PubMed Health⌕ Search

Biomedical subjects

C Dahlin

Publications and source records attributed to C Dahlin.

At least 19 recordsLinked to original sources
PubMed2006

Osseointegration of oxidized and turned implants in circumferential bone defects with and without adjunctive therapies: an experimental study on BMP-2 and autogenous bone graft in the dog mandible.

The aim of the study was to compare the integration and implant stability of turned and oxidized titanium implants when placed in experimental bone defects with autogenous bone graft, BMP-2 or without adjunctive therapy. Four defects were prepared on each side of the mandible of 12 mongrel dogs five months after tooth extractions. Implants with turned and oxidized surfaces were placed in the defects. The circumferential gaps were filled with either autogenous bone grafts, a BMP-allogeneic dog mixture in a thermoplastic carrier, carrier alone or left without any treatment (control). There were no statistically significant differences between control and treated sites, neither for turned nor for oxidized implants with regard to histomorphometric measurements in ground sections and to implant stability as measured with resonance frequency analysis (RFA) after 4 and 12 weeks of healing. However, oxidized implants showed a significantly higher stability after 4 weeks and a tendency (p < 0.1) of that after 12 weeks. Histomorphometry showed more bone contacts for oxidized than for turned implants. It is concluded that oxidized implants gain stability more rapidly and integrate with more bone contacts than implants with a turned surface when placed in bone defects.

Animals↗
PubMed2001

The importance of the C-terminal region and Cys residues for the membrane association of the NADPH:protochlorophyllide oxidoreductase in pea.

In vitro chloroplast import reactions and thylakoid association reactions have been performed with a series of C-terminal deletions and Cys-to-Ser substitution mutants of the pea NADPH:protochlorophyllide oxidoreductase (POR; EC 1.6.99). C-terminal deletions of the precursor POR (Delta362-400, Delta338-400, Delta315-400 and Delta300-400) were efficiently translocated across the chloroplast envelope. However, except the Delta396-400 mutant, no C-terminal deletion mutants or Cys-to-Ser substitution (Cys119, Cys281 and Cys309) mutants resisted post-treatment with thermolysin after the thylakoid association reactions. This suggests that these mutants were unable to properly associate to the thylakoids due to changes of the protein conformation of POR.

Binding Sites↗
PubMed2001

Association of the NADPH:protochlorophyllide oxidoreductase (POR) with isolated etioplast inner membranes from wheat.

Membrane association of NADPH:protochlorophyllide oxidoreductase (POR, EC: 1.6.99.1) with isolated prolamellar bodies (PLBs) and prothylakoids (PTs) from wheat etioplasts was investigated. In vitro-expressed radiolabelled POR, with or without transit peptide, was used to characterize membrane association conditions. Proper association of POR with PLBs and PTs did not require the presequence, whereas NADPH and hydrolysable ATP were vital for the process. After treating the membranes with thermolysin, sodium hydroxide or carbonate, a firm attachment of the POR protein to the membrane was found. Although the PLBs and PTs differ significantly in their relative amount of POR in vivo, no major differences in POR association capacity could be observed between the two membrane systems when exogenous NADPH was added. Experiments run with only an endogenous NADPH source almost abolished association of POR with both PLBs and PTs. In addition, POR protein carrying a mutation in the putative nucleotide-binding site (ALA06) was unable to bind to the inner membranes in the presence of NADPH, which further demonstrates that the co-factor is essential for proper membrane association. POR protein carrying a mutation in the substrate-binding site (ALA24) showed less binding to the membranes as compared to the wild type. The results presented here introduce studies of a novel area of protein-membrane interaction, namely the association of proteins with a paracrystalline membrane structure, the PLB.

Adenosine Triphosphate↗
PubMed2000

Alveolar ridge repair in a canine model using rhTGF-beta 1 with barrier membranes.

