Some notes on vertiprep

Vertical preparations or vertipreps are simply crown preparations with no defined finish line as it is prepared to a knife edge or feather edge. Vertiprep avoids traditional shoulder or chamfer margins and therefore is more conservative of tooth structure in the pericervical area. Additionally, as less thickness of tooth is removed, more ferrule can be preserved in borderline cases. Vertipreps can be taken far subgingivally with good tissue tolerance until the biologic attachment and therefore the crown can provide more of a ferrule effect than Supragingival or equigingival traditional preps. However, vertipreps are difficult and technique sensitive and therefore should be reserved for the cases that would benefit from them i.e teeth where there is insufficient tooth structure or ferrule. The difficulty arises as narrow burs are needed to fit subgingivally and it is hard to make smooth preps with these. They tend to dig into the tooth and cause grooves and bleeding. When considering tissue control and the time taken to smooth the prep, equigingival marginned preps are much faster.

• When prepping vertiprep, firstly you must break the contacts with a thin bur and remove tooth undercuts with a fat bur. Then switch to a fine vertiprep bur to shape the preparation
• Teflon retraction is important before preparation to protect the tissue if you intend on taking final impressions in the same visit. Placing a fine 00 cord will dry the sulcus and allow your teflon cord to slip in easier. Ensure a dry sulcus and a wet instrument to aid in handling. The teflon should surround the whole tooth and overlap ends slightly. This will lock it into place and help to avoid the teflon being pulled out when prepping. Use downwards pressure with the vertiprep bur to pack the teflon down while prepping. This virtually assures that you stay out of the biologic width. Provided the tissue is healthy, the teflon will be stopped by the gingival attachment and the bur will be stopped be the teflon tape. Therefore, in theory the prep should not invade the biologic width.
• When prepping subgingivally, use a finer diamond bur. It is easier to stop the bleeding from the damage from a fine bur than a rough bur. Special vertiprep burs exist where there is a non cutting end that can slip subgingivally and guide the prep. You must ensure that the burs you purchase have a smooth transition between the cutting diamonds and the non cutting tip. Some cheaper burs have a small disparity and result in a microscopic margin at the transition point which will affect tissue health
• You must request no glaze at the crown margin as soft tissue reacts to zirconia better than other ceramics and the glaze is a type of feldspathic porcelain.
• Vertiprep teeth tend to have crowns that fit very snugly on try in as there is no horizontal margin to seat positively against. Therefore, the crown intaglio surface fits in close relationship with the preparation surface. However, due to this snug fit, spacing needs to be applied by the lab to account for cement film thickness as once the cement is applied, the crown will be jacked up by the cement thickness and the crowns will be high in occlusion. This will also place the stress of occlusion on the cement itself which is the weak interface between two strong materials. You want more spacing at the cervical than the occlusal surface as the thickness of the crown margin is very thin and prone to fracture. This will ensure that the crowns will seat where they are thicker i.e the occlusal surface and there will be less stress at the thin margin. You should ask for 30-50 micron spacing on the occlusal and 60 microns at the margin (Figure 1). 
• When the lab is constructing the crown to fit a vertiprep you have to instruct them to mill a 0.2 micron margin with a flat spot at there they will finish the crown and a 45 degree upwards flange and hand finish the margin to a knife edge with a bur. This is because mill can't automatically produce a knife edge margin (Figure 2). 

Figure 1: Spacings required for crowns over vertical preparations. There is no horizontal margin to provide support for the crown so spacing must be provided by the technician that is preferentially supported by the occlusal surface. 

Figure 2: The crowns must be milled with a small platform and a 45 degree upwards rise at the margin. Feather edge margins are too fragile to be milled and the crowns must be hand finished by grinding back the red areas under a laboratory microscope.