. The principles and practice of dental surgery. vacuum cavity, do not necessarily requirethis suction efiort on the part of the patient: it is sufficient, simply,to put them in place with slight pressure to force out the air. In replacing the loss of the bicuspids and molars of the upperjaw with artificial substitutes, mounted upon an atmospheric orsuction plate, some dentists seek to give increased stability to thepiece by constructing the plate in such a manner that a narrowband shall pass in front of the alveolar border, as represented inFig. 251. But unless this is fitted with great accur
. The principles and practice of dental surgery. vacuum cavity, do not necessarily requirethis suction efiort on the part of the patient: it is sufficient, simply,to put them in place with slight pressure to force out the air. In replacing the loss of the bicuspids and molars of the upperjaw with artificial substitutes, mounted upon an atmospheric orsuction plate, some dentists seek to give increased stability to thepiece by constructing the plate in such a manner that a narrowband shall pass in front of the alveolar border, as represented inFig. 251. But unless this is fitted with great accuracy it will irritatethe gums : it is also very apt to be seen in talking or laughing,we, therefore, decidedly prefer to give the required strength byincreasing the thickness of the plate. Where the second or thirdmolars remain on either or both sides, an atmospheric-pressure plate 724 THE VACUUM CAVITY. will answer better than any other kind. This principle may becombined with the use of clasps, as in Fig. 246, or the plate Fig. 251. Fig. may be cut out, so as to pass over the remaining teeth as re-commended by Dr. Hayes, (Fig. 252,) or it maybe carried alongthe inside only of the ridge. In the application of one or two teeth by atmospheric pressure,it is necessary to employ a wide plate, in order to present asmuch surface for the atmosphere to actupon as possible. A substitute for thetwo central incisors mounted upon a singleplate, to be applied upon this principle,is represented in Fig. 253. ProfessorAustens method is to prevent lateralmotion by a stay or narrow semi-claspon each side, to cut the plate as much aspossible from around the intervening teeth,and to depend for adhesion upon accuratelyfitting the plate to such part and extent of the mouth as the varyingcircumstances of each case may require.
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