course platinum or platinum alloyed with iridium may be employed for posts, but the crown metal is in every way superior.

"There are some cases of a class which has hitherto presented difficulties that may not be easily overcome by grinding the post flat on the crown side after it has been set and bent in the root (Fig. 214), so as to be clear of the occluding tooth; and then the crown-pins may be bent over the reduced post, the crown fitted and ground to clear the opposing tooth (Fig. 215), and the backing added.

"A similar case, in which the opposing tooth and a proper

FIG. 214.

FIG. 215.

FIG. 216.

FIG. 217.

FIG. 218.

alignment require an oblique bending of the pins, is seen in Fig. 216, while the reverse arrangement of parts is shown in Fig. 217. The crown is thus seen to be adapted to a wide range of adjustments because its point of contact with the root is at the labial portion of the neck, on which as on a hinge the crown may be swung out or in (Fig. 218, dotted lines), over an arc of at least sixty degrees, at any point of which it may be quickly and firmly fixed. The labio-cervical junction is made just under the gingival margin, and I usually interpose a thin layer of cement, amalgam, or gutta-percha, or a narrow ribbon or several large blocks of soft gold; the joint always

to be made smooth, and hid from view under the free margins of the gums.

"The obviously great advantages of such a plan led to the adoption of a single size for post and appliances, but a second size has been proved to be a necessity, and hence the B size is now designed for superior centrals, and cuspids, while the A size is used for laterals and bicuspids, as also for all the inferior roots anterior to the molars. The handles of the tap-chucks and post-chucks are made of small diameter to insure that too great force shall not be used with the thumb and finger in turning in the tap and the post; and it is enjoined upon the operator to remove the tap when it begins to turn at all hard, and repeat the removal until it has been easily turned down to the gauge depth. The cuttings must then be carefully blown or wiped out, so that the post may be easily turned down to the bottom of the hole without risk of splitting the root, as there is danger of doing with too great force acting on the debris as a wedge-hence this caution to employ only a reasonable amount of force and to do thorough work. The disk for grinding the crown-rib is an essential part of the equipment, and when the engine is not at hand, may be used in the lathe by means of lathe-chuck No. 8."

Baldwin's Crown.-" The modus operandi is as follows: Select a Logan crown slightly shorter than would be used for setting without a ferrule. Countersink, and prepare the inside of a root as for a Bonwill or any ordinary crown. If the outside of the root at the margin of the gum presents an irregular surface, then with Dr. Walter Starr's reducers shape it to such a size that the ferrule may be perfectly adapted to all parts. Then take an impression, and produce in zinc or Babbitt metal a die, to form which take a plaster model of the root end an eighth of an inch long, and shellac it to the point of a cone, which can be easily made by turning down a large spool, thus making the deep mold in sand, into which the metal is poured. With this die strike the gold (twenty-two carat, No. 30 gauge, is most commonly in use) laid upon soft lead. A

few blows will produce a seamless and perfectly-fitting cover and ferrule. After trimming this to fit the festoon of the gum, drill in it from the lower side a hole for the pin of the crown, leaving the ragged edge produced by the drill. Then fill the countersunk portion in the porcelain crown with oxyphosphate of zinc, and with the gold ferrule or cap in place adjust the crown as you would wish it when completed. When the oxyphosphate is hard, you will find the ragged edge on the upper side of the cover will materially aid in removing and keeping the cap where it belongs. Unite the cover to the platinum pin in the crown with a small amount of soft solder

FIG. 219.

FIG. 221.

FIG. 220.

-tin and lead-using muriate of zinc as a flux, a few blasts from the blowpipe being all the heat required. Then fill the root with oxyphosphate and firmly press to place. These caps might be made up at leisure, providing a few variations for double and single-rooted teeth. When a case is met that you cannot fit from your stock, choose a cap larger than the end of the root, and with a single clip of the shears cut to the centre of the cap, and with pliers spring together and lap the edges until the size required is obtained. Solder with gold solder by holding over the spirit lamp and proceed as before. Fig. 219 shows a root cover and Logan crown ready to be

assembled for the soldering of the crown-pin to the cover; Fig. 220 shows the cap cemented and soldered to the crown; and Fig. 221 the completely crowned root." *

Low's Crown.-In our first cut, Fig. 222, we present seven instruments. No. 1, the smallest, will be used most frequently.

Any tooth generally considered beyond restoration can be crowned with this instrument.

"We now have before us in Fig. 223 a central incisor badly decayed. There is little tooth-substance exposed below the margin of the gum, the little remaining being the outer walls. The first step to be taken to place on this root a strong and serviceable crown is to cut or grind even with the gum what tooth-substance remains. We start off with the supposition that the root is in a healthy condition; if not, it must first be treated and made so, as this is the first consideration in the final result of a successful operation. The next step is to select the instrument in accordance with the size of the opening in the root to be crowned. The larger the opening in the root the larger the inside or centre cutters must be, and the narrower the cutters that bevel and prepare the end of the root. The reason for this is that the space is nearly all taken by the inside cutters in order to reach and cut away the decayed tooth-substance, and prepare the root to properly receive the step-plug with bevel cap which covers the end.

"We have seven sizes of instruments, and if the right one is selected, no tooth-substance will be removed that ought not to be, cutting, as it does, the least where the tooth is smallest, or, in other words, we cut the opening in the tooth tapering to the shape of the root.

"These cutters leave the root in the shape of Fig. 224, with graded steps.

"We next select the graded step-plug seen in Fig. 225.

"This is the same size as the instrument, and will perfectly fit the opening and cover the end in a beveled saucer shape, and by its attachment to the inside step-plug when cemented make a combined union of great strength, and so made as to be impossible for the root to split. Fig. 226 shows the stepplug placed in position.

"After placing the plug in position, an articulation of wax and impression of the space to be supplied and of the adjoining teeth are taken in plaster-of-Paris. Before taking the