PART PREPARATION (cementable) ZIRCONIA ABUTMENT

Virgin abutment
Zirconia abutments usually need some form of reduction in height,
path of insertion and margin placement. If the stock abutment is
pre machined with a sloping collar, position the abutment with
the narrow part of collar were the tissue height is the thinnest.
Screw down the abutment with a laboratory screw
(do not use the final screw while working on the case) and lift
up the soft tissue to verify the abutment is properly engaged
and seated.

Height reduction
Reduce the abutment height with a water cooled, high-speed hand piece and a
Brasseler® diamond bur
(part # 2855.31.025) to create enough room for the zirconia coping and porcelain (2mm). Use only light
pressure to prevent overheating the abutment which might cause micro cracks.
Next reduce the mesial and distal aspects
of the abutment to allow for proper draw. Looking down from the
occlusal, check if the facial and lingual portion also need reduction
to create enough room for the restorative material.

Buccal reduction
Any part of the pre
machined collar above the tissue needs to be adjusted down to the crest
of the tissue. Mark the collar of the abutment with a sharpie marker
on the facial aspect of the abutment and remove the abutment from the working
model. Attach the abutment to a second analog for ease of handling and
protection of the indexing feature. Reduce the collar where marked with the
sharpie marker to the desired tissue depth without creating a undercut on the
abutment. Cut antirotational grooves on the mesial and distal long axis of the
abutment.

Finished preparation
Each dentist
has different preferences how deep the margin should be placed below
the tissue. Placement of the margin more than 1.5mm below the tissue
will make it difficult for the dentist to clean excess cement or bonding agents from the
sulcus at the time of delivery.

Before & after
Reposition the abutment back on to the
working model and double check for clearance, path of insertion and
proper margin design with the soft tissue mulange in place. The
abutment portion to which the crown will be cemented should not be
shorter than 3mm.