Permanent dental restorative material

Wear-resistant, high compressive strength permanent dental restorations are prepared from novel compositions comprising (a) a liquid monomer system comprised of one or more monoethylenically unsaturated monomers and one or more polyethylenically unsaturated monomers, (b) a solid particulate system insoluble in the liquid monomer system (a) comprised of a mixture of both organic and inorganic particulate substances, and (c) a free radical initiator system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the composite dental restorative material art, 
and to permanent dental restorations made from such materials. 
2. Description of the Prior Art 
Compatability of Various Materials with Oral Tissues, I: The Components in 
Composite Restorations. Bowen, J. Dent. Res. 58 (5): 1493-1503, May 1979, 
summarizes the current status of the art with respect to composite 
restorative materials used for dentistry. 
U.S. Pat. No. 4,197,234, Temin is directed to dental restorative 
compositions. The '234 patent discloses a dental restorative composition 
which includes an acrylic monomer, a fluorinated polymer as a filler, and 
other filler materials. The fluorinated polymer is present in an amount of 
from about 1% to 10% of the total amount of filler. The dental restorative 
composition of the '234 patent, although an advance in the art, still 
suffered from the disadvantage that, dental restorative materials prepared 
from the '234 compositions exhibited poor wear resistance thereby 
rendering them undesirable for prolonged use in the mouth of a patient. 
SUMMARY OF THE INVENTION 
It is one object of the present invention to provide compositions useful 
for preparing permanent dental restorations having high compressive 
strength and wear resistance. 
It is another object of the present invention to provide methods for making 
such permanent dental restorations and to provide the restorations 
themselves. Another object of the present invention is to provide 
compositions for preparing permanent dental restorations which can be cast 
in a dental office in a short period of time, or in a dental laboratory. A 
still further object is to provide permanent dental crowns having minimum 
compressive strengths of at least 20,000 psi and preferably at least 
30,000 psi, and rotary wear values of at least 200 hours/mil. 
These objects, and others as will become apparent from the following 
description, are achieved by the present invention which in one aspect is 
a composition comprising (a) about 10 to 60 parts by weight of a liquid 
monomer system comprised of one or more monoethylenically unsaturated 
monomers and about 10% to 80% by weight, based on liquid monomer system, 
of one or more polyethylenically unsaturated crosslinking monomers; (b) 
about 40 to 90 parts by weight of a solid particulate system comprised of 
a mixture of both organic and inorganic particulate substances, each of 
said substances being insoluble in said liquid monomer system, wherein the 
weight ratio of the organic particulate substance to inorganic particulate 
substance is from about 2:1 to about 10:1 respectively and (c) a free 
radical initiator system. In another aspect, the invention comprises 
permanent dental restorations having high compressive strength and wear 
resistance cast from such compositions, and to methods of making such 
permanent dental restorations comprising mixing the liquid monomer system, 
the solid particulate system, and the components of the free radical 
initiator system, filling a mold with the mixture, allowing the 
composition to set, and then to cure. 
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS 
When used herein, the term "permanent" means long lasting, as opposed to 
temporary dental restorations. Temporary restorations are only designed to 
last six months or less, whereas the restorations of the invention are 
designed to last for the life of the patient, although these "permanent" 
restorations can be removed by a dentist if necessary. The term 
"restorations" refers to crowns, bridges, fillings, repairs to damage 
caused by trauma; repairs to existing crowns, and cosmetic repair in 
general. "Restorative material" refers to material used for such 
restorations. The term "crown" refers to the whole tooth surface rather 
than selected portions thereof. 
The solid particulate system is comprised of the mixture of both organic 
polymeric and inorganic substances, each of said substances being 
insoluble in the liquid monomer system. The organic polymeric particulate 
substance which is used should have a coefficient of friction such that 
the final dental restorative has a coefficient of friction of not greater 
than 0.3. Although an organic polymeric substance may be used which 
results in a final dental restorative product having a coefficient of 
friction in excess of 0.3, such higher coefficient of friction will, when 
used, result in a dental restoration having a reduced wear resistance. 
