GB1580132A

GB1580132A - Dental alloy

Info

Publication number: GB1580132A
Application number: GB15304/77A
Authority: GB
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1980-11-26

Description

(54) IMPROVED DENTAL ALLOY (71) We, JOHNSON, MATTHEY & CO., LIMITED, a British Company, of 43, Hatton Garden, London, EC1N 8EE, 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 dental alloys. In particular the invention is concerned with a particulate dental amalgam alloy which, when reacted with mercury, will provide an improved composition for filling dental cavities, that is, in teeth.

Alloys for use in dentistry, particularly for filling dental cavities, typically have compositions falling within the range silver 55-75 wt %, tin 20-40 wt.% and copper 0-10 wt.%. Optionally, up to 2 wt.% zinc may also be present. These alloys are generally supplied in powder or particulate form and are reacted in small quantities, as and when required, with mercury to produce a mouldable, pliant composition suitable for impressing, or "condensing", into dental cavities. The composition is designed to harden quickly, thus effecting a restoration of the fabric of the tooth. Since the alloys react with mercury to form amalgams, they are generally referred to as "dental amalgam alloys".

In the past, particulate dental amalgam alloys have generally consisted of irregularlyshaped particles, for example flakes. These alloys suffered from certain disadvantages, however, particularly in that they required a high proportion of mercury in order adequately to wet the surface of the particles to ensure complete amalgamation. This in turn led to excess mercury being expressed under condensation pressure and also rendered the amalgam prone to corrosion. Furthermore, high condensation pressures were required to fill a dental cavity.

In an attempt to overcome these disadvantages, particulate dental amalgam alloys consisting of spherically-shaped particles have been introduced but these suffer the particular drawback that, when amalgamated with mercury and introduced into a tooth cavity, the amalgam tends to extrude between the condensing tool and the wall surfaces of the cavity with consequent loss of packing firmness.

In an attempt to overcome the above disadvantages, a particulate dental amalgam alloy has been proposed comprising a mixture of substantially spherically-shaped and irregularlyshaped particles, the mixture containing a major proportion of the substantially spherically-shaped particles. We have found, however, that the problem of extrusion of the resulting amalgam past the condensing tool is not solved by the use of such a mixture and furthermore, marginal adaptation - that is to say, the way the amalgam fits the contours of the cavity - is poor. Also, on storage and in transit, the essentially spherically-shaped particles tend to settle to the bottom of the container with the result that the dentist, immediately prior to preparing a batch of amalgam, must agitate the particles to ensure an even shape distribution of particles throughout the sample.

We have found that these disadvantages may be considerably reduced, if not avoided by the use of a particulate dental amalgam alloy in which a major proportion of particles is irregularly shaped and a minor proportion is essentially spherically-shaped.

According to one feature of the invention there is provided a particulate mixture of a dental amalgam alloy, the alloy consisting, apart from impurities of 55-75 wt % silver, 20-40 wt. % tin and 0-10 wt%. copper and the mixture comprising a major proportion of irregularly-shaped particles and a minor proportion of essentially spherically-shaped particles.

Optionally, the alloy may also contain up to 2% by weight zinc.

Preferably, the irregularly-shaped particles comprise 55-90% by weight of the particulate mixture, the balance being essentially spherical particles, with an amount of about 60% by weight iregularly-shaped particles being most preferred. By "essentially spherical" we mean that the individual particles are cither spherical in shape or approximate to the shape of a sphere; a atypical lolcrance for all csscllliollly spherical particle in diverging from a spherical shape is that the larcsl (liltlllSi()ll sllall be no grc;itcr than about 120-130% of the smallest dimension. The particles gCIIClillIy have a fairly smooth surface. By "irregularly shaped", on the other hand, we mean thit the particles are typically in the form of flakelets, plates or filings. They are often, in fact, referred to in the art as "lathc-cut" particles. The surface of an irregularly-shaped particle, whilst not necessarily being rough or abrasive in nature, can nevertheless be expected to show various irregularities, angular and/or sharp projections and the like.

The particle size of the essentially spherical particles should preferably be less than 1()() microns and we prefer that they should he less than 75 microns. The smallest dimension of the irregularly shaped particles should, if anything, be slightly smaller than the size of the essentially spherical particles. sly about 6() microns, although the largest dimension may be several times larger than this, for example about 300 microns or cven larger.

The dental amalgam alloys of the invention may be reacted with mercury by trituration using standard equipment and techniques except that a given weight of an alloy according to the invention requires less mercury for amalgamation than an equivalent weight of an alloy consisting wholly of either spherical or or irregularly-shaped particles. Generally speaking, a weight ratio of mercury to alloy of 0.8 : 1 - 1 : 1 is sufficient. The resulting amalgam condenses firmly into the dental cavity with little or no extrusion between the condensing tool and the inner surfaces of the cavity.

