Intraoral low-temperature degradation of monolithic zirconia dental prostheses: 5-year results of a prospective clinical study with ex vivo monitoring.

OBJECTIVES: To investigate the 5-year intraoral evolution and kinetics of low-temperature degradation (LTD) of second-generation monolithic prostheses made of 3% molar yttrium-doped tetragonal zirconia polycrystal (3Y-TZP) and the influence of masticatory mechanical stresses and glaze layer on this evolution. METHODS: A total of 101 posterior tooth elements were included in this prospective clinical study, which comprised ex vivo LTD monitoring (at baseline, 6 months, 1 year, 2 years, 3 years, and 5 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and scanning electron microscopy (SEM). Four types of areas (1-2 mm2 surface, six on molars, and four on premolars) were analysed on each element surface: occlusal, axial, glazed, or unglazed. Raman mapping, high-resolution SEM, and focused ion beam-SEM were performed on selected samples. RESULTS: The dental prostheses developed a tetragonal-to-monoclinic transformation at the extreme surface of the material after six months in a buccal environment, and this process increased significantly over time. Over the five years of monitoring, the transformation developed nonuniformly with the presence of localised clusters of monoclinic grains. Tribological stresses generate grain pull-out from these clusters, which may raise questions regarding the release of 3Y-TZP nanoparticles into the body. The prosthesis fracture rate was 4.5% after 5 years. SIGNIFICANCE: LTD developed in vivo on the surfaces of 3Y-TZP dental prostheses and progressed slowly but significantly over time, up to 5 years investigation. However, the effects of aging on the failure rate recorded and of zirconia nanoparticles released into the body require further investigation.

A new concept of gentamicin loaded HAP/TCP bone substitute for prophylactic action: in vivo pharmacokinetic study.

Despite systemic prophylaxis, infection rates after orthopedic surgery can reach more than 1%. A new HAP/TCP bone substitute loaded with 125 mg of gentamicin was designed for prophylactic use. Its aim was to enhance the efficacy of systemic prophylactic treatments by increasing the local antibiotic concentration. The release rate of gentamicin from the bone substitute was investigated after implantation in the femoral condyle of five sheep. In order to investigate the local and systemic gentamicin concentrations, synovial fluids and blood samples were assessed over a 5-day period. The mean gentamicin concentration peak in blood was 4.2 µg/ml and the mean local concentration in synovial fluids during the first 8 h was 305 µg/ml. After 48 h, the concentrations in blood and synovial fluids were less than 0.5 µg/ml. No remaining gentamicin was detected in bone substitutes explanted after 8 days of implantation. The gentamicin release rate from the bone substitutes assessed corresponds to the recommendations for the prophylactic use of antibiotics: high local concentration but limited in time (less than 48 h) not to select antibiotic-resistant bacterial strains. Our results indicated that this implant should be an effective prophylactic tool in orthopedic surgery in combination with systemic prophylaxis.

Intraoral low-temperature degradation of monolithic zirconia dental prostheses: Results of a prospective clinical study with ex vivo monitoring.

OBJECTIVE: To investigate the intraoral development and kinetics of low-temperature degradation (LTD) in second-generation 3 mol.% yttria-doped tetragonal zirconia polycrystal (3Y-TZP) monolithic prostheses, as well as the influence of masticatory mechanical stress and glaze layer on it. METHODS: A total of 101 posterior tooth elements were included in a prospective clinical study, which included ex vivo LTD monitoring (at baseline, 6 months, 1 year, and 2 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and SEM. Four types of areas (1-2 mm2 surface, 6 on molars, and 4 on premolars) were analyzed on each element surface: occlusal, axial, glazed, or unglazed. Raman depth mapping and high-resolution SEM were performed on the selected samples. RESULTS: LTD developed in 3Y-TZP monolithic restorations 6 months after intraoral placement and progressed with time. After two years, the tetragonal-to-monoclinic transformation was non-uniform, with the presence of localized clusters of transformed grains. In axial areas, the grain aspect was typical of the classical nucleation-growth process reported for LTD, which progresses from the surface to a depth of several tens of microns. However, in occlusal areas, tribological stress generated surface crushing and grain pull-out from the clusters, which induced an underestimation of the aging process when the evaluation was limited to monoclinic phase quantification. Glazing cannot be considered a protection against LTD. SIGNIFICANCE: If LTD occurs in dental prostheses in the same way as in orthopedic prostheses, its clinical impact is unknown and needs to be further studied.

