Otto R. Trautz

Apatite crystallites: effects of carbonate on morphology.

Carbonate is a substituent in the apatite structure; when present, it limits the size of the growing apatite crystals and so influences their shape that they grow more equiaxed than needle-like. The tendency for carbonate apatites to be equiaxed is related to the nature of the chemical bonds formed in the crystal. The interference of carbonate with the good crystallization of apatite, and its weakening effect on the bonds in the structure, increase the dissolution rate and the solubility, thereby presumably contributing to the susceptibility to caries of dental apatites containing carbonate.

Two types of carbonate substitution in the apatite structure.

Um die Art des Karbonateinbaues in die Apatitstruktur zu klären, wurden zwei Typen von synthetischen Karbonatapatiten untersucht: solche, die sich in wässrigen Medien bildeten, und andere, die bei hohen Temperaturen und unter Ausschluss von Wasser entstanden.

Precipitation of calcium carbonates and phosphates. I. Spontaneous precipitation of calcium carbonates and phosphates under physiological conditions

Abstract The slow spontaneous precipitation of calcium carbonates and calcium phosphates was studied under physiological conditions. Calcium carbonate precipitation was prevented by the presence of phosphate ions at concentrations too low for the precipitation of calcium phosphate. The composition of most biological fluids does not allow the deposition of calcium carbonate. The suggestion is made that such deposition will occur under the influence of metabolic processes which locally raise the bicarbonate and lower the phosphate concentration. Aragonite was metastable under the conditions of the experiments. The aragonite present in the early precipitates of calcium carbonate transformed into calcite, when kept in contact with the supernatant solution. The crystallization of apatite is disturbed when bicarbonate is present in the solution. At sufficiently elevated calcium concentrations and bicarbonate/phosphate concentration ratios, an amorphous precipitate of calcium carbonate phosphate formed, which failed to crystallize into apatite when kept in contact with the supernatant solution. The Ca P molar ratio of the apatitic and amorphous precipitates varied between approximately 2.3 and 1.4. This large variation is due to the coprecipitation of carbonate, HPO4, and Na ions. These and other impurities interfere with the crystallization of the biological apatites and limit the size of the crystallites in bone and dentine. Dental enamel is better crystallized because it contains lesser amounts of these impurities.

X-RAY DIFFRACTION OF BIOLOGICAL AND SYNTHETIC APATITES

The improvement during the last 5 to 10 years in the design of X-ray diffraction equipment gives us an opportunity to re-examine our concepts of the structure of calcified tissues and the structure of the apatites. The microbeam techniques now permit the study of the crystal species and crystal orientation in tissue sections on areas as small as 30 microns.‘ Further reduction of the area is possible, but entails considerable inconveniences. When accompanied by a corresponding reduction in the thickness of the section, then the amount of diffracting matter which is irradiated by the beam is so small that the exposure times are prolonged to several hundred hours. The microfocus X-ray diffraction tubes of high brilliance can reduce the exposure times by a factor of 50. The new Geiger counter X-ray diffractometer, with its higher precision in the measurement of the reflection angles and the higher sensitivity in the detection of weak reflections, is essential in the study of the chemical composition of the apatites. The only crystal species found in the mineralized tissues of vertebrates, i.e., in enamel, dentin, cementum, and bone, is an apatite. In spit.e of pressing the search to the finest details, no reflection has been found on the diffractograms indicating the presence of another crystalline compound. Naturally, for the X-ray diffraction studies, dental enamel has been chiefly used, since its apatite is much better crystallized than the apatite of bone. In human incisor enamel, usually two fiber structures are observed intersecting at angles up to 60’. In shark’s enamel they intersect a t right angles? The physical properties of the enamels are conditioned by this orientation. The factors directing the orientation must be found in the organic matrix. The diffractograms of dentin, cementum, and bone usually do not reveal such an orientation, as the individual protein fibers of the matrix are oriented in many directions. However, if special small areas are selected in which histological methods have shown a parallel orientation of the protein fibers, then X-ray examination will also reveal the preferred orientation of the apatite. In certain special varieties of cementum and bone, a high degree of parallel orientation of the apatite crystallites has been observed. The size of the crystallites is estimated from broadening of the diffraction lines. Thus, in human incisor enamel and in bone, one finds an average size of 600 and 200 A.,3 respectively, or of 870 and 290 A? The difference in the results obtained by the various investigators is chiefly due to differences in the The crystallites in the tissues are oriented, forming “fiber” structures,

