الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Background: Minimizing and controlling the amount of tooth reduction during the preparation
of ultrathin laminate veneers is a challenge for esthetic dentistry. Ultra-thin, highly translucent
zirconia laminate veneer may be an appropriate option with the aid of a 3D printed reduction
guide in a minimally invasive esthetic restoration due to their enhanced translucency, higher
mechanical qualities, and ease of fabrication at a minimum thickness. It is important to consider
the impact of sintering conditions on yttria-partially stabilized zirconia. Nevertheless, there is a
lack of data in this area.
Aim of the study: To evaluate the effect of speed sintering on the translucency and microstructure
of two types of yttria-partially stabilized zirconia (Y-PSZ). Also to fabricate ultra-thin, highly
translucent zirconia laminate veneers with the aid of a 3D printed reduction guide.
Materials and Methods: For the in vitro study, 120 disk-shaped zirconia specimens
(10x10x0.4mm) were prepared from five types of yttria-partially stabilized zirconia. For each
material group, specimens were either conventionally sintering (CS) using a 7-hour cycle or
speed sintering (SS) using a rapid 90-minute cycle (n=12). The microstructure was inspected
with a scanning electron microscope (SEM), and phase identification was detected using x-ray
diffraction analysis (XRD). Translucency (TP00) and contrast ratio (CR) were measured using
a spectrophotometer (VITA Easyshade V). Color differences (ΔE00) between both sintering
processes were calculated with the CIEDE2000 formula. ΔE00 up to 1.8 was set as the
acceptability threshold. For the clinical study, ultra-thin translucent zirconia laminate veneers
of 0.4 mm thickness were fabricated with the aid of 3D printed reduction guide to reach the
optimal space required for the definitive restoration without excessive reduction. Each veneer
was air abraded with 50 μm aluminum oxide particles at a pressure of 0.2 MPa and adhesively
bonded to the tooth structure by using an MDP-containing primer and light-cure resin cement.
Results: The in vitro results revealed that speed sintering altered the internal structure of the
tested zirconia materials, which resulted in reductions in translucency parameters, an increased
contrast ratio, and significant color changes (lightness decreased and chroma increased).
However, the color difference between speed and conventionally sintered groups was within
the clinically acceptable threshold. Grain size was significantly decreased after speed sintering for
all tested materials (P < .0001). 5Y-PSZs had significantly larger average grain sizes than 3Y-PSZs.
Differences in yttria concentration, crystal size, and tetragonality between conventional and speed
sintered materials affected atomic structure, microstructure, and translucency. The clinical
outcomes revealed the effectiveness of employing a digitally produced 3D printed reduction
guide to control the tooth preparation to receive ultrathin laminate veneers. Zirconia laminate
veneers demonstrated conservative and esthetically successful results.
Conclusions: Speed sintering altered the internal microstructure and resulted in color changes
within the clinically acceptable threshold. Ultrathin zirconia laminate veneers demonstrated
satisfactory functional, esthetic, and clinical performance results. Highly translucent zirconia
could be selected as a conservative esthetic laminate veneer restoration that requires a
minimally invasive preparation. Combining alumina abrasion of size 50 μm at 0.2 MPa to the
intaglio surface of zirconia with using zirconia cleaner, primers, and resin cement containing
MDP produced a durable and reliable bond to zirconia.
Keywords: speed sintering; microstructure; phase content; highly translucent zirconia;
translucency parameter; yttria-partially stabilized zirconia; x-ray diffraction; contrast ratio;
conventional sintering; color differences; zirconia laminate; ultra-thin.