СНАР. VI.

OF THE IRREGULARITY of the TEETH.

As that part of each jaw, which holds the ten fore-teeth, is exactly of the same size when it contains those of the first set, as when it contains those of the second; and as these last often occupy a much larger space than the first *, in such cases the second set are obliged to stand very irregularly.

This happens much oftner in the upper-jaw, than in the lower; because, the difference of the size of the two sets is much greater in that jaw.

* Vide Natural History, p. 101, 102, Pl, 6. fig. 2.

This irregularity is observed almost solely in the incisores and cuspidati; for they are the only Teeth which are larger than their predecessors.

It most frequently happens to the cuspidati, because they are often formed later than the bicuspedes; in consequence of which, the whole space is taken up before they make their appearance: in such cases they are obliged to shoot forwards or outwards over the second incisor. However, it frequently happens to the incisores, but seldom to such a degree. This arises often from the temporary cuspidatus of one or both sides standing firm. I have feen the irregularities so much as to appear like a double row.

The bicuspedati generally have sufficient room to grow, because even more space, than what they can occupy, is kept for them by the temporary grinders *. This however is not universally the case; for I have seen where the bicuspidati were obliged to grow out of the circle, very probably from their being later in growing than common.

* Vide Natural History, page 83.

That it is from want of room in the jaw, and not from any effect that the first set produce upon them is evident; first, because in all cases of irregularity we find that there is really not room in the Jaw, to allow of placing all the Teeth properly in the circle; so that some are necessarily on the outside of the circle, others within it, while others are turned with their edges obliquely as it were, warped; and secondly, because the bicuspides are not out of the circle, although they are as much influenced by the first set as any of the others.

As they are not influenced by the first set, it cannot be of any service to draw the first poffessor; for that gives way in the same proportion as the other advances. As the succeeding Tooth however is broader, it often interferes with a shedding Tooth next to it, the fang of which not being influenced by the growth of its own succeeding Tooth, it does not decay in proportion as the other advances, and therefore the drawing of the adjoining hedding Tooth is often of service *.

* Vide Nat. Hist. page 107.

In cases of considerable irregularity for want of room, a principal object is to remove those which are most out of their place, and thereby procure room for the others which are to be brought into the circle.

To extract an irregular Tooth would answer but little purpose, if no alteration could be made in the situation of the rest; but we find that the very principle upon which Teeth are made to grow irregularly, is capable, if properly directed, of bringing them even again. This principle, is the power which many parts (especially bones) have of moving out of the way of mechanical pressure.

The irregularity of the Teeth is at first owing to mechanical pressure; for one Tooth getting the start of another, and fixing firmly in its place, becomes a resistance to the young, loose, forming Tooth, and gives it an oblique direction. The fame principle takes place in a completely formed Tooth, whenever a pressure is made upon it. Probably a Tooth might by flow degrees be moved to any part of the mouth, for I have seen the cuspedati pressed into the place of the incisores. However it is observed, that the Teeth are easier moved backwards than forwards, and when moved back that they are permanent, but often, when moved forwards, that they are very apt to recede.

The best time for moving the Teeth is in youth, while the jaws have an adapting disposition; for, after a certain time, they do not so readily fuit themselves to the irregularity of the Teeth. This we see plainly to be the case, when we compare the loss of a Tooth at the age of fifteen years, and at that of thirty or forty. In the first case we find, that the two neighbouring Teeth approach one another, in every part alike, till they are close; but in the second, the distance in the jaw, between the two neighbouring Teeth, remains the same, while the bodies will in a small degree incline to one another from want of lateral support *.

And this circumstance of the bodies of the Teeth yielding to pressure upon their base, shews that, even in the adult, they might be brought nearer to one another by art properly applied.

* Vide Nat. Hist. Plate XVI. fig. 1, a, b, c..

As the operation of moving the Teeth is by lateral pressure upon their bodies, these bodies must first have passed through the gum sufficiently for a hold to be taken.

The best time seems to be, when the two grinders of the child have been shed; for at this time a natural alteration is taking place in that part of the jaw.

The means of making this pressure I shall only, slightly describe, as they will greatly vary according to circumstances, so considerably indeed, that scarcely two cases are to be treated alike, and in general the dentists are tolerably well acquainted with the methods.

In general, it is done with ligatures or plates of silver. The ligatures answer best when it is only required to bring two Teeth closer together, which are pretty much in the circle. The trouble attending this is but trifling, as it is only that of having them tied once a week or fortnight.

Where Teeth, growing out of the circle, are to be brought into it, curved silver plates, of a proper construction, must be used. These are generally made to act on three points, two fixed points on the standing Teeth, and the third on the Tooth which is to be moved. That part of the plate, which rests on the two standing Teeth, must be of a sufficient length for that purpose, while the curved part is short, and goes on the opposite side of the Tooth to be moved. Its effect depends very much on the attention of the patient, who mu t frequently press hard upon it with the Teeth of the opposite jaw; so that this method is much more troublesome to the patient than the ligature.

It is impossible to give absolute directions what Tooth or Teeth ought to be pulled out. That must be left to the judgment of the operator; but the following general hints may be of service.

1. If there is any one Tooth very much out of the row, and all the others regular, that Tooth may be removed, and the two neighbouring ones brought closer together.

