GB2108132A

GB2108132A - Improvements in dental cements based on metal oxides or hydroxides and eugenol

Info

Publication number: GB2108132A
Application number: GB08125619A
Authority: GB
Inventors: Michael Braden
Original assignee: DOUBLE H INTERNATIONAL MARKETI
Current assignee: DOUBLE H INTERNATIONAL MARKETI
Priority date: 1981-08-21
Filing date: 1981-08-21
Publication date: 1983-05-11
Also published as: GB2108132B

Abstract

In a dental cement containing as first component fine particles of zinc oxide or calcium hydroxide or magnesium oxide or hydroxide and as second component a hydroxyl- containing organic liquid such as eugenol that on mixing with the first component sets to form a hard mass, the particles of the first component are coated with a fatty acid such as stearic or oleic acid. Mixing of the cement is facilitated and speeded and higher proportions of first component can be incorporated in cements of a given consistency whereby good strength and low solubility in oral fluids is achieved.

Description

SPECIFICATION Improvements in dental cements based on metal oxides or hydroxides and eugenol The present invention relates to improved dental cements based on metal oxides or hydroxides and eugenol and in particular on the zinc oxide eugenol and chemically related systems.

Dental cements are a known class of materials and are used for the cementation of dental appliances and restorations, as lining materials under metallic restorations to provide thermal, chemical and electrical insulation for the pulp, as temporary filling materials and as a root filling material.

On mixing zinc oxide and eugenoi, the paste so formed ultimately sets to a hard mass by the formation of a zinc eugenate:

This essentially slow reaction is accelerated by Zn++ ions, either present as a small. quantity of zinc acetate in the zinc oxide powder or released from the latter by a trace of acetic acid in the Eugenol liquid.

It is well known that this basic system can be improved, notably its mechanical properties, by (a) dissolving a small quantity of polymer such as polystyrene in the eugenol, (b) adding alumina or silica to the zinc oxide powder and (c) replacing eugenol by up to 60% of o-ethoxybenzoic acid, see Brauer et al [J. Dent. Res. 37 547 (1958)]. But these materials are very difficult to mix, especially when a resinous reinforcing material is present.

It is also well known to dental surgeons that maximum strength and minimum solubility in oral fluids is achieved by as high a powder/liquid ratio as possible. But the powder/liquid ratio is limited by the consistency with which the dentist can work, and furthermore the time necessary to incorporate a high quantity of powder will be greater than that required for significant setting to occur.

This invention is based on the realisation that in a dental cement comprising as first component particulate zinc oxide or calcium hydroxide or magnesium oxide or hydroxide and as second component eugenol or a mixture of eugenol with a compatible material such as o-ethoxybenzoic acid it is advantageous that the particles of the first component should be surface treated with a fatty acid such as stearic or oleic acid.

It has long been the practice in, for example, the rubber industry, to surface treat fillers to faciliate their incorporation in rubbers in mixing equipment and to reduce the power consumption of the mixer.

And surface treated zinc oxide is commercially available under the name Extrox 5 from Durham Raw Materials. But the incorporation of such materials into dental cements has never hitherto been reported, notwithstanding that the Brauer eft at composition was described as long ago as 1 958 and its mixing problems are well known. We have found that providing a fatty acid surface coating not only facilicates and speeds up mixing but allows a higher proportion of metal oxide or hydroxide to be incorporated into a dental cement of a given consistency. Other preferred features of the invention are to be found in the claims, to which attention is hereby directed.

The invention is illustrated by the following examples: Example 1 A powder comprising 70% stearic acid coated zinc oxide, and 30% aluminium oxide, was mixed with eugenol containing 1% w/v glacial acetic acid. At a powder liquid ratio of 5 g/l ml, a homogeneous paste was easily obtained after mixing for 30 seconds on a glass pad. This paste was initially of a butter-like consistency but set to a hard mass in 10 minutes at 250C.

Example 2 Powders as described in Example 1 but with differing amounts of acetic acid exhibited setting times ranging between 45 minutes and 10 minutes, depending on the acetic acid content of the eugenol.

Example 3 Dental cements as described in Examples 1 and 2 were prepared but without any alumina present. Dental cements of an initial butter-like consistency but which subsequently set to a hard mass were obtained but the set hard mass was weaker than that of Examples 1 and 2.

Example 4 Products even stronger than those described in Examples 1 and 2 but with similar facile mixing properties were obtained by dissolving 5% w/v polystyrene in the eugenol before it was mixed with the zinc oxide.

Example 5 Analogous products to those in Examples 1 4 were obtained when all or part of the eugenol was replaced by o-ethoxybenzoic acid.

Claims

1. In a dental cement comprising as first component fine particles of zinc oxide or calcium hydroxide or magnesium oxide or hydroxide and as second component an organic liquid containing hydroxyl groups that on mixing with the first component reacts therewith to form a hard mass the improvement which comprises coating the particles of the first component prior to mixing with the second component with a fatty acid whereby mixing of said cement is facilitated.

2. A dental cement according to claim 1, wherein the first component comprises particles of zinc oxide surface coated with stearic or oleic acid.

3. A dental cement according to claim 1 or 2, wherein the first component further comprises particles of silica or alumina.

4. A dental cement according to any preceding claim, wherein the organic compound of said second component contains phenolic hydroxyl groups and sets by forming a chelate with the zinc, calcium or magnesium of said first component.

5. A dental cement according to claim 4, wherein the organic compound is eugenol or a mixture thereof with o-ethoxybenzoic acid.

6. A dental cement as claimed in any preceding claim, wherein the second component contains polystyrene or other organic reinforcing polymer dissolved in the eugenol or eugenol-containing mixture.

7. A dental cement as claimed in any preceding claim, wherein the first component further comprises as setting accelerator zinc acetate.

8. A dental cement as claimed in any of claims 1-6 wherein the second component further comprises as setting accelerator acetic acid.

9. A dental cement substantially as hereinbefore described in any one of the Examples.

10. The use of zinc oxide or calcium hydroxide or magnesium oxide or hydroxide coated with a fatty acid as an ingredient of dental cement.