Care of the mouth and teeth; a primer of oral hygiene . not thor-oughly cleansed after eating, some remnants ofthis glucose would remain between the teeth orbe held by means of a gluey substance in some pitor crevice of the tooth. Now in our mouths arealways present hordes of microscopic bodies orgerms, amongst which are a kind called bacteria,whose ability to flourish and grow is due to thepresence of heat, moisture and food remnants,always found in the oral cavity. One of thesebacteria, called the bacillus lactis, or lactic acidforming germ, always occurs in large number, so 28 CARE OF THE M
Care of the mouth and teeth; a primer of oral hygiene . not thor-oughly cleansed after eating, some remnants ofthis glucose would remain between the teeth orbe held by means of a gluey substance in some pitor crevice of the tooth. Now in our mouths arealways present hordes of microscopic bodies orgerms, amongst which are a kind called bacteria,whose ability to flourish and grow is due to thepresence of heat, moisture and food remnants,always found in the oral cavity. One of thesebacteria, called the bacillus lactis, or lactic acidforming germ, always occurs in large number, so 28 CARE OF THE MOUTH AND TEETH 29 that when it finds the glucose to feed upon it causesa fermentation, or chemical change, by the forma-tion of two parts of lactic acid from one part ofglucose. Lactic acid, when present, is the activecause of tooth decay, and it first acts upon theenamel, seldom attacking the root of the toothbecause the latter is guarded by the gum whichsurrounds it. When the lactic acid, after beingformed, accumulates upon the enamel, it eats away. Fig. 6.—Progress of Dental Decay 1. Superficial Stage of Decay 2. Progressive Stage of Decay 3. Deep-seated Stage of Decay 4. Complicated Stage of Decay or dissolves the salty or inorganic material ofwhich we spoke in the preceding chapter. How-ever, in order that the process of decay may con-tinue, another kind of micro-organism is neces-sary to destroy the organic or albuminous part ofthe enamel. This is done by what are called sa-prophytic bacteria or germs that live on decom-posing organic tissues. Thus, after the lactic acid 30 CARE OF THE MOUTH AND TEETH Starts the destruction of the enamel, the saprophyticgerms complete it. This beginning of decay inwhich the enamel is destroyed, is called the super-ficial stage of dental caries, which latter wordmeans decay. The next stage of decay involves the process of decay goes on in the same manner,except that more of the dentine is organic thanthe enamel, and therefore
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