Placing Conservative Posterior Zirconia Restorations

A patient presented with a large occlusal composite restoration on the mandibular left first molar (tooth No. 19) that was experiencing transient hot and cold sensitivity, which were not persistent, along with sensitivity to sweets (Figure 1). Due to the patient's history of habitual clenching, the diagnosis indicated reversible pulpitis attributed to mechanical trauma from excessive force.³ The recommended treatment was a conservative zirconia onlay.

Preparation

After a local anesthetic (Septocaine^®, Septodont) was administered, 1-mm depth cuts were made into the occlusal surface of the tooth (Figure 2), and the old restorative material was removed. The pulpal floor was then air-particle abraded using 27-µm aluminum oxide particles at 40 psi (PrepStart^™, Zest Dental Solutions). Following this, a dual-cure, calcium and fluoride-releasing, self-adhesive liner (TheraBase^®, BISCO) was applied (Figure 3), and the tooth was conservatively prepared for an onlay with an extension to the buccal aspect to improve the esthetics (Figure 4). A digital impression was then acquired using an intraoral scanner (iTero^®, Align Technology), and the tooth was temporarily restored with a bisacryl restoration (Luxatemp^®, DMG America) while the final zirconia onlay was being designed and fabricated (Figure 5).

Restoration

During the cementation visit, the APC concept was executed. First, the final zirconia onlay was tried in, checked for contacts and occlusion, and verified using 20-µm articulating film (AccuFilm^®, Parkell). A radiograph was then acquired to confirm marginal fit. After the restoration was removed from the mouth, it was cleaned with alcohol and then air-particle abraded using 27-µm aluminum oxide particles at 40 psi (Figure 6).⁴ Next, two coats of a zirconia primer (Z-Prime^™ Plus, BISCO) were applied to the intaglio surface of the onlay and gently dried using an air syringe only (Figure 7).

To ensure moisture control and reduce contamination, a rubber dam (Rubber Dam, Nic Tone) was placed. PTFE tape was then applied to protect the adjacent contacts during air-particle abrasion and the etching process. Both the enamel and dentin were cleaned and air-particle abraded using 27-µm aluminum oxide particles at 40 psi (Figure 8). Following air abrasion, a 32% phosphoric acid etchant (Uni-Etch^® w/BAC, BISCO) was applied to the enamel only for 15 seconds (Figure 9), and then the preparation was rinsed and dried.

After etching the enamel, the bonding protocol was initiated with a universal adhesive (All-Bond Universal^®, BISCO). Two coats were applied using a microbrush and scrubbed into the preparation for 15 seconds each (Figure 10). After each application of the adhesive, the solvent was evaporated with a gentle burst from the air-syringe that lasted for at least 10 seconds. The adhesive was then light cured for 10 seconds. Following application of the bonding agent, air thinning, and curing, a dual-cure universal adhesive resin cement (Duo-Link Universal^™, BISCO) was applied to the intaglio surface of the onlay. The restoration was then delivered intraorally, and firm finger pressure was applied to ensure complete seating. Tack curing was performed on both the restoration and the tooth. Using a No. 12 surgical scalpel blade, any excess tack-cured cement was carefully removed (Figure 11). Any excess interproximal cement was removed with a proxy brush and dental floss. The tooth was then light cured again for 15 seconds from each aspect: buccal, lingual, and occlusal (Figure 12). Once the final occlusion was verified using an articulating film and occlusion foil (Shimstock, Almore International), the restoration was finished and polished using a fine diamond bur and rubber polishers (A.S.A.P.^® All Surface Access Polishers, Clinician's Choice) (Figure 13).

In an era in which minimally invasive dentistry is increasingly valued, the APC concept, with MDP at its foundation, provides a pathway to preserve natural tooth structure while delivering robust and dependable posterior zirconia restorations. This innovative approach brings dentists closer to achieving the ideal balance of esthetics, strength, and conservation in modern dental practice.

Acknowledgement

The author would like to thank Swiss Dental & Technical Art in Seattle, Washington, for designing and fabricating the final zirconia onlay.

Alex Vasserman, DMD
Private Practice
New York, New York

BISCO, Inc.
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