In both normal and membrane-assisted situations, healing events are modulated by the activity of endogenous protein molecules known as cytokines. Due to its mitogenic and chemotactic characteristics, the addition of rhTGF-beta 1 should increase the rate of osteogenesis or increase the potential for bone regeneration in oral osseous defects. This study evaluates the effects of an osteoconductive biodegradable matrix incorporating human recombinant transforming growth factor beta 1 (rhTGF-beta 1) in conjunction with barrier membranes on bone regeneration in canine alveolar ridge defects. A matrix of calcium carbonate and hydroxyethyl starch served as the carrier for test concentrations of 2.0 micrograms/0.8 ml and 20.0 micrograms/0.8 ml of rhTGF-beta 1. One surgically prepared site in each of 13 adult male fox-hounds received 1 of 4 experimental treatment regimens, with 6 sites utilizing barrier membranes. Four sites in each of 2 additional animals, two containing carrier matrix only and 2 with the additional barrier membrane, served as controls. Specimens were retrieved after 2 months of healing and processed for routine light microscopy. The quantity and composition of regenerated bone was examined. Analysis of variance revealed a statistically significant increase (P < 0.05) in the development of bone with the use of rhTGF-beta 1. Likewise, a statistically significant increase in regeneration was found in membrane-protected sites over nonmembrane-protected sites. No statistically significant difference was noted between the low and high dose treatments. The authors conclude that the use of rhTGF-beta 1 in conjunction with a barrier membrane greatly enhances bone regeneration in osseous oral defects.

Alveolar Process↗
PubMed1999

The role of protein surface charge in catalytic activity and chloroplast membrane association of the pea NADPH: protochlorophyllide oxidoreductase (POR) as revealed by alanine scanning mutagenesis.

NADPH:protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide (pchlide) to chlorophyllide (chlide) in the biosynthesis of chlorophyll. POR is a peripheral membrane protein that accumulates to high levels in the prolamellar bodies of vascular plant etioplasts and is present at low levels in the thylakoid membranes of developing and mature plastids. Clustered charged-to-alanine scanning mutagenesis of the pea (Pisum sativum L.) POR was carried out and the resulting mutant enzymes analyzed for their ability to catalyze pchlide photoconversion in vivo and to associate properly with thylakoid membrane preparations in vitro. Of 37 mutant enzymes examined, 5 retained wild-type levels of activity, 14 were catalytically inactive, and the remaining 18 exhibited altered levels of function. Several of the mutant enzymes showed temperature-dependent enzymatic activity, being inactive at 32 degrees C, but partially active at 24 degrees C. Mutations in predicted alpha-helical regions of the protein showed the least effect on enzyme activity, whereas mutations in predicted beta-sheet regions of the protein showed a consistent adverse affect on enzyme function. In the absence of added NADPH, neither wild-type POR nor any of the mutant PORs resisted proteolysis by thermolysin following assembly onto the thylakoid membranes. In contrast, when NADPH was present in the assay mixture, 13 of the 37 mutant PORs examined were found to be resistant to thermolysin upon treatment, suggesting that the mutations did not affect their ability to be properly attached to the thylakoid membrane. In general, the replacement of charged amino acids by alanine in the most N- and C-terminal regions of the mature protein did not significantly affect POR assembly, whereas mutations within the central core of the protein (between residues 86 and 342) were incapable of proper attachment to the thylakoid. Failure to properly associate with the thylakoid membrane in a protease resistant manner was only weakly correlated to loss of catalytic function. These studies are a first step towards defining structural determinants crucial to POR function and intraorganellar localization.

Alanine↗
PubMed1999

Effect of different microstructures of e-PTFE membranes on bone regeneration and soft tissue response: a histologic study in canine mandible.

The purpose of the present study was to compare the effect of 3 types of titanium reinforced e-PTFE membranes (GTRM #1, #2, and #3) on bone regeneration and tissue integration. GTRM #1 was a standard titanium reinforced membrane, GTRM #2 was a prototype characterized by a more open total surface microstructure and GTRM #3 was a prototype characterized by two extremely porous external layers separated by a totally occlusive internal layer. The membranes were used to cover saddle type ridge defects surgically created in the mandible of 6 dogs. After a healing period of 6 months, all the membrane protected sites demonstrated almost complete osseous healing of the defects. GTRM #3 specimens showed the most favourable biologic response, in fact they were characterized by a larger surface of contact between the membrane and the regenerated bone, but from a clinical point of view GTRM #3 material was too difficult to remove. The results of this study suggest that an extremely open porous microstructure, in combination with a totally occlusive barrier, may provide significant improvements in regenerative outcomes. However, these design characteristics may be applied only to resorbable devices, which do not require removal.

Alveolar Process↗
PubMed1999

Five-year evaluation of implants placed at extraction and with dehiscences and fenestration defects augmented with ePTFE membranes: results from a prospective multicenter study.

