NIOM scientists develop new etching technique for zirconia ceramics – improves adhesion of resin cements
 Ketil Kvam
Senior Engineer, Metallurgist M.Sc.

Melt etching improves adhesion between resin cement and zirconia.

NIOM scientists have developed a surface etching technique that improves adhesion between resin cement and zirconia. Bond strength is increased by a factor of five over sandblasting according to a recent study in Acta Biomaterialia Odontologica Scandinavica. This new method called Melt Etching is based on melting of fluoride compounds, and can be readily adapted by dental technicians.

Chemically, zirconia is extremely stable and sandblasting crushes the surface. Both factors make it difficult to obtain long-lasting adhesion. Melt etching creates a rough surface with undercuts, which improves adhesion compared to surfaces treated by sandblasting (Figure 1).

Figure 1. Scanning electron microscopy (SEM) images showing zirconia surfaces after different treatments; (a) sandblasted and (b) etched with potassium hydrogen difluoride.
The zirconia phase structure is not compromised by melt etching.

Shear bond testing

Adhesive strength was measured by a shear bond test. The test measures the force needed to remove zirconia stubs cemented with resin to zirconia discs. The tests were performed on specimens that had been sandblasted or melt etched, with and without silanization of the zirconia surfaces. All etched specimens had higher shear bond strength than the sandblasted ones and significantly higher than the unsilanized, sandblasted specimens.

Melt etching method

After sintering, zirconia’s phase structure consists of tetragonal crystals. The impulsive energy of sandblasting gradually changes the surface structure to unfavorable cubic or monoclinic phases. Melt etching limits structural changes because it is quick and the temperature remains low.

This was confirmed by X-ray diffraction analyses. The changes in surface phase structure during melt etching are due to the removal of zirconium ions, as confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) showing release of potassium hexafluorozirconate, K2[ZrF6].

Clinical implications

  • Zirconia has become a widely used as dental crown and bridge material thanks to its high strength and biocompatibility. Inferior bonding after cementation to implant abutments and prepared natural teeth has been a concern.
  • The melt etch method is an easy method to improve adhesion.

The newsletter is based on the article:
Ruyter EI, Vajeeston N, Knarvang T, Kvam K: A novel etching technique for surface treatment of zirconia ceramics to improve adhesion of resin-based luting cements. Acta Biomaterialia Odontologica Scandinavica. 2017; 3(1): 36-46. (full-text available)