Dental Dentures: Partial | Cosmetic Dentistry
In an arch with only the anterior dentition remaining, the extension of the partial denture base is dependent upon the static situation. When a free-end saddle is subjected to occlusal forces the denture rotates around an axis formed by connecting the distal rest on the same side with the end of the base on the opposite side. Occlusal forces acting on the opposite saddle produce the mirror-image of this same reaction.
Care must be taken here to insure that the denture base is not extended ventral to the junction of the two axes of rotation (Fig. 58).
If the base were to be extended ventral to the axes of rotation the possibility exists that during mastication the ventral border would be lifted and that food debris could get under the base.
Finally after a certain amount of bone resorption and subsequent settling of the denture on the dorsal side of the transverse axis formed by connecting the most distal rest on each side of the arch, the ventral portion of the denture base would be raised from its original position and no longer lie firmly against the palatal mucosa (Fig. 59).
|For this reason, an extension of the base ventrally for indirect retention is disadvantageous (Fig. 60). As a means of stress distribution this ventral extension is also ineffective since intrusion of the teeth equipped with dental rests is so minute that a compression of the tissue covered by the ventral extension hardly occurs.|
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