The absence of effective preventive dental programme leads to a multiplication of patients with single or multi-tooth edentations. Clinical and technical difficulties for prosthetic treatments appear in totally edentulous patients due to sharp bone atrophy. Depending on the mandibular reorganisation due to age and edentation, mandibular canal presents calibre (it diminishes) and position changes (it approaches to the alveolar mandibular ridge) modifications. Prosthetic treatments with dental implants imply a series of local and regional contraindications. In the present article, we studied a number of 32 computerised topographies (CT), on which we could establish the cranio-caudal and vestibulo-oral position of the mandibular canal. The CT also presents the relation of the mental foramen with the edentulous ridge. The relation of the mandibular canal with the alveolar ridge presents a very important aspect for establishing the treatment plan for the patient. The clinical safe-zone must be established regarding the topography of the mandibular canal, in such way that neither the osteotomy, nor dental implant placement will harm in any way the integrity of the contents of the mandibular canal.