Hydroxylapatite blocks and particles as bone graft substitutes in orthognathic and reconstructive surgery

J Oral Maxillofac Surg

44:597-605.1986

Hydroxylapatite Blocks and Particles as Bone Graft Substitutes in Orthognathic and Reconstructive Surgery JOHN N. KENT, DDS,· MICHAEL F. ZIDE, DDS,t JOHN F. KAY, PHD, AND MICHAELJARCHO, PHD A three-year clinical evaluation of 98 patients in whom dense hydroxylapatite in particle and block form had been placed in facial contour defects and osteotomy sites, and in cystic and reconstructive defects, alone or with autogenous bone, was conducted. The results indicate that the implants were effective in reducing operating time and potential for infection and relapse, as well as in reducing or eliminating the necessity of a donor site. The clinical response was excellent, and complications with both forms were minor, generally related to lack of initial fixation or failure to use autogenous bone in specific situations.

Materials and Methods

Traditionally, autogenous and homogeneous corticocancellous bone grafts have been inlaid or onlaid to enhance stability and improve function and cosmetic appearance with orthognathic, craniofacial, and other reconstructive procedures. The desire to avoid the creation of a second surgical site as well as to reduce operating time and risk of infection and relapse has led to the development and use of dense hydroxylapatite (HA) blocks and particles. Since March 1982, these materials have been placed in osteotomy and facial contour defects, as well as in cystic and reconstructive defects, alone or with autogenous bone, to advance, lengthen, widen, or reconstruct the facial skeleton. This article describes the indications, techniques of application, preliminary stability of results, and limitations of these procedures.

The successful use of HA for alveolar ridge preservation, atrophic alveolar ridge reconstruction, and correction of periodontal defects justified further clinical research directed toward the extension of its use in other clinical situations. t-7 Prospective multi-institutional clinical trials were therefore established to evaluate HA blocks and particles for use in orthognathic and reconstructive surgery. The design of the clinical research protocol included five specific categories of cases: I) obliteration of cystic cavities, 2) filling of mandibular and facial bone osteotomy defects, 3) facial bone augmentation, 4) alveolar ridge defect and cleft grafting, and 5) reconstruction of mandibular continuity (Tables I and 2). The indications for the use of HA particles or blocks in reconstructive surgery were limited to cases in which autogenous bone or allografts would have been used previously. The particles were dense hydroxylapatite, 20- to 40-mesh (Calcititev 20-40; Calcitek Inc, San Diego, California). These particles were placed directly into defects, and the wounds were closed primarily. When the need for containment of the particles was anticipated, a surgical splint was used or microfibrillar collagen (Avitene, Aricon, Inc, Humacao, PR.) or plaster of paris was added to the HA . The blocks consisted of textured dense hydroxylapatite (TDH) (Calcitite® Orthoblocks, Calcitek) in rectangular, triangular, trapezoid, and

* Boyd Professor and Head, Department of Oral and Maxillofacial Surgery, Louisiana State University Medical Center, School of Dentistry. t Co-Director, Department of Oral and Maxillofacial Surgery, John Peter Smith Hospital, Fort Worth, Texas. Former Associate Professor, Department of Oral and Maxillofacial Surgery, Louisiana State University Medical Center, School of Dentistry. t Director of Engineering, Calcitek, Inc, San Diego, California . § President, Calcitek, Inc, San Diego, California. Addre ss correspondence and reprint requests to Dr. Kent: Department of Oral and Maxillofacial Surgery, School of Dentistry, LSU Medical Center, 1100 Florida Avenue, New Orleans, LA 70229·2799.

