Complications associated with segmentation of the maxilla: a retrospective radiographic follow up of 82 patients.

The aim of the present study was to retrospectively examine the clinical and radiographic incidence and frequency of injuries to teeth and their surrounding tissues adjacent to interdental osteotomies in conjunction with segmentation of the maxilla. Vertical interdental osteotomies have been performed in combination with Le Fort I osteotomy for correction of various dento-facial deformities. All our orthognathic patients are followed prospectively in a standardized manner. Eighty-two consecutive patients who underwent dento-facial correction by segmented maxillary osteotomy alone or in combination with simultaneous mandibular surgery between 1992 and 1998 were included in the study. They were followed for up to 30 months postoperatively. A total of 158 interdental osteotomies were performed, involving a total of 316 teeth. Only a small number of complications such as osteolytic processes, marginal bone destruction, root resorption or mechanical injuries to the teeth were seen.

Gastrectomy has no effect on bone regeneration in rats despite a decrease in bone mass.

BACKGROUND: Gastrectomy, specifically the removal of the acid-producing part of the stomach (fundectomy), is known to cause osteopenia. This effect has been ascribed to the elimination of a hypothetical osteotropic peptide hormone, presumably produced in the oxyntic mucosa. Since osteopenia is due to a disturbed balance between bone formation and resorption, we assessed the effect of gastrectomy on osteogenesis, more specifically mandibular orthotopic bone regeneration. METHODS: Adult rats were either gastrectomized or sham-operated. Two weeks later, unilateral 5-mm transosseous defects were made in the mandibles and covered with microporous barrier membranes (GORE-TEX Membrane). After 6 weeks of healing. bone-bridging of the defects was analyzed by computerized light microscopic image analysis. Furthermore, bone mass was analyzed in the contralateral untreated mandibular side, in calvarial bone, and in femora by morphometry and dry/ash weights. RESULTS: While gastrectomy resulted in a clearly decreased bone mass, manifested as increased marrow spaces in all bones and as decreased dry and ash weights in femora, no difference in mandibular bone healing rate was found between the groups. CONCLUSIONS: Since secluding of the defect space by membrane barriers implies that osteogenic cells have to be recruited primarily from intra-osseous stem cells by their proliferation and differentiation into actively bone-forming osteoblasts, the results indicate that gastrectomy has no effect on these processes. The findings thus imply that the disturbed balance in bone remodeling caused by gastrectomy, resulting in osteopenia, may be due to stimulated bone resorption rather than to reduced bone formation.

Effects of recombinant human fibroblast growth factor-2 on osteogenic cell populations during orthopic osteogenesis in vivo.

The osteogenic effects of fibroblast growth factor-2 (FGF-2) in vivo on different cell populations of the osteoblastic cell lineage have not been fully elucidated. In this study, the efficacy of recombinant human fibroblast growth factor-2 (rhFGF-2) to stimulate orthopic bone formation in transosseous rat mandibular defects, with different cell populations allowed access to the defects, was investigated with the aim to further decipher FGF-2 effects. Three different doses of rhFGF-2 (10 ng, 100 ng, and 1 microg) were delivered in an absorbable collagen sponge carrier, whereas some defects were implanted with the carrier only, and some were left untreated. Barrier membranes, made of microporous expanded polytetrafluoroethylene, were simultaneously placed over half the number of defects in each treatment group, thus forcing osteogenic cells to be derived from intraosseous sources. Evaluation was made by light microscopy and computerized image analysis after 12 and 24 of days healing. Whereas no general stimulatory effect could be ascertained at 12 days, higher rhFGF-2 doses decreased bone formation by both intraosseously and periosteally derived cells. At 24 days, a clear, although rather limited, stimulatory effect on osteogenesis was observed, but again a decrease was observed with the 1 microg dose. At both observation periods, an increased number of osteocytes was found in the newly formed bone at sites treated with the lower rhFGF-2 doses, whereas the high-dose rhFGF-2 resulted in a return to control levels, irrespective of whether cells were intraosseously derived or from the periosteum also. Based on differential analysis of bone healing by cells from different sources as well as on bone cellularity, the results suggest that rhFGF-2 in vivo exerts a stimulatory effect on proliferation of committed osteoblastic cells. This effect is biphasic, in that higher doses are without effect or may even be inhibitory. No inductive effect on osteoblast recruitment could be found. These effects differ from those of, for instance, BMP-2 and TGF-beta1.

