This trial pretends to validate for clinical use a bioengineered product composed of MSV cells (mesenchymal stem cells produced by IBGM, Valladolid, which have already been approved by the Spanish Regulatory Agency for three previous clinical trials) and a cross-linked matrix of autologous plasma patented by The Blood and Tissue Bank of Asturias (WO2008/ 119855) for bone maxillary cysts refilling. These two groups collaborate in the present project with the team of Maxillofacial Surgery of the Hospital Universitario del Río Hortega, who leads the clinical trial and deals with the medical aspects. The proposed trial is based on positive results obtained in previous animal studies performed by the present multidisciplinary team. The investigators propose a phase I / II clinical trial with 10 patients suffering from bone cysts in the maxillofacial region. Autologous mesenchymal stem cells isolated from a bone marrow sample will be seeded in the autologous plasma matrix and cultivated for 3 weeks. At this time, the cyst will be removed by surgery and the cavity filled with the protein matrix containing the mesenchymal cells. Checks will be conducted at 3 weeks, 3 and 6 months following the evolution of the cavity by panoramic radiography and computerized tomography scan.