Angiogenesis in newly augmented bone observed in rabbit calvarium using a titanium cap

Objectives: In our previous work using a rabbit experimental model, we identified the importance of using a rigid support device for augmenting the development of mineralized bone. In the early stage of healing, newly generated tissue has not filled occlusive spaces, and mineralized bone forms and tends to climb along the inner wall of a device. Even though the blood supply is critical for successful bone augmentation, few studies have been conducted on angiogenesis in augmented bone. The purpose of the present study was to evaluate a method for observing angiogenesis in newly augmented bone. Material and methods: The right and left sections of the calvarium of six adult male Japanese white rabbits were exposed. The cortical bone was penetrated, and custom‐made, standardized, hemispherical titanium caps were fixed to the exposed bone. The caps on the right side of each rabbit were filled with granulated β‐tricalcium phosphate (β‐TCP). After a healing period of 1 month, the animals were injected with MICROFIL^® into the right and left common carotid arteries to form a three‐dimensional cast of the vasculature, and the newly generated blood vessels in the augmented bone were observed. Results: The newly generated blood vessels were observed entering the space beyond the existing calvarial bone. Furthermore, angiogenesis was seen to have occurred to a similar extent through the inter‐granular β‐TCP in the right caps. These areas of angiogenesis were observed in a histological study with cross‐sections. Conclusions: The results of the present study suggest that this observation method allows the examination of angiogenesis in hard tissue before the preparation of histological specimens.     

Influence of decortication of the donor bone on guided bone augmentation. An experimental study in the rabbit skull bone

The aim of the present study was to evaluate if early access to the endosteal bone compartment by removal of the outer cortical bone plate will enhance bone augmentation in a secluded space. Two titanium cylinders were placed on the skull of each of 8 rabbits. Each cylinder was placed into a circular slit, secured to the skull bone via two mini-screws and supplied with a titanium lid. On the test side, the outer plate of the cortical bone, demarcated by the slit, was removed. The subsequent bleeding resulted in blood fill of the cylinders to various degrees. On the control side, the corfical bone plate was left intact and no bleeding was observed at the time of the placement of the titanium lids. After 3 months, the animals were sacrificed to obtain histology and histomorphometry. No differences in the total amount of augmented bone tissue, in relation to the total experimental area (75.5% +/- 10.9% at the test sites and 71.2% +/- 13.5% at the control sites) or of the augmented mineralized bone tissue in relation to the total amount of augmented bone tissue, was revealed (17.8% +/- 3.0% and 16.0% +/- 4.9% respectively). There was no difference in the morphological appearance of the augmented bone between test and control sites and there were no obvious similarities in the appearance between the newly formed bone tissue and the donor bone. The augmented bone consisted of slender bone trabeculae, distributed in abundant marrow spaces. A conspicuous finding was that the bone trabeculae tended to climb along the inner walls of the titanium cylinder. It is concluded that decortication of the calvarial bone in the rabbit does not result in more bone formation beyond the skeletal envelope after a healing period of 3 months compared to no removal of the cortical bone plate inside a secluded experimental area.     

Influence of surface roughness of barrier walls on guided bone augmentation: experimental study in rabbits

Background: By using the guided tissue regeneration concept it is possible to augment bone, beyond the skeletal envelope, provided certain biologic, surgical, and barrier-related demands are met. Among barrier-related factors of importance are the surface properties. Purpose: The aim of this study was to evaluate whether different surface roughness of the barrier wall influences the amount and morphology of augmented bone in a secluded space, using a titanium cylinder as barrier device placed on the rabbit skull. Materials and Methods: Cylinders of commercially pure titanium were fabricated by machining, using a turning tool. The inner cylinder wall was either left untreated or grit-blasted with titanium dioxide to increase surface roughness. The topographic profile of the inner surface of two cylinders (1 turned and 1 grit-blasted) was measured in vitro to achieve a numeric characterization of each type of surface topography. Two cylinders, one with grit-blasted and one with turned inner walls, were surgically placed and secured to the skull bone of each of eight rabbits. The plate of the cortical bone, facing the experimental area framed by the cylinder wall was removed, and care was taken to ensure total blood fill of the cylinders. After 3 months, the animals were sacrificed to obtain histology for histomorphometry. Results: The relative volume of augmented tissue in the grit-blasted cylinders (77.9 ± 10.5%) did not differ significantly from that in the turned cylinders (73.4 ± 5.5%, p =.118), neither did the volume of mineralized bone (20.1 ± 8.2% vs. 22.1 ± 7.2%, p =.064). The trabecular density of the augmented bone was higher close to the walls of both the turned and the grit-blasted cylinders compared to the overall trabecular density within the cylinders, but with no significant difference between the two groups. However, the area of mineralized bone in direct contact with the inner surface of the titanium cylinder was significantly larger in the grit-blasted (33.9 ± 13.3%) compared to the turned cylinders (12.0 ± 8.5%, p =.01). Conclusions: The use of titanium barriers with a grit-blasted inner surface compared to barriers with a turned surface resulted in the formation of similar amounts of bone beyond the skeletal envelope of the rabbit skull. However, a larger area of augmented mineralized bone was found in direct contact with the inner surface of the grit-blasted cylinders.     

