Functional evaluation of mineral trioxide aggregate cement with choline dihydrogen phosphate.

To improve the cytocompatibility of mineral trioxide aggregate (MTA) cement and its ability for reparative dentin formation, the effect of adding choline dihydrogen phosphate (CDHP), which is reported to be biocompatible, to MTA cement was investigated. The L929 cell proliferation showed that the addition of CDHP improved cell viability. The addition of CDHP shortened the setting time of MTA cement, with a significant decrease in consistency above 0.4 g/mL. Diametral tensile strength of the set cement was improved by the addition of 0.4 g/mL CDHP. Solubility was judged to be within the range of clinical application. The spontaneous precipitation of low crystalline hydroxyapatite was examined by immersing the set cement in phosphate buffer saline, and it was found that the ability of the cement with 0.4 g/mL of CDHP was significantly improved compared with that of the cement without CDHP.

Fabrication of bioresorbable hydroxyapatite bone grafts through the setting reaction of calcium phosphate cement.

We prepared hydroxyapatite (HAp) bone grafts by the setting reaction of calcium phosphate cement, and investigated the effects of the porosity and crystallinity on the osteoconductivity and bioresorbability. We examined the effect of the water-mixing ratio, pressure, and post-heat treatment temperature during preparation on the crystallite size and porosity of the HAp blocks. The quantity of protein adsorption increased with increasing porosity and specific surface area (SSA) of the HAp blocks, whereas the initial cell attachment was similar despite the different porosities and crystallinities. In in vitro dissolution tests with a pH 5.5 buffer, which mimics an osteoclast-created Howship's lacuna, both the porosity and SSA of the HAp blocks affected the solubility; most likely due to the increased contact area with the buffer. Thus, HAp blocks prepared by the setting reaction of calcium phosphate cement could be applicable for bioresorbable HAp bone grafts because of the high porosity and SSA.

Development of an error-detection examination for conservative dentistry education.

OBJECTIVE: For dental students, textbooks and lectures provide basic knowledge, and simulated and actual clinical training provide learning in technical and communication skills. At our college, conservative dentistry is taught in the third and fourth years of a 6-year undergraduate degree. Clinical training is undertaken subsequently in the fifth year and includes cavity preparation and composite resin filling tasks. However, despite the clinical importance of a full understanding surrounding these procedures, sixth-year students occasionally provide incorrect answers regarding these procedures in assessments. Although they demonstrated a basic understanding of the procedures, they may have forgotten the acquired knowledge during their clinical training. Therefore, we developed an error-detection examination to evaluate and improve fifth-year students' knowledge. METHODS: Written detailed treatment procedures for standardized, typical, cases were presented to students. Some critical steps were intentionally written incorrectly, and students had to identify and correct these. After correcting the steps, students gave a presentation to their peers on their corrections. This was followed by a summary of the correct answers and a short lecture by the teacher. Students then completed a questionnaire investigating their experience of the examination. RESULTS: Students misunderstood some key treatment steps, such as pretreatment of composite resin filling, amalgam removal, and ceramic inlay fitting. The questionnaire revealed that this method of testing applied knowledge was new to students and helped them to identify knowledge gaps. The test also increased their motivation to study conservative dentistry. Students were open to taking similar tests in different areas. CONCLUSION: Although conservative dentistry is a basic field of dental treatment, mistakes in treatment can lead to early treatment failure or reduce the lifetime of a restored tooth. Therefore, students need to have a deep understanding of procedures. Error-detection examinations may help students identify knowledge gaps and provide useful feedback to teachers to identify areas that they should stress in earlier years.

Characterization and thermal decomposition of synthetic carbonate apatite powders prepared using different alkali metal salts.

Two types of synthetic carbonate apatite [potassium-containing carbonate apatite (CAK) and sodium-containing carbonate apatite (CANa)] were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy. The chemical formulas of carbonate apatite were determined to be Ca9.36K0.12(PO4)5.12(CO3)0.88(OH)1.73 and Ca8.72Na1.33(PO4)4.96(CO3)1.04(OH)1.80, respectively. Thermogravimetric analysis showed that the final weight loss at 1,200°C reached about 11.2% for CAK and 13.9% for CANa. Carbonate loss gradually occurred above 150°C and continued to 1,200°C. The crystallinity of the apatite phase was found to be much improved between 800 and 850°C for CAK and 750 and 800°C for CANa, where rapid carbonate loss occurred. A small amount of CaO formed above 900°C. For CANa, NaCaPO4 also formed above 700°C in both apatites. Although the lattice parameters of the carbonate apatites varied with temperature, the final a and c lattice parameters attained constant values of 0.9421 and 0.6881 nm.

Characterization and in vitro evaluation of biphasic α-tricalcium phosphate/ß-tricalcium phosphate cement.

