Influence of bone marrow on membrane-guided bone regeneration of segmental long-bone defects in rabbits.

Defects 10 mm long were created in long bone in the diaphysis of both radii of 18 rabbits (test and control side). On the test side, ingrowth of bone marrow into the defects was hindered or delayed by: plugging the opening of the cut bone ends with gutta-percha points (n = 7); plugging with Gelfoam (n = 6); or by removing the bone marrow by flushing with saline (n = 5). The defects on both test and control side were covered with an expanded polytetrafluoroethylene membrane, shaped as a tube. Healing was followed with radiographs for four to five months, after which the animals were killed and ground sections of the areas of the defects were prepared for histological examination. On the control side, nine of 18 animals had complete osseous bridging of the defect, and a small transverse non-mineralised zone remained in the centre of the healed defect in the other animals. This zone consisted of loose connective and cartilagenous tissue as well as connective tissue obviously derived from the outside of the membrane. By preventing or delaying the ingrowth of bone marrow we retarded the regeneration of mineralised bone, particularly in the gutta-percha and flushed bone marrow groups. The principle of guided tissue regeneration may be used to achieve regeneration of extensive long-bone defects. Any attempts to delay or prevent bone marrow ingrowth into the defects did retard regeneration of segmental long-bone defects.     

Membrane-guided bone regeneration: Segmental radius defects studied in the rabbit

We tested the principle of guided tissue regeneration (GTR) for healing segmental long-bone defects. 7 mm (3 animals) or 10 mm (5 animals) long segmental defects were created in the diaphyses of both radii in 8 rabbits. The defect on one side was covered with a barrier membrane of expanded polytetrafluoroethylene membrane shaped as a tube, while the contralateral side with no membrane served as the control. Healing was followed with radiographs obtained repeatedly during a 13- (n 3) or 27- (n 5) week period. Thereafter, the animals were killed and ground sections of the defect sites were prepared for histologic examination.

Radiographically, the control sites showed some early subperiosteal callus formation and nonunion of the defects after 6 weeks. The bone ends were rounded off and sealed with cortical bone. No major changes were noted after 6 weeks.

At the test sites, subperiosteal bone formation at the bone ends was first observed radiographically at 2 weeks. At 9 weeks, a thin cortical bone bridged the defect along the inner surface of the membrane. Histologically, an interrupted line of thin, cortical bone was observed along the inner surface of the barrier membrane. Fatty bone marrow occupied the central and largest volume of the defect.

We conclude that it seems possible to use the principle of GTR to accomplish bone union of segmental long-bone defects.     

Healing of maxillary and mandibular bone defects using a membrane technique. An experimental study in monkeys

Cyst-like cavities in the jaw bone often heal incompletely owing to ingrowth of connective tissue, thus preventing osteogenesis from occurring. In the present study, a new membrane technique has been utilized in an attempt to improve bone healing. By means of an inert, porous membrane, placed in close contact with the bone surface, a secluded space is created which can only be repopulated by cells from the adjacent bone. Thus, osteogenesis is able to occur without interference from other tissue types. Through-and-through bone defects were produced bilaterally (1) in edentulous areas of monkey (n = 5) mandibles, and (2) in conjunction with apicectomy of the lateral maxillary incisors, also in monkeys (n = 7). On one side, the defects were covered buccally as well as lingually/palatally with expanded PTFE membranes, whereas the defects on the other side served as controls (no membrane). In the mandible, complete bone healing was seen at all test sites after a healing period of 3 months. On the control side, 3 experimental sites showed bone discontinuity with a transosseous core of connective tissue, whereas some bone healing had occurred lingually at 2 sites, but with massive soft tissue ingrowth from the buccal side. In the maxillary periapical defects, all the membrane-covered defects had healed with bone closure after 3 months but with a minute portion of connective tissue, probably derived from the periodontal ligament, around the tooth apices. None of the control defects (no membrane) healed spontaneously, but all were filled with connective tissue to varying degrees.(ABSTRACT TRUNCATED AT 250 WORDS)     

胶原膜引导和促进骨缺损修复的实验研究

目的 探讨促进骨缺损修复和防止骨不连接的新途径。方法 25只新西兰兔双侧桡骨作成10mm骨缺损，实验侧用胶原膜包绕，对照侧不包绕胶原膜。通过X线检查、骨密度测定以及组织学检查，判断骨缺损愈合情况。结果 实验侧愈合速度及愈合率明显高于对照侧。结论 胶原膜有引导和促进骨缺损修复、防止骨不连接的作用。     

