'Could be worn as a brooch': cast gold alloy partial dentures

This 1950s appliance exemplifies well the amazing skills and lengthy work required of a dental technician, when producing complex castings from a given design by the dentist.

 

Partial denture. ADAQ MoD

Here is the story behind the partial.

The patient

Shirley*, 22 years old. Moved from the country to Brisbane in 1952. The edentulous area in the upper right of her mouth resulted from extractions for gross caries as a teen during WW2.

The dentist

Dr John Barwick 'Barry' Porter. Barry practised in the old Courier Mail Building, Queens St, Brisbane.

The technician

Mr Percy Polhman. Percy's rooms were in the same building as Dr Barry's. Percy regularly demonstrated to dental students at the UQ college in Turbot Street.

The process

Dr Barry performed surgery on Shirley to reduce the alveolar heights in the class II saddle. This created space for the prosthesis. The opposing lower teeth had over-erupted too much.

  1. Barry designed a stress-reduction partial for long-term protection of the saddle under masticatory load.
  2. Percy waxed up Barry's design on a cast stone plaster model from an impression made with Zelex compound on a tray.
  3. Then, he immersed the model in a mix of inlay investment plaster, leaving wires to several parts of the wax, before immersing it in the casting plaster. The wires would be removed after it set.
  4. The sprue channels gave access to the molten gold. The die is created when the strong gas flame heat is applied to vaporise the blue wax: this leaves the space for the molten gold.
  5. The plaster sets in a centrifugal device to force the molten gold into the die. The temperature from the gas flame matches the melting point of the gold alloy.
  6. After the casting cooled, the technician washed it away from the mold. Then smoothed it and polished with abrasive discs.
  7. Shirley was called back at Dr Barry's rooms to take an upper impression that included the casting fitted.
  8. Manufactured acrylic teeth were shaped to fit the space available on a stone wheel in a lathe.
  9. Using a bite plane, sheet was and a wax knife over a Bunsen burner flame, Percy carved the casting and shaped it.
  10. A cast of the lower teeth would have been set on an articulator to position teeth in good occlusion.
  11. This cast was then placed in a flask: the base cast with the appliance in situ set using a plaster mix, the top half covered with another plaster mix.
  12. When separated, the denture half of the flask was flooded with very hot water to melt the wax.
  13. Into the space left by the wax, Percy mixed acrylic monomer and polymer (pink) granulated powder into a putty consistency.
  14. Percy pressed together the two halves of the flask, and removed excess acrylic, before curing the whole set in boiling water. This process hardened the polymer mix.
  15. Percy then opened the flask, polished the pink part on a lathe with a cloth wheel and there you have it: the finished product!
  The result

Shirley successfully wore her prosthesis for three decades, until her premature death at 57. Shirley's dad commented, when first shown the denture: "It could be worn as a brooch!!'.
(*not her real name)