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When is bone augmentation needed in the alveolar ridge?
- atrophy of the edentulous mandible
- local or extensive bone loss
- these defects can occur from trauma produced from the removal of teeth, accidents, or disease
Previous technique for augmenting bone:
- Bone grafting from a donor site in the patient
- Advantages
- creates an environment more suitable for osteogenesis
- biocompatibility with patient not an issue
- Disadvantages/Clinical Problems:
- 25% chance of donor site morbidity
- expensive, increased operative time, extended hospital stay
- recurrent pain at the harvest site
-Calcium phosphate ceramics are becoming more common to eliminate such clinical problems
- Purpose: to investigate tissue responses, especially osteogenesis and resorption of Hydroxyapatite(HA) and beta-tri-calcium phosphate(TCP) blocks implanted onto bone.
Materials:
- Hydroxyapatite(HA)
- used as a bone substitute material because of biocompatibility and nonantigenicity
- high osteocompatibility and bone binding capacity
- slow degradation in vivo
- slow resorption rate when compared to rate of new bone formation
- can produce an immunological response where HA is attacked as a foreign substance
- Beta-TCP
- resorbs at a higher rate than HA
- avoids immunological response
- highly porous and three-dimensional
- promotes vascularization
- structure and porosity resemble human cancellous bone
- not studied as extensively as HA
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| Figure 1. Optical micrograph of porous beta-TCP. |
Methods:
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HA and Beta-TCP blocks with interconnected pores
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74 six-week-old rats as implant hosts
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50% implanted with HA blocks, 50% with Beta-TCP blocks
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implantation site was between the parietal bone and periosteum
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rats were killed after 1,2,4,8 and 24 weeks and samples were removed
Results:
- HA had a larger compressive strength over time than Beta-TCP
- HA = 3.324 MPa, Beta-TCP = 1.732 MPa
- amount of newly formed bone was the same for both materials up to 8 weeks
- new bone growth of HA exceeded that of Beta-TCP after 8 weeks
- degradation of Beta-TCP occurred after 8 weeks, while HA remained stable
- fragments engulfed by foreign body giant cells
- more foreign body giant cells observed on Beta-HCP than HA
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| Figure 2. Optical micrograph of bone growth(darker spots) on a hydroxyapatite sample after 24 hours. |
Conclusions:
- HA is more structurally stable that Beta-TCP in vivo and is better for long-term bone tissue growth
- Beta-TCP cannot be used in any implant site that contains biomechanical stress or micromotion
- Beta-TCP is more prone to creating an immune response after implantation in the form of foreign body giant cells
Shortcomings/Future Directions:
- study fails to compare the similarities and differences between implant site and alveolar ridge other than biomechanical response
- clinical studies should be conducted for several years in order to legitimize HA use in the alveolar ridge
- Beta-TCP blocks containing osteocytes and growth factors can increase tissue growth
- divalent ions like Zn and Mg can assist growth factors in being osteoinductive agents
- heavily cross-linked polymers can be used with Beta-HCP to increase material lifespan in vivo
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| Hydroxyapatite blocks before implantation(courtesy of Berkeley Advanced Biomaterials, Inc.) |
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Resources:
Reference Manuscripts and Other Articles of Interest:
- A Gaggl, G Schultes, H Karchner. Distraction implants: a new operative technique for alveolar ridge reconstruction. Journal of Craniofacial Surgery 4 (1999), pp. 214-221.
- Orthovida Biological Products. http://www.orthovita.com/products/vitoss/tcp/us.html (2003).
- I.T. Jackson, G. Helden and R. Marx, Skull bone grafts in maxillofacial and craniofacial surgery. J Oral Maxillofac Surg 44 (1986), p. 949.
- S.A. Wolfe, Autogenous bone grafts versus alloplastic material in maxillofacial surgery. Clin Plast Surg 9 (1982), p. 539.
- J.L. Ricci, N.C. Blummenthal, J.M. Spivak et al., Evaluation of a low temperature calcium phosphate particulate implant material: Physical chemical properties and in vivo bone response. J Oral Maxillofac Surg 50 (1992), p. 969.
- L.L. Hench and E.C. Ethridge, Biomaterials, an interfacial approach. In: A. Noordergraaf, Editor, Biophysics and Bioengineering Series, Academic Press, New York, NY (1982), pp. 126148.
- C.P.A.T. Klein, A.A. Driessen, K. de Groot et al., Biodegradation behavior of various calcium phosphate materials in bone tissue. J Biomed Mater Res 17 (1983), p. 769.
- H.A. Hoogendoorn, W. Renooij and L.M.A. Akkermans, Long-term study of large ceramic implants (porous hydroxyapatite) in dog femora. Clin Orthop 187 (1984), p. 281.
- R. Fujita, A Yokohama, T. Kawasaki, T Kohgo. Bone augmentation osteogenesis using hydroxyapatite and b-tricalcium phosphate blocks. Journal of Oral and Maxillofacial Surgery. 61 (2003). pp 1045-1053.
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