| A single screw retained all ceramic restoration maybe fabricated
with a through and through stock zirconia abutment (BioHorizons) if
the spacing is favorable. Some manufacturers produce stock zirconia
abutments with a removable titanium interface (Nobel Biocare™),
these types of abutments are also suitable for direct bake on procedures
since the interface can be removed prior to baking the porcelain onto
the abutment and repositioned in to the abutment after the porcelain
fusing process. |
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1. |
| Stock abutments with a prebonded titanium interface
(Biomet 3i™) are not suitable for direct bake
on procedures because the bonding agent breaks down during
the porcelain fusing process in the oven. |
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| 2. |
| In cases where stock zirconia abutments are inadequately
dimensioned a custom zirconia abutment may be acquired through the
implant manufacturers CAD CAM program (Biomet 3i™ Encode®,
Nobel Biocare™ Procera, Straumann Etkon)or through third
party manufacturers (Atlantis™, Whip Mix Vericore®, GC Aadva). |
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| 3. |
| Screw retained all ceramic bridges and splinted restorations
require custom CAM milled substructures. Substructures may be
designed entirely through computer programs (CAD) or a mockup sub frame
is manufactured by hand and then copy milled in zirconia. |
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| 4. |
| The accuracy of the master model needs to be verified prior to
the manufacturing process because ill fitting zirconia substructures
can not be sectioned and reluted. A rocking zirconia sub frame will
require a costly remanufacturing. Therefore a verification index
needs to be tried in the patients mouth to assure the analogs in
the master model are related to each other in the exact same way
as the implants are related to each other in the patient. The
verification index may be utilized during the manufacturing process
for the zirconia substructure. |
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| 5. |
| To fabricate a mockup frame, denture teeth need to be set up in
wax to gain a full understanding of the spatial relationship
between the position of the implants in relation to the planned
final restoration. Screw access holes should emerge through the
center, or close to it of the occlusal table of the final
restoration. Screw access holes emerging through buccal or lingual
cusps may indicate a necessary change in restoration type to a
cementable or full metal restoration. |
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| 6. |
| A putty matrix is then made to capture the buccal and occlusal
aspect of the teeth in wax set up. The matrix should extend slightly
over the occlusal on to the lingual surface of the denture teeth. |
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| 7. |
| Remove the matrix and teeth in wax from the model after the
matrix material has set adequately. |
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| 8. |
| Steam clean the model and reposition the verification index on
to the model. Utilizing the matrix, reduce the verification index
until the matrix can be repositioned on to the model without
interference from the verification index. |
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| 9. |
| Block out any undercuts of adjacent teeth and obturate the screw
access holes after securing the verification index with screws on the
master model. Use #8 gage wax sprues, this will ensure adequate screw
access hole dimensions later and eases locating the screw access
channel after conversion of the wax up in to acrylic. Apply a acrylic
separator to the stone model and fasten the matrix to the model. |
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| 10. |
| Backfill the matrix with cold cure acrylic and place in a
pressure pot to ensure a porosity free acrylic polymerization. |
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| 11. |
| After the acrylic is polymerized to the manufacturers
recommendation remove the master model from the pressure pot. Drill
through the acrylic in the area of the screw access holes to gain
access to the screw head and steam out the number 8 gage wax sprue.
Detach the matrix and inspect the acrylic for voids and porosity. |
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| 12. |
| Remove the flanges with rotary tools, taking care not to
damage the implant/abutment interface. Utilizing the matrix,
reduce the height of the mockup to allow for 1.5mm to 2mm of
space between to mockup and the opposing occlusal surface. |
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| 13. |
| After removal of the flange and reduction of the mockup height,
modify the matrix by cutting the occlusal portion off. Now reduce
the buccal aspect of the mockup by 1.5mm to 2mm followed by reduction
of the lingual aspect. Basal surfaces also need to be cut back to
allow for adequate bake on porcelain thickness. |
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| 14. |
| At this point the mockup and master model could be sent to a
CAD CAM milling center to copy mill the zirconia frame work. |
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| 15. |
| If the substructure and model will be scanned in house for in
house or off site milling, scan pegs are attached to the mockup
and model for data acquisition through mechanical or optical scanners. |
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| 16. |
| After the sintered zirconia substructure is received, passive
seating of the zirconia frame needs to be verified by utilizing
only one screw in a terminal abutment. Tighten the screw by hand
and observe if seating discrepancies are evident at the remaining
abutments. |
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| 17. |
| Apply appropriate zirconia frame compatible porcelain according
to manufacturers recommendation. This may be achieved through press
on techniques or traditional build up with powder porcelain.
A shortened slow speed drill shank, coated with a separator and
inserted in to the screw access hole may be utilized to keep the
screw access hole free of porcelain during the traditional
porcelain build up technique. Although the drill shank needs to be
removed before the bake on process. The seating surface of the
zirconia frame needs to be kept free of any bake on porcelain to
prevent seating discrepancies. |
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| 18. |
| Shape the baked porcelain in the usual manner, ensuring the
abutment screw will fit in to the screw access hole without
premature binding. Glaze and stain the bisque stage restoration
to desired shade. Care should be taken not to stain or glaze the
seating surfaces of the abutments. |
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| 19. |