Dental restoration composition and method

A dental filling and sealing composition and method for human tooth restoration. The method includes pulverizing bovine teeth into small particles and separating the particles containing only enamel from the remaining particles and mixing with an adhesive such as gloss ionomer cement, methyacrylate or the like. For restoration using a glass ionomer cement, the enamel particles are mixed directly with the cement and applied to a human tooth by techniques commonly known in the dental profession. For restoration using an acrylic adhesive, the enamel particles are subjected to an acid-etch treatment followed by forming a mixture comprising the enamel particles and the acrylic adhesive, which is applied by commonly known techniques.

BACKGROUND OF THE INVENTION 
The present invention relates to a material and method for filling and 
otherwise restoring human teeth. 
Historically, dentists have utilized various metals and metal amalgamations 
to fill cavities and otherwise replace missing or removed tooth structure. 
However, tooth restoration with such metals does have certain 
deficiencies, one of the principal deficiencies being the aesthetic 
appearance of the metal. 
Numerous organic compounds have also been used in a variety of mixtures and 
proportions in an attempt to discover materials for dental composites and 
restoratives that would have improved characteristics as compared to the 
metals. Dental composite and restorative materials must not only have good 
forming characteristics in order to be shaped to fit a cavity or be molded 
in place to repair chipped or damaged teeth but must also have physical 
and chemical properties which are compatible with a dental, physiological 
environment, such as thermal coefficient of expansion, non-toxic, 
insoluble, non-corrosive, etc. 
Further, such restorative compositions must exhibit satisfactory hardness 
and durability characteristics in order to meet the requirements of their 
intended purpose. In attempts to satisfy the hardness and durability 
characteristics, researchers have utilized various compounds often 
including some type of resin integrated with various amounts of 
particulate material, such as organic polymers, various kinds of metals, 
ceramics, and the like. Such compounds usually also include other 
materials, such as pigments, catalysts, handling agents and opacifiers, 
and the like, for aesthetic and other purposes. 
When such restorative materials are placed in the mouth, the materials must 
securely bond both to itself integrally and to a tooth being restored. 
Since the final bonding occurs during installation in the mouth, it is 
particularly essential that satisfactory adhesion be obtainable in the 
environment of the mouth. 
One method which has been utilized to enhance securement of composites and 
adhesives to tooth enamel is to severely etch the enamel with a highly 
acidic solution. This procedure intentionally demineralizes the enamel and 
creates deep pits and irregularities in the surface of the enamel to 
provide mechanical interlocking with the underlying tooth structure as the 
primary means of retention of the restorative. Although such etching of 
the underlying tooth structure for bonding purposes usually does provide 
adequate adhesion, it also causes deteriorative effects on the underlying 
tooth structure. 
Another method which has helped alleviate such destructive treatment of the 
underlying tooth structure is the utilization of an adhesive, such as a 
glass ionomer cement which bonds strongly and directly to the tooth 
structure. Glass ionomer cements consist of a particulate glass powder and 
a mixing fluid which may generally be described as an aqueous solution of 
a polycarboxylic acid. The diameter range of particles in the glass powder 
must be suitable for dental applications. The particle size and size 
distribution of the glass particles can be adjusted using conventional 
techniques, such as by grinding, screening, sedimentation or other 
particle classification methods. Control of the range and distribution of 
particle size is an important characteristic for influencing the strength, 
work time and set time of the cement. 
Work time and set time can also be adjusted by affecting the surface area 
of the glass particles, such as by etching with an acid and thoroughly 
washing the treated glass to leave substantially no soluble calcium salts 
on the surface of the glass particles. 
One process for making glass ionomer cement powder involves comminuting 
carboxylic acid with a chemically active glass, such as an aluminosilicate 
glass which has been prepared with a fluoride flux. The work time and set 
time of the cement may be influenced by the molecular weight and carboxyl 
equivalent weight of a particular polyacid or by the relative quantity of 
carboxylic acid added during the comminution step. For example, a low 
relative quantity of carboxylic acid, such as approximately 3% by weight 
or less, will extend work time without substantially affecting set time. 