597

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HA BLOCKS AND PARTICLES IN ORTHOGNATHIC SURGERY

Table 1. Indications for Use of Hydroxylapatite Particles Procedure Clefts

Cysts

Tumor and osteomyelitis defects Facial contour and osteotomy defects

Reason Alone for minor defect; with cancellous bone for major defect and ridge augmentation Alone if closure was possible to avoid packing open and long period of patient compliance; with bone if mandible susceptible to fracture or defect was refractory to treatment HA:cancellous bone mixture (I :4) in continuity defect; alone or with bone for recalcitrant chronic sclerosing osteomyelitis Alone as an onlay or inlay material when particle control wa~ possible

curved shapes with a variety of dimensions for interpositional and onlay application in orthognathic and craniofacial surgery (Fig. 1). Initially, they consisted of dense HA ceramic with two opposing porous surfaces, 1 mm deep, containing pores 150 to 400 urn in diameter. The porous layers were reduced in depth to a "monolayer" of hemispherical cells, 100 to 300 urn in diameter, for initial grip, stabilization, and prevention of slippage while allowing positive displacement of two bone segments. Subsequent animal studies showed that a roughened nonporous surface provided adequate mechanical stability." Waffle texturing of the surface provided a greater gripping surface area for strong mechanical stability and bonding to bone than a smooth surface. Therefore, a textured or positive waffled surface was incorporated on two sides. The TDH blocks were easily contoured in the operating room with medium-grit diamond burs to obtain an exact fit. Stainless steel models with handles facilitated size selection (Fig. 2). The blocks were firmly wedged in place, and transosseous wires encircling the blocks were frequently used for stabilization. Blocks placed on the inferior· border of the mandible were usually ligated to the bone with wires. Pterygoid plate blocks and Le Fort I widening blocks were wedged in position after the maxilla had been down-fractured and stabilized with splints or transosseous wires. Holes for wires were not drilled through the blocks because they would have predisposed to fracture. Grooves or mortises prepared with diamond burs were sometimes used to enhance stability in such areas as the lateral maxillary wall and inferior border of the mandible. No deviations from conventional surgical technique were used in performing the osteotomies or I

other reconstructive procedures. Patients were given antibiotics and anti-inflammatory and pain medications identical to those ordinarily given. Clinical and radiographic examination occurred weekly through the first eight weeks, and then every three to six months for two years. Results PARTICLES

Beginning in March 1982, HA particles were placed in 43 patients (54 procedures). Follow-up periods ranged from four to 40 months, through June 1985(Table 3). The amounts of HA ranged from 3 to 75 g. In patients undergoing horizontal osteotomy of the symphysis without HA blocks, particles were frequently mixed with collagen and layered on the osteotomy ledge to soften the labiomental crease. Complications with the use of particles occurred exclusively in primary reconstruction of large mandibular continuity defects, i.e., in patients undergoing hemimandibulectomy. No problems were encountered with cysts or facial bone defects. In patients with continuity defects the HA particles were mixed with autogenous bone, I g of HA to 4 cc of finely ground iliac cancellous chips, and placed in titanium cribs. Intraoral dehiscence, with small loss of graft material, occurred in two patients, and significant loss of graft material occurred in two additional patients. An insignificant number of particles was lost from cystic cavities. No complications were associated with genioplasty, whether the particles were placed alone or with HA blocks.

Table 2. Indications for Use of Hydroxylapatite Blocks Procedure LeFort I-III osteotomy

SSO and C osteotomy Genioplasty downgrafting Inferior border of mandible

Reason Expansion of palate; advancement at pterygoid plates, zygomatic buttress step, body of zygoma, and frontal nasal areas with blocks alone or blocks with autogenous corticocancellous bone graft for stability Provide stability. prevent segment rotation. and avoid cosmetic defects with blocks alone Lengthen or widen the chin with blocks alone Lengthen the body/angle region in asymmetry or micrognathia, or restore defects secondary to trauma. tumors. and osteotomies with blocks alone

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KENT ET AL.