Bone-inductive efficacy of recombinant human bone morphogenetic protein-2 expressed in Escherichia coli: an experimental study in rat mandibular defects.

Because to our knowledge the efficacy of prokaryotically expressed recombinant human bone morphogenetic proteins (rhBMP) to promote orthotopic osteogenesis has not previously been investigated, our aim was to test the efficacy of rhBMP-2 produced in Escherichia coli to promote bone healing in a standardised experimental bone healing model in rat mandibles. Different doses of rhBMP-2 were delivered in an absorbable collagen sponge carrier, and microporous barrier membranes were placed over half the number of defects in each treatment group, thereby making intraosseous cells the only recruitment source for new osteogenic cells. Results were evaluated by computerised image analysis after 12 and 24 days. The relative efficacy of rhBMP-2 preparations of different purity was also compared. E coli-produced rhBMP-2 stimulated bone healing, but its efficacy was estimated to be about one order of magnitude less than that of rhBMP-2 expressed in eukaryotic cells. We conclude that bacterially expressed rhBMP-2 is osteogenic in vivo, although higher doses will be required than of rhBMP-2 expressed in mammalian cell lines.

Bone neogenesis in domes made of expanded polytetrafluoroethylene: efficacy of rhBMP-2 to enhance the amount of achievable bone in rats.

For bone reconstructive purposes, it would be a great advantage to be able to gain bone without grafting. In experimental studies, barrier membranes have been used to accomplish this, however, with limited efficacy. In this study, the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the early onset of bone formation, as well as on the final amount of achievable bone, was investigated in an experimental osteo-neogenesis model. In 60 adult rats, dome-shaped barrier membranes made of expanded polytetrafluoroethylene (Gore-Tex membrane), with an inside volume of approximately 60 mm3, were placed on the left parietal bone. The domes were pretreated according to four different alternatives: (1) filled with autogenous blood only (n = 15); (2) filled with 5 microg of rhBMP-2 in an absorbable collagen sponge carrier (n = 15); (3) filled with 15 microg of rhBMP-2 in absorbable collagen sponge carrier (n = 15); or (4) filled with the absorbable collagen sponge carrier only (n = 15). The animals treated according to each alternative were then divided into three equal groups with five rats in each, and subsequently killed after 3, 6, or 12 weeks. The amount of bone formed within the domes was evaluated by light microscopy and computer-assisted image analysis. It was found that the amount of newly formed bone could be enhanced by approximately 100 percent by simultaneous implantation of rhBMP-2, irrespective of dose. The early onset of bone formation was, however, not affected by the rhBMP-2 supplementation. This finding was interpreted as being due to the delivery system used, because as long as the carrier was still present, no significant difference between the treatment groups was observed. The bone formed in domes with carrier implantation, with or without rhBMP-2, displayed more marrow spaces in comparison to controls. The combined treatment with barrier membranes and local delivery of rhBMP-2 may be a useful tool in reconstructive surgery, for instance replacing onlay grafting, especially when a more delicate anatomy is necessary, because membranes can be shaped in multiple ways.

Autoclaved bone for craniofacial reconstruction: effects of supplementation with bone marrow or recombinant human fibroblast growth factor-2.