胶原膜引导骨再生的实验研究

目的观察胶原膜引导骨组织再生的形式,了解膜的理化特性、降解情况,并探讨引导性骨再生的机制。方法成年新西兰兔造成10mm桡骨缺损,实验组缺损处移植胶原膜及表面脱钙异体骨,对照组仅移植表面脱钙异体骨,并行X线、组织学及免疫组化检查。结果实验组移植区域存在明显骨膜反应,新骨增生明显,骨重建顺利,骨缺损完全修复。对照组移植区域由于纤维结缔组织的占据,新骨生长及成熟骨替代均较实验组延缓。结论胶原膜能有效地发挥阻隔与引导的作用,同时,膜管能使内、外源性BMP不断聚集,有效分布,BMP分布特征影响着组织细胞及骨愈合方式。     

The use of autologous free fat tissue in prevention of calvarial bone regeneration: an experimental study

Autologous free fat grafts have been successfully used to limit ingrowth of postlaminectomy fibrous tissue and to prevent reossification after bone resection in long bones. This study was designed to test the effect of placing autologous adipose tissue in standardized craniotomy defects and also to determine the effect of the presence of periosteum and dura in the area of the fat augmented defects. In 18 immature rabbits, aged 18–21 days, two identical full-thickness defects were made bilaterally in the parietal bone. An autologous free fat graft was placed in one of the defects, the second being an internal control. The study groups were as follows: Group I: dura and periosteum left intact; Group II; periosteum removed; dura left intact; Group III; periosteum and dura removed. The animals were sacrificed after ten weeks. Histological examination of all groups demonstrated prevention of bone regeneration at the margins of the defect with some variations. In the first and second groups, new bone formation appeared over the dura, creating an incomplete plate of bone. On the periosteal side of the graft, a smaller amount of bone formation appeared close to the osteotomy line. The third group demonstrated a total prevention of bone regeneration. The use of free fat tissue graft can prevent calvarial bone regeneration and may be a useful adjunct for the treatment of craniosynostosis. Measures should be taken regarding the new bone formation over the dura, since this may cause reoccurrence of craniosynostosis.     

A long-term study on defect filling and bone ingrowth using a canine fiber metal total hip model.

When performing primary and revision total hip arthroplasty (THA), bone defects are often encountered. At present, grafting osseous defects with autogeneic bone is a common means of treatment. In this study, defects in bone were created in the femora and acetabula of dogs being treated with cementless THA with a fiber metal implant (Group A) or a hydroxyapatite tricalcium phosphate (HA/TCP) sprayed implant (Group B). The following methods of defect filling were compared: (1) leaving defects unfilled, (2) filling with autogeneic bone graft, (3) filling with a 50:50 mixture of autograft and a biphasic ceramic composed of HA/TCP, and (4) filling with a collagen-HA/TCP-bone marrow mixture. Analysis of defect healing and the extent of ingrowth into the overlying fiber metal, at defect sites and sites distant from defects, was made at six, 12, and 24 weeks postimplantation. Defect healing was enhanced at six and 12 weeks in all grafted groups when compared with ungrafted controls. Bone ingrowth into the porous fiber metal overlying the defects was not significantly affected by grafting the defects, compared with the ungrafted defects. The extent of bone ingrowth into the fiber metal acetabular implant at sites away from the defects increased during the entire study. In contrast, the extent of bone ingrowth on the femoral side was maximal at 12 weeks. The HA/TCP coating enhanced ingrowth into the acetabular component at 12 weeks, compared with the uncoated prosthesis, but did not enhance ingrowth on the femoral side. The data from this study demonstrate that defect healing is enhanced with graft materials. However, this does not necessarily result in increased ingrowth into porous surfaces overlying osseous defects. General bone ingrowth and ingrowth at defect sites at 12 weeks postimplantation can be enhanced on the acetabular side with the use of HA/TCP-sprayed implants. However, no positive effect is seen with the use of an HA/TCP-sprayed femoral implant.     

