. The Dental cosmos. a partial vacuum in the mouth * See Items of Interest for February 1001,vol. xxiii, p. 80. 926 THE DEXTAL COSMOS. just back of the denture, and air isdrawn from beneath the plate. It isestimated that under the most favorablecircumstances it is possible to obtainwith a vacuum chamber three-quartersof a square inch in area, a sustainingforce of about two and one-half is of course augmented by the ad-hesion of the denture. The vacuum cannever be perfect, and, after a shortwhile, owing to leakage, the air is onlypartially rarefied. so reduces the retentive value of
. The Dental cosmos. a partial vacuum in the mouth * See Items of Interest for February 1001,vol. xxiii, p. 80. 926 THE DEXTAL COSMOS. just back of the denture, and air isdrawn from beneath the plate. It isestimated that under the most favorablecircumstances it is possible to obtainwith a vacuum chamber three-quartersof a square inch in area, a sustainingforce of about two and one-half is of course augmented by the ad-hesion of the denture. The vacuum cannever be perfect, and, after a shortwhile, owing to leakage, the air is onlypartially rarefied. so reduces the retentive value of thedevice that its use is not justified; alsothe irritation of the soft tissues at theedge of the chamber is a serious draw-back to its use. It is never safe to say that anythingmay not serve some useful purpose, butit is absolutely certain that the vacuumchamber ought never to be a sole reli-ance for retention. From the nature ofthe case it cannot be, and the other fac-tors concerned in the matter should be Fig. Casts with plate outline and form of vacuum chamber marked uponthem. (Am. Text-bk. Pr. Dent.) The advocates of this method main-tain that by its use in the beginning, theretention of all upper plates is improved;that even if it is of only temporary util-ity, this primary firm retention tidesthe patient over that trying period dur-ing which practice in the use of thedenture is being acquired. They furthersay that, despite the drawing of themucous membrane into the cavity, thelatter is never completely filled, andsome service is still performed; also thatthe space affords a relief of plate pres-sure upon the hard areas found in thecenter of all mouths. On the other hand,it may be argued that in course of timethe drawing-in of the mucous membrane utilized to their full extent. Further-more, it should never be used withoutsuch careful attention to the techniqueof its construction that all of its seriousdisadvantages are avoided; and it shouldnever be used when satisf
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