In 48 postextraction sites, sockets were grafted with bovine bone mineral plus collagen membrane (test) or had spontaneous healing (control). After 4 months, horizontal ridge width reduction was 0.71 mm in the test group and 4.04 mm in the control group, while vertical ridge loss was 0.58 mm and 1.67 mm, respectively. No correlation was found between the thickness of the buccal bone wall and the alveolar bone loss in the test group, while an inverse correlation was found in the control group. Ridge preservation compensated for postextraction alveolar ridge resorption irrespective of the buccal plate thickness, whereas leaving the extraction socket undisturbed may result in alveolar bone loss. (Int J Periodontics Restorative Dent 2014;34:211-217. doi: 10.11607/prd.1885)