Triple-tray Impressions: How to Save Time and Improve Outcomes

Indirect restorations that are fabricated after taking a triple-tray impression can be highly predictable if certain guidelines are followed and the clinician has realistic expectations.

What are reasonable expectations?

1. The morphology of the restoration will not match the contra-lateral tooth. The reason why? The technician does not have a cast of the tooth.
2. The occlusal contact may require more adjustments at the time of insertion compared to full-arch impressions and casts mounted on a semi-adjustable articulator. The reason for this is:
   1. It is difficult to confirm the exact patient bite when taking the triple-tray impression.
   2. The filament used to separate the upper and lower compartments of the impression may slightly distort the occlusal morphology of the adjacent teeth and negatively affect the occlusion.
3. Eccentric contacts must be evaluated and adjusted intraorally. This is because:
   1. The small articulators do not represent the normal distance from the condyles to the teeth.
      1. i.No lateral or protrusive movements of the articulator can replicate the contacts that will occur intraorally, so it cannot be checked in the laboratory.

Following these guidelines will improve outcomes and save time during the insertion appointment.

1. Always impress a minimum of one tooth anterior and posterior to the prepared tooth or teeth.
   1. Never prepare the last tooth in the arch
2. The fewer the number of prepared teeth in a quadrant, the better.
3. The more rigid the tray, the better.
4. Check the tooth contacts on the contralateral side before and during the impression to be certain they are identical.
5. Hold the patient's chin firmly closed while the impression material is going through its setting phase.
   1. The patient can also use their fist under their chin and apply upward pressure.
6. Use a fast-setting impression material
7. Take a bite registration over the prepared teeth only so the lab can confirm the accuracy of the bite.
   1. Trim and check the bit intraorally to confirm its accuracy.
8. The laboratory should have a solid model to check interproximal contacts. A mounted solid model will make the occlusion more accurate.

By following these guidelines and having realistic expectations, you will save chair time and have outcomes that are more predictable.

(Click this link for more dentistry articles by Dr. Bob Winter.)