胶原膜联合自体骨髓基质细胞及富血小板血浆修复牙槽骨缺损的实验研究

目的初步探讨胶原膜与骨髓基质细胞（bone marrow stromal cells,BMSCs）、富血小板血浆（plateletrich plasma,PRP）复合后修复牙槽骨缺损的应用潜能。方法将犬BMSCs与BME-10X胶原膜复合培养。取3只雄性杂种犬,拔除双侧上下颌第1、2前磨牙,保留唇舌侧牙槽嵴,制备一近远中向15mm×5mm,冠根向8mm的骨内缺损,随机分为四组。A组（空白对照组）：直接缝合牙龈;B组：缺损区上覆盖Bio-Gide胶原膜;C组：缺损区植入BMSCs胶原膜复合物后覆盖Bio-Gide胶原膜;D组：缺损区注入PRP,覆盖Bio-Gide胶原膜。分别于术后4、8、12周进行大体、X线片和组织学观察。结果BMSCs与胶原膜复合培养1d,细胞近似圆形或短梭形,3d左右可见多数细胞有突起,呈多边形及长梭形。大体观察：术后4周A组见骨缺损中央有明显凹陷,骨缺损区内见明显血肿机化物;B、C及D组骨缺损区主要为新生骨样组织充填,间杂少量血肿机化物。8周A组见骨缺损区凹陷基本长平,骨缺损顶部为纤维组织,血肿机化物被新生骨组织所取代;B、C及D组膜边缘破裂,与深面组织稍粘连,针头均不能刺入骨缺损表面。12周各组骨缺损区凹陷完全长平,A组牙槽嵴顶部纤维组织较其他组厚。X线片观察：各组骨质均长满骨缺损区;A、B、C及D组灰度值,4周分别为68、50、56及49,8周时为46、30、24及30,12周时为24、17、15及20。组织学观察：术后4周,A组缺损区可见大量纤维结缔组织及及新生血管形成的肉芽组织,未见明显新骨生成;B、C及D组膜的胶原结构均存在,其内侧面有新骨生成。8周A组缺损区新生骨小梁呈团灶状、网状;B、C及D组膜的胶原结构不完整,多个骨岛和少量纤维结缔组织连接整个骨缺损区。12周各组骨缺损区均被新生骨充填。结论使用胶原膜引导骨再生（guided boneregeneration,GBR）技术可促进牙槽骨缺损区成骨,将骨修复时间缩短为8周,但单独应用GBR的成骨作用与胶原膜复合BMSCs或PRP的成骨作用差异不明显,提示二者与GBR的联合应用还有待进一步研究。     

膜引导组织再生技术联合自体骨移植在下颌骨缺损中的临床研究

目的评价膜引导组织再生技术(GTR)联合自体骨移植在重建下颌骨的完整性,恢复下颌骨、口腔的功能,矫正颌面部畸形中的应用效果。方法应用GTR技术联合自体游离髂骨,按缺损区设计切取一定长度和形状的自体游离髂骨,经剪磨削成颗粒,植入下颌骨缺损区,上以胶原膜覆盖,用细丝线缝合固定膜后,加压包扎。并观察切口愈合、骨生长情况、X线检查的临床效果。结果7例患者术后切口均Ⅰ期愈合,骨生长情况良好,缺损处覆盖完全,达到骨整合的效果。结论膜引导组织再生技术在修复下颌骨缺损中显示了较高的临床应用价值。     

自体颅骨粉末修复颅骨缺损的实验研究

目的 建立兔自体颅骨粉末移植修复颅骨缺损的动物模型,进行相关基础问题的研究,以更好地指导自体颅骨粉末移植修复颅骨缺损的临床工作.方法 新西兰大白兔30只,每只大白兔的顶部人工形成3个直径为1 cm颅骨全层缺损孔A、B、C.孔A为对照组;孔B、C作为实验组移植人工形成缺损时收集的骨粉,其中孔B在移植的骨粉上下面放置生物膜.术后4、8、12周各处死10只动物并取材分析.结果 孔A大部分由纤维结缔组织修复.孔 B早期就能迅速地以松质骨完全修复整个缺损,但松质骨后期的生长、改建、成熟过程比较缓慢.孔C新生骨更成熟,骨性修复慢且不完全.移植的骨粉被逐步吸收.早期新骨形成区可见大量的毛细血管分布.同一缺损,术后12周与术后4、8周形成的新骨钙含量差异有统计学意义(P＜0.05),同一时期,术后8、12周孔C形成的新骨钙含量比孔B的高,差异有统计学意义(P＜0.05).结论 新生骨的形成与血管的增生在时间和空间上有着密切的关系.生物膜可以促进移植的骨粉早期迅速形成初级松质骨.     

