BACKGROUND OF THE INVENTION

Dental amalgam is the most widely used material for permanent restoration of teeth because of its well-established properties of durability and resistance to physical, chemical and biochemical breakdown in the oral cavity, in addition to its ease of manipulation by the dentist and its relatively low cost (when compared to gold, for example) . A major disadvantage of the material is its unesthetic dark or metallic color which usually limits its use to posterior teeth. Even in posterior teeth in which fillings are not directly visible in speaking, smiling, etc., the material often has the effect of darkening or shadowing the surrounding tooth structure to the detriment of appearance.

A material which can eliminate or markedly diminish the darkening or shadowing effects on tooth structure of amalgam fillings would enhance their esthetic acceptability and there¬ fore the utility of amalgam.

The instant invention pertains to a material and a method of application of such material to prepared tooth cavity ^' walls. The material is a liner containing pigments or dyes to prevent penetration of the dentin by components of the amalgam filling and to mask or conceal the dark shadow of amalgam at

and beyond the interface of amalgam with enamel.

The pertinent areas of classification are believed to be U. S. Classes 32, 106 and 433; Sub-Classes 35, 217 and 266. The applicant, in his review of these areas and other art areas of which he is aware, has been unable to find or to uncover any prior art which would unfavorably bear upon the question of nov¬ elty of the method herein disclosed.

SUMMARY OF THE INVENTION

The instant invention comprises a material and a meth¬ od of application of said material for the purpose of preventing discoloration of surrounding tooth structure, which is a common accompaniment of amalgam fillings placed within the tooth. The material is a cavity-liner of viscous composition, containing pigments and/or dyes, which seals the dentin walls of the pre¬ pared tooth cavity, coats the enamel walls and blocks transmis¬ sion of the dark amalgam color or shadow through the enamel. The material is supplied in a selection of shades to permit matching the natural color of the enamel. The method of appli¬ cation is direct placement upon the prepared tooth cavity sur¬ faces by means of- brush, cotton pellet, metal loop or other in¬ strument. It can constitute a sole cavity liner or be applied over a base as a secondary liner. It is applied as a coating which quickly dries at mouth temperature, or can be assisted to dry by application of the dentist's air syringe. It is to be applied on all walls of the prepared cavity, excluding the outer¬ most margins.

Further objects of the invention will become apparent

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from the hereinafter set forth detailed description of the in¬ vention and the claims affixed hereto.

DETAILED DESCRIPTION OF THE INVENTION

It is well accepted procedure in reparative dentistry that a lining material be applied to deep or moderately deep prepared cavities in teeth to insulate against thermal and elec¬ trical conductivity and help to seal against the ingress of sa¬ liva and micro-organisms. The usual procedure is to complete the preparation, clean and dry the prepared cavity surfaces, apply the lining material, and allow it to set.

Deep or extensive cavities are additionally protected by placement of a base, usually containing calcium hydroxide or eugenol as the active ingredient. Liners are applied to the tooth structure and onto the set base, when a base is used.

It is to be understood that the term "liner" as used herein, refers to materials applied to protect the prepared den- tinal surface, including varnishes and dental cements.

Many formulations have been used for tooth cavity liners. A basic liner formula as illustrated in U. S. 3,367,788 consists of calcium hydroxide, methyl cellulose and water.

Another type of liner consists of solutions of synthe¬ tic resins in a volatile organic solvent wherein calcium hydrox¬ ide and/or zinc oxide are suspended. An example of the resin used in the lining material as disclosed in U. S. 3,243,411 is a prepolymer of tolylene di-iso-cyanate and propylene glycol polymer which is cured in the tooth cavity by addition of a

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curing catalyst, such as triethylene diamine dissolved in a vol¬ atile solvent, such as acetone, chloroform or cellosolve acetate (2-methoxyethyl acetate) .

Another liner composition consists of a polymer which is described in U. S. 2,794,016. It is prepared by mixing methyl-methacrylate or other ester of methacryiic acid with polyme hy1-methacr late powder and allowing the monomer to polymerize in situ in the presence of a catalyst such as benzoyl peroxide.

Additional examples of liner compositions are iso- phthalate and terphthalate polyesters as well as polysiloxanes.

Another available resin liner is bisphenol A glycidyl methacrylate (BIS-GMA) which can be polymerized chemically or by ultraviolet or visible light radiation in the presence of a catalyst.

Commercial liner compositions generally contain some quantity of pigment to aid visibility in placement and control.