Example 60% by weight of irregularly-shaped particles having minimum and maximum dimensions of 60 microns and 300 microns respectively and 40% by weight of essentially spherical particles having a maximum diameter of 75 microns were mixed mechanically. The composition of the alloy particles was within the range: silver 67-69% tin 26-29% copper 3-6 % zinc 0-2 /ó The resulting dental amalgam alloy according to the invention was triturated in a conventional manner in an automatic mixing machine with 8.7 - 8.8 parts by weight of mercury to 10 parts by weight of alloy. Examples of suitable mixing machines are a "Silomat" shaker and a "Degussa Mischer II". Mixing times vary with the quantity of material but are typically between 5 and 40 seconds.

One particular alloy according to the invention has the following composition: Spherical Irregular Ag 67-7 % Ag 68% Sn 28.7 % Sn 26.8% Cu 3.6 % Cu 5.2% and was mixed as above in a 60-40 irregular:essentially spherical ratio.

Samples of this alloy, after amalgamation as above, possessed the following properties: i) Carvability after trituration: a) with rapid condensation 8 mins b) with condensation over 5 mins 10 mins c) with condensation over 10 mins 17 mins (as per B.S. 2938) ii) Plastic deformation after 24 hours: always < 2.5% iii) Linear expansion over 24 hours: 9-12R/cm (always A201l/cm) iv) Average compressive strength a) after 20 min at 37 C 5,800 psi 40N/mm2 b) after 1 hr at 37"C 18,500 psi 127N/mm2 c) after 24 hr at 370C 53,000 psi 365N/mm2 d) after 60 hr at 370C 56,000 psi 385N/mm2 v) Diametrical tensile strength after 15 mins at 37% always > 500 psi.

WHAT WE CLAIM IS 1. A particulate mixture of dental amalgam alloy, the alloy consisting, apart from impurities, of 55-75 wt.% silver, 20-40 wt.% tin and 0.10 wt.% copper and the mixture comprising a major proportion of irregularly-shaped particles and a minor proportion of essentially spherically-shaped particles.

2. A mixture according to claim 1 wherein the alloy also contains up to 2 wt.% zinc.

3. A mixture according to claim 1 or claim 2 wherein the irregularly-shaped particles are present in the mixture in an amount of 55-90 wt.% of the mixture.

4. A mixture according to claim 3 wherein the amount of irregularly-shaped particles in the mixture is 60 wt.%.

5. A mixture according to any preceding claim wherein the particle size of the essentially spherical particles is less than 100 microns.

6. A mixture according to claim 5 wherein the particle size of the essentially spherical particles is less than 70 microns.

7. A dental amalgam containing a mixture according to any one of claims 1 to 6 and mercury wherein the ratio of mercury to mixture falls within the range 0.8:1 and 1:1.

8. A particulate mixture of a dental amalgam alloy substantially as hereinbefore described and exemplified.

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Claims

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ii) Plastic deformation after 24 hours: always < 2.5%

iii) Linear expansion over 24 hours: 9-12R/cm (always A201l/cm)

iv) Average compressive strength a) after 20 min at 37 C 5,800 psi 40N/mm2 b) after 1 hr at 37"C 18,500 psi 127N/mm2

c) after 24 hr at 370C 53,000 psi 365N/mm2 d) after 60 hr at 370C 56,000 psi 385N/mm2

v) Diametrical tensile strength after 15 mins at 37% always > 500 psi.

WHAT WE CLAIM IS 1. A particulate mixture of dental amalgam alloy, the alloy consisting, apart from impurities, of 55-75 wt.% silver, 20-40 wt.% tin and 0.10 wt.% copper and the mixture comprising a major proportion of irregularly-shaped particles and a minor proportion of essentially spherically-shaped particles.
2. A mixture according to claim 1 wherein the alloy also contains up to 2 wt.% zinc.
3. A mixture according to claim 1 or claim 2 wherein the irregularly-shaped particles are present in the mixture in an amount of 55-90 wt.% of the mixture.
4. A mixture according to claim 3 wherein the amount of irregularly-shaped particles in the mixture is 60 wt.%.
5. A mixture according to any preceding claim wherein the particle size of the essentially spherical particles is less than 100 microns.
6. A mixture according to claim 5 wherein the particle size of the essentially spherical particles is less than 70 microns.
7. A dental amalgam containing a mixture according to any one of claims 1 to 6 and mercury wherein the ratio of mercury to mixture falls within the range 0.8:1 and 1:1.
8. A particulate mixture of a dental amalgam alloy substantially as hereinbefore described and exemplified.