Spectral Properties of Carbonate in Carbonate-Containing Apatites

A study of the infrared absorption spectra of carbonate — containing synthetic and biological apatites is reviewed. The implications of the results for the nature of the incorporation of the CO3 2- ion into biological apatites is discussed.

The Interpretation of the X-Ray Diffractograms Obtained from Human Dental Enamel

V -RAY diffraction studies are applied to dental tissues and bone to obtain Ainformationn about the constituents and their structural arrangement in these tissues. They supplement information obtained by studies with other tools, such as chemical analyses, radioactive tracers, optical studies in plain and polarized light, and histologic studies on mature and developing tissues. Each tool furnishes information with its own particular limitations; together they can give a more complete understanding of the structure of these tissues and of their development. By extending these studies to pathologic deviations in the development of the tissues caused by metabolic disturbances, to changes in structures induced by disease, and to new structures produced by experimental methods, as pulp capping, we hope to help the dentist repair and prevent damages to dental tissues caused by metabolic disorder and disease. In a previous paper1 we described a diffraction microcamera for routine work with thin sections of teeth, bone, and other biologic preparations. The camera is a short cylindrical chamber. A lead glass capillary, inserted in the center of the front plate, serves as slit system, defining direction and aperture of the entering x-ray beam. The x-ray then passes through the specimen, which is mounted immediately over the inner end of the capillary. A fiat film, 15 mm. distant at the opposite end of the chamber, records the rays diffracted by the specimen, while the undiffracted beam leaves through a center hole in the film and in the back of the camera. When an x-ray diffractogram (the record of the diffracted rays on the film) is examined, there are two specific aims: (1) to identify the substance or substances causing the diffraction, and (2) to describe the directional arrangement of the diffracting matter in the specimen. The diffraction pattern is typical for the crystalline substance of the specimen, provided certain conditions regarding the arrangement of the diffracting matter in the x-ray beam obtain. However, deviations from these conditions may profoundly alter the appearance of the diffraction pattern. If one wishes to deduct all information possible from such variations in the pattern, utilizing the x-ray diffraction tool to the limits of its powers, one is in need of some crystallographic knowledge. Although this article deals chiefly with diffraction patterns obtained from dental enamel, much of the argumentation will hold also for dentin and bone, to which we shall occasionally refer.

Contribution to the micro-dumas method

Some phases of the Micro-Dumas method have been studied, and the magnitude of several errors encountered determined. The amount of air adsorbed to the CuO charge of the tube and often the air content of the CO2 used should be corrected in more accurate measurements. A new determination of the volume reduction of the azotometer capillary by the KOH solution yielded smaller corrections than applied heretofore. Minor alternations in the course of analysis and the method of calculating the results are therefore advised.

Carbonic Anhydrase and the Precipitation of Apatite

On theoretical grounds it is unlikely that the catalytic action of the enzyme carbonic anhydrase would be required for the precipitation of apatite in vitro. The presence of carbonic anhydrase in either active or inactivate form did not initiate precipitation in a metastable calcifying solution. It is unlikely that carbonate (or bicarbonate) ions are essential for the precipitation of apatite in vitro or in vivo.

Polarized Infrared Reflectance of Single Crystals of Apatites

Experiments are described using the polarized specular-reflectance technique to determine the dipole directions and relative intensities of the PO4 vibrations in F-apatite and hydroxyapatite single crystals. Use of this information to make assignments of the frequency bands is discussed.