Such characteristics are generally desired for luting cements, veneer 
cements or orthodontic bracket adhesives. Similarly, a larger relative 
quantity of carboxylic acid, such as approximately 5% by weight or more, 
will extend both work time and set time. Such characteristics are 
generally desired for endodontic sealants or bone cements and for 
applications where high glass loading levels are desired, such as for 
basing cements, crown build-up cements or posterior liners. 
In addition to controlling particle size distribution and area of the 
glass, selection of a polyacid, and adjusting the ratio of glass to 
polyacid, work time and set time of the cement may be further adjusted by 
the addition of a chelating agent, such as tartaric acid or the like. 
To form the glass ionomer cement, the glass particles and acid are 
comminuted under sufficiently vigorous, substantially anhydrous 
pulverization conditions, such as by ball milling, to cause reaction 
between the glass and carboxylic acid such that carboxylate salt is formed 
in the glass powder. The comminution must be conducted under substantially 
anhydrous conditions as the presence of moisture can result in the 
formation of carboxylate salt having entrained water, which results in 
poor mix properties and shortened work times. The comminuted glass and 
carboxylic acid forms a water-hardenable cement. 
When actually using the glass ionomer cements to restore a tooth, a 
solvent, such as water, is added to the cement, whereupon multivalent 
ions, such as calcium ions, leach from the glass and cross-link the 
carboxylic acid chains during curing which results in formation of the 
restorative composition. The mixture undergoes a brief working period, 
during which the reactants are converted from a creamy paste to a 
relatively firm, carvable solid. The working period is followed by a brief 
setting period, during which the carvable solid becomes sufficiently 
strong to function as a dental cement. 
Glass ionomer cements have generally enjoyed widespread application since 
they generally exhibit excellent adhesion characteristics to calcified 
tooth structure, including both enamel and dentin tooth substances. 
Besides superior adhesion characteristics, glass ionomer cements also 
excel in marginal sealing and durability in the mouth over a long period 
of time. In addition, glass ionomer cements generally exhibit little or no 
irritant action, detrimental corrosion, or other harmful pathological 
action upon the dental pulp. Further, glass ionomer cements maintain 
excellent resistance to the mouth tissues or fluids over extended periods 
of time. 
Unfortunately, however, glass ionomers have not been particularly useful 
for certain applications. For example, glass ionomers by themselves are 
visually inferior to composite resins. As a restorative, glass ionomers 
are extremely sensitive to technique and usually are not polishable. Glass 
ionomer cements are usually overly brittle which limits their use in the 
molar region and at corners and edges of a tooth. 
Further, a glass ionomer generally has a relatively weak cohesive strength. 
As a result, the glass ionomer bonds more strongly to the underlying tooth 
structure than it bonds to itself. This is sometimes observed where a 
filling comprising a glass ionomer fails; the failure occurs within the 
bulk of the glass ionomer while the bond between the tooth and the glass 
ionomer remains intact. 
To compensate for some of the deficiencies of glass ionomer cements, the 
cement powder can contain or be combined with appropriate quantities of 
viscosity modifiers such as microfine silica, wetting agents, milling 
agents, extending fillers, radiopacifiers, metal powders such as silver or 
silver alloys, medicants, and the like. In addition, such a composition 
may include materials having beneficial aesthetic properties such as 
adjuvants including pigments for matching those of natural healthy human 
teeth, plaque repellency, polishability and opacity. 
Another approach used to prepare a composition for restoring teeth involves 
imbedding glass particles in a binder, such as methyacrylate which usually 
achieves good bonding characteristics with the underlying tooth structure. 
Unfortunately, the methyacrylate does not simultaneously achieve 
acceptable bonding with the glass particles imbedded therein unless they 
have been subjected to acid etching. 
A suitable, self-adhering dental restorative should preferably provide 
certain beneficial attributes at the juncture between the restorative and 
the abutting tooth structure or at the exposed surfaces thereof. Such 
attributes include availability of leachable calcium, availability of 
leachable fluoride to minimize the formation of secondary caries, sealing 
characteristics to minimize microleakage by providing a substantially 
impervious protective barrier, hydrophilic characteristics sufficient to 
adequately wet dentine in vivo, an ability to bond to both dentin and 
enamel, natural appearance, optimal placement consistency, substantially 
pH-neutrality for maximum healing potential, extremely low solubility and 
disintegrability, and non-bioresorbability. One of the principal benefits 
of glass ionomer cement or methacrylate lies in the fact that such 
materials for tooth restoratives can be placed directly on or into a human 
tooth without any underfilling or other similar measures and obtain a 
result which is physiologically satisfactory cosmetically and mechanically 
and substantially meet the above noted criteria. 
