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Biomedical subjects

M Sharawy

Publications and source records attributed to M Sharawy.

At least 19 recordsLinked to original sources
PubMed2001

The effects of rhBMP-2 on human osteosarcoma cells and human gingival fibroblasts in vitro.

Certain cells of the periodontium are necessary for the regeneration of tissues that are destroyed as a result of periodontal disease. There has been debate regarding which cells are the primary participants in periodontal regeneration. It is a well-known fact that osteoblasts are essential in new bone formation, but controversy surrounds the role that gingival fibroblasts may play in the regeneration of the hard tissues of the periodontium. If gingival fibroblasts could contribute to the regeneration of these tissues, they might provide an additional source of progenitor cells. The bone morphogenetic proteins are potent stimulators of cell differentiation and have been shown to induce new bone formation in many experimental models. This project investigated the ability of recombinant human bone morphogenetic protein-2 (rhBMP-2) to (1) enhance the production of markers of osteoblastlike cells (osteocalcin and mineralization in culture) in human osteosarcoma cells (MG63) and to (2) induce the expression of an osteoblast phenotype in cultured human gingival fibroblasts (HGFs). MG63 cells and pooled HGFs were exposed to varying concentrations of rhBMP-2 for 24, 48, and 72 hours after 9 days in culture, and osteocalcin levels were measured by enzyme immunosorbent assay in the cell supernatants. In addition, the cells were exposed to rhBMP-2 for 72 hours after 18 days in culture, and mineralization was determined by the Von Kossa stain. The rhBMP-2 had an inhibitory effect on both osteocalcin production and mineralization (p < 0.05) in MG63 cells compared with untreated controls. In addition, increasing doses of rhBMP-2 inhibited both osteocalcin and mineralization in HGF cells. These results suggest that HGFs can express an osteoblastic phenotype when exposed to rhBMP-2; however, rhBMP-2 has inhibitory effects at higher rhBMP-2 doses in both cell types and may, in fact, be inhibitory to MG63 cells.

Bone Morphogenetic Protein 2↗
PubMed2001

A bioengineered implant for a predetermined bone cellular response to loading forces. A literature review and case report.

The presence of fibrous tissue has long been known to decrease the long-term survival of a root-form implant. Excessive loads on an osseointegrated implant may result in mobility of the supporting device, and excessive loads may also fracture an implant component or body. Although several conditions may cause crestal bone loss, one of these may be prosthetic overload. Excessive loads on the bone cause strain conditions to increase. These microstrains on the bone may affect the bone remodeling rate in a direct relationship. When strain conditions to the interfacial bone are in the mild overload zone, an increased bone remodeling response occurs, which results in a reactive woven bone formation that is less mineralized and weaker. Greater stresses may cause the interfacial strain to reach the pathologic overload zone and may cause microfracture of the bone, fibrous tissue formation, and/or bone resorption. Recent reports suggest that the bone remodeling rate next to an implant may be used to evaluate biomechanical conditions and their influence on the implant-to-bone interface. These include a number of factors, such as loading conditions, implant body surface conditions, and implant design. For a given load condition, the implant design is one of the primary factors that determine the resultant strain at the interface. A predetermined goal was established to bioengineer a dental implant to load the bone at the interface in a predetermined stress strain relationship, in order to maintain lamellar bone at the interface. A case report is presented of 2 bioengineered implants loaded for 1 year, which demonstrates that the bone was primarily lamellar in structure, the bone turnover rate was less than 5 microns/day, and was the same as the bone away from the interface. These findings corroborate those observed in a prior animal study reported with the same implant design. Although the number of implants evaluated in those 2 reports is few, they support a predetermined histological outcome.

Adult↗
PubMed2000

Ultrastructural characterization of the rabbit mandibular condyle following experimental induction of anterior disk displacement.

