Anders Linde

Healing of bone defects by guided tissue regeneration.

In this study we describe a principle for the accomplishment of bone regeneration based on the hypothesis that different cellular components in the tissue have varying rates of migration into a wound area during healing. By a mechanical hindrance, using a membrane technique, fibroblasts and other soft connective-tissue cells are prevented from entering the bone defect so that the presumably slower-migrating cells with osteogenic potential are allowed to repopulate the defect. Defects of standard size were created bilaterally through the man-dibular angles of rats. On one side of the jaw the defect was covered with Teflon membranes, whereas the defect on the other side served as control. Histologic analysis after healing demonstrated that on the test (membrane) side, half the number of animals showed complete bone healing after 3 weeks and all animals showed complete healing after 6 weeks. Little or no sign of healing was evident on the control side even after an observation period of 22 weeks.

Shh signaling within the dental epithelium is necessary for cell proliferation, growth and polarization

Sonic hedgehog (Shh), a member of the mammalian Hedgehog (Hh) family, plays a key role during embryogenesis and organogenesis. Tooth development, odontogenesis, is governed by sequential and reciprocal epithelial-mesenchymal interactions. Genetic removal of Shh activity from the dental epithelium, the sole source of Shh during tooth development, alters tooth growth and cytological organization within both the dental epithelium and mesenchyme of the tooth. In this model it is not clear which aspects of the phenotype are the result of the direct action of Shh on a target tissue and which are indirect effects due to deficiencies in reciprocal signalings between the epithelial and mesenchymal components. To distinguish between these two alternatives and extend our understanding of Shhs actions in odontogenesis, we have used the Cre-loxP system to remove Smoothened (Smo) activity in the dental epithelium. Smo, a seven-pass membrane protein is essential for the transduction of all Hh signals. Hence, removal of Smo activity from the dental epithelium should block Shh signaling within dental epithelial derivatives while preserving normal mesenchymal signaling. Here we show that Shh-dependent interactions occur within the dental epithelium itself. The dental mesenchyme develops normally up until birth. In contrast, dental epithelial derivatives show altered proliferation, growth, differentiation and polarization. Our approach uncovers roles for Shh in controlling epithelial cell size, organelle development and polarization. Furthermore, we provide evidence that Shh signaling between ameloblasts and the overlying stratum intermedium may involve subcellular localization of Patched 2 and Gli1 mRNAs, both of which are targets of Shh signaling in these cells.

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)

OSTEOPROMOTION : A SOFT-TISSUE EXCLUSION PRINCIPLE USING A MEMBRANE FOR BONE HEALING AND BONE NEOGENESIS

The research reviewed in this paper constitutes a series of investigations intended to develop and evaluate a new membrane technique, which provides improved conditions for osteogenesis during healing of bone defects and restitution of earlier existing bone. The technique has also been shown to aid in bone grafting as well as having the capacity to create new bone for reconstructive purposes. According to this methodology, membranes are utilized to create a space in the tissue in which osteogenesis can occur relatively unimpeded. The paper provides a review of our initial animal experimental work as well as some clinical studies with special emphasis on membrane use in conjunction with dental implants. Possible mechanisms behind the efficacy of the membrane technique are reviewed, and future perspectives of development are also discussed. The osteopromotive membrane technique represents a principally new and major advance in bone biology and reconstructive skeletal surgery. Based on the results obtained by us and by others, the technique is presently utilized clinically in some routine applications. J Periodontol 1993; 64:1116-1128.

Creation of new bone by an osteopromotive membrane technique : an experimental study in rats

Domes, 5 and 8 mm in diameter, were made of expanded polytetrafluorethylene membrane with different degrees of stiffness and internodal distance. The domes were placed on denuded calvarial bones of rats and covered by the skin and periosteal flaps. Histologic evaluation 9 to 16 weeks after surgery showed the formation of various amounts of new bone on the calvarial bone surface inside the domes. The amount of bone neogenesis was dependent on membrane qualities, such as stiffness and porosity, and the length of the healing period. In the most successful experiments, about 80% of the dome volume was filled with newly formed bone, whereas in other experiments considerable amounts of connective tissue were present. Using bioabsorbable membrane domes proved less successful in that they did not maintain their shape and thus did not provide space for bone formation. This study showed that it is possible to obtain bone neogenesis by an osteopromotive membrane technique. This possibility may eventually be of great significance for reconstructive 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.

