The aim of the present study was to compare the half-packed grafts that are covered with either a collagen or a nonresorbable membrane to the conventional alveolar ridge preservation procedures involving full-packed grafts and collagen membrane. The primary purpose was to evaluate the bone dimensional changes between the groups, and the secondary objective was to assess the potential contributing factors to clinical, radiographic and implant-related outcomes under different alveolar ridge preservation procedures.

Regarding different surgical approaches in alveolar ridge preservation, limited studies directly compare collagen and non-resorbable membrane, and the comparison between half- and full- grafting strategy in clinical and radiographic outcomes was still lacking. The comparable effect of dimensional preservation between groups was shown except for more radiographic bone gain in full-grafting group. Contributing factors, including thin bone thickness , vertical root fracture related sockets, non-molar sites and large BPD might attenuate the effect of ARP. At implant placement, similar results in bone quality and keratinized mucosal width was found in all groups, while thicker vertical mucosal thickness was obtained when using nonresorbable membrane. All surgical modalities in alveolar ridge preservation yield stable peri-implant health 1 year after implant placement.

Inclusion Criteria:

1. ≥ 20 years old
2. presence of one or more hopeless teeth requiring extraction and subsequent implant placement due to reasons such as crack tooth, vertical root fracture, endodontic failure, unrestorable caries and severe periodontitis
3. the extraction socket should have more than two walls for ARP, which includes type I-II sockets (Palatal/ lingual defects were also included)
4. participants should have a stable periodontal condition or history of periodontitis that is well-controlled with good oral hygiene. The pocket depth of the adjacent tooth around the socket should be less than 3 mm as assessed with a periodontal probe (Hu-Friedy, Chicago, IL, USA).

Exclusion Criteria:

1. heavy smokers consuming more than half pack of cigarettes daily
2. women who were pregnant, lactating, or planning to be pregnant
3. history of psychiatric disorders
4. uncontrolled and complicated medical conditions that might hinder wound healing or bone metabolism, including poorly controlled diabetes, autoimmune disorders, receiving current radiotherapy in the head and neck regions, taking bisphosphonate and other antiresorptive agents.

Raw data were generated at Taipei Chang Gung memorial hospital. Derived data supporting the findings of this study are available from the corresponding author(CYL) on request.

The operator (L.C.Y.) was blinded to the assignment and opened the envelope just before the alveolar ridge preservation procedures, while both the participants and the examiners (C.M.Y., P.Y.K.) remained completely blinded to the assignments in the study protocol.