BACKGROUND: Barrier membranes have been used to promote bone ingrowth on implants with dehiscences and fenestrations. Membranes also have been used to protect defects adjacent to implants placed at the time of extraction. The concept of guided bone regeneration relates to preferentially allowing cells from bone to migrate into various defects while excluding fibrous tissue and epithelium. The purpose of these procedures is to enhance bone-to-implant contact at the treated sites and to prevent mucosal complications. PURPOSE: The purpose of this article is to report clinical outcomes for implants placed at the time of extraction and augmented with expanded polytetrafluoroethylene (ePTFE) and followed for 5 years. The outcomes for implants with dehiscences and fenestrations augmented with ePTFE barriers and followed up to 5 years also are reported. METHODS AND MATERIALS: Four treatment centers participated in this study (Tucson, Gothenburg, Spokane, and Leuven). In the extraction group, teeth were removed for varying reasons, and Brånemark implants were placed and stabilized within the host bone. Defects present at the coronal implant aspect were covered with ePTFE barrier membranes. Flaps were rotated to cover the membrane-treated sites. If exposure of the material occurred prior to second-stage surgery, the membranes were removed. Barriers remaining unexposed were removed at second-stage surgery. The implants were followed up to 5 years. In the fenestration and dehiscence group, implants with exposed threads were augmented with ePTFE barrier membranes. The barriers were removed at appropriate intervals, and the patients were followed up to 5 years. Radiographic measurements were made from nonstandardized periapical radiographs at abutment connection and 1, 3, and 5-year follow-up visits. RESULTS: Forty patients participated in the extraction group. They received a total of 49 implants. Three implants failed prior to loading. The 5-year cumulative survival rates for implants placed at the time of extraction were 93.9% and 93.8%, respectively, for maxillary and mandibular implants. The average maxillary mesial and distal marginal bone loss (1-5 yr) was 0.3 mm (standard deviation [SD] = 1.5) and 0.3 mm (SD = 1.0). In mandibles, the average mesial and distal bone loss (1-5 yr) was -0.2 mm (SD = 0.5) and -0.05 mm (SD = 0.6), respectively. The dehiscence and fenestration group included 44 patients. Twenty-six were followed for up to 5 years. Eight patients experienced total implant failure. For dehiscences and fenestrations, the cumulative survival rates were 76.8% and 83.8% for maxillary and mandibular implants, respectively. The average maxillary mesial and distal bone loss (1-5 yr) was 0.4 mm (SD = 0.8) and 0.2 mm (SD = 0.9), respectively. In mandibles, the average mesial and distal marginal bone loss was 0.3 mm (SD = 0.9) and 0.3 mm (SD = 0.8), respectively. CONCLUSIONS: Implants placed at the time of extraction and augmented with ePTFE barrier membranes have favorable long-term predictability. On the other hand, long-term evaluation of implant dehiscences and fenestrations augmented with barrier membranes indicates that they have less favorable 5-year survival rates. Membrane augmentation of these may be questioned.

Adolescent↗
PubMed1998

Histological morphology of the e-PTFE/tissue interface in humans subjected to guided bone regeneration in conjunction with oral implant treatment.

The purpose of the present investigation was to study the histological morphology of the e-PTFE membrane/tissue interface in 5 humans subjected to GBR treatment in conjunction with oral implant treatment. Oral implants (Brånemark System) were inserted in extraction sockets 1 to 2 months after extraction of periodontally diseased teeth. The implants were placed approximately 2 mm below the surrounding bone margins. Specially designed 3 mm high cover-screws with horizontal slits for tissue ingrowth were applied to the implants and covered with e-PTFE membranes (GoreTex Augmentation Material). Re-entry was made 7 months later, except in 1 case where the membrane was removed 1 month postoperatively due to exposure and infection. In the remaining 4 sites, circular biopsies comprising membranes, tissues and cover-screws were retrieved. The specimens were fixated, processed and sectioned for light- and transmission electron microscopy. The space between the membrane and the cover-screw was occupied by fibrous tissue and varying amounts of bone. A cell- and vessel-rich fibrous tissue separated the bone from the membrane in the majority of the specimens. The membrane itself was penetrated by fibrous tissue. Fibroblasts and macrophages were the main cell types found in the fibrous tissue. The presence of irregularly shaped cells and unevenly distributed collagen fibres, indicated that the absence of bone formation may be due either to micromovements in the e-PTFE/tissue interface or to formation of fibrous tissue underneath the membrane by penetrating fibroblasts or a combination of these 2 phenomena.

