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Aspects of bone healing and bone substitute incorporation. An experimental study in rabbit skull bone defects.

After an initial assessment of the experimental approach this experimental project was undertaken to study the regenerative response and incorporation of various implanted materials in calvarial bone defects in rabbits. Four 5-mm full-thickness defects were trephined in the frontal and parietal bones of the rabbits. After removal of the circular bone plugs the defects were used as recipient sites for inlay bone tissue and bone substitutes. In five separate studies the impact of bone regeneration of autogeneic bone grafts or eight bone substitutes were evaluated mainly by contact radiography, light microscopy and morphometry. The observation periods were four and 15 weeks. The main findings were: Autogeneic bone chips offered only minor advantages over controls in the model used and, also, differences in bone regeneration between diversified amounts of bone chips were negligible. In contrast, after bone paste implantation a cellular and mature bone was rapidly produced. Natural bone mineral (Bio-Oss) and synthetic dense hydroxylapatite ceramic proved to be biocompatible and a definite long term bone regeneration around all implants regardless of granulae size or resorbability was observed. Initial bone regeneration in and around the Bio-Oss particles was more extensive. Demineralized bone matrix of membranous and enchondral origins displayed extensive osteoinductive capacity and early bone production significantly exceeded that of control groups. The embryonic origin implied minor effects on the initial regenerative response only. Lyophilized bone allografts of two embryonic origins showed a low osteoinductive potential and a similar fashion of bone regeneration. No marked difference between these groups were displayed. HTR-polymer alone or combined with membraneous mineralized autogeneic bone chips showed a more rapid early bone regeneration than the groups containing lactomer beads, resorbable gel and controls. Also, the HTR-material proved to be a well-tolerated implant material by the recipient tissue bed.

Animals↗

Quantification of guided regeneration of weight-bearing bones.

An accurate histological evaluation system was established to improve and quantify the compatibility of membranes to provide bone regeneration in a large mid-diaphyseal bone defect, complementing radiographic evaluation. New bone formation obtained in critical segmental defects covered with tubular ethyl cellulose membranes was examined. Computerized radiography showed gradual new bone formation, which slows after 6 weeks. In a parallel histomorphological assessment, a characteristic process of new bone formation occurs inside the confined space and surrounding tissues. Histological findings are summarized according to the new scoring system, which clarifies the mechanism and provides complementary quantification of guided bone regeneration.

Animals↗

Titanium foil-guided tissue regeneration in the treatment of periimplant bone defects.

Resorbable membranes are often not stable enough for complete corrections of deep periimplant bony defects. Nonresorbable polytetrafluoroethylene membranes require removal after osseous healing. In this study the use of titanium foils for reconstruction of deficient alveolar ridge structures around dental implants is described. The advantages and disadvantages of the titanium foil-guided bone regeneration technique is discussed. Forty-two patients with deep intra alveolar periimplant defects were treated by means of a titanium foil-guided bone regeneration technique. Autologous bone in combination with a demineralized freezedried bone allotransplant was used for augmentation. Clinical and radiological control was performed 3, 6, and 12 months after surgery. In 37 cases, the average 12-month postoperative increase in bone was 4.2 mm, and the decrease in augmented bone was only 4% compared with the postoperative situation. Acceptable augmentative results were achieved in 88% of patients after the first operative treatment using a titanium foil-guided bone regeneration technique for reconstruction of periimplant defects and in all patients after the second augmentation. The main problem with foil loss was denudation and infection 6 weeks after surgery.

Adult↗

[Stimulating regeneration of bone defects by implantation of bioceramics and autologous osteoblast transplantation].

QUESTION: Does artificial stimulation of osteoconduction and osteogenesis lead to improved bone formation in defects of critical size? MATERIAL AND METHODS: Full-thickness, critical-sized defects in the anterior mandible were created in 24 adult mini-pigs. These defects were treated with a new kind of bioactive ceramic (60% hydroxylapatite and 40% beta-tricalcium phosphate), applied as a unique sol gel [9]. The bioceramic was tested alone and in combination with autologous osteoblasts. In a control group, periosteum was the only bone-producing source. After 5 weeks, the animals were sacrificed and the defects analyzed clinically, histologically, and by X-ray examination. The effects of periosteum, bioceramics, and osteoblasts were investigated in particular. RESULTS: The new bioceramic was degraded at the same speed as new bone was laid down. The rate of newly formed bone was highest in the bioceramic group at 72.3% (control group with periosteal covering only 59.3%). Additional transplantation of autologous osteoblasts did not result in faster bone production. CONCLUSION: It seems that this bioactive ceramic is successful as a bone replacement material and will be suitable as a carrier for osteoinductive substances such as bone morphogenetic proteins.

Animals↗

[Effect of sodium fluoride on bone tissue regeneration in hypodynamia].

