The material science of calcium phosphate ceramics.

Tricalcium, tetracalcium phosphate and hydroxyapatite ceramics exhibit distinct differences in their chemical and structural composition. Only hydroxyapatite ceramic is identical with the original bone mineral. Different preparation methods lead to compact hydroxyapatite ceramic or to porous material with interconnecting macropores as structural equivalents of the spatial structure of cancellous bone. Concerning the behaviour in a biological environment, high crystallinity and large material density result in resistance to dissolution and long lasting stability. Amorphous ultrastructure and porous formation enhance interface activity and bone ingrowth, but also biological degradation of the ceramic implant material.

[The importance of the choice of materials and their design for the efficacy of orthodontic appliances]. / Die Bedeutung von Werkstoffauswahl und konstruktiver Anwendung für die Wirksamkeit kieferorthopädischer Geräte.

The aim of this study is to stress the importance of correct selection of materials for orthodontic appliances, and thereby emphasize the functional relationship between choice and use of material. The outlined state of the art is the result of carefully-conducted research, the development of which has been briefly mentioned; however, the type of problem resulted from critical observations by orthodontic practitioners who apply the research results for the benefit of their patients.

[Natural fluorides. The distinction between technically produced and naturally occurring fluorides in caries prophylaxis]. / Natürliches Fluor. Zur Unterscheidung von technisch hergestellten und natürlich vorkommenden Fluoriden bei der Kariesprophylaxe.

In the controversial discussion of the bio-availability of fluoride in caries prophylaxis by fluoridation, fluorides coming from the geochemical circulation to the biochemical circulation are sometimes differentiated from synthetic fluorides introduced into fluoride medication. The question as to whether such a differentiation is essential can be answered from the physical-chemical point of view. This requires a wide field of scientific research starting with geochemistry and the knowledge of fluoride deposits, sedimentology, hydrology, technology of inorganic and organic fluorine compounds, thermodynamics of dissolved fluorides, up to biocrystallography and biochemistry of fluorine.

[Dental implants and their materials]. / Dental-Implantate und ihre Werkstoffe.

Some new trends in materials for dental implants, which also effect in the operative techniques and implant design, are described. Advantages and shortcomings of the different material types are exemplified and correlated with their bioinert resp. bioactive functions. The practical interest in metallic implants focussed in titanium resp. oxide ceramics in the ceramic field, whereas the special goal of implant research follows from the improvement of the bioactive principle with loaded calcium phosphate implants.

High temperature behaviour of hydroxy- and fluorapatite. Crystalchemical implications of laser effects on dental enamel.

The application of laser rays for caries prevention as for restorative purposes in oral rehabilitation causes severe changes in the structural and textural assembly of the dental hard tissue. Electron microscopical and X-ray investigations of the new calcium phosphate phases which arise demonstrate a deterioration of the affected tooth regions.

[Review of implantation materials]. / Ubersicht über Implantatwerkstoffe.

The use of nonmetalic, ceramic materials has led to encouraging developments. Some metal implants have proved to be more reliable in general practice in respect to the mechanics and statics; part of the developmental goal however should include compound materials. Metal implants, tolerated by the organism under favorable conditions, were not accepted as well as the ceramic material. Recently, the long-term prognosis therefore has been viewed with reservation. Even though the tensile values were favorable, the mechanical properties were good, and the corrosion rate in terms of adequate tissue tolerance was generally satisfactorily low for metal, the organism still responded to metal as a foreign body.

[Crystal chemical and micromorphologic evaluation of ancient bone discoveries (Arabia Petraea, Jordan) from the 10th millennium B.C]. / Kristallchemische und mikromorphologische Bewertung von alten Knochenfunden (Arabia Petraea, Jordanien) aus dem 10. Jahrtausend v. u. Z.

