| The main reasons to fabricate custom abutments are miss aligned
implants, excessive tissue above the implant abutment interface and as a
work around in cases where there are no zirconia abutments available for
the particular implant diameter or brand.
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1. |
| Custom abutments are waxed and cast with indexed UCLAs. All plastic
or gold plastic combinations are utilized for custom abutments. All
plastic UCLAs are considerably cheaper but sacrifice the precision fit
of gold plastic combination UCLAs. Choose appropriate platform diameter
UCLAs from the implant manufacturer or clone parts
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2. |
Remove the soft tissue moulage and position the UCLA on to the analog on the working model, ensure
proper
seating and engaging the anti rotational feature. Use a lab screw if
available
to secure the abutment in place, final screws should not be used while
working
on the case. The final screws are in some instances coated or surface
treated
to prevent screw loosening and the coating or surface treatment might get
damaged
during the production process.
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3. |
Reduce the plastic tube pressed on to the machined abutment-implant
interface
with a rubber wheel or a carbide bur in height to allow 2mm of room for
the
restorative material. Next reduce the buccal and lingual surfaces as
needed
to allow adequate room for the restorative material. Often the mesial
and
distal surfaces also need reduction to accommodate the restorative
material
and draw purposes.
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4. |
| Wax up the remaining abutment to ideal contour, creating a collar
and finish line for the restorative material. The margin should not
be placed more than 1.5mm below the crest of the tissue because it is
difficult for the restoring dentist to clean excess cement or bonding
agents from the sulcus if it is placed deeper than 1.5mm below the
tissue.
Placing the margin less than 1.5mm below the tissue might expose the
collar of the custom abutment in the future because of bone loss and
tissue recession around the implant. Dr.'s often have specific
preferences
how far below the tissue the margin should be placed. Develop the
emergence profile according to the restoring dentists preferences.
Some Dr.'s prefer zero tissue displacement while others dictate
total disregard of the existing tissue contour. |
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5. |
| Remove the finished wax up from the working model and meticulously
clean the abutment-implant interface with a cotton swab and
rubbing alcohol to remove any wax residue. |
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6. |
| Sprue the wax up following the long axis of the sprue as close as
possible. This will allow the investment to freely flow through the screw
access channel of the UCLA when pouring the investment into the casting
ring. The investment expansion should be adjusted to achieve zero
expansion, no special investment liquid, just distilled water.
Cast the wax up in a yellow gold alloy (If the
cast custom abutment is being made because no zirconia abutment is
available for the particular implant brand or diameter at hand, use
white precious metal for porcelain application). Do not use
non precious alloys for
any implant restoration because this might cause a galvanic reaction
due to the dissimilar non precious alloy and the titanium of the
implant. Take care not to exceed the solidus of the UCLA during preheating.
Pre heat time, heat climb rate, hold temperature and time need to
be fine tuned to avoid "flash cast on" on to the implant abutment
interface. |
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7. |
Divest the cast custom abutment with great care as not to damage the
abutment-implant interface with hand tools or sand blasting.
Instead place the abutment in acid and a ultra sonic unit to remove any
investment material.
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8. |
| Cut the sprue and screw the abutment on to a second analog to
protect the
abutment-implant interface. |
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9. |
| Refine the cast abutment to final contour
and chamfer margin. |
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10. |
| For anti rotational purposes cut grooves in the mesial, distal and
lingual surfaces of the abutment. |
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11. |
| Polish and high shine the collar portion of the
abutment. |
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12. |
| Mark the buccal surface of the abutment with a round bur to ease
proper abutment transfer and positioning for the restoring dentist at
the time of delivery or fabricate seating index (Tutorial). |
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| 13. |
| Alternative custom abutment cast in white precious metal with
porcelain application for situations where no zirconia abutment is
available. |
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