Ossix as cross-linked and BioGide as non cross-linked degradable collagen membranes, both used in combination with biphasic Calcium-Phosphate (BoneCeramic) as bone substitute. Clinical measurements and impressions from the sites of interest are to be taken at the stage of augmentation and 6 months after. At six months re-entry non-standardized biopsies from augmented sites will be taken to determine newly grown tissue in quality and quantity.