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A

B

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m UD

c

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E

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FIGURE I (left). Textured dense hydroxylapatite (TDH) blocks (A-E) in rectangular, square, trapezoid, and curved shapes with a variety of thicknesses for interpositional and onlay applications in orthognathic surgery. Warne texturing of the surface provides for grip and stability between bony surfaces. The trapezoid blocks for maxillary widening (D and E) are smooth on the mucosal surfaces and grooved on the lateral surfaces for retention to bone . FIGURE 2 (right). Metallic models with handles used to determine the correct size ofTDH blocks.

TDH BLOCKS Beginning in November 1982, 120 TDH blocks were placed in 55 patients, with or without autogenous iliac crest bone grafts. Follow-up periods ranged from four to 36 months, through October 1985 (Table 4). Sixty-six procedures were performed: maxillary advancement with or without bone grafting (18), maxillary down-grafting with or without bone grafting (ll), maxillary widening (8), Le Fort III advancement with bone grafting (4), mandibular advancement (3), genioplasty downgrafting/advancements with or without bone Table 3.

grafting (ll), inferior border augmentation (5), correction of facial contour deficit (two), and subapical osteotomy (four). The movement of bone segments or onlay augmentation ranged from 2 to 13 mm. Wire fixation was used for Le Fort I osteotomies. No bone plates were used in this study, except for one down-grafted genioplasty and one subapical osteotomy. Direct stabilization of the blocks by wires was achieved in one third of the procedures. In the remaining two thirds stability was achieved only by wedging the blocks in position. No TDH blocks were lost or removed because of undesirable tissue reaction or infection. Although

Use of Hydroxylapatite (HA) Particles Follow-up (mo)

Amount of HA (g)

Surgical Procedure

No . of Patients

Range

Average

Range

Avera ge

Genioplasty Craniofacial augmentation Cystic cavity Mandibular continuity defect Alveolar clefts Totals

21 8 5 8 I 43

4-38 9-36 11-40 8-39 31 4-40

16 17 20 16 31 20

3-20 3-75 3-24 3-52 3 3-75

10 20 II 20 3

13

600

HA BLOCKS AND PARTICLES IN ORTHOGNATHIC SURGERY

Table 4.

Use of Textured Dense Hydroxylapatite Blocks Movement (mm)

Surgic al Procedure

No. of Procedures (9C)

No . of Blocks ('70)

Le Fort I advancement without bone Le Fort advancement with bone Le Fort down-grafting without bone Le Fort down-grafting with bone Maxillary widening Le Fort III advancement Mand ibular advancement Genioplasty down-grafting without bone Geniopl asty down-grafting with bone Inferior border augmentation Contour deficit Maxillary/m andibular subapical Totals

15 (22.7) 3 (4.5) 5 (7.6) 6 (9.1) 8 (12.1) 4 (6.1) 3 (4.5) 7 (10.6) 4 (6.1) 5 (7.6) 2 (3.0) 4 (6.1) 66 (100)

30 (25) 5 (4.2) 5 (4.2) 10 (8.3) 10 (8.3) II (9.2) 4 (3.3) 14 (11.7) 4 (3.3) II (9.2) 3 (2.5) 13 (10.8) 120 (100)

one infection developed after a Le Fort III advancement, requiring removal of the associated bone graft, the TDH block was left to ensure postoperative stability. Four complications were encountered with the blocks. Displacement during maxillomandibular fixation occurred in three patients who had undergone Le Fort I osteotomy. Long-term results and stability were not affected in two of these patients, but postoperative mobility required an additional grafting procedure in the third patient. In the fourth patient dehiscence of the mucosa over one block placed at the pterygoid plate for maxillary advancement was observed eight weeks after surgery. The protruding portion of the block was trimmed, and the wound healed without further complication. STABILITY STUDIES

Two years into the study, radiographic stability studies were performed. Lateral preoperative, and immediate and most recent postoperative cephalograms were digitized and stored as files, with measurements based on horizontal, vertical, and angular projections of cephalometric data points performed on a personal computer. Twenty-nine patients with a minimal follow-up period of six months (mean, 9.7 months; range, 6-25 months) were evaluated." Relapse in patients with maxillary advancement/down-grafting was less than 20% both vertically and horizontally, regardless of whether concomitant mandibular ramus procedures or iliac crest bone grafting had been performed . There was no relapse in patients who had undergone genioplasty down-grafting advancements and ramus surgery; however, soft tissue thickness over the chin decreased slightly (10%), as expected in genioplasty. Le Fort III advancements relapsed 10 to 15% at the dental level.