Aging resistance, mechanical properties and translucency of different yttria-stabilized zirconia ceramics for monolithic dental crown applications.

OBJECTIVES: The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with - or without - a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency. METHODS: Four different commercial zirconia materials were investigated, including one standard 'full-strength' 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134°C). Aging was conducted on crowns with and without glaze to better represent clinical uses. RESULTS: Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side.

Sub-surface assessment of hydrothermal ageing in zirconia-containing femoral heads for hip joint applications.

Zirconia-based materials have been used in orthopaedics since the 1980s, with large success, mainly thanks to transformation toughening. On the other hand, their main drawback is their potential sensitivity to hydrothermal ageing, i.e. tetragonal to monoclinic phase transformation on their surface in the presence of water. Hydrothermal ageing may result in roughness increase and microcracking of the surface. In this article the hydrothermal ageing behaviour of three medical-grade zirconia-based materials is assessed at high temperature and extrapolated to room or body temperature. The degradation is also characterized by FIB/SEM nano-tomography to better assess sub-surface evolutions. In both zirconia and alumina-toughened zirconia (ATZ), ageing results in the presence of a homogenous transformed layer of constant thickness whose growth rate is about 8 times slower in ATZ than in zirconia. Microcracking occurs in the entire transformed layer in zirconia, but was much less relevant in ATZ. Zirconia-toughened alumina (ZTA) is much less prone to ageing. In ZTA ageing results in a thin transformed layer in which the monoclinic fraction decreases with depth. No microcracking was observed in ZTA. STATEMENT OF SIGNIFICANCE: This article details the microstructural evolution of the surface of three zirconia-based ceramics when exposed to water (hydrothermal ageing), and establishes a time-temperature equivalences of these evolutions. It shows that different zirconia-alumina composites do not degrade the same way: zirconia and alumina-toughened zirconia present a homogeneous degraded zone of constant thickness, whereas zirconia-toughened-alumina presents a gradient of transformation. These new findings will help understanding better the hydrothermal degradation of zirconia based materials, and in particular will facilitate a better prediction of the durability of zirconia-based devices such as orthopaedic implants and dental devices (implants, crowns, abutments…).

Grain-Boundary Engineering for Aging and Slow-Crack-Growth Resistant Zirconia.

Ceramic materials are prone to slow crack growth, resulting in strength degradation over time. Although yttria-stabilized zirconia (Y-TZP) ceramics have higher crack resistance than other dental ceramics, their aging susceptibility threatens their long-term performance in aqueous environments such as the oral cavity. Unfortunately, increasing the aging resistance of Y-TZP ceramics normally reduces their crack resistance. Our recently conducted systematic study of doping 3Y-TZP with various trivalent cations revealed that lanthanum oxide (La2O3) and aluminum oxide (Al2O3) have the most potent effect to retard the aging kinetics of 3Y-TZP. In this study, the crack-propagation behavior of La2O3 and Al2O3 co-doped 3Y-TZP ceramics was investigated by double-torsion methods. The grain boundaries were examined using scanning transmission electron microscopy and energy-dispersive spectroscopy (STEM-EDS). Correlating these analytic data with hydrothermal aging studies using different doping systems, a strategy to strongly bind the segregated dopant cations with the oxygen vacancies at the zirconia-grain boundary was found to improve effectively the aging resistance of Y-TZP ceramics without affecting the resistance to crack propagation.

Detergent extraction of membrane proteins related to the action of antidiuretic hormone.

Antidiuretic hormone (ADH) induces, in the apical plasma membrane of target cells, the insertion of intramembranous particle aggregates that probably contain water channels. A mild attack of this membrane by a polyoxyethylene nonylphenyl detergent, which reversibly depressed ADH-induced water permeability, has been found to modify aggregate structure while extracting additional proteins. This simple procedure could be a valuable approach to the problem of aggregate isolation and characterization.

Electron microscopic location of mRNA in the rat kidney: improved post-embedding in situ hybridization.

We determined the optimal technical conditions for post-embedding non-radioactive in situ hybridization applied to ultrastructural location of collagen I mRNA in rat kidney. The signal-to-noise ratio was improved by enhancing hybridization efficiency and distinguishing nonspecific labeling. Probes were labeled with digoxigenin or biotin and detected after hybridization by immunogold or peroxidase techniques. Under these conditions, the signal was located in fibroblasts. With digoxigenin, clusters of gold particles were observed on the endoplasmic reticulum (ER) or scattered throughout the cytoplasmic matrix and nuclei. With the enzymatic method, diaminobenzidine deposits were found on the ER but endogeneous peroxidase partly interfered with the results. Gold particles were less numerous in fibroblast cytoplasm with biotin than with digoxigenin. Moreover, gold particles condensed on fibroblast and tubular cell mitochondria when biotin was used, a phenomenon shown to be due to endogenous biotin by means of a histochemical method. The digoxigenin-immunogold system appeared to be the best method. The biotin system was subject to limitations such as interference from endogenous biotin and poor sensitivity, and mRNA localization was more precise and reliable by the immunogold method than by the enzymatic method.

Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses.

Mono-phase bio-ceramics (alumina and zirconia) are widely used as femoral heads in total hip replacements (THR) as an alternative to metal devices. Unfortunately, the orthopaedic community reports significant in-vivo failures. Material scientists are already familiar with composites like alumina zirconia. Since both are biocompatible, this could prove to be a new approach to implants. This paper deals with a new generation of alumina-zirconia nano-composites having a high resistance to crack propagation, and as a consequence may offer the option to improve lifetime and reliability of ceramic joint prostheses. The reliability of the above mentioned three bio-ceramics (alumina, zirconia and zirconia toughened alumina) for THR components is analysed based on the study of their slow crack-growth behaviour. The influence of the processing conditions on the microstructure development, of the zirconia toughened alumina composites and the effect of these microstructures, on its mechanical properties, are discussed.

[Comparative study of 3 implanted micrografts placed in the abdominal aorta of the rat]. / Etude comparative de trois microgreffes implantées en position aortique abdominale chez le rat.

A comparative study was conducted on three micrografts of 2 mm diameter: a frozen umbilical artery, a bovine heterograft and an inert P.T.F.E. material graft. These were implanted in the infrarenal aorta of 158 Wistar rats. Each graft was examined on eight occasions: after 4, 24 and 48 hours, one and two weeks, and 1, 2 and 6 months. Excluding 46 animals that died within 24 hours, the overall permeability rate for all grafts was 87.7% (88.9% for umbilical arteries, 82.8% for bovine heterografts and 85.4% for P.T.F.E.). All grafts were examined by optical and electron microscopy. The inert material showed excellent parietal stability. In contrast, alteration and resorption of the primary matrix were moderate in extent for bovine heterografts, and major for frozen umbilical arteries which appear to be a very unstable grafts.

[External ionizing radiation on the prosthesis-arterial anastomosis for the prevention of intimal hyperplasia and study of biomechanical resistance. Experiments and results]. / Radiations ionisantes délivrées par voie externe sur l'anastomose prothéto-artérielle pour limiter l'hyperplasie intimale et étude de la résistance biomécanique. Expérimentations et résultats.

PURPOSE: To evaluate the use of external ionizing radiation for the prevention of intimal hyperplasia in anastomosis between PTFE and artery. METHODS: Bypass using a 6 mm PTFE was performed on a swine subrenal aorta with a distal conventional anastomosis (N = 35) associated (test group; N = 17) or not (control group; N = 18) with post-operative external radiation (20 Gy) on this anastomosis. At 45 days, histological studies and morphometric studies were performed on the aorta receiving the anastomosis. Two protocols were performed, the first protocol with standard analysis and the animals were randomly assigned to either group (test group; N = 11 and control group; N = 13) and the second protocol with test of extraction comparing the biomechanical resistance between the irradiated group (N = 6) and the control group (N = 5). RESULTS: Twenty-one animals survived the procedure in the first protocol, 11 in the second. The endothelium was restored in either group. Histological recasting was observed in the media after radiation with fibrosis and areas of necrosis. Intimal thickness was significantly lower after irradiation in the heel (P < 0.01), the head (P < 0.01) and the suture line (P < 0.001) of the artery in the first protocol. The intimal thickness was also significantly lower in the second protocol after radiation in the heel (P < 0.05) and the head of the artery (P < 0.05). There was no difference between the two groups comparing the resistance. CONCLUSION: After external irradiation, the thickness parameter of the intima decreased significantly in comparison with the control group with similar resistance. Media fibrosis and necrosis need to be confirmed by further investigation.

[Cellular culture of osteoblasts and fibroblasts on porous calcium-phosphate bone substitutes]. / Culture cellulaire d'ostéoblastes et de fibroblastes sur substituts osseux poreux en phosphate de calcium.

