Constant composition dissolution kinetics studies of human dentin

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Principles of demineralization: modern strategies for the isolation of organic frameworks. Part II. Decalcification

This is the second paper on principles of demineralization. The initial paper is dedicated to the common definitions and the history of demineralization. In present work we review the principles and mechanisms of decalcification, i.e., removing the mineral Ca-containing compounds (phosphates and carbonates) from the organic matrix in its two main aspects: natural and artificial. Natural chemical erosion of biominerals (cavitation of biogenic calcareous substrata by bacteria, fungi, algae, foraminifera, sponges, polychaetes, and mollusks) is driven by production of mineral and organic acids, acidic polysaccharides, and enzymes (cabonic anhydrase, alkaline and phosphoprotein phosphataes, and H(+)-ATPase). Examples of artifical decalcification includes demineralization of bone, dentin and enamel, and skeletal formations of corals and crustacean. The mechanism and kinetics of Ca-containing biomineral dissolution is analyzed within the framework of (i) diffusion-reaction theory; (ii) surface-reaction controlled, morphology-based theories, and (iii) phenomenological surface coordination models. The application of surface complexation model for describing and predicting the effect of organic ligands on calcium and magnesium dissolution kinetics is also described. Use of the electron microscopy-based methods for observation and visualization of the decalcification phenomenon is discussed.

Differentiation ability of rat postnatal dental pulp cells in vitro

The current rapid progression in stem cell research has enhanced our knowledge of dental tissue regeneration. In this study, rat dental pulp cells were isolated and their differentiation ability was evaluated. First, dental pulp cells were obtained from maxillary incisors of male Wistar rats. Immunochemistry by stem cell marker STRO-1 proved the existence of stem cells or progenitors in the isolated cell population. The dissociated cells were then cultured both on smooth surfaces and on three-dimensional (3-D) scaffold materials in medium supplemented with beta-glycerophosphate, dexamethasone, and L-ascorbic acid. Cultures were analyzed by light and scanning electron microscopy and, on proliferation, alkaline phosphatase activity and calcium content were determined and the polymerase chain reaction was performed for dentin sialophosphoprotein, osteocalcin, and collagen type I. These cells showed the ability to differentiate into odontoblast-like cells and produced calcified nodules, which had components similar to dentin. In addition, we found that the "odontogenic" properties of the isolated cells were supported by three-dimensional calcium phosphate and titanium scaffolds equally well.

Octacalcium phosphate–based cement as a pulp-capping agent in rats

OBJECTIVE

The purpose of this study was to evaluate the pulpal response to an octacalcium phosphate (OCP)-based cement used as a pulp-capping material.

STUDY DESIGN

The pulps of 60 maxillary first molars of male Sprague-Dawley rats were exposed and then capped directly by using either OCP-based cement or a calcium hydroxide slurry (control). Histologic examinations were performed at 1, 2, and 5 weeks after the surgical procedure, and the results were analyzed statistically by using the Mann-Whitney U test (P<.05).

RESULTS

One week after pulp capping, the initial formation of reparative dentin in the exposed areas was more notable in the calcium hydroxide group than in the OCP-based cement group. At 2 weeks, reparative dentin covered by a layer of odontoblast-like cells was observed in both groups. However, at 5 weeks, reparative dentin consisting of regular dentinal tubules was observed more frequently in the OCP-based cement group.

CONCLUSION

OCP-based cement allowed favorable healing processes to occur in the dental pulp.

Demineralization in enamel and hydroxyapatite aggregates at increasing ionic strengths

Subsurface demineralization of dental enamel is a curious feature of both in vivo and in vitro lesion formation. Numerous explanations have been proposed to explain this. One general hypothesis is that subsurface demineralization in enamel and synthetic hydroxyapatite (HAP) aggregates may result from the phenomenon of coupled diffusion between the inward transport of acid and the outward transport of dissolution products. The aim of this study was to test the validity of this explanation. Inert electrolyte was added to demineralizing solutions in order to reduce electrostatic coupling between the diffusive flows that occur during lesion formation. Scanning microradiography (SMR) was used to examine surface layer formation, and to measure the rate of mineral loss at increasing ionic strengths. It was found that surface layer formation was significantly reduced as the concentration of inert electrolyte was increased. Further, the rate of mineral loss from the developing lesion increased as the concentration of inert electrolyte (and therefore the ionic strength) in the demineralizing solution increased. It is concluded that electrostatic coupling between counter diffusing acid and dissolution products during lesion formation can significantly influence the mineral concentration within the surface layer.

