INTEGRATING DIGITAL TECHNOLOGIES FOR DENTAL PROSTHESES: FROM IMPRESSION TO
SINGLE CROWNS. A PILOT STUDY
Table 1: Key steps for the new digital procedures in prosthodontics (IOI: intraoral impression)
The completed scan data were digitally delivered
to a manufacturing facility (3d Objects and Data
Software, Taverne, Switzerland).
The manufacture of 3d printed models from the
plaster casts scanning used an STL file where
approximately 350,000 vertices and 600,000 faces
were depicted; file size was approximately 30-35
MB. The resolution of the scanning (and of the
obtained model too) was 10 μm. The resolution of
the 3d printer was approximately between 0 to 50
μm, so no reduction and re-mesh of the digitized
models was necessary. A trained operator digitally
modified the file with particular attention to selfintersecting or duplicated faces, non-manifold
edges and vertices filling of the holes, thus
rendering the model ready and fully valid for the
3d printer.
Finally, the STL model was sliced into individual
layers, the path of printing nozzle was computed
and the STL file was converted to GCODE file by
Slic3r and printed.
At the same time, the plaster models were sent to
the manufacturer by traditional delivery. The new
individually zirconia CAD/CAM core was milled in
the presintered state (Zirite, Keramo, Tavernerio,
Como, Italy) and subsequently sintered in accord
with the manufacturer. Feldspathic porcelain
(CZR Noritake Kizai Co. Ldt., Nagoya, Japan) was
fused on the core with zirconium oxide margins
by one master ceramist in accordance with a slow
cooling protocol.13 From the manufacturer the
milled crowns were randomly assigned to group
A with fabrication steps controlled on 3d printed
model, and group B with procedures controlled
on traditional plaster models. The trial insertion
of the milled restorations was completed in the
sintered state to allow verification of the marginal
fit and internal adaptation. Each fabrication step
was evaluated to control prosthesis accuracies,
occlusal function and esthetic results. At the end
of the process, dental prostheses and traditional
models were returned to the dental laboratory and
consequently to the dentist.
At the insertion appointment, the marginal
adaptation and restoration fit were verified with
a polyvinyl siloxane material (Fit Checker Black;
GC America, Alsip, IL, USA). By using 8-mm-wide,
8-mm-thick shimstocks (Hanel, Roeko, Langenau,
Germany), proximal contact points and occlusal
contacts were adjusted as necessary and tested in
maximum intercuspation with no interferences in
lateral excursions. Final crowns polishing and luster
prior of insertion were achieved by using pearl
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