GB2033822A

GB2033822A - An improved method of manufacturing cast dental crowns

Info

Publication number: GB2033822A
Application number: GB7933031A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-09-23
Filing date: 1979-09-24
Publication date: 1980-05-29
Also published as: GB2033822B

Abstract

A method of forming a dental crown on a model of a jaw comprises filling a preformed deformable shell in the general form of a crown for a tooth with a setable material, fitting the deformable shell on the stump of the tooth to be crowned, arranging the stump into position between and against its neighbouring and opposing teeth such that it partially deforms to correspond and match with said teeth, retaining the stump in position until the material contained within the deformable shell sets, removing the shell from the set material, forming a further shell over the set material such that the further shell conforms to the shape of the material thereafter removing the further shell and utilising it in an investment casting technique to provide a crown with its outer surface corresponding to the outer surface of the shell.

Description

SPECIFICATION An improved method of manufacturing cast dental crowns The present invention concerns an improved method of manufacturing cast dental crowns especially gold dental crowns.

The manufacture of gold dental crowns is an expensive operation, not only as a result of the cost of the material used but also in view of the fact that each crown has to be manufactured individually, this resulting in the requirement of skill from the dental technician and considerable time.

The dentist prepares a tooth for capping by shaping the tooth such that an ujpwardly converging substantially frusto-conical stump is left projecting above the gum. Impressions are then taken of the upper and lower teeth, models are poured, for example from plaster, and the technician manufactures the crown from the models.

The technique presently employed comprises removing the portion of the model containing the tooth to be crowned and after suitably lubricating the stump portion thereof building up a crown in wax, the crown being so designed that its upper surface provides a correct bite with the corresponding surface of the tooth against which it normally acts, is of the correct dimensions to fit between and match with its neighbouring teeth, and is shaped so as to resemble a normal tooth. Clearly the necessary sculpting in wax requires considerable skill. After the wax crown has been manufactured a casting sprue is attached thereto and a solid gold replica crown is formed by a normal investment casting technique.

By suitably modifying the technique only an outer shell is cast in gold, the resultant shell crown being fitted over a suitable cement filling the space between it and the stump. Present casting techniques result in relatively thick and consequently expensive shell crowns.

According to the present invention a method of forming a dental crown on a model of a jaw comprises filling a preformed deformable shell in the general form of a crown for a tooth with a setable material, fitting the deformable shell on the stump of the tooth to be crowned, arranging the stump into position between and against its neighbouring and opposing teeth such that it partially deforms to correspond and match with said teeth, retaining the stump in position until the material contained within the deformable shell sets, removing the shell from the set material, forming a further shell over the set material such that the further shell conforms to the shape of the material thereafter removing the further shell and utilising it in an investment casting tech nique.

Preferably said shells are formed from sheet plastics material.

Preferably a replica of the stump is utilised with the further shell in the casting operation to form a solid crown.

Alternatively only the further shell alone is used in the casting technique such that a shell crown is formed.

The present invention provides also crowns when manufactured by the techniques disclosed in the preceding five paragraphs.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which shows diagrammatically part of an upper and lower dental model, the tooth A being the tooth to be crowned.

The drawing shows a dental model of a molarA which has been prepared by the dentist for crowning by the removal of the shaded area such that an upwardly coverging frusto-conical stump 10 remains, the stump being separated from the tooth root by a ridg4e 12.

The first stage of the process of forming a solid crown comprises removing the stumped tooth A from the model and forming a shell of plastics material sheet over the stump to provide a thimble which is removed from the stump and placed aside.

Another deformable shell conforming in shape to a tooth similar to the original tooth a is filled with a setable rubber-like material and an assembly of the outer shell and the unset rubber-like material is set up on the stump which is then refitted to the model.

As the shell is deformable under pressure and the material within it has not set, when the tooth A is fitted into its model X and the opposing model Y brought against it it deforms such that it corresponds with and matches it opposing and neighbouring teeth. It is then held in this position until the material sets thus providing a tooth A which corresponds in shape to a major extent with the tooth shape of the dformable shell selected but has had this shape modified such that the "bite" of the tooth corresponds with its opposing tooth and its di mensions match the original tooth such that it fits between its neighbouring teeth B and C.

At this stage the outer shell is removed from the set material and a further substitute shell of a material suitable for use in the subsequent casting operation is formed in its place. The resultant tooth thus has an outer shell corresponding to the outer surface of the crown to be formed, a filling of set rubber-like material and an innerthimblewhose inner surface corresponds exactly with the surface of the stump.

The set material is discarded and the outer shell and thimble are set up on the impression stump using wax at only the ridge 12, the composite hollow assembly then being suitable for use in a normal investment casting operation to provide a solid gold crown with its outer surface corresponding to the outer surface of the shell and its inner surface corresponding to the inner surface of the thimble.

Thus a solid crown is formed in such a way that an unskilled operator can be employed and since the shape of the crown is derived from the shape of the deformable shell and from the opposing tooth D and neighbouring teeth B and C in the model X and Y no skill is required by the technician in shaping the tooth.

In an alternative method an even less expensive crown can be produced by utilising only the outer substitute shell and wax at the ridge 12 in the investment casting operation. This results in the formation of a shell crown which corresponds exactly to the shape of the outer substitute shell only and correspondingly contains much less weight of gold.

In fitting such a shell crown to the patient's stumped tooth Athe dentist simply fills the shell crown with a suitable cement material and fixes it over the stump, the cement filling the space between the stump and shell.

The thickness of the outer shell is suitably betwen 0.4 and 0.8 millimetres.

Various modifications can be made without departing from the scope of the invention, for example otherthan plastics materials may be employed for the shells provided that they are otherwise suitable, that is the replacement for the outer shell should be deformable and the replacement for the further substitute shell should be relatively rigid after forming and suitable for use in an investment casting technique. These alternative shells may be applied by any suitable technique, for example they can be painted or sprayed on in solution form and allowed to set in position, dipped in molten wax, or vacuum pressure formed or deep drawn.

Claims

1. A method of forming a dental crown on a model of a jaw comprises filling a preformed deformable shell in the general form of a crown for a tooth with a setable material, fitting the deformable shell on the stump of the tooth to be crowned, arranging the stump into position between and against its neighbouring and opposing teeth such that it partially deforms to correspond and match with said teeth, retaining the stump in position until the material contained within the deformable shell sets, removing the shell from the set material, forming a further shell over the set material such thatthe further shell conforms to the shape of the material thereafter removing the further shell and utilising it in an investment casting technique.

2. A method as claimed in claim 1, in which said shells are formed from sheet plastics material

3. A method as claimed in claim 1 or claim 2, in.

which a replica of the stump is utilised with the further shell in the casting operation to form a solid crown

4. A method as claimed in claim 1 or claim 2, in which only the further shell alone is used in the casting technique such that a shell crown is formed.

5. A method of forming a dental crown substantially as hereinbefore described with reference to the accompanying drawing.

6. A dental crown when manufactured by the method of any one of the preceding claims.

7. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claim.