自体骨髓促进引导性骨再生

目的　研究自体骨髓增强引导性骨再生 (GBR)修复骨缺损的能力。方法　 18只兔分为 5组 ,每组 3只 (第 5组 6只 ) ,造成双桡骨干 10 mm骨缺损 ,以硅胶管桥接骨断端 ,实验组于 0、2和 4周分别在硅胶管内注射自体骨髓 0 .3ml;对照组于相同时间点注射等量外周静脉血。在不同时间内作 X线片、大体、组织学观察及生化检测。结果　实验组成骨活跃 ,10周骨缺损完全修复 ,对照组各时间点均较实验组差 ,10周时仍无 1只兔骨性愈合。术后 2、4周实验组钙及碱性磷酸酶含量明显高于对照组。结论　自体骨髓可明显增强 GBR修复骨缺损的能力     

Demineralized bone implants

There are three mechanisms of bone formation that underlie the use of the different types of implants. In osteogenesis, viable osteoblasts and preosteoblasts are transplanted from one part of the body to the site where new bone is needed; cancellous marrow grafts are an example of such osteogenic engraftment. In osteoconduction, the implant does not provide many viable cells but rather acts as a scaffolding for the ingrowth of new bone from the margins of the defect with the concurrent resorption of the implant; cortical bone grafts or banked bone segments are examples of this "creeping substitution." In osteoinduction, the implant stimulates the transformation of connective tissue to produce endochondral bone, even in extraskeletal sites; demineralized bone implants promote bone formation by osteoinduction. The physiology, cell biology, biochemistry, and endocrinologic regulation of induced osteogenesis are areas of active investigation. Fresh autogenous cancellous bone grafts are preferred for non-stress-bearing defects, but are often of limited availability for extensive procedures, especially in infants. Demineralized bone implants have been used successfully in certain types of craniomaxillofacial, orthopedic, periodontal, and hand reconstruction. Tissue transformation may become as important to reconstructive surgery as is tissue transplantation.     

Restoration of bone defect and enhancement of bone ingrowth using partially demineralized bone matrix and marrow stromal cells

PURPOSE: This study aimed to investigate the capability of combining marrow stromal cells (MSC) and partially demineralized bone matrix (PDBM) to fill bone defect and enhance bone ingrowth using a canine non-weight-bearing gap model. METHODS: Custom-made implants with 3mm gap between the porous surface and the host bone were used. The implants were inserted into the distal femurs of 25 mongrel dogs and the gaps were randomly assigned to be filled with culture-expanded autologous MSC-loaded PDBM, autograft, fresh-frozen allograft, PDBM alone, or nothing as controls. Histomorphometry using backscattered scanning electron microscopic examination, and mechanical push-out test were performed at 6 months after surgery. RESULTS: Histomorphometry showed that amounts of bone regeneration in the gap and bone ingrowth into the porous-coated surface in the MSC-loaded PDBM-treated group were comparable to those of autograft-treated group and were significantly greater than those of allograft-treated, PDBM-treated, or non-grafted groups. Mechanical test showed the same differences. CONCLUSION: The results of this study showed that combining PDBM and autologous culture-expanded MSC restored bone stock and enhanced bone ingrowth into the porous-coated area in a canine non-weight-bearing gap model. This combination may provide an option for reconstructing bone defect when we perform a cementless revision arthroplasty.     

The early phase influence of bone marrow concentrate on metaphyseal bone healing

Bone marrow concentrate (BMC) contains high densities of progenitor cells. Therefore, in critical size defects BMC may have the potency to support bone healing. The aim of this study was to investigate the effect of BMC in combination with calcium phosphate granules (CPG) on bone defect healing in a metaphyseal long bone defect in mini-pigs. A metaphyseal critical-size bone defect at the proximal tibia of 24 mini-pigs was filled with CPG combined with BMC, CPG solely (control group) or with an autograft. Radiological and histomorphometrical evaluations after 6 weeks (42 days) showed significantly more bone formation in the BMC group in the central area of the defect zone and the cortical defect zone compared to the CPG group. At the same time the resorption rate of CPG increased significantly in the BMC group. Nevertheless, compared to the BMC group the autograft group showed a significantly higher new bone formation radiologically and histomorphometrically. In BMC the count of mononuclear cells was significantly higher compared to the bone marrow aspirate (3.5-fold). The mesenchymal progenitor cell characteristics of the cells in BMC were confirmed by flow cytometry. Cells from BMC created significantly larger colonies of alkaline phosphatase-positive colony forming units (CFU-ALP) (4.4-fold) compared to cells from bone marrow aspirate. Nevertheless, even in the BMC group complete osseous bridging was only detectable in isolated instances of the bone defects. Within the limitations of this study the BMC + CPG composite promotes bone regeneration in the early phase of bone healing significantly better than the isolated application of CPG. However, the addition of BMC does not lead to a solid fusion of the defect in the early phase of bone healing an still does not represent an equal alternative to autologous bone.     