PURPOSE OF THE STUDY: Calcium phosphate ceramics are synthetic bone substitutes able to fill in bone destruction as a support of the bone growth. This work consisted in an in vitro assessment of osteoblasts and fibroblasts cultures on macroporous calcium-phosphate bone substitutes to analyze the interaction between cells and bone substitute. MATERIALS AND METHODS: The macroporous ceramic was composed of 70% hydroxyapatite and 30% tri-calcium phosphate with known mechanical and physico-chemical properties. Three compounds were processed with different size of macropore and with or without microporosity on their surface. Cells were seeded on discs measuring 10 mm in diameter and 2 mm in thickness. Cellular viability was evaluated by the MTT test for every stage of observation. An histological study to observe the invasion in the depth of discs was performed. Scanning electron microscopy was used to analyze the cellular comportment in contact with the surface of substitutes. RESULTS: An exponential cellular growth was effective on each substitute with the two cellular types. Cells spread on the surface of the compounds covering macropores and colonized the depth of the discs. A size of macropore of 300 microm or more seemed to support this invasion. 15 microm sized interconnections appeared to be effective to allow cell migration between macropores. The cell proliferation was similar on substitutes with or without microporosity. CONCLUSION: Biomaterials currently used as bone substitute are more or less osteoconductive but they have no osteoinductive property. A hybrid association of calcium-phosphate ceramic with osteogenic cells should promote the development of a calcium phosphate compound with osteoinductive capacity.

Effect of different surface treatments on the hydrothermal degradation of a 3Y-TZP ceramic for dental implants.

OBJECTIVES: Implant surface modifications are intended to enhance bone integration. The objective of this study was to assess the effect of different surface treatments on the resistance to hydrothermal degradation, hardness and elastic modulus of a 3Y-TZP ceramic used for dental implants. METHODS: Samples grouped according to their surface morphologies (AS, as-sintered; C, coated; P, dry-polished; R, roughened; PA, polished and annealed; RA, roughened and annealed) were subjected to accelerated hydrothermal degradation (LTD) by exposure to water steam (134°C, 2bars) for 100h. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR) and by combined focused ion beam and scanning electron microscopy (FIB-SEM). Elastic modulus and hardness before- and after prolonged aging (100h) were assessed by nanoindentation. RESULTS: AS and C specimens presented a better resistance to hydrothermal degradation than P and R samples. After prolonged aging, the depth of the monoclinic transformed layer ranged from 11µm to 14µm. Hydrothermal degradation led to a significant decrease of elastic modulus and hardness. SIGNIFICANCE: Surface treatments affected the resistance to hydrothermal degradation of the 3Y-TZP ceramic. Dry mechanical surface modifications should be avoided since a high t-m transformation rate associated to the initial monoclinic content was observed. Annealing was useful to reverse the initial t-m transformation, but did not improve the resistance to hydrothermal degradation.

Evaluation of a new press-fit in situ setting composite porous scaffold for cancellous bone repair: towards a "surgeon-friendly" bone filler?

In this study, a composite porous material obtained by coating a poly(ester urethane) foam with a calcium phosphate cement is proposed as novel cancellous bone filler with easy handling, in situ hardening and press-fitting properties. The coating can be applied to the foam in the surgical theater, allowing refinement of scaffold shape to the needs of the ongoing surgery. An innovative experiment was developed in order to determine the setting curve of the composite scaffold as well as the time of manipulation available to the surgeon without risk of material damage. This composite material is soft and can be press-fit in a cavity without damaging the scaffold in the first 5 min after coating application. The composite scaffold hardens quickly (22 min) and, once the cement has set, its compressive strength and fracture energy are increased by over an order of magnitude as compared to the initial poly(ester urethane) foam. This set of interesting properties makes calcium phosphate cement-coated elastomeric scaffolds a new promising strategy for cancellous bone filling.

Sintering behaviour of 45S5 bioactive glass.

In this study, we report on the effect of Bioglass structural transformations on its sintering behaviour. While heating up to 1000 degrees C, five successive transformations occur: glass transition, glass-in-glass phase separation, two crystallization processes and a second glass transition. The sintering of the material exhibits two main shrinkage stages associated with the two glass transitions at 550 and 850 degrees C. At 580 degrees C, the glass-in-glass phase separation induces a decrease in the sintering rate immediately followed by the major crystalline phase crystallization (Na(2)CaSi(2)O(6)) between 600 and 700 degrees C, from the surface to the bulk of the particles. A complete inhibition of sintering takes place followed by a minor shrinkage effect due to crystallization. A plateau is then observed until the second glass transition temperature is reached. A modification of Frenkel's model allows the determination of the glass-in-glass phase separation kinetics and the identification of the structural transformations effects on sintering behaviour.

