When using an open tray impression technique, the impression tray must have a window. The window permits the guide screw to protrude past the boundaries of the impression tray and allows the tray to seat fully as well as providing access to the screw for removal of both the tray and the impression coping.
(Click this link for a course on fixture-level impression copings for bone-level implants.)
The problem with creating the window in the impression tray is the impression material “falls out” while the tray is loaded. Additionally, impression material can easily escape during seating of the impression.
Placing a single layer of Scotch tape over the window will prevent the impression material from escaping while the tray is loaded and then transferred to the mouth. While strong enough to initially contain the impression material, the tape is easily displaced by the guide screw so that tray seating is not impeded.
Impressioning for implants in an edentulous arch can also benefit from this technique. In the case above, an open tray impression was made using a stock impression tray. The impression tray required modification, including preparation of a large window. In this case, two layers of Scotch tape were applied over the window.
Alternatively, wax could be used instead of tape. Many clinicians have found that adding wax to the tray becomes a little messy and in some cases a little less predictable.
(Click this link to read more dental articles by Dr. Darin Dichter.)
Darin Dichter, D.M.D., Spear Faculty and Contributing Author