The aim of the study was to evaluate the histological response and dimensional ridge alterations following application of a nanocrystalline hydroxyapatite paste (NHA) into fresh extraction sockets in dogs. Immediately following vertical tooth separation and extraction, NHA was inserted in the extraction socket of the second molar in the lower jaws of 10 dogs. Untreated extraction sites on the opposite side served as controls. Wounds were closed using resorbable sutures after vertical flap elevation. After three and six months, 5 animals were killed. Lingual and buccal bone height, alveolar wall and total bone width 1, 3 and 5mm underneath the top of the crest were evaluated. Histological analysis revealed a high variability of NHA resorption and osteoconductive properties with different rates of material resorption. No statistically significant differences could be observed between the corresponding aspects of test and control sites. Both groups revealed higher alveolar wall resorption on the buccal than on the lingual side at both time periods. NHA does not seem to be useful for socket preservation procedures since it failed to prevent dimensional ridge alterations while revealing osseous integration but unpredictable material resorption. The role of non-resorbed hydroxyapatite remnants for implant placement is unclear and requires further investigation.