GB2162068A - Tooth dowel - Google Patents

Abstract

A tooth dowel 13 for fixing in a drilled root canal is electrolytically etched to give a micro-retentive surface yielding a strong bond with a luting agent 12. The dowel is preferably tapered made of cobalt chrome, nickel chrome, or nickel chrome beryllium alloy, and is cast and etched in nitric acid followed by ultrasonic cleaning in hydrochloric acid. The dowel may have projections at its top end. It may also have a fibre optic bundle in a spiral groove along its length, the fibres being of varying lengths, to allow light to be supplied to the whole mass of surrounding luting agent if a light- setting luting agent is being used. <IMAGE>

Description

SPECIFICATION Tooth dowel The present invention relates to dentistry, and more specifically to root dowels for retaining crowns on tooth roots.

A modern method of rebuilding a very damaged tooth is by first obturating (stopping) the root canal, then enlarging the coronal portion of the canal, then inserting a dowel or post, and finally fabricating a core on the dowel and cementing a crown on the core.

Various designs of dowel or post for this purpose are available. For example, there are screws of various lengths and diameters; custom castings made to approximate the internal size of the root canal; and parallel stainless steel knurled wire, which may have a vent channel up one side. All these known dowels are normally fixed in the root canal by means of some form of luting agent (cement), though simple screwing into place in dentine has also been proposed.

A problem which arises with these dowels is that of dowel fixing failure; that is, the dowel is liable to pull out of the fixing. The literature is replete with discussions of this problem, which remains substantial despite such measures as the use of screwed dowels or knurled surfaces to improve the keying of the luting agent to the dowels.

According to the invention, there is provided a tooth dowel with an electrolytically etched surface.

The dowel is preferably of non-precious metal, and is preferably tapered at a standard taper angle.

The provision of the electrolytically etched surface results in a micro-retentive surface which forms a mechanically strong bond with the luting agent. As a result, the bond of the luting agent to the dowel can withstand a substantial tension. This is important for the retention of the dowel in the root canal of the tooth, since transverse forces on the dowel produce tension between parts of the dowel and the luting agent, and dowel-cement interface failure under such tension tends to gradually decrease the area of sound bond retaining the dowel. It has been found that such failure does not occur with the present invention.

The use of a tapered dowel has the advantage that the taper approximates to the taper of many root canal preparations. The taper is preferably the international standard taper of 0.01875 mm per mm of length.

The dowel may be formed with a lengthwise groove containing a fibre optic bundle. This is advantageous if the dowel is to be used with a luting agent the setting of which is promoted by light, since the fibre optic bundle allows a pulse of light to reach all parts of the mass of the luting agent along the whole length of the dowel.

A dowel in accordance with the invention, and the way in which it is made, will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. lisa section (enlarged and not to scale) through a tooth rot with the dowel cemented in place; Fig. 2 shows a modified dowel; and Fig. 3 shows (on a smaller scale) how the fibre optic bundle of the modified dowel is made.

The dowel is made from cobalt chrome, nickel chrome, or nickel chrome beryllium alloy, and is formed by casting. After casting, the surface of the dowel is etched electrolytically. Low voltage DC with a stainless steel cathode is used, and the cast dowel is mounted on a conductive anode. Both electrodes are immersed in a 0.5 N nitric acid bath, and the current is adjusted to a level of 2 to 3 mA/mm2 for about 5 min. The resulting etched surface has a debris layer, and the dowel is rinsed in water and then immersed in an ultrasonic bath of hydrochloric acid solution of about 18% for some 10 to 15 min.

After rinsing and drying, the etched casting is then ready to be luted within the root canal by a resin.

Obviously, the material of the dowel, and the etching regime, can be varied from the values just stated, provided that the result is a micro-retentive surface which will form a mechanically strong bond with the luting agent.

A set of dowels may be made in a convenient sequence of lengths and tip diameters. It is also possible to make the dowel with an angle or bend near the top end, for use in resetting the crown of a projecting (buck) tooth.

To preserve the etched surface, the dowels are preferably stored in sealed vials containing nitrogen or alcohol, which avoids oxidation of the surface of the dowels.

Referring to Fig. 1, a tooth root 10 is shown which has been levelled off at the top. The root canal has been obturated by a stopping agent 11 at the bottom end, and has been drilled above the obturation to a standard taper. The dowel 13 has been inserted into the drilled root canal, and fixed by means of a luting agent 12, which has also been used to form a core 14 above the top surface of the tooth root. A crown (not shown) would then be fixed to the core.

The luting agent is preferably an agent which forms a strong bond with dentine, since the interior of the tooth root is dentine.

Figure 2 shows a modified form of dowel 13. One of the modifications is in the shape of the top end of the dowel, which is shown with projecting lobes 20 and a jagged to 21. Obviously the top end of the dowel can be made with a myriad of different shapes, such as finger-like projections, to help in retaining the core material to be attached to the dowel.

The other modification shown in the dowel of Fig.

2 is that it has a spiral groove 22 along its length with a fibre optic bundle 23 retained in it. Certain luting agents have been deveioped in which setting is promoted by light. These present the difficulty that although a strong light can be shone on the upper end of the root canal, where the dowel protrudes, the light does not diffuse satisfactorily down to the lower end of the dowel and root canal.

By providing the fibre optic bundle along the dowel, this problem can be overcome. A pulse of strong light of suitable length, typically several seconds, shone on the upper end of the bundle 23 will be transmitted down the bundle to all parts of the canal, so that setting of the luting agent will occur throughout its mass.

Fig. 3 shows diagrammatically how the fibre optic bundle 23 is formed. A bundle of parallel optic fibres is spread out slightly, and is then cut by means of a cut at a glancing angle (indicated by line 24) to the bundle, so that a substantially uniform spread of fibre lengths is obtained. In consequence, light will be emitted substantially uniformly along the length of the fibre optic bundle, i.e. from the top to the bottom of the dowel.

Claims (8)

1. Atooth dowel with an electrolytically etched surface.

2. A tooth dowel according to claim 1 having a taper.

3. A tooth dowel according to either previous claim made of cobalt chrome, nickel chrome, or nickel chrome beryllium alloy.

4. A method of making a dowel according to claim 3 comprising electrolytically etching the dowel in a nitric acid bath at a current level of between 1 and 5 mAImm2.

5. A dowel according to any one of claims 1 to 3 and having a lengthwise groove containing a fibre optic bundle.

6. A dowel according to claim 5 wherein the groove is spiral.

7. A dowel substantially as herein described and illustrated.

8. A method of making a dowel substantially as herein described.