Dentistry is both an art and a science requiring today’s practitioner to be versatile and ready to adapt. Not every patient fits into the same treatment box, calling for an identical approach. A comprehensive examination is needed to discover and establish a list of each patient’s requirements.

Generally, most patients’ dental treatments call for conventional and time-tested procedures. However, at times we are faced with challenges that require us to be able to think and operate “outside the box,” relying on our ingenuity and creativity. As practitioners gain experience, they gather their own personal “bag of tricks” to turn to. New procedures and innovations in dental materials provide us with increasing options.

Our patient presented with a discolored upper left central incisor (Fig. 1). His dental history noted that trauma occurred to the tooth in his youth. His tooth tested vital and had never been restored. Although the dark tooth bothered the patient, he had always been reluctant to compromise its integrity. Full-coverage crowns, pressed-ceramic veneers and bonded-composite restorations had been previously proposed as possible esthetic solutions. However, these restorations called for significant tooth reduction in order to mask the dark underlying dentin. Because his tooth was healthy and asymptomatic, he had been seeking a more conservative option.

Presented with the desires of the patient, we studied his restorative choices and considered the currently available dental materials. An ultra-thin zirconia core veneered with porcelain was acceptable to him.

Zirconia has recently become a popular dental material because it has high strength, is resistant to fracture and, being opaque, has the ability to mask discolored underlying tooth structure.¹ Its flexural strength of 900 to 1,100 MPa and fracture toughness of 8 to 10 MPa make it a suitable material to create both conservative esthetic restorations and pontic spans for bridge work. It can be milled to a 0.2 mm thickness and then layered with a compatible porcelain to yield a restoration of less than 0.6 mm in total thickness. A restoration of this nature would be minimally invasive, with the ability to alter the color of the dark tooth to approximate that of the other central incisor. However, in order to achieve a restoration of this description, we require the necessary chemistry to create adhesion between the zirconia and the tooth.

To understand the challenges of the required chemistry, we must realize that enamel and dentin are living tissue requiring primers and adhesives that infiltrate into created microretention on the surface. Zirconia is a nonliving, oxide-based substrate requiring a primer with phosphate comonomers to covalently bond to the oxide. In order to fuse the zirconia to the tooth, we require a cement interface that cohesively re-creates the dentoenamel junction among the living enamel, dentin and the inert zirconia oxide-based substrate. The resin cement chosen should be hydrophobic and dual-curing (light- and self-curing), as zirconia is opaque and may not allow light to totally pass through it to fully cure the resin.^2,3,4

Until recently, the zirconia-to-tooth bonded interface was not possible, as hydrophobic cements do not adhere to oxides. New products, however, such as Z-PRIME™ (Bisco Inc.; Schaumburg, Ill.), have been developed. These are primers that utilize a combined phosphate and carboxylic monomer to create a cohesive interface, allowing the hydrophobic resin cement to create a linked, cohesive hydrophilic seal between the tooth and the indirect zirconia restoration. New universal primers (such as Monobond^® Plus [Ivoclar Vivadent; Amherst, N.Y.]) have also been developed to accomplish this task with zirconium oxide, metals, porcelain glass and lithium disilicate.

An initial reference shade was taken and photographed before any preparation to the tooth occurred. The other incisors matched a VITA^® (Vident; Brea, Calif.) A1 shade (Fig. 2).

An impression of the unprepared tooth was then taken using a clear plastic tray in order to have a matrix ready for subsequent bis-acryl temporary fabrication. This clear silicone impression material, Affinity™ Crystal (CLINICIAN’S CHOICE; New Milford, Conn.), allows the dentist to visualize the underlying teeth as a reference, making it easy to reposition in the patient’s mouth when filled with the provisional material (Fig. 3).

