Checking Functional Movement

The filled impression tray is gently seated and immobilized with respect to the mandible with one hand while the dentist manipulates the buccal frena and cheeks with the other. The patient is instructed to wet the lower lip with the tongue and to open wide for a short period of time, returning the mandible to a rest position for the remainder of the setting of the material.

The Completed Mandibular Final Impression

The final impression should reveal a highly detailed negative likeness of the denture base tissue surface. All frena should be visible. In this example, zinc oxide-eugenol was used as the impression material because little saliva was present. However, it should be noted this material will set rapidly in the presence of saliva, makikng polysulfide, silicone, or polyvinvyl siloxane materials more appropriate choices for making the final impression of the mandibular arch.

Creating a Land Area

The master cast that is made from the final impression dictates the final shape and extent of the denture borders. It also has to withstand the pressures associated with the flasking procedure. To this end, a 2mm wide "land" area parallel to the occlusal plane should be formed to surround the master cast and be located far enough from the depth of the vestibule to define the width of the functionally-defined denture borders.

A 2 mm wide land area can be lengths of square beading wax onto the impression. The wax is added 2-4 mm below the greatest height of the vestibule and 2 mm beyond the posterior extent of the final denture. Modeling clay can be used for this process as well.

A third alternative is for the impression to be inverted in a wet 50/50 mix of plaster and pumice. As the mix hardens, it can be carved to the desired extent and form.

For the mandibular impression, the full lingual area is blocked out by one of the methods described.