It was demonstrated in rat experiments that a nonsupported position of the extremity attained by exarticulation of the leg in 10 to 40 days leads to a sharp inhibition of posttraumatic regeneration of bone tissue. Daily injection of 0.4 mg/100 g sodium fluoride, which was used in the clinic for the prevention and treatment of osteoporosis, inhibited still more the regenerative processes both under conditions of hypodynamia and also when the supporting function of the extremity was maintained.

Animals↗

[Expression of matrix metalloproteinase-3 and tissue inhibitor metalloproteinases-1 in regenerated rabbit bone after mandibular osteodistraction].

OBJECTIVE: To observe the expression patterns of matrix metalloproteinase-3 and its inhibitor, tissue inhibitor metalloproteinases (TIMP)-1, in remodeling phase of mandibular distraction osteogenesis. METHODS: Bilateral mandibular osteotomies were performed in 8 mature rabbits. The mandibles were lengthened 6 mm using a custom-made distractor with a rate of 1 mm/d. All animals were killed in 4 weeks after completion of distraction. The distracted calluses were harvested and processed for histology and immunohistochemistry of MMP-3 and TIMP-1. RESULTS: Elevated expression of both MMP-3 and TIMP-1 was found in the distracted calluses resulting from mandibular lengthening. Positive staining for MMP-3 was seen in the osteoblasts and osteocytes, and TIMP-1 was mainly localized in osteoblasts. CONCLUSION: MMP-3 and TIMP-1 appear to play important roles in the remodeling of new bone created by mandibular distraction osteogenesis.

Animals↗

Vertical ridge augmentation using a membrane technique associated with osseointegrated implants.

The purpose of this study was to evaluate: (1) the surgical protocol, effectiveness, and reliability for vertical ridge augmentation using a new titanium-reinforced membrane and osseointegrated implants; and (2) the histologic characteristics of the interface between a pure titanium implant and newly regenerated human bone. Five patients received 15 conical Brånemark-type implants in six different surgical sites requiring vertical augmentation. The implants protruded 4 to 7 mm from the bone crest. Pure titanium miniscrews (1.3 x 10 mm) were positioned distally to the implants, protruding 3 to 4 mm from the bone level. The implants and the miniscrews were covered with a titanium-reinforced membrane, and the flaps were sutured. Membranes were removed at the stage 2 surgery after 9 months of healing. Measurements of biopsy specimens showed a gain in bone height from 3 to 4 mm. Histologic examination showed that all retrieved miniscrews were in direct contact with bone. Histomorphometric analysis of bone contact gave a mean value of 42.5 +/- 3.6% for five of the six examined miniscrews. The results suggest that the placement of implants protruding 3 to 4 mm from the top of resorbed bone surfaces may result in vertical bone regeneration to the top of the implant cylinder and that the regenerated bone is able to osseointegrate pure titanium implants.

Adult↗

A multiphase system bone implant for regenerating the calvaria.

The regeneration of bone with a biodegradable, biocompatible carrier and osteo-regenerative proteins may be possible if the carrier has the appropriate architecture to support osteoconduction and prevent soft-tissue prolapse into ablated bone segments. Using radiomorphometry and histomorphometry, our group assessed individually and combined the components of a multiphase system bone implant (MSI) in rabbit cranial defects (critical-size defects: CSDs): two disks of biodegradable polymer (PLG) and demineralized bone matrix (DBM), a recognized osteo-regenerative material. We used 48 rabbits evenly divided between four treatment groups and two time periods. Six weeks after treatment, both DBM and PLG had significant positive effects on bone regeneration (based on a three-factor analysis of variance, p < 0.05). These effects were synergistic when the components were combined (MSI). Defects treated with DBM or PLG alone continued to regenerate bone through 12 weeks. By this time, bone within the defects treated with MSI appeared to be maturing and consolidating. We conclude that the concept of placing osteo-regenerative factors between two biodegradable disks for regenerating segments of calvaria is viable.

Animals↗

Localized ridge augmentation using titanium micromesh.

Guided bone regeneration (GBR) has been used recently for the regeneration of bone in conjunction with the placement of dental implants, for augmentation of resorbed alveolar crests, and to treat localized ridge deformities. Twenty-two patients with alveolar crest defects or peri-implant dehiscences participated in this study. Titanium implants were inserted, and the defects were covered with a titanium micromesh, above which was positioned an e-PTFE membrane. After healing, the 2 membranes were removed and a small specimen of the underlying tissues was retrieved with a small trephine. The postoperative healing was mostly uneventful, and only a few dehiscences with membrane exposure were observed. The space under the membranes was, in all patients, filled by a tissue with the macroscopic features of newly formed bone. No residual bone defects were observed and an increase of the alveolar width or height was observed. No untoward effects on bone regeneration were observed in the cases with membrane exposure. Histology showed that the underlying regenerated tissues were composed, in all cases, by newly formed bone. In conclusion, our results show that very satisfactory results concerning GBR techniques can be obtained even without the use of grafts under barrier membranes.

Adult↗