In dentistry, a fenestration is a buccal or lingual window defect of either denuded bone or soft tissue occurring over a tooth root, implant, or alveolar ridge. The term may also apply to a man-made fenestration which is created when opening a lateral window to the maxillary sinus for a sinus augmentation procedure. A naturally occurring fenestration leaves the exposed root surface in direct contact with either the alveolar mucosa or the gingiva. The condition may be caused by a variety of factors including tooth movement due to orthodontics, pathology (both endodontic and periodontal), root apex contours, and occlusal issues. Treatment of a fenestration can include guided tissue regeneration, flap surgeries, or free gingival grafting. For some patients, a bone graft may also be required. Prior to orthodontic procedures, it is important that both the root positions and the periodontium condition be evaluated to reduce the risk of fenestration.