Among the preferred organic polymeric particulate substances which may be 
used are those which are fluorinated, for example 
poly(ethyleneco-chloro-trifluoroethylene), poly(vinylidene fluoride), and 
the like. Other organic polymeric particulate substances such as 
polyacetal, various nylons such as nylon 6, nylon 610, nylon 66, and nylon 
11 are also suitable, but are less preferred. 
When the composition is to be used to cast a restorative material such as a 
dental crown, it is preferred that the inorganic particulate substance 
used should comprise at least about 97% by weight of the total inorganic 
substance, of a material which has a Moh hardness of up to about 5. If the 
Moh hardness of more than 3% of the inorganic substance substantially 
exceeds 5, then the final dental restoration such as a crown, will be too 
abrasive and will result in excess wear of the opposing tooth surface. 
Among the inorganic particulate substances which have a Moh hardness of up 
to about 5 are hydroxyapatite, stearate-coated calcium carbonate, calcium 
carbonate generally, calcium metasilicate, talc, clay, calcium sulfate, 
and combinations of any of the aforementioned inorganic substances can be 
used. 
The following inorganic particulate substances have a Moh hardness which 
exceeds 5. This other class of inorganic particulate substances may be 
present in an amount of up to about 3%, based on the weight of total 
inorganic particulate substance present, when the final dental restorative 
is to be used as a crown or bridge (total dental restorative), and the 
like. However, when the final dental restorative is to be used as a 
filling, inlay, (partial dental restorative) and the like, up to about 
80%, by weight of the inorganic particulate substance may have a Moh 
hardness in excess of 5. Among the inorganic particulate substances having 
a Moh hardness in excess of 5 which may be used are quartz, silica, glass 
beads, glass fibers and the like. 
About 40 to 90 parts, by weight, of the solid particulate system (inorganic 
plus organic) is used with about 10 to 60 parts of the liquid monomer 
system. The preferred amount of solid particulate system is about 50 to 70 
parts by weight. The particle size of the inorganic particulate substance 
is about 0.1 micron to about 75 microns and the particle size of the 
organic polymeric particulate substance is about 0.1 micron to about 75 
microns. The weight ratio of organic polymeric particulate substance to 
inorganic particulate substance is about 2:1 to about 10:1 broadly, and 
about 4:1 to about 8:1 preferably. Further, optional ingredients such as 
tinting agents, stabilizers to control polymerization rate, exotherm, and 
yellowing, fluorescing agent, x-ray opacifying agent, and the like, can be 
included in either component. 
In addition to the aforementioned organic polymeric particulate substance 
and the inorganic particulate substance, when a putty-like consistency of 
the uncured restorative material is desired, we have found it helpful to 
add as part of the organic particulate material, either suspension or 
emulsion prepared polymers in bead form or finely ground dental 
restorative resin, or both. 
The polymers in bead form are typically prepared by suspension 
polymerization in an aqueous medium as described by C. E. Schildknecht, 
Vinyl and Related Polymers, 211-214, J. Wiley & Sons, 1954. The beads 
should pass through a 200 mesh screen and have an average particle 
diameter in the range of about 1 to 75 microns. Examples of suitable 
suspension polymer beads are polymethyl methacrylate or polyethyl 
methacrylate having average particle diameters in the range from about one 
micron to about 75 microns. Crosslinked or non-crosslinked beads may be 
used. 
The finely ground dental restorative resin is typically the cured system of 
the invention, finely ground, and added back to the uncured system. 
Uncrosslinked regrind may also be used. 
About 10 to 75 parts by weight, based on final composition, of the 
suspension polymer in bead form or the finely ground crosslinked or 
non-crosslinked dental restorative resin or both are normally suitable. 
