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Low‐crystallinity hydroxyapatite (HAP) foam is an ideal material for bone substitutes and scaffolds for bone tissue regeneration, because its interconnected pores provide the space for cell growth and tissue penetration, and its composition induces excellent tissue response and good osteoconductivity. In this study, the feasibility of low‐crystallinity HAP foam fabrication was evaluated based on the phase transformation reaction or the so‐called dissolution‐reprecipitation reaction of α‐tricalcium phosphate (α‐TCP) foam granules. When α‐TCP foam granules were placed in water at 37°C for 1 day, no reaction was observed. However, α‐TCP foam granules set to form low‐crystallinity HAP by treating it hydrothermally at 200°C. The network of fully interconnected pores was retained, and porosity was as high as 82%. Pore size ranged from 50 to 300 μm with an average pore size of 160 μm. Compressive strength was 207 kPa. Although no setting reaction was observed at 37°C, the setting reaction caused by the hydrothermal treatment of α‐TCP foam granules allowed the fabrication of any shape of low‐crystallinity HAP. Therefore, this method may be useful for the fabrication of bone substitutes and scaffolds in bone tissue regeneration. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009 [ABSTRACT FROM AUTHOR]

We have reported that low-crystalline porous calcite block, which is useful as a bone substitute or a source material to prepare apatite-type bone fillers could be fabricated by exposing calcium hydroxide compact to carbon dioxide gas saturated with water vapor. In the present study, we investigated the effect of molding pressure on the transformation of calcium hydroxide into calcite and the mechanical strength of the carbonated compact. Transformation into calcite was almost completed within 72 h, however, a small amount of Ca(OH)2 still remained unreacted at higher molding pressure because of incomplete penetration of CO2 gas into the interparticle space due to dense packing of Ca(OH)2 particles. On the other hand, high molding pressure resulted in an increase in diametral tensile strength (DTS) of the calcite compact formed. Critical porosity of the calcite block was calculated as approximately 68%. [ABSTRACT FROM AUTHOR]

Bone mineral of human is different in composition from the stoichiometric hydroxyapatite (Ca10(PO4)6(OH)2) in that it contains additional ions, of which CO is the most abundant species. Carbonate-substituted hydroxyapatite (CHA) bodies were prepared by the hydrothermal treatment of highly porous calcium carbonate (CaCO3) body at 120 °C in 1 M M2HPO4 and M3PO4 solutions ( M = NH4 or K). It was found that CaCO3 body was almost transformed into CHA body after hydrothermal treatment for 24 h irrespective of type of phosphate solution. However, a small amount of CaCO3 still remained after the treatment in K3PO4 for 48 h. Crystal shape of CHA bodies prepared in those solutions except for K2HPO4 was flake-like, which was different from that (stick-like) of original CaCO3 body used for the preparation of CHA body. CHA prepared in the K2HPO4 showed globule-like crystal. Average pore size and hole size of the CHA bodies were 150, 70 μm and their porosities were about 89% irrespective of the solution. Carbonate content was slightly higher in the CHA bodies obtained from potassium phosphate solutions than in those obtained from ammonium phosphate solutions. Mostly B-type CHA was obtained after the hydrothermal treatment in the potassium phosphate solutions. On the other hand, mixed A- and B-type CHA (ca. 1–2 in molar ratio) was obtained in the ammonium phosphate solutions. The content of CO in the CHA body depended on the type of phosphate solution and was slightly larger in the potassium phosphate solutions. [ABSTRACT FROM AUTHOR]

Calcium carbonate is one of the bioceramics and has been used clinically as a bone substitute in dental and orthopedic surgery. Introduction of macropores into the bioceramics is highly recommended because those pores enable tissue ingrowth and accelerated osteointegration. We tried to prepare calcium carbonate body with macropores through the new carbonation method of calcium hydroxide/sodium chloride composite. Sodium chloride acted as a water-soluble porogen in developing macropores in calcium carbonate body and was removed completely by washing with distilled water after carbonation. We investigated effects of sodium chloride content and molding pressure on the porosity and the mechanical strength of the calcium carbonate body. Through this study, it was found that the porosity of body increased with the sodium chloride content in composite and was hardly affected by molding pressure. On the other hand, the mechanical strength was increased with the molding pressure and reduced with the porosity. In addition, the increase in content of sodium chloride caused the enlargement of hole size as well as the enhancement of extent of interconnection among pores through hole. Especially, the calcium carbonate body with over 90% porosity could be prepared when 90 wt.% sodium chloride was used under 10 MPa molding pressure. Its average pore and hole size were 177 and 80 μm, respectively. [ABSTRACT FROM AUTHOR]

