The Mandibular Impression

Impression material is distributed into the tray in a manner that reflects the anticipated final form of the impression. Using the fingers or a disposable 50 cc syringe, some impression material is placed into areas likely to otherwise yield voids, such as deep vestibules or undercut areas. Next, the filled tray is positioned over the residual ridge. The patient is instructed to raise the tongue, and then the impression tray is slowly seated as the labial and buccal frena are gently manipulated and the patient relaxes the tongue.

The best access and visualization is provided by approaching the patient from the front.

Check List for the Completed Mandibular Impression

The mandibular preliminary impression should be free of voids and provide detailed reproduction of all of the following:

• Retromolar pad
  
• Sublingual areas
  
• Vestibular areas
  
• Labial and buccal frena (if applicable)

No inner portion of the tray should be visible through the material.

Evaluating the Maxillary Impression Tray

The properly selected stock maxillary impression tray approximates the shape and height of the ridge and adequately covers the tuberosities. To compensate for an extremely high palatal vault, deep vestibules, or wider tuberosities, the impression tray can be bent as necessary; or wax or compound can be added to extend the tray or to fill large voids between the tray and the anatomy (e.g., a very high palatal arch).

By standing slightly behind the dental chair, the clinician can readily seat the maxillary impression while retracting cheek tissue. When a patient presents with an exceptionally high vault, impression material should be placed gently into the vault area prior to taking the impression to avoid entrapping air. For the patient with a strong gag reflex, the patient should be seated upright and be cautioned not to breathe through the mouth.

The impression tray is positioned beneath the ridge by centering in the anterior region. The posterior is seated first and the tray is rotated anteriorly. This technique will avoid trapping air and will minimize excess alginate flowing to the back of the throat.