About 20 to 50 parts by weight, based on final composition, are preferred. 
The free radical initiator system may be any free radical initiator system 
such as a thermal initiator, a photochemical initiator or a redox 
initiator and the like. 
The thermal initiator may be any thermal initiator such as a 
peroxydicarbonate, an azo initiator such as azoisobutyronitrile and the 
like. The thermal initiator is dispersed in the solid portion of the 
composition and may be used, as the free radical initiator system, when 
polymerization of the composition is to take place either inside or 
outside the patient's mouth. 
The photochemical initiator may be any photochemical initiator such as the 
aliphatic ethers of benzoin (particularly the methyl ether), alpha 
methoxydioxybenzoin, an alpha-diketone (particularly dl-camphoroquinone) 
and the like. Additionally, a polymerization accelerator, such as a 
tertiary aliphatic amine (particularly triethanolamine) may also be 
present. The photochemical initiator may be dispersed in either the liquid 
monomer system or the solid phase of the composition, or, if the 
photochemical system is composed of more than one component, said 
components may be dispersed so that one or more component(s) is in the 
liquid monomer system and the other component or components is in the 
solid phase of the composition. The use of photochemistry, as applied to 
dental materials is described in Polymer Science and Technology, Vol. 14, 
(Biomedical and Dental Applications of Polymers), entitled "The 
Application of Photochemistry To Dental Materials," pages 411-417, R. J. 
Kilian (1981). 
If a thermal or photochemical free radical initiator system is to be used, 
then such initiator system is present in an amount of from about 0.01 part 
to about 2.0 parts, by weight, per 100 parts of liquid monomer system and 
preferably, if photochemical, from about 0.1 to about 1.0 part by weight, 
as aforesaid and if thermal, preferably from about 0.5 to about 2 parts by 
weight, as aforesaid. 
The redox initiator system which may be used is added to the composition in 
a manner such that the oxidizing agent is kept separate from the reducing 
agent until the liquid monomer phase is mixed with the solid phase. This 
may be accomplished by adding the reducing agent to the liquid monomer 
system and the oxidizing agent to the solid phase. The liquid monomer 
system is kept separate from the solid phase until it is desired to use 
the composition, at which time the liquid monomer system is mixed with the 
solid phase. Other methods of avoiding premature redox initiation of the 
composition will be apparent to one skilled in the art. 
Although a wide range of redox initiator systems are known in the art and 
are suitable, a particularly suitable system is a combination of benzoyl 
peroxide and N,N-bis-(hydroxyethyl)-p-toluidine. Other suitable 
combinations are described by J. M. Antonucci et al., in J. Dent. Res., 58 
(9), 1887-99. Suitable amounts of redox pair to be used are about 0.5 to 
10 parts by weight, preferably about 1 to 5 parts by weight, per 100 parts 
of the total composition (liquid monomer system plus solid phase). The 
redox pair consists of an oxidizing agent and reducing agent. In practice, 
it is preferred to include the oxidizing agent with the solid phase 
(organic particulate substance plus inorganic particulate substance) as 
one component, and the reducing agent with the liquid monomer system as a 
second component. 
The liquid monomer system is comprised of about 10 to about 60 parts by 
weight of one or more monoethylenically unsaturated monomers and about 10 
to 80% by weight, preferably about 20% to about 80% by weight, based on 
liquid monomer system, of one or more polyethylenically unsaturated 
crosslinking monomers. 
If the crosslinking monomer is present in an amount of less than 10% by 
weight, then the polymerized composition will have reduced wearability and 
compressive strength. If the crosslinking monomer is present in an amount 
of more than 80%, as aforesaid, then the polymerized composition will tend 
to be brittle. 
The liquid monomer system will generally contain at least about 70%, by 
weight of said monomer system, of an acrylic monomer and preferably at 
least 95%. of acrylic monomer. The term "acrylic monomer" as used in the 
specification and claims includes acrylic and methacrylic monomers as well 
as the vinyl aromatic monomer, styrene. 
