Morphologic characteristics of bony edentulous jaws.

PURPOSE: The objective of this study was to examine bone tissue characteristics of edentulous arches and residual ridges in different regions of the human jaws.

MATERIALS AND

METHODS

For the study, 24 maxillary and 99 mandibular completely edentulous dry specimens were examined macroscopically and by linear and caliper measurements. Width and length of the edentulous arches were registered from the molar regions to the crest of the incisor zone. Residual ridges were quantified at the incisor, premolar, and molar regions.

RESULTS

Arches and ridges varied in size and shape. A trabecular bone track was present at the edentulous surface. In the maxillary arch, trabecular tissue was external to the cortical palatal vault, and in the mandible, the trabecular bony stretch was inside the cortical plates along the entire edentulous surface of the jaw. Of the ridges, 38% were thin knife-edged. In the maxilla, bone resorption was centripetal, and the crest of the edentulous arch was external to the osseous base of the cranium. In the mandible, resorption was centrifugal, forming an edentulous crest lingual to the mental protuberance anteriorly and to the mandibular base posteriorly. This discrepancy produced a reverse horizontal overlap of the residual crests, where the edentulous maxilla was at the same level or internal to the facing edentulous mandible.

CONCLUSIONS

This study, performed on 123 human edentulous dry bone specimens, indicates that the edentulous arch and the residual ridge take many forms. At the occlusal surface of the edentulous jaw a trabecular track is the remaining scar after tooth extraction. To accommodate an entire metal osseointegrated implant within the residual bone volume, crest reduction and bone grafts may be required as preprosthetic surgical measures. After tooth loss, maxillary resorption was centripetal and apical, whereas mandibular resorption was centrifugal and also apical, resulting in a reversed horizontal relationship in fully edentulous subjects.