GB2084987A

GB2084987A - Improvements In or Relating to Dental Porcelains

Info

Publication number: GB2084987A
Application number: GB8130714A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-10-10
Filing date: 1981-10-12
Publication date: 1982-04-21

Abstract

A porcelain dental restorative having a desired colour on a colour chart is made by mixing selected quantities, given by a respective recipe, of six constituent porcelain powders, the first three having respective red, yellow and blue tinges, the fourth being predominantly white, the fifth grey and the sixth giving a colourless, transparent porcelain, the resulting mixture being formed into the restorative and fired. The restorative core, dentine and enamel layers are made from different mixtures, the core and preferably also the dentine layer including an opacifier and the enamel comprising mainly the sixth powder.

Description

SPECIFICATION Improvements in or Relating to Dental Porcelains The present invention relates to dental porcelains, especially dental porcelain powders for use in the restoration of damaged teeth, that is in the production of crowns.

Two different techniques are used in dental restorations, the construction of a jacket crown in which a porcelain cap replaces the outer tooth structure or, the construction of a bonded crown in which a metal coping is interposed between the tooth structure and the porcelain cap. The latter construction has the advantage of greater strength and the possibility of replacing missing teeth by the use of multi-unit bridges.

Porcelains of different compositions are used for each different method of crown construction.

Each porcelain construction when built up must simulate the narrow range of mainly yellow and grey tones in natural teeth and the variation of colour and translucency within a single tooth, to produce a satisfactory aesthetic effect. To enable the dental technician to achieve this, the normal practice is to supply porcelain compositions in a range of shades comprising very small differences in colour, the total number of shades included in current porcelain systems ranging from 25 to 50.

Clearly to provide such a large range is expensive.

It is an object of the present invention to obviate or mitigate the disadvantages exhibited in existing porcelain systems.

According to the present invention there is provided a method of manufacturing a porcelain dental restorative in which a porcelain powder mixture is made up from selected quantities of some or all of a group of constituent porcelain powders comprising: a first powder having a red tinge; a second powder having a yellow tinge; a third powder having a blue tinge; a fourth powder which is predominantly white; and a fifth powder which is predominantly grey or black; and the powder mixture is utilised in the production of the restorative, the constituent powders and quantities thereof selected determining the shade of the finished restorative.

Preferably the group of constituent porcelain powders includes a sixth powder for forming a substantially colourless, transparent or translucent porcelain.

The method may also include adding opacifiers to any one of the five constituent powders.

Further according to the present invention the dental restorative may be formed in more than one layer, each layer comprising a different porcelain powder mixture of the group of constituent porcelain powders, and the outer layer comprising predominantly the sixth powder to simulate the translucent enamel of teeth on the finished restorative. The restorative is preferably subjected to firing as each layer is completed.

Preferably coloured porcelain powders are added to the enamel layer.

In a preferred embodiment of the invention a first porcelain powder, including an opacifier, is made up from one of more of the group of constituent porcelain powders and is formed into a core of the dental restorative, a second porcelain powder is made up from at least two of the group of constituent porcelain powders including the said sixth powder and is formed into a dentine layer on the core, and an enamel layer is formed on the dentine layer from a third porcelain powder comprising predominantly the said sixth powder.

The present invention also provides a combination for use in the manufacture of a dental restorative, including: a group of constituent porcelain powders comprising; a first powder having a red tinge; a second powder having a yellow tinge; a third powder having a blue tinge; a fourth powder which is predominantly white; and a fifth powder which is predominantly grey or black; a colour chart indicating finished restorative shades; and a recipe for each of the shades indicating the constituent powders and quantities thereof required in the making of a powder mixture for forming restoratives, or part thereof, of that shade.

An embodiment of the present invention will now be described by way of example.

The manufacture of a dental restorative or crown, whether it is a jacket crown or a metal bonded crown, normally involves the use of three different types of porcelain. The core porcelain provides a base for the crown and gives it a suitably coloured background and, in metal bonded restorations must be sufficiently opaque to mask the dark colour of the metal coping. On top of this core is formed a dentine or body layer of porcelain which forms the main body of the crown and is chiefly responsible for its colour and overall aesthetic effect. On top of the dentine or body porcelain layer there is formed the enamel or incisal porcelain layer which is generally applied to the incisal third or half of the crown, increasing in thickness towards the incisal edge having the purpose of simulating the translucent edge of a natural tooth.