As specialisations of osteoarchaeometry become increasingly developed, so the need of new analytical techniques and tests of a skillful applicability becomes more necessary. The crystal-chemical and micromorphological evaluations of preserved bone discoveries implicate reliable methods as X-ray diffraction, electron microscopy, and spectroscopy with the skeletal materials and the soil environment in which bones are found. The reactivity of soils varies widely as geological and sedimentological conditions offer typical but different environments: gravels, chalk soil, clay, salt soils, sands, cave earths are examples of this wide variety, including atmospheric and biogenetic implications. The last mentioned features are strongly effective also in aride regions, with the well known fluctations of high parching and dewiness. However, despite the diversity in deposition and burial modes only few parameters govern the gradual decomposition of bone material: 1. pH value of the surrounding medium; 2. humidity of the surrounding medium, may be governed directly by autolysis; 3. transport of matter, related to grain size, pore volume, solubility behaviour; 4. physical pressure; 5. destruction by microorganisms; as well as the surrounding medium will be altered by the uptake and the transformation of the products of bone decomposition. The materials of investigation were skeletal fragments buried of ea. 10,000 a within the soft dune sediment of the western border mountains of Wadi el Araba (Arabia Petraea, Jordan). The discovered bones are, as a common feature of this locality Basta, strongly sintered--indication on the afore mentioned reactivity of the aride soil as well. Bone fragments were partially burnt at Sabra locality and discolored, and sintered also at these circumstances. The reactivity of the bone fragments is shown in terms of exchange reactions within the crystal structure of the bone mineral, apatite Ca5(PO4)3OH at the calcium sites, hydroxyl sites, and phosphate sites. These reaction schemes are interpreted in the details. This decomposition by substitution will often preserve the external appearance of buried bones. Fig. 1 and 2 show the extent of the actual ion exchange with the surrounding soil strata resp. transformed areas (sinter sheets); in the case of Basta material as a nearly total rearrangement of the anion lattice (phosphate, silicate vs. carbonate) as well as verified by Scanning-electron microscopy (Fig. 3, 4) and phase analyses by X-ray diffraction (Fig. 5-7): calcite and quartz are the principal components of the sinters, additional diffuse apatite lines appear in bone samples.(ABSTRACT TRUNCATED AT 400 WORDS)

[Lead and arsenic resorption in the hard tissues (crystallochemical studies)]. / Zur Blei- und Arsenresorption der Hartgewebe (kristallchemische Untersuchungen

Histologic-analytical observations on the resorption of lead and arsenic compounds are put into relationship with crystal-chemical analogies in the composition of hard tissue and the structure of calcium phosphate apatites with lead and arsenic substitution. Chemical analyses and x-ray diffraction of calcium and lead apatites with phosphate and arsenate represented as mixed precipitates in solution equilibrium show that - with the exception of calcium arsenate apatite - linear diadochocinetic substitution conditions are existing. The composition of calcium arsenate apatite is clearly shown to contain much less arsenic. This result is explained by the crystallographic laws of substitution in the crystal lattice (diadochocinetic laws). The clinical and physiological findings in lead and arsenic resorption are confirmed by the found distributional equilibria.

[The damage caused by caustic acids during sealing of the dental enamel]. / Zur Noxe durch den Atzvorgang mit Säuren bei der Schmelzversiegelung

The chemical etching of enamel required for adhesion of sealant layers on the dental surfaces means that the enamel structure is weakened, especially due to the fact that after application of the sealant the cauterized layers are no longer in a remineralization equilibrium with the dental environment. The reactions on which cauterization is based are critically discussed. Newly developed synthetics are mentioned whose application as a sealant renders previous cauterization of the enamel by acids superfluous.

[Inhibition of hard dental plaques by reactive components of dentifrices]. / Inhibition harter Zahnbeläge durch Wirkstoffe in Zahnpasten.

Active components of toothpastes which are intended to inhibit plaque mineralization are discussed with their physiological and chemical implications on the formation and calcification of dental plaque. The decisive factors are defined as part of the biocrystallographic reactivity in the oral milieu.

[Enamel abrasion and enamel tears by porcelain brackets]. / Schmelzabrasionen und Schmelzausrisse bei Keramikbrackets.