Nanostructured ceramic oxides with a slow crack growth resistance close to covalent materials.

Oxide ceramics are sensitive to slow crack growth because adsorption of water can take place at the crack tip, leading to a strong decrease of the surface energy in humid (or air) conditions. This is a major drawback concerning demanding, long-term applications such as orthopaedic implants. Here we show that a specific nanostructuration of ceramic oxides can lead to a crack resistance never reached before, similar to that of covalent ceramics.

Comparative study on the antimicrobial effects of Hexomedine and Betadine on the human skin flora.

Studies were carried out to detect the modifications, if any, on the peri-umbilical flora of six healthy volunteers after two or three daily applications of Hexomedine solution (HEX) and Betadine solution (PVI) repeated for five consecutive days. A standardized scrubbing method was used for bacterial sampling. Surviving bacteria were selected with both selective and non-selective media, and then identified by gas chromatographic fatty acid analysis. Both antiseptics were highly effective, showing both immediate and residual antimicrobial activities. The use of HEX led to a slight increase in Gram-positive cocci and a small decrease in coryneforms, but PVI produced a marked increase in Gram-positive cocci and a sharp decrease in coryneforms. The two antiseptics, however, caused no major alteration in the cutaneous microbial population. Indeed, neither the overgrowth of Gram-negative bacilli nor the emergence of resistant species was observed.

[Value of a standard exudate in the in vitro study of antiseptics]. / Intérêt d'un exsudat standard dans l'étude de l'activité in vitro des antiseptiques.

Bactericidal activity of antiseptics is generally determined in France according the AFNOR norms the principles of which have recently been reconsidered by the Pharmacopoeias. These norms preconize the use of either hard water (12 Ca++ milliequivalents) or a mixture of proteins (albumin-yeast extract) to appreciate any loss of activity by interference. However these two interfering substances are very different from exudates on wounds or burns. This is why we have prepared a standard exudate composed of dried bovine albumin (Cohn fraction V for bacteriology) 4% m/V; Ca++ 0.01% m/V and Mg++ 0.003% m/V. These protein and ion concentrations correspond to the percentage of these elements in plasma. A first sequence of assays on two antiseptics, one with a chlorhexidine base, the second with a iodine polyvidon base allowed us to study individually the interference of proteins, of ions, and that of the standard exudate. The first results showed that for the iodine polyvidon the effect of ions was slight compared with the effect of proteins whereas for chlorhexidine the effect of ions was a strong as that of proteins. Therefore we have used this standard exudate in the study of other antiseptics according to the protocol of the norms NF T 72-170. Results showed that the standard exudate strongly inhibits the bactericidal activity of antiseptics. We propose that its use be generalised in the in vitro study of antiseptics destined for cutaneous or mucous lesions.

Influence of Tween 80 on the mycolic acid composition of three cutaneous corynebacteria.

Changes in the mycolic acid composition of three cutaneous strains of corynebacteria were caused by the addition of Tween 80 to the culture medium. Gas chromatography-mass spectrometry showed that the carbon chain length and the degree of unsaturation had been affected: the levels of corynomycolic acid with 36 carbon atoms and two double bonds increased significantly.

[Role of Tween-80 used in the culture of cutaneous corynebacteria (JK group) on the composition of cellular fatty acids]. / Rôle du Tween-80 utilisé dans la culture des corynébactéries cutanées (groupe JK) sur la composition en acides gras cellulaires.

This study of 8 strains of cutaneous corynebacteria, including 5 strains of "JK corynebacteria", concerns the fatty acid composition of cells grown in the presence or not of Tween 80, which enhances their growth rate. The fatty acid methyl esters were analysed by gas-liquid chromatography. The fatty acid profile of the 8 strains agreed with the general pattern of the genus Corynebacterium, with major amounts of palmitic acid (C16:0) and oleic acid (C18:1) and with only trace amounts of 10-methyl octodecanoic acid (tuberculostearic acid). Iso and anteiso branched acids were not present. The 5 strains had high levels of stearic acid (C18:0). When cells were grown in the presence of Tween-80, the fatty acid composition was modified for all strains: their profiles showed high levels of oleic acid (C18:1) and smaller quantities of palmitoleic acid (C16:1). These results confirm the advantage of fatty acid composition for identification of Corynebacteria, and particularly for cutaneous strains, and emphasize the influence of the culture medium, especially that of Tween-80.