The present embodiment provides five opacified porcelain powders for use in forming the core layer, the powders coloured white, grey, yellow, pink and blue and four porcelain powders for forming the dentine layer coloured grey, yellow, pink and blue. There is provided also a clear porcelain which can be added to the appropriate coloured porcelains to control the translucency of the dentine layer and forms the major part of the incisal layer.

A chart setting out the full range of colours of the finished layers which the dental technician may wish to employ is provided and for each colour there are directions giving the types and quantities of powder to be mixed such that that particular colour will be obtained on manufacturing the crown. Thus there is no need for the technician to have a large number of individual shades, some of which are seldom used. Furthermore he has the opportunity of making up his own shades. Since there are considerably fewer basic powders the task of colour control, one of the chief problems in dental porcelain manufacture, will be less serious.

In producing the core layer the basic hue thereof depends on the relative portions of the primary colours red, yellow and blue employed and the intensity of colour and lightness on the proportions of white and grey powders applied.

Similar considerations pertain in the production of the dentine layer, the translucency of this layer being controlled by the proportion of clear porcelain added. In a similar manner the enamel layer, which is primarily clear porcelain powder, is produced by the addition of small proportions of other powders to the clear porcelain.

A non-limitative example of the present invention will now be given, the restorative manufactured being on a metal base.

The constituent powders were made up by the method commonly used in the manufacture of dental porcelain from a pure potash feldspar and reagent chemicals. Commercial ceramic stains and opacifiers are added in appropriate proportions to the base porcelain composition and fused at 1 2500C in refractory crucibles.This porcelain was crushed to a particle size required in dental porcelain and utilised in the formation of crowns which were fired at 94OOC. The composition of the base porcelain is given in the following table:- 63.5% SiO2 63.5% Awl203 16.5 CaO BaO 1.0 K2O 11.5 Na2O 5.5 B203 1.0 Suitable primary powders, that is the powders including red, blue and yellow had the following CIELAB colour co-ordinates:- Reds71.7 a; 16.3 b; 3.7 Blue L 53.1 a;-8.6 b;-14.8 Yellow L 77.3 a-i 1.4 b; 44.0 Various modifications can be made without departing from the scope of the invention, for example the composition of the porcelain can be modified within normally accepted limits and the colour primary need not be pure yellow, red or blue but should be such that by admixture of the constituent powders the entire range can be achieved.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to whether or not particular emphasis has been placed thereon.

Claims

1. A method of manufacturing a procelain dental restorative in which a porcelain powder mixture is made up from selected quantities of some or all of a group of constituent porcelain powders comprising: a first powder having a red tinge; a second powder having a yellow tinge; a third powder having a blue tinge; a fourth powder which is predominantly white; and a fifth powder which is predominantly greay or black; and the powder mixture is utilised in the production of the restorative, the constituent powdera and quantities thereof selected determining the shade of the finished restorative.

2. A method as claimed in Claim 1, in which at least one of the five constituent porcelain powders includes an opacifier.

3. A method as claimed in Claim 1 or Claim 2, in which the group of constituent porcelain powders includes a sixth powder for forming a substantially colourless, transparent or translucent porcelain.

4. A method as claimed in Claim 3, in which the dental restorative is formed in at least two layers, each layer comprising a different porcelain powder mixture of the group of constituent porcelain powders, and the outer layer comprising predominantly the sixth powder.

5. A method as claimed in Claim 4, in which the restorative is fired after the formation of each said layer.

6. A method as claimed in Claim 4 or Claim 5, in which a first porcelain powder including, an opacifier, is made up from one or more of the group of constituent porcelain powders and is formed into a core of the dental restorative, a second porcelain powder is made up from at least two of the group of constituent porcelain powders including the said sixth powder and is formed into a dentine layer on the core, and an enamel layer is formed on the dentine layer from a third porcelain powder comprising predominantly the said sixth powder.

7. A method of manufacturing a porcelain dental restorative substantially as herein described with reference to the example.

8. A combination for use in the manufacture of a dental restorative, including: a group of constituent porcelain powders comprising: a first powder having a red tinge; a second powder having a yellow tinge; a third powder having a blue tinge; a fourth powder which is predominantly white; and a fifth powder which is predominantly grey or black; a colour chart indicating finished restorative shades; and a recipe for each of the shades indicating the constituent powders and quantities thereof required in the making of a powder mixture for forming a restorative, or part thereof, of that shade.

9. A combination as claimed in Claim 8, in which the group of constituent porcelain powders includes a sixth powder for forming a substantially colourless, transparent or translucent porcelain.

10. A combination for use in the manufacture of a dental restorative substantially as herein described with reference to the example.

11. A dental restorative made by the method of any one of Claims 1 to 7.