Effects of added a-tricalcium phosphate (α-TCP) and β-TCP were investigated to shed light on the setting reaction of apatite cement (AC) consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous8 (DCPA). Added β-TCP showed no reactivity, and thus resulted in extended setting time and decreased mechanical strength. In contrast, α-TCP dissolved to supply calcium and phosphate ions after initial apatite crystal formation by the reaction of TTCP and DCPA. Although setting time was delayed because α-TCP was involved only in the latter reaction of apatite cement, larger apatite crystals were formed due to its addition. As a result of larger apatite crystal formation, the mechanical strength of α-TCP-added apatite cement increased by approximately 30%, as compared to α-TCP-free apatite cement. [ABSTRACT FROM AUTHOR]

Biporous (macro- and microporous) calcium phosphate gains much attention as a bone substitute material because of its large surface area and that it improves cell penetration In the present study, we evaluated the feasibility of biporous, low-crystalline apatite hosed on dissolution of mannitol from self setting apatite cement (Biopex®). Mannitol known as a biocompatible, easily dissolved monosaccharide alcohol -- was recrystallized to obtain larger crystals. It was crushed with pestle and mortar, sieved to obtain crystals which passed through a 500-µm mesh but which remained against a 300-µm mesh, and then used as porogen. Although Biopex® containing 60 wt% mannitol was not able to be taken out of the mold, addition of mannitol caused no initial setting inhibition to Biopex® if the amount was 40 wt% or less. Similarly, transformation to apatitic product was confirmed when the apatite cement was immersed in 0.9% saline kept at 37°C for seven days The set mass became low crystalline, hiporous apatite with approximately 60% porosity. [ABSTRACT FROM AUTHOR]

Porous hydroxyapatite (HAP) foam permits three-dimensional (3D) structure with fully interconnecting pores as well as excellent tissue response and good osteoconductivity. It is therefore thought to be a good candidate as scaffold material for bone regeneration and as a synthetic bone substitute material. To fabricate better porous HAP foam, improved physical and structural properties as well as higher osteoconductivity are desired. In the present study, the effects of sintering temperatures on the physical and compositional properties of porous HAP foam were evaluated by employing high sintering temperature starting at 1,300°C up to 1,550°C. The mechanical strength of porous HAP foam increased with sintering temperature to reach the maximum value at 1,525°C, then decreased slightly when sintering temperature was further increased to 1,550°C. Alpha tricalcium phosphate (α-TCP) was formed, and thus the porous HAP foam became biphasic calcium phosphate. Biphasic calcium phosphate consisting of both α-TCP and HAP had been reported to show higher osteoconductivity than HAP alone. We therefore recommend 1,500 1,550°C as the sintering temperature for porous HAP foam since this condition provided the most desirable physical properties with biphasic calcium phosphate composition. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the feasibility of fabricating low-crystalline, porous apatite block using set gypsum as a precursor based on the fact that apatite is thermodynamically more stable than gypsum. When the set gypsum was immersed in 1 mol/L diammonium hydrogen phosphate aqueous solution at 100°C, it transformed to low-crystalline porous apatite retaining its original shape. The transformation reaction caused a release of sulfate ions due to an ion exchange with phosphate ions, thus leading to a decrease in the pH of the solution. Then, due to decreased pH, dicalcium phosphate anhydrous-which has similar thermodynamic stability at lower pH-was also produced as a by-product. Apatite formed in the present method was low-crystalline, porous B-type carbonate apatite that contained approximately 0.5 wt% CO3, even though no carbonate sources-except carbon dioxide from air-were added to the reaction system. We concluded therefore that this is a useful bone filler fabrication method since B-type carbonate apatite is the biological apatite contained in bone. [ABSTRACT FROM AUTHOR]

