Many studies have shown that alloplastic bone grafts are clinically stable and safe. Nevertheless, postoperative problems such as ankylosis and root resorption are associated with alloplastic bone grafts. This report examined two cases of ankylosis of nonresorbable hydroxyapatite (NHA) alloplastic grafts associated with recurrent periodontitis. There was no clear border between the NHA particles and dentin. The particles were irregularly shaped and had plaque on the surfaces. It is postulated that ankylosis of NHA particles and dentin is a contributing factor in recurrent periodontitis.