Fluorcanasite glass-ceramics for dental applications

Fluorcanasite, a chain silicate glass ceramic, displaying a combination of high flexural
strength and high fracture toughness in comparison with currently available resin-bonded
ceramics, is being developed as a material that should be easy to fabricate into a dental
restoration. Previous work has focussed on producing a chemically durable formulation of
fluorcanasite. Unfortunately, in an attempt to achieve low solubility, the mechanical
properties of this material have been compromised. The aim of this study was to assess the
influence of compositional changes on the crystallisation and fracture toughness of the
fluorcanasite crystalline phases.
This study has focused on compositional variations to the tluorcanasite composition of
6OSi~-8Na20-7K20-15CaO-l OCaF2. Fluorite additions were attempted to ascertain the
extent to which the 'known' nucleating agent influences the crystalline phase development.
Zirconia and silica additions were made to the formulation to improve the mechanical
properties while maintaining the chemical solubility of the material. It was found that
fluorcanasite glasses of these formulations crystallize to give a combination of canasite and
frankamenite phases and at higher zirconia additions, a potassium zirconium silicate phase
called wadeite.
The attempted reformulations resulted in a composition (6.11Na20-S.35K20-11.46CaO-
11.46CaF2-64.82Si02-0.80Zr<h) which upon a standard two-stage heat treatment schedule
crystallised to give a glass ceramic with substantially improved mechanical properties. A
greater than three-fold increase was achieved in the fracture toughness in comparison to the
base composition and is comparable to current commercial dental materials indicated for
use as posterior restorations. This formulation has resulted in a solubility which is within
the solubility limits for use as a core material (class 2, ISO 6872:1995 (E» and the glass
ceramic has been shown to have adequate machinability for development using the CAD
CAM process.