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.