Primary / Preliminary Edentulous Impressions – Tray Selection
In order to make accurate edentulous impressions for the purpose of making dentures, a custom tray is required to more accurately adapt to the patient’s mouth. In the reference to complete dentures, it is particularly importantly to accurately capture the vestibular tissue anatomy, in order to create an effective seal for retention. Stock trays can result in distortion and shortening of the final denture flange. Custom trays are most easily made on accurate diagnostic casts made from preliminary impressions using an irreversible hydrocolloid (alginate) syringe technique. The use of the syringe technique ensures that alginate captures critical anatomy that is sometimes missed using a simple tray technique. The use of border molding in conjunction with the custom tray helps prevent distortion of the movable vestibular tissues. Displacement of these tissues could lead to dislodgment of the dentures during functional movements of muscles and frenal attachments, which could cause unseating of the denture.
Irreversible Hydrocolloid Storage
1. Pre-weighed pouches make dispensing easier, and minimizes contamination
2. Store bulk material in airtight containers, store in cool dry containers
3. Alginate deteriorates if stored above 54°C, or with repeated openings
4. Deterioration results in thin mixtures, reduced strength, permanent deformation
1. Select a tray with 5 mm of clearance with soft tissues – alginate requires bulk for accuracy, strength and stability.
2. Maxillary trays should extend from the labial vestibule to slightly beyond the vibrating line. Mandibular trays should cover the retromolar pads.
3. Sto-K trays or equivalent edentulous trays give the best results, but stock dentate trays
can be used (distortion, overextensions are more common with dentate trays).
4. Trays can be modified with compound to extend the tray if desired.
Irreversible Hydrocolloid Syringe Technique
Using a syringe to make preliminary impressions helps to register critical anatomy, which can be otherwise missed. In particular, these areas are captured more easily with a syringe technique:
– Retromylohyoid area
– Hamular notches
– Retrozygomal area