Contamination of a restoration is unavoidable. Oil from (chairside) milling can interfere with proper etching and pre-treatment. After try-in, remnants of try-in paste can remain and phospholipids from blood or saliva actively bond with the intaglio surface of metal and zirconia restorations, occupying spaces and thus preventing chemical adhesion with resin bonding systems.
Lithium disilicate and zirconia crowns exhibit distinct chemical behaviours. Hence, cleaning and pretreatment procedures are different as well.
Cleaning lithium disilicate crowns
(e.g. Initial LiSi Press or LiSi Block)
Chairside milling
If milled chairside, etching the crown with hydrofluoric acid (HF; 5% during 20 seconds) should be done after try-in to obtain a clean surface.
Laboratory milling
If not milled chairside, it's crucial to ascertain whether a lab-fabricated crown has been pre-etched with HF before arriving at the office. Excessive etching can adversely affect the overall strength of the restoration. If pre-etched, the surface can be cleaned with phosphoric acid (H3PO4; 37% during 60 seconds).
Special, dedicated cleaning solutions also exist as an alternative.
Pre-treating lithium disilicate crowns
The application of silane as a separate step is always recommended prior to adhesive cementation of lithium disilicate. Hence, when using G-CEM ONE, use G-Multi PRIMER to silanate the inner surface of the crown.
Cleaning zirconia crowns
Zirconia crowns should not be etched! Phosphoric acid blocks the oxide’s bonding sides needed for bonding. Whether or not the zirconia crown has been sandblasted in the lab, it needs to be sandblasted again after try-in. Sandblast with 25-50 μm Al2O3 at 0.15 MPa/1.5 bar. Here too, special, dedicated primers can be used for cleaning on the condition that the crown has already been sandblasted.
Pre-treating zirconia crowns
Reliable and long-lasting adhesive bonding to zirconia is achievable through use of a phosphate ester primer like MDP (10-methacryloyloxydecyl dihydrogen phosphate). The universal primer G-Multi PRIMER contains MDP and two other monomers and can also be used for all other types of indirect restorations. However, it’s not necessary to apply prior to the use of G-CEM ONE since the latter already contains MDP. For glass ionomer cements like FujiCEM ONE, an MDP primer is redundant.
- Zogheib LV, Bona AD, Kimpara ET, McCabe JF. Effect of hydrofluoric acid etching duration on the roughness and flexural strength of a lithium disilicate-based glass ceramic. Braz Dent J. 2011;22(1):45-50.
- Yoshihara K, Nagaoka N, Sonoda A, Maruo Y, Makita Y, Okihara T, Irie M, Yoshida Y, Van Meerbeek B. Effectiveness and stability of silane coupling agent incorporated in 'universal' adhesives. Dent Mater. 2016 Oct;32(10):1218-1225.
- Thammajaruk P, Inokoshi M, Chong S, Guazzato M. Bonding of composite cements to zirconia: A systematic review and meta-analysis of in vitro studies. J Mech Behav Biomed Mater. 2018;80:258-268.