Hydroxyapatite dental fluorosis. Therefore it is necessaryHydroxyapatite dental fluorosis. Therefore it is necessary

Hydroxyapatite (HAp, Ca10(PO4)6OH2)
belongs to the calcium phosphate (CaP) family and is the main mineral component
of human bone and teeth 1. The application of calcium phosphates, especially
HAp, for bone regeneration is known for a hundred years, but only last fifteen
years CaP have been studied extensively as promoters of tooth enamel and
dentine remineralisation. Since 96-97% of tooth enamel consists of mineral
phase, mainly HAp 2, 3, and fluorine is known for its anti-caries effect 4,
several scientific papers 5-7 are devoted to synthesis and characterization
of F-doped hydroxyapatite (FHAp, Ca10(PO4)6OH2-xF2x).
FHAp is of high interest due to its bioactivity, mechanical properties and
chemical similarity to teeth 4. The structural and chemical stability of FHAp
against chemical and physical factors are the main properties promising for
remineralisation of tooth enamel. As reported in 8, too high intake of
fluorine can lead to bone and teeth diseases like osteomalacia and dental
fluorosis. Therefore it is necessary to control F- content in the
HAp structure and also release afterwards.
Once the OH
groups were partially substituted by the F- ions, the existing
hydrogen ions of the OH groups were bound to the nearby F ions because of the
higher affinity of the F ions with respect to the oxygen ions, producing a quite
well-ordered apatite structure, which caused an increase of the thermal and
chemical stabilities of the HA matrix. Therefore, when a certain amount of F
ions substituted the OH groups in the HA matrix, a certain level of chemical
and thermal stability of the FHA ceramics was achieved. Theoretically, a F ion
concentration of 50% in the FHA should be enough to remove the disorder of the
crystal structure of HA and hence stabilize the structure F due to the
alternating arrangement of the F ions between each pair of OH groups.9  In this research, synthesis of
fluorapatite nanopowder via modified wet-chemical method by using sodium
fluoride and the resulting FA powder was characterized by instrumentation
techniques

                                                                                                                                              
I.     Experimental procedure

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A.   
Synthesis of FA nanopowder

Modified wet chemical method was used to prepare the pure FA sample.
The precursors for  synthesis were
calcium hydroxide(Ca(OH)­2)(Merck,India), ammonium dihydrogen
phosphate (NH­4)H2PO4 (Merck, India)(ADP)
and sodium fluoride (NaF) (Sigma Aldrich, India). 1.0M calcium hydroxide
and 0.67M ammonium dihydrogen phosphate were dissolved in 100ml of double
distilled water for 1hour in magnetic stir. The dissolved solution of ADP was
added drop wise to the (Ca(OH)­2) solution for 35mins and
continuously stirred for 18hours. The pH of the solution was maintained in 11.
The obtained slurry was irradiated to microwave radiation for 30mins and the
dried powder were grinded well by using mortar and pestle.