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Technical Discussion: Common Cause of Distortions
Technical Discussion: Denture Relines with No Retention

Technical Discussion: Denture Relines with No Retention

Problem: I struggled to remove the upper impression but the finished reline fell out of the mouth. What happened?

L.T. Armstrong, DMD: When a liquid is compressed between two solids, pressure increases. This applies when your impression material (liquid) is seated (compressed between the denture and the maxillary bone). The resulting pressure compresses the oral mucosa covering the maxilla.

The impression is tight (difficult to remove) because the surface tension between the impression material and the oral mucosa, both hydrophilic, is greater than blood pressure (the spring back force). There is no surface tension between a hydrophobic denture base and the tissue. Consequently, blood pressure in the compressed mucosa prevails and the denture is pushed out.

The solution to this problem is to drill 5 or 6 holds with a #6 or #8 round bur in the rugae area of the base or tray. Then seat the impression very slowly and gently. The holes will permit the release of pressure and help solve this problem. Always check the bite by having the patient close their teeth together (gently) but never let them hold the impression in place with their teeth. They will bite too hard, causing excess pressure.

A similar problem exists with two-step crown and bridge impressions, click here for more information.

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