The mental foramen (MF) is a very important anatomic structure for local anesthetic, implant placement, periapical and orthognathic surgery. Its variations have to be recognized in order to prevent further complications. We are reporting two very rare cases of patients with unilateral absence of MF. The patients were examined with CBCT and one of them had sensory disturbances appeared immediately after implant installation in the region the missing right MF. In cases when the mandibular canal and mental foramen are not clearly visible on plain X-rays in order to see them and to avoid injury of the neurovascular bundle CBCT is a method of choice.