Another class of liners are varnishes which dry as thin films and provide marginal seal. Cavity varnishes general¬ ly consist of solutions of one or more resins, derived from nat¬ ural gums or rosin or synthetic resins in an organic solvent such as acetone, benzene, toluene, alcohol, ethyl acetate or amyl acetate. Eugenol, thymol and chlorobutanol may be added as potential thereaputic agents.

Dental cements may be either inorganic, containing zinc phosphate or zinc silicophosphate, or organic, for example, zinc oxide eugenol or eugenol in combination with polymers such as bisphenol A glycidyl methacrylates (BIS-GMA) resin, poly- meth l-methacrylate, cyanoacrylate resins, polyacrylate, glass

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ionomer cements.

All of the above mentioned materials have overlapping uses as sealers and therapeutic agents.

It is understood that the liner compositions are well known in the art and form no part of the present invention.

In accordance with this invention, any of the above- mentioned liner compositions, including other possible composi¬ tions not mentioned, may be a carrier for the pigments and dyes. The pigment may consist of finely ground particles of titanium dioxide, zinc oxide, iron oxide, barium sulfate or other commer¬ cially available pigments or a mixture thereof. The dye may be ferric chloride or commercially available dyes known to dentis¬ try. The pigment acts as an opacifying or opaquing agent. It masks the enamel against the dark color of the amalgam restor¬ ation. The pigment and/or dye is blended into the liner mater¬ ial in sufficient quantity to prevent the color of the amalgam from being visible through the enamel. The amounts of pigment and dye in the liner material are adjusted to yield a liner color closely matching the color of enamel of the tooth being restored. The liner material can be prepared in any one of a number of shades, including tan, light yellow, dark yellow, light cream and ivory white, by varying the amount of pigments and dyes added to the other liner ingredients. A liquid thin¬ ner such as acetone or methylethyl ketone or other organic sol¬ vent dictated by the polymer may be used to modify the visco¬ sity of the liner material, thereby affecting the film thick¬ ness, the desired opacity, and chromatic appearance of the liner material.

In general, it may be appreciated that the liner mat¬ erial according to the present invention known as AMALGA MASK, is a thin cavity liner containing a pigment and/or dye capable of reducing or eliminating the transmission of dark shadow from an amalgam restoration. AMALGA MASK is also effective against transmission of metal casting and the color of other filling materials. The AMALGA MASK is intended for use in conjunction with all amalgam fillings inserted against the facial (buccal or labial), mesial-facial, mesio-occlusal and occlusal walls of the cavity. It can be placed in any area that would otherwise dis¬ play the gray discoloration characteristic of an amalgam res¬ toration, such as the inner aspect cavity-side of the visible walls of the cavity. Typical sites for application include large or ^" small restorations on the distal surface of the upper canine teeth (proximal or labial walls) , extensive lingual res¬ torations in anterior teeth (maxillary and mandibular) , and the mesio-occlusal and/or proximal surfaces, and mesial buccal sur¬ faces in upper and lower molars and premolars.

The AMALGA MASK can also be used in lieu of conven¬ tional cavity liners since it exhibits all teh desirable proper¬ ties of a cavity liner in addition to the capabilities for re¬ ducing the transmission of a shadow or dark color from amalgam filling through the adjacent enamel.

This invention is innovative in that tooth cavity liners as herein defined containing pigment and dye have never been employed to block out shadow in the tooth being filled amalgam. The use of AMALGA MASK is simple and economical. In practicing this invention, the dentist selects one of the

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AMALGA MASK preparations which most nearly matches the color of the patient's tooth being filled. The liner which has a viscous consistency is applied to the wall of the cavity and is allowed to dry. This procedure may be repeated where necessary to in¬ crease opacity. The tooth cavity is then filled with amalgam. An example of the liner composition in accordance to the inven¬ tion is as follows:

Methyl methacrylate polymer 8-15% by wt. Titanium dioxide 4-8%,

Metallic oxide 0.1-0.5%

Calcium hydroxide 0.5-3.5%

Methylethyl ketone 73-87%

Inerts remainder

The above components can be substituted by, or com¬ bined with, other resins, pigments or dyes and other chemical additives with varying percentages for each.

The AMALGA MASK products have been laboratory tested by Franklin Research Center of The Franklin Institute and have been found to be practical for the uses intended and effective in shielding or masking the enamel from shadowing associated with amalgam fillings.

While there have been shown examples, and the embodi¬ ment of the present invention described, it will be understood that numerous modifications or alterations equivalent thereto are within the spirit or scope of this invention as set forth in the appended claims.

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