The major drawback in using glass ionomer cement or methacrylate in tooth 
restoration is that such compositions tend to wear relatively quickly when 
used in locations where teeth engage or where wear otherwise frequently 
occurs. 
There is a definite need for a dental filling and sealing composition which 
requires minimal removal of healthy tooth structure while providing a 
strong, permanent, long-wearing restoration having a pleasing, natural 
appearance. Such a composition should possess good bonding internally as 
well as with the underlying tooth structure and should possess structural 
properties which closely match those of natural healthy teeth, such as 
cohesive strength, wearability, coefficient of thermal expansion and 
durability. 
SUMMARY OF THE INVENTION 
An improved composition and method are provided for filling dental cavities 
and for other dental restoration having a substantially natural enamel 
appearance and being relatively long-wearing. A filler comprising finely 
ground particles is prepared from enamel of animal teeth. The animal teeth 
are first sterilized and pulverized. The unwanted portions of the animal 
teeth are then separated from the particles containing only enamel. The 
enamel particles are then separated into ranges of particle sizes, with 
the particular range of sizes depending on the particular application, 
with an example range being approximately 10-100 microns. The bonding and 
wearing characteristics of the enamel particles when embedded in a bonding 
matrix for restoring human teeth are enhanced by subjecting the particles 
to various acid and alkaline baths in order to etch and desiccate the 
enamel particles. Preferably the animal teeth are bovine teeth. 
The filler comprising the selected range of ground or comminuted tooth 
enamel is mixed with binding means suitable for fixedly binding to enamel 
of a tooth to be repaired by the composition and being non-injurious or 
non-harmful when used on the tooth of a human. Suitable binding means 
include methyacrylate and preferably is a glass ionomer cement. 
Combining the enamel particles with the translucency of the glass ionomer 
cement or the methyacrylate provides naturally appearing fillings and 
restoratives, which are pleasing and naturally appearing aesthetically and 
which bond directly to the tooth, substantially eliminating the 
destructive treatment of the underlying tooth structure observed with 
other dental techniques. Also, by intermingling the enamel particles in 
the bulk of a filling and binding material, such as the glass ionomer 
cement or the methyacrylate, wherein the strength of the bond between the 
binding material and the enamel particles is greater than the strength of 
the bond of the binding material to itself, internal cross-linking occurs 
between the binding material and the enamel particles which enhances the 
cohesive strength of the mixture. 
For those applications where it is desired to use an ionomer cement, the 
animal enamel particles are intimately mixed with the glass ionomer cement 
and applied in accordance with techniques commonly known in the dental 
profession. For those applications where it is desired to use an acrylic, 
such as methyacrylate, the animal enamel particles are acid etched to 
achieve desired micromechanical, internal bonding and are then 
appropriately mixed with the acrylic and applied in accordance with 
commonly known techniques. 
OBJECTS OF THE INVENTION 
Therefore, the objects of the present invention are: to provide a strong, 
durable, polishable material for dental restoratives; to provide such a 
material that is relatively long-wearing; to provide such a material with 
a substantially natural enamel coloring with improved color stability; to 
provide such a material with a more naturally appearing hue; to provide 
such a material which forms strong and reliable bonds both internally and 
with the underlying enamel and dentin structure of a human tooth; to 
provide such a material having internal cross-linking such that cohesive 
strength of the material is enhanced; to provide such a material which 
minimizes or eliminates the need for undercutting in order to retain 
fillings and other restorations made therefrom; to provide such a material 
which has a translucency closely approximating that of a normal human 
tooth; to provide such a material which exhibits corrosion resistance in a 
human oral environment; to provide such a material which is adaptable for 
mounting in a moist oral environment; to provide such a material which can 
be used for inlays, onlays, crowns, bridgework or orthodontic appliances 
and other dental applications; to provide such a material which has 
desirable working and setting times; to provide a method of tooth 
restoration using such a material; and to generally provide such a 
material which is relatively easy and inexpensive to manufacture and which 
generally performs the requirements of its intended purposes. 