黄芪多糖/壳聚糖/聚乳酸为支架的组织工程骨修复牙周组织缺损的实验研究

目的 探讨以黄芪多糖／壳聚糖／聚乳酸（astragalus polysaccharides／chitosan／polylacticacid，AP／C／PLA）为支架的组织工程技术修复水平型牙周组织缺损的可行性。方法成年健康雄性杂种犬10只，体重13±2kg，以犬骨髓基质细胞（marrow stromalcells，MSCs）为种子细胞，分别与AP／C／PLA及C／PLA支架构建组织工程复合物。10只实验犬于双侧下颌第3、4前磨牙颊侧制备水平型牙周缺损模型。将牙周缺损模型随机分为4组（n=10）：A组，缺损直接龈瓣冠向复位缝合，作为空白对照；B组，缺损处植人AP／C／PLA和条件培养基，龈瓣冠向复位缝合，作为培养基对照；C组，缺损处复合植入C／PLA和MSCs，龈瓣冠向复位缝合，作为材料对照；D组，缺损处复合植入AP／C／PLA和Mscs，龈瓣冠向复位缝合，作为实验组。术后8周，分别收集牙周标本行大体观察、X线片及组织学观测。结果 体外诱导培养的MSCs表达1型胶原及碱性磷酸酶，具有成骨细胞活性。各组动物对手术耐受性好，术后观察期内未见支架材料暴露，伤口愈合良好。X线片检查可见，A组牙槽骨密度及高度无明显增加；B组骨密度有一定程度增加，根分叉处增高的牙槽骨量少，邻间牙槽骨无明显增加；C组骨密度增加，根分又处牙槽骨基本恢复原有高度，邻间牙槽骨增加不明显；D组骨密度明显增加，根分叉处和邻间牙槽骨基本恢复原有高度。组织学观察显示，与A组相比，D组形成更多的新生牙槽骨、牙周膜和牙骨质，且新生牙槽骨矿化程度高，骨板排列趋向规则，出现整齐同心圆状的哈佛系统，基本具备骨组织的正常结构；牙槽骨与牙周膜的连接面呈锯齿状，沿根面还可见薄层的牙骨质沉积；新生牙周膜纤维呈束状，排列较密集且呈方向性，类似Sharpey’s纤维。A、B、C、D组新生牙槽骨高度分别为0．83±0．30、1．46±0．55、2．67±0．26及2．90±0.41mm；新生牙骨质高度分别为0．78±0．45、1．30±0．60、2．29±0．18及2．57±0．22mm；新生结缔组织附着高度分别为0．80±0．22、1．33±0．34、2．23±0．42及2．64±0．27mm；各指标D组与A、B、C组比较，差异均有统计学意义（P〈0．05）。结论 以AP／C／PLA为支架材料构建的组织工程骨修复水平型牙周骨缺损可以获得部分牙周组织再生。     

Histomorphometric analysis of the repair of a segmental diaphyseal defect with ceramic and titanium fibermetal implants: Effects of bone marrow

We used a rat femoral diaphyseal defect/implant model to quantify the ingrowth of bone, cartilage, and fibrous connective tissue in a comparative study of woven sintered titanium fibermetal and porous hydroxyapatite/tricalcium phosphate ceramic implanted with and without the addition of syngeneic bone marrow cells. The patterns of tissue growth into the implants were analyzed with respect to time, type of implant, and the presence or absence of syngeneic marrow. Significantly more bone was found in ceramic implants than in fibermetal implants, with the addition of syngeneic marrow than without it, and at 4 months than at 2 months. Significantly more bone was found at both time periods in ceramic implants with bone marrow than in any other combination studied. We hypothesize that these findings resulted from interactions between the implanted material and its surroundings, specifically its ability to serve as a substratum for cell attachment, and cells in and around the defect, whether surgically implanted or arising from the soft-tissue bed.     

