Transcrestal Sinus Lift With OSSIX Bone vs BIOSS Collagen

Primary: Histologically analyse the quality of bone regeneration after graft material insertion in severely resorbed maxilla. Secondary: Radiological analysis of the volume of the bone regenerations with the shirnkage rate of the graft material. clinical study of 20 patients 13 in OSSIX Bone group 13 in Bio-Oss Collagen group all patients requiring a regenerative procedure (sinus lift) having less than 3mm of residual bone height (RBH) with the impossibility to place the implants at the time of regenerative proc 6 months follow up for the first endpoint. (collection of the histological sample) 12 months follow up - long term clinical evaluation. tests performed: Cone Beam Computed Tomography (CBCT), clinical evaluation, X-ray