Biphasic calcium phosphate consisting of hydroxyapatite (HA) and ß-tricalcium phosphate(ß-TCP) is an excellent bone substitute with controllable bioresorbability. Fabrication of biphasic calcium phosphate with self-setting ability is expected to enhance its potential application as bone substitute. In this study, mixtures of α-TCP and ß-TCP with various compositions were prepared through α-ß phase transition of α-TCP powder at 1000°C for various periods. These powders were mixed with 0.25M Na2HPO4 at a P/L ratio of 2, and then hardened at 37°C at 100% RH for up to 24h. Material properties of biphasic HA/ß-TCP cement with different α-TCP/ß-TCP composition were characterized. These cements were also evaluated with respect to cell response in vitro using MC3T3-E1 cell lines. In conclusion, mechanical and biological properties of HA/ß-TCP cement could be controlled by changing the heat treatment time of α-TCP powder at 1000°C. In vitro results indicated that cell proliferation and ALP activity increased with increase ß-TCP content.

Effects of the method of apatite seed crystals addition on setting reaction of α-tricalcium phosphate based apatite cement.

Appropriate setting time is an important parameter that determines the effectiveness of apatite cement (AC) for clinical application, given the issues of crystalline inflammatory response phenomena if AC fails to set. To this end, the present study analyzes the effects of the method of apatite seed crystals addition on the setting reaction of α-tricalcium phosphate (α-TCP) based AC. Two ACs, both consisting of α-TCP and calcium deficient hydroxyapatite (cdHAp), were analyzed in this study. In one AC, cdHAp was added externally to α-TCP and this AC was abbreviated as AC(EA). In the other AC, α-TCP was partially hydrolyzed to form cdHAp on the surface of α-TCP. This AC was referred to as AC(PH). Results indicate a decrease in the setting time of both ACs with the addition of cdHAp. Among them, for the given amount of added cdHAp, AC(PH) showed relatively shorter setting time than AC(EA). Besides, the mechanical strength of the set AC(PH) was also higher than that of set AC(EA). These properties of AC(PH) were attributed to the predominant crystal growth of cdHAp in the vicinity of the α-TCP particle surface. Accordingly, it can be concluded that the partial hydrolysis of α-TCP may be a better approach to add low crystalline cdHAp onto α-TCP based AC.

Fabrication of bone cement that fully transforms to carbonate apatite.

The objective of this study was to fabricate a type of bone cement that could fully transform to carbonate apatite (CO3Ap) in physiological conditions. A combination of calcium carbonate (CaCO3) and dicalcium phosphate anhydrous was chosen as the powder phase and mixed with one of three kinds of sodium phosphate solutions: NaH2PO4, Na2HPO4, or Na3PO4. The cement that fully transformed to CO3Ap was fabricated using vaterite, instead of calcite, as a CaCO3 source. Their stability in aqueous solutions was different, regardless of the type of sodium phosphate solution. Rate of transformation to CO3Ap in descending order was Na3PO4>Na2HPO4>NaH2PO4. Transformation rate could be affected by the pH of solution. Results of this study showed that it was advantageous to use vaterite to fabricate CO3Ap-forming cement.

Fabrication of carbonate apatite blocks from set gypsum based on dissolution-precipitation reaction in phosphate-carbonate mixed solution.

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.

Effect of precursor's solubility on the mechanical property of hydroxyapatite formed by dissolution-precipitation reaction of tricalcium phosphate.

The effect of the solubility of the precursors, alpha tricalcium phosphate (α-TCP) and beta tricalcium phosphate (ß-TCP) on the mechanical strength of hydroxyapatite (HAp) bone substitute was investigated. Uniaxially pressed block starting from these precursors were treated hydrothermally with 1 mol/L of ammonia solution at 200°C for various durations. XRD analysis revealed that α-TCP block took 3 h whereas ß-TCP block took 240 h for complete transformation to HAp. The porosity of HAp obtained from ß-TCP block was found to be lower than that of HAp from α-TCP block. Diametral tensile strength of HAp from ß-TCP block showed a significantly higher value than that of HAp from α-TCP block. It is therefore concluded that solubility of precursor affects the mechanical strength of the HAp block.

Fabrication of solid and hollow carbonate apatite microspheres as bone substitutes using calcite microspheres as a precursor.

Spherical carbonate apatite (CO3Ap) microspheres approximately 1 mm in diameter were fabricated by granulation of calcium hydroxide around a core followed by carbonation and phosphatization through dissolution-precipitation reaction. CO3Ap microspheres with high uniformity could not be achieved without using a core. Solid CO3Ap microspheres were obtained using a calcite core whereas hollow CO3Ap microspheres were obtained using a NaCl core. The obtained microsphere was identified as B-type CO3Ap by Fourier transform infrared analysis and the carbonate content was approximately 7-8 wt% regardless of the type of core used for sample preparation. The mechanical strength of both the solid and hollow CO3Ap microspheres was sufficient for practical use as a bone substitute.

Fabrication of microporous calcite block from calcium hydroxide compact under carbon dioxide atmosphere at high temperature.