几丁质-硅胶复合膜引导性骨再生的实验研究

目的通过对GBR连续组织学研究及放射学检查,探讨几丁质-硅胶复合膜在引导性骨再生(guided bone regeneration GBR)中的作用.方法取新西兰兔24只,造成双侧桡骨15mm骨缺损,将48只肢体平均分为A、B、C、D组,每组各12只肢体,分别用几丁质-硅胶复合膜、几丁质膜、硅胶管及空白对照.于手术后2、4、6、8、12、16周处死每组各两只兔,标本行X线及组织学检查.结果几丁质-硅胶复合膜组的骨缺损区在成骨活动的活跃程度、骨再生量和再生髓腔结构等方面均优于单纯几丁质、硅胶管及空白对照组(P<     

Induced regeneration of calvaria by bone morphogenetic protein (BMP) in dogs

In the adult dog, a 14-mm skull trephine defect regenerates only incompletely in the lifetime of the individual. Only about half of the defect is repaired; the regenerated part develops by extension of growth from the bony rim. Correlated roentgenographic and histomorphometric methods demonstrate that new bone develops by proliferation of preexisting osteoprogenitor cells lining the diplo? and perivascular cells of the bone marrow stroma. An autogeneic bone graft, including bone marrow, provides a supplementary supply of cells in a homostructural framework and generally completes the repair process. Transplants of bone marrow alone fail to repair the defect. Implants of bovine bone morphogenetic protein (bBMP) and a carrier consisting of matrix gamma-carboxyglutamic acid rich protein (without any additional bone or bone marrow) induce repair almost as completely as an autograft. BMP-induced bone regeneration is incomplete in the thin lateral temporal marrow-deficient part of the cranium. Implants of BMP plus bone marrow induce complete repair, suggesting that calvarial bone regeneration is bone marrow stroma-dependent for a supply of target cells. The target for BMP in cranial bone regeneration is the perivascular connective tissue cells (pericyte) of the host bed marrow stroma and endosteum. The molecular mechanism of differentiation of pericytes into osteoprogenitor cells is not known, but the process is irreversible, heritable, and presents a solvable problem.     

Induction of bone ingrowth from acetabular defects to a porous surface with OP-1

Reliable ingrowth of bone into porous-coated cementless total hip components can be expected in primary surgery. In the revision scenario, however, bone deficiency frequently is encountered and the remaining bone may have less ingrowth potential. Allograft bone and bone graft substitutes may be successful in healing bone defects, but have virtually no capacity to induce bone growth from the defect into the porous surface. To evaluate the role osteoinductive bone proteins may play in enhancing bone ingrowth, six canines had bilateral total hip arthroplasties with a cementless press-fit porous-coated acetabular component. A defect 8 mm in diameter and 5 mm in depth was created in the superior weightbearing area of each acetabulum. One defect in each animal was filled with recombinant human osteogenic protein-1. Each contralateral defect was filled with allograft bone, left empty (defect healing control), or no defect was created (intact) to serve as a control for ideal conditions for bone ingrowth. The osteogenic protein-treated defects healed more completely than allograft bone-treated or empty defects and achieved a bone density equivalent to the intact acetabulum. Bone ingrowth also occurred to a significantly higher degree in the osteogenic protein group compared with the allograft or empty defects achieving a degree of ingrowth equivalent to the intact acetabulum controls. The osteogenic bone protein was successful in achieving complete defect healing and inducing extensive ingrowth from the defect into the adjacent porous coating.     

Temporal changes during bone regeneration in the calvarium induced by osteogenin

Summary Repair of rat craniotomy defects, 8 mm in diameter, was compared with that of defects treated with either rat insoluble collagenous bone matrix (ICBM) or partially purified bovine osteogenin, a bone-inductive protein, reconstituted with ICBM (OG/ICBM). Repair of all defects was similar histologically throughout the first 3 days, characterized by acute, then chronic inflammation and granulation tissue formation. In defects treated with OG/ICBM, cartilage and osteoblasts were present at day 5. By day 9, cartilage and osteoid production were active. New bone showed hematopoietic tissue by day 11; a complete bone bridge was established by day 21. By day 42, fatty marrow was present. Defects treated with ICBM alone showed islands of cartilage and bone embedded in connective tissue at day 9, which reached peak maturity by day 14. In these and in untreated defects, significant osteoblastic and osteoclastic activity, located primarily at the margins of the defects, subsided by day 28. Untreated defects gradually filed in with fibrous connective tissue which matured throughout 156 days. Radiopacity, quantified by computerized image analysis, increased significantly between days 9 and 11 in OG/ICBM-treated defects, and remained greater (P < 0.05) than that of the ICBM-treated defects. There was a more gradual increase in radiopacity in ICBM-treated defects. The sequence of morphologic events during calvarial bone regeneration was very similar to that described previously for heterotopic bone formation induced by demineralized bone matrix.