Tooth anchoring means and method

Abstract

Means and methods for anchoring pins in a tooth for restorations are described. One feature is the use of a cyanoacrylate cement for cementing and sealing the pin in a hole drilled in the tooth. Another feature is a special pin construction to increase the adhesion strength. Still another feature is provision of the pins in the form of a elongated strip from which individual pins are severed after mounting.

Description

This invention relates to means and methods for building superstructure on a tooth, and in particular to means and methods for anchoring pins in a tooth.

Various techniques have been described in the prior art for building superstructure or restorations onto a tooth. One known method is to drill several small holes in the tooth, anchor in each hole a small pin, and then anchor the superstructure to the pins. Such pins have been anchored to the tooth in various ways. In one technique the pin has a slightly smaller diameter than the hole, and a zinc phosphate (acidic) type cement is used to hold the pin in place. In another technique, the pin has about the same or slightly smaller diameter as that of the hole and is force-fitted or friction-locked into the hole to hold the pin in place. In still another technique, an oversized pin with threaded end is used which is self-threaded into the tooth hole.

Certain difficulties may be encountered in the practice of these known techniques. The undersized pin cemented in place uses a cement formed by mixing a liquid with a powder. Such cements have an excessively long setting time, poor adhesion strength, can only be applied as a thick layer, which is not always satisfactory, and have a low PH and can be irritating to the patient. Moreover, often a varnish is added to the hole to reduce leakage and protect the pulp, and the varnish further reduces the adhesion strength of the cement. Other cements suggested, such as zinc oxide or calcium hydroxide, have similar disadvantages and especially even poorer adhesion strength.

The force-fitted or screwed pins are more difficult to mount in the tooth, and can cause excessive strains and even cracking of the tooth if the dentine drys and contracts, which can happen especially with non-vital teeth.

The chief object of the invention is an improved method for anchoring a pin in a tooth hole.

A further object of the invention is an improved pin construction capable of good tooth retention and capable of easier and faster installation by the dentist.

These and other objects of the invention are achieved, in accordance with one feature of the invention, through the use of a cyanoacrylate as a cementing medium for retaining and sealing a dental pin in a tooth. In accordance with a further feature of the invention, a cyanoacrylate cement is used in combination with a threaded, ringed, or knurled pin. Preferably, the pin has a non-circular cross-section to increase its retention in the hole. In accordance with still another feature of the invention, the pin is supplied in a long strip form comprising at least four discrete pins, each of which is separable from the strip by a simple breaking operation. This form makes handling and insertion of the pins considerably easier for the dentist.

These and other advantages of the invention will become clearer from the detailed description that follows hereinafter taken in conjunction with the accompanying drawing wherein:

FIG. 1 is an enlarged side view of a strip of pins in accordance with the invention;

FIG. 2 is an enlarged cross-sectional view along the line 2--2 of FIG. 1.

There are many cements that have been suggested for cementing metal pins into a tooth. As indicated above, they all suffer from a number of drawbacks, which include long setting time, relatively poor adhesion strength, and the necessity for forming a spreadable paste starting from a powder. This results in a relatively thick paste which therefore is applied as a relatively thick layer which further reduces adhesion strength. There are many other types of cements commercially available, but of these others few are found to be capable of adhering to tooth dentine or are compatible therewith from the standpoint of being safe, non-toxic and non-irritating.

A principal feature of my invention is that a cement based on a cyanoacrylic monomer is uniquely suited for cementing steel pins to tooth dentine. Any cyanoacrylate based cement can be used for this purpose but I prefer a material from the adhesive family known as alkyl 2-cyanoacrylates, having the general formula CH.sub.2 = C(CN)--COOR, where R can be methyl, butyl, isobutyl, propyl, ethyl, and also higher homologues such as hexyl, heptyl, and octyl cyanoacrylates. I prefer to use butyl 2-cyanoacylate or ethyl 2-cyanoacylate. Such materials are available commercially. For example, methyl 2-cyanoacrylate is available from Eastman Kodak under the name "Eastman 910." Isobutyl 2-cyanoacrylate is available from Johnson & Johnson under the name "I BC-1." These cyanoacrylate cements are available as a clear, thin liquid (low viscosity) monomer, which polymerizes and hardens instantly upon exposure to moisture. The cement can thus be applied as a thin coating to the pin end and then the coated pin end immediately inserted in the previously drilled tooth hole. This cement sets and hardens instantly in the presence of water or blood, and no time is wasted by the dentist having to wait for hardening of a slow-setting cement. This allows 5-10 pins to be mounted in the same time it would take for one pin to be mounted with the prior art techniques. There is no objection to applying the cyanoacrylate cement directly to the tooth as it is non-irritating. Thus, the varnishes previously used to seal against leakage and to protect the tooth pulp may be eliminated as the cyanoacrylate can perform these same functions of the varnish in addition to the adhering function. The cyanoacrylate bonds strongly to the dentine and quite well to a threaded steel pin. As the cementing coating is thin, it is not only useful with undersized pins, but can also be used to strengthen the adherence of the friction-locked and threaded pins. Thus, for a typical steel pin diameter of 0.027 inches, the tooth hole can be made with a larger drill of say 0.029 inches, or with a similar-sized drill of 0.027 inches or even a smaller drill of say 0.025 inches.

