Hydroxyapatite as a Substrate for Bone Reconstruction

Hydroxyapatite as a Substrate for Bone Reconstruction To combat the shortcomings of autografts and allografts associated with limited availability of tissue, morbidity of the donor site, risk of disease transmission and immunogenic rejection; clinicians have started centuries ago implanting artificial materials in the body to aid and restore functioning of organs or tissues.1-6 The high incidence of morbidity, skill required to harvest bone from donor, and so many factors have been the rationale for the increase in applications of bone substitute materials.7-9 Hydroxyapatite (HA) ceramics produced synthetically or by processing biological substrates and is used widely and successfully for bone reconstruction. There are many natural sources for HA which include human bone, bovine bone1,2 coral3,4 chitosan5,6fish bone7and egg shell8, and so. However a concern with natural HA is risk of transmission of diseases when proper preparation is not followed to remove all protein9. Synthetic HA is more commonly used, because of easily availability, and free from disease transmission risk. HA are available as granules and blocks with different pore sizes or as injectable material. HA is osteoconductive in nature and serves as a structural scaffold for the building of new bone tissues. Several authors have suggested HA is prone to intraoral degradation or dissolution10-25 but others have shown no resorption13-22 like our case. Here we report clinical cases which showed the radiological evidence of bone formation after more than 4 years of follow up. Clinical Report 1- In our study group the Male patient aged 65 yrs had recurrent OKC on lateral part of the mandible (Figure-1) which required partial hemi mandibulectomy with disarticulation. Patient was not ready for any other modalities of reconstruction except condylar stainless steel recon plate. Considering patient age and denial for distant or free flaps, our team of doctors inspired by orthopedic replacement strategies and indigenously designed hydroxyapatite block. Which has been prepared by Biograft (IFGL Ceramics Kolkota, India) on request. This has been used for reconstruction of lateral mandibular defect distal to canine. The block fixed to stainless steel condylar plate using 26 gauze wires. (Figure-2 Figure-3)After 5 years of evaluation the patient had no complications, absorption, dislocation but very little bone formation seen radiologically (Figure -4, Figure-5 Figure-6). Clinical Report 2- The Male Patient of 20 yrs, reported to our department with swelling in anterior mandible since 8 yrs which was small initially and progressively grown to the present size.( Figure-7) Under general anesthesia the lesion has been resected leading to a mid-line defect. The patient denied for any other reconstruction options including distant flaps and free flaps because of affordability. So it is decided to have reconstruction using SS recon plate with a block graft for support. (Figure-9) In this case we are expecting connective tissue and later bone formation as the graft block is in contact with the bony edges on both sides. Clinical report 3- Case of unicystic ameloblastoma in a patient aged 55 years male crossing the midline, undergone resection and reconstruction using BBHA and SS reconstruction plate. (Figure-9 Figure-10) In this case we are expecting bony bridging between interface of the bone fragment and graft end on both midline and ramus area of mandible. Surgical Considerations: The surgeon should change gloves before handling the BBHA material because oral flora and debris previously picked up on gloves during the pre-grafting stages of surgery could contaminate the BBHA, resulting in a subsequent infection. In its initial form, BBHA is brittle and must be handled and shaped carefully so it does not inadvertently fracture, although the material becomes very strong after healing. It is important to use irrigation when cutting the individual grafts from the larger blocks with a bur and when refining the contours. BBHA grafts can be used as interpositional (inlay) grafts placed between osteotomies or as facial augmentation (onlay) grafts or for mandibular reconstruction of lateral/midline defects. They can be applied to the maxilla, mandible, chin, orbit, zygoma, nose, forehead, and cranium. Onlay grafts may require stabilization by placing bone screws through the material, as in BBHA chin or cheek onlay grafts. A lag screw/wire technique should be used with m inimal tightening to prevent fracturing of the grafts. Rigid fixation is paramount to provide the necessary stability and stress protection for the BBHA grafts to heal properly. The grafts in the maxilla should be accurately contoured and wedged in position. If there is excessive mobility between the bone segments and BBHA grafts or a functional overload, the grafts may displace or fracture. Alternatively, a significant decrease in the amount of bone growth through the implants could occur, resulting in a nonunion. A soft diet is encouraged for 3 to 4 months during the initial post-surgery healing phase to minimize loading and micro movement, thus preventing displacement, fracture, or nonunion of the grafts. The use of 4 bone plates is recommended to stabilize the maxilla, with 2 bone screws above and 2 