Replantation of resected bone after autoclaving is employed by many units in both craniofacial and orthopedic tumor reconstructive surgery. The procedure is attractive because it maintains the original anatomy, is reliable, and provides a good immediate clinical result. However, doubts have been raised about the ability of the autoclaved bone to revitalize. The present study aimed to explore, in an animal model, the revitalization of autoclaved bone and to determine whether it would be possible to enhance graft revitalization using either autogeneic bone marrow or recombinant human fibroblast growth factor-2, a peptide with stimulatory effects on both endothelial and osteogenic cells. Twenty-eight adult rats were subjected to bilateral parietal cranioplasties (4 x 6 mm), and 75 percent of the grafts were subjected to autoclaving (121 degrees C; 20 minutes) and subsequently treated randomly according to one of the following strategies: no further treatment, or supplementation with bone marrow or recombinant human fibroblast growth factor-2. The remaining grafts were replanted as fresh autografts. The results were evaluated after 4 and 12 weeks by radiologic, histologic, and histomorphometric analyses. After 4 weeks, no major differences were observed between treatments. At 12 weeks, however, no distinction in graft revitalization between autografts and autoclaved grafts supplemented with recombinant human fibroblast growth factor-2 was observed, whereas autoclaved grafts with or without bone marrow displayed significantly less revitalization compared with autografts. The results indicate that autoclaved bone will revitalize by remodeling, and that the efficacy of this process can be increased significantly by simultaneous supplementation with recombinant human fibroblast growth factor-2.

Growth factors and bone regeneration. Implications of barrier membranes.

Insufficient or absence of bone healing is a frequent problem within all surgical fields. This often necessitates treatment by autogenous bone grafting. Recently, two new techniques to promote bone healing were introduced, the osteopromotive membrane technique, and local delivery of growth-stimulatory factors, both with a high rate of success in preclinical experiments. The aims of the present series of investigations were to further develop the membrane barrier technique, both by itself as well as in combination with local delivery of growth factors, in animal experiments. During membrane-promoted bone formation, the membrane porosity was found to be of importance for the initial rate of bone formation as well as for the performance of the material in the tissue. In contrast, the final amount of bone was not affected. In a well-known bone healing model, the 5 mm in diameter 'critical size defect' at the rat mandibular ramus, the efficacy of rhBMP-2, rhTGF-beta 1 and rhFGF-2 to promote bone regeneration alone and in combination with barrier membranes was evaluated. Under both conditions, rhBMP-2 was found to be an efficient promoter of bone healing. rhFGF-2 had some stimulatory effect both with and without barrier membranes, whereas rhTGF-beta 1 was found to have a minor stimulatory effect by itself, but in combination with barrier membranes it was inhibitory. These observations were interpreted as being the result of an effect of the growth factors at different levels of the osteoblastic lineage; rhBMP-2 being an inducer of osteoblastic cells from stem cells, whereas rhTGF-beta 1 may primarily act on already committed cells. In contrast, rhFGF-2 may have stimulatory effect at different levels of the lineage. Based on the positive results obtained by the combination of rhBMP-2 and barrier membranes in the rat mandible, this combination was then applied to (i) rabbit radius defects; and (ii) a rat calvarial osteoneogenesis model. In the long bone model, membranes by themselves were insufficient to promote bone healing, but the combination resulted in complete regeneration. In the osteoneogenesis model, the combination of barrier membranes and rhBMP-2 resulted in a 100% increase in the final amount of achievable bone. In the last study, rhFGF-2 (no barrier membranes) was shown to enhance revitalization of autoclaved autogenous bone grafts, a procedure clinically used in craniofacial reconstruction mainly after tumor surgery. The combined use of rhBMP-2 and barrier membranes has great potential to be a useful treatment for improving bone healing and might be an alternative to bone grafting.

Opposite effects of recombinant human transforming growth factor-beta 1 on bone regeneration in vivo: effects of exclusion of periosteal cells by microporous membrane.

