Plaster Impressions
Wax was not the only material used for creating impressions, plaster was widely used at this time as well. Plaster was prepared by first being mixed with water, becoming tough and malleable in the process. (9) (10)
Upper Dental Impression
Patients were advised to avoid swallowing while the plaster was in their mouth and to breathe through the nostrils to prevent involuntary retching. (9) To create impressions for full upper dentures in plaster, dentists instructed patients sit to upright and with their heads inclined forward. (10) They poured the dental cup with the plaster mixture, and then introduced the cup into the patient’s mouth, gently pressing upward. Importantly, the cup was held still by the dentist at this point until the plaster hardened. If the cup moved even slightly during the hardening process, this procedure was restarted. Once hardened, the plaster was removed carefully to avoid injury to the patient’s mouth. (9)
Lower Dental Impression
Taking impressions for full lower dentures, as with previous cases, required a unique dental cup as illustrated here. The cup was filled with plaster and then pressed downwards on the patient’s lower jaw. (9)
Dentists at this time avoided using plaster for partial dentures because it was difficult to detach plaster from teeth without breaking the impression. Though there were some workarounds such as removing the impression by breaking it away piecemeal, the overall preference was to avoid plaster for partial impressions. (9)