Effects of occlusiveness of a titanium cap on bone generation beyond the skeletal envelope in the rabbit calvarium

We evaluate the effects of occlusiveness of a titanium cap on bone generation beyond the skeletal envelope. In eight rabbits, the calvarial bone was exposed and a circular groove was prepared with a trephine drill. After marrow penetration, a standardized hemispherical titanium cap, either with or without small holes (1.5 mm in diameter), was then placed into the bone and covered by a cutaneous flap. After 1 month or 3 months of healing, the animals were euthanized and examined histologically. The percentage area of newly generated tissue consisting of mineralized bone and marrow spaces in each section was calculated relative to the area bounded by the hemispherical shape of the titanium cap and the parent bone; this latter volume was taken to be 100%. Furthermore, the cross-sectional areas of generated mineralized bone expressed as percentages of the total tissue area generated within each space were determined. In the 1-month specimens, there was no statistically significant difference between the two caps in the amount of tissue generated, 54.7%+/-12.2% with holes vs. 60.4%+/-8.8% without holes (p=0.225). However, in the 3-month specimens, we observed a significant difference between the caps (55.9%+/-7.4% with holes vs. 89.9%+/-6.5% without holes, P<0.05). Also, there was a statistically significant difference between 1- and 3-month specimens in the amount of tissue generated under the cap without holes (60.4%+/-8.8% vs. 89.9%+/-6.5%, P<0.05). Although there was no significant difference in the relative amount of mineralized bone generated between the caps with holes and those without holes in the 1-month specimens (27.7%+/-4.8% vs. 30.8%+/-6.4%, P=0.225), there was a statistically significant difference between the two caps in the 3-month specimens (24.3%+/-4.1% with holes vs. 34.0%+/-8.6% without holes, P<0.05). A substantial ingrowth of fibrous connective tissue through the holes appeared to prevent further new tissue generation in a defined area adjacent to the bone surface. We concluded that total occlusiveness, sufficient stiffness of the cap, as well as the passage of time will allow predictable mineralized bone augmentation to occur in spaces beyond the skeletal envelope.     

Bone morphology and vascularization of untreated and guided bone augmentation-treated rabbit calvaria: evaluation of an augmentation model

OBJECTIVES: Cranial vault is widely used in experimental models on membranous bone healing in general, guided bone augmentation (GBA) studies being one example. To our knowledge, however, few studies on the characteristics of the untreated calvaria regarding bone density, vessel topography, and their intra/interindividual variations and associations are available. The aims of this investigation were to (1) map the large vessel topography of the skull vault, (2) describe the parietal bones of the adult rabbit histologically and morphometrically, and (3) histologically compare untreated parietal bone with parietal bone that had been treated with a GBA device. MATERIAL AND METHODS: Ten adult untreated rabbits were microangiographed. General anesthesia was induced and the mediastinum was opened. Heparin and lidocaine were injected in the aorta followed by perfusion with India ink. After death, en bloc biopsies of the skull vault including the overlying soft tissues and dura mater were taken. The specimens were cleared with the Spalteholtz technique, microscopically examined, and digitally imaged. Thereafter, circular biopsies were harvested to obtain decalcified sections. In addition, sections from 14 GBA-treated rabbit skulls (of the same race, sex and age as the untreated animals) served as reference specimens for comparison. Histomorphometric examinations were carried out. RESULTS: In the cleared specimens, all parietal bones were found to be supplied by one major branch of the meningeal artery. From each of these, separate branches supplied the dura wherein a fine vessel network covered the bone. No major vessels were found in the supracalvarial soft tissue. Numerous fine vessels were found within the periosteum and dura entering the cortical plates. The decalcified sections of the parietal bones revealed an outer and inner cortical plate enveloping a diploic space containing bone trabeculae, marrow tissue and larger sinusoids. Hollow connections were frequently found in both the outer and inner cortical plates in both the untreated and the GBA-treated specimens. These connections contained marrow tissue that extended to the periosteum and the dura. The morphometric measurements revealed similar proportions of cortical, trabecular, and marrow areas in the right and left untreated bones. The area of the outer cortical plate was significantly larger than the area of the inner cortical plate. Bone density was similar in the right and left untreated and GBA-treated specimens, as was the frequency and width of hollow connections through the cortical bone plates. CONCLUSIONS: The symmetry between the left and right parietal bones concerning the large vessel topography and the histomorphometric parameters assessed was high. Hollow connections in the cortical plates were frequently found. The bilateral use of the parietal bones is suggested to be reliable in experimental GBA models regarding the blood supply and bone quality.     

