Investigation of the physical properties of tricalcium silicate cement-based root-end filling materials.

OBJECTIVE: Tricalcium silicate-based cements have been displayed as suitable root-end filling materials. The physical properties of prototype radiopacified tricalcium silicate cement, Bioaggregate and Biodentine were investigated. Intermediate restorative material was used as a control. METHODS: The physical properties of a prototype zirconium oxide replaced tricalcium silicate cement and two proprietary cements composed of tricalcium silicate namely Bioaggregate and Biodentine were investigated. Intermediate restorative material (IRM) was used as a control. Radiopacity assessment was undertaken and expressed in thickness of aluminum. In addition the anti-washout resistance was investigated using a novel basket-drop method and the fluid uptake, sorption and solubility were investigated using a gravimetric method. The setting time was assessed using an indentation technique and compressive strength and micro-hardness of the test materials were investigated. All the testing was performed with the test materials immersed in Hank's balanced salt solution. RESULTS: All the materials tested had a radiopacity value higher than 3mm thickness of aluminum. IRM exhibited the highest radiopacity. Biodentine demonstrated a high washout, low fluid uptake and sorption values, low setting time and superior mechanical properties. The fluid uptake and setting time was the highest for Bioaggregate. SIGNIFICANCE: The addition of admixtures to tricalcium silicate-based cements affects the physical properties of the materials.

Nanostructure-loaded mesoporous silica for controlled release of coumarin derivatives: a novel testing of the hyperthermia effect.

The synthesis of three types of mesoporous materials is reported: pure mesoporous silica (MCM-41), a nanocomposite of mesoporous silica with hydroxyapatite (MCM-41-HA) and mesoporous silica/gold nanorods nanocomposite (MCM-41-GNRs). The mesoporous materials were characterized by X-ray diffraction, N(2) adsorption isotherms, FTIR spectroscopy, transmission electron microscopy, and scanning electron microscopy. The samples were loaded with coumarin thiourea derivatives (I-IV) having functional groups of varying sizes and the in vitro release assays were monitored, and the release behavior was investigated as a function of soaking time in simulated body fluid. Two release stages were obtained in MCM-41, MCM-41-HA and MCM-41-GNRs loaded samples with the early release stages accounting for about 30% of loaded derivatives. These early release stages are characterized by Higuchi rate constant values nearly twice the values associated with the second release stages. The influence of substituent size on the release rate constants was explained in terms of sorption sites and hydrogen bonding with silanol groups on silicates. The release of coumarin derivatives loaded on MCM-41, MCM-41-HA and MCM-41-GNRs occurs over remarkably long time of the order of about 260 h with faster release rates in loaded MCM-41 and MCM-41-GNRs samples compared with MCM-41-HA ones. The role of hyperthermia effect in enhancing release rates was investigated by subjecting loaded MCM-41-GNRs to near infrared (NIR) radiation at 800 nm. This would be of significance in targeted drug release using hyperthermia effect. Unlike hydroxyl apatite, loading MCM-41 with gold nanorods does not affect the release kinetics. Only when these samples are irradiated with NIR photons, does the release occur with enhanced rates. This property could be valuable in selected targeting of drugs.

The mechanism of CO2- radical formation in biological and synthetic apatites.

Biological apatites (tooth enamel, bone) and their synthetic analogues were exposed to gamma rays, UV light, or thermal treatment and studied by electron paramagnetic resonance (EPR). The thermal generation of CO2- radicals in synthetic apatite was observed for the first time. It was shown that the experimental EPR spectra of all of the above-mentioned materials are caused by the contribution of two types of CO2- radicals: axial and orthorhombic. The ratio of their concentrations depends on the characteristic energy of the external influence (i.e., the energy of quantum for radiation or kT for thermal treatment) and also on the quality of the initial material (defectiveness). Based on the analysis of EPR spectra recorded immediately after gamma-irradiation, the authors conclude that the main short-lived radical in bioapatites is CO3(3)- . The unified mechanism of CO2- radical formation in hydroxyapatites at different external influences is proposed; the main stages of transformation are CO3(2)- + e --> CO3(3)- --> CO2-, where the electron (e) originates from the ionization of impurities by radiation/temperature.