bone screws below the level of osteotomy for each bone plate.47,48 Postsurgical displacement or fragmentation of the BHA grafts can occur as a result of the following:38 1. Inadequate rigid fixation and stress protection, 2. Improper contouring or placement of the implant into the osteotomy site, 3. Parafunctional habits (i.e., clenching, bruxism), 4. Poor patient compliance, 5. Trauma. Discussion: The use of bone graft material both particulate12,14,16,18,19,21,38-40,54and block graft13,15,17, 19,20,22,23,41 studied in humans and animals. The majority of animal studies found bone formation within graft material10,11,18,42-51 and others reported connective tissue formation.43,52,53 The human studies reported formation of bone 12-17,29-32,37-40,54 and others reported connective tissue surrounding HA particles.18,19,29 Long-term retention biocompatibility of BHA has been established fact in orthognathic and craniofacial surgery.50 Histologic studies29,30,35 and a long-term clinical study demonstrate good biologic acceptance of the grafts in association with the maxillary sinus. The immobility of HA is crucial factor for initial healing20 as mobile particles induce connective tissue formation and immobile foster bone formation. Wolford et al. introduced the use of porous BHA as a bone graft substitute in orthognathic and craniofacial surgery.30 Rosen and Ackerman reported complication rate of 4.3% after a follow-up period of 6 to 20 months in orthognathic surgical BHA grafting48,49 Ayers et al17 Holmes et al31 and Nunes et al.16 demonstrated an average composition of 48.5-53% hydroxyapatite matrix, 18-27% bone, and 33.5-21% soft tissue in BBHA grafts through histomorphometry after 4.7 to 16.4, mean 19.1 months respectively with biopsies of BBHA grafts which were used in corrective jaw surgery in patients. The composition of the adjacent normal maxillary and mandibular bone averaged 66.5% bone and 33.5% soft tissue, indicating that the ratio of hydroxyapatite/bone to soft tissue/vascular space is equivalent to normal bone.17 The study also demonstrated that bone growth through the BBHA grafts was essentially complete in 4 months, with further progression of the healing process resulting in maturation of the ingrown bone. The grafts had less soft tissue than the adjacent bone (30% soft tissue) and bone contact over 60% of their surfaces which is a near-balance between the BBHA grafts and surrounding bone.16 There was no significant difference in micro hardness values between the bone in the BHA grafts and the adjacent maxillary bone.17 Bone ingrowth appeared to plateau at around 20 months, reaching an equilibrium in which the relative amount of osseous tissue remained constant. 17 Different theories proposed on the mechanism of bone formation. Early vascularization followed by connective tissue formation16,43,44 bone gradually inserted around the HA particles21,43,44 and non-inducing creeping substitution21,22 also proposed. Very recently the bone induction has been seen with nano-crystalline HA. The use of BBHA as an alloplastic grafting material has several advantages over other types of grafts: no donor site morbidity is involved, adjacent bone will not be resorbed, there is no known hypersensitivity or immune response, the substance is easily manipulated, there are no working time constraints, surgical time is decreased, blood loss is decreased, the volume is unlimited, and healing is faster resulting in a shorter recovery time. Interpositional bone grafting is indicated in orthognathic surgery to provide bony continuity, improve healing, improve stability, decrease surgical relapse in traditionally unfavorable jaw repositioning movements during orthognath ic surgical procedures. This type of reconstruction options will increase the survival rate and lesser morbidity. The incorporation of autogeneous bone, platelet rich plasma, rhBMP-2 showed good bone formation.50 The studies have shown hydroxyapatite is osteoinductive.51,52 Recently studies have shown use of Platelet derived growth factor (PDGF), transforming growth factor ÃŽ ² (TGF-ÃŽ ²), BMP, and stem cells in bone regeneration.50 The BBHA will provide structural architecture for BMP to achieve better and earlier function. These laboratory concepts were regarded a visionary a few years ago, but now they reached clinical reality.53-59 Our report is milestone in reconstruction of continuity defects of mandible. Hydroxyapatite is a versatile biocompatible graft substitute that does not cause any chronic inflammatory, allergic, or toxic reaction. Results of both densitometric and radiographic studies suggested that the use of synthetic hydroxyapatite graft material has the potential to accelerate bone formation in an economical way.60-63 Conclusion: The primary aim of the reconstruction was to have a proper face form, aesthetics and structural balance for face which has been achieved in a very economical way. Our plan to have implant supported prosthesis in the HA blocks in near future for these patients is planned. This type of reconstruction with indigenously designed and prepared block graft can suffice the aim and objective of successful reconstruction which is a viable modality economical. No clinical signs of pathosis were identified around the graft, no infection or discomfort was elicited upon palpation.