Marking the Initial Border of the Maxillary Custom Impression Tray

The border of the custom tray prior to border-molding should be shorter than the anticipated functional border of the finished prosthesis: 1 mm short of the depth of the vestibule and 2 mm short around frena and muscle attachments.

The posterior extent of the impression tray should extend 2-3 mm beyond the vibrating line, in order to later provide adequate visualization and marking of the posterior palatal seal and the pterygomaxillary seals.

The initial border of the maxillary impression tray is marked on the preliminary cast prior to fabricating the tray.

Blockouts

Relief between the custom tray and the preliminary cast is achieved by selectively placing small amounts of wax on strategic areas of the cast. Relief is provided for undercut areas, to minimize likelihood for thin areas in the final impression, and to allow free flow of the impression material from areas of excess to areas deficinet in material.

Blocking out undercuts with wax will facilitate separation of the impression from the master cast and make the patient more comfortable during insertion and removal of the tray.

For the maxillary tray, a single thickness of baseplate wax can be placed over the palatal suture and anterior crest of the ridge to ensure even flow of the material and to prevent pressure spots.

Marking the Border of the Mandibular Custom Impression Tray

The initial border of the mandibular custom tray should be 1 mm shorter than the anticipated functional border of the finished prosthesis, all around the periphery. The oblique ridge usually can be visualized on the preliminary cast, and the initial tray border should be 1 mm short of this inferior attachment of the buccinator muscle. The retromolar pad area must be fully covered. If the mylohoid groove is visible, the tray will extend approximately 1 mm beyond it.

Mark the border of the mandibular impression tray on the preliminary cast as described.

A single thickness of baseplate wax can be placed over the crest of the ridge and retromolar pads to ensure that pressure is not exerted on these areas. Undercut areas should be blocked out to avoid tray beakage and to ensure patient comfort curing insertion and removal.