CASE SERIES Amnion-Chorion Membrane in Open-Wound Approach for Localized Horizontal Ridge Augmentation: A Case Series Report Shan-Huey Yu, ∗ Tae-Ju Oh, ∗ Hom-Lay Wang ∗ and Hsun-Liang Chan ∗ Introduction: Guided bone augmentation often requires extensive releasing of the mucoperiosteal fap to achieve primary wound closure, an invasive procedure that can compromise the keratinized tissue volume and increase patient morbidity. Amnion-chorion membranes have been used to actively promote healing in chronic open-wound situations in the medical feld, suggesting that they could be used in a similar manner in the oral cavity.The ability to use open-wound healing techniques for guided bone regeneration would allow clinicians to avoid invasive procedures that cause additional tissue trauma at the surgical site. Case Series: Amnion-chorion membranes were applied over the bone grafting material augmenting localized horizontal ridge defects, and a gap between the faps was left intentionally during healing. Minor fap releasing procedures were performed in these cases, which demonstrated uneventful soft tissue healing, good volume of bone regeneration and preserved keratinized tissue. Conclusions: Preliminary clinical outcomes suggested contained minor horizontal ridge defects may be treated satisfactorily in a controlled, open-wound healing manner that reduces surgical trauma, chair time, and patient morbidity. Clin Adv Periodontics 2022;12:101–105. Key Words: Alveolar ridge augmentation; amnion; chorion; dental implants; microsurgery; surgical faps; wound healing. Background Guided bone regeneration (GBR) is an established and predictable method to augment defcient ridges. 1 Cur- rently, primary wound closure is considered a prerequisite for a predictable outcome in GBR cases because it is the safest way to ensure that the augmentation site is not compromised following the placement of graft materials. 2 Because graft materials add volume to the ridge, soft tissue releasing techniques have been developed to mobilize faps that can be stretched over the site to achieve primary wound closure. 3 Flap releasing procedures are technically challenging, especially in cases with shallow vestibule and low elasticity (scar) tissues, according to clinical experi- ences, and the additional internal cuts or vertical releasing incisions used to mobile the faps increases tissue trauma, surgical time, and post-surgical morbidity. 3 Even with deliberate soft tissue management, wound exposure is estimated to occur in ≈20% of the cases, indicating that primary closure, alone, is susceptible to failure. 4 A systematic review showed that when either pas- sive absorbable or non-resorbable membranes were used, some bone formation was observed even when wound exposure occurred. 5 In socket augmentation procedures, it ∗ Department of Periodontics and Oral Medicine, University of Michi- gan School of Dentistry, Ann Arbor, MI †BioXclude, Snoasis Medical, Denver, CO. ‡Cortical allograft bone particulates, Maxxeus Dental, Dayton, OH. § Biomend Membrane, Zimmer Biomet, Warsaw, IN. Received October 14, 2020; accepted December 23, 2020 doi: 10.1002/cap.10144 has become a routine that primary closure is not required, and an additional beneft is the maintenance/increase in keratinized tissue width. 6 Arguably to say the extraction socket has a high healing potential; nevertheless, certain less-challenging ridge defects could render open-wound healing to mitigate the adverse outcomes of fap releas- ing. It is especially benefcial if a material can actively promote healing in open-wound environment. Such an example is the amnion-chorion membrane, † which has been widely used for accelerating healing of chronic open wounds in the extremities, 7 corneas, 8 and oral mucosa 9 . In contrast to commonly used passive membranes, this mem- brane contains active growth factors, cytokines, extracel- lular matrix components and antibacterial properties that allow for rapid revascularization, re-epithelialization and bacterial inhibition. 10,11 Satisfactory open-wound healing of intact extraction sockets with this membrane has also been demonstrated. 12 Therefore, the goal of the following cases was to evaluate the use of amnion-chorion mem- branes in the open-wound approach for treating localized small (2 to 3 mm) horizontal ridge defects. 1 A written consent for treatment was received for the three cases described below. Case 1 Clinical Presentation/Management and Clinical Out- comes. The patient was a 48-year-old female patient without signifcant medical history, presenting on May 24,2019 with a horizontally defcient edentulous ridge at #3 and #4 sites (Fig. 1a). While performing lateral window sinus lift, the buccal concavity was confrmed (≈3-mm defect) upon full thickness fap refection (Fig. 1b). Allo- graft cortical bone particulates ‡ were placed and covered © 2020 American Academy of Periodontology. Clinical Advances in Periodontics, Vol. 12, No. 2, June 2022 101