ORAL REHABILITATION
prostheses according to grades 2 and 3 of the three
grade scale of chipping fractures (13). Both grades
indicate that the alteration of the veneer surface
cannot be polished without altering the original
anatomic form. In contrast, grade 1 of chipping
fractures is used if the altered surface does not
involve a functional area and with polishing it is
possible to maintain the original anatomy.
Clinical procedures for FMIZBRs
Four to six dental implants (Titanmed, Milde
Implants, Bergamo, Italy) were placed in each of
the jaws of each patient in a one-stage surgical
procedure with the aid of a surgical guide (Fig. 2).
Primary stability, with an implant stability quotient
(ISQ) (14) of 65 at least, was obtained for all
the implants. Wi th the use of a rubber dam for
isolation, autopolymerized acrylic resin (Takilon BB,
Salmoiraghi srl, Melegnano, Lodi, Italy) was used
to isolate the gingiva and to record the location of
the titanium temporary abutments (Cylinder, Milde
Implants, Bergamo, Italy). All the implants were
immediately loaded with an acrylic screw-retained
interim prosthesis. The patients were instructed
to remain on a soft diet for the subsequent two
weeks. After two months, all implants showed good
osseointegration at clinical, instrumental (resonance
frequency analysis) and radiographic tests.
Using a pick-up technique, polyether completearch impression (Impregum/Permadyne, 3M ESPE
AG,Seefeld,Germany) was performed in a customized
open tray (Apex trays, Megadenta Dentalprodukte
Radeberg, Germany). A plaster model (Esthetic-base
gold, Dentona AG, Dormund, Germany) was made
and used to obtain an anatomical contour wax-up.
Soft tissue was reproduced in the impression using
vinylpolysiloxane (Gingifast Rigid; Zhermack, Rovigo,
Italy). The maxillary relation was taken with a postural
facebow (15). The occlusal vertical dimension and an
interocclusal centric relation were transferred to the
articulator using occlusal rims.
Afterward, a verification device was fabricated
intraorally to evaluate the accuracy of the definitive
cast. Impression copings were connected to the
abutments and splinted to each other with acrylic
resin (Duralay, Reliance, Dental Mfg. Co. Worth, IL).
The verification jig was sectioned and reconnected,
unscrewed, and transferred to the definitive cast.
Passive fit of the index on the definitive cast was
confirmed, and the accuracy of the definitive cast
was verified. The wax contour was then impressed
on the plaster model.
The plaster model, the silicone mask, and then
both components together were scanned with
a laser scanner (Dental Wings series 3, Dental
Wings Inc., Montreal, Canada). The zirconia core
was designed with respect to the ceramic support
and directly screwed on 1 to 4 mm shoulder multiunit abutments implant connection (3dObjects,
Taverne, Switzerland). Using a reverse engineering
technique, the STL files were transformed in JGESS
140
files (Geomagic, Research Triangle Park, NC, USA)
and modified by using a CAD system (Rhinoceros,
Seattle, WA, USA).
For all prostheses, the zirconia core was devised
also considering the veneering ceramic. The core
was covered by a uniform thickness of veneering
ceramic, and a maximum of 2 mm of unsupported
porcelain was allowed. The connectors within the
crowns were designed with a 10 mm2 area at least,
as measured by the software used for the CAD
technique. A Computer Aided Manufacturing
(CAM) system was used to mill the zirconia
core in the pre-sintered state (Zirite, Keramo,
Tavernerio, Como, Italia). The cores were then
sintered (3dObjects, Taverne, Switzerland), and
covered by feldspathic porcelain (CZR Noritake
Kizai Co. Ldt, Nagoya, Japan). Porcelain fusion was
made with zirconium oxide margins by a single
master ceramist (SST Dental Clinic, Milano, Italia),
following a slow cooling protocol (16, 17).
The passive fit of the fixed detachable
prostheses on the abutments was evaluated in
three ways. First, pressure was applied first on
one end abutment and then on the other one (18)
to look for movement of the prostheses. A visual
check was then carried out, and fit was evaluated
with an explorer (19). Passivity was verified with
an individual screw (20) in both sides of the end
abutments. No movement of the restoration was
noticed at finger sensibility, and the restoration
remained in its position at the opposite unscrewed
end abutment. The fit between the prostheses
and all abutments was clinically verified in three
dimensions (21). By using 8-mm-wide, 8-mm-thick
shim stock foils (Hanel, Roeko, D-89122 Langenau,
Germany), occlusal contacts were tested in
maximum intercuspation without interferences in
lateral excursions, and adjusted as necessary.
All prostheses were polished and lustered
before final insertion by using a pearl surface paste
(Noritake Kizai Co. Ldt, Nagoya, Japan). According
to a previously standardized protocol (22), all
patients were submitted to functional analysis of
their masticatory muscles after the detachable
prostheses were hand screwed in the mouth
(Fig. 3). At the achievement of a good neuromuscular
equilibrium (23, 24), the screw access holes were
filled with gutta percha (Temporary stopping, GC)
followed by light-cured composite resin (Filtek Z250,
3M ESPE).
Follow-up evaluation
Clinical events were recorded as irreversible
events (failures) or as reversible/ adjustable
events (complications) (25). Failures require the
replacement or removal of the prosthesis; the
causes could be fractures, loss of retention of the
prosthesis, loss of osseointegration of the implant,
persistent pain. Technical (loss of retention,
crown fractures) and biological (periodontal/
STOMA.EDUJ (2014) 1 (2)