Effects of carbonation temperature and compacting pressure on basic properties of calcite block were studied using Ca(OH)2 compact made with 0.2-2.0 MPa and their carbonation at 200-800ºC for 1 h. Microporous calcite was obtained only when carbonated at 600ºC using Ca(OH)2 compact made with 0.2 MPa even though thermogravimetry analysis showed that calcite powder was stable up to 920ºC under CO2 atmosphere. CaO formed by carbonation at 700ºC and 800ºC is thought to be caused by the limited CO2 diffusion interior to the Ca(OH)2 compact. Also, unreacted Ca(OH)2 was found for Ca(OH)2 compact prepared with 0.5 MPa or higher pressure even when carbonated at 600ºC. As a result of high temperature carbonation, crystallite size of the calcite, 58.0 nm, was significantly larger when compared to that of calcite prepared at room temperature, 35.5 nm. Porosity and diametral tensile strength of the microporous calcite were 39.5% and 6.4 MPa.

Hydrothermal calcium modification of 316L stainless steel and its apatite forming ability in simulated body fluid.

To understand the feasibility of calcium (Ca) modification of type 316L stainless steel (316L SS) surface using hydrothermal treatment, 316L SS plates were treated hydrothermally in calcium chloride (CaCl(2)) solution. X-ray photoelectron spectroscopic analysis revealed that the surface of 316L SS plate was modified with Ca after hydrothermal treatment at 200°C. And the immobilized Ca increased with CaCl(2) concentration. However no Ca-modification was occurred for 316L SS plates treated at 100°C. When Ca-modified 316L SS plate was immersed in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma, low crystalline apatite was precipitated on its surface whereas no precipitate was observed on non Ca-modified 316L SS. The results obtained in the present study indicated that hydrothermal treatment at 200°C in CaCl(2) solution is useful for Ca-modification of 316L SS, and Ca-modification plays important role for apatite precipitation in SBF.

Fabrication of low-crystalline carbonate apatite foam bone replacement based on phase transformation of calcite foam.

Carbonate apatite (CO(3)Ap) foam may be an ideal bone substitute as it is sidelined to cancellous bone with respect to its chemical composition and structure. However, CO(3)Ap foam fabricated using α-tricalcium phosphate foam showed limited mechanical strength. In the present study, feasibility of the fabrication of calcite which could be a precursor of CO(3)Ap was studied. Calcite foam was successfully fabricated by the so-called "ceramic foam" method using calcium hydroxide coated polyurethane foam under CO(2)+O(2) atmosphere. Then the calcite foam was immersed in Na(2)HPO(4) aqueous solution for phase transformation based on dissolution-precipitation reaction. When CaO-free calcite foam was immersed in Na(2)HPO(4) solution, low-crystalline CO(3)Ap foam with 93-96% porosity and fully interconnected porous structure was fabricated. The compressive strength of the foam was 25.6 ± 6 kPa. In light of these results, we concluded that the properties of the precursor foam were key factors for the fabrication of CO(3)Ap foams.

Fabrication of carbonate apatite block based on internal dissolution-precipitation reaction of dicalcium phosphate and calcium carbonate.

In this study, we investigated a novel method for fabrication of carbonate apatite block without ionic movement between precursor and solution by using precursor that includes all constituent ions of carbonate apatite. A powder mixture prepared from dicalcium phosphate anhydrous and calcite at appropriate Ca/P ratios (1.5, 1.67, and 1.8) was used as starting material. For preparation of specimens, the slurry made from the powder mixture and distilled water was packed in a split stainless steel mold and heat - treated, ranging from 60 degrees C to 100 degrees C up to 48 hours at 100% humidity. It appeared that carbonate apatite could be obtained above 70 degrees C and monophasic carbonate apatite could be obtained from the powder mixture at Ca/P ratio of 1.67. Carbonate content of the specimen was about 5-7%. Diametral tensile strength of the carbonate apatite blocks slightly decreased with increasing treatment temperature. The decrease in diametral tensile strength is thought to be related to the crystal size of the carbonate apatite formed.

Effects of sintering temperature on physical and compositional properties of alpha-tricalcium phosphate foam.

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.

Effects of added mannitol on the setting reaction and mechanical strength of apatite cement.

Apatite cement containing porogen can be a useful material for the fabrication of biporous (macro- and microporous) apatite, which has gained much attention as a bone substitute material because of its large surface area and that it improves cell penetration. In the present study, the effects of added mannitol on the setting reaction and mechanical strength of apatite cement were evaluated. Apatite cements containing 0-40 wt% of mannitol were prepared and allowed to set in 0.9% saline kept at 37 degrees C for 1-7 days. Although the diametral tensile strength (DTS) value increased with time, it decreased with the amount of added mannitol. SEM observation and XRD analysis revealed that mannitol had no inhibitory effect on the transformation reaction of apatite cement to apatite. It was thus concluded that mannitol was a good candidate for the fabrication of biporous apatite because it is biocompatible, exhibits satisfactory dissolution behavior, and that it caused no inhibitory effects on the compositional transformation to apatitic material.

Effect of temperature on crystallinity of carbonate apatite foam prepared from alpha-tricalcium phosphate by hydrothermal treatment.

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.

Fabrication of biporous low-crystalline apatite based on mannitol dissolution from apatite cement.

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 based 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-microm mesh but which remained against a 300-microm 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 degrees C for seven days. The set mass became low-crystalline, biporous apatite with approximately 60% porosity.