Silicon Impression Materials Support Better Border Molding

Dentistry Today
Dobromira Shopova, PhD


Dobromira Shopova, PhD

Silicone impression materials spread on the edge of the custom tray as well as on the alveolar ridge, making them superior to other choices in border molding, according to researchers at Plovdiv Medical University in Bulgaria.

Typically, clinicians treat edentulism via the placement of a complete denture. Previous research has found that the application of a border molding procedure (or functional shaping) results in significantly fewer cases of pressure ulcers (decubitus) and soft tissue deformations, increasing the prosthesis’ retention and stability both at rest and in function.

Since many factors affect optimal treatment such as anatomical structures (muscles, muscular and soft-tissue gripping) and the asymmetry between the left and right halves of the upper and lower jaws, special care is important in determining the depth and width of the tissue where the teeth normally would be nested (gingivobuccal sulcus), the researchers said.

With border molding, the researchers said, it is possible to determine the depth and width of that tissue. However, they added, the accuracy of the impression still would largely depend on the materials used in the procedure.

The researchers then set out to evaluate and determine the accuracy of two different groups of impression materials for border molding, thermoplastic and elastomers. They examined four different brands:

  • Detaseal function (additive silicone for border molding)
  • Sta-seal F (condensation silicone for border molding)
  • GC Iso functional sticks (synthetic resin for border molding)
  • Kerr Impression compound green sticks for border molding

The researchers used a vacuum measurement technique to measure negative pressure after the border molding procedure on an edentulous upper jaw. They also assembled a special custom tray from a light-curing base plate with a metal adapter fixed to the midline on the palatal slope. To create and measure the negative pressure, they used a combined pressure pump. The maximum was 3 bars for positive pressure and -1 bar for negative pressure.

For all materials, the researchers:

  • Applied the impression material along the edge of the individual tray
  • Inserted, positioned, and performed Herbst functional tests
  • Waited for the elasticity of hardening of the material
  • Assembled the clinical unit for negative pressure measurement
  • Measured the negative pressure created between the custom tray and prosthetic field
  • Recorded the result
  • Released the individual impression tray from the patient’s mouth

The researchers observed a statistically significant difference between the two thermoplastic materials, the GC Iso functional sticks and the Impression compound green sticks. No statistically significant difference was observed between the other groups of materials.

The measured mean negative pressure values created between the prosthetic field and the custom tray showed close values for each patient, with a difference of -0.05 to 0.1 bar. This showed that the anatomical features of the prosthetic field were of great importance, the researchers said.

The researchers concluded that quantitative measurement of negative pressure is entirely possible under clinical conditions. Thermoplastic materials for border molding are retained and formed only along the edge of the custom tray.

However, the researchers said, silicone impression materials spread on the edge of the custom tray as well as on the alveolar edge, demonstrating their superior manipulative qualities and accuracy in border molding.

The study, “Clinical Negative Pressure Measurement After Border Molding Procedure,” was published by Folia Medica.

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