The efficacy of local delivery of recombinant human transforming growth factor-beta 1 (rhTGF-beta 1) to promote bone regeneration, with or without cellular contribution from the periosteum, was evaluated in transosseous defects. Implantation of rhTGF-beta 1 into 5 mm in diameter "critical size defects" in the rat mandible resulted in a dose-dependent (0.1-20 micrograms/defect) bone bridging at both 12 and 24 days, independent of the type of delivery system [3% methyl cellulose gel, porous CaCO3 particles, or poly(lactide-co-glycolide) beads]. The bridging, however, never exceeded 24% at 12 days or 34% after 24 days. In contrast, when access of cells from the periosteum to the defect was prevented by means of microporous expanded polytetrafluoroethylene barrier membranes (GORE-TEX membrane), rhTGF-beta 1 caused a dose-dependent inhibition of bone regeneration. The bioactivity of the growth factor was confirmed by implantation of 5 or 10 micrograms rhTGF-beta 1 in 12 mm in diameter bicortical defects in rabbit calvaria, which resulted in complete bone healing within 28 days, whereas control defects displayed a bridging of 40%-50%. The findings support the concept, based on in vitro experiments by others, that TGF-beta 1 primarily has a proliferative effect on cells already committed to the osteoblastic lineage, but also imply that TGF-beta 1 may be inhibitory to induction of osteogenic cells in vivo.

Repeated bone repositioning in the growing rabbit calvarium hampers bone segment incorporation.

There has been concern among surgeons that multiple extended craniofacial procedures might be detrimental to the viability of the involved skeletal structures. This study aimed to explore the result of repeated bone repositionings in the growing rabbit calvaria. Seven immature rabbits were subjected to a three-stage surgical procedure, implying that four calvarial bone segments were originally harvested and repositioned according to a rotational scheme; after 6 weeks only three of the bone segments were harvested and repositioned and, finally, after an additional period of 6 weeks, two segments were repositioned. The results were evaluated by radiographic, histologic (with a special scoring system), and histomorphometric analysis. It was found that one or two cranioplasties did not markedly affect graft incorporation, but three procedures significantly reduced graft revascularization and integration. The findings are discussed with special reference to syndromic craniofacial disorders.

Treatment of segmental defects in long bones using osteopromotive membranes and recombinant human bone morphogenetic protein-2. An experimental study in rabbits.

The purpose of this study was to investigate whether barrier membranes that were earlier shown to promote bone healing in the craniofacial skeleton are capable of producing bone healing in long bone. defects by themselves or in combination with recombinant human bone morphogenetic protein 2 (rhBMP-2). Segmental defects (10 mm long) in the rabbit radius, known to heal as pseudoarthrosis-like defects, were used as the experimental model. Treatment with expanded polytetrafluoroethylene membranes (GORE-TEX Membrane) (n = 10) resulted in only minor amounts of bone formation within the defect and collapse of the membranes was common. When placement of membranes was combined with implantation of rhBMP-2 in a beaded biodegradable copolymeric PLA/PGA carrier, total bony bridging of the defects was accomplished within 10 weeks (n = 5). Osteopromotive membranes combined with mBMP-2 can therefore bring about complete healing of long bones. The membranes exclude soft tissue from the defect and at the same time keep the growth-stimulatory implant in place and maintain the anatomical contour of the bone. The combination of osteopromotive membranes and rhBMP-2 may be of. value in reconstructive bone surgery.

Importance of delivery systems for growth-stimulatory factors in combination with osteopromotive membranes. An experimental study using rhBMP-2 in rat mandibular defects.