Factors in implant integration failure after bone grafting: An osteometric and endocrinologic matched analysis

In a retrospective analysis of 49 patients who received bone graft augmentation to the maxillary sinuses in conjunction with implant insertion, 11 patients had a significantly reduced success rate. The aim of the present study was to determine whether bone quality, as assessed by osteometry and selected haematologic and urinary tests, influences the integration of implants, and whether such data can be prognostically useful. Relative bone mass density (BMD%) differed significantly among these patients as compared to age- and sex-matched control patients receiving the same reconstructive treatment (P=0.01). Other parameters tested did not demonstrate any significant differences. In addition to local complications, general disorders, such as osteoporosis, must be considered in cases of excessive implant loss.

Recombinant bone morphogenetic protein-2 enhances bone healing, guided by osteopromotive e-PTFE membranes: an experimental study in rats.

It has been shown earlier that it is possible to improve bone healing, to regenerate previously existing bone, and to create new bone by means of an osteopromotive membrane technique. The present study addresses the question of whether it is possible to combine this technique with a locally applied factor, stimulatory to osteogenesis. Circular transosseous ‘critical size’ defects in mandibles of rats were either implanted with recombinant human bone morphogenetic protein type 2 (rhBMP-2) or were left empty; half the number of implanted and half the number of empty defects were covered with an expanded polytetrafluoroethylene (e-PTFE) membrane (GORE-TEX®). Results were evaluated after 12 and 24 days of healing by a histomorphological scoring system. Implantation of rhBMP-2 alone resulted in bony bridging of the defect after only 12 days, but also in voluminous amounts of new bone outside the original defect area. When rhBMP-2 was combined with membrane, newly formed woven bone bridged the defect and the bone contour was maintained by the membrane. The combined treatment with membrane and rhBMP-2 demonstrated a significantly better bone healing than with e-PTFE membrane alone at both 12 days and 24 days of healing. It was concluded that rhBMP-2 has a strong osteoinductive potential and, in contrast to what was found earlier with other types of BMP preparations, this potential was retained when combining the rhBMP-2 with the osteopromotive membrane technique, yielding better bone healing than with the membrane alone, and at the same time maintaining the bone contour. This combination may have important therapeutic applications for osseous healing and in reconstructive surgery. The study also shows the importance of an appropriate carrier material when applying stimulatory substances to enhance bone formation in combination with a membrane.

Abnormal Hair Development and Apparent Follicular Transformation to Mammary Gland in the Absence of Hedgehog Signaling

Summary We show that removing the Shh signal tranducer Smoothened from skin epithelium secondarily results in excess Shh levels in the mesenchyme. Moreover, the phenotypes we observe reflect decreased epithelial Shh signaling, yet increased mesenchymal Shh signaling. For example, the latter contributes to exuberant hair follicle (HF) induction, while the former depletes the resulting follicular stem cell niches. This disruption of the niche apparently also allows the remaining stem cells to initiate hair formation at inappropriate times. Thus, the temporal structure of the hair cycle may depend on the physical structure of the niche. Finally, we find that the ablation of epithelial Shh signaling results in unexpected transformations: the follicular outer root sheath takes on an epidermal character, and certain HFs disappear altogether, having adopted a strikingly mammary gland-like fate. Overall, our study uncovers a multifaceted function for Shh in sculpting and maintaining the integrity and identity of the developing HF.

Role of osteopromotion in experimental bone grafting to the skull: A study in adult rats using a membrane technique

This study explores the effect of an osteopromotive membrane technique in a mature animal model on the survival of membranous and endochondral bone inlays in mandibular defects and membranous bone onlays on the calvarial roof. Twenty-eight adult male rats received fibular or mandibular inlay bone grafts to trephine defects in the mandibular angle, as well as mandibular disc onlay grafts to the parietal and frontal bone regions. The results were assessed by gross inspection and light microscopy after 12 weeks. Membrane use markedly promoted bone deposition in the defects. The membranous bone inlays showed complete incorporation to the margins of the defect, whereas the endochondral grafts at all times were covered by a thin fibrous capsule and failed to incorporate. Onlay grafts generally resorbed substantially, but the grafts covered by a membrane seemed more active, developed an increased cancellous component, and showed less pronounced volumetric loss. The findings confirm the fact that a biological difference exists between membranous and endochondral bone. They also confirm the osteopromotive effect of the membrane technique, and suggest that the amount of bone needed for transplantation can be reduced using this method.