Three-dimensional evaluation for augmented bone using guided bone regeneration

OBJECTIVE: This study evaluated new bone regeneration beyond the skeletal envelope within an occlusive titanium cap on rabbit calvaria using microfocus computed tomography images. METHODS: In 10 rabbits, the calvaria was exposed and a circular groove was prepared. After penetrating the marrow, a standard hemispherical titanium cap was placed in the groove and covered with a cutaneous flap. After 1 or 3 months, the animals were killed and the calvariae and titanium caps were dissected. After taking microfocus computed tomography images of the specimens, histological sections were made. The specimens were observed using three-dimensional images constructed from the microfocus computed tomography images, and the histological sections were examined to compute bone parameters. RESULTS: The three-dimensional images and histological specimens showed that new bone formed in flat, cup-like, and dome shapes. The bone parameters trabecular thickness and the proportion of marrow space to the capacity of the titanium cap increased, whereas bone density decreased, and there were significant differences between the 1- and 3-month groups. DISCUSSION: First, a cylinder of new bone formed from the existing bone. Gradually, bone formed along the cap wall and the new tissue formed in a crater indented centrally. Finally, the new tissue formed in the shape of a dome. CONCLUSION: Trabecular bone formed along the wall of the titanium cap, and bone filled the inside of the cap within 3 months.     

Effects of ipriflavone on augmented bone using a guided bone regeneration procedure

: This study investigated the effects of ipriflavone (IP) on augmented bone using a guided bone regeneration (GBR) procedure. In 15 rabbits, two titanium caps were placed into calvarial bone for GBR. The animals were divided into three groups: the No-IP (no intake of IP), Post-IP (IP orally, 10 mg/kg/day after GBR), and Pre-IP (IP intake beginning before GBR) groups. One cap was removed from each rabbit after 3 months, and the remaining site was a control. One month after one cap removal, all the animals were euthanized, and histologic and histomorphometric analyses were performed. In all of the groups, the newly generated tissue was of varying size, and it consisted of thin pieces of mineralized bone and large marrow spaces with fat cells and some hematopoietic cells. In all of the control sites, the newly generated tissue was noted and almost filled the space under the cap. There was a significant difference between groups No-IP and Pre-IP (93.8+/-4.6% vs. 98.5+/-0.8%, P<0.05). The tissue generated at the test sites in all of the groups was resorbed, and its original shape and volume were not maintained 1 month after one cap removal. In particular, the greatest percentage, approximately 20% of the newly generated tissue, was resorbed in the No-IP group (93.8+/-4.6% vs. 73.9+/-3.7%, P<0.05), and approximately 11% and 15% in groups Post-IP and Pre-IP, respectively. The relative amount of mineralized bone generated at the control and test sites was significantly larger in groups Post-IP and Pre-IP when compared with group No-IP, except for the test site between groups No-IP and Post-IP (P<0.05). Therefore, the amount of mineralized tissue generated appeared to increase with an increase in the total IP dose. Within the limitations of this rabbit experimental model, we conclude that the daily intake of IP before or after GBR inhibits the resorption of augmented tissue and would be useful for improving the quality of newly generated bone beyond the skeletal envelope.     

