The document discusses exploring different solvents to increase the volume percentage of titania filler in a dental composite polymer matrix. Three solvents - acetone, acetic acid, and isopropyl alcohol - were tested. Samples with 60% and 70% filler by weight were attempted. None of the 70% samples survived curing. The acetone samples appeared most uniform with little porosity while acetic acid performed worst, failing to properly disperse the filler. More investigation is needed to reduce titania agglomeration during silanization and allow higher filler percentages.

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Nathan Cloeter
ENMA 499
Final Report
Due 11-21-2014
Exploration of Solvents to Raise the Volume Percent of Titania Filler in a Polymer Matrix
Abstract
There are a wide variety of materials to choose from for dental fillings, but each choice
has a downside. Metallic fillings have favorable mechanical qualities, and can last for as long as
fifteen years, but do not have the same color as teeth, and can therefore be unsightly. Ceramic
fillings work as well as metallic fillings, and look the part as well. However, ceramic fillings are
also highly expensive, and are therefore not a viable option for anyone who is on a budget. The
final option to consider is a composite filling. Composite fillings, like ceramics, resemble teeth
in color and texture. They bond to teeth and are extremely versatile. Most composite fillings that
exist today are expensive and do not last for a long period of time. However, the versatility of
composite samples presents a chance for further research. More combinations and materials exist
for composites to be tested with, and can give people a preferable balance between cost,
performance, and aesthetics. A good combination of polymer and matrix already exists from
previous research [1]. However, designing and producing a composite that has a high percentage
of ceramic filler has proven to be difficult. This paper looks into two different possibilities to
increase the weight percent of the filler, and some of the early results that have been extracted by
these methods. A change in the traditional polymer matrix, and the introduction of a solvent as a
diluent can help lower the viscosity of the composite before it cures, and theoretically allow us to
increase the weight percent of the ceramic filler and allow us to come one step closer to a dental
filling that can perform just as well as teeth while looking the part.
Introduction
The overarching goal of this project is to create a composite that can be used as a dental
filling that utilizes ceramic filler in a polymer matrix. The ceramic filler that is used is a rutile
titanium oxide nanopowder. The titanium oxide filler utilizes a polymer matrix that is a 50:50
mixture of 2,2-Bis [4-(2-Hydroxy-3-Methacryloxypropoxy) Phenyl] Propane, or Bis-GMA, and
tri(ethylene-glycol) dimethacrylate, or TEGDMA [2]. It may be possible to create a preferable
dental filling with this combination if the filler is able to be used in a composite with a high

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weight percent [3]. Adding the filler in high level in a method where strong bonding to the
matrix can help properly configure the filler in a way so that it can optimize the matrix to an
optimal degree [4]. It is possible to raise the amount of filler in the sample by adding a solvent to
the sample to act as a diluent. By using a solvent as a diluent it is possible to disperse the filler
over a greater area, which allows for a higher percentage of the filler to not only be added to the
matrix, but to properly optimize it as well. This project looks into experimenting with three
different diluents and determining if any of them can be effectively used to increase the
percentage of a composite’s weight that is made up of ceramic filler.
Materials Used
The composites are focused around a ceramic filler that utilizes a polymer matrix. The
ceramic that was used in these experiments was titanium oxide, or titania. The version of titania
that was used was rutile, and has an average particle size in the nanoscale. Rutile is the most
common version of titanium oxide that can be found, and has a tetragonal crystal structure.
Rutile titanium oxide has highly favorable mechanical properties, such as a bulk modulus of
15.02 GPa, and has a Vickers Hardness of 877. However, titanium oxide is an ionic solid, and as
a result is susceptible to breaking down and dissolving over a period of time from a polar
solvent, such as water. The polar bonds of the titanium oxide also make it unable to bond in a
strong fashion to the mostly nonpolar matrix. This is combated by silanizing the titanium oxide
powder with methacryloxypropyltrimethoxysilane, or MPTMS. MPTMS is used with titanium
oxide to form a covalent siloxane coating across the surface of the powder. This makes the
surface hydrophobic, and allows for it to covalently bond to the polymer matrix and create a
stronger bond than if it was not silanized. Silanizing the powder also makes the surface harder,
and gives it more favorable mechanical properties as a result. The combination of the increased
hardness of the ceramic powder and covalent bonding to the polymer matrix allows it to optimize
the matrix at a higher level. Optimizing the matrix makes the sample stronger, because when the
composite fails, it is almost always due to a failure in the matrix.
The one downside to silanizing the filler is that it often leads to the powder
agglomerating. This agglomeration decreases the amount of spaces in the matrix that the filler
can fit into, and results in a limited percentage of the volume that the filler can utilize. To combat
this, a solvent is introduced to the composite to act as a diluent, and to break apart the
agglomeration that is occurring. The three solvents that were used were acetone, acetic acid, and