Bone Regeneration↗
PubMed1996

Connective tissue grafting for primary closure of extraction sockets treated with an osteopromotive membrane technique: surgical technique and clinical results.

This article describes a grafting technique using connective tissue to predictably obtain primary closure of extraction sockets treated with an osteopromotive membrane technique. This technique was used for a total of 24 sites in 22 consecutive patients to regenerate alveolar bone in severely damaged ridges and in conjunction with implants immediately installed into extraction sites. Two sites (8.3%) were complicated by premature membrane exposure that necessitated early removal. In the remaining 22 sites, membranes remained completely covered for a mean period of 23.75 weeks (SD = 8.21 weeks; range = 10 to 38 weeks).

Adult↗
PubMed1995

The in vitro assembly of the NADPH-protochlorophyllide oxidoreductase in pea chloroplasts.

The NADPH-protochlorophyllide oxidoreductase (pchlide reductase, EC 1.6.99.1) is the major protein in the prolamellar bodies (PLBs) of etioplasts, where it catalyzes the light-dependent reduction of protochlorophyllide to chlorophyllide during chlorophyll synthesis in higher plants. The suborganellar location in chloroplasts of light-grown plants is less clear. In vitro assays were performed to characterize the assembly process of the pchlide reductase protein in pea chloroplasts. Import reactions employing radiolabelled precursor protein of the pchlide reductase showed that the protein was efficiently imported into fully matured green chloroplasts of pea. Fractionation assays following an import reaction revealed that imported protein was targeted to the thylakoid membranes. No radiolabelled protein could be detected in the stromal or envelope compartments upon import. Assembly reactions performed in chloroplast lysates showed that maximum amount of radiolabelled protein was associated to the thylakoid membranes in a thermolysin-resistant conformation when the assays were performed in the presence of hydrolyzable ATP and NADPH, but not in the presence of NADH. Furthermore, membrane assembly was optimal at pH 7.5 and at 25 degrees C. However, further treatment of the thylakoids with NaOH after an assembly reaction removed most of the membrane-associated protein. Assembly assays performed with the mature form of the pchlide reductase, lacking the transit peptide, showed that the pre-sequence was not required for membrane assembly. These results indicate that the pchlide reductase is a peripheral protein located on the stromal side of the membrane, and that both the precursor and the mature form of the protein can act as substrates for membrane assembly.

Adenosine Triphosphate↗
PubMed1994

Restoration of mandibular nonunion bone defects. An experimental study in rats using an osteopromotive membrane method.

Standardized through-and-through critical size defects were created in rat mandibles. After 12 weeks, the sites revealed a massive ingrowth of soft connective tissue, forming a transosseous core filling the defects. Upon reentry, the soft tissue inside the remaining bone defects was removed. On one side of the jaw, the defect was covered both buccally and lingually with an expanded polytetrafluoroethylene (e-PTFE) membrane, but on the other side no membrane was placed. Histologic analysis after 6 weeks revealed an essentially complete healing with bone of the membrane-covered defects. No cartilage was present in any of the specimens. At the control sites (no membrane), the amount of newly produced bone showed variations, most through defects revealing the presence of a remaining central portion of connective tissue. This investigation thus showed that predictable and successful bone regeneration can be achieved by the osteopromotive membrane method in treatment of nonunion defects filled with mature connective tissue.

Animals↗
PubMed1994

Qualitative and quantitative comparative study on different filling materials used in bone tissue regeneration: a controlled clinical study.

This study compared, in a human model, the ability of (1) expanded polytetrafluorethylene (e-PTFE) membranes plus bone-chip autografts, (2) e-PTFE membranes plus demineralized freeze-dried bone, (3) e-PTFE membranes plus a new form of demineralized allograft bone tissue, and (4) e-PTFE membranes alone to enhance bone regeneration around dental implants placed into recent extraction sockets. The histologic results demonstrated that, in humans, guided tissue regeneration techniques are capable of producing new bone osseointegrated with titanium dental implants. Among the graft materials, autogenous bone provided the densest and the greatest amount of bone formation, but use of demineralized freeze-dried bone and a new form of de-mineralized allogenic bone matrix also improved bone regeneration compared to membranes alone after 6 months of healing.