The monoethylenically unsaturated monomer is selected from the group 
consisting of those having homopolymer glass temperatures of from about 
50.degree. C. to about 120.degree. C., with about 65.degree. C. to about 
110.degree. C., preferred. Examples of such monomers and their homopolymer 
glass temperatures (.degree.C.) are methyl methacrylate (105), ethyl 
methacrylate (65), isopropyl methacrylate (81), tertiary-butyl 
methacrylate (107), acrylic acid (103), acrylonitrile (96), sec. butyl 
methacrylate (60), cyclohexyl methacrylate (75), phenyl methacrylate 
(112), chlorotrifluoroethylene (52) and styrene (100). Preferred are 
methyl methacrylate and ethyl methacrylate. If more than one such monomer 
is chosen, the calculated glass temperature of each monomer need not be 
within that range, but that of the uncrosslinked copolymer should be 
within such a range. The calculated glass temperature of the hypothetical 
uncrosslinked copolymer of the two or more monoethylenically unsaturated 
monomers employed is determined by the Fox equation as described in S. 
Loshaeck, T. G. Fox, Bull. Amer. Phys. Soc. 1, (3), p. 123 (1956); as 
follows, with Tg expressed in .degree.Kelvin: 
##EQU1## 
Monomers which can be used along with other monomers but not as the sole 
monoethylenically unsaturated monomer are, for example, methyl acrylate 
(8), methyl acrylate (-22), isopropyl acrylate (-5), n-butyl acrylate 
(-54), isobutyl acrylate (-43), sec. butyl acrylate (-20), tert-butyl 
acrylate (41), cyclohexyl acrylate (15), n-octyl acrylate (-35), n-propyl 
methacrylate (35), n-butyl methacrylate (20), isobutyl methacrylate (48), 
methacrylic acid (230), vinyl acetate (29), hydroxyethyl methacrylate, 
octafluoropentyl methacrylate, hexafluoroisopropyl methacrylate, 
pentafluoropropyl acrylate, pentafluoropropyl methacrylate, 
heptafluorobutyl acrylate, ethylene, and heptafluorobutyl methacrylate. 
An example of such a combination of monomers is a 65:35 ratio, by weight, 
of n-propyl methacrylate and methacrylic acid, which has a calculated 
copolymer glass temperature of 83.degree. C. 
The amount and type of polyethylenically unsaturated monomer is selected so 
as to achieve curing in the desired length of time (up to about 20 minutes 
and preferably up to about 10 minutes), to control exotherm temperature, 
and to synergistically contribute to the wear resistance and compressive 
strength of the resultant permanent dental restoration. The preferred 
polyethylenically unsaturated monomers are polyfunctional acrylates or 
methacrylates or mixtures thereof and are preferably selected from the 
group consisting of trimethylolpropane trimethacrylate, 
2,2-bis-4-(2-hydroxy-3-methacryloxypropoxy)phenylpropane (bis-GMA), 
divinylbenzene, diallyl maleate, ethylene glycol dimethacrylate, 
diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 
higher polyethylene glycol dimethacrylates, butylene glycol 
dimethacrylate, 1,6-hexanediol dimethacrylate, 1,10-decamethylene glycol 
dimethacrylate, butylene diacrylate, pentaerythritol tetraacrylate, and 
ethoxylated bis-phenol-A-dimethacrylate. 
The composition may also include a thickener polymer dissolved in the 
liquid monomer system. Such thickener polymer can be any polymer soluble 
in the liquid monomer system, for example, C.sub.1 to C.sub.4 alkyl esters 
of acrylic acid and methacrylic acid. Alternatively, thickeners insoluble 
in the liquid monomer system such as very finely divided hydrophobic 
silicon dioxide may be included. 