Carbonate apatite (CO3Ap), fabricated by dissolution-precipitation reaction based on an appropriate precursor, is expected to be replaced by bone according to bone remodeling cycle. One of the precursor candidates is gypsum because it shows self-setting ability, which then enables it to be shaped and molded. The aim of this study, therefore, was to fabricate CO3Ap blocks from set gypsum. Set gypsum was immersed in a mixed solution of 0.4 mol/L disodium hydrogen phosphate (Na2HPO4) and 0.4 mol/L sodium hydrogen carbonate (NaHCO3) at 80-200°C for 6-48 h. Powder X-ray diffraction patterns and Fourier transform infrared spectra showed that CO3Ap block was fabricated by dissolution-precipitation reaction in Na2HPO4-NaHCO3 solution using set gypsum in 48 h when the temperature was 100°C or higher. Conversion rate to CO3Ap increased with treatment temperature. CO3Ap block containing a larger amount of carbonate was obtained when treated at lower temperature.

Effects of sintering temperature on the physical and compositional properties of alpha-TCP foam fabricated using the polyurethane foam method were examined. When a polyurethane foam coated with alpha-TCP slurry was sintered at 1,400-1,550 degrees C, alpha-TCP foam having basically the same fully interconnected porous structure was produced although shrinkage occurred with increasing sintering temperature. On porosity of the alpha-TCP foam, a higher foam porosity of 95% was obtained when sintered at 1,400 degrees C as compared to the 90% porosity obtained at a higher sintering temperature of 1,550 degrees C. Further, at 1,500 degrees C or higher temperature, frame became dense with disappearance of micropores. On compressive strength, it increased from approximately 50 to 250 kPa when sintering temperature was increased from 1,400 to 1,550 degrees C. Nonetheless, no compositional changes were observed even when the alpha-TCP foam was cooled in the furnace without quenching process. In light of the results obtained, it was concluded that alpha-TCP foam fabricated using the polyurethane method was useful as a bone substitute and/or scaffolding material for tissue engineering. Besides, alpha-TCP foam could be useful as a precursor for the fabrication of other calcium phosphate foams.

Low-crystallinity hydroxyapatite (HAP) foam is an ideal material for bone substitutes and scaffolds for bone tissue regeneration, because its interconnected pores provide the space for cell growth and tissue penetration, and its composition induces excellent tissue response and good osteoconductivity. In this study, the feasibility of low-crystallinity HAP foam fabrication was evaluated based on the phase transformation reaction or the so-called dissolution-reprecipitation reaction of alpha-tricalcium phosphate (alpha-TCP) foam granules. When alpha-TCP foam granules were placed in water at 37 degrees C for 1 day, no reaction was observed. However, alpha-TCP foam granules set to form low-crystallinity HAP by treating it hydrothermally at 200 degrees C. The network of fully interconnected pores was retained, and porosity was as high as 82%. Pore size ranged from 50 to 300 mum with an average pore size of 160 mum. Compressive strength was 207 kPa. Although no setting reaction was observed at 37 degrees C, the setting reaction caused by the hydrothermal treatment of alpha-TCP foam granules allowed the fabrication of any shape of low-crystallinity HAP. Therefore, this method may be useful for the fabrication of bone substitutes and scaffolds in bone tissue regeneration., ((c) 2008 Wiley Periodicals, Inc.)