Previous studies in our laboratory have shown that surgical induction of anterior disk displacement (ADD) in the rabbit craniomandibular joint (CMJ) leads to cellular and extracellular alterations consistent with osteoarthritis. Similar findings were also reported in human ADD as well as osteoarthritis of other joints. The purpose of this study was to further characterize these histopathological findings at the ultrastructural level. The right joint of 15 rabbits was exposed surgically and all discal attachments were severed except for the posterior attachment. The disk was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Mandibular condyles were excised 2 weeks following surgery and processed for transmission electron microscopy. Experimental condyles showed neovascularization, fibrillation and vacuolation of the extracellular matrix and an increase in the number of apoptotic cells compared to controls. In addition, chondrocytes in osteoarthritic cartilage showed an increase in the amounts of rough endoplasmic reticulum and Golgi complex suggesting an increase in protein synthesis. The presence of thick collagen fibers in osteoarthritic cartilage supports our previous immunohistochemical results of the presence of type I collagen instead of normally existing type II collagen. It was concluded that surgical induction of ADD in the rabbit CMJ leads to ultrastructural changes in the mandibular condylar cartilage consistent with degenerative alterations known to occur in osteoarthritis.

Animals↗
PubMed1997

Implant site assessment using panoramic cross-sectional tomographic imaging.

OBJECTIVES: The purpose of this study was to evaluate the ability of two different panoramic imaging systems to produce cross-sectional images with accurate vertical dimensions of the posterior mandible. STUDY DESIGN: Three partially edentulous human cadaver mandibles were used for this study. On each mandible, three potential implant sites were arbitrarily identified in an area between the mental foramen and the ascending ramus. Each site was imaged using two different panoramic machines. Using each image, the mandible's outline, cortical thickness, and position of the mandibular canal were traced on clear acetate film. The mandibles were then sectioned at each site to serve as a gold standard. The cadaver sections and tracings (corrected for magnification) were measured, recording the overall mandibular height, distance from the crest of the ridge to the superior aspect of the mandibular canal, and the thickness of the cortical bone at the most inferior aspect of the mandible. RESULTS: There were no significant differences between either of the system's image measures and the gold standard when considering the distance between the crest and the mandibular canal. Differences were noted between the systems measures and the gold standard in the assessment of the cortical bone thickness and the overall mandibular height. CONCLUSIONS: Both imaging systems can be useful for vertical measurements of a potential implant site in the posterior mandible.

Alveolar Process↗
PubMed1997

Regional differences of dura osteoinduction: squamous dura induces osteogenesis, sutural dura induces chondrogenesis and osteogenesis.

Dura plays an important role in calvarial morphogenesis. However, precisely what that role is remains unclear. We present here in vivo evidence that dura without other central nervous system components induces both chondrogenesis and osteogenesis. The mechanism is, at least in part, by proximate tissue interaction. The objectives of this experiment were to answer the following: (1) Can dura actually induce osteogenesis without the influence of the underlying brain? (2) What are the requirements of this dura-induced heterotopic osteogenesis? (3) What are the differences between dura underlying sutures and dura underlying the squamous portions of the cranial bones? Dura underlying the metopic, sagittal, and lambdoidal sutures and dura underlying the flat portions of frontal and parietal bones were obtained from neonatal Lewis rats and transplanted into the posterior thoraces of adult Lewis recipients. In group I, dura underlying the metopic, sagittal, and lambdoidal sutures (n = 20) and dura underlying the flat portions of frontal and parietal bones (n = 20) were transplanted individually into separate epitheliomesenchymal pockets. Group II animals had dura underlying the metopic, sagittal, and lambdoidal sutures (n = 10) and dura underlying the flat portions of frontal and parietal bones (n = 10) transplanted individually into surgically created mesenchymal pockets by placing the dura grafts between panniculus carnosus and latissimus dorsi muscles. The animals were sacrificed at 2-week intervals. Light microscopy, special histochemical analysis, immunohistochemistry, and electron microscopy were performed. Bone formation was seen in 15 of the 18 animals (83 percent) in group I. No bone or cartilage formation was seen in group II. Chondrogenesis was seen in 4 animals receiving dura underlying the metopic, sagittal, and lambdoidal sutures in group I. Cellular hyperproliferation was seen at 2 weeks when dura was transplanted close to the hair follicles. These cells had a high nucleus-to-cytoplasm ratio and were positive for transforming growth factor beta. This hyperproliferation was followed by production and accumulation of Alcian blue-positive extracellular matrix that resisted digestion by hyaluronidase. Cellularly active cartilage was seen at 6 weeks. There was no chondrogenesis in animals receiving dura underlying the flat portions of frontal and parietal bones in group I. Electron microscopy demonstrated the presence of proteoglycan-like ground substance and type II collagen in the inner layer of sutural dura and the predominance of dense type I collagen in the squamous dura and the external layer of the sutural dura. The important findings of this experiment are that (1) heterotopically transplanted neonatal dura can induce osteogenesis, (2) this heterotopic osteoinduction by dura requires epitheliomesenchymal interaction, and (3) separating dura into sutural dura and squamous dura, chondrogenesis occasionally occurred in addition to osteogenesis with the former, while only membranous ossification occurred with the latter, indicating intrinsic differences within the dura mater. This dural heterogeneity is supported by direct ultrastructural data.

Animals↗
PubMed1996

Histochemical and immunohistochemical studies of the effects of experimental anterior disc displacement on sulfated glycosaminoglycans, hyaluronic acid, and link protein of the rabbit craniomandibular joint.

PURPOSE: The purpose of this study was to determine the effects of surgically induced anterior disc displacement (ADD) on sulfated glycosaminoglycans (GAGs) such as keratan sulfate (KS), chondroitin-4-sulfate (C4S), and chondroitin-6-sulfate (C6S), hyaluronic acid (HA), and link protein (LP) of the rabbit craniomandibular joint (CMJ) using histochemical and immunohistochemical techniques. MATERIALS AND METHODS: The right joint of 20 rabbits was exposed surgically, and all discal attachments were severed except for the posterior attachment. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after surgery. Discs, bilaminar zones, condyles, and articular eminences were excised. Condyles and articular eminences were decalcified in ethylenediaminetetraacetic acid (EDTA). All tissues were sectioned at 10 microns in a cryostat. Sections were incubated with alcian blue and monoclonal antibodies directed against KS, C4S, C6S, HA, or LP. After incubation in the appropriate fluorescein isothiocyanate (FITC)-labeled secondary antibodies, tissue sections were studied under the fluorescence microscope. RESULTS: The results showed a reduction in alcian blue staining and KS, C4S, C6S, HA, and LP immunostaining in the disc and articular surfaces at 2 weeks after induction of ADD. This reduction was followed by an increase in their immunostaining at 6 weeks. Also, there was a progressive increase in alcian blue staining, and KS, C4S, C6S, and HA immunostaining in the bilaminar zone at 2 and 6 weeks. CONCLUSION: It was concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in KS, C4S, C6S, HA, and LP content, consistent with similar changes accompanying osteoarthritis of other synovial joints.

Alcian Blue↗
PubMed1995

An immunohistochemical study of the effects of surgical induction of anterior disc displacement in the rabbit craniomandibular joint on type I and type II collagens.

The right craniomandibular joint (CMJ) was exposed surgically and all the discal attachments severed except for the posterior one. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control; 10 other joints were used as non-operated controls. Deeply anaesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after the induction of the anterior disc displacement (ADD). The articular disc, bilaminar zone, mandibular condyle and articular eminence were excised. The condyles and the articular eminences were demineralized in EDTA. All tissues were then sectioned at 10 microns in a cryostat. Sections were incubated with polyclonal antibodies directed against type I or type II collagens. Following incubation in the appropriate fluorescein isothiocyanate-labelled secondary antibodies, these specimens were studied under the fluorescence microscope. At 2 weeks there was a reduction in type II collagen immunostaining; some areas of the experimental condylar cartilage showed a switch from type II to type I collagen. However, at 6 weeks there was an increase in type II collagen immunostaining and a decrease in type I compared to the 2-week group. It is concluded that surgical induction of ADD in the rabbit CMJ leads to alteration in the condylar cartilage collagen phenotype similar to that reported for osteoarthritic cartilage of other synovial joints.

Animals↗
PubMed1995

Enlargement of the rabbit mandibular condyle after experimental induction of anterior disc displacement: a histomorphometric study.

PURPOSE: Clinical and autopsy studies have shown that patients with temporomandibular joint dysfunction are more likely to have enlargement and deformity of the condyle and subsequently occlusal disharmony. However, it is not known what causes this enlargement. This study was designed to test the hypothesis that surgical induction of anterior disc displacement (ADD) in the rabbit craniomandibular joint (CMJ) could lead to enlargement and deformity of the condyle. MATERIALS AND METHODS: The right CMJ was exposed surgically, and the discal attachments were severed except for the posterior discal attachment (bilaminar zone). Then, the disc was repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. CMJ tissues then were removed after fixation at 24 hours (5 rabbits), 1 week (10 rabbits), 2 weeks (10 rabbits), or 6 weeks (10 rabbits), processed, and stained with hematoxylineosin. Histomorphometric assessment was used to evaluate changes in condylar volume, and thickness of the fibrous, reserve cell, and condylar cartilage layers. RESULTS: The results showed a progressive enlargement of the condylar volume in all experimental joints compared with controls (P < .01). The enlargement was attributable to a significant increase in the cartilage thickness and surface area of the nonarticulating portion of the condyle in the 1-week group (P < .01). In the 2- and 6-week groups, there were significant, progressive increases in cartilage thickness and surface area of the articulating portion of the condyle (P < .01). In all animals, increased cartilage thickness was associated with a decrease in the thickness of the fibrous and the reserve cell layers (P < .01). CONCLUSION: It is concluded that surgical induction of ADD in the rabbit CMJ causes enlargement of the condyle, which is in part caused by hyperplasia of the condylar cartilage.

Animals↗
PubMed1993

Morphological alterations in the elastic fibers of the rabbit craniomandibular joint following experimentally induced anterior disk displacement.

Elastic fibers are important components of the connective tissue that attaches the articular disk of the craniomandibular joint (CMJ) to the skull and mandible. Biopsies of the articular disk proper and bilaminar zone (BZ) tissues from patients with anterior disk displacement (ADD) have shown previously that there is a marked loss of elastic fibers. In the present study, the effects of inducing ADD on the elastic fibers in the rabbit CMJ disk proper, BZ and condylar cartilage were investigated. The right CMJ was exposed surgically and the discal attachments were severed except for the BZ attachments. Then, the disk was displaced anteriorly and sutured to the zygomatic arch. The CMJs were removed after 1, 2 or 6 weeks and processed for histochemical demonstration of elastic fibers. The results showed osteoarthritic changes following ADD, and a significant decrease in the number of the elastic fibers in the disk proper and BZ. The remaining elastic fibers were abnormal in their appearance and orientation. In addition, ADD led to the appearance of fine elastic fibers among the chondrocytes in the hyaline cartilage of the condyle that were not present in the cartilage of the control condyle. We conclude that induced ADD can lead to a significant loss of elastic fibers in the articular disk, and result in the appearance of elastic fibers within the cartilage of the mandibular condyle.

Animals↗
PubMed1993

New technique for creating permanent experimental alveolar clefts in a rabbit model.

Alveolar bone grafting is an adjunctive procedure that has become increasingly popular in the rehabilitation of patients with cleft lip and palate. A histologic basis of the performance of bone grafts is required to evaluate properly different grafting materials. This, however, cannot be provided by clinical studies on humans. Therefore, an animal model with a simulated alveolar cleft is needed. A number of animal models has been previously proposed by other investigators. The problems associated with each model are presented and a surgical technique for the creation of permanent alveolar clefts in rabbits is described. Clinical and histologic findings 6 weeks postoperatively confirm the establishment of a 1-cm wide defect with oronasal communication and healthy epithelial lining. This animal model can be efficiently used for the testing of various bone grafting materials.

Alveolar Process↗
PubMed1992

Evidence for an ATP-driven H(+)-pump in the plasma membrane of the bovine corneal epithelium.

In a highly enriched plasma membrane fraction isolated from the bovine corneal epithelium, MgATP dependent intravesicular acidification was identified by measuring Acridine Orange quenching. The rate of acidification was increased 2.7-fold by pre-exposure of the membranes to 1% cholate which was subsequently removed by Sephadex G-50 column chromatography. However, in a lysosomal fraction whose enrichment with respect to the homogenate was 82-fold in N-acetyl-beta-D-glucosaminidase, cholate pre-exposure had no significant effect on the rate of intralysosomal acidification. This difference is assumed to reflect reorientation by cholate of the H(+)-pump's normally inaccessible ATP-binding site in right-side-out vesicles of the plasma membrane-enriched fraction to a configuration in which this site becomes accessible to externally added ATP. In contrast, the ATP-binding site of the H(+)-pump in the lysosomal fraction is completely exposed to the exterior even in the absence of cholate treatment. The characteristics of the H(+)-pump in the plasma membrane fraction was subsequently determined using cholate-pretreated membrane vesicles. The rank order of nucleotide support of the H(+)-pump activity was: ATP >> GTP > ITP. However, UTP and CTP were totally inactive. The pump is electrogenic because the activity of the pump was enhanced in voltage-clamped membrane vesicles. Substitution of Mg2+ with Mn2+ did not change the acidification rate but Co2+ only partly activated whereas Ca2+ and Zn2+ were ineffective as activators. The H(+)-pump was relatively unaffected by oligomycin, azide or vanadate but completely inhibited by 10 microM NEM or NBD-Cl and 92% inhibited by 20 microM DCCD.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1992

In vitro effects of elastase on rabbit craniomandibular joint articular disks.

