Prosthetic dentistry / by James Harrison Prothero.

  • Prothero, James Harrison.
Date:
1916
Catalogue details

Licence: Public Domain Mark

Credit: Prosthetic dentistry / by James Harrison Prothero. Source: Wellcome Collection.

    110/1222 (page 84)
    to the mouth, properly seated, the muscles drawn outward, and steady pressure applied for two or three minutes. ‘The amount of force necessary to apply varies from three to ten, or even fifteen pounds, according to conditions. Extremely soft, spongy, but not resilient, tissues are copied better with moderate, while harder areas require a greater amount of pressure. DISTRIBUTION OF THE PLASTIC COMPOUND UNDER MAINTAINED PRESSURE When the layer of softened compound is of uniform thick- ness and is sufficiently plastic, under continued pressure the material gradually flows from the hard to the soft areas, com- pressing the latter and relieving the pressure on the former, until a sort of equilibrium is established. If care is taken in carrying out the technical details, the finished denture will have a similarly uniform bearing on the tissues, which will add greatly to its stability. At the time of forcing the impression up against the tis- sues, the excess compound is naturally moved from the inter- ior of the tray, externally and over the flange margin. The tendency is for the compound to curl outward, away from the process. It therefore becomes necessary to readapt the per- iphery of the impression to the border, to seal against the in- gress of air. This step is accomplished as follows: PERIPHERAL READAPTATION On removal of the impression the second time, it is chilled and the peripheral margins, buccally, labially, and lingually, are reheated. It is again returned to the mouth and seated. With the index finger the softened margins are firmly pressed into close contact with the border, buccally and labially first, correcting the vault portion last. Sometimes, however, the adaptation of this margin is carried out as a separate, final step. Only the periphery is softened in this rim adjustment, since if the whole impression is reheated, the effect of the previous compressive steps would be lost and adaptation would be impaired. The impression can be tested as to adaptation by having the patient make muscular effort to displace it or by biting on something to see if it can be tipped. The removable handle trays of the Greene type are very convenient for testing the stability of the impression. They are also, on account of their small size and generally correct form, especially adapted to