DENTAL TARTAR. 



287 



swallow them directly, without much mastication, and because such 



objects are then retained in one or another of the stomachs. The 



fourth molar, which stands in the centre of the curved row, and 



suffers most under the severe friction of one grinding surface on the 



other, is most frequently affected. Without doubt want of hardness, 



which is often produced by caries, greatly favours splitting, while 



other causes may lower the resistance of the tooth. Such conditions 



may possibly originate during foetal life, a view which receives 



confirmation from corresponding teeth on 



either side being often splintered. Hard 



substances accidentally present in the food 



also produce splitting, especially in animals 



which masticate energetically. Sometimes 



only a piece of the crown breaks off, but 



very frequently the crack extends as far as 



the root. The tooth may be broken into 



several pieces, which separate, injure the 



tongue or cheek, and make chewing painful. 



While Assuring is confined to the crown no 



serious consequences ensue ; but should the 



fracture extend to the alveolus, particles of 



food and fluids may enter and inflame the 



alveolar periosteum. 



Treatment consists in removing the 

 splintered tooth, and is seldom difficult. 

 Sometimes the pieces are too small to be 

 grasped by ordinary forceps, and in such 

 cases Gunther's pointed forceps are useful 

 (Fig. 291). 



Fig. 286.— Teeth scalers for 

 dogs. 



DENTAL TARTAR (CREMOR DENTIUM). 



Alike in animals and man the fluids 

 of the mouth deposit on the teeth a grey-brown coating called 

 tartar. It is commonest in dogs and vegetable feeders, but 

 very rare in cats. Pet dogs suffer oftener than others. According 

 to Fiirstenberg's investigations tartar in dogs and horses consists 

 principally of phosphate of calcium, carbonate of calcium, car- 

 bonate of magnesium, and organic substances. Iron and manganese 

 have also been detected. Microscopical examination shows that 

 the material is formed chiefly of vegetable particles, various 

 bacteria, epithelium from the cavity of the mouth, and salts 

 of calcium held together by salivary mucus. The deposit is 



