A flat ridge where very little bone exists above the inferior alveolar canal is usually an indication for a subperiosteal implant, fig. 1. As flat as the ridge looks covered with tissue, the under-lying dense bone very often exhibits a great deal of surface area, fig. 2, for the support of a subperiosteal implant. Carefully the mental nerve bundles are dissected out. In this case, besides the main bundle a very thin accessory branch was seen several mm. distal to it, fig. 3, and was also noticed on the opposite side, fig. 4. If the impression was accurate the fit of the implant will also be exact, fig. 5. The buccal peripheral strut must accommodate the mental nerve and vessels exiting the mental foramina on both sides by circumventing them, figs. 6, 7. This case healed uneventfully, fig. 8, and the implant denture which is implant borne and not tissue borne con-

252