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PubMedDate not supplied

Marginal adaptation of 1 fiber-reinforced composite and 2 all-ceramic inlay fixed partial denture systems.

PURPOSE: The aim of this in vitro study was to evaluate the marginal adaptation and retention of inlay fixed partial dentures (IFPDs) made with 1 fiber-reinforced composite and 2 different ceramic materials using quantitative scanning electron microscope analysis after thermal cycling and mechanical loading, which simulated approximately 5 years of oral service. MATERIALS AND METHODS: Eighteen IFPDs made with fiber-reinforced composite (SR Adoro/Vectris), zirconium oxide-TZP (Cercon), and magnesia partially stabilized zirconia (DC-Leolux) covered with silica-based ceramics were tested in this study. The specimens were mechanically loaded in the vestibular cusp of the pontic element in a computer-controlled masticator with 1,200,000 half-sinusoid mechanical cycles of maximum 49 N each at a frequency of 1.7 Hz. A total of 3,000 thermocycles at 5 degrees C and 55 degrees C, 2 minutes each, were performed simultaneously. The marginal adaptation was analyzed at the interface of the luting composite and the abutment inlay/onlay (CI) and at the interface of the tooth and the luting composite (TC). RESULTS: The percentages of continuous margin at the CI interface were 94.6 +/- 3.1 and 88 +/- 6.7 for Adoro/Vectris, 92.9 +/- 5 and 85.7 +/- 6.1 for Cercon, and 96.2 +/- 2.1 and 82.2 +/- 9.8 for DC-Leolux, respectively, before and after loading. The percentages of continuous margin at the TC interface were 86.7 +/- 6.7 and 62.5 +/- 16.4 for Adoro/Vectris, 93.3 +/- 3.4 and 83.2 +/- 5.9 for Cercon, and 96.1 +/- 2.4 and 75.3 +/- 7 for DC-Leolux. Statistically significant differences were found after loading between the fiber-reinforced composite and the 2 ceramic systems at the TC interface. CONCLUSION: Within the limitations of this experimental study with regard to the sample size and contacting vectors, the results showed that flexibility of the framework may play an important role in the marginal adaptation of the IFPDs. More rigid materials may transfer less stress to the margins, thus promoting a more stable adhesion to the dental tissues.

Acid Etching, Dental↗
PubMed1990

[Diffusion bonding of hydroxyapatite ceramics and biometals].

To improve the mechanical characteristics of hydroxyapatite (HAP) ceramics, a metal-ceramic composite formed by a solid state direct diffusion bonding system was studied. The joining treatment was carried out of a high vacuum and high temperature, for the bioactive ceramics (HAP) and the following biometals; platinum, gold-platinum alloy, titanium and titanium alloys, zirconium, niobium and aluminium alloy. The effects of the variations of thermal expansion mismatch and the interactive reactions at the interface were investigated by fractographic observation (SEM), X-ray diffraction method and EPMA analysis. On some of these joining combinations, the bonding strength had the same bonding strength as the adhesive materials. The results of interface observations showed that the bonding strength is affected by the interface reactions and the diffusion phenomena.

Adhesiveness↗
PubMed1989

Histologic evaluation of tissue response to sintered lanthanum-containing hydroxyapatites subcutaneously implanted in rats.

Hydroxyapatite, lanthanum-containing hydroxyapatite, and lanthanum- and zirconium-containing hydroxyapatite discs were implanted subcutaneously in the backs of rats. The implanted discs and surrounding tissues were removed at 5 and 12 hours, and 1, 3, 7, 14, 30 and 60 days after implantation, and fixed in paraformaldehyde. Tissue samples were dehydrated and embedded in paraffin. Paraffin sections were cut and stained with hematoxylin and eosin, van Gieson's, and Masson's trichrome. The early tissue reaction was exudative due to fibrin deposition and infiltration by polymorphonuclear leukocytes and macrophages. The later reaction was characterized by the formation of fibrous tissue without inflammatory cell infiltration. The tissue reaction to all three types of material was identical by two months after implantation.

Animals↗
PubMed1974

Formation of multinucleate giant cells in organized epitheloid cell granulomas.