2. If there are two or more Teeth of the fame side very irregular, (as for instance, the second incisor and cuspidatus) and it appears to be of no consequence, with respect to regularity, which of them is removed, I should recommend the extraction of the farthest back of the two, viz. the cuspidatus ; because, if there should be any space, not filled up, when the other is brought into the row, it will not be so readily seen.

3. If the above-mentioned two Teeth are not in the circle, but still not far out of it, and yet there is not room for both; in such a case I would recommend the extraction of the first bicuspis, although it should be perfectly in the row, because the two others will then be easily brought into the circle; and, if there is any space left, it will be fo far back as not to be at all observable.

The upper jaw is often rather too narrow from side to fide, near the anterior part which supports the fore Teeth, and projects forwards considerably over the lower, giving the appearance of the rabbit-mouth, although the Teeth be quite regular in the circle of the jaw.

In such a case it is necessary to draw a bicuspis of each side, by which means the forepart of the circle will fall back; and if a cross bar was to be stretched from side to side across the roof of the mouth, between cuspis and cuspis, it would widen the circle. The fore Teeth might also be tied to this bar, which would be a means of assisting nature in bringing them back. This has been practised, but it is troublesome.

As neither the bodies nor the fangs of the Teeth are perfectly round, we find that this circumstance often becomes a cause of their taking a twist; for, while growing, they may press with one edge only on the completely formed Tooth; by which means they will be turned a little upon their center.

The alteration of these is more difficult than of the former, for it is, in general, impossible to apply, so long and constantly as is necessary for such an operation, any pressure that has the power of turning the Tooth upon its center. However, in the incisores, it may be done by the same powers which produce the lateral motion; but where these cannot be applied, as is frequently the case, the Tooth may be either pulled out entirely, and put in again even, or it may be twisted round sufficiently to bring it into a proper position, as hath been often practised.

It may not be improper, in this place, to take notice of a case which frequently occurs. It is a decay of the first adult grinder at an early age, viz. before the temporary grinders are shed, and before the second grinder of the adult has made its appearance through the gum. In this case, I would recommend removing the diseased Tooth immediately, although it may occasion no kind of trouble; for, if it be drawn before the temporary grinders are shed, and before the second adult grinder has cut the gum, it will in a short time not be missed because the bicuspis of that side will fall a little back, and the second and third grinders will come a little forward; by which means the space will be silled up, and these Teeth will be well supported. Besides, the removal of this Tooth, will make room for the fore Teeth, which is often very much wanted, especially in the upper jaw.

CHA P. VII.

OF IRREGULARITIES between the TEETH and JAW.

CERTAIN disproportions, between the Teeth and Jaw, sometimes occur, one of which is, when the body of the lower jaw is not of sufficient length for all the Teeth. In such cases, the last grinder never gets perfectly from under the coronoide process, its anterior edge only being uncovered; and the gum, which still in part lies upon the Tooth, is rubbed against the sharp points of the Tooth, and is often squeezed between the Tooth upon which it lies, and the corresponding one of the upper jaw. This occasions so much uneasiness to the patient, that it becomes necessary to relieve the gum, if possible, by dividing it freely in several places, that it may shrink and leave this surface of the Tooth wholly uncovered. If this does not answer, which is sometimes the case, it is advisable to draw the Tooth.

Sometimes, although but seldom, an inconvenience arises from the dentes sapientiæ being in the upper Jaw, and not in the lower; these Teeth pressing upon the anterior part of the root of the coronoide process, when the mouth is shut; for the coronoide processes are farther forwards in such cases, than when the lower Jaw also has its dentes sapientiæ; in short, the exact correspondence between the two Jaws is not kept up.

In such cases I know of no other remedy, but the extraction of the Tooth.

OF SUPERNUMERARY TEETH.

WHEN there are Supernumerary Teeth *, it will, in general, be proper to have them drawn; for they are commonly either troublesome, or disfigure the mouth.

• Vide Natural History, page 105.

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PLATE XVI.

Fig. I.

The outlines of a Lower-Jaw, in which one or two Grinders have been lost out of the space a, and where the bodies of the two adjacent Teeth, bc, have approached one another, by the pressure which has been applied to their basis in mastication, from the want of their support on that side: we see also the waste of the Alveoli which belonged to the lost Teeth.

Fig. II.

Four Lower-Jaws at different periods of life, from the age when the five shedding Teeth are completely formed, to that of a complete set. This figure shews four things:

1. The lengthening of the Jaw backwards, which is seen by the oblique line made by the four condyles:

2. The gradual rise of the two processes above the line of the Teeth:

3. The gradual increase of the Teeth in proportion as the Jaw lengthens And fourthly, the part formed, always keeping of the fame size.

aaaa The Condyles.

bbbb The Coronoide Processes. The Alveolus, in which the Grinder of the Adult is forming.

ddd The first Grinders formed.

ee The Alveoli for the formation of the second Grinder.

ff These completely formed.

gg The Alveoli for the third Grinder.

b That Grinder formed.

The two lines i k and i m mark the distance between the symphysis of the chin and sixth Tooth; they are parallel, or nearly so: it is impossible that there should be a mathematical exactness in four different Jaws. The line il separates the Inciseres and Cuspidatus from the Molares in the child, and the Bicuspidates in the adult. This line is oblique, and the distances between the two ends of the two lines, i k and il, at ii, is nearly the same with the distance between the ends of the two lines il, and im, at lm.

FINIS.