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Zirconia is Special: The Optimal Procedure for Zirconia Bonding

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Clinical case conducted by Dr. Jordan Sebastian and Dr. Burgos Hugo.

Introduction

Zirconia-based restorations are the fastest growing segment in the North American laboratory mar-ket. Based on their aesthetics, biocompatibility, and mechanical properties, they can be used for various types of restorations, including crowns, bridges, endodontic posts, and implant abutments. As new den-al materials come onto the market, it is important to keep up to date with information so that every cementation procedure is successful.

Surface Preparation

Treating the surfaces of your restorations is the first step to obtaining lasting results in the cementation process. Making sure the surfaces are decontaminated and primed with the appropriate primer will ensure a stronger bond between the restoration and the tooth, reducing bond failure.

After try-in, it is important to decontaminate the crowns. Phosphate contaminants from saliva can weaken bond strengths, and removing these will result in a better long-term restoration. This adverse effect cannot be eliminated by simply cleaning with water or organic solvents. Only a strong alkaline solution (such as potassium hydroxide solution) can clean the contaminant and eliminate the adverse effect. ZirClean (BISCO) is a strong alkaline gel, formulated with potassium hydroxide. It addresses the clinical issue of zirconia saliva contamination, as compared to untreated samples (data on file).
 
Technique
A 27-year-old patient presented with a cast metal post and core as a component of a crown preparation (Figure 1).
 
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Figure 1. Cast metal post and core cemented on the first upper left bicuspid.
 
 
After the cementation of the post and core, the final preparation was completed and scanned in order to design and mill the CAD/CAM restoration. The material of choice was Noritake KATANA Zirconia UTML (Kuraray Noritake Dental) (Figure 2).
 
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Figure 2. CAD/CAM Noritake KATANA Zirconia UTML (Kuraray Noritake Dental).
 
This material displays adequate mechanical properties and, being an ultra-translucent zirconia, aesthetic appearance is not an issue for the posterior region.
 
Once the restoration was completed, a try-in was performed (Figure 3) and subsequently treated with ZirClean Restoration Cleaner for 20 seconds (Figure 4). It was then thoroughly rinsed with water spray and dried with oil-free air.
 
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Figure 3. Try-in to check proper fit and occlusion. 
 
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Figure 4. ZirClean was applied for 20 seconds to remove surface contaminates.
It was then rinsed and dried.
 
We prefer a self-adhesive, dual-cured resin cement for retentive preparations. TheraCem (BISCO) self-adhesive resin cement was chosen because it contains MDP. TheraCem offers an optimal bond to both zirconia and the tooth structure without the need to apply a primer prior to cementation. It releases calcium and fluoride to the tooth structure while providing an alkaline pH. TheraCem was applied to the intaglio surface of the restoration (Figure 5).
 
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Figure 5. TheraCem was dispensed into the intaglio surface of the restoration.
 
Then the restoration was seated with gentle passive pressure and tack cured for 2 to 3 seconds. TheraCem is easy to clean up with hand instruments and floss (Figures 6 and 7).
 
 
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Figure 6. The restoration was seated and tack cured, and excess cement was removed.
 
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Figure 7. The final restoration.
 
Conclusion
ZirClean and TheraCem offer a cohesive bond between the zirconia interface and resin cement, ensuring long-term durability.
 
December 2019
 

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