Organized epithelioid cell granulomas were produced experimentally by injecting intradermally dilute suspensions of zirconium and beryllium salts into individuals who had been previously sensitized to these metals. Biopsies were obtained at intervals of between 5 days and 13 months later, and the specimens were fixed and prepared for light and electron microscopy. Tritiated thymidine was injected into a number of the granulomas; the biopsy specimens were secured from 40 minutes to 2 or more weeks later, and the tissues were processed for light microscopic autoradiography. Giant cells occurred commonly, both within organized tubercles and in relation to areas of necrosis, and had markedly different cytoplasmic features from typical secretory epithelioid cells which enabled them to be readily recognized at scanning magnifications. The characteristic hallmark of these giant cells was the presence of myriads of small mitochondria adjacent to nuclei with numerous membrane-lined vesicles in the center of the cell. Giant cells occurred mainly in edematous disrupted tubercles. In these tubercles, epithelioid cells contained cytoplasmic components more like giant cells. Direct evidence of cell fusion was not seen, although fusion of membranes seemed to occur between cells having similar cytoplasmic features. The failure to find labeled nuclei in any giant cells 40 minutes after injection of tritiated thymidine indicates that normal nuclear division does not occur within giant cells. We postulate that epithelioid cells containing vesicles develop in damaged and necrotic areas, and that mainly this type of epithelioid cell fuses to form giant cells.

Autoradiography↗
PubMedDate not supplied

Removal of excess inorganic phosphate by haemoperfusion with composite beads.

New composite beads, made by encapsulating hydrous zirconium oxide powder in agarose, are evaluated in vitro and in vivo for the removal of inorganic phosphate from the blood. Phosphate adsorption is rather good and calcium removal can be controlled. Thus, a 250 to 300 ml column is capable of reducing phosphate plasma level by some 5 mg per cent, thus making it attractive for the treatment of acute renal failure. Biocompatibility tests showed that supplementing the standard heparinization procedure by adding some citrate, as ACD, to the extracorporeal circuit greatly improves platelet and leucocyte count. No adverse haemodynamic effects were noted in repeated haemoperfusions of five dogs.

Acute Kidney Injury↗
PubMed1983

Recent results of the German Thorotrast study--dose relevant physical and biological properties of Thorotrast equivalent colloids.

As a prerequisite for quantifying the non-radiation effect of Thorotrast, nonradioactive and radioactive aquasols with identical physicochemical properties and with biophysical behavior comparable to that of Thorotrast were developed and produced for a second long-term animal experiment. Comparative investigations with hafnium and zirconium (zirconotrast) dioxide aquasols showed the latter to be most appropriate considering the size of both the dispersoids and the aggregates in the liver tissue. The average particle diameters of ThO2, ZrO2 and HfO2 proved to be values of 9.3 nm, 15 nm and 45 nm, respectively. The size of the aggregates shows a slight dependence on the applied amount but no dependence on the duration of body burden of the colloid. The aggregate diameters in the 600 microliters group turned out to be 9.6 microns, 14.4 microns and 5.3 microns, respectively. Radioactive zirconotrast was prepared by radiochemical incorporation of 230Th and 228Th at dose rates which produce accumulated doses in the liver of rats equivalent to those of commercial 230Th enriched Thorotrast after 1.5 yr. Five different colloids were prepared with alpha-energy emission rates increased by factors of 1, 2.5, 5, 10 and 25 compared to Thorotrast and then injected into rats.

Animals↗
PubMed1993

Localized wear and marginal integrity of posterior resin composites.

In vitro localized wear testing was completed on several commercially available and experimental resin composites to evaluate the loss of occlusal contact wear. Marginal deterioration after localized stressing was also evaluated by SEM observation. The compositions containing zirconium silicate and quartz exhibited the least amount of wear. However, an experimental 4-META bonding resin exhibited the best marginal integrity.

Acrylic Resins↗
PubMed1996

Wear-resistant, hemocompatible Ti-Nb-Zr and Zr-Nb alloys to improve blood pump design and performance.

Over the past several years, we have developed novel titanium-niobium-zirconium (Ti-Nb-Zr) alloys to address the long-term performance needs of orthopedic implants. The unique properties of these alloys also render them promising candidates for blood pumps. These properties include excellent biocompatibility in combination with high strength and toughness, and low elastic modulus (low stiffness). Additionally, these metal alloys are readily hot or cold worked into complex shapes including wire, foil, tubing and bar. They are readily machined and polished, and they can be surface oxidized to form a hard, wear-resistant, low-friction ceramic surface layer. In this diffusion-hardened condition, oxygen also hardens the underlying metal to optimize the bone between the ceramic oxide surface and the tough metal substrate. Unlike metal surfaces, oxidative wear, which can alter surface energy, friction, and hemocompatibility, does not occur. Consequently, the combined benefits of a stable, wear-resistant, low-friction ceramic surface layer with the toughness, strength, formability, and thermal conductivity of metal may provide improvements in the design and performance of blood pumps and peripheral graft and percutaneous (power) components of the pump.

Alloys↗
PubMed1996

Surface reaction between titanium castings and investments.

The selection of investments suitable for titanium castings is critical because the surface-reacted layer greatly affects their mechanical properties. This study analyzed the interfacial zone of titanium castings obtained from various commercial investments and examined the relationship between the surface-reacted layer and the hardness. CP titanium disks (20 mm diameter, 1 mm thick, n = 5) were cast using eight commercial casting systems and investments for titanium casting: two alumina-based investments (T-invest, CD-titan investment), two spinel-based investments (Titanmold, Titavest MZ), three zirconia-based investments (Asahivest-D, Titaniumvest EX, Tycast investment TM), and a magnesia-based investment (Selevest CB). The Vickers hardness of cast disks in cross-section was tested at 50 microns intervals from the surface to 0.5 mm in depth. The cross-section was observed metallurgically, and an elemental mapping measurement of the reacted layer was conducted under the EPMA. The Vickers hardnesses at 50 microns from the surface of the specimens ranged 312 to 624 and were significantly different among the investments (p < 0.01). The thickness of the reacted layer, rich in O, Si, Al, Zr, Mg, and P, ranged from 10 to 60 microns. No correlation was seen between the thickness of reacted layer and the hardness (p > 0.05). However, the specimens cast with alumina-based and zirconia-based investments were harder than the spinel-based and magnesia-based investments at 500 microns. Although the free energies of metal oxide formation of alumina and zirconia were lower than titania, these data suggest that silica, alumina and zirconia were reduced by contact with molten titanium. Accordingly, silicon, aluminum and zirconium diffused to the interior of the titanium castings and changed their mechanical properties.

Aluminum Oxide↗
PubMed1997

Reinforcement of acrylic resins for provisional fixed restorations. Part I: Mechanical properties.

Acrylic resins are commonly used in many dental applications; especially in the fabrication of provisional fixed partial dentures. Among noticed technical drawbacks associated with this material are unsatisfactory mechanical properties. Moreover, if acrylic resins are exposed to moist environment, water sorption results in further mechanical deterioration. In order to improve the mechanical properties, aluminum, magnesium, and zirconium oxide powders and pulverized E-glass particles were separately admixed with pre-polymerized acrylic resin beads prior to mixing with monomer liquid. Particle loading ratios were 1, 2 and 3 vol.% with respect to pre-polymerized beads. Poly(methyl methacrylate), poly(ethyl methacrylate) and poly(isobutyl methacrylate) were used as resin matrices. Furthermore, a metal primer agent was employed in order to form a strong interphase between admixed particles and polymer matrix phase. Samples were subjected to three-point transverse bending tests at a crosshead speed of 10 mm/min. It was concluded that (1) addition of particles generally increases the water sorbed by the composite resins systems, (2) however, two vol.% admixtures in a PMMA resin matrix showed significant improvements in the mechanical properties (p < 0.05), (3) among the oxide particles, zirconia exhibited the greatest improvements in modulus of elasticity, transverse strength, toughness and hardness, and (4) mechanical properties (transverse strength, 0.2% offset yield strength and modulus of elasticity) were linearly correlated to hardness numbers.

Acrylic Resins↗
PubMed1997

[Ceramic implants to benefit complete lower dentures].

In our Department of implantology, 141 ceramic implants were put in place with the objective of stabilizing a complete mandibular prosthesis in 39 patients. Despite the small number of cases reported, statistical analysis was informative because of the homogeneity of the conditions: the same indication for a prosthesis; the same operator for the surgery as well as the prosthesis; The very good follow-up with all but 2 patients having been monitored regularly. In addition to the finding that our results are practically superposable on those obtained with titanium implants over the same period of time. We share our experience with ceramic materials; dispel their reputation of fragility, especially since the advent of zirconium; and emphasize the simplicity of these "artificial roots" that can be use without prefabricated and costly intermediate parts.

