GB1600399A - Dowel or post for dental or orthopaedic prostheses - Google Patents

Description

(54) AN IMPROVED DOWEL OR POST FOR DENTAL OR ORTHOPAEDIC PROSTHESES (71) We, MICHAEL JOSEPH GROSS, British, of 14, Edith Road, London, W14, and CHRISTOPHER HUGH TURNER, British, of Cherry Tree Cottage, Hursley, Nr. Winchester, Hampshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to dowels or posts for dental or orthopaedic prostheses, particularly for the attachment of a tooth crown to a tooth root or an orthopaedic prosthetic joint to the shaft of a bone, and to a pattern for use in the manufacture of such posts by investment casting. The invention also extends to a method of anchoring a tooth crown to a tooth root using the said dowel or post.

Dowels or posts, usually of metal, have been used for securing dental crowns to roots for many years and recent developments in artificial joints have enabled damaged or diseased natural joints to be replaced by artificial joints similarly attached to the shaft of a bone by a dowel or post.

In the traditional method of securing the dowel or post in position in the tooth root or bone shaft, a blind hole is drilled in the tooth root or in the bone shaft and lined with a cement. The dowel post is then inserted into the previously prepared blind hole to be secured therein by the cement.

For this purpose a dowel or post is used which traditionally is circular cross-section.

Screw-threaded dowels have been proposed which are screwed into a threaded hole tapped into the tooth root, but again a cement is usually required to prevent the post unscrewing.

Recent research has shown that during the cementation of circular or threaded posts of dowels, considerable hydrostatic pressures are developed within the tooth root or the bone shaft due to the action of the post as it is inserted or threaded into the prepared blind hole, which tends to wipe the cement lining off the walls of the prepared hole and to compress the wiped-off cement at the end of the blind hole ahead of the post. In some cases this hydrostatic pressure is sufficient to cause cracking of the tooth root or the bone.

In accordance with the present invention, there is provided a dowel post for anchoring a dental or orthopaedic prosthetic device, comprising an end on which said device may be formed or mounted and a parallel-sided shaft extending therefrom for insertion into a previously prepared parallel-sided blind hole and securement therein by a cement, said end and said shaft being integrally formed from a biologically suitable metal or alloy, wherein said shaft has a plurality of contiguous helical flutes formed in the surface thereof and helically wound thereabout at a pitch angle not exceeding 60 to the axis of the shft and providing a flow path for the cement when said shaft is inserted into the blind hole. The flute or flutes in the surface of the shaft are preferably at an angle of 45" to the longitudinal axis.Dowel posts according to the invention provide all or some of the following advantages: a) an improved distribution of the luting cement between the post or dowel and the side walls of the prepared cylindrical hole; b) a reduction in the maximum hydrostatic pressure generated during the insertion of the post or dowel into the unset cement within the prepared hole; c) an increase in the strength of retention of the post or dowel within the prepared hole after the cement has set.

A dowel or post according to the invention is illustrated in the accompanying drawings.

In the single figure of the accompanying drawing d represents the root of the tooth which is to be crowned and e represents the parallel-sided blind hole which is prepared in the tooth to receive the dowel post b. It will be understood that in actual practice a dental cement will be placed in the hole e before actual insertion of the post b. On the exposed end of the dowel or post b is formed the tooth crown diagrammatically represented at a. As will be understood, this will in fact be mounted on the exposed end of the dowel or post a after setting the post in the tooth root, e.g. by soldering or integral casting.

In accordance with this invention, the dowel or post b is provided on its surface with one or more helical flutes or channels c preferably at least two, at an angle of about 45" to the longitudinal axis of the post. As the dowel or post b is inserted into the blind hole e these flutes or channels provide pressure relieving channels up which the cement can flow to relieve the hydrostatic pressure which might otherwise build up in the blind hole e ahead of the post b as it is inserted.

The dowel or post according to the invention will be wrought or cast from any biologically suitable metal or alloy. Usually, the post will be formed by casting in a mould in accordance with the lost wax technique, i.e. investment casting and, accordingly, this invention also extends to a pattern having a configuration as defined above for the dowel post of the invention, and suitable for use in the manufcture of such a dowel or post by an investment casting technique, said pattern being an exact replica of the dowel post but in a low melting point material rather than said biologically inert metal or alloy.

