Abstract: The ceramic yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) has been used as a dental biomaterial for several decades. The strength and toughness of this material can be accounted for by its toughening mechanisms, which include transformation toughening, crack deflection, zone shielding, contact shielding, and crack bridging. Prevention of crack propagation is of critical importance in high-fatigue situations, such as those encountered in mastication and para-function. However, the poor translucence of Y-TZP in polycrystalline form is such that it may not meet the aesthetic requirements due to its white/grey appearance. To improve the optical properties of Y-TZP, more detailed study of the optical properties is required; in particular, precise evaluation of the refractive index, absorption coefficient, and scattering coefficient are necessary. The measurement of the optical parameters has been based on the assumption that light scattered from biological media is isotropically distributed over all angles. In fact, the optical behavior of real biological materials depends on the angular scattering of light due to the anisotropic nature of the materials. The purpose of the present work is to evaluate the optical properties (including color, opacity/translucence, scattering, and fluorescence) of zirconia dental ceramics and their control through modification of the chemical composition, phase composition, and surface microstructure.
Abstract: Dental porcelain composites reinforced and toughened
by 20 wt.% tetragonal zirconia (3Y-TZP) were processed by hot
pressing at 1000°C. Two types of particles were tested: yttriastabilized
zirconia (ZrO2–3%Y2O3) agglomerates and pre-sintered
yttria-stabilized zirconia (ZrO2–3%Y2O3) particles. The composites
as well as the reinforcing particles were analyzed by the means of
optical and Scanning Electron Microscopy (SEM), Energy Dispersion
Spectroscopy (EDS) and X-Ray Diffraction (XRD). The mechanical
properties were obtained by the transverse rupture strength test. Wear
tests were also performed on the composites and monolithic
porcelain. The best mechanical results were displayed by the
porcelain reinforced with the pre-sintered ZrO2–3%Y2O3
agglomerates.
Abstract: The dental composites are preferably used as filling
materials due to their esthetic appearances. Nevertheless one of the
major problems, during the application of the dental composites, is
shape change named as “polymerisation shrinkage" affecting clinical
success of the dental restoration while photo-polymerisation.
Polymerisation shrinkage of composites arises basically from the
formation of a polymer due to the monomer transformation which
composes of an organic matrix phase. It was sought, throughout this
study, to detect and evaluate the structural polymerisation shrinkage
of prepared dental composites in order to optimize the effects of
various fillers included in hydroxyapatite (HA)-reinforced dental
composites and hence to find a means to modify the properties of
these dental composites prepared with defined parameters. As a
result, the shrinkage values of the experimental dental composites
were decreased by increasing the filler content of composites and the
composition of different fillers used had effect on the shrinkage of
the prepared composite systems.