Rod shaped apatite crystals with a specific length-to-width ratio

Abstract

The rod-shaped apatite crystals of the formula Ca 5 (PO 4 ) 3 (OH) x F y have the following features a) the length-to-breadth ratio of the crystals is at least ≧5 and b) x+y=1, where if x or y≠0 the total amount of the crystals is present as a mixture of individual hydroxyapatite crystals and fluoroapatite crystals and/or as mixed crystals, such that, based on the total amount of the crystals, (1−x)·100% of the hydroxide ions present if y=0 are replaced by fluoride ions. The invention furthermore describes dispersions which contain such rod-shaped apatite crystals, and a process for the preparation of the dispersions or of the apatite crystals.

1 . A rod-shaped apatite crystal of the formula Ca 5 (PO 4 ) 3 (OH) x F y , wherein 
 a) the length-to-breadth ratio of the crystals is at least ≧5 and    b) x+y=1, where if x or y≠0 the total amount of the crystals is present as a mixture of individual hydroxyapatite crystals and fluoroapatite crystals and/or as mixed crystals, such that, based on the total amount of the crystals, (1−x) 100% of the hydroxide ions present if y=0 are replaced by fluoride ions.    
     
     
         2 . A rod-shaped apatite crystal as claimed in  claim 1 , wherein if y≠0 the calcium ions are partially substituted by other cations, in particular sodium, potassium and/or ammonium ions.  
     
     
         3 . A rod-shaped apatite crystal as claimed in  claim 1  or  2 , wherein the length-to-breadth ratio of the crystals is 5 to 20, preferably 8 to 15, particularly preferably 9 to 12.  
     
     
         4 . A rod-shaped apatite crystal as claimed in one of  claims 1  to  3 , wherein, based on the total amount of the crystals, 0.01 to 30%, in particular 0.5 to 20%, of the hydroxide ions present if y=0 are replaced by fluoride ions.  
     
     
         5 . A rod-shaped apatite crystal as claimed in one of  claims 1  to  4 , wherein the thickness of the individual crystals corresponds approximately to their breadth.  
     
     
         6 . A rod-shaped apatite crystal as claimed in one of  claims 1  to  5 , wherein the thickness and the breadth are 0.01 to 0.02 μm and the length of the crystals is 0.1 to 0.2 μm.  
     
     
         7 . A dispersion comprising rod-shaped apatite crystals as claimed in one of  claims 1  to  6 , wherein the solids content of apatite crystals is 5 to 70% by weight, preferably 10 to 40% by weight, particularly preferably 15 to 30% by weight.  
     
     
         8 . A process for the preparation of dispersions as claimed in  claim 7 , which comprises 
 a) producing, in an autoclave, a mixture which contains the starting materials and water,    b) generating a temperature of at least 100° C. and a pressure of >1 bar in the interior of the autoclave and maintaining these conditions for at least 1 hour,    c) if appropriate, following step b), adding at least one fluoride-containing compound to the mixture present as a dispersion situated in the autoclave and mixing with this dispersion over a period of time of at least 1 hour.    
     
     
         9 . A process as claimed in  claim 8 , wherein the starting materials used are calcium hydroxide and phosphoric acid.  
     
     
         10 . A process as claimed in  claim 8  or  9 , wherein the fluoride-containing compound is sodium fluoride, calcium fluoride, potassium fluoride and/or ammonium fluoride.  
     
     
         11 . A process as claimed in one of  claims 8  to  10 , wherein a pressure of between 1.5 and 6 bar, in particular between 2 and 5 bar, is generated in the interior of the autoclave.  
     
     
         12 . A process for the preparation of rod-shaped apatite crystals as claimed in one of  claims 1  to  6 , wherein a dispersion is prepared by the process as claimed in one of  claims 8  to  11  and the rod-shaped apatite crystals are then isolated from the dispersion by spray drying.  
     
     
         13 . The use of rod-shaped apatite crystals as claimed in one of  claims 1  to  6  and/or of dispersions as claimed in  claim 7  as a remineralizing component for teeth and/or bone in cleansing and care formulations, and formulations for the treatment of tooth and bone defects, in particular in tooth gel, toothpaste, mouthwash and chewing gum, in formulations for the induction or promotion of the new growth of bone tissue and for the coating of implants.