Compositions: coating or plastic – Coating or plastic compositions – Dental
Patent
1995-03-23
1997-02-11
Bonner, Melissa
Compositions: coating or plastic
Coating or plastic compositions
Dental
4332281, 523116, 523115, 526278, 524547, A61K 608, A61K 606
Patent
active
056016409
DESCRIPTION:
BRIEF SUMMARY
This invention relates to compositions curable on command, e.g. by the action of incident energy e.g. light (ultraviolet or visible) or ultrasound. Such compositions may contain inert or reactive fillers, in which case they can be classed as cements, and may be particularly useful in surgical, especially dental, applications.
As dental cements, glass ionomers as described in for example GB Patents 1422337 and 1484454 have attained wide popularity for their compressive strength, their inherent adhesion to tooth material, their relatively fast setting time and their anti-caries action. However, a drawback in clinical practice is that, once mixed, the glass ionomer cement composition stays workable for a strictly limited time only, and sets rapidly.
It has been proposed in EP-A-323120 to formulate a glass ionomer with modifying agents to delay its setting, with photocurable characteristics too, so that a photocure can be effected by the dentist when he is ready, with the acid-base glass ionomer reaction proceeding in parallel. However, those formulations having acceptable adhesiveness remain workable for only about five minutes, which could still be too short to deal with unexpected clinical eventualities.
Nonetheless, light-cured glass-ionomer cements have now become widely available for use as lining materials. The photocurable characteristics are supplied by adding, to the glass and polyacid required for the acid-base reaction, polymerisable monomers such as hydroxyethylmethacrylate (HEMA) which participate in the photopolymerisation reaction.
These light-cured glass-ionomers have proved to be very sensitive to the presence of moisture. This is because the set cement has a structure similar to that of a hydrogel. The structure is lightly crosslinked and contains hydrophilic groups, the light-cured methacrylates. Hence the cement has an affinity for water, which, once absorbed, acts as a plasticiser within the materials and reduces the strength of the cement. The water also tends to swell the cement.
WO-A-88/05651 discloses a light-curable glass ionomer lining material detectable by X-rays, comprising a fluoroaluminosilicate glass, barium glass, benzoyl peroxide and a resinous binder particularly bis-GMA or urethane dimethacrylate. This WO lists desirable criteria which this liner should meet as including translucency, formulation as a two-paste system, long shelf life, low solubility in oral fluids, strong adhesion to tooth, suitable working and setting times, and adequate strength.
EP-A-0 395 427 discloses a phosphonate ester which will cure on exposure to light in the presence of an initiator, this being mixed with poly(vinyl phosphonic acid), glass powder and water, to form a light-curable glass ionomer as already mentioned, which can remain workable for some 30 minutes in normal indoor light.
It would be desirable to have a command-curable composition which, despite comprising a number of dissimilar chemical compounds, was presented in a stable non-separating common solution and which, when set, did not tend to swell upon the absorption of water.
According to the present invention, a command-curable composition comprises (a) a partly esterified phosphonic acid being equivalent to the reaction product between a precursor of a polyphosphonic acid (e.g. poly(vinyl phosphonic acid)) and an esterifying group such as a polyhydric alcohol in the mole ratio (0.2-5.0) phosphonic acid groups: 1 esterifying group, (b) an initiator suitably a light-activated initiator system or a chemical initiator system, (c) cation-leachable glass powder, (d) poly(vinyl phosphonic acid) and is characterised by (e) a bulky molecule compatible with component (a) and having at least two vinyl groups through which it may cross-link/polymerise to yield a completely hydrophobic polymer. The composition preferably further comprises water. The said mole ratio is preferably (0.5-1.5):1 such as (0.8-1.2):1. The precursor may be vinyl phosphonic dichloride. The OH groups in the alcohol are preferably interconnected via from two to twenty s
REFERENCES:
patent: 4259117 (1981-03-01), Yamauchi et al.
patent: 5204426 (1993-04-01), Elis et al.
Anstice Helen M.
Nicholson John W.
Bonner Melissa
British Technology Group Limited
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