Particulate synthetic hydroxyapatite (HAP) is rapidly gaining importance as a biomimetic agent in oral care products. The prerequisite for an adequate effect of the treatment is an efficient attachment of the HAP particles to the tooth substance. However, quantitative data about the interaction and affinity parameters involved are scarce. The authors used an in vitro approach with standardized bovine tooth enamel surfaces and aqueous dispersions of chemically pure synthetic HAP particles as a model system. Structural characterization of the HAP powder using high-resolution scanning electron microscopy (SEM) shows that the particles are micrometer-sized stable clusters of crystallites that closely resemble the structure of natural enamel. Using SEM image analysis, the authors investigated the influence of HAP particle concentration and particle size on the efficiency of attachment to bovine tooth enamel based on pure mineral-mineral interaction. The results show that both play an important role and can be tailored for optimizing the efficiency of corresponding oral care formulations. The results also reveal the presence of structures resembling mineral bridges at the interfaces between HAP particles and enamel that provide indications for possible interaction mechanisms. Notation A r aspect ratio d max crystallite length d min crystallite width N particles number of particles 141 Cite this article

Background: Particulate Hydroxyapatite (HAP; Ca5(PO4)3(OH)) is being increasingly used as multifunctional active ingredient in oral care. Due to its high similarity to human enamel crystallites, it is considered as a biomimetic agent. Objective: The aim of this narrative review is to identify the modes of action of HAP in preventive oral health care based on published studies. The outcomes are expected to improve the understanding of the effects of HAP in the oral cavity and to provide a knowledge base for future research in the field of biomimetic oral care. Methods: The data analyzed and discussed are primarily based on selected published scientific studies and reviews from in vivo, in situ, and in vitro studies on HAP in the field of preventive oral health care. The databases Cochrane Library, EBSCO, PubMed and SciFinder were used for literature search. Results: We identified different modes of action of HAP in the oral cavity. They are mainly based on (I) Physical principles (e.g. attachment of HAP-particles to the tooth surface and cleaning properties), (II) Bio-chemical principles (e.g. source of calcium and phosphate ions under acidic conditions and formation of an interface between HAP-particles and the enamel), and (III) Biological principles (e.g. HAP-particles interacting with microorganisms). Conclusion: Although more mechanistic studies are needed, published data show that HAP has multiple modes of action in the oral cavity. Since the effects address a wide range of oral health problems, HAP is a biomimetic agent with a broad range of applications in preventive oral health care.

Hexapoda have been traditionally seen as the closest relatives of the Myriapoda (Tracheata hypothesis) but molecular studies have challenged this hypothesis and rather have suggested a close relationship of hexapods and crustaceans (Tetraconata hypothesis). In this new debate, data on the structure and development of the arthropod nervous system contribute important new data ("neurophylogeny"). Neurophylogenetic studies have already provided several examples for individually identifiably neurons in the ventral nerve cord that are homologous between insects and crustaceans. In the present report, we have analysed the emergence of Engrailed-expressing cells in the embryonic brain of a parthenogenetic crayfish, the marbled crayfish (Marmorkrebs), and have compared our findings to the pattern previously reported from insects. Our data suggest that a group of six Engrailed-expressing neurons in the optic anlagen, the so-called secondary head spot cells can be homologised between crayfish and the grasshopper. In the grasshopper, these cells are supposed to be involved in establishing the primary axon scaffold of the brain. Our data provide the first example for a cluster of brain neurons that can be homologised between insects and crustaceans and show that even at the level of certain cell groups, brain structures are evolutionary conserved in these two groups.