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isopropyl alcohol. Acetone was used as a control due to it being used as a solvent in previous
experiments. Acetic acid and isopropyl alcohol are two polar protic solvents. Protic solvents are
highly polar solvents that have a high dielectric solvent, and are used to break down salts. Due to
the silane producing a nonpolar surface on the filler, there was a limited chance of the titanium
oxide being dissolved. The design of the experiments and development of the samples has been
built around using these strong solvents to prevent agglomeration. Some of the significant
properties associated with these solvents can be seen below on Table 1.
The titanium oxide filler utilizes a polymer matrix that is a 50:50 mixture of Bis-GMA,
and TEGDMA. Bis-GMA is a monomer that has been used as a resin for dental fillings for a
long period of time. It can create a very sturdy resin, and is a commonly formed monomer [5].
However, Bis-GMA cannot be used on its own due to the incredibly viscous nature that it has.
TEGDMA is added to the Bis-GMA to help reduce this viscosity [1]. In a further attempt to
reduce the viscosity and allow for more filler to be added, BPO is added to the resin to act as a
initiator. Only a smaller amount of BPO is used, and it only accounts for one percent of the resin
that is formed.
Devices Used
Several devices were used in the preparation and testing of the samples. Once the filler
was silanized, it was washed in a centrifuge for three cycles using ethanol. The powder is
suspended in ethanol and washed at 10,000 RPM for three ten minute cycles.
A vacuum chamber and oven were used during the final stages of sample preparation.
The vacuum helped to remove the solvent from the sample, and the oven helped to polymerize
the samples to finish forming the composites. After the composites are formed a polisher is used
to make the sides of the samples smooth and uniform to minimize interference with the
mechanical tests that are performed on them. The polishing is performed with a puck polisher
over several stages of varying sandpaper grits. The progress of the polishing is followed by the
means of optical microscopy.
Several testing devices were used to determine the properties of the composite and to
figure out if the goals of the project were met. One of the initial questions that needed to be
answered was figuring out if agglomeration was occurring during the silanization of the powder.
If agglomeration was occurring, it needed to be determined to what extent it was, and how much
it could factor into the interactions that the filler was having with the polymer matrix during the

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formation of the samples. To determine this, a zetasizer was used on titania nanopowder that was
suspended in ethanol. Portions of powder from before and after the silanization were used in the
zetasizer to determine changes in average particle size, and if the changes were significant
enough to make agglomeration a concern. The majority of the mechanical properties could be
determined with tests that were performed on two testing apparatuses. One of the main on the
samples was the three point bend test. The three point bend test was performed with a Universal
Testing Machine [6]. The other apparatus, the Tukon 2100 Hardness Tester, was used to perform
the Vickers Hardness test to determine the hardness and uniformity of the samples [7]. This data
is taken and compared to other samples and similar materials to determine the effectiveness of
the sample.
Procedure
Both of the constituents had to be prepared before the composites could be formed. The
polymer matrix was prepared by mixing together the BisGMA and TEGDMA in a 50:50 ratio.
Once the mixture was uniform a small percentage of BPO was added to act as an initiator in the
matrix. The matrix was magnetically stirred until it became uniform. Once the matrix reached
uniformity it was placed in an unlit refrigerator. The matrix was kept in these conditions until it
was needed to prevent the matrix from reacting by itself.
The filler was silanized with MPTMS, and was added in a proportion of one gram of
MPTMS for every ten grams of titanium oxide. From there the powder was suspended in ethanol
for twenty four hours while the suspension underwent magnetic stirring. There was ten milliliters
of ethanol added for every tenth of a gram of powder that was used, and it was kept under
constant stirring to ensure that the powder didn’t settle and agglomerate further than it did. Once
the solution was stirred, it was taken and distilled into 250 mL bottles, and centrifuged for three
cycles at speeds of 10,000 RPM for periods of ten minutes. After the first two washing periods,
new ethanol was put in, and the titanium oxide was re-dispersed throughout the new ethanol.
Once the third cycle was completed, the ethanol was once again removed, and what remained
was put in a fume hood to allow any remaining ethanol to evaporate. These cycles of washing
were carried out to remove any excess MPTMS and impurities to be removed from the filler.
Once the ethanol is fully evaporated than the filler is removed from the bottles and ground up in
a mortar. The product that comes from this is stored until it is time to create the samples.