Range

4-8 4-6 3-9 3-9 4-13 2-15 6-15 4-10 3-6 6-10 8-10 2-6 2-15

Follow-up (mo)

Average

Range

Average

6 5 6 5 5 8 10 6 5 8 9 4 6

7-33 14-19 6-26 8-33 10-22 10-36 12-22 4-25 5-13 4-17 11-12 5-9 4-36

12 17 14 14 15 17 16 II 7

9 12 7 13

Discussion The purpose of this study was to evaluate dense HA as a graft substitute in several clinical procedures. Several factors determine the success of a bone graft substitute in orthognathic or reconstructive surgery. These factors include the nature of the hard tissue interface, the clinical indication for supplemental autogenous bone, the method of fixation, the duration of immobilization, the structural integrity and biomechanics of the material at the graft site , the incidence of complications , and short- and long-term stability. Bone bonds chemically to the HA surface by a natural bone-cementing substance if the HA graft is inlaid or onlaid with intimate bone contact.P-'! Separation may not occur at the interface, even when established implants are purposely fractured after three weeks of healing.P Mobility of the interface will delay and encourage fibrous connective tissue formation. The blocks used in the study were initially coated with a l-rnrn porous layer for surface roughness and tissue ingrowth . The surface was later changed to a waffled structure to strengthen the block, minimize the potential for infection associated with a porous structure, and maintain surface roughness and area for stability. Since bone bonds biochemically directly to HA, the benefit of porous interlock was negligible. Clinical response of the HA blocks was excellent. Patients undergoing genioplasty received HA blocks primarily for down-grafting and facial lengthening. Concomitant advancement was usually achieved. However, advancement beyond 6 to 8 rnrn was difficult, since contact and stability of the advanced segment with the block limited the advancement. Most of the genioplasties were performed by a standard intraoral horizontal osteotomy technique (Fig. 3).

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FIGURE 3. Patient with vertical and horizontal deficiency of the chin and normal occlusion. Top left, intraoperative view of sliding horizontal osteotomy demonstrating the textured dense hydroxylapatite (HA) block in position with the remaining defect filled with HA particles. Top right, postoperative radiograph. Bottom right, cephalometric tracings made two weeks (solid lines) and two years (broken lines) after surgery show the stability of the result.

Lengthening the inferior border to the mandibular angle in micrognathia or condylar hypoplasia was difficult with the previously used techniques. Onlay bone grafts resorb unpredictably. Downgrafting the inferior border with interpositional grafts adds the risk of injury to teeth or the inferior alveolar nerve on these shortened mandibles. Intraoral exposure and access to the angle is difficult. In this study HA blocks were frequently ligated with wires. Vertical grooves were usually placed on the "bottom" of the blocks to control movement of the wires and blocks (Fig. 4). A smooth inferior border contour was achieved by tapering the block at the junction with the horizontal osteotomy of the

symphysis. When the periosteal pocket was tight and the block was horizontally grooved to cup the inferior border, stability of the block was achieved without wire ligation. Stability of maxillary advancement was achieved with HA blocks placed either anterior to the pterygoid plates or at a vertical step of the zygomatic buttress. The blocks were grooved to straddle the maxillary walls (Fig. 5). Our c1incial data were not adequate for comparison of these two Le Fort I techniques. Separation of the maxilla with sharp chisels or, preferably, oscillating saws helped to maintain the integrity of the pterygoid plates and the continuity of the posterior maxillary wall. As

FIGURE 4. Microgriathic patient with vertical and hor izontal deficiency of the entire mand ibular inferior border. Top left, preoperati ve frontal view. Top right, postoperative front al view following lengthening of the inferior bord er and advancement and lengthening of the symphysis with textured dense hydroxylapatite blocks. Bottom, postoperative radiogr aph taken at 18 month s.

