1) Description

The principal object of this work relates to the preparation of novel dental composites, curable by chemical or photoactivation methods, suitable for the restoration of both anterior and posterior teeth. They comprise a blend of fine and coarse particle fillers dispersed in a resinous matrix. More particularly, formulations are disclosed which contain particula glass fillers whole composition is believed to be novel to composite technology, which confer beneficial physical propertie to the composites, to be described herein. Further objects of this invention are to provide compositions which cure rapidly but which exhibit good workability prior to curin _β

2) Prior Art

Many commercially used dental composites contain a binder resin prepared from the reaction of bisphenol A and glycidyl ∑nethacry- late, commonly referred to as BIS-GMA. Various research workers have synthesised resins which are claimed to show superior properties to BIS-GMA, although none have attained professional acceptance, for example, U.S. Patents 4,102,856 4,131,729,3, 730,947 and 3,853,962.

More recently, urethana dimethacrylate resins, synthesised from a hydroxyalkyl acrylate and an organic di-isocyanate, have been used -in composites as a whole or partial replacement for BIS-GMA

The resin functions as a binder for inorganic, particulate rein¬ forcements which confer hardness, strength, low polymerisation shrinkage, low water absorption, low thermal expansion and dimensional stability to the product. Quartz was the most widely used reinforcing filler until the late 1970s, but various glasses are used currently which are often softer than quartz, thereby improving the polishability of the composite, and certai glass fillers also impart radiopacity. Recently, the most significant changes in the properties of composites»have resulte

from changes in the size and size distribution of filler particl Both chemical curing and visible light curing mechanisms are in widespread use nowadays for hardening of composites after placement by the dentist.

Composites were evaluated initially for application to anterior teeth, and were extended to posterior teeth in the early 1970s.

The Invention

Base resins pertinent to this work are those used in restorative compositions, namely BIS-GMA and urethane dimethacrylate. They are used at 10 to 20% by weight of the composite.

Since these resins are viscous liquids at room temperature, it is necessary to dilute them with a compatible copolymerisable diluent in order to facilitate subsequent blending of fillers.

Relevant liquids include diacrylate functional monomers, especially mono-,di-,tri- and tetra-ethyleneglycol dimethacrylat ethylene dimethacrylate, and also 1,1,1-trimethylolethane trimethacrylate and methyl methacrylate. The preferred reactive diluents are triethyleneglycol dimethacrylate and 1,6-hexanediol dimethacrylate. While the relative proportions of binder and diluent vary depending on their identity and type and particle size and quantity of filler,- ratios of binder to diluent are from about 12:1 to 1:2 by weight, and preferably from about 6:1 to 2:1. Alternatively, diluents are used a about 5 to 25% by weight of the total composite, preferably at the lower end of this range.

Chemically cured composites of this invention are formulated as two components, namely a catalyst paste and a base paste. It is preferred that the catalyst paste contains the BIS-GMA resin and the base paste contains the urethane dimethacrylate resin. Light-cured composites of this invention are formulated as a single paste, which may contain either or both resins in ' equal or unequal quantities.

The fillers for the hybrid composites of this invention comprise a blend of both small and large particles, lying within the size range 0.04 to 50u, and preferably within the range 0.04 to 15u.

The total filler content should be at least 70% by weight of the total weight of the composite, the maximum loading depending on the particle size and size distribution of each filler, and the nature and viscosity of the resins. It must be greater for posterior composites than for anterior composites, as the former are subjected to greater masticatory stresses and thus require greater strength.

The small particle filler is preferably colloidal silica of average particle diameter less than 0.5u, incorporated at a maximum of 8% of the total weight of composite, and preferably within the range 1 to 2% by weight. Its purpose is to improve the surface finish and polishability of the final composite, and so render it less likely to trap plaque, and also be more resistant to staining.

The larger particle fillers comprise at least two different types of glass, both of which have a maximum wet film thickness when dispersed in water of 15u„ In light-cured composites and in one component of chemically cured composites, preferably the base paste, it is desirable to use barium glass at a minimum level of 20% by weight of the total composite, to confer radiopaclty and strength.

The remainder of the filler content consistsof an ion-leachable fluoroaluminosilicate glass, to give a total minimum filler content, including the barium glass of 70% by weight of the total composite. The glass frit has a ternary oxide composition consisting of chemically combined Calcium oxide and silicon dioxide wherein:

(a) alumina comprises from 15 to 50% by weight;

(b) calcium oxide comprises up to 50% by weight;

(c) silica comprises from 10 to 65% by weight; and

(d) the weight ratio of Calcium oxide: Silicon dioxide is greater than 0.92 or

(e) the weight ratio of Calcium oxide: is between 0 and 0.74;

(f) the glass comprises less than 14% by weight of fluorine, introduced by the addition of aluminium fluoride, calcium fluoride and/or fluorine-containing minerals such as cryolite.

