COPYRIGHT © 2000 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY . NO PART OF THIS ARTICLE MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITH- OUT WRITTEN PERMISSION FROM THE PUBLISHER. 44 Volume 13, Number 1, 1998 T he search for allografts and new techniques intended for either the replacement or the regeneration of bone has intensified in the last three decades. Bone substitutes, grafting, and mechanical barrier membranes that allow bone to regenerate without interfering soft tissue (guided bone regener- ation) have been developed, and these techniques have been successfully applied in surgical procedures aimed at alveolar ridge augmentation, periodontal bony defect corrections, and ridge height mainte- nance after tooth extraction. 1–4 The calcium phosphate ceramics, particularly hydroxyapatite (HA) because of its chemical similari- ties to bone, have undergone intense study. Sintered HA is used as a bone substitute material, but it is dif- ficult to sinter unless pure and free of any ß-trical- cium phosphate, which is thought to confer the bioactive and bone-bonding properties reported with H A. 5,6 Hydroxyapatite has seen wide clinical use as a bone substitute in particulate and block forms. 7 However, it is not an ideal bone substitute for alveo- lar augmentation and situations where it is subject to mechanical stress. Hydroxyapatite has poor bio- mechanical properties (high elastic modulus [40 to 117 GPa] compared to compact bone [12 to 18 GPa]); adverse biologic responses associated with ***Department of Oral Surgery, School of Clinical Dentistry, University of São Paulo at Ribeirao Preto, Brazil. ***Department of Oral Pathology, School of Clinical Dentistry, University of Sheffield, Sheffield, England, UK. ***Department of Oral and Maxillofacial Surgery, School of Clinical Dentistry, University of Sheffield, Sheffield, England, UK. Reprint requests: Prof I. M. Brook, Department of Oral and Maxillofacial Surgery, School of Clinical Dentistry, University of Sheffield, Sheffield, England, UK. E-mail: i.brook@sheffield.ac.uk Bone H ealing Following the U se of H ydroxyapatite or Ionomeric Bone Substitutes Alone or Combined W ith a Guided Bone Regeneration Technique: An Animal Study Luiz A. Salata, DDS, PhD*/Geoffrey T. Craig, BDS, FDS, FRCPATH, PhD**/ Ian M. Brook, MDS, FDS, PhD*** The healing of standardized bone defects grafted with either particulate ionomeric or hydroxyapatite bone substi- tutes was compared in the mandibular ramus of 30 Sprague-Dawley rats. The possible additional response achieved when combining these materials with a guided bone regeneration (GBR) technique was also evaluated. Three groups of 10 animals received either no implant material or ionomeric or hydroxyapatite bone substitute in defects in the right ramus. The left mandibular defects received the same treatment, except that the operation site was covered by a membrane (GBR technique). Half of the animals were sacrificed at 4 and 10 weeks follow- ing surgery, and the inflammatory response at the implant site and the amount of new bone formed in the defects were determined histomorphometrically. Defects implanted with ionomeric bone substitute exhibited more bone formation (4 weeks = 3.19 ± 0.38 mm 2 , 10 weeks = 5.35 ± 0.26 mm 2 ) than both defects that received no treatment (4 weeks = 0.88 ± 0.35 mm 2 , 10 weeks = 2.1 ± 0.49 mm 2 ), membrane alone (4 weeks = 1.21 ± 0.05 mm 2 ) or hydroxyapatite bone substitute (4 weeks = 1.41 ± 0.46 mm 2 , 10 weeks = 3.34 ± 0.41 mm 2 ) at 4 weeks (P ≤ .01) and at 10 weeks (P ≤ .05). The use of a GBR technique did not increase the amount of bone formed, compared to the use of bone substitutes alone. Hydroxyapatite and ionomeric bone substitutes used alone were more effective in inducing repair of the defects than was GBR membrane alone. The use of hydroxyapatite was associated with a greater inflammatory reaction (P ≤ .01) than was ionomer in this model. (INT J ORAL MAXILLOFAC IMPLANTS 1998;13:44–51) Key words: bone regeneration, glass-ionomer cement, hydroxyapatite, ionomeric