;r

"'.:~. ._~ ~-~ with bone grafts, the blocks were positioned from above before intermaxillary fixation or from the side after fixation of the mandible . Metal try-ins with handles were helpful for determining the exact size in this situation and in palatal widening. Fixation of blocks will be dictated by the clinical conditions. Wedging a waffled or ground surface without wires or plates may be adequate in certain situations (such as inferior border onlays, palatal widening, or maxillary advancement with blocks placed at the pterygoid plate in Le Fort I osteotomies); however, transosseous wires encircling the blocks are necessary in other areas (Le Fort I down-grafting, Le Fort I advancement with step osteotomy at the zygomatic buttress, genioplasty down-grafting, and inferior border onlay). Holes, drilled through brittle ceramic materi als are associated with a high incidence of fracture. Attempts were made to place thin rectangular blocks in lateral defects of sagittal ramus osteotomies for cosmetic reasons and prevention of proximal fragment rotation and relapse of large mandibular advancements, but fixation and stabilization were difficult. The blocks occasionally fractured during attempts to drill holes. Blocks with holes made previously may be beneficial in this and other clinical sites. Our clinical experience strongly suggests that HA blocks or paticles adequately serve as space fillers and onlay graft substitutes, without retarding bone growth. Bone-to-bone contact along some

areas of the osteotomy lines, however, is necessary whenever functional stress is significant. For example, TDH blocks alone are not adequate for Le Fort I down-grafting or Le Fort III advancement, since it is not known whether the ceramic will withstand long-term shear forces without the resiliency of autogenous bone (Fig . 6). In contrast, in Le Fort I advancement or down-grafting, in which bone-tobone contact is present along some areas of the lat-

FIGURE 5. Intraoperative view of groo ved textured dense hydroxylapatite into position at the zygomatic buttress region after Le Fort I osteotomy to level the occlusal plane. No autogenous bone was used since bone contact is present anteriorly. Otherwise, bone grafting would be necessary.

KENT ET AL.

603

FIGURE 6. Patient with mandibular prognathism and horizontal and vertical deficiency of the maxilla, corrected by bilateral sagittal split osteotomy and Le Fort I osteotomy of the maxilla with textured dense hydroxylapatite (TDH) blocks and autogenous bone for advancing and down-graft lengthening of the maxilla. A, intraoperative view demonstrating the position of the TDH blocks at the zygomatic buttress with iliac crest bone graft along the lateral maxillary walls. B. preoperative radiograph. C. postoperative radiograph. D, cephalometric tracings, before surgery (solid lines) and immediately after surgery (broken lines). E, cephalometric tracings, immediately (solid lines) 2Yz years (broken lines) after surgery. F. preoperative profile view. G. postoperative profile view.

