Improved bonding of zirconia crowns with resin-based cement

Acid etching with heated KHF2 improved fracture strength.

Air-abrasion with Al2O3 should be used with caution for pre-treating zirconia with higher yttria content (5Y), as it has possible negative effects on strength.

Several pre-cementation procedures advocate enhancing adhesion between zirconia and resin-based cements. There is, however, limited documentation on how these pre-treatments affect the strength of high translucent zirconia.

A recent study by Marit Øilo, NIOM’s Amund Ruud and others, has looked into this.

– We assessed two dental zirconia materials with different yttria content (3Y/3 mol% and 5Y/5 mol% Y₂O₃ in ZrO₂), and tested two different surface treatment methods, says Amund Ruud.

The testing
They tested both discs (n = 45) and crown-shaped specimens (n = 30). The two materials were pre-treated with either air-abrasion or hot etching with KHF₂ and cemented to composite abutment. Cement adhesion to zirconia and fracture strength were then compared with untreated controls.

– We found that acid etching with heated KHF₂ improved fracture strength and cement retention for 5Y zirconia than control and air-abraded samples. The procedure for etching was, however, complicated, says Ruud, and needs further optimization.

On the other hand, air-abrasion with Al₂O₃ should be used with caution for pre-treating zirconia with higher yttria content (5Y), as it has possible negative effects on strength. Air-abrasion does, however, improve fracture strength of the 3Y zirconia.

Conclusion
– In short, the different pre-cementation procedures affected the load at fracture and cement retention. Understanding and optimizing the surface treatment of zirconia is important. In the current study, we further highlight the importance of adjusting the surface treatment depending on the yttria content of the zirconia materials, in order to achieve high strength and retention, Ruud says.

Pictured: A shallow chamfer preparation on an artificial upper canine. Buccal (A) and distal (B) view of the prepared tooth, the crown was designed with a flattened incisal edge. Buccal (C) and distal (D) view of the designed crown.

References: Pre-cementation procedures’ effect on dental zirconias with different yttria content. By: Øilo M, Haugli K, Rønold HJ, Ulsund AH, Ruud A, Kvam K
Dent Mater (2021). https://doi.org/10.1016/j.dental.2021.07.001

NIOM Newsletter August 2021

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