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Three sets of samples were created using three different solvents to see if any could break
down the filler to a satisfactory level such that samples could achieve up to seventy percent filler
by weight. Six bars were made for each sample set. Four of them were made to have sixty
percent of the weight be filler. The other two were designed to have seventy weight percent
filler. Since it takes around half a gram of matrix to make a sample bar, two grams of matrix
were used to make the sixty weight percent bars, and one gram was used for the seventy percent
bars. Once the matrix was measured out the solvent was added to the matrix to try to decrease its
viscosity. Three milliliters of solvent were added to the sixty percent bars, and two milliliters for
the seventy percent bars. The solutions were mixed until they become mostly homogeneous to
ensure that there is a good distribution of solvent throughout the matrix. Soon after the solvent
and matrix are mixed the amount of powder needed for the necessary weight percents are added
to the mixture, and are mechanically stirred until the mixtures become uniform. Once the powder
is added the samples are placed in a vacuum that is kept at 20 mm Hg for a period of twenty four
hours. This is done so that the solvent can evaporate from the samples before the matrix
undergoes polymerization. Once the solvents have evaporated from the samples they are placed
into bar molds and put into an oven for twelve hours. It is important that the solvents have been
completely removed from the samples before they are put into the molds/oven, because if any
solvent remains and it evaporates from the samples while they are in the oven/bar molds the
resulting sample will be extremely porous, and would be unsuitable to use as a filling. The filling
would be unusable due to the resulting loss in mechanical properties, as well as the ability for
water and other contaminants to bypass the filling, and cause the user a great deal of pain.
Once the samples have been cured in the oven they are removed from their molds and are
polished on all four sides. This is a necessity for the three-point bend test and the hardness
testing. If the sides are not uniform they can throw off the tests and give inaccurate values for
their mechanical properties. The samples are polished by gluing them to cylindrical pucks and
polishing them on a puck polisher. The puck polisher is used in several stages of varying
sandpaper grits that range from 400 grit, to 1 micron grit. The progressions of the samples are
followed with optical microscopy to inspect the samples for any cracks or holes that they may
have.
Once the process of polishing is completed on all four sides, most of the samples are then
tested for their properties. Some of the samples will be left in water for a long period of time to

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simulate an accelerated environment that is similar to what teeth are in. Leaving these samples in
this environment gives a chance to see what kind of breakdown a sample may experience over
time. The remaining samples are placed on a Universal Testing Machine to undertake a three
point bend test. This test is performed to give us the flexural modulus of the samples, as the bars
are placed under stress until they fracture. This testing is extremely useful, as the information
provided from it can be used to not only give the flexural modulus of the sample, but other
values for it as well, such as the toughness. This is also a key test to perform because this test
puts the samples under similar types of stress that teeth face when someone is chewing food.
The fractured samples are then taken and tested for their hardness values. Hardness testing is
performed throughout the sample to not only give a more accurate determination of a sample’s
hardness, but to also determine how uniform the sample is.
Results and Analysis
One of the major changes that occurred from previous semesters was that the silane was
changed from 3-mercaptotrimethylsilane to MPTMS to more closely replicate the work done by
Yijun Wang [1]. The new silane caused the filler to undergo more agglomeration than previously
encountered. It was more difficult to break down the agglomeration, even after introducing the
solvent. This agglomeration was measured with the zetasizer, and can be seen below as Table 2.
This increase in agglomeration and the increased difficulty in breaking it down meant that fewer
filler particles were able to fit in the matrix than desired, and samples could not achieve a higher
weight percent as a result. None of the seventy weight percent samples survived the curing
process. They fell apart on themselves and were unable to form solid bars. The resulting
composites were clumps of powder that could not be effectively tested or used. Due to the new
silane being much more effective than the previous silane that was used, it may be possible that
simply using less of it while the filler is being silanized may allow for less agglomeration to
occur, and can result in a higher percentage of the powder being used in the future and allowing
for more than sixty percent of the composite’s weight to be filler.
When the first sets of samples were made and the higher weight percent bars were unable
to be made, there were several attempts that were made in trying to do the process over to get
those higher weight percent samples made. This resulted in too much time being spent in trying
to make the samples, and no time being left to test for the mechanical properties of the samples.
That means that there is a lack of quantitative results that can be used in their evaluations, and