This study was undertaken to investigate whether the choice of carrier/delivery system might be crucial for rhBMP-2 induced osteogenesis beneath osteopromotive membranes. Standardized 5-mm transosseous rat mandibular defects were implanted with recombinant human BMP-2 (rhBMP-2) with or without membrane placement. Two doses of rhBMP-2 (1 microg and 8 microg per defect) were delivered with either collagen sponge or bioabsorbable poly(D,L-lactide-coglycolide) (PLA/PGA) beads plus allogenic blood as carriers. Membrane-covered defects (no BMP) served as controls. Virtually all defects treated with rhBMP-2 without membrane placement already were bridged by new bone after 12 days, independent of rhBMP-2 dose or carrier material, and lateral bone growth was extensive outside the original defect. Membrane placement significantly decreased the stimulatory activity of the BMP, as seen after 12 days, even though osteogenesis was more advanced with rhBMP-2 and membrane compared to membrane alone. After 24 days, defects treated with membrane and rhBMP-2 in the PLA/PGA carrier were totally bridged with regenerated bone, whereas defects covered with membrane without BMP implantation displayed an average bone bridging of only 53%. In an overall analysis of the bone regeneration, the PLA/PGA carrier material was found to be superior to the collagen carrier in the presence of membranes, which was, in turn, more efficient than membrane placement alone (no rhBMP-2). There was much less lateral bone growth when BMP implantation was combined with membrane placement. It was concluded that bone formation beneath osteopromotive membranes may be significantly enhanced by rhBMP-2 and that the delivery system can affect the amount of bone formation obtained. For eventual clinical use, membrane placement has the advantage of keeping the growth-stimulatory implant in place as well as obtaining the desired anatomical contour of the bone formed.

Effects of different osteopromotive membrane porosities on experimental bone neogenesis in rats.

Biologically inert expanded polytetrafluorethylene (e-PTFE) membranes (GORE-TEX) have earlier been shown to improve healing of different types of bone defects, to be able to restore earlier existing bone, and to produce bone neogenesis. This study was performed to investigate the influence of membrane porosity on the osteopromotive efficacy and to determine bone neogenesis times in the rat. Three different e-PTFE membrane qualities with different porosities (internodal distances < 8, 20-25 and 100 microns) and four healing periods (6, 12, 18 weeks and 6 months) were studied. Dome-shaped e-PTFE membranes (5 mm inner diameter) were placed on denuded rat calvaria and covered with the periosteum and skin. After the respective time intervals, specimens were prepared for histology, and the bone obtained within the domes was quantified by an image analysis system. The results confirmed that it is possible to produce new bone by the use of the osteopromotion technique. The rate of bone neogenesis depended on the quality of membrane used; the membranes with the smallest internodal distance were less efficient than the others in that osteogenesis was somewhat delayed. The amount of new bone achievable was essentially already obtained after 6 weeks with the two most porous membranes, whereas the least porous one lagged behind. After 12 weeks there was no difference in the amount of newly formed bone. There was an obvious time sequence, in that the newly formed bone showed an increased maturity with longer observation periods. The material with the smallest internodal distance did not integrate well with the surrounding soft tissue, leading to a lack of stabilization of the membrane and more soft tissue ingrowth from the side. It is concluded that there is a porosity range within which osteogenesis beneath the membranes is optimal, tissue integration for stability is adequate enough, and soft connective tissue ingrowth is avoided.

Bone regeneration by a combination of osteopromotive membranes with different BMP preparations: a review.

The aim of these studies was to see if a combination of osteopromotive membranes of expanded polytetrafluoroethylene (e-PTFE; GORE-TEX) and BMP, known to separately promote bone healing, would be stimulatory if combined. Bilateral transosseous 'critical size' defects at the mandibular angles in adult male rats were treated with either (i) various BMP preparations only; ii) lateral and medial coverage with e-PTFE membranes only; iii) a combination of various BMPs and membranes; or iv) left untreated. Two semi-purified bovine BMPs (bBMP), comprising collagen as carrier material, and recombinant human (rh) BMP-2 (1, 2 or 8 micrograms), delivered in either biodegradable beads of polylactide/polyglycolide acid (PLA/PGA) or purified collagen, were tested. After 12 or 24 days, block biopsies were taken for histological analysis. The different materials were well tolerated by the hosts and elicited large amounts of newly formed bone widely spread in the surrounding soft tissue. The combinations of bBMP and membranes did not improve the rate of bone healing compared to membranes only. In contrast, the combination of rhBMP-2 in PLA/PGA with membranes was more efficacious than membrane placement only and resulted in bone bridging at 24 days, with a bone contour resembling the original anatomy. The combination of membrane placement with rhBMP-2 may be of value in the clinic for bone regenerative purposes. The results are also of general importance for choosing carrier materials for delivery of other growth-stimulatory substances in combination with membranes.

