The present invention is generally directed to compositions and methods for preparing the surfaces of teeth prior to their repair or filling, and in particular to an acid etchant composition and method of use thereof.
In preparing teeth for application of a dental restorative (such as a sealant, filling material, or the like), a common first step is etching the surface to which the dental restorative is to be applied, with an acid etchant. Acid etchants are commonly thought to clean and demineralize dentin and enamel surfaces so as to promote effective bonding of the restorative material.
Conventional acidic etchant solutions are well known, generally comprising phosphoric acid in an amount of about 10% to about 40% by weight phosphoric acid in aqueous solution or in a gel form. Although the use of conventional phosphoric acid etchants has been generally acceptable in practice, a significant drawback of aqueous solutions is that they tend to run upon application, thereby resulting in etching of healthy tooth surfaces. Gel compositions have accordingly been developed, generally comprising hydrocarbon polymers and/or fumed silica as thickening agents. While such gels do not run upon application, many nonetheless tend to be xe2x80x9cstringyxe2x80x9d, rendering precise application more difficult. Gels which are not stringy tend to be bulky or dry, resulting in clogged dispensing tips. There accordingly remains a need in the art for acid etchant compositions which are thixotropic, not stringy, and easy to dispense.
The above described drawbacks and deficiencies of the prior art are alleviated by an aqueous, acid gel etchant composition comprising an acid, a colloidal silica sol having pearl-like or elongated forms, and an optional organic thickening agent. The acid is preferably phosphoric acid, present in an amount from about 5 to about 50 weight percent of the total composition. The particles of pearl-like colloidal silica sol preferably have diameters in the range from about 10 to about 60 nanometers. The elongated particles of colloidal silica sol have diameters of about 10 nanometers and lengths in the range from about 50 to about 100 nanometers. The silica portion of the sol comprises from about 3 to about 20 weight percent of the total etchant composition. The optional organic thickening agent, for example carboxypolymethylene or polyethylene oxide, is generally present in an amount from about 0.1 to about 3.0 weight percent of the total composition.
In use, the aqueous, acid gel etchant composition is applied to the tooth surface to be restored using conventional methods such as wiping or dispensing through a needle, after which the gel is removed from the surface of the tooth by rinsing with water while the area is aspirated. The surface is then dried with a jet of air, or blotted dry.
Since the present composition is thixotropic and not stringy, the surface of a tooth to be repaired or restored may be precisely etched without injury to the surrounding gum tissue, or destruction of adjacent teeth surfaces, and without enamel fracture or pitting. Since the present composition is further not stringy or dry, the dispensers used may have small lumens (thus facilitating precise placement) without clogging.
A thixotropic, aqueous acid gel etchant composition comprises an acid, a colloidal silica sol, and an optional organic thickening agent. Use of a colloidal silica sol thickening agent results in a thixotropic composition which is not stringy and which does not run upon application to the tooth surface, yet which is nonetheless liquid enough to not clog dispensers, e.g. needles, having small lumens.
The preferred acid is phosphoric acid, present in an amount effective to provide etching within about 2 minutes, preferably within about 1 minute. Such quantities are generally in the range from about 10 to about 50 weight percent of the total composition. Other suitable acids include mineral acids such as nitric acid, hydrochloric acid, or sulfuric acid, and organic acids such as tartaric acid, maleic acid, itaconic acid, 5-sulfosalicylic acid, propionic acid, citric acid, oxalic acid, or lactic acid. Combinations comprising at least one of the foregoing acids may also be used. Effective quantities of these acids generally provide a pH of around 1, and are readily determined by one of ordinary skill in the art.
Colloidal silica sols consist of microfine particles of silicon dioxide dispersed in water. Such colloids may be obtained by dispersing negatively charged amorphous silica particles in water. In the present composition, the sol particles are xe2x80x9cpearl-likexe2x80x9d or elongated. The particles of pearl-like colloidal silica sol preferably have diameters in the range from about 10 to about 60 nanometers. Such sols are commercially available from Nissan Chemical, under the tradename SNOWTEX. The colloidal particles of elongated SNOWTEX sols are chain molecules of silica being 5 to 20 nm in width and 40 to 300 nm in length. The pearl-like particles of the SNOWTEX sols are bound to lengths of 50 to 200 nm. The diameter of the particles of the xe2x80x9cST-PSMxe2x80x9d product are in the range from about 18 to about 22 nanometers, and the diameters of the particles of the xe2x80x9cSTP-SLxe2x80x9d product are in the range of about 40 to about 50 nanometers. The elongated particles of colloidal silica sol preferably have diameters of about 10 nanometers and lengths in the range from about 50 to about 100 nanometers. Elongated, acidic colloidal silica sols are available from Nissan Chemical under the tradename SNOWTEX, product designation xe2x80x9cST-OURxe2x80x9d.
The silica portion of the sol comprises from about 3 to about 20 weight percent of the total etchant composition.
Optional organic thickening agents for inclusion in the present compositions are known, including for example carboxymethylcellulose, polyethylene oxide, gum or salts of polyacrylic acids.
The etching compositions may include other components, for example fluoride, dyes such as methylene blue, or antimicrobial agents.
The acid gel etchant compositions are generally formed by providing a concentrated aqueous phosphoric acid solution and adding the colloidal silica sol solution with mixing. The optional organic thickener and/or other components may be added at any time.
In use, the surface to be repaired or restored is treated with the etchant composition for a period of time effective to etch the surface, and yet not damage the tooth. Effective periods of time are readily determined by those of ordinary skill in the art, and are generally less than about one minute. The composition can be dispensed from a conventional push syringe or squeeze bottle, or applied with a brush. Once the surface of the tooth has been treated with the acid gel etchant composition, the tooth is rinsed with water while the area is aspirated and thereafter the area is dried with a jet of air or by blotting. As with conventional acid etch compositions, care should be taken to avoid skin contact or contact with oral mucosa and eyes to prevent possible injury to the patient. Conventional prophylactic, repair and restorative materials are then applied using known methods, for example sealants, primers, primer/adhesives, adhesives, glass ionomer cements, filling materials, and the like.
The following nonlimiting examples illustrate the invention.