The permanent dental restorations of the invention have a combination of 
high compressive strength (20,000 psi) and wear resistance (200 hours/mil) 
never before achieved in the prior art, and are competitive with amalgam, 
gold, or crown grade porcelain. The restorations to which this invention 
is most applicable are crowns and bridges, especially crowns. 
The method of making the permanent dental crowns of the invention is 
generally to mix the liquid monomer system, the solid particulate system, 
and the free radical initiator system, fill a tooth-shaped mold with the 
mixture, and apply the filled mold to the tooth which has been prepared to 
receive a crown. If the free radical initiator system used is a redox 
initiator system, it is important to keep the reducing agent and oxidizing 
agent separated until the composition is mixed at the time of use. The 
composition can be in the form of two pastes, a paste and a powder, a 
paste and a liquid, or a powder and a liquid. The composition is allowed 
to set, and then to cure. A preferred method comprises (I) mixing (A) a 
first component comprising about 10 to 60 parts by weight of a liquid 
monomer system comprised of one or more monoethylenically unsaturated 
monomers, about 10% to about 80% by weight, based on liquid monomer 
system, of a polyethylenically unsaturated crosslinking monomer(s), and a 
small amount of a reducing agent (if a redox initiator is used) with (B) a 
second component comprising about 40 to about 90 parts by weight of a 
solid particulate system comprised of a mixture of both organic polymeric 
and inorganic particulate substances, both of said substances being 
insoluble in the first component, and an oxidizing agent (if a redox 
initiator is used), (II) allowing the resultant mixture to achieve a 
suitable viscosity, (III) filling a tooth shaped preformed mold or 
impression tray with the thickened mixture, (IV) applying the filled mold 
or tray to the prepared tooth to which the crown is to be applied, (V) 
allowing the composition to set, (VI) removing the set crown from the 
mouth and then from the mold or impression tray, (VII) finishing and 
polishing the cured crown, (VIII) filling the crown with dental cement and 
placing the dental crown on the prepared tooth. 
In one embodiment of this invention, the aforedescribed method may be 
practiced using from about 25 to about 60 parts by weight, of a liquid 
monomer system which comprises one or more monoethylenically unsaturated 
monomers, such as methyl methacrylate, and about 15% to about 50%, by 
weight, based on said liquid monomer system, of a polyethylenically 
unsaturated crosslinking monomer. The solid phase of this embodiment of 
this invention comprises about 40 to about 75 parts by weight of a mixture 
of (1) organic polymeric particulate substance which is insoluble in the 
liquid monomer system and (2) an inorganic particulate substance insoluble 
in the liquid monomer system. The weight ratio of the organic particulate 
substance to the inorganic particulate substance is from about 2:1 to 
about 10:1. The inorganic particulate substance which is used may be one 
or more of hydroxyapatite, calcium carbonate, stearate coated calcium 
carbonate, calcium silicate, calcium metasilicate, talc, clay, and calcium 
sulfate as well as one or more of the above with glass beads, quartz, 
silica, and glass fibers. The composition also includes a free radical 
initiator system such as a redox initiator system. 
The temperature rise during the setting is generally below 15.degree. C. 
thereby avoiding discomfort to the patient, and is preferably within the 
range of 5.degree. to 10.degree. over a set time of about 5 to 15 minutes. 
It is preferred that the crown be prepared in a dental office by applying 
the composition to the prepared tooth and allowing it to set, then curing 
the crown outside the mouth by applying heat at about 70.degree. C. to 
about 140.degree. C. for about 15 to 30 minutes, then applying dental 
luting cement to the inside of the crown, then reapplying the crown to the 
prepared tooth. An alternative method is to leave the crown on the 
prepared tooth until it sets, and then allow it to cure in place without 
removing it. Another method is to send a mold of the prepared tooth to a 
dental laboratory where the crown is made from the composition of the 
invention at the laboratory, then having the dentist at a later time apply 
luting cement to the prepared tooth of the crown and affix the crown to 
the prepared tooth. 
