THE CURIOUS USES OF TEETH

Evening Post, Volume CXXII, Issue 106, 31 October 1936, Page 27

THE CURIOUS USES OF TEETH

' The main function of the teeth of human beings is mastication; yet it is remarkable how many folk' manage to get'along with'broken-down teeth, illfitting artificial dentures, ,and•;' even .'without any,, teeth at all, writes Dr. T. D.-■':-Campbell -in the :- "Adelaide Chronicle." But there are two other important' uses for human teeth, J called the secondary functions—the 'import-ance-of teeth in the facial appearance of the individual and in the function 'of speech." " '"■' '■ Of. the aesthetic function is one which varies with different peoples, jror example, some native groups think it much-more attractive to have one or more'front teeth knocked out; others ■go to long- and tedious, pains to file .down th.eir anterior teeth Into gro-tesque--shapes. But there is no doubt absence of one 6r two anterior teeth ruins many a smile which starts off, quite, attractively. Trien, as far as speech-is concerned, one has only to concentrate'thoughtfully on the mover ments of the tongue in pronouncing, for example, the sounds of "t," "d," "th," and "y," to "appreciate the important part .played by a. row of teeth.

When we turn from human beings to other creatures of the earth we find that the uses of teeth are many and varied —some extraordinary- .A tooth in its most primitive and simplest form is of a simple sharp, conical shape; and from this simple form have evolved many remarkable, complex, and highly, specialised forms. Along with the modification in shape and function there has frequently resulted a diminution in the number of teeth in the; mouth, and a restriction in position to the jaw margin. Among the teeth of fishes, perhaps, two of the most spectacular departures from the usual conical or triangular blade-like teeth—such as, are seen in ..the cod and--shark families—are the teeth of some of the rayfish and the sawfish. In some1 of the rays the teeth are exactly like flat, hexagonal tiles; and they are set together in the mouth like a -wonderful geometric ; mosaic

pavement. The sawfish has its main dental equipment situated along the sides of. its remarkable, elongated snout, giving it the appearance of a •peculiar, double-edge saw. In certain fishes called the Chaetpdonts, the teeth are long, very slender, and' flexible; their main function is to sift' out the food from a mouthful of water.

In reptiles is seen one of Nature's most wonderful experiments in specialisation of tooth form and 'function. . In a few of the .most.venompus of snakes the : whole .functioning Heritition" of the upper jaw consists of only two -teeth.: These two teeth function in effect in precisely the same manner asa hypodermic syringe. Thei snake sinks its fangs ■ into ;the ..flesh.- of its ejiemy or prey, and from a little opening at the tip of each fang the poison is ' automatically injected into the tissues of the creature bitten. Each little opening'at the-tip of the tooth is: the lower end of a canal in the1 body of the tooth, and its upper end is connected with a duct which comes from the poison!, gland at the side of the- head. This highly-specialised function is obviously quite unlike the usUal function of seizing, holding, and tearing- of food.

. In the typical carnivorous or flesheating set of teeth the scissors-like action of the teeth of the lower jaw against those of the' upper arch is an entirely different .mechanical function from that of the typical herbivorous dentition.; the latter type have broad, flat, wrinkled surfaces between which are-ground large quantities of vegetable •food -by -side to- side movements of the lower.jaw. ■.-..■' '-. v

" Then there are the peculiar 'front teeth of the rodents, which have a working edge exactly like the business" end of a' carpenter's chisel. And the" structure of 'this rodent;'tooth is such that, as the tooth ' wears' away in its gnawing function, the chisellike bevel edge is' constantly maintained; and also .by means of a persistent pulp or formative organ, the body of the tooth is continually being formed.- ' ■ ■' ' .'■..■■"••• \ '