The effect of temperature on crystallinity of carbonate apatite (CAp) foam prepared from alpha-tricalcium phosphate (alpha-TCP) foam by hydrothermal treatment was investigated in the present study. The alpha-TCP foams were prepared through a conventional sintering method using polyurethane foam as template. Then, the resultant alpha-TCP foams were hydrothermally treated with Na2CO3 aqueous solution at 100 degrees C, 150 degrees C and 200 degrees C for 72 h. After hydrothermal treatment, the cancellous bone-like macroporous structure of the alpha-TCP foams was maintained. However, microscopic morphology of the foams' frame significantly changed after the 72 h treatment period. The smooth surface of alpha-TCP foam disappeared and the whole surface was covered with plate-like deposits. The plate-like deposits treated at 150 degrees C and 200 degrees C had smooth surface while those treated at 100 degrees C were constructed from spherical particles of approximately 200 nm in diameter. The results of X-ray diffraction and Fourier transform infrared analysis showed that alpha-TCP was completely converted to CAp and the crystallinity of CAp prepared at 100 degrees C was significantly lower than those prepared at 150 degrees C and 200 degrees C. Hydrothermal treatment of alpha-TCP foam at 100 degrees C allowed the formation of low-crystalline CAp foam but complete conversion needs a longer treatment period.

We have reported that low-crystalline porous calcite block, which is useful as a bone substitute or a source material to prepare apatite-type bone fillers could be fabricated by exposing calcium hydroxide compact to carbon dioxide gas saturated with water vapor. In the present study, we investigated the effect of molding pressure on the transformation of calcium hydroxide into calcite and the mechanical strength of the carbonated compact. Transformation into calcite was almost completed within 72 h, however, a small amount of Ca(OH)(2) still remained unreacted at higher molding pressure because of incomplete penetration of CO(2) gas into the interparticle space due to dense packing of Ca(OH)(2) particles. On the other hand, high molding pressure resulted in an increase in diametral tensile strength (DTS) of the calcite compact formed. Critical porosity of the calcite block was calculated as approximately 68%.

Calcium carbonate (CaCO(3)) has been widely used as a bone substitute material because of its excellent tissue response and good resorbability. In this experimental study, we propose a new method obtaining porous CaCO(3) monolith for an artificial bone substitute. In the method, calcium hydroxide compacts were exposed to carbon dioxide saturated with water vapor at room temperature. Carbonation completed within 3 days and calcite was the only product. The mechanical strength of CaCO(3) monolith increased with carbonation period and molding pressure. Development of mechanical strength proceeded through two steps; the first rapid increase by bonding with calcite layer formed at the surface of calcium hydroxide particles and the latter increase by the full conversion of calcium hydroxide to calcite. The latter process was thought to be controlled by the diffusion of CO(2) through micropores in the surface calcite layer. Porosity of calcite blocks thus prepared had 36.8-48.1% depending on molding pressure between 1 MPa and 5 MPa. We concluded that the present method may be useful for the preparation of bone substitutes or the preparation of source material for bone substitutes since this method succeeded in fabricating a low-crystalline, and thus a highly reactive, porous calcite block.

Objective: To test the hypothesis, derived from a previous short-term (7-day) assessment, that the absence of conventional pulp protection is not responsible for long-term pulp complications of composite resin restorations with self-etching adhesives., Methods: All 150 patients who received the restorations with self-etching adhesives were recalled at least 2 years after the placement of restorations. Of the 47 patients (31%) who responded, 106 restorations aged from 2.2 to 6.5 years were examined for tooth sensitivity and pulp vitality regarding long-term pulp complications. The results were subjected to a multivariable logistic regression analysis with regard to cavity depth, provision of conventional pulp protection and short-term pulp complications., Results: No positive cases were found in the assessment of tooth sensitivity. Four restorations (3.7%) made in deep cavities with conventional pulp protection resulted in pulpectomy due to inflammation, of which three cases presented short-term pulp complications. The 95% confidence intervals for the odds ratios estimated by the multivariable logistic regression analysis were (1.54, infinity) for cavity depth (1.50, infinity) for short-term pulp complications and (0.02, infinity) for conventional pulp protection. Namely, the last variable had no significant effect on long-term pulp complications and thus the hypothesis was verified., Conclusions: The absence of conventional pulp protection was not responsible for long-term pulp complications even in deep cavities with the use of self-etching adhesives. A deep cavity and the existence of short-term pulp complications were two critical predictors for the occurrence of long-term pulp complications.

