Bone regeneration
Efficacy of reconstruction of alveolar bone using an alloplastic hydroxyapatite tricalcium phosphate graft under biodegradable chambers
Mazen Almasri a , Mostafa Altalibi b
https://doi.org/10.1016/j.bjoms.2010.06.021
Abstract
Our aim was to test the efficacy of a synthetic alloplastic graft under biodegradable chambers to reconstruct a horizontal bony deficiency as an alternative to autogenous, allogeneic, or xenogenic grafts. We used 11 New Zealand white rabbits. On each rabbit's mandible one test sample (grafted chamber) was placed on the (right or left) body, while its control sample (empty (E) chamber) was placed on the other side. Twelve weeks postoperatively the animals were sacrificed and the samples extracted for gross assessment, micro-computed tomographic imaging, and histological and histomorphometric analyses. There was significantly more new bone with a greater surface area in the test group than in the control group, and the alloplastic graft was osteoconductive when used as an onlay graft under a synthetic biodegradable chamber. Synthetic products can be efficient alternatives to autogenic, allogeneic, or xenogenic grafts.
Introduction
The placement of dental implants is often compromised by deficiencies in alveolar bone in the horizontal or vertical dimension, or both, as a result of atrophy, periodontal disease, trauma, or infections.1 Reconstruction of the alveolar ridge has been attempted using autogenous bone grafts, allogeneic bone grafts, xenografts, alloplasts, and the concept of guided bone regeneration.2 Autogenous bone has been considered to be the gold standard because of its unique osteogenic, osteoconductive, osteoinductive, and continuous remodelling capabilities.3 However, autogenous bone grafts have some disadvantages, such as morbidity at the donor site, limited quantity, and rapid resorption when compared with non-autogenous grafts.4 These drawbacks were enough for some groups of patients to refuse autogenous grafts and prefer non-autogenic sources such as allogeneic, xenogeneic, and alloplastic grafts.5 The fact that allogeneic and xenogeneic grafts are derived from humans and animals, respectively, means that they became a concern to other groups of patients.2, 5 We are therefore investigating a third option which is the alloplastic and synthetic grafts.
We used hydroxyapatite/tricalcium phosphate (HA/TCP; Bone Ceramic, Straumann®, Canada), which is composed of a combination of hydroxyapatite (Ca5-(PO4)3-OH) 60% and beta tricalcium phosphate (bTCP; Ca3-(PO4)2) 40%. The hydroxyapatite component supports the bulk of the graft with its hard particles, but the faster degradation of the TCP increases the subsequent replacement of its degradation products with blood vessels and mature lamellar bone. The osteoconductivity of the HA/TCP mixture has been confirmed by many studies4, 5, 6; Gosain et al.7 illustrated it by successfully filling defects in calvarial bone in sheep. Using it as an onlay graft, Gosain et al.8 compared facial augmentation in 10 sheep using autogenous calvarial bone and HA/TCP. Blocks 16.8 mm × 5 mm were constructed, and implanted at different sites on the faces and craniums. One year later, samples were harvested for analysis of volume, and the results showed that the HA/TCP blocks had more predictable volumes of graft than the autogenous calvarial blocks, which had significantly reduced volume (p < 0.0001). This indicates that the HA/TCP graft may be an excellent option for operators to consider according to the demands of the case and the patient's preference.
Another important consideration when planning alveolar reconstruction using particulate grafts is the type of membrane (mesh) that covers the graft. These membranes/meshes are used to stabilise and protect the particulate graft in place. There are several types of membrane available for clinical use that include resorbable, non-resorbable, and hard or soft products. The most common hard and non-resorbable form is titanium mesh, which has the following advantages4, 9: it is biocompatible; it is easy to manipulate to form a volumetric chamber; it gives excellent support to the underlying graft; and it has a low resorption rate.
The chief disadvantage of titanium meshes is that they do not resorb,9 so 3-5 months after placement they must be removed before dental implants are placed. The process of removal is usually traumatic to the bone graft and the soft tissue flap, so care should be taken while this is being done. This can be avoided if polylactic acid/polyglycolic acid (PLA/PGA) biodegradable membranes are used. PLA/PGA products are biocompatible,10 can maintain proper geometric stability,11 and degrade favourably.12
We investigated the combination of two alloplastic synthetic materials-the HA/TCP graft under PLA/PGA biodegradable chambers. To our knowledge this is the first experimental trial that has investigated this combination.
Section snippets
Materials and methods
Eleven adult female New Zealand white rabbits 3-4 months old and weighing 3-4 kg were used. To reduce variability all the operations were done by one surgeon, and the animal health team dealt with all the handling, preparation, feeding, drug injections, and general anaesthetics. Water and food were withheld from each animal 12 h preoperatively and each animal was given a preoperative dose of a first-generation cephalosporin (cefazolin 12.5 mg/kg) intravenously (Novopharm Ltd., Toronto, Canada).
Gross description
When the masseter muscle and periosteum had been dissected off the mandible, the titanium screws were identified, and these helped to locate the chambers. The samples were harvested using bone clippers and were trimmed to produce 2 cm × 2 cm specimens (Fig. 2). Next, the remaining muscle layer and fibrous tissue were dissected from the sample, which uncovered partial degradation of all the PLA/PGA chambers. The screws were removed easily using a screwdriver and the specimens were stable.
Discussion
Implant surgeons often encounter patients for whom alveolar bone augmentation is necessary to place dental implants in the proper sites. Alveolar bone can be reconstructed with autogenous bone, or allogeneic, xenogeneic, or alloplastic grafts.1
Each grafting technique has advantages and disadvantages. For example, autogenous bone grafts, although considered to be the best grafting material, require a second operative donor site. Allogeneic and xenografts need no second surgical site, but the
Acknowledgment
The authors would like to thank Dr. Timothy Head, for his supervision and guidance throughout the project, Mrs. Anne Guey, for her help in providing the needed armamentarium, and the FORCE Alumni Foundation for their financial assistance.