Different surface pretreatments in combination with universal adhesives and their influence on the bond properties between zirconium oxide and luting composite
Nina Lümkemann, Annett Kieschnick, Bogna Stawarczyk
The adhesive bonding of zirconium oxide restorations is becoming increasingly important in view of increasingly translucent materials, minimally invasive treatment concepts and the resulting low layer thicknesses. The advantage is not only the good aesthetics through the use of a tooth-colored luting composite, but also the possibility of increasing the overall stability of the restoration. In order to achieve a long-term stable bond, surface pretreatment by corundum blasting and the use of a phosphate-containing adhesive to condition the zirconium oxide surface have become established.
However, corundum blasting of the zirconium oxide surface can lead to a weakening of the material properties. The idea is therefore to use this form of surface pretreatment with a more gentle method - for example Plasma treatment - to replace. But what influence does plasma treatment have on the surface properties of zirconium oxide compared to corundum blasting? And what influence can be expected in terms of bond strength? These questions are answered below.
Investigation setup
For the investigation, test specimens were made from zirconium oxide, embedded, polished to a high gloss and pre-banded with different surfaces:
- Plasma (cold oxygen plasma, 10 s)
- Corundum blasting (aluminum oxide, 50µm, 0,5bar)
- corundum blasting and plasma
- without pretreatment (polished surface)
The surface energy (SFE) and surface roughness (Ra) have been determined. To examine the bond strength (TBS), the surface-pretreated test specimens were divided into a further 9 subgroups and conditioned with 7 different universal adhesives. Conditioning with an established zirconium oxide primer and the unconditioned surface served as control groups:
- Clearfil Ceramic Primer (PCG, Control)
- Adhesion Universal (AU)
- All-Bond Universal (ABU)
- Clearfil Universal Bond (CUB)
- G-Premio Bond (GPB)
- Futurabond U (FBU)
- iBond Universal (IBU)
- One Coat 7 Universal (OCU)
- Scotchbond Universal (SBU)
- without conditioning (control)
After cementation with a conventional luting composite (DuoCem, Coltène/Whaledent) or a phosphate-containing luting composite (Panavia F2.0, Kuarary Noritake) for the positive control group, the test specimens were stored in an incubator (37 °C, 24 h) and then subjected to thermoload cycling aged (5 °C/55 °C, 5000 ×). The bond strength was determined in tensile tests in a universal testing machine.
Results
Pretreatment with plasma resulted in an increase in surface energy but showed no influence on surface roughness. Corundum blasting achieved the highest surface roughness and higher bond strengths compared to the plasma pretreatment or no pretreatment groups. SBU and AU resulted in the highest bond strength compared to the positive control group (PCU). However, the bond strength of OCU, FBU, ABU, IBU, and GPB was comparable to the positive control group (PCG). CBU achieved the lowest bond strength values.
Conclusion
The surface pretreatment of zirconium oxide with plasma cannot replace the pretreatment using corundum blasting in order to achieve a permanent bond. The use of MDP-containing adhesives is important for a successful clinical outcome.
Conclusion for everyday practice and laboratory life
To avoid damaging the zirconium oxide surface, moderate blasting pressure should always be used.
Publication: Lümkemann N, Eichberger M, Stawarczyk B. Different surface modifications combined with universal adhesives: the impact on the bonding properties of zirconia to composite resin cement. Clin Oral Investig 2019 [epub ahead]