Biocompatible Materials↗
PubMedDate not supplied

Post and core reconstruction for fixed prosthodontic restoration.

If the previous restorative therapy or dental caries has resulted in substantial loss of tooth structure, the abutment teeth for fixed prosthodontic restorations require a core reconstruction or a post and core. Small dentin defects can be restored with bonded cores; more extensive dentin defects that are often accompanied by previous endodontic treatment generally require additional support for the core material. A direct procedure with a bonded post is a viable treatment method. The decision to use either light-conducting all-ceramic zirconium or titanium as a post material depends on the aesthetic requirements present. The indications for a cast post and core as an indirect procedure for prosthodontic reconstructions appear to be decreasing. The learning objective of this article is to review the past and current post and core materials and techniques. Indications for core reconstruction with vital teeth and posts and cores for pulpless teeth are discussed.

Aged↗
PubMedDate not supplied

Alumina-zirconia machinable abutments for implant-supported single-tooth anterior crowns.

Innovative materials and application techniques are constantly being developed in the ongoing search for improved restorations. This article describes a new material and the fabrication process of aesthetic machinable ceramic anterior implant abutments. The ceramic material utilized is a mixture of alumina (aluminum oxide) and ceria (cerium oxide) with partially stabilized zirconia (zirconium oxide). The initial core material is a cylinder with a 9-mm diameter and a 15-mm height, obtained by ceramic injection and presintering processes. The resultant alumina-zirconia core is porous and readily machinable. It is secured to the analog, and its design is customized by machining the abutment to suit the particular clinical circumstances. The machining is followed by glass infiltration, and the crown is finalized. The learning objective of this article is to gain a basic knowledge of the fabrication and clinical application of the custom machinable abutments.

Aluminum Oxide↗
PubMedDate not supplied

Interfacial reactions of cast titanium with mold materials.

PURPOSE: Dental casting requires replication of complex shapes with high fidelity. To achieve this objective, the problem of scale formation on titanium dental castings must be overcome. Scaling occurs readily at high temperatures because of the high reactivity of molten titanium with investment materials. The purpose of this study was to examine the effectiveness of using stable oxide coatings on the mold surface to reduce the interfacial reactions. MATERIALS AND METHODS: A traditional phosphate-bonded dental investment, a commercial titanium investment, and an experimental oxide coating were used for the molds. Pure titanium samples were cast, divested, and prepared for scanning electron microscopic and energy dispersive x-ray spectroscopic analyses. RESULTS: Layers of 7- to 10-micron-thick scale were formed on titanium castings during reaction with traditional mold materials. Interface reaction was reduced between the molten titanium and the investment material when yttrium oxide or zirconium oxide coatings were applied to the mold before casting. CONCLUSION: Less titanium-mold interfacial reactions occurred when protective coatings were used as diffusion barriers for titanium casting. Y2O3-coating oxide particles applied without binder were entrapped in the cast titanium surface layer. Further study of a binder system for Y2O3 coating is needed.

Dental Casting Investment↗
PubMed2000

Ni-Zr alloys: relationship between surface characteristics and electrocatalytic behavior

A relationship between electrocatalytic activity for the hydrogen evolution reaction and the surface composition of the electrode was established for Ni-Zr crystalline and amorphous alloys by means of secondary ion mass spectrometry (SIMS). Electrocatalytic activity was tested by means of cathodic polarization in 1 M KOH at 25 degrees C and the resulting exchange current density has been taken as a measure of catalytic efficiency. Surface activation treatment involved chemical etching in HF solutions; the consequent morphological and compositional surface changes were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical behavior of the pure elements (Ni and Zr) was also considered for comparison. All samples submitted to chemical etching in HF solutions showed an increase in electrocatalytic activity, particularly the alloy with the highest Ni content. The beneficial effect of chemical etching is due to dissolution of the zirconium oxide layer and to the formation of nanocrystalline Ni on the surfaces.

Journal Article↗
PubMed1996

Migration of metal and polyethylene particles from articular prostheses may generate lymphadenopathy with histiocytosis.