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that a higher reliance will have to be put into qualitative results and observations. A collection of
these qualitative results can be seen below on Table 3.
The samples that had acetone as their solvent resulted in the most uniform samples. There
is very little porosity that is visible with these samples, and from what was observed from the
polishing process they will perform the best mechanically. The samples that were made with
isopropyl alcohol were not that much worse. There are some pores that are visible on the
samples, and the solvent was not able to disperse all of the powder. Despite this, the sample is
not that far behind in appearance and apparent performance from the acetone samples. This
solvent would most likely perform at a higher level if a lower amount of MPTMS was used in
future samples, and merits further investigation.
When performing background research on which solvents to use, it seemed like acetic
acid would work the best out of all of them. This assumption was based on how well acetic acid
interacted with titanium oxide, especially on a prolonged period of time. However, this solvent
performed the worst out of the three. Even after keeping the samples in the vacuum for an extra
twelve hours it was not possible to remove all the solvent from the samples. This resulted in a
highly porous sample forming in the oven that is full of holes and cracks. The samples also seem
to have a slightly yellow tint, which signifies the possibility that the solvent reacted with the
matrix. This would explain the difficulties that came from trying to get the solvent to leave the
sample. There was also a lingering smell that resulted from the usage of acetic acid. It remained
through the entire creation of the process, and remained after the samples were made. The smell
would be a significant reason as to why someone would not want to use this composite as a
dental filling, and adds another reason why this solvent should not be used with this composite in
further research.
Conclusion
Several problems prevented the creation of composites that have an increased percentage
of ceramic filler in a polymer matrix. Two of the solvents present a potential that require further
research into their usage, while one gave a lot of indications that it would not being suitable for
this application. Research and testing is still ongoing to find an ideal process to get samples to
have a high enough filler content so they can effectively be used as a dental filling.
References

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[1] Wang Y, James J. Lee, Lloyd IK, Wilson OC, Rosenblum M, and Thompson V. "High
Modulus Nanopowder Reinforced Dimethacrylate Matrix Composites for Dental Cement
Applications." Journal of Biomedical Materials Research Part A 82A.3 (2003): 651-57.
[2] Chen Q, Zhao Y, Wu W, Xu T, Fong H. "Fabrication and Evaluation of Bis-GMA/TEGDMA
Dental Resins/ Composites Containing Halloysite Nanotubes." Dent Mater 28.10 (2007):
1071-079.
[3] Chen YH, Lloyd IK. "Mechanical Properties of Dental Composites with Mixed Alumina and
Silica Fillers." Thesis. University of Maryland, n.d. Print.
[4] Chan, K. S., Y. -D. Lee, D. P. Nicolella, B. R. Furman, S. Wellinghoff, and R. Rawls.
"Improving Fracture Toughness of Dental Nanocomposites by Interface Engineering and
Micromechanics." Engineering Fracture Mechancis 74 (2007): 1857-871.
[5] Ferracane JL. "Resin Composite—State of the Art." Dental Materials 27 (2011): 29-38.
[6] Udomphol, T. "Laboratory 7: Bend Testing." Suranaree University of Technology.
[7] England G. "Vickers Hardness Test." GordonEngland. Surface Engineering Forum
[8] ScienceLab.com. "Acetic Acid MSDS." Acetone MSDS.
[9] ScienceLab.com. "Acetone MSDS." Acetone MSDS.
[10] ScienceLab.com. "Isopropyl MSDS." Acetone MSDS.
[11] LSU. "Polarity Index." LSU Polarity Index. Louisiana State University
[12] FDA. Guidance Compliance Regulatory Information. Q3C — Tables and List.
Tables
Table 1: Properties of Potential Solvents [8] [9] [10] [11] [12]
Solvent Chemical
Formula
Boiling
Point
(Degrees
C)
pKa Polarity FDA
Limit
Hazardous
To
Irritant
To
Acetic
Acid
𝐶𝐻3 𝐶𝑂2 𝐻 118.1 20 6.2 5000
ppm
Ingestion,
Inhalation
Skin
Contