Mechanical and ultrastructural evaluation of quartz post-endodontic reconstructions.

Aesthetics is a very important element in dentistry, but requires the support of good mechanical performance. Quartz fiber used in post-endodontic reconstruction is an aesthetic material, although there is little research concerning its mechanical properties. This study evaluated the retentive property of post-endodontic reconstruction, composed of a quartz fiber post. Different thermal stresses were applied in vitro to post-endodontic reconstructions, in order to simulate oral thermal action on post-system dental structure linkage. We chose 30 human extracted teeth, endodontically treated and restored, and then divided them into three groups of 10 teeth. A different treatment was applied to each group before mechanical testing: in the 1st group no treatment was done (controls); in the 2nd group teeth were subjected, in a climatic chamber, to 10 thermo-cycles between 4 degrees C and 58 degrees C; in the 3rd group teeth were stored in a saline solution at 37 degrees C for 48 hr. The teeth then underwent tensile shear stress tests at break point using a computerized electronic dynamometer. After mechanical testing, two teeth from each group were longitudinally half-sectioned, sputter-coated in gold and observed by scanning electron microscopy (SEM). The extracted quartz fiber post of each tooth also underwent SEM observation. Mechanical test results demonstrated that thermal cyclic variations could affect bond stability between dental structures and posts in quartz fiber reconstructions, whereas their bond strength seemed unaffected by humidity increases. Quartz fiber post SEM observation demonstrated a homogeneous structure and a regular fiber disposition. Dental root canal morphology SEM images always showed a different thickness in the cement layer. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 156-61).

Perfluorohexyloctane (F6H8) induces structural modifications and increases apoptosis in rat primary retinal cultures.

The effects of perfluorohexyloctane (F6H8), recently investigated as a long-term artificial vitreous substitute, were studied in vitro, with the use of rat retinal cultures seeded on microporous inserts that allow the cell layer to be in contact with the material to be tested, on the apical side, and with the nutrient medium, on the basal side. After 72 h of treatment with F6H8, retinal cultures lost the characteristic two-layered organization with glial cells at the bottom and neuronal cells on top of them. They appeared to be composed of only one layer of polyhedrical, flattened, and disconnected cells. TUNEL assay revealed an evident increase in the percentage of apoptotic cells in F6H8-treated cultures (30.1 +/- 4.5), compared to control (10.3 +/- 2.6) and perfluoroctane-treated cultures (10.1 +/- 1.7). Immunolabeling of MAP-2, a protein of neuronal cytoskeleton, evidenced a marked loss of neurites. The results suggest that F6H8 is harmful to retinal cells in vitro and can therefore be potentially noxious to the retina as an artificial vitreous substitute.

Influence of dacron tissue thickness on the performance of the Pintucci biointegrable keratoprosthesis: an in vitro and in vivo study.

PURPOSE: In 1979 Pintucci developed a biointegrable keratoprosthesis with polymethylmethacrylate optical cylinder integrated with a Dacron tissue-colonizable supporting element to avoid the complications caused by the interaction between the haptic element and the eye. The purpose of this article is to compare the colonization of three Dacron fabrics (thicknesses of 0.25 mm, 0.6 mm, and 1.4 mm) in vitro and in vivo to optimize the device performance. METHODS: In vitro three different Dacron fabrics were cultured for 3 days with 3.5 x 10(5) human fetal lung fibroblasts and observed with a scanning electron microscope. In vivo three different Dacron fabrics were implanted on the sclera near the superior rectus insertion in the right eye of six albino rabbits and were observed after 4 days with light and scanning electron microscopy. RESULTS: In the in vitro experiments, the cells were preserved and their structure was found to be normal. The 0.25-mm thick fabric was coated only on the surface, and the other fabrics were colonized in three dimensions. In the in vivo experiments, the 0.25-mm thick fabric appeared coated only on its surface. The other fabrics were three-dimensionally colonized and the Dacron filaments appeared embedded in neovascularized connective tissue with minimal foreign body reaction. The 1.4-mm thick colonized fabric showed a substantial loss of pliability. CONCLUSION: Given that the 0.25-mm thick fabric was coated only by connective tissue, that the 0.6-mm and 1.4-mm thick fabrics were perfectly colonized, and that the 1.4-mm thick fabrics showed a substantial loss of pliability, the 0.6-mm thick fabric haptic part of the Pintucci keratoprosthesis is preferred. For 19 years, the 0.6-mm Dacron fabric Pintucci keratoprosthesis was implanted in 159 eyes with good results, overcoming the apparently inseparable difficulties represented by mechanical anchorage and biointegrability of a keratoprosthesis.

Evaluation of guided bone regeneration in rabbit femur using collagen membranes.

The aim of the study was to evaluate the mechanical performance and the structure of neoformed bone around hydroxyapatite-coated titanium fixtures according to guided bone regeneration techniques. Ten hydroxyapatite-coated titanium fixtures were inserted in the femurs of five rabbits, in which a cortical defect was created and after the insertion of the fixture, covered with a resorbable membrane obtained from bovine Achilles tendon collagen Type I (A implant). In the same femur, a second fixture was inserted in similar cavities without application of the membrane (B implant). After 60 days, the animals were sacrificed, and block sections of the femoral bone containing the implants were embedded in polymethylmetacrylate and subjected to tensile shear-stress at break testing. After the detachment of the implants from the bone, their surfaces were examined with a scanning electron microscope. Tensile shear-stress values for A and B implant specimens were comparable to some extent, but the former had a lower performance. In this regard, scanning electron microscope observations showed that the neoformed cortical bone present cervically around implant A was much thicker than around implant B.

Alteration of organized structure of biofilm formed by Staphylococcus epidermidis on soft contact lenses.

The effect of a nonsteroidal antiinflammatory drug commercially available in eye drop form (sodium diclofenac) was assayed for its ability to affect biofilms formed by clinical Staphylococcus epidermidis isolates. Biofilms produced by one strain positive for a slime-associated antigen, suggested to be expressed by more virulent strains, was not affected by sodium diclofenac treatment. On the other hand, biofilm produced by the slime-positive, antigen-negative strain showed dramatic alterations already after short treatments with sodium diclofenac as reported for salicylate and other nonsteroidal drugs. Such results suggest further investigation of the possible use of sodium diclofenac drops in the treatment of ophthalmic infections in soft contact lens wearers.

PEDF (pigment epithelium-derived factor) promotes increase and maturation of pigment granules in pigment epithelial cells in neonatal albino rat retinal cultures.

Pigment Epithelium-Derived Factor (PEDF), purified from human retinal pigment epithelial (RPE) cell culture medium, is a neurotrophic factor which potentiates the differentiation of human Y-79 retinoblastoma cells and increases the survival of cerebellar granule cells. To investigate the effects of PEDF on non-transformed retinal cells, we used primary cultures of neonatal albino rat retinas, where the three principal cell types of the retinal layers (neuronal, glial and epithelial) were all present and focussed our attention on RPE cells, which are of special relevance for retinal pathophysiology. PEDF had a dramatic effect on these cells. They showed a modified phenotype, with larger dimensions, higher cytoplasmic spreading, presence of phagocytic vacuoles, development of wide intercellular contacts, and increase and maturation of pigment granules. These results suggest that PEDF may have a role in regulating RPE cell differentiation.

Perfluorodecalin modifies the pattern of cell arrangement and induces loss of neurites in rat retinal cultures.

Perfluorodecalin (PFD), a high specific weight, water-immiscible perfluorocarbon, previously studied as a potential blood substitute, now is used widely in the field of ophthalmic surgery as a tool for maneuvering intraocular tissues and as a short- or medium-term vitreous substitute. In in vivo experiments, several types of lesions in retinal tissue have been described in conjunction with long-term PFD treatment. To better evaluate the biological effects of PFD on retinal cells, we tested it on primary cultures of rat retina seeded on special cyclopore wells that allow the culture to be fed from the bottom side while the top side is in contact with the water-immiscible compound. We found that PFD changed the pattern of cell arrangement and induced loss of neurites. The modification of cell arrangement was less evident at the periphery of the wells where the amount of PFD, and consequently the pressure exerted, was lower. This observation suggests that the changes may be due more to a physical than to a toxic effect of PFD.

The Dacron felt colonizable keratoprosthesis: after 15 years.

Keratoprostheses (KP) are made of an optical cylinder integrated with a supporting element which governs their biocompatibility. The Pintucci KP with a Dacron tissue three-dimensionally colonizable support was designed in 1979 and has since been improved in order to reduce the complications associated with the use of KP. The biological background (in vivo and in vitro), electron microscopy observations and the surgical technique will be discussed. Sixty-three patients were operated from 1979 with different surgical techniques and Dacron tissues. Twenty transoral mucous KP were implanted with our most recent technique in severely vascularized corneas from 1985 to 1991, with a follow-up ranging from 48 to 85 months. The favorable results may be indicative of their better reliability.

New Dacron tissue colonisable keratoprosthesis: clinical experience.

BACKGROUND: Keratoprostheses (KPs) are made of an optical cylinder integrated with a supporting element which conditions their biocompatibility. A new KP with a Dacron tissue colonisable support has been designed in order to reduce significantly the complication rate. METHODS: This new KP was implanted into 20 eyes of 20 patients with bilateral corneal blindness unsuited to a corneal implant. The follow up ranged from 24 to 96 months. RESULTS: All 20 patients had some improved visual acuity with 13 retaining this improvement for more than 2 years. CONCLUSION: These favourable results may be indicative of the reliability of the new KP.

VAD Biomer blood sacs: mechanical tests and ultrastructural observations.

Ventricular Assist Devices (VADs) are a support to the heart function and are used as bridge to transplantation for a brief period in patients awaiting a donor heart. They consist of two sacs with two artificial valves that allow blood flow, the whole connected to a specific electronic equipment. This study examines the performance of a segmented-polyurethane elastomer, namely Biomer, that has been extensively used to manufacture pneumatically actuated VAD blood sacs. Specimens obtained from three VAD blood sacs explanted from three human patients and specimens from one unimplanted blood sac were investigated for mechanical performance of the material and for the changes it undergoes as a result of mechanical stress and interaction with the surrounding biological environment. The application of tensile strength at break yielded no relevant differences between unimplanted and explanted specimens. Biomer exhibited a high elongation at break for both groups, with somewhat lower values for explanted specimens. SEM observations carried out on the inner surface--in contact with blood--of unstressed explanted specimens showed no thrombotic deposits, calcifications, microbial contamination or structural changes. The complementary broken surfaces of stressed specimens showed a distinctive fracture pattern.

Bone regeneration guided by resorbable collagen membranes in rabbits: a pilot study.

Artificial cross-shaped intrabony defects were created in the mandibles of 12 rabbits and the cavities covered with Type I highly cross-linked resorbable collagen membranes for 30 days. Similar cavities were prepared in three control animals and left uncovered for the same time period. Morphological and analytical data were obtained by means of light microscopy, scanning electron microscopy, and x-ray energy-dispersive spectrometry. After the experimental period, the membrane covered cavities were completely filled with regenerated bone. In the control specimens, the artificial cavities were occupied by fibrous connective tissue.

Evaluation of an experimental periodontal ligament for dental implants.

To improve the devices used in dental implantology, a new experimental supporting element has been developed. The device, made of titanium, poly(methylmethacrylate) and Dacron tissue, has been tested for the osteointegrability of its outer Dacron coat by implants in mandibular bone of rabbits. The Dacron filamentous tissue became incorporated by the bone at 3 month post-implantation. This might provide a reliable mechanical anchorage of the device and a barrier against epithelial proliferation and microbial contamination. Preliminary results relating to in vitro evaluation of the poly(methyl methacrylate)-Dacron fixation strength predict favourable mechanical behaviour at this interface and in the complete implanted device.

Exceptional case of bone resorption in an osteo-odonto-keratoprosthesis. A scanning electron microscopy and X-ray microanalysis study.

This article reports the findings of investigations on an osteo-odonto-keratoprosthesis in an eye that was enucleated owing to severe complications 12 years after implantation. Scanning electron microscopy and electron probe X-ray microanalysis showed extensive resorption of the bone that was used as a supporting element in the kind of transcorneal prosthesis developed by Strampelli. The destructive process, in addition to surgical trauma, has been associated with the early and recurrent bacterial infections relating to the presence of Staphylococcus epidermidis. The need to control the occurrence of primary bacterial infections in traumatized tissues during operations as well as further infectious situations, given the enhanced antibiotic-resistence of bacteria, is emphasized.

Particle migration from haemodialysis circuit: electron microscopy and microprobe analysis.

It has been recognized that storage inflammation in organs of uraemic patients is due to silicone particle migration from tubing segments of the haemodialysis circuit to blood. Nevertheless, iatrogenic storage of foreign material containing Si has been also observed in long-term dialysis patients which, in our Unit, used only PVC or PU-PVC tubings. The origin and the nature of the particulate has been investigated in vivo and in vitro on bioptical samples as well as on cuprophan dialyser and PVC tubing eluates. This study carried out by means of TEM, SEM and microprobe EDS revealed the presence of variously shaped material and particles containing Si in bioptical samples and in eluates. Si containing contaminants were not demonstrated in eluates filtered in absence of the dialyser. This result suggests that leachable products can result from the dialyser and that such release can be an additional risk for uraemic patients.

Ultrastructural aspects and clinical implications of PFC/non-phagocytic cell interactions.

Many in vivo studies showed the accumulation of PFC particles in reticuloendothelial cells of target organs such as spleen, lungs and liver. Surprisingly, an uptake of PFCs particles by liver parenchymal cells as well was described by some authors. In order to clarify whether Kupffer cells and/or liver environmental factors could be involved in particle uptake we exposed cultured rat hepatocytes to Fluosol 43. PFC particles were noted, after a 3-hour incubation, in lysosomes. This result suggests that more attention must be paid to liver toxicity of PFC blood substitutes. Isolated mouse myocytes were exposed as well to Fluosol 43 for 3 hours. Preliminary results confirm the absence of the particle uptake previously noted also in our in vivo studies on rat and guinea pig heart-lung preparation. The possible subsequent absence of cytotoxicity at myocardial level could underline the reliability of using optimized PFCs as components of cardioplegic solutions in open heart surgery.

Mineral particles in the lungs of subjects resident in the Rome area and not occupationally exposed to mineral dust.

We studied the inorganic particulate contained in the lung parenchyma of 10 subjects (5 males and 5 females) resident in an urban area and not occupationally exposed to dusts. A total of 17 mineral types were identified, along with 16 metal elements in the form of oxides and sulfides. Approximately 70% of the minerals were made up of phyllosilicates, in particular clay, mica, and talc; three metal elements, Fe, Al, and Ti, accounted for more than 75% of the recovered oxide particles. The mean concentration of the observed inorganic particles was approximately 1.8 X 10(5) pp/mg dry tissue. No significant differences were observed in terms of total particulate concentration in the various areas of the lungs and between the right and left lung. Instead we observed a larger concentration of fibrous particles in the upper lobes. The analysis of the data made it possible to determine the presence of a high degree of correlation between the concentrations of silicates and the concentrations of metal oxides and sulfides, implying the existence of a ubiquitous environmental source of these mineral particles. The frequent observation of tremolite fibers is remarkable. This finding, confirmed elsewhere, indicates that the magnitude of the sources of these fibers in the environment, constituted by contaminated talc dusts, has been underestimated until today.

[Fluorocarbons as artificial blood substitutes: an electron microscopy study]. / Fluorocarbures comme substituts artificiels de sang: une étude au microscope électronique.

In spite of the great interest in developing a perfluorocarbon (PFC) blood substitute with a wide range of applications, the in vivo and in vitro knowledge of the interactions between PFCs and cells, from the ultrastructural point of view is limited up to now. In this framework, our observation confirmed the PFC particle uptake by rat hepatocytes in vivo as well as in vitro. The absence of endocytosis by rat and guinea pig myocytes in vivo, to be confirmed by in vitro experiments, could favour a safe use of PFCs as components of cardioplegic solutions.

Implant effects on polyurethane and silicone cardiac pacing leads in humans: insulation measurements and SEM observations.

Recently, polyurethane cardiac pacing leads have been under discussion because of some failures, probably due to modification of surface insulating properties. In order to verify the reliability of polyurethane versus silicone rubber as coating material, the authors, starting from previous clinical research, have carried out a study of electrical insulation related to implant time. At the same time the outer and inner lead surfaces have been submitted to scanning electron microscope (SEM) analysis. The results show, for the polyurethane leads, a significant increase in the leakage or currents in explanted samples, and a significant degradation (cracking) of the outer surfaces.

Electron microscopy and microprobe analysis of dialysis contaminants.

A migration of plastic particles from haemodialysis circuit to blood has been recognized to be cause of storage inflammation. Its origin from segments of silicone tubing has been demonstrated by in vivo and in vitro experiments. A similar finding with a peculiar histology picture has been observed in patients who used only PVC and PU-PVC tubing. In this case too microprobe analysis revealed the presence of silicon (Si) in fibril inclusions of liver and spleen cells. TEM, SEM and EDS of cuprophane dialyzer perfusates filtered through Nuclepore revealed the presence of particles with an intense Si Ka. The release from the dialyzer of silicon containing contaminants seems to be an additional risk for uremic patients.