Intraoral Repair of a Zirconia-Based Restoration

Despite the best intentions to fabricate and deliver durable metal-free res­torations, from time to time patients may present requiring repairs to such dental work. When this occurs, a solution must be considered that will not only function properly, but also satisfy patient needs as well. Testing a dentist’s and technician’s knowledge and skill set, such cases may require unconventional methods and material selections to achieve optimal results.
That said, it is important to remember that when selecting restorative materials, it is essential to choose the proper material for the indication at hand to prevent postoperative complications.
Although many of the restorative materials used in dental laboratories and dental offices today are much stronger than those used in the past, there may still be a propensity among certain products to develop complications. When teeth have been restored with veneers, partial dentures, or full dentures, it is important to communicate to the patient the proper methods of caring for their restorations. Even then, fractures and chips may be unavoidable.

Before Image. View of the prepared porcelain pontic. (Note: The preparation was left in existing porcelain and not taken to the depth of the zirconium oxide substructure in order to have a stronger porcelain-porcelain bond.)	After Image. Close-up view of the repaired restoration after cementation.
Figure 1. Hydrofluoric (HF) acid (9% HF [Ultradent Products]) was applied to the No. 9 pontic.	Figure 2. The HF was rinsed thoroughly with copious amounts of water.
Figure 3. Monobond Plus (Ivoclar Vivadent) was then applied to the internal aspect of the restoration.	Figure 4. The porcelain at the pontic site also was treated with Monobond Plus.

ZIRCONIA-BASED RESTORATIONS
Of the many materials used today, zirconia-based ceramics have been widely used in the fabrication of crowns and dental prostheses.1 Although approved for indications such as single crowns, fixed partial dentures, and implant abutments; chipping and fractures are seen as major problems and clinical setbacks when using this material.1 This is a direct result of the different pressures at which the porcelain and zirconia are prepared before being placed together.¹ As a result, there is a greater chance of separation and, consequently, chipping and fractures of the porcelain that overlays the underlying zirconia substructure.¹
Researchers and dental laboratory technicians are still conducting studies to determine the best way to fabricate zirconia-based restorations, since the incidence of chipping and fracture is believed to originate in the fabrication and design processes, not the material itself.² Given the challenges presented by zirconia restorations, dentists and technicians have sought alternative methods to correct the intraoral cracks and fractures that occur in order to preserve the structures that are still intact.2 These methods save patients chair and recovery time, as well as cost.²

LITHIUM DISILICATE
Lithium disilicate, another recently introduced all-ceramic material for restorations, has been gaining in popularity for several reasons.^3,4 The controlled size, shape, and density of this material’s crystalline structure contributes to a ceramic that demonstrates greater strength and durability.^3,5 Lithium disilicate can be used to fabricate a very strong and durable monolithic restoration.6 These single-material restorations are more resistant to chipping and fracture, since there are no layering porcelains present to separate.^7,8 The material’s relatively low refractive index produces optical properties, such as translucency, that produce excellent aesthetics.^3,8 Materials like lithium disilicate eliminate the chipping and fracture problems that have plagued patients in the past, even though zirconia-based restorations are still considered aesthetic and effective.

Figure 5. Multilink Automix (Ivoclar Vivadent) universal adhesive cement (Ivoclar Vivadent) was placed into the restoration.	Figure 6. Excess cement was removed from around the restoration.
Figure 7. The restoration was held in place and tacked with a light-curing unit.	Figure 8. View of the restoration being tacked into place.
Figure 9. Once cured, the restoration was polished.	Figure 10. Retracted view of the completed restoration immediately following cementation.

SELF-CURING LUTING COMPOSITES
The characteristics of recently developed universal self-curing luting composites (such as Multilink Automix [Ivoclar Viva­dent]) allow for innovative solutions when repairing zirconia-based restorations that present with chipped overlaying porcelain. However, one must keep in mind that this is not an official indication endorsed by the manufacturer. (Multilink Automix is a self-curing luting composite indicated by the manufacturer for the adhesive cementation of indirect restorations composed of metal, all-ceramics, metal-ceramics, and composites. Please note the discussion/disclaimer below.) Aside from providing a strong bond on all surfaces, this category of adhesive ce­ments allows for universal application and uncomplicated use, making the cementation technique easier.

CASE REPORT
Diagnosis and Treatment Planning
The patient, a 58-year-old female, presented with a fixed 6-unit (zirconia-based) pressed ceramic partial denture that had a fractured porcelain pontic at the No. 9 position. The fracture occurred from the intubation process while the patient was under general anesthesia during a surgical procedure. The bridge, which had been placed 3 years prior to the fracture, was still serving the patient well. Because the framework and porcelain remained intact, and to save the patient from having to go through the procedure and expense to replace the bridge, it was decided to use an unconventional method to repair and restore the existing dental work to its original function and aesthetics.