Impact of cortical perforations of contiguous donor bone in a guided bone augmentation procedure: an experimental study in the rabbit skull

Background: It has been shown that bone can be augmented beyond the original skeletal envelope by using space‐making barriers. Further, it has been suggested that perforation of the contiguous donor bone enhances bone formation in guided bone augmentation procedures. Purpose: The goal of the present investigation was to evaluate whether perforations into the donor bone marrow through the cortical plate, located contiguous to an extracalvarial experimental space, influence bone generation into this space with regard to augmented bone tissue volume and bone density 3 months postoperatively. Materials and Methods: Two titanium cylinders, each with a titanium lid, were subcutaneously placed with their open ends facing the parietal bones of eight rabbits and secured with miniscrews. The cortical bone plate on the test side was perforated with seven evenly distributed holes, each with a diameter of 1.2 mm, using carbon‐steel burs. Together, these perforations corresponded to about one‐third of the total experimental bone area. The bone on the control side was left intact, and no bleeding occurred during the placement of the titanium lid. The perforation procedure (test side) resulted in various degrees of blood fill. After 3 months, the animals were sacrificed to obtain ground sections for histology and histomorphometry. Results: The cylinders were found to be partly filled with tissue containing slender bone trabeculae and marrow spaces in abundance. The bone consistently reached a higher level at the inner wall compared with the central part of the cylinders (p=.001). Hollow connections between the experimental space and the skull bone marrow were found in the contiguous outer cortical plate in four of the seven control sites. No statistically significant differences could be demonstrated between the perforated test sites and the control sites regarding augmented tissue volume (64.4 ± 18.9% vs. 64.9 ± 22.2%) or bone density, although there was a tendency toward denser bone in the test sites (21.5 ± 11.1%) versus control sites (14.7 ± 5.4%). There was no statistical difference regarding relative bone‐to‐titanium wall contact (27.4 ± 14.7% for test; 38.6 ± 25.9% for control). Thickness (height) and density of the skull bone vault were measured in the area beneath and lateral to the cylinders. No significant differences could be observed regarding these parameters between the test and control side. There were no correlations between thickness (height) or density of donor bone versus amount or density of augmented bone. The degree of immediate blood fill could not be shown to correlate with augmented tissue volume or augmented bone density. Conclusions: In the present model, as observed 3 months postoperatively, cortical perforations of contiguous donor bone or degree of immediate blood fill of an extracalvarial experimental space were not found to enhance augmented tissue volume beyond the skeletal envelope. Although there was a much higher mean value for bone density of augmented bone in the test sites, the large variations failed to show significant intergroup differences.     

Influence of barrier occlusiveness on guided bone augmentation. An experimental study in the rat.

The present study was designed to test perforated and non‐perforated barriers for their ability to promote augmentation of bone tissue. More specifically, 1 totally occlusive barrier and 6 barriers with perforation sizes of about 10, 25, 50, 75, 100, and 300 μm and 1 group with no barriers placed (open test chambers) were used to test the effect of a barrier's occlusiveness on the amount and composition of augmented tissue over time. The skull of the rat was used as the experimental area. Prefabricated, flexible silicone frames with an inferior flange for peripheral sealing to the bone surface and a central vertical through hole with a diameter of 3.6 mm and a height of 2 mm were used as test chambers. The barriers were inserted to cover the superior opening of the through hole. The healing periods were 4, 8, and 12 weeks. All test chambers exhibited newly formed skull bone which was augmented over time. The placement of totally occlusive barriers resulted in the slowest rate of bone tissue augmentation but in a highly predictable manner, i.e., there were only small individual variations. Placement of barriers with perforations exceeding 10 pm, on the other hand, resulted in a faster rate of bone augmentation with larger individual variations and a totally different augmentation pattern. A pronounced augmentation of calvarial soft tissue from the sagittal suture of the skull as well as ingrowth of supra‐bony connective tissue through the barriers were also observed. After 12 weeks of healing, no differences in the amount of augmented mineralized bone related to perforation sizes >lO μm were found. The open test chambers also showed bone augmentation, although most of their volume was occupied by suprabony connective tissue.     

