Implant Supported Single Crowns With Different Retention Modes

Inclusion Criteria: * capability of giving an informed consent * good health as defined by the subjects medical history (no contraindications as described in the exclusion criteria below) * age 18 to 99 years * Good periodontal status: BOP \< 20%, PI \< 30%, no PD \> 4mm * No heavy smokers (\< 10 cigarettes/day) * at least 1 missing tooth in the premolar and molar region (with at least a mesial neighboring tooth/implant showing adequate hard- and soft tissue situation without the need of crestal hard- or soft tissue augmentation) either in the maxilla or in the mandible requiring implant therapy for reconstruction, requiring sinus floor augmentation or not. Exclusion Criteria * Insufficient bone volume for implant placement requiring GBR (guided bone regeneration) procedure in crestal area. * Heavy Smokers (\>10 cigarettes/day) * Medication with a contraindication for implant therapy (especially antiresorptive therapy, ongoing or recently completed local radiotherapy, systematic diseases, ongoing immunosuppressive therapy, functional disorders like Bruxism). * Skeletal immaturity. * Any active malignancy or ongoing treatment for malignancy. * An active infection (e.g. caries, gingivitis, periodontitis) at or in the neighboring area of the operative site. * Pregnancy * unable or unwilling to return for follow-up visits for a period of at least 16 months