A study on grafting and characterization of HMDI-modified calcium hydrogenphosphate

It is known that the organic molecules can provide an effective means to manipulate the surface properties of the biodegradable ceramic. There are two ways to modify the surface of the biodegradable ceramic by organic molecules. The first one is through surface adsorption but organic molecules will easily be washed out in the physiological environment. The second approach is to graft organic molecules through covalent bond to the hydroxyl groups that are available on the surface of the ceramics. Isocyanate group has been reported as a coupling agent for hydroxyapatite and organic molecule. The studies showed that the isocyanate could react with hydroxyl groups of hydroxyapatite and form a covalent bond between isocyanate and hydroxyapatite. In the study, hexamethylene diisocyanate (HMDI) was used as coupling agent and calcium hydrogenphosphate (CaHPO4, CHP) was the candidate ceramic. CHP will react with HMDI at the temperature of 20 degrees C, 30 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C for 4h. Dibutyltin dilaurate and hydroquinone were used as catalyst and inhibitor, respectively. The effect of reaction temperature on the grafted yield will be described. The linkage between CHP and HMDI will be characterized by DTA, TGA, FTIR, XRD, and 31P, 13C liquid state NMR. From the results, we successfully modified the surface of CHP with coupling agent of HMDI. The grafted yield of HMDI on CHP was increasing with the reaction temperature. The best temperature for CHP modified by HMDI is around 50 degrees C. The linkage between HMDI and the surface of CHP is a urethane linkage as CHP-O-CO-NH-(CH2)6-N=C=O. After further treatment, the terminal group of CHP treated with HMDI (MCHP) will be converted into a primary amine group as the formula of CHP-O-CO-NH-(CH2)6-NH2. If reaction temperature is 60 degrees C, long extension chain will occur with a urea linkage between the isocyanate groups as the formula of CHP-O-CO-NH-(CH2)6-(NH-CO-NH-(CH2)6)n-NH2. At reaction temperature higher than 60 degrees C, the HMDI will become prepolymerized forms in solution. The prepolymerized forms such as allophanate, biuret, uretidione and urea linkage will turn the solution into gel type mixture, which will lead to low grafted yield of HMDI on CHP. When MCHP prepared at the temperature 20 degrees C, there is no evidence of long extension but the grafted yield is the lowest only 0.9 wt% around.

A study on the promotion and suppression of demineralization of human dental hard tissues and hydroxyapatite

Demineralization of human dental enamel and dentine and their analogue compound, hydroxyapatite, was examined by using pH-metry to measure the time-courses of neutralization of acetate, formate, lactate or propionate buffer solution or of acidification of EDTA solution. The extent of neutralization by enamel, dentine and hydroxyapatite was different for each acid but increased in the same order: propionate, acetate, lactate and formate. This order was consistent with that of the K values of these acids. The pH-metry was used to determine the influences of sodium chloride and sucrose on demineralization of enamel, dentine and hydroxyapatite by acetate, formate, lactate and propionate and by EDTA. The demineralization by these bioorganic acids was suppressed by sucrose but promoted by sodium chloride, except that the demineralization of enamel by acetate and propionate was little affected. The demineralization of enamel, dentine and hydroxyapatite by EDTA was little affected by sucrose but promoted by sodium chloride. The promotive effect of sodium chloride on demineralization may be due to the increasing of solubility product by this salt and the suppressive effect of sucrose may be due to the formation of a calcium saccharate formed from the sucrose reacted with calcium on the surface of apatite crystal and/or the reduction of solubility product by the sucrose. In this study, it was also ascertained that the use of pH-metry made it possible to determine easily the demineralization.

Surface Reactions of Apatite Dissolution

New experimental data about surface processes of interaction between natural apatite and phosphoric acid solutions were obtained by scanning electron microscopy, Auger electron spectroscopy, and IR reflection spectroscopy. The interaction was found to occur nonstoichiometrically (incongruently) on the very thin surface layer of apatite. The experimental data obtained were compared and extended with results taken from literature. The following sequence of ionic detachment from the surface of apatite to a solution was suggested: first fluorine for fluorapatite or hydroxyl for hydroxyapatite, next calcium, and afterward phosphate. A new chemical mechanism of apatite dissolution was proposed as a result. The mechanism for the first time described the surface irregularity of the dissolution process at the nanolevel. A comparison between this new dissolution mechanism and earlier mechanisms described in the literature was made.