In conclusion it may be pointed out that the present invention is to be distinguished over conventionally used screw-threaded posts in that the flutes described herein are quite distant from a conventional screwthread, both in the pitch angle of the flute, and in the cross-section of the channel formed by the thread. In the case of a screwthread, the helical channel formed in the surface of the post is usually of a V-shaped configuration, rather than a concave 'flute', as required by the present invention, and moreover is at a relatively high pitch angle e.g. greater than 60 , so that as the screw is rotated, the post is axially advanced relative to the hole, a relatively high angular rotation of the post producing only a relatively small axial advancement.

WHAT WE CLAIM IS: 1. A dowel post for anchoring a dental or orthopaedic prosthetic device, comprising an end on which said device may be formed or mounted and a parallel-sided shaft extending therefrom for insertion into a previously prepared parallel-sided blind hole and securement therein by a cement, said end and said shaft being integrally formed from a biologically suitable metal or alloy, wherein said shaft has a plurality of contiguous helical flutes formed in the surface thereof and helically wound thereabout at a pitch angle not exceeding 60 to the axis of the shaft and providing a flow path for the cement when said shaft is inserted into the blind hole.

2. A dowel post according to claim 1, wherein said flutes are at a pitch of about 45" to the axis of the shaft.

3. A dental crown comprising a dowel post as claimed in claim 1 or 2 and a crown mounted on said end thereof.

4. An orthopaedic prosthetic device in the form of an artificial joint comprising a dowel post as claimed in claim 1 or 2 and an artificial joint member formed or mounted on the end thereof.

5. A pattern for use in the manufacture of a dowel post according to claim 1 or 2 by investment casting said pattern consisting of an exact replica of the dowel post but in a low melting point material other than said biologically inert metal or alloy.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. which is to be crowned and e represents the parallel-sided blind hole which is prepared in the tooth to receive the dowel post b. It will be understood that in actual practice a dental cement will be placed in the hole e before actual insertion of the post b. On the exposed end of the dowel or post b is formed the tooth crown diagrammatically represented at a. As will be understood, this will in fact be mounted on the exposed end of the dowel or post a after setting the post in the tooth root, e.g. by soldering or integral casting. In accordance with this invention, the dowel or post b is provided on its surface with one or more helical flutes or channels c preferably at least two, at an angle of about 45" to the longitudinal axis of the post. As the dowel or post b is inserted into the blind hole e these flutes or channels provide pressure relieving channels up which the cement can flow to relieve the hydrostatic pressure which might otherwise build up in the blind hole e ahead of the post b as it is inserted. The dowel or post according to the invention will be wrought or cast from any biologically suitable metal or alloy. Usually, the post will be formed by casting in a mould in accordance with the lost wax technique, i.e. investment casting and, accordingly, this invention also extends to a pattern having a configuration as defined above for the dowel post of the invention, and suitable for use in the manufcture of such a dowel or post by an investment casting technique, said pattern being an exact replica of the dowel post but in a low melting point material rather than said biologically inert metal or alloy. In conclusion it may be pointed out that the present invention is to be distinguished over conventionally used screw-threaded posts in that the flutes described herein are quite distant from a conventional screwthread, both in the pitch angle of the flute, and in the cross-section of the channel formed by the thread. In the case of a screwthread, the helical channel formed in the surface of the post is usually of a V-shaped configuration, rather than a concave 'flute', as required by the present invention, and moreover is at a relatively high pitch angle e.g. greater than 60 , so that as the screw is rotated, the post is axially advanced relative to the hole, a relatively high angular rotation of the post producing only a relatively small axial advancement. WHAT WE CLAIM IS:

1. A dowel post for anchoring a dental or orthopaedic prosthetic device, comprising an end on which said device may be formed or mounted and a parallel-sided shaft extending therefrom for insertion into a previously prepared parallel-sided blind hole and securement therein by a cement, said end and said shaft being integrally formed from a biologically suitable metal or alloy, wherein said shaft has a plurality of contiguous helical flutes formed in the surface thereof and helically wound thereabout at a pitch angle not exceeding 60 to the axis of the shaft and providing a flow path for the cement when said shaft is inserted into the blind hole.

2. A dowel post according to claim 1, wherein said flutes are at a pitch of about 45" to the axis of the shaft.

3. A dental crown comprising a dowel post as claimed in claim 1 or 2 and a crown mounted on said end thereof.

4. An orthopaedic prosthetic device in the form of an artificial joint comprising a dowel post as claimed in claim 1 or 2 and an artificial joint member formed or mounted on the end thereof.

5. A pattern for use in the manufacture of a dowel post according to claim 1 or 2 by investment casting said pattern consisting of an exact replica of the dowel post but in a low melting point material other than said biologically inert metal or alloy.