Biomedical Engineering Reference
In-Depth Information
propagation. The more crystals a dental ceramic contains, the more
resistant it is, meaning that it can be used in high-stress areas, such as
posterior regions (premolars and molars), or for larger prosthesis
frameworks, which replace several teeth. Indications for each class of
dental ceramics regarding mechanical resistance, and depending on
the chemical nature of the crystals, are summarized in Figure 9.4.
However, glass is fragile, but promotes material translucency, helping
to reproduce enamel appearance, which is why veneering ceramics
contain a lot of glass. Moreover, glass, which is silicium oxide in an
amorphous state, can be etched with hydrofluoric acid to create the
micromechanical retentions required for resin cement adhesion and
then for bonding the prosthesis to tooth tissues. It can also be treated
with silanes, i.e. bifunctional molecules binding to the silicium
atoms, which complete adhesion mechanisms by adding a chemical
bond between resin cement and ceramic. The adhesion properties
are crucial from a clinical point of view, since these “bondable”
materials allow the carrying out of minimally invasive treatments,
for which there is no longer a need to eliminate peripheral tooth
tissue to ensure the retention of the prosthesis, as was required
for conical tooth preparations performed for crowns or bridges
(Figure 9.2(a)). Glass-based ceramics can then be used for veneers and
onlays, i.e. small-bonded prostheses, which only replace part of the
tooth, on non-retentive and non-invasive preparations (Figure 9.5).
Figure 9.4.
Limits of indications of each class of dental ceramics and for each type of
crystal chemical nature, respectively. From left to right, the clinical indications
require more mechanical resistance