604 eral maxillary walls, autogenous bone is not required (Fig . 5). Similarly, the down-grafted symphyseal border in a genioplasty will do well with only an HA-bone interface, since shear forces are negligible. In fact, one patient had sustained trauma to the chin one week following genioplasty and elected to delay correction of the resultant asymmetry for one year. On re-entry at one year, an HA-bone union was observed, and a bone saw was necessary to separate the segments. Migration of the blocks into bone after genioplasty has not been observed clinically. Radiographs and measurements also confirm the stability of the blocks. Maxillary stability was greater than that reported for down-grafting and advancement with transosseous wiring, or freeze-dried or autogenous bone grafts. 13, 14 Freeze-dried blocks have the advantage of being easily shaped; however, revascularization is slow, requiring prolonged immobilization unless autogenous bone is used. Relapse may be significant during this period of healing, since the structural integrity of the homograft may diminish by as much as 60%. IS Although present trends toward rigid fixation seem to offer some obvious advantages, and certainly could be used with HA blocks, standard transosseous· wiring techniques were used in all maxillary procedures. We believed that this would allow for nonrigid occlusal settling and physiologic positioning of the condyle and disc. We also observed subjectively that the stability of osteotomy segments appeared to be comparable with that seen in surgical cases of grafted bone or even rigid fixation at six to eight weeks . Complications with blocks were minor and usually related to lack of fixation or, in one instance, failure to use autogenous bone in one specific situation. No blocks were lost from infection or mucosal dehiscence. Most blocks were textured on two faces for initial stability and grip between osteotomy segments. However, trapezoidal blocks for expansion of the palate were grooved laterally and were smooth on the inferior and superior mucosal surfaces. Although midline. placement was done in a few patients, parasagittal osteotomy of the palate-alveolar process is preferred for extensive widening (Fig. 7). Mucosal stretching and tearing are less .likely, since expansion and filling of the defect at each site involve one half of the total distance. The selection of nonporous rather than porous forms of HA for the present applications was based on a critical review of animal and clinical studies reported during a decade of experience. It is recognized that bone grafts during their avascular period and porous implant materials, whether HA, other

HA BLOCKS AND PARTICLES IN ORTHOGNATHIC SURGERY

ceramics, or polymer composite metals, have a greater potential to become infected than do nonporous materials, as a result of the wicking effect of the interconnecting pores.P-!" In the present surgical applications, transient exposure of the implants to bacterial contamination is often unavoidable due to the intraoral surgical approach and possible postoperative dehiscence of the incision. Additionally, in some cases (down-grafting and maxillary widening) permanent communication of the implants with sinus cavities may be established. Clearly, dense implants, which have the lowest potential for infection, would appear to be more suitable than porous implants. From the point of view of biomechanical suitability, the dense HA implants, with compressive strengths of greater than 25,000 psi, are more than adequate for these applications .Ui'" Dense HA ceramics have served as permanent implants, showing no tendency to bioresorb even after prolonged periods of implantation (more than seven years in burnans).? In contrast, porous HA implants are weak, with compressive strengths of approximately 1000 psi. While some authors have suggested that porous HA implants can ultimately develop adequate strength by virtue of tissue ingrowth;" others have reported a slow pattern of bony ingrowth, with the implants becoming crushed even after prolonged periods of implantation (1.5 years).20 The prolonged time required for bone growth into porous ceramic blocks may limit the use of these blocks in clinical situations, in which stability must be achieved within a twomonth period. Additionally, because of their large surface area that becomes exposed to the physiologic environment, porous HA implants cannot realistically be expected to serve as permanent spacers. In fact, one type of "permanent" porous HA (coral HA) was reported to have undergone biodegradation of approximately 30% after only one year of implantation." The current surgical approach seeks to achieve permanent changes in contour or bony relationships so as to maintain occlusal balance. Therefore, dense HA blocks were chosen to eliminate the biomechanical uncertainties associated with porous HA implants. The complications seen with particles in reconstructive surgery, and the factors related to or causing mucosal dehiscence, are probably related to the size of the reconstruction . The difficulty of particle containment in alveolar ridges is magnified with larger defects. Extrusion and gravitational drift are more difficult to control without external splints. Splints eliminate hematomas or seromas within HA ridge augmentations. However, in major reconstruction edema and the risk of pressure ne-

605

KENT ET AL.

FIGURE 7. Left. intraoperative view of textured dense hydroxylapatite (TDH) blocks used with a Le Fort I osteotomy and separation of the palate from the alveolar process to widen the maxilla. Right. intraoperative view ofTDH blocks placed at the midpalatal division following Le Fort I osteotomy and widening of the maxilla.

crosis of tissues are uncontrollable variables that preclude the use of splints. The future may present attractive methods for controlling particles within matrix vehicles, but it will be necessary to maintain homogeneous concentrations of HA particles so that when the matrix vehicle dissolves, a stable, smooth contour will result.