The final upper impression was taken using an extremely firm vinyl polysiloxane (VPS) impression material (Honigum^® Putty [DMG America]). The Honigum Putty, which was dispensed from an automatic mixer (MixStar^® eMotion [DMG America]), has a setting time of five minutes. It easily displaced the very viscous KOPY Single Crown Light Body (Dental Savings Club; Montreal, Quebec, Canada) into the subgingival sulcus, yielding a sharp and accurate impression. The author has found that this impression material is pleasant tasting and is easily removed from the mouth. The opposing lower model was taken with a VPS alginate substitute (StatusBlue^® [DMG America]). Totally rigid and inflexible metal impression trays (Rim-Lock^® Metal Trays [DENTSPLY Caulk]) were used for both impressions, thus minimizing distortions and inaccuracies.

Next, the patient’s tooth was cleaned and treated with a desensitizing agent (Gluma^® [Heraeus Kulzer; South Bend, Ind.]). The provisional restoration was then cemented with a translucent, dual-cured, eugenol-free resin temporary cement (Temp-Bond^® Clear [Kerr Corp.; Orange, Calif.]).

At the dental lab, a sintered zirconia core (keyed to the desired A1 shade) was milled using the Zenotec T1 7-axis CAD/CAM milling system to a thickness of 0.2 mm (Fig. 10). A feldspathic porcelain (Cerabien™ ZR [Kuraray America; New York, N.Y.]) was used to create a 0.4 mm porcelain buildup (laminate) over the zirconia substructure, yielding a total restoration thickness of 0.6 mm. The Noritake feldspathic porcelain has a coefficient of thermal expansion carefully matched to the zirconia, permitting the ceramist to create lifelike esthetics that display internal detailing and transparencies. The finished zirconia veneer offers precise marginal fit, excellent esthetics and high strength.

Upon receiving the restoration from the laboratory, its fit was verified on the laboratory work model to ascertain that it met our expectations. We then telephoned the patient to schedule an appointment. (In our office protocol, delivery appointments are not prescheduled according to the lab return dates, as we always want to have the flexibility of being able to return the case to the dental laboratory team if obvious corrections are needed.) In this case, the restoration was acceptable as received from the laboratory, so the internal surfaces were treated with a zirconia primer (Z-PRIME) (Fig. 11). The phosphate monomer in this special primer interacts with the oxide surface of the zirconia to form a covalent bond, thus optimizing the bond strength between the resin cement and the zirconia surface.

With the patient in the chair, and before removing the provisional, we first assessed the esthetics of the restoration next to the natural teeth to see if they looked the same (Fig. 12). If they had not, we would have returned the case to the dental ceramist with photos and a description of the changes required.

Once approved, the provisional was removed by first placing a slit in the labial surface using a flame-shaped diamond (KUT 3205 C [Dental Savings Club]). It was then separated and removed using an EB134 instrument (Brasseler USA; Savannah, Ga.) (Figs. 13a–13c). The underlying prepared tooth was cleaned with pumice, and then treated with a 32% phosphoric acid gel (UNI-ETCH^® [Bisco Inc.]) containing benzalkonium chloride, an antimicrobial agent (Fig. 14). A universal adhesive (ALL-BOND UNIVERSAL™ [Bisco Inc.]) with low film thickness was then brushed on the tooth structure (Fig. 15).

No single restorative material can satisfy every esthetic need. By having current knowledge of procedures and materials available, the practitioner is better able to adapt and satisfy the patient’s desires. Porcelain-layered zirconia veneers can be a useful addition to our dental “bag of tricks.”

Dr. Elliot Mechanic practices esthetic dentistry in Montreal, Canada. He is the esthetic editor of Canada’s Oral Health dental journal and is on the editorial board of Dentistry Today. Contact him via email at info@drmechanic.com.

The author would like to thank Adrian Jurim, CDT, MDT, for inspiration and the exquisite technical fabrication of this zirconia-based layered veneer (Zeneer™ [Jurim Dental Studio Inc.; Great Neck, N.Y.]).