occlusion, and good contacts, but if the restoration is not properly seated, it is destined to fail. With the zirconium-based restorations, we have 3 options available. We can cement these restorations using any conventional crown and bridge luting cement, such as RelyX Luting Plus (3M ESPE) or Fugi IX (GC America); we can also use our total-etch technique with any dual-cure resin cement such as Calibra (DENTSPLY) or Variolink (Ivoclar Vivadent); or we can use self-etch and bond with resin cements such as Unicem from 3M ESPE or Maxcem from Kerr (Figure 8).

CONCLUSION

With the seemingly daily advances being made in aesthetic restorative materials, today's dental patients have a menu of aesthetic options from which to choose. Given the ever-increasing aesthetic demands of society as a whole, it is not surprising that more and more patients select metal-free restorations. Today's clinicians are fortunate to have so many restorative options to offer their patients, thanks in large part to several of today's tooth-colored alternatives that ex-hibit excellent strength and durability.
Zirconium has been developed to meet a broad range of clinical needs in reconstructive dentistry, and to date the clinical predictability looks very promising. Long-term stability and functionality must be seen in 5-year studies and beyond, which will confirm the material's true success.


References

1. Snyder MD, Hogg KD. Load-to-fracture value of different all-ceramic crown systems. J Contemp Dent Pract. 2005;6:54-63.
2. Blatz MB. Long-term clinical success of all-ceramic posterior restorations. Quintessence Int. 2002;33:415-426.
3. Sorensen JA. The Lava All-Ceramic System: CAD/CAM Zirconia Prosthodontics for the 21st Century: A supplement to CERP. 2003;2:3-6.
4. Tinschert J, Natt G, Mautsch W, et al. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. Int J Prosthodont. 2001;14:231-238.
5. Piwowarczyk A, Ottl P, Lauer HC, et al. A clinical report and overview of scientific studies and clinical procedures conducted on the 3M ESPE Lava All-Ceramic System. J Prosthodont. 2005;14:39-45.
6. Baltzer A, Kaufmann-Jinoian V. Shading of ceramic crowns using digital tooth shade matching devices. Int J Comput Dent. 2005;8:129-152.
7. Shannon A. Expanded clinical uses of a novel tissue-retraction material. Compend Contin Educ Dent. 2002;23(1 suppl):3-6.
8. The periodontal-restorative interface in fixed prosthodontics: tooth preparation, provisionalization, and biologic final impression- Part II. Pract Periodontics Aesthet Dent. 1994;6:49-60.


Dr. Shannon is a 1987 graduate of Dalhousie University School of Dentistry, Halifax, Nova Scotia. He lectures throughout North America, Australia, Asia, and Russia on mastering aesthetic restorative dentistry. Dr. Shannon sits on a number of peer-reviewed editorial boards and has been a part-time clinical instructor at a number of post-graduate clinical programs in the area of aesthetic restorative dentistry. He maintains a full-time private practice in Vancouver, BC, with a primary focus on comprehensive aesthetic restorative dentistry. Dr. Shannon can be reached at (604) 669-6700 or at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .



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