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A new surface treatment for improving bond strength of veneering ceramics to zirconia framework

 

Objectives:

Etching by fluoride compounds may give a rough zirconia surface and improved bond strength to veneering ceramics with less tetragonal to monocline transformation than with sandblasting. An additional silicatization treatment is assumed to give an extra contribution. The purpose of this study was to investigate different fluoride etchants for zirconia and compare bond strength of veneering ceramics with surfaces treated under different conditions.

 

Methods:

Ninety-six zirconia (Lava Multi XL) specimens were divided into sixteen groups, four were as sintered, four were sandblasted and the rest were etched with two different etchants. Two groups of each category were also silicatized with heat treatment. Two different veneering ceramics, a fluoroapatite glass ceramic (IPS e.max Ceram) and a feldspathic porcelain (Prismatik CZ Porcelain) were fired to the zirconia specimens and the bond strength was measured according to the Schwickerath crack initiation test of ISO 9693-1:2012. Fractions of monoclinic structure were measured by X-ray diffraction after all surface treatments.

 

Results:

The etching methods made rough surfaces with limited tetragonal to monocline transformation, 0.8 % and 2.8 % for the two etchants respectively, compared to 13.5 % for sandblasting. The following silicatization resulted in increased structural transformation (19.5 and 20.0 %). Significant higher bond strength was obtained for all silicatized zirconia groups with feldspathic porcelain (36.0 – 45.7 MPa) compared to nonsilicatized groups (29.0 – 29.7 MPa), except for the as sintered and silicatized group (33.2 vs 40.3 MPa). No improvement was obtained with fluorapatite glass ceramics samples and only the as sintered group met the requirements for bond strength (>25 MPa).

 

Conclusions:

The etching techniques were effective to create rough zirconia surfaces. The combination of etching and silicatization of zirconia gave significant higher bond strength than no etching and silicatization with feldspathic porcelain. No improvment was obtained with fluoroapatite glass ceramic veneering.

 

Authors:
Kvam, K., Knarvang, T., Ruyter, E. I. NIOM – Nordic Institute of Dental Materials, Oslo, Norway.