There are two choices of restorations and implant abutments connection now: cemented and screw-retained.The excess cement, which would be difficult to completely remove, might lead to series of biological complications. The angulated screw channel (ASC) abutments, which recently introduced by Nobel Biocare , largely address the problem with visible screw access that may compromise esthetics. However, all of the present studies were clinical reports, thus the clinical efficacy of ASC abutments still needs the verification of evidence-based medicine with larger sample. Therefore, we designed a randomized controlled clinical trial study, aiming to verify the clinical efficacy of the ASC abutments by comparing screw-retained (with ASC abutments) single implant crowns with cemented ones in esthetic region.

Inclusion Criteria:

1. ≥18 years old and in good health;
2. Single tooth implant (type 1) in the esthetic region;
3. Patients with natural teeth adjacent to single implant crowns;
4. Patients with periodontal treatment before implant surgery;
5. The implants are from Nobel Biocare system with tapered link and the permanent restoration is a single crown and all-ceramic;
6. Soft tissue in the implanting-and-adjacent areas is healthy and free of infection

Exclusion Criteria:

1. Multiple implants in the esthetic region, or the restoration is a bridge
2. Patients with bone augmentation procedures;
3. Heavy smokers (>10 cigarettes/day);
4. Medically compromised patients (American Society of Anesthesiologists (ASA) classification III-IV);
5. Implants in an incorrect three-dimensional position (definition according to ITI VOL1);
6. Uncontrolled diabetes mellitus;
7. Unwilling to participate in the present study.