Photoactive chitosan switching on bone-like apatite deposition.

The work was focused on the synthesis and characterization of the chitosan-g-fluorescein (CHFL) conjugate polymer as a biocompatible amphiphilic water-soluble photosensitizer, able to stimulate hydroxyapatite deposition upon visible light irradiation. Fluorescein (FL) grafting to chitosan (CH) chains was confirmed by UV-vis analysis of water solutions of FL and CHFL and by Fourier transform infrared spectroscopy (FTIR-ATR) analysis of CHFL and CH. Smooth CHFL cast films with 4 microm thickness were obtained by solvent casting. Continuous exposure to visible light for 7 days was found to activate the deposition of calcium phosphate crystals from a conventional simulated body fluid (SBF 1.0x) on the surface of CHFL cast films. EDX and FTIR-ATR analyses confirmed the apatite nature of the deposited calcium phosphate crystals. CHFL films preincubated in SBF (1.0x) solution under visible light irradiation and in the dark for 7 days were found to support the in vitro adhesion and proliferation of MG63 osteoblast-like cells (MTT viability test; 1-3 days culture time). On the other hand, the mineralization ability of MG63 osteoblast-like cells was significantly improved on CHFL films preincubated under visible light exposure (alkaline phosphatase activity (ALP) test for 1, 3, 7, and 14 days). The use of photoactive biocompatible conjugate polymer, such as CHFL, may lead to new therapeutic options in the field of bone/dental repair, exploiting the photoexcitation mechanism as a tool for biomineralization.

Selective laser sintering of porous tissue engineering scaffolds from poly(L: -lactide)/carbonated hydroxyapatite nanocomposite microspheres.

This study focuses on the use of bio-nanocomposite microspheres, consisting of carbonated hydroxyapatite (CHAp) nanospheres within a poly(L: -lactide) (PLLA) matrix, to produce tissue engineering (TE) scaffolds using a modified selective laser sintering (SLS) machine. PLLA microspheres and PLLA/CHAp nanocomposite microspheres were prepared by emulsion techniques. The resultant microspheres had a size range of 5-30 microm, suitable for the SLS process. Microstructural analyses revealed that the CHAp nanospheres were embedded throughout the PLLA microsphere, forming a nanocomposite structure. A custom-made miniature sintering platform was installed in a commercial Sinterstation((R)) 2000 SLS machine. This platform allowed the use of small quantities of biomaterials for TE scaffold production. The effects of laser power; scan spacing and part bed temperature were investigated and optimized. Finally, porous scaffolds were successfully fabricated from the PLLA microspheres and PLLA/CHAp nanocomposite microspheres. In particular, the PLLA/CHAp nanocomposite microspheres appeared to be promising for porous bone TE scaffold production using the SLS technique.

RF-magnetron sputtering technique for producing hydroxyapatite coating film on various substrates.

A sputtering technique is an effective method for surface modification of materials, but there are many complex process parameters to influence on the physical and chemical properties of the sputtered coating films. In this paper the process parameters were investigated when the hydroxyapatite (HA) was coated onto various substrates including titanium (Ti), alumina ceramic (Al(2)O(3)) and stainless steel (SUS) plates under various sputtering conditions, target type, Ar gas pressure, and discharge power. The deposition rate of HA was much higher in a solid plate target than in a powder lump target owing to the difference of apparent density 75%, 18%, respectively. Ar gas pressure little influenced on the deposition rate. The HA coating thickness increased in proportion with discharge power. After hydrothermal treatment the thickness of HA slightly decreased, on the other hands Ca/P ratio slightly raised. The surface of the HA coating was smooth, homogeneous and dense.

Crystallographic analysis of demineralized human enamel treated by laser-irradiation or remineralization.