The following specific examples are presented to illustrate a few 
embodiments of the invention, but it is to be understood that the 
invention is not limited thereto.

EXAMPLE 1 
Test specimens are prepared by mixing in a capsule which is placed in a 
Vari-Mix.RTM. high speed shaker, 42 parts, by weight, of the liquid 
monomer system containing the reducing agent and 58 parts of the mixture 
of organic polymeric particulate substance insoluble in the liquid monomer 
system and inorganic particulate substance insoluble in the liquid monomer 
system. The mixture of organic and inorganic particulate substances also 
contains the oxidizing agent. The test specimens are mixed, in the 
Vari-Mix.RTM. high speed shaker for 20 seconds. Thereafter, the mixture is 
poured into a disc-shaped mold, allowed to set at 37.degree. C. and is 
then cured for 10 minutes at 80.degree. C. and for an additional 20 
minutes at 140.degree. C. The liquid monomer system has the following 
composition: 
______________________________________ 
Material Parts by Weight 
______________________________________ 
Methyl Methylacrylate 60 
Trimethylolpropane Trimethacrylate 
40 
Tinuvin P (a benzotriazole) 
0.10 
N,N--bis-(2-hydroxyethyl)-p- 
0.35 
toluidine 
______________________________________ 
The mixture of organic and inorganic particulate substances has the 
following composition: 
______________________________________ 
Material Parts by Weight 
______________________________________ 
Crosslinked regrind* 
28 
Polyvinylidene fluoride 
16 
Crosslinked beads** 
14 
Uncrosslinked regrind*** 
1.5 
Stearate coated 0.6 
calcium carbonate 
Calcium metasilicate 
1.7 
Benzoyl peroxide (98%) 
1.75 
Di-(2-phenoxyethyl) 
0.75 
peroxy-dicarbonate 
______________________________________ 
*The crosslinked regrind has the following composition, in parts by 
weight: 
42 methyl methacrylate, 28 trimethylolpropane trimethacrylate, 12 
polyvinylidene fluoride, 18 stearate coated calcium carbonate. The 
crosslinked regrind is made by a bulk casting polymerization procedure an 
is granulated and pulverized. The crosslinked regrind which is used is 
that which passes through a 325 mesh screen. 
**Crosslinked beads have the following composition, in parts by weight: 
60 methyl methacrylate, 40 trimethylolpropane trimethacrylate. The 
crosslinked beads are made by emulsion polymerization and are isolated by 
spray drying, followed by washing and are then dried in vacuo at 
125.degree. C. The crosslinked beads which are used are those which pass 
through a 325 mesh screen. 
***Uncrosslinked regrind has the same composition as the crosslinked 
regrind except that the 28 parts of trimethylolpropane trimethacrylate is 
replaced with an equivalent amount of methyl methacrylate. 
Small cylindrical samples are prepared, in the manner set forth in this 
Example, by pouring the mixed composition into a cylindrical mold which 
measures 1/2 inch in height and 1/4 inch in diameter. The resultant 
compositions are tested for wear life and compressive strength. 
The wear life test consists of rotating a cast disc sample under an 
off-center ceramic scriber having a cylindrical tip 60 mils in diameter 
under a load of one kilogram/mm.sup.2 at 27 rpm for 64,800 revolutions. 
The test is conducted at 37.degree. C. with continuous water washing. 
Reference to this test may be found in Powell, J. M., and Dickson, G., J. 
Dent. Res. 54 (special Issue A) 134 (1975). 
The compressive strength test is conducted in accordance with ASTM D-595 
and consists of presoaking a rod having a diameter of 1/4 inch and a 
length of 1/2 inch, in water, for 24 hours and at a temperature of 
37.degree. C. The compressive strength is measured immediately after 
removal of the rod from the water and the test consists of crushing a rod, 
along its length at a rate of 0.05 in./min. 