This type of glass contributes the following advantageous properties:

(a) superior compressive strength and diametral tensile strength compared with certain commercially available composites;

(b) correct colour and translucency for colour matching and shading;

(c) release of fluoride ions which have a cariostatic effect;

(d) may enhance bonding strength to enamel.

These fillers may be used, alone or jointly, in fissure sealants, orthodontic, composite cements, composite luting cments and related dental compositions.

All fillers should be surface treated with a suitable silane coupling agent especially for use with glass to promote strong bonding between the filler particles and the resin binder. The preferred coupling agent is ^-methacryloxypropyltrimethoxy silane.

The chemical curing system employed in the composites of this invention is composed of an organic peroxide oxidising agent in conjunction with an amine reducing agent. The peroxide is blended into the paste containing the BIS-GMA, and the amine blended into the paste containing the urethane dimethacrylate. On no account should the two pastes be mixed except immediately prior to use.

Benzoyl peroxide is the preferred initiator, while the amine component may be selected from N,N-dimethyl-p-toluidlne, N,N-diethyl-p-toluidine, N,N-dihydroxyethyl-p-toluidine, ,N-dimethyl-3,5-xylidine and p-(dimethylamino) phenylacetlc acid, with N, -dihydroxyethyl-p-toluidine being the preferred activator. Both ingredients are used in the range 0.3 to 3.0% by weight of the total composite paste, and preferably at 0.3 to 1.0% by weight. When approximately equal portions of the two components are blended curing should occur in 1 to 10 minutes', preferably 2 to 4 minutes.

The photosensitising system employed in the composites of this invention comprises two components, and< -diketone photosensitive species together with an amine reducing agent. Representative σ-diketones include biacetyl, camphoroquinone, 2,2 ^f -furil,

p-toluilo(r-and B-naphthil, benzil, phenanthraquinone and naphthoquinone, with camphoroquinone being the preferred photoinitiator.

Representative amines include tributylamine, tripropylamine, N-alkyl dialkanolamines and 2-(dimethylamino) ethyl methacrylate with the latter being the most preferred. For reasons of colour curing time and stability, the quantity of both ingredients is carefully controlled within the range 0.01 to 0.20% by weight of the total composite, and most preferably within the range 0.03 to 0.08% by weight. When exposed to an intense beam of visible light of wavelength 420-450nm hardening should occur in 5 to 60 seconds; suitably in 10 to' 20 seconds.

Other additives may optionally be incorporated into tlje formula¬ tions, such as pigments (for colour-matched shaded compositions) ultra-violet stabilisers, anti-oxidants and polymerisation inhibitors.

The methods of use of both types of composite of this invention are those practiced by those skilled in the art. For chemically cured composites, equal quantities of the two components are thoroughly mixed immediately prior to application, and then moulded into place in the conventional manner in the acid-etched cavity (which may have been previously coated with a bonding agent). For light-cured composites, the material is applied directly to the coated, acid-etched cavity, then exposed to an intense beam of visible light for the correct time to induce hardening.

EXAMPLE 1

A two-paste composite restorative material based on the standard peroxide/amine curing system having the following composition was prepared by mixing and reacting the ingredients by spatulation.

SUBSTITUTE SHEET

Part A Part B

BIS-GMA 17.0

Urethane dimethacrylate - 15.0 triethylene glycol dimethacrylate 8.5 7.5 colloidal silica 1.6 1.6 barium glass - 37.7 fluoridated alumino silicate glass 72.4 - 37.7 antioxidant 0.01 0.01 bun uyl purυxido 0.55 -

N,N-dihydroxyethyl-p-toluidine - 0.55

Compressive strength : 185.5 MP _a Diametral tensile strength : 40.1 MPa

EXAMPLE 2

A single-paste composite restorative material using a light curing system having the following composition was prepared in an analogous manner to the composite of Example 1:

% W/W

Urethane dimethacrylate 18.2

1,6 —hexanediol dimethacrylate 9.0 colloidal silica 1.3 barium glass 31.4 fluoridate.d alumino silicate glass 40.0 antioxidant 0.01 camphoroquinone 0.06

2-(dimethylamino) ethyl methacrylate 0.06

Compressive strength : 187.1 MPa Diametral tensile strength : 39.7 MPa

EXAMPLE 3

•Pearl', a commercially available chemically cured composite not containing fluoridated alumino silicate glass:

Compressive strength : 135.6 MPa Diametral tensile strength : 38.7 MPa

SUBSTITUTE SHF Γ

EXAMPLE 4

1 'Pearl-Lite', a commercially available light cured composite no containing fluoridated alumino silicate glass:

\

Compressive strength : 158.4 MPa Diametral tensile strength : 30.5 MPa

EXAMPLE 5 v

•Elcefill 60', a commercially available single paste light-cure composite not containing fluoridated alumino silicate glass:

Compressive strength : 132.0 MPa Diametral tensile strength : 34.5 MPa

SUBSTITUTE SHEET