Crystallographic information on dental hard tissue is helpful in evaluating whether incipient caries that has received preventative treatments is resistant to subsequent attack. The aim here was to analyse crystallographically by means of high-resolution electron microscopy (HREM) demineralized human enamel that had been laser-irradiated or remineralized. Electron-microscopic observation identified a distinct layer at a depth of 100 nm in the demineralized and laser-irradiated enamel. The crystallinity in the shallower area was inferior to that in the deeper area. Comparison of the HREM findings from the deeper area with the data provided by the Joint Committee on Powdered Diffraction Standards revealed that the mineral in the demineralized and laser-irradiated enamel was either alpha- or beta-tricalcium phosphate, while that in the remineralized enamel was thought to be tetracalcium diphosphate monoxide.

Influence of sterilization by gamma irradiation and of thermal annealing on creep of hydroxyapatite-reinforced polyethylene composites.

Sterilization of medical devices by gamma (gamma)-irradiation is common. The effect of irradiation on a bone replacement material, HAPEX (hydroxyapatite-reinforced polyethylene composite), was investigated. Unfilled and hydroxyapatite-filled polyethylene at 0.20 and 0.40 filler volume fractions were gamma-irradiated at 2.5 Mrad, and the modified properties were studied by differential scanning calorimetery, isochronous experiments, and creep tests. The effect of thermal annealing of the samples from 140 degrees C also was examined. The results suggest that both irradiation and annealing increase creep resistance of the materials. These are associated with the formation of crosslinks and an increase in crystallinity, respectively.

Compatibility of the argon and KTP lasers with middle ear implants.

Visible-spectrum lasers (argon, KTP) are becoming common tools in otology. Concern over transmission of disease by homograft tissue has focused attention on synthetic materials such as Silastic, Polycel, hydroxylapatite, and Teflon. This study sought to determine the effects of argon and KTP lasers on materials used in stapes and chronic ear surgery. Silastic sheeting, hydroxylapatite and polycel total ossicular replacement prostheses (TORPs) and partial ossicular replacement prostheses (PORPs), and platinum wire/Teflon stapes prostheses were exposed to argon and KTP laser energy at clinical power settings. Effects of the two lasers were similar. The presence of pigment (char or blood) was necessary to produce any effect. Silastic transmitted energy to underlying material. Hydroxylapatite cracked and shattered. Polycel vaporized and melted, as did Teflon. Clinical implications of these interactions on primary and revision otologic surgeries will be discussed.

The effect of therapeutic radiation on canine alveolar ridges augmented with hydroxylapatite.

The purpose of this investigation was to evaluate the effect of radiation on hydroxylapatite (HA) implanted subperiosteally for alveolar ridge augmentation in dogs. All bicuspids and molars were extracted from 16 dogs. After 6 weeks, nonporous HA granules were implanted subperiosteally on the alveolar ridge. Following 4 months of healing, 12 dogs (experimental group) underwent therapeutic radiation therapy (Co60, 4,000 rad [40 Gy]) to the head and neck region. Four dogs were not irradiated and served as controls. Four animals (three experimental and one control) were killed at 5,6,7, and 8 months after HA augmentation. Light microscopic evaluation showed that approximately 25% of HA granules were encased by bone while the others were surrounded by fibrous connective tissue. Dissolution of the HA was observed. Microparticles of HA were phagocytized as part of a granulomatous inflammatory reaction. This reaction decreased significantly as time elapsed after implantation. Osteoclastic activity was seen at the junction of HA and periosteum and as part of bone remodeling. Dissolution of the HA granules and the granulomatous inflammatory reaction were not significantly increased by therapeutic radiation. The radiation did not cause development of dehiscence or osteonecrosis.

Influence of coralline hydroxyapatite used as an ocular implant on the dose distribution of external beam photon radiation therapy.

Coralline hydroxyapatite spheres are used as buried integrated ocular implants after enucleation or evisceration surgery. Because such implants are used after surgery for intraocular malignancy and because some patients may require postoperative radiation therapy for orbital tumor recurrence, the radiation attenuation characteristics of the implant are of interest. The authors evaluated the attenuation and scattering properties of coralline hydroxyapatite implants using a 4 MV photon beam and film dosimetry. Optical density analyses indicate that coralline hydroxyapatite implants have no significant influence on the attenuation or scattering properties of the photon beam. As such, there is no basis for concern that such implants might adversely affect external beam photon irradiation.