Alveolar Bone Loss↗
PubMed1993

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.

Animals↗
PubMed1993

Bone regeneration by the osteopromotion technique using bioabsorbable membranes: an experimental study in rats.

An osteopromotive technique has been developed that allows improved bone regeneration as well as bone neogenesis using porous, inert, nondegradable membranes made of expanded polytetrafluoroethylene (e-PTFE). For certain applications, however, it would be advantageous to use bioabsorbable membranes (BAMs), thus avoiding a surgical reentry for membrane removal. In this randomized comparison study the osteopromotive potential of BAMs was investigated in standardized "critical size defects" (5 mm in diameter) in the rat mandible. Three membrane types were tested and comparisons were made with e-PTFE membrane. The BAMs consisted of polylactic/polyglycolic acid copolymers designed to give the membranes different absorption times when implanted in the tissue. Histologic analysis after healing periods of 1 to 12 weeks demonstrated the BAMs to be well tolerated by the tissue, causing just a mild inflammatory reaction along the membrane surfaces as long as the material remained in the tissue. The BAMs were found to be as efficient as e-PTFE membranes in that the bone repair was not significantly different with any of the four membrane types. However, healing in conjunction with one type of BAM seemed to occur somewhat more rapidly. Some cartilage was present at the early healing stages in the defects treated with BAMs, but disappeared at later stages. The results of this study show that BAMs are a valid alternative to e-PTFE membranes to improve bone regeneration, but indicate that further technical development of the membrane material is necessary.

Absorption↗
PubMed1993

The role of early versus late removal of GTAM membranes on bone formation at oral implants placed into immediate extraction sockets. An experimental study in dogs.

The purpose of this study was to compare the effect of early versus late removal of expanded polytetrafluoroethylene (e-PTFE) membranes on bone formation at oral implants. Thirty Brånemark fixtures were placed into immediate extraction sockets with buccal bone dehiscences augmented by e-PTFE membranes. At 4 weeks, the membranes and underlying soft tissues were removed from 5 implants, but at 16 sites only the membranes were extirpated. In 9 sites, the membranes remained in place during the healing period. Sixteen weeks after fixture insertion, the sites in which the membrane was retained (MRET) showed an average of 5.2 mm of clinical bone height increase (100% of bone fill). For sites where the membrane together with underlying soft tissues were removed (MRB), the corresponding value was 2.0 mm (42% of bone fill). Implants at which only the membrane was removed (MR) showed the least clinical bone height increase (1.0 mm), resulting in 21% coverage of original threads. Histometric measurements verified that the MRET sites had the least distance from the top of the fixture to the newly formed bone level (0.4 mm). However, in contrast with the clinical findings, the histometric analyses showed that the MRB group had the greatest remaining bone defect (3.3 mm). The clinical and histometric results of the MRET group were statistically better, though, compared with those of the other two groups. Biopsies, removed from beneath the membranes, revealed slightly inflamed connective tissue, containing spicules of newly formed bone, indicating that more bone might have been created if the membranes had been retained longer.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Bone Loss↗
PubMed1993

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.

Animals↗
PubMed1993

Stimulation of early bone formation by the combination of an osteopromotive membrane technique and hyperbaric oxygen.

Large bone defects often heal incompletely as a result of ingrowth of connective tissue. By using a mechanical hindrance, a porous expanded polytetrafluoroethylene (e-PTFE) membrane, it is possible to prevent fibroblasts and other soft connective tissue cells from entering the defect, thereby allowing osteogenesis to occur unhindered. As evidenced in several investigations, this osteopromotive membrane technique causes a strongly improved bone regeneration of well defined osseous lesions. Hyperbaric oxygen treatment has also been shown to accelerate bone healing. In this study the value of combining the two techniques was investigated. Through-and-through bone defects, 5 mm in diameter, were produced unilaterally in the angular region of the mandibles of adult rats (n = 60); the defects in half the number of animals were covered lingually and buccally with membranes. The animals were then divided into four groups: treatment with membrane alone, treatment with hyperbaric oxygen alone, combined treatment, and no treatment. Histological examination of the defects after 14 days showed that the combination of techniques had resulted in significant improvement in bone healing, compared with hyperbaric oxygen or the membrane technique alone. Synergistic effects can thus be achieved by the use of membranes and stimulatory factors for bone regeneration.

Animals↗