Healing of mandibular defects with different biodegradable and non-biodegradable membranes: an experimental study in rats.

Membranes, clinically used to improve bone regeneration according to the osteopromotion principle, have primarily been made of expanded polytetrafluoroethylene (Gore-Tex Membrane). Recently, different types of biodegradable membranes have become available. This investigation explored the osteopromotive potential of 10 different biodegradable and non-biodegradable membrane materials. Scanning electron microscopy revealed quite different surface configurations of these membranes, even though some of them were chemically closely related. Standardized, transosseous, critical size mandibular defects were made bilaterally in adult rats and were randomly covered with the different types of membrane. After 6 wk of healing, evaluation was performed by light microscopy according to a histological scoring system. Varying degrees of bone healing were seen beneath the different membranes. Some of the membranes (such as Gore-Tex Augmentation Material, Millipore and Resolut 'long term') revealed a good osteopromotive effect, whereas others had little or no beneficial effects on bone healing. Certain membrane materials caused a pronounced inflammatory response in the surrounding soft tissue, while others displayed a low inflammatory reaction. The study shows that different membranes differ strongly in osteopromotive efficacy, even if seemingly chemically closely related. Furthermore, the study demonstrates that membranes developed primarily for periodontal regeneration purposes may not be adequate to promote bone healing.

Malformations of the maxillofacial region induced by retinoids in an experimental system.

Treatment of pregnant Sprague-Dawley rats with etretinate or retinoic acid on pregnancy Day 8.5-9.0 resulted in craniofacial malformations in 100% of the embryos. A morphological investigation of the maxillofacial malformations was undertaken. Retinoid-exposed embryos showed a reduced skull base, flattened and elongated occiput and micrognathia. The malar bones were reduced or missing. Meckel's cartilage was delayed in differentiation as was the mandibular bone. The fusion between different facial processes was disturbed which resulted in facial and palatal clefts. Disturbance of the development of the hypophysis was combined with persisting Rathke's pouch. Aplasia of incisor and molar tooth buds was seen as was aplasia of salivary gland ducts. The facial artery was hyperplastic.

Enzyme histochemical analysis of Meckel's cartilage.

Osteogenesis of the body of the mandible in embryonic and neonatal rats was studied histologically and by histochemistry to determine the role of Meckel's cartilage in bone formation. Meckel's cartilage showed intense activity of lactate dehydrogenase and NADH2-diaphorase and weak activity of acid phosphatase, indicating a functioning citric acid cycle, pentose phosphate shunt and a capacity for anaerobic metabolism. The activity of these enzymes declined after hypertrophy of Meckel's cartilage. Alkaline phosphatase was the major enzyme of mineralising mandibular osteoid and was present in the osteoblasts and osteoprogenitor cells but not in Meckel's cartilage. After the differentiation of Meckel's cartilage and intramembranous bone, Meckel's cartilage supported mandibular bone formation by endochondral ossification in the anterior part of the mandible.

Characterization of phosphoglycerate mutase isoenzymes from free dissected facial processes.

To characterize the three phosphoglycerate mutase (PGM) isoenzymes present in rat facial processes (types MM, BB, and MB), their sensitivity to reagents of the sulfhydryl groups and to heat treatment has been studied. Type BB PGM was not affected by the -SH group reagents; type MB PGM was inhibited about 50%, and type MM PGM was fully inhibited. Type MB PGM showed a greater heat lability than type MM PGM. There was a developmental change from type BB PGM from the 9th embryonic day to isoenzymes MB and MM on the 15th embryonic day. Isoenzyme development was first seen in mandibular processes, followed by maxillary, lateral nasal, and medial nasal processes.