The Clinical Technique
The porcelain at the No. 9 pontic area was prepared to a uniform depth of 0.75 mm (Before Image) for the fabrication of a pressed ceramic veneer (IPS Empress [Ivo­clar Vivadent]). A rounded shoulder margin was completed using red-stripe diamonds (Brasseler USA) under copious amounts of air, water, and light pressure. Care was taken during this time in the procedure to keep the preparation in the existing veneering porcelain and away from the zirconia substructure. By keeping the repair bond between porcelain and porcelain, the highest bond strength would be achieved. Next, a slight groove was then placed mid-body to facilitate seating and to also increase the surface area for bonding. A vinyl polysiloxane upper im­pression (Take One [Kerr]) was taken, along with photographs. These were sent to the dental laboratory team for use in creating a single-pressed porcelain veneer with ideal aesthetics according to our instructions.
When the veneer was completed and returned to the dental office, the placement procedure began with a 40-second hydrofluoric (HF) acid porcelain etch (9% HF [Ultradent Products]) of the pontic area (Figure 1), after which it was rinsed for 20 seconds (Figure 2). The internal aspect of the restoration had already been etched in a similar fashion during laboratory fabrication. Upon assurance that the surfaces were dry, Monobond Plus (Ivoclar Vivadent) was applied to both porcelain surfaces for 60 seconds (Figures 3 and 4) and then air thinned with dry, oil-free air. Cementation was completed using Multilink Automix cement (Figure 5). The excess cement was re­moved (Figure 6) and then the restoration was held in place and tack cured (Bluephase curing light [Ivoclar Viva­dent]) (Figures 7 and 8). After the ce­ment had been fully light-cured, the restoration was polished (Astropol polishing system [Ivoclar Vivadent]) (Fig­ure 9) and the occlusion was checked.
The patient was extremely satisfied with the outcome (Figure 10 and After Image ) and the simplicity of the procedure. In cases such as this, functional rescues can be simple, predictable, and highly aesthetic when the proper materials are selected.

DISCUSSION
Although the product is recommended for a variety of applications, the manufacturer (Ivoclar Vivadent) does not endorse the use of Multilink Automix for the bonding of porcelain veneers for a variety of reasons. Because the product is self-curing, it begins to cure as soon as it is dispensed and the user has no control over polymerization as one would when using a light-curing product. When placing multiple veneers, it is crucial that the dentist have longer working time using light-cured only products to ensure sufficient time for accurate placement. It is also more prone to shade shifts (unlike light-cured only products) which can lead to uneven shading and coloring.

CONCLUSION
In cases like the one described above, intraoral repairs using unconventional methods may be possible when dentists and their dental laboratory technicians apply their skills and ma­terial knowledge to develop viable fun­ctional and aesthetic solutions. Al­though not indicated for the ce­men­tation of veneers, in the case presented here, a universal self-curing res­in ad­hesive cement and a pressed all-ceramic veneer was utilized successfully to aesthetically and functionally repair a porcelain-pressed-to-zirconia fixed partial denture in order to save the patient chair time and cost.

Acknowledgement
The author would like to thank the talented team at Aurum Ceramic Dental Laboratories for their beautiful technical work in this case.

References
1. Roediger M, Gersdorff N, Huels A, Rinke S. Prospective evaluation of zirconia posterior fixed partial dentures: four-year clinical results. Int J Prosthodont. 2010;23:141-148.
2. Al-Amleh B, Lyons K, Swain M. Clinical trials in zirconia: a systematic review. J Oral Rehabil. 2010;37:641-645.
3. McLaren EA, Phong TC. Ceramics in den­tistry: classes of materials. Inside Dentistry. 2009;5:94-103.
4. Tysowsky GW. The science behind lithium disilicate: a metal-free alternative. Dent Today. 2009;28:112-113.
5. Helvey GA. Chairside cad-cam. Lithium disilicate restoration for anterior teeth made simple. Inside Dentistry. 2009;5:58-66.
6. Dudney TE. Unlock that combination. Dental Products Report. 2009; 43:60-62.
7. Fabianelli A, Goracci C, Bertelli E, Davidson CL, Ferrari M. A clinical trial of Empress II porcelain inlays luted to vital teeth with a dual-curing adhesive system and a self-curin resin cement. J Adhes Dent. 2006;8:427-431.
8. Ritter RG, Rego NA. Material considerations for using lithium disilicate as a thin veneer option. J Cosmet Dent. 2009;25:111-117.

Dr. Mowery is an adjunct professor at the University of Florida, College of Dentistry, department of Prosthodontics, in Gainesville, Fla. He maintains a private practice also in Gainesville, Fla. He can be reached via e-mail at mowery@gator.net.

Disclosure: Dr. Mowery reports no disclosures.

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