Effects of cortical bone perforation on experimental guided bone regeneration

This study was designed to evaluate the effects of cortical bone perforation histologically and histomorphometrically on guided bone regeneration (GBR) in rabbits. After elimination of the periosteum, cortical bone defects of two sizes were made in the external cortical plate of the frontal bone (Group A: 1 x 15 mm; Group B: 3 x 15 mm). A non-resorbable membrane filled with autogenous blood was placed in the experimental area and secured with titanium pins. After 1 and 2 weeks, vascularized connective tissue and new bone were generated in the space surrounding the defects in both the groups. The amount of vascularized connective tissue generated in Group B was greater than that in Group A at 1 week. Alkaline phosphatase (ALP) was expressed on the bone surrounding the perforation. The expression of ALP was more extensive in Group B than in Group A and was proportional to the breadth of perforation. At 2 weeks, the perforated region was almost covered with new bone in Group A. ALP was expressed at the periphery of newly formed bone. The expression of ALP was proportional to the breadth and height of perforation. At 6 weeks, semicircular outgrowth of bone towards the periphery of the perforated region was observed in both the groups. Newly formed bone volume and ALP expression in Group B were more extensive than those in Group A. At 12 weeks, the space was filled with bone and connective tissue in both the groups. There was no difference in ALP expression between Groups A and B. Histomorphometric analysis showed significant differences between both the groups (two-way ANOVA, P<0.01). We conclude that a larger perforation is associated with prompter bone formation in the secluded space during GBR.     

Freeze-dried homogeneous and heterogeneous bone for sinus augmentation in sheep. Part I: histological findings

Freeze-dried bone has been reported to possess an osteogenetic potential, i.e. to be osteo-inductive or osteoconductive depending on the grafted site. In this animal study homogeneous demineralized freeze-dried bone from the sheep (s-DFDB) and heterogeneous human demineralized freeze-dried bone (h-DFDB) used for single-stage sinus elevation were examined for their potential to improve bone-to-implant bonding. In 72 sinuses of 36 adult female mountain sheep Schneider's membrane was elevated from the local bone through an extra-oral approach and two cylindrical plasma-flame sprayed titanium implants were inserted in the lateral wall of each sinus. At the same time 18 sinuses were reinforced with s-DFDB, another 18 with h-DFDB and yet another 18 with autogenous cancellous bone from the iliac crest. In 18 animals the subantral space remained ungrafted. At each follow-up date, i.e. at 12, 16 and 26 weeks, 12 animals were re-examined and one randomly selected implant from each sinus was analyzed histologically and histomorphometrically. With both s-DFDB and h-DFDB extensive fragmentation and disintegration were seen side by side with sporadic areas of remineralization. These were mainly located in the vicinity of the local host bone and coalesced over time to be ultimately replaced and consolidated by woven bone. But most of the h-DFDB/s-DFDB particles continued to be embedded in abundant collagenous connective tissue and were surrounded by mononucleated and multinucleated giant cells, ultimately causing extensive resorption. The mean bone-to-implant contact length was 16.4% of the implant surface for s-DFDB, 16.9% for h-DFDB, 32.8% for autogenous bone and 22.2% in ungrafted controls. In the autogenous bone group the mean bone-to-implant contact length progressively increased with increasing contact time. In the control group, by contrast, the mean bone-to-implant contact length initially increased in the first two follow-up periods, but dropped again at 26 weeks. Both in the h-DFDB and the s-DFDB group the percent bone contact area was lower at 16 weeks than at 12 weeks but increased again by 26 weeks. In apical implant sections, s-DFDB produced significantly less bone-to-implant contact than autogenous cancellous bone from the iliac crest. In basal implant sections, both DFDB-grafted groups did significantly less well than the two control groups. The results of this experimental study showed that DFDB homografts and heterografts cannot be recommended alone instead of cancellous autografts from the iliac crest for augmenting the maxillary sinus in single-stage sinus elevations. Longer follow-up times than in the present study may perhaps show better results at the bone-implant interface.     

Bone augmentation at titanium implants using autologous bone grafts and a bioresorbable barrier. An experimental study in the rabbit tibia.

The aim of the present investigation was to compare the effect of using autologous bone particles covered with a bioresorbable matrix barrier with the use of bone particles alone on bone augmentation at titanium implants installed in the rabbit tibia. Two Brånemark System® implants, one in each tibia, were inserted in each of 9 rabbits in such a way that 5 threads were not covered with bone. Autologous bone particles were harvested from the skull and placed over the exposed implant surfaces on each tibia. The bone graft on one tibia was covered with a Guidor® Matrix Barrier, while the bone graft on the other tibia served as a control. After a healing period of 12 weeks, the animals were sacrificed and specimens taken for histomorphometrical analyses. The analyses showed that a significantly larger volume of augmented bone tissue had formed at the test sites. There were, however, no differences in the amount of mineralized bone. In fact, the difference in tissue volume was due to an increased amount of bone marrow at the test sites. The degree of mineralized bone to implant contact as well as the degree of mineralized bone within the threads at the test implants were similar to that at the controls. In conclusion, it was found that the coverage of particulate autologous bone grafts with a bioresorbable barrier resulted in a larger volume of augmented bone than the use of bone grafts not covered with a barrier.     

