Short Implants in Edentulous Mandible

Inclusion Criteria: General criteria: * Age: 18 to 70 * Edentulous mandible with reduced bone level in the posterior region (\> 5 mm and \< 8 mm above nerve conduit) * Physical and mental condition that allow surgery and a 5-year follow-up period to be carried out without foreseeable problems * Obtained informed consent from the patient Specific criteria: * Limited vertical space for implant placement, where conventional implants with lengths of more than 4 mm cannot be used * Tooth loss or extraction at least 8 weeks before implant surgery * Healthy implantation site * Favorable and stable occlusal relationship * Complete denture in the mandible. If no denture available, an interims prosthesis will be fitted * Natural full dentition or sufficient complete or partial dentures in the maxilla Exclusion Criteria: General criteria: * Any conditions or circumstances which would interfere with the requirements for oral surgery * Allergy to any metallic implant component * Acute, untreated periodontitis * Previous oro-maxillo-facial radiotherapy * Any disorders in the planned implant area such as previous tumors or chronic bone disease (e.g., rheumatoid disease) * Any ongoing application of interfering medication (steroid therapy, bisphosphonate, etc.) * Alcohol or drug abuse * Heavy smoking (\>10 cigarettes/day) * Uncontrolled diabetes * Severe bruxism or other destructive oral habits * Pregnant or lactating women Specific criteria: * Need for a major bone regeneration technique * Infections in adjacent tissue of the planned implantation site. * Bleeding on probing (BOP) and plaque index (PI) higher 25% * Insufficient bone volume in the posterior region for placing a Straumann Roxolid® / SLActive® 4mm short implant and in the interforaminal region for placing a Straumann Roxolid® / SLActive® implant with a minimum length of 10 mm determined by radiographic analysis (OPG)