Since the cyanoacrylate bonds more strongly to the dentine than to the metal of the pin, I prefer to improve the adhesion strength of the pin to the cement by roughening the pin surface forming crevices in which the cement can lodge and impede pull-out or rotation of the pin. This can be achieved most simply by providing threads, annular rings, or knurls on the pin. A preferred construction is the use of square stock rather than round stock in the manufacture of the pins, and then rolling, machining or stamping threads or rings in the pin surface. The transverse recesses formed between the threads or rings when filled with cement resist pull-out of the pin, while the longitudinal recesses formed by the flat sides of the pin, between the square corners, when filled with cement resist pin rotation.

The quick setting property of the cyanoacrylate cement also permits the use of a novel pin strip for extremely fast mounting of the pins. One embodiment is illustrated in FIG. 1, which is an enlarged side view of an elongated pin 10 comprising five connected discrete pins 11 separated by regions 12, 13, 14, 15 of reduced cross-section. The pin may be of round stock and threaded throughout, or preferably of square stock and threaded throughout as illustrated. The reduced cross-section regions 12-15 may have a diameter of approximately one-half that of the pins.

In use, the dentist first drills in the tooth the desired number of holes to receive pins. Then, holding one end 17 of the long strip 10, he applies a thin layer of cyanoacrylate cement to the free end 18 and quickly inserts the coated pin end in one of the drilled holes. Instantly the cement hardens and the pin end is locked in place. The dentist then breaks off the four remaining pins at the first thinned-down region 12, applies a new coat of cement to the free pin end and inserts the coated end into a second hole. He then breaks off the three remaining pins at the second thinned down region 13, and continues the procedure until all five discrete pin sections 11 have been mounted. In this technique, the pins are initially handled as a long strip, at least having a length of four pins, which makes it much easier for the dentist to handle. Moreover, the pin strip need never leave the dentist's hand, thereby saving the time normally spent in picking up tiny loose pins with pliers and then inserting in a special tool or handled directly by the pliers. It is evident that this technique will shorten considerably the time required to install a large number of tooth pins. To make it easier to break off the remaining pins, preferably the pin to be mounted is first bent over to weaken the joint at the thinned down region. Then the cement is applied and the bent-over pin end inserted into the tooth hole. This practice can also be applied to the remaining pins.

FIG. 2 illustrates the square cross-section of the pin 10 with the corners 19 threaded, thereby forming longitudinally extending crevices 20 along the flat sides for receiving cement to resist pin rotation.

The threaded pins can be mounted in a drilled oversized hole, or a drilled hole of the same size, or a drilled or threaded undersized hole, and its anchoring therein established or enhanced by means of the cyanoacrylate cement as described above. The cyanoacrylate cement also serves to seal the hole in the tooth thereby eliminating the need for using an additional varnish.

The typical cyanoacrylate cement available commercially, as above noted, hardens very rapidly, typically in 10-15 seconds. If the user prefers a somewhat slower setting cement, within say 30-45 seconds, to provide a little more time for adjustment of the pin position, such cements too are readily available commercially. Setting time is readily controlled in a known way by the addition of known inhibitors and by controlling viscosity.

While the principles of the invention have now been made clear in several illustrative embodiments, there will be immediately obvious to those skilled in the art many modifications in structure, arrangement, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operating requirements, without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications, within the limits only of the true spirit and scope of the invention.

Claims

What is claimed is:

1. A method of anchoring a metal pin to a tooth, comprising forming in the tooth a hole having a width approximately equal to that of the pin, applying a thin coating of a liquid cyanoacrylate cement to an end of the pin, then before the cyanoacrylate cement hardens rapidly inserting the pin end into the hole in order to anchor it therein by means of a bond formed between the cyanoacrylate cement and each of the tooth and the pin, and wherein the pin is supplied in the form of an elongated strip of at least four pins of the same width separated by regions of reduced cross-section, and after the first pin is anchored, the remaining pins still in strip form are broken off, cement again applied to a free pin end, the latter inserted in another tooth hole, and so-on until all the pins on the strip have been anchored in place.

2. A method as set forth in claim 1 wherein the pin has a roughened exterior.

3. A method as set forth in claim 2 wherein the pin has laterally-extending crevices for receiving cement to resist pin pull-out.

4. A method as set forth in claim 2 wherein the pin has longitudinally extending crevices for receiving cement to resist pin rotation.

5. A method as set forth in claim 4 wherein the pin has a square cross-section with threaded corners.

6. A method as set forth in claim 1 wherein the tooth hole has a diameter of the order of about 0.03 inches.

7. A method as set forth in claim 6 wherein the pin is threaded, and the hole formed in the tooth is several thousandths of an inch wider than the threaded pin.