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 beta-tricalcium phosphate (beta-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 beta-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.

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.

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.