Other objects and advantages of this invention will become apparent from 
the following description wherein are set forth, by way of illustration 
and example, certain embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION 
As required, detailed embodiments of the present invention are disclosed 
herein; however, it is to be understood that the disclosed embodiments are 
merely exemplary of the invention, which may be embodied in various forms. 
Therefore, specific structural and functional details disclosed herein are 
not to be interpreted as limiting, but merely as a basis for the claims 
and as a representative basis for teaching one skilled in the art to 
variously employ the present invention in virtually any appropriately 
detailed structure. 
In an application of the present invention, tooth restoration shall mean 
facing, filling, replacing, rebuilding, or the like, of a tooth or missing 
portions thereof caused by decay, breakage, or the like. For discussion 
purposes and without limiting the application of the present invention, 
examples are provided herein to demonstrate one or more of the many uses 
available for applications of the invention. 
The present invention generally includes imbedding a matrix of ground or 
pulverized filling material in a binding or adhesive means. The adhesive 
means is preferably tightly and strongly bonding to tooth enamel and is 
compatible for use in the human mouth with respect to safety and 
organoleptic properties such as taste. Adhesive means include glass 
ionomer cement, methyacrylate, or the like. The pulverized filling 
material comprises tooth enamel which, for purposes of the present 
invention, may be obtained from animal teeth, including tusks, preferably 
of bovine origin. Bovine teeth not only provide the desired 
characteristics but are readily available and plentiful. 
The imbedding of pulverized animal tooth enamel provides substantially 
greater surface area of tooth enamel which generally forms a stronger bond 
with the adhesive means than the adhesive means forms with itself. As a 
result, cross-linking occurs between the adhesive means and the pulverized 
animal tooth enamel such that the cohesive strength of the restorative is 
substantially greater than is obtainable from the adhesive means alone. 
Also, the animal tooth enamel provides substantially greater wearability 
characteristics than is generally obtainable with adhesive means without 
such imbedded animal tooth enamel. Such an arrangement also enhances the 
abrasion resistance of the restorative. 
The binder material preferably allows the pulverized tooth enamel contained 
therein to color the composite composition such that a natural tooth 
enamel color is presented by the composition in use. It is foreseen that 
pulverized tooth enamel of various colors may be selected to better match 
the color of the teeth being restored or, if the color cannot be closely 
matched with the pulverized tooth enamel, additional pigments of the type 
currently used may be incorporated in the composition. 
Animal teeth to be used for preparation of the pulverized filling material 
are obtained from any appropriate source, such as from a meat packing 
plant. Before processing such teeth, they are subjected to a sterilization 
procedure and may be sorted as to color. In one application of the present 
invention, the teeth are sterilized by boiling in water for approximately 
eight hours. This procedure also coagulates proteins in the teeth. 
Following sterilization, the animal teeth are desiccated, such as by 
placement at an elevated temperature in a drying oven. 
After sterilization, the animal teeth are crushed into coarse particles to 
expose dentin and non-enamel material contained in the teeth. In one 
application of the present invention, the teeth are crushed in a 
hammermill, with the resulting particles ranging from approximately 1 to 5 
millimeters in size. 
After exposing the dentin and non-enamel material, it is then essential to 
separate the enamel therefrom. As an example, the teeth particles are 
boiled in a solution of concentrated sodium hydroxide for approximately 
16-20 hours in order to hydrolyze the organic bond between the enamel and 
the dentin in the teeth particles. After boiling, the teeth particles are 
subsequently allowed to cool, rinsed with water, pH-neutralized with an 
inorganic acid, and desiccated with acetone. 
The tooth enamel particles are then further finely crushed or pulverized, 
such as in a hammermill. In one application of the present invention, the 
enamel particles are finely crushed into particles ranging from 
approximately 10 to 200 microns in size. 