This in vitro study correlates morphologic and radioimmunoassay (RIA) findings on the effects of elastase on the elastic fibers that are found in the rabbit craniomandibular joint (CMJ) articular disk. Articular disks were removed from rabbit CMJs at necropsy, and cut sagittally into two pieces which were incubated in 0.3 ml of phosphate-buffered saline containing either 0, 12.5, 25 or 50 units of porcine pancreatic elastase for either 1, 3 or 24 h. The quantitative RIA findings correlated well with the qualitative light-microscopic observations in that both methods showed a reduction in the amounts of elastin in the CMJ disks following enzyme treatment. However, the morphologic appearance of most of the elastase-treated disks suggested that the destruction of the elastic fibers was more extensive than was suggested by the results of the RIA which indicated that some elastin remained in the tissues of the disks even when the highest enzyme level and longest incubation period were combined. The results of this study also support the interpretation that the resorcin-fuchsin-stained fibers in the rabbit CMJ disk are elastic fibers.

Animals↗
PubMed1989

Alveolar ridge augmentation in Macaca fascicularis using polysulfone with and without demineralized bone powder.

The purpose of this study was to test the soft tissue and bone response to the implantation of porous polysulfone (PPSF) with and without demineralized bone powder (DBP) for ridge augmentation in Macaca fascicularis. The mandibular molar teeth were extracted in five adult female monkeys, followed by massive alveolectomy. Five to eight months later, PPSF + DBP was inserted subperiosteally on the left side, while PPSF alone was inserted on the right side. The animals were killed 42, 60, and 90 days following implantation. Specimens were processed for light microscopy, scanning electron microscopy, tetracycline labeling, and histomorphometric measurement of new bone. The 42-day specimens of the PPSF + DBP and PPSF revealed penetration of fibrous tissue rich in fibroblasts and blood vessels into the pores of the PPSF. At 60 and 90 days, the PPSF side showed organized fibrous tissue, but bone grew only for a short distance into the implant. In contrast, the PPSF + DBP side showed large amounts of bone formation, and bone almost covered the implant. The qualitative results were confirmed by histomorphometric examination.

Alveolar Process↗
PubMed1989

Osteogenesis in composite grafts of allogenic demineralized bone powder and porous hydroxylapatite.

This study evaluated the osteoinductive capabilities of porous hydroxylapatite (PH) and the tissue response following intramuscular implantation of PH alone or in combination with demineralized bone powder (DBP). Six rhesus monkeys each received the implants in three separate soft tissue pockets created in the thoracic region. The implants consisted of 2 cc of either PH alone or DBP alone, or a 1:1 combination of DBP and PH. Two animals were killed at 2 weeks, two at 4 weeks, and two at 12 weeks postimplantation. Histologically, bone formation was seen in the DBP mixed with PH and in the DBP group as early as 4 weeks postimplantation; bone was also occasionally observed within the pores of the PH particles. The PH alone showed no evidence of formation of bone and the material was surrounded by a thick layer of fibrous tissue. It was concluded that PH is not osteoinductive, but can act as a scaffold for growth of bone, and that when mixed with an osteoinductive material, it allows for formation of bone within the implant.

Animals↗
PubMed1989

Distribution of putative elastic fibers in rabbit temporomandibular joint tissues.

This study describes the general distribution of putative elastic fibers in the connective tissues that comprise the articular disk and some of the adnexal tissues of the rabbit temporomandibular joint. Joints were removed en bloc and processed for light-microscopic study. The fibroelastic tissues of the bilaminar zone of the articular disk and the various attachments of the disk to the mandibular condyle contained numerous elastic fibers. Since these morphologic data indicate the presence of many elastic fibers, we suggest that the rabbit temporomandibular joint may serve as a model system to study the functional consequences of selectively altering the quality or quantity of elastic fibers in these tissues.

Animals↗