Effects of the Nd:YAG dental laser on plasma-sprayed and hydroxyapatite-coated titanium dental implants: surface alteration and attempted sterilization.

The Nd:YAG dental laser has been recommended for a number of applications, including the decontamination or sterilization of surfaces of dental implants that are diseased or failing. The effects of laser irradiation in vitro (1) on the surface properties of plasma-sprayed titanium and plasma-sprayed hydroxyapatite-coated titanium dental implants, and (2) on the potential to sterilize those surfaces after contamination with spores of Bacillus subtilis have been examined. Surface effects were examined by scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction after laser irradiation at 0.3, 2.0, and 3.0 W using either contact or noncontact handpieces. Controls received no laser irradiation. Melting, loss of porosity, and other surface alterations were observed on both types of implants, even with the lowest power setting. For the sterilization study, both types of implants were first sterilized by exposure to ethylene oxide and then contaminated with spores of B subtilis. After laser irradiation, the implants were transferred to sterile growth medium and incubated. Laser irradiation did not sterilize either type of implant. The spore-contaminated implants in the control group were successfully sterilized with ethylene oxide.

Effects of carbon dioxide, Nd:YAG and carbon dioxide-Nd:YAG combination lasers at high energy densities on synthetic hydroxyaptite.

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J.cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 A and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. alpha-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of TCP.

Laser induced molar tooth pulp chamber temperature changes.

Temperature changes in enamel tissue and the pulp chamber under the influence of a CO2 laser were measured by direct methods in vitro. X-ray diffraction analysis revealed alpha-Ca3(PO4), the high-temperature modification of enamel hydroxyapatite, thus indicating that the enamel melting temperature was above 1,000 degrees C in the interaction area of laser (continuous wave, 15 s exposure time, 1 mm spot size) and tissue. Powers of 0.5 and 1 W (continuous wave), 1.5 mm spot size, and 10 s exposure time vaporize and carbonize dentin tissue at the cavity bottom of class I preparation molars. The observed temperature rise of 4 degrees C indicates that thermal injury to the pulp tissue does not occur.

[Solubility of enamel and synthetic hydroxylapatite on irradiation]. / Uber das Lösungsverhalten von Zahnschmlez und synthetischem Hydroxylapatit nach Bestrahlung.

The effect of Co 60-irradiation (70 Gy) on pulverized human enamel and synthetic hydroxyapatite was studied in vitro. Irradiated and non-irradiated samples were experimentally demineralized (pH 5.1) during a period of 28 days. In terms of solubility, defined as the equilibrium of saturation, there was no statistically significant difference between irradiated and non-irradiated enamel. However, in terms of solubility rates, defined as the amount of dissolved substance during the demineralization period, irradiated enamel showed a statistically significantly higher solubility rate than non-irradiated enamel. There was no effect of Co 60-irradiation on synthetic hydroxyapatite.

HREM study of irradiation damage in human dental enamel crystals.

Several phenomena have been observed during the examination of human dental enamel crystals (mainly constituted by hydroxyapatite (OHAP] by high-resolution electron microscopy (HREM) at 300 and 400 keV: orientation-dependent damage in the form of mass loss from voids or uniform destruction of crystal structure, beam-induced diffusion creating outgrowths at the crystal surfaces, recrystallization of the bulk crystal and crystallization of the inorganic components of the matrix surrounding the crystals. These beam-induced crystals have the CaO structure. The phenomena observed are most likely due to various electron-crystal interaction mechanisms (ballistic knock-on damage, electronic excitations, temperature rise, etc.). In this paper, the contribution of the ballistic process to the phenomena observed is discussed. The quantitative description of the knock-on collisions rests on the McKinley-Feshbach cross-section formula. The minimum ion displacement energies which appear in this expression have been estimated on the basis of the electrostatic ion binding energies, and the covalent bond energies if required. It is shown that hydroxyl, calcium and oxygen ions can effectively be displaced by the incident 300 and 400 keV electrons. Thus, the formation of CaO crystals by the combination of calcium and oxygen ions diffusing from their initial sites inside the OHAP lattice can tentatively be explained.