Wear particles released from hip or knee prostheses are known to be involved in the fibrohistiocytic membrane interposed between bone and implant. During surgical treatment for pelvic carcinoma (5 cases) and for isolated pseudomalignant lymphadenopathy (4 cases) lymph nodes in 9 patients who had had lower limb articular replacement were harvested. Light microscopy and image analysis of the nodes showed florid endosinusal histiocytosis, predominant in the cortical area. Using Oil Red O staining and polarized light, metal particles and polyethylene particles were detected in the large histiocytes. Scanning electron microscopy with electron backscattering allowed us to localize metal particles and perform elemental microanalysis. Iron, cobalt, chromium, nickel, zirconium, and barium, known to be used in prosthetic and cementing materials, were identified as component of these particles. Large amounts of polyethylene particles appeared in all cases while metal particles were found to be abundant in only 2 cases. Thus, migration of polyethylene debris from the prosthetic site seems to be the major factor in development of the histiocytes induced in satellite lymph nodes.

Aged↗
PubMed1996

Wear testing of materials and surfaces for total knee replacement.

A simple wear test was investigated for evaluating the wear and damage of material pairs when used in total knee replacement. The test consisted of an axially loaded metallic femoral indentor and a reciprocating ultrahigh molecular weight polyethylene (UHMWPE) flat disk that represented the tibial component. A number of variables were studied including the effect of conformity by varying the radii of the femoral surface, distilled water or serum as a lubricant, different femoral materials, and different types of UHMWPE. In general, the different morphologies of the surface wear of the UHMWPE were similar to those seen on retrieved total knee replacements. Increased conformity with a cylindrical indentor gave a reduced wear rate initially, compared with that of the lower conformity spherical indentor. However, the wear rates were similar subsequent to this initial wearing in phase. Transfer films of UHMWPE were observed on the cobalt-chrome indentors for both serum and distilled water lubrication, although this film was more extensive for distilled water. The lowest wear rate was observed when oxidized zirconium was used on the femoral side, which was attributed to greater wettability, surface hardness, and immunity to oxidative wear. Tests using cobalt-chrome femoral cylinders and different grades of UHMWPE showed different wear rates. Of these PEs, GUR 415 showed less wear than both RCH 1000 and UHMWPE containing numerous fusion defects. For the latter, wear was attributed to a fatigue mechanism, although in most cases it was associated with surface phenomena rather than subsurface cracking. However, in some specimens of UHMWPE subsurface crack propagations occurred with defects. The test method is discussed in relation to its applicability to the evaluation and comparison of bearing materials and surfaces, with particular application to total knee replacements.

Alloys↗
PubMed2000

(N-pyrrolyl)B(C6F5)2--a new organometallic Lewis acid for the generation of group 4 metallocene cation complexes.

Treatment of the (C6F5)2BF x OEt2 (3) complex with N-pyrrolyl lithium gives bis(pentafluorophenyl)(N-pyrrolyl)borane (2), a strong organometallic Lewis acid, which was characterized by X-ray diffraction (B-N bond length: 1.401(5) A). It exhibits a columnar superstructure in the crystal and contains pi-stacks of pyrrolyl units. Compound 2 readily abstracts alkyl anions from a variety of alkyl Group 4 metallocene-type complexes and leads to the clean formation of the respective metallocene ions or ion pairs. For example, the treatment of Cp3ZrCH3 (9) with 2 transfers a methyl anion to yield the ion pair [Cp3Zr]+[(C4H4N)B(CH3)(C6F5)2]- (12). The X-ray crystal structure analysis of 12 shows a close contact between zirconium and the pyrrolyl-beta-carbon (2.641(2) A). The borane 2 adds to (butadiene)zirconocene (13) to yield the betaine system [Cp2Zr]+[(C4H6)B- (NC4H4)(C6F)2]- (15). Complex 15 contains a distorted eta3-allyl moiety inside the metallacyclic framework and it features an internal Zr+...(pyrrolyl)B- ion pair interaction with a Zr...pyrrolyl-alphacarbon separation of 2.723(3) A (determined by X-ray diffraction). From the dynamic NMR spectra of 15 the bond strength of the internal ion pair interaction was estimated to be deltaGdiss (223 K) approximately = to15 kcalmol(-1). Treatment of dimethylzirconocene (16) with 2 yields the metallocene borate salt [Cp2ZrCH3]+[(C4H4N)B(CH3)(C6F5)2]- (17), which is an active catalyst for the polymerization of ethene.

Journal Article↗