adapted one if not kept clean. The accumulation and retention of foreign matter under such circumstances is one of the most potent agents for evil. Antiseptic and astringent washes may be applied as occasion demands.

But by far the greatest evil is to be apprehended from badly-fitting apparatus. The importance of more care and more skill than are usually exhibited can not be too strongly insisted upon.

Wherever it is proper that a regulating plate should touch a tooth, it should be made to fit the neck of the tooth accurately; otherwise, in a short time will be developed a spongy growth of the gum which would not have taken place if the apparatus had been properly adjusted. Whenever irritation of the gums is discovered arising from this cause, the remedy, which lies principally and many times. wholly in the removal of the cause, should be immediate, even if it should involve remaking the apparatus.

CHAPTER V.

FORCES.

THE treatment of irregularities of the teeth is almost entirely mechanical, but is lifted above the plane of ordinary mechanics because it has to do with vital organs, and thus becomes an important branch of mechanical surgery.

To the anatomical, physiological, and pathological knowledge required of the operator, there must be added a knowledge of mechanics and a clearness of perception and ingenuity to apply it. Precisely the same ability is required as would be demanded of a mechanical engineer in the construction of a machine for a given purpose. He is to apply, directly, one of the mechanical powers, or to invent a combination of those powers, as shall best answer the purpose. Levers, pulleys, inclined planes, wedges, and screws are all at his command; and it is quite as impossible to describe an apparatus, such as would be applicable to every case, as it would be to anticipate the future and describe every invention that the fertile mind of man may make for his comfort or convenience. It is impossible for one to overcome a complicated case of irregularity who has not a comprehension of each and all the above-named powers, singly and in combination with each other.

As an illustration: There came to me a dentist, with his patient, for consultation. The fixture was very nicely made, and had been in the mouth for some days, but with no observable change. As I had previously suggested the kind of appliance to be used, the question very properly followed,

why it did not work. It needed but a single glance to see that its force was working against itself, and this fact was unrecognized by the operator. All that was required was to change the bearings of the ligature, using the same appliance, and within forty-eight hours there was a perceptible movement of the teeth.

Every case of complicated irregularity requires a variation in the application of forces necessary to produce the result. No complex case that I have ever seen could be corrected by following the exact steps of any preceding case, which might have been, to all appearances, precisely like it. Consequently no plan of treatment, however detailed in description or profuse in illustration, can be of much benefit to the reader who has not a knowledge of mechanical powers and a ready ability to apply them, or to combine and apply such as are best adapted to the end.

Regulating appliances call into requisition the power to be derived from screws, wedges, levers, inclined planes, and elasticity.

SCREWS.

The screw is one of the most valuable adjuncts at our command in regulating teeth. On its first introduction it seemed a cumbersome apparatus, taking up valuable room in the mouth, interfering with mastication and articulation, irregular in its movements, requiring constant attention, and liable to injure the teeth by impinging and wearing upon them. It was a common idea that the pressure on the teeth, for their safety, must be moderate, uniform, and uninterrupted, and the action of a screw could be neither uniform nor uninterrupted. But experience has demonstrated its safety and its wonderful adaptability. By it a narrow arch of the most refractory character can be made to yield, and with it almost every movement we desire can be accomplished. It is not recommended for universal use, but, if we were deprived of every other mechanical power, we could do

70

FIRST USE OF JACK-SCREWS.

nearly all things in regulating by the aid of a screw. The jack-screw of the present day is a delicate and strong instrument of steel, with provision made to prevent oxidation. This contrivance was first used in dentistry by Dr. William H. Dwinelle, to whose ingenuity, skill, and various attainments, during a period of forty years, the profession is largely indebted for its rapid advancement. His discovery of a simple means to avoid oxidation rendered a screw of steel admissible, and thus overcame the instability of screws which theretofore he had made of gold. The form used by Dr. Dwinelle is shown in Fig. 16 and again in Fig. 20. The application of jack-screws in the author's practice is illustrated in the following cuts.

It is seldom desirable to use the screw alone; metallic bearings upon and in contact with the teeth are generally objectionable. An excellent plan is, to make a plate reaching across the mouth and bearing against the offending teeth. The jack-screw is placed in a straight line across from or near the extremes of the plate, the plate being made light enough in the center or slit up a certain distance to allow it to straighten under pressure. By this method the pressure can be distributed among all the teeth on one side, and concentrated upon one tooth upon the other side if desired. Such an arrangement is shown in Fig. 16. Before jack-screws were made by the instrument-makers and placed on sale, those which I required were made in my own laboratory,

DIFFERENT APPLICATIONS OF JACK-SCREWS.

71

and especially adapted to the case under treatment, and even now the plan then followed would be found advantageous.

Fig. 17 shows the employment of two screws upon the upper jaw. The plate was of vulcanite, and the screws have no other nut than the plate itself. The plate was vulcanized

around the screws, thus making the thread very perfect. This plate was used to drive out a very stubborn canine,.and also to twist a central incisor.

FIG. 18.

Fig. 18 shows another combination of plate and screw, and adapted to the lower jaw. In this case a piece of gold was inserted to form the nut of the screw, as shown in the engraving. This apparatus was used to force out two bicuspids, the first of which was considerably within the line, and the second one less so. Its action can readily be com