9. 10. II. 12.

References . 13. I. Kent IN, Quinn JH, Zide MF, et al: Alveolar ridge augmen-

2. 3. 4. 5. 6. 7. 8.

tation using nonresorbable hydroxylapatite with or without autogenous cancellous bone . J Oral Maxillofac Surg 41:629, 1983 Kent IN, Finger 1M, Quinn JH, et al: Hydroxylapatite alveolar ridge reconstruction: complications and technique modifications. J Oral Maxillofac Surg 44:37, 1986 Kent IN, Jarcho M: Reconstruction of the alveolar ridge with hydroxylapatite, ill Fonseca R, Davis H (eds): Preprosthetic Surgery. St. Louis , CV Mosby, 1985 Quinn JH, Kent IN: Alveolar ridge maintenance with solid nonporous hydroxylapatite root implants. Oral Surg 58:511, 1984 Quinn JH, Kent IN, Hunter RG, et al: Preservation of the alveolar ridge with HA tooth root substitutes. J Am Dent Assoc 110:189, 1985 Block MS, Kent J: Healing of mandibular ridge augmentation using hydroxylapatite with and without autogenous bone in dogs . J Oral Maxillofac Surg 43:3, 1985 Block MS, Kent IN: Long term evaluation of hydroxylapatite augmentation of deficient mandibular alveolar ridges. J Oral Maxillofac Surg 42:793, 1984 Zide MF, Geist E, Block MS, et al: Canine mandibular re-

14. 15. 16. 17. 18. 19. 20. 21.

sponse to porous surfaced textured HA blocks. In press, J Oral Maxillofac Surg Kent IN, Zide MF, Jarcho M. et al: Hydroxylapatite blocks for stability in orthognathic surgery. J Dent Res 64 (part I): 1985 Jarcho M, Kay JF, Gumaer KI, et al: Tissue, cellular and subcellular events at a bone-ceramic hydroxylapatite interface . J Bioeng 1:79, 1977 Jarcho M: Calcium phosphate ceramics as hard tissue prosthetics. Clin Orthop 157:259, 1981 Jarcho M, Jasty V, Gumaer KI, et al: Electron microscopic study of a bone-hydroxylapatite implant interface. Trans 4th Annu Mtg Soc Biomater 10th Int Biomater Symp. San Antonio, Society of Biomaterials, 1978, p 112 Epker BN, Friedlander G, Wolford LM, et al: The use of freeze dried bone in middle third face advancements. Oral Surg 42:278, 1976 Enneking WF , Morris JL: Human autologous bone transplants . Clio Orthop 87:28, 1972 Araujo A, Schendel SA, Wolford LM, et al: Total maxillary advancement with and without bone grafting. J Oral Surg 36:849, 1978 Kent IN, Zide MF: Wound healing: bone and biomaterials. Otolaryngol Clin North Am 17:295, 1984 Feldman D, Estridge T: Factors affecting soft tissue ingrowth into porous implants. Proc Soc Biomater, Washington, DC, April 1984, p 37 Jarcho M, Bolen C, Thomas 1\1, et al: Hydroxylapatite synthesis and characterization in dense polycrystaline form. J Mater Sci II :2027, 1976 Holmes R, Mooney V, Bucholz R. et al: A corralline hydroxylapatite bone graft substitute. Clin Orthop 188:252, 1984 Piecuch JF, Topazian RG, Wolfe S: Experimental ridge augmentation with porous hydroxylapatite implants. J Dent Res 62:148,1983 Holmes RE: Bone regeneration within a coralline hydroxylapatite implant. Plast Reconstruct Surg 63:626, 1979