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.

    296/1222 (page 270)
    Lhird: The group of muscles which control and guide the movements of the mandible. ; Fourth: The group of muscles which control the position of the food and keep it within the working limits of the teeth in masticatory effort. } | THE UPPER MAXILLA The two superior maxillary bones join at the median line in a firm, strong suture to form the maxilla. .This united bone constitutes the anterior portion of the cranial base, be- ing directly and indirectly firmly united with all of the other cranial bones except the mandible. . Since the maxilla moves only as the entire cranium is sub- ject to movement, it may justly be regarded as the base or fixed factor of the masticatory apparatus. The upper teeth are imbedded in its alveolar process, and against these the food is forcibly carried in the process of reduction. The body of the bone in general is composed of rather thin, frail plates, but these are reinforced at various points where stress is heavy by what are termed buttresses. The alveolar process in which the teeth are imbedded is especially heavy and resistant to stress. This process in turn is reinforced by vertical ridges or columns running upward and merging into the malar processes opposite the first mo- lars, while anteriorly the cuspid eminences pass upward and merge into the nasal plates. .The tuberosities are supported by the thickened perpendicular posterior walls of the maxilla itself. Kach maxillary bone has within its body a cavity known as the mawillary sinus, or antrum. The floor of this sinus les immediately over the roots of the second and third molar teeth, some of which at times penetrate the bony plate. It can thus be seen how easily oral infection may be transmitted to the tissue lining the antrum when these teeth contain dis- eased pulps. The several plates composing the upper maxilla enter into the formation of the floor and outer walls of the nasal fossa, the palatal vault, floor of the orbit and spheno maxillary fissure. THE MANDIBLE The mandible is the active working factor of the masti- catory apparatus. In its alveolar process the lower teeth are imbedded, and through its movements they are brought in