Porous hydroxyapatite (HAP) foam permits three-dimensional (3D) structure with fully interconnecting pores as well as excellent tissue response and good osteoconductivity. It is therefore thought to be a good candidate as scaffold material for bone regeneration and as a synthetic bone substitute material. To fabricate better porous HAP foam, improved physical and structural properties as well as higher osteoconductivity are desired. In the present study, the effects of sintering temperature on the physical and compositional properties of porous HAP foam were evaluated by employing high sintering temperature starting at 1,300 degrees C up to 1,550 degrees C. The mechanical strength of porous HAP foam increased with sintering temperature to reach the maximum value at 1,525 degrees C, then decreased slightly when sintering temperature was further increased to 1,550 degrees C. Alpha tricalcium phosphate (alpha-TCP) was formed, and thus the porous HAP foam became biphasic calcium phosphate. Biphasic calcium phosphate consisting of both alpha-TCP and HAP had been reported to show higher osteoconductivity than HAP alone. We therefore recommend 1,500-1,550 degrees C as the sintering temperature for porous HAP foam since this condition provided the most desirable physical properties with biphasic calcium phosphate composition.

In this study, the effects of added bioactive glass on the basic setting properties of a commercially available resin-modified glass ionomer cement were investigated with respect to setting time, mechanical strength, and setting mechanism. It was found to be clinically acceptable whether the setting time was extended or shortened depending on the type of bioactive glass added. The compressive strength of the set cement containing the bioactive glass decreased and was much higher when compared with the conventional type glass ionomer cement containing bioactive glass. The Fourier-transform infrared and 13C CP/MAS-NMR spectroscopies revealed that the extent of the acid-base reaction was larger in the cements containing bioactive glass than in the commercial resin-modified glass ionomer cement because of its high basicity in the bioactive glass. The 27Al MAS-NMR showed that crosslinking of the carboxylates in the polymeric acid by Al proceeded less in the cement containing the bioactive glass.

Fluoride and various cations release from three commercial compomers (Dyract, Dyract AP and Compoglass-F) and a resin-modified glass ionomer (Fuji-II LC) as a control were measured up to 7 days in distilled water and 0.01M lactate buffer solution with pH 4.1. The surface morphological change before and after the release experiment was observed with a scanning electron microscopy. Fluoride, aluminum and strontium ions were released from Dyract, Dyract AP and Fuji-II LC much more in the lactate buffer than in the distilled water. With compoglass-F containing barium instead of strontium, barium was released in the same way. X-ray diffraction analysis confirmed that fluoride release from Dyract and Dyract AP was derived mainly from SrF(2) contained in Dyract and Dyract AP. However, fluoride release from Compoglass-F was derived from glassy phase though it contained much fluoride as YbF(3). Cumulative release amount of each species versus square root of time plot showed good linearity, indicating that the dissolution was controlled by the diffusion mechanism. The surface characteristics of disks for each material, which were immersed in the lactate buffer, were quite different from the surface before and after immersion in deionized water, especially with Dyract. After immersion in the lactate buffer, many voids which were left after dissolution of the filler particle, were seen obviously on the surface of Dyract., (Copyright 2003 Elsevier Science Ltd.)

The amount of water absorption of poly(methyl methacrylate) (PMMA) containing 0, 1, 3 and 5 wt% of an adhesive monomer, 4-methacryloxyethyl trimellitic anhydride (4-META), was measured at 7 degrees C, 37 degrees C and 60 degrees C. After the water uptake reached equilibrium in specimens, they were desorbed to obtain a constant value and the absorption process was repeated. Mass changes in the second desorption were recorded for the storage temperatures of 37 degrees C and 60 degrees C. Multiple regression analyses were conducted on three independent variables, 4-META concentration, storage temperature and absorption-desorption cycle. A statistically significant relationship was found between the maximum water uptake and 4-META concentration, while there was no relationship between the maximum water uptake and diffusion coefficient obtained using the Fick's law. The negative relationship in the latter did not support the free space theory. The significant and positive relationship between the maximum water uptake and 4-META concentration demonstrates that water molecules diffuse through the formation of a hydrogen bond at polar sites. The maximum water uptake was not influenced by temperature, while the diffusion coefficient increased with the rise in temperature. The activation energy was 41-47 and 50-53 kJ/mol in the first and second absorption tests, respectively., (Copyright 2002 Elsevier Science Ltd.)