On the measurement of the degree of retraction of the human tympanic membrane using alginate impression material Part 1. Experimental studies

The present author, to measure the human thmpanic membrane by making a mold of the external ear with alginate impression material, made preliminary fundamental experiments on phantoms and rabbits. 1. When alginate impression material was introduced to a phantom with rubber membrane 0.1mm thick, the pressure on the membrane being only 23mm Hg, an accurate mold was obtained. On the contrary, with wood's alloy, the membrane of the phantom swelled markedly and no accurate mold could be obtained. 2. The bony bulla of a rabbit being opened, the picture of the tympanic membrane was taken from the tympanumside through the opening, and it was compared to the alginate mold obtained by introducing the material into external auditory canal simultaneously. In this way, it was proved that the mold represented faithfully the shape of the tympanic membrane. 3. With alginate impression material several molds could be obtained repeatedly on one rabbit. 4. With wood's alloy, because it perforated the tympanic membrane of the rabbit by its weight and heat, no mold could be obtained. 5. The deformations of the tympanic membrane at various negative and positive pressures into rabbit's tympanum could be recorded in molds by introducing alginate impression material into the external auditory canal. 6. When more than 10mm Hg negative or positive pressure was loaded on rabbit's tympanic membrane from the external auditory canal, perforation was evoked at the pars flaccida in 15 out of 18 ears. 7. When the external ear and bony bulla of the rabbit are fixed and imbedded in celoidin, they contracted as a whole and the tympanic membrane underwent a considerable deformation.