After cleaning and desiccating with acetone, the fine enamel particles are 
separated from the fine dentin and non-enamel particles. In one 
application of the present invention, the fine enamel and dentin particles 
are separated by placing the finely crushed particles in a concentrated, 
saturated solution of zinc iodide. Since the zinc iodide solution has a 
specific gravity which lies between the specific gravity of the fine 
enamel particles and the specific gravity of the fine dentin particles, 
the fine enamel particles sink to the bottom of the container containing 
the zinc iodide while the fine dentin particles rise to the top of the 
zinc iodide solution. It is then a simple matter to pour off the zinc 
iodide solution along with the floating fine dentin particles, leaving the 
fine enamel particles in the container. The fine enamel particles are then 
washed with water and dried with acetone. 
The fine enamel particles are then separated into narrower ranges of 
particle sizes, with each particular range of particle sizes depending on 
the type of restoration work to be performed therewith. For example, 
laboratory sieves may be used to select fine enamel particles ranging from 
approximately 1 to 100 microns in size for a particular restoration. 
As an example of preparing material for a tooth restorative using the fine 
enamel particles with a glass ionomer cement, a mixture is formed by 
admixing the components and stirring that contains approximately 85% by 
weight of a glass ionomer cement in the form of a powder, such as that 
disclosed in U.S. Pat. No. 4,342,677, which is incorporated herein by 
reference, and approximately 15% or more by weight of fine enamel 
particles ranging from 1-100 microns in size as hereinbefore described. 
The combined mixture of glass ionomer cement and enamel particles is then 
mixed with carboxylic acid solution in an approximate ratio of 4.5 grams 
of mixture to 1 gram of acid solution, with the resulting material then 
applied as a restorative by techniques commonly known and applied in the 
dental profession. 
For those applications where it is desired to use a composite comprising a 
matrix of an acrylic material filled with the fine enamel particles, 
further processing of the enamel particles is preferred as follows. The 
fine enamel particles are chemically etched to promote micro-mechanical 
bonding between the acrylic component and the fine enamel particles. In 
one application of the present invention, the fine enamel particles are 
treated with a 30% by weight phosphoric acid solution for approximately 60 
seconds, followed by rinsing with water and then treating with a 1% by 
weight sodium fluoride solution for approximately 8 hours. The neutralized 
particles are then thoroughly rinsed with water and dried with acetone. 
As an example of preparing material for a tooth restorative using such fine 
enamel particles in an acrylic matrix, the fine enamel particles are 
kneaded into an acrylic component such as that disclosed in U.S. Pat. Nos. 
4,503,169 and 4,719,149 which are incorporated herein by reference. The 
resulting material is then applied as a restorative by techniques commonly 
known and applied in the dental profession. 
Broadly speaking, an application of the present invention first involves 
preparation of the tooth to be restored, such as by first removing the 
decayed portion of the tooth and leaving underlying dentin and enamel 
surfaces exposed. Such initial decay removal can be performed by any 
appropriate technique, such as by the use of caries removal materials 
which may be advantageous for the reduction of patient discomfort, or by 
conventional drilling, or the like. 
The exposed tooth structure is then preferably cleaned of all debris and 
dried. This is particularly important since surfaces in the oral 
environment are usually coated with water and organic matter, such as 
proteins, bacteria, and food residue which are deposited on the surfaces 
by saliva. Washing the exposed tooth structure with a dilute acid solution 
will generally remove the undesired organic matter, leaving the surface 
more suitable for bonding. The exposed structure is then rinsed clean of 
the acid wash and dried, such as with clean, dry compressed air or with a 
solvent, such as acetone, which carries away water as an azetrope. 
While bovine teeth have been described herein as a source of enamel for use 
in the invention, it is foreseen that enamel of other animals, including 
humans, could be utilized. Likewise, it is foreseen that other adhesive 
agents besides those specifically described could be utilized in the 
invention provided such adhesive agents bond well to enamel and are not 
otherwise unacceptable because, for example, the agent is poisonous to 
humans, does not have acceptable wear even when combined with a hard 
material such as the enamel, requires too much time to harden after use or 
has a lingering taste. 
It is to be understood that while certain forms of the present invention 
have been illustrated and described herein, it is not to be limited to the 
specific forms or arrangement of parts described and shown.