| case report Fig. 9 Fig. 10 Fig. 9: Ten days post-op before removal of the sutures and membrane. Fig. 10: Ten days post-op after removal of the sutures and membrane. ated cells, which contribute significantly to the cellular col- onisation of the granulation tissue that forms towards the centre of the alveolus left after the exodontia.1, 3 Four days after the procedure, irregularly formed trabeculae of prim- itive bone fill the defect. Owing to its restricted function, it only serves as filling and is unable to withstand more in- tense mechanical forces, such as more vigorous mastica- tion.11, 12 After seven days, angioblastic proliferation occurs in the alveolus centre. Additionally, in the osseous corti- cal walls, mature or secondary bone tissue interposes the granulation tissue.2, 3 Three weeks after the surgery, there is complete isolation between the postoperative alveolus and the oral cavity. Apicocervically, there is the formation of secondary bone. Up to 35 days after the surgery, new osteoblasts form from osteoprogenitor cells, with osteoid tissue developing. After 45 days, connective tissue is per- meated by mature bone tissue with incompletely formed trabeculae. Osteocytes are trapped in the newly formed adult bone tissue.13 After only four months, the bone tis- sue is considered morphologically able to withstand more severe mechanical stresses and already reliable regarding upcoming prosthetic restoration. Prior to implant-supported rehabilitation, a period of four months for the maxilla and six months for the mandible is usually required after the surgery.14 Even the execu- tion of pre-prosthetic surgeries requires planning based on terminal bone maturation.15, 16 The importance of the immobility of the clot within the context of alveolar bone rehabilitation after the surgical procedure needs to be emphasised. Bone sequestration, restorative material remains, surgical wound infections, abrupt increases in local temperature of higher than 47 °C for a duration of longer than one minute (which causes protein denatur- ation and minimisation of alkaline phosphatase), untimely movements of the flap or traumatic removal of sutures, among others, hinder alveolar repair.17 If replacements and fillings for tooth extraction sites are needed, autogenous bone grafts are considered to be the gold standard. Bone substitutes were developed with the purpose of saving surgical time and making the need for a second surgical stage, with greater morbid- ity for the patient, redundant.18–21 Membranes or screens have made it possible for the grafts to remain in position, since the periosteum does not always provide adequate containment owing to extensive bone defects. Surgeries such as maxillary sinus lift, correction of bone defects due to trauma or periodontal problems, augmentation of aesthetic areas after extraction, or periodontal surgeries with connective tissue grafts and apposition of blocks or particles of autogenous bone use membranes or barriers as an aid to bone repair.22–24 Membranes made of different materials can be em- ployed for guided bone regeneration. The ideal material should have the following features: it must be able to be cut and shaped; it should be easily adaptable; its me- chanical resistance should be compatible with applied loads; it should have great malleability; it should not be expensive; it should not require additional fixation, such as screws or tacks; it should be exposable to the oral en- vironment without promoting infections; it should be ap- plicable without making relaxing incisions; and it should be, if necessary, removable without the use of drills or punch instruments. The polypropylene membrane, as presented in this article, met most of these requirements and fostered osteopromotion.25 The polypropylene membrane bears numerous poten- tial advantages. It can be intentionally exposed to the oral environment and the flaps can be kept apart from each other for healing by secondary intention. Moreover, there is no supremacy in the use of granular biomaterials in the alveolus—only the blood clot. In addition, it is not linked to greater financial cost regarding complementary instru- ments. Furthermore, there is no need for prior hydration. It is dimensionally stable during its retention in the surgical area. It is waterproof and can be removed between seven and 14 days after placement. Moreover, it does not adhere to scar tissue, and the inner surface promotes the adsorp- tion of osteoblasts and precursor cells. It can be used when implants are placed, employing the Schroeder technique with immediate loading, allowing the simultaneous regen- eration of bone and grafted gingival tissue and hindering the accumulation of dental biofilm and food debris.26–30 14 1 2019