Orthodontic brackets manufactured of poly- or monocrystalline alumina ceramics are aesthetically appealing, but unfortunately show disadvantages for clinical application primarily causing (1) Abrasions of the enamel of antagonistic teeth, and (2) Tear-outs of the underlying enamel through debonding. To determine whether hardness and/or textural and structural qualities of the ceramics (as characterized by SEM investigations) are responsible for the deleterious clinical effects of abrasion, the amount of decrease of the height of human enamel-molar-cusps was measured. Enamel loss was shown to be significantly more than 100 microns at 10 min. operating time in an abrasive testing device. Also debonding of the ceramic brackets proved to be problematic. Whereas metals and polymeric brackets allow some deflection of the material in addition to the tensile stress, separating the bracket from the enamel at the bracket-to-adhesive interface, or within the adhesive composite, the lacking workability in the ceramic brackets may induce a shift of the break-line during debonding to the adhesive-enamel interface or even into the dental enamel. Development and clinical application of ceramic brackets should improve safety for the enamel. Regardless of ceramic brand the abrasiveness endangers enamel through ceramic/enamel interferences. To avoid tear-out defects, brackets should debond at the ceramic-adhesive interface.

[Long-term decomposition of bones. 1. Mineral phase]. / Dekompositionsvorgänge des Knochens unter langer Liegezeit. 1. Die mineralishche Phase.

Based on the alteration of microstructure and gross features caused by long term fate of bony substance a model of decomposition of bone mineral is outlined. Destruction of the corps by microorganisms leads on the whole to an acid milieu. Hence hydroxyapatite is turned into brushite, which is more soluble in acid media. As this mineral is formed in a space consuming way, the expanding brushite-masses support mechanical destruction of bony substance by cracking the lamellary systems. Both mechanical stress by formation of brushite and transformation of hydroxyapatite to this mineral compound are main features for dead bone decomposition.

Metallographic texture analysis of dental materials by polarizing microscopy in the incidental light.

Incidental polarized light microscopy can be used for the optical analysis of crystal phases with similar anisotropic behavior or preferred textures in polished sections. In this method, the vibration mode of the reflected light is determined by remarkable interference colors in the microscope using a compensator plate. The application of this method for the analysis of dental materials is demonstrated with amalgams and gold-reduced alloys. As a prerequisite, a modified procedure for preparing suitable polished sections of inhomogenous materials is described. Employing this optical and a crystallographic computing method, more detailed information about the way of element replacement in the course of the chemical reaction can be obtained. The results of these investigations also warrant the assumption that coherent crystal intergrowth which prefers low indicated and closely packed lattice directions, gives rise to a good adhesive strength of the bonding in the alloy.

Cleanser solution effects on denture base resins: Electronmicroscopic investigation.

Scanning electron microscopic investigations were conducted to determine morphostructural alterations on denture base resin surfaces after immersions in commercially available oxygen liberating denture cleansers. The topography of properly processed denture resins did not show corrosive effects, whereas inconsistent surface characteristics of improperly processed wet-mix acrylates could suggest less resistance. In spite of thorough rinsing after immersion, deposits were noted on the resins of varying amount, size, and quality according to the cleanser used. A possible clinical relevance of such deposits is yet to be evaluated.

[Inclusion compounds of collagen (author's transl)]. / Kollagen-Einschlussverbindungen.

Small angle X-ray diagrams of collagen of rat tail treated with phospho tungstic acid or mercury chloride or cobalt- and uranyl-nitrate, osmiumoxide or hydroxy apatite show the same characteristic new reflections and reflection lines. The only remarkable difference exists between fibers treated under stress or relaxed. These experiments give new evidence for the paracrystallinity of collagen. More than 100 parallel aligned ca. 40 A thick octafibrils consist of 670 A long microparacrystals with 5 ca. 25 A thick soft segment layers. In these soft segments the holes of the octafibrils build up a lattice of vacancies with lattice cells of 38,5 x 35 x 135 A3 length. The above mentioned molecules penetrate from the lateral sides through the soft segments into these vacancies building up complexes with peptide groups of collagen. Under stress only a small amount of vacancies is occupied, statistically distributed over the vacancy-lattice, because the soft segments of the octafibrils are constricted. Without stress about 10 to 25% of the octafibrils within one paracrystal are filled up with sediments in the soft regions. With increasing precipitation finally 500 A long needles are formed of the inclusive material as detected by Höhling with the electron microscope in collagen of turkey tendon. The importance of the paracrystalline collagen model is emphasized to understand the biological process like the mineralisation of collagen and beta-keratin in organism or the activity of bone apatite in exchanging calcium ions.