52 PHYSIOLOGY FOR DENTAL STUDENTS. 



Tartar Formation and Salivary Calculi. Under certain con- 

 ditions a precipitate, varying in color from pale yellow to almost 

 black, collects on the teeth, particularly on the lower incisors 

 and molars. This precipitate is called tartar, and it may be 

 either hard (as on the incisors) or soft (as on the molars). Its 

 chemical composition varies considerably, but may be given as 



follows : 



I II 



Water and organic matter 32.24 per cent 31.48 per cent 



Magnesium phosphate 0.98 per cent 4.91 per cent 



Calcium phosphate 63.08 per cent 72.73 per cent 



Calcium carbonate 3.7 per cent 



(Talbot) 



The organic matter consists of epithelial scales, other extran- 

 eous matter and leptothrix chains. The place and manner of 

 deposition shows clearly that the tartar is largely derived from 

 the saliva, the chemical explanation of the precipitation being 

 probably as follows : Saliva, as it is produced in the gland, con- 

 tains calcium bicarbonate, which is soluble in water, and is pre- 

 vented from changing into the insoluble carbonate by the pres- 

 ence of free carbon dioxide in solution. When the saliva is dis- 

 charged into the mouth some of the carbon dioxide escapes from 

 it so that the bicarbonate changes to carbonate and becomes pre- 

 cipitated. The precipitate carries down with it phosphates as well 

 as any organic debris or mico-organisms that may be present. 



The precipitation of calcium carbonate may even take place 

 in the salivary ducts (Wharton's), thus forming salivary calculi, 

 which may reach the size of a pea or larger. Such calculi may 

 contain as much as 3.8 per cent of organic matter, the remainder 

 being largely calcium carbonate. The following table gives the 

 composition of three such calculi : 



I II III 



Calcium carbonate 81. 2 per cent 79.4 per cent 80.7 per cent 



Calcium phosphate 4.1 per cent 5.0 per cent 4.2 per cent 



Magnesium phosphate ... present 

 Organic matter and other 



soluble solids 13.3 per cent 13.3 per cent 13.4 per cent 



Water 1.3 per cent 2.3 per cent 1.7 per cent 



(Talbot) 