Changes in the volume and density of calvarial split bone grafts after alveolar ridge augmentation

OBJECTIVES: One main problem occurring after bone grafting is resorption, leading to insufficient bone volume and quality, and may subsequently cause dental implant failure. Comparison of graft volume and bone density of iliac crest and calvarial transplants determined by animal studies demonstrates significantly lower resorption of bone grafts harvested from the skull. This paper is the first clinical study evaluating bone volume and density changes of calvarial split bone grafts after alveolar ridge reconstruction. MATERIAL AND METHODS: Bone volume and density were determined using CT scans and the software program Dicom Works in a total of 51 calvarial grafts after alveolar ridge augmentation in 15 patients. CT scans were taken in all 15 patients immediately after grafting (T0) and before implantation after a postoperative period of 6 months (T1). In five patients (26 calvarial grafts), a 1-year follow-up was performed (T2). RESULTS: A mean volume reduction of 16.2% at T1 (15 patients) and 19.2% at T2 (five patients) was observed. Bone density was high--about 1000 Hounsfield units--and did not change during the 1-year period. At the time of implantation, 41 transplants were classified as quality 1 bone and 10 as quality 2-3 bone. Grafting area and the technique used for grafting (inlay or onlay graft) did not affect the postoperative bone volume reduction. Generalized osteoporosis did not increase the resorption rate of calvarial transplants. CONCLUSION: Based on these findings, calvarial split bone grafts are a promising alternative for alveolar ridge reconstruction in dental implantology.     

引导骨组织再生膜应用于自身骨移植的研究现状

自身骨移植是种植术前骨增量的一种重要的技术手段。对于在常规骨移植后是否在移植物上覆盖引导骨组织再生膜,临床上存在着较大争议。笔者拟就引导骨组织再生膜在自身骨移植中的应用研究作一综述。     

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由于种植体生物相容性的不断改良和完善,目前的牙种植体均能获得理想的可预期的骨结合,在新拔除患牙的牙槽窝内即刻植入种植体已经成为一种常规的术式拔牙后即刻种植可有利于减少外科手术次数,有利于牙槽嵴骨量的保存,降低治疗费用并减少缺牙时间,更易被患者接受.但由其解剖生理因素决定,牙槽嵴在牙缺失后通常要出现唇侧骨板的吸收萎缩,这常导致种植体唇面暴露,出现美学上的问题.即刻种植的同时,在充分理解和使用引导骨再生原理的基础上配合骨增量材料的应用才能获得理想的修复效果,本文就我们的临床体会结合文献进行了分析讨论.     

Vertical ridge augmentation with guided bone regeneration in association with dental implants: an experimental study in dogs

AIM: To evaluate the effect of using guided bone regeneration (GBR) with a titanium-reinforced e-PTFE membrane in alveolar bone defects with titanium implants. MATERIAL AND METHODS: Following extraction of three mandibular premolars and a molar on both sides of the jaw in three dogs, alveolar bone defects (depth: 5-7 mm) were produced. After 4 months, three implants were inserted into each defect to a depth of approximately 4 mm, so that their coronal portion was protruding about 5 mm. Four sides in the dogs were assigned to a test group and the remaining two sides to a control group. The 12 implants in the test group were covered with a reinforced e-PTFE membrane. The space under the membrane was filled with peripheral venous blood from the animal, and the flaps were sutured over the membrane. The six control implants received no membrane before the suturing of the flaps to complete wound closure. The animals were sacrificed after 6 months, and non-decalcified histological specimens of the implants and surrounding tissues were prepared. RESULTS: Histologic and histomorphometric analyses revealed a significantly (Mann-Whitney test; P=0.08) larger amount of bone fill in the test group (mean=57.42%) than in the controls (mean=11.65%), and clinical evaluation of one test site showed that the implants were completely covered with tissue resembling bone. In most of the specimens, bone had grown in height close to, or in direct contact with the membrane. However, the new bone generally was not in direct contact with the implants. Regularly, a zone of dense connective tissue was interposed between the implants and the newly formed bone. CONCLUSION: The formation of even considerable amounts of bone following vertical ridge augmentation with GBR and implants was not accompanied by predictable osseointegration of the implants.