Insolubilized properties of UV-irradiated CO3 apatite-collagen composites.

To examine the response to biological hard tissues, a carbonate-containing hydroxyapatite with chemical composition and crystallinity similar to those of bone was synthesized at pH 7.4 and 60 degrees C. The apatite powder was mixed with collagen solution, whose antigenicity had been removed by enzymatic treatment, and formed into apatite-collagen pellets. After insolubilization by UV-irradiation for 4 h, the composites showed remarkably reduced disintegration and maintained their shape under 3.6 MPa of stress after 1 wk incubation in 0.9% NaCl solution. They showed good biocompatibility when implanted beneath the periosteum cranii of rats. The UV-irradiated sample kept its features well and was packed with newly created material 3 wk after implantation.

Effect of laser irradiation on the dissolution kinetics of hydroxyapatite preparations.

This research investigated the effects of a laser irradiation treatment on the dissolution characteristics of hydroxyapatite (HAP), and the results provide an insight into the relationship between the effects of laser treatment and the two-site dissolution kinetics of HAP samples. The HAP samples prepared by aqueous precipitation and digestion at approximately 100 degrees C were irradiated with a CO2 laser (20-50 W) with a beam diameter of 14 mm for a total of 10-400 s. Dissolution rates of the laser-treated HAP samples were subsequently determined in acetate buffer (pH = 4.5, mu = 0.50) at various levels of partial saturation (0-24% with respect to the HAP thermodynamic solubility of pKsp = 116). The following were the important findings. The X-ray diffraction and the IR spectroscopy results suggested that the HAP crystalline structure was not changed by laser treatment. Laser treatment of HAP powder at 50 W for 400 s, however, caused an approximately 3.5-fold reduction in the specific surface area of HAP and reduced the initial dissolution rate of HAP in acetate buffer by a factor of approximately 22.9. Also, this laser treatment appeared to reduce the dissolution rate of HAP in 16 and 24% partially saturated acetate buffer from substantial levels to essentially zero. These results may be summarized as follows. Laser treatment of HAP results in a reduction in the dissolution rate and also a reduction in the specific surface area of this material. However, the dissolution rate reduction is significantly greater than the reduction in the specific surface area.(ABSTRACT TRUNCATED AT 250 WORDS)

A possible mechanism of acquired acid resistance of human dental enamel by laser irradiation.

A possible mechanism of acquired acid resistance of lased enamel was proposed on the basis of the investigations of optical properties, compositional and structural changes and permeability of lased and unlased human dental enamel. Lased enamel showed a high positive birefringence, suggesting the formation of 'microspaces' in enamel. No new products were found, though a decrease of lattice strain and a slight a-axis contraction were recognized in lased enamel compared with unlased enamel. The contents of water, carbonate and organic substances were reduced in lased enamel. Gradual changes of birefringence were observed in lased enamel during treatment with acid solutions, and this change was attributed to mineralization of the microspaces. The ions released by an acid decalcification would be trapped in the microspaces in lased enamel, whereas such ions diffuse to the surrounding solution in unlased enamel.

Insolubilization of apatite-collagen composites by UV irradiation.

The physico-chemical properties and biocompatibility of insolubilized apatite-collagen composites were examined. A carbonate-containing hydroxyapatite with chemical composition and crystallinity similar to that of bone was synthesized at pH 7.4 and 60 degrees C. The apatite powder was mixed with collagen solution, whose antigenicity had been removed by enzymatic treatment and formed into apatite-collagen pellets. After insolubilization by UV irradiation for 4 h, the composites showed remarkably reduced disintegration and showed good biocompatibility when implanted into rat abdomen.