EXAMPLE 2 
Example 1 is repeated except that the liquid monomer system used is 80 
parts by weight of ethyl methacrylate and 20 parts by weight of 
trimethylolpropane trimethacrylate. 
EXAMPLE 3 
Example 1 is repeated except that the liquid monomer system used is 90 
parts by weight of ethyl methacrylate and 10 parts by weight of 
trimethylolpropane trimethacrylate. 
EXAMPLE 4 
Example 1 is repeated except that the liquid monomer system used is 12 
parts by weight of methyl methacrylate, 8 parts by weight of ethyl 
methacrylate and 80 parts by weight of triethylene glycol dimethacrylate. 
EXAMPLE 5 
Example 1 is repeated except that the liquid monomer system used is 60 
parts by weight of bis-GMA and 40 parts by weight of triethylene glycol 
dimethacrylate. 
EXAMPLE 6 
Example 1 is repeated except that the liquid monomer system used is 60 
parts by weight of ethyl methacrylate and 40 parts by weight of 
triethylene glycol dimethacrylate. 
EXAMPLE 7 
Example 1 is repeated except that the liquid monomer system used is 36 
parts by weight methyl methacrylate, 24 parts by weight ethyl methacrylate 
and 40 parts by weight of triethylene glycol dimethacrylate. 
EXAMPLE 8 
This example demonstrates the importance of the range of organic 
particulate substance to inorganic particulate substance. Example 7 is 
repeated except that the polyvinylidene fluoride used in the particulate 
system is replaced with an equivalent amount of calcium hydroxyapatite so 
that the weight ratio of organic particulate substance to inorganic 
particulate substance is 1 to 6. 
EXAMPLE 9 
Example 7 may be repeated and the polyvinylidene fluoride used in the 
particulate system may be replaced with a 1:1 mole ratio copolymer of 
ethylene and chlorotrifluoroethylene. 
EXAMPLE 10 
The procedure of Example 7 may be repeated and the polyvinylidene fluoride 
may be replaced with nylon 66. 
EXAMPLE 11 
The procedure of Example 7 may be repeated and the monomer-particulate 
substrate ratio may be changed to 50 parts of liquid monomer system and 50 
parts of the mixture of organic polymeric substance and inorganic 
polymeric substance. 
EXAMPLE 12 
Example 1 may be repeated and the liquid monomer system may be changed to 
30 parts by weight of tertiary-butyl methacrylate, 30 parts by weight of 
ethyl methacrylate and 40 parts by weight of triethylene glycol 
dimethacrylate. 
EXAMPLE 13 
The procedure of Example 1 may be repeated and the liquid monomer system 
may be 30 parts by weight of phenyl methacrylate, 30 parts by weight of 
ethyl methacrylate and 40 parts by weight of triethylene glycol 
dimethacrylate. 
EXAMPLE 14 
Example 1 may be repeated and the liquid monomer system may be changed to 
30 parts by weight of 3,3,5-trimethylcyclohexyl methacrylate, 30 parts by 
weight of ethyl methacrylate and 40 parts by weight of triethylene glycol 
dimethacrylate. 
EXAMPLE 15 
Example 1 may be repeated and the liquid monomer system may be changed to 
30 parts by weight of styrene, 30 parts by weight of methyl methacrylate 
and 40 parts by weight of triethylene glycol dimethacrylate. 
EXAMPLE 16 
The results of wear life tests and compressive strength for the polymerized 
compositions of Examples 1 through 8 are reported in the following Table: 
TABLE I 
______________________________________ 
Compressive 
Strength - Wear Test Results (thousands of lbs 
Example (hours/mil) per sq. inch) 
______________________________________ 
1 249 36 
2 217 29 
3 208 22 
4 310 22 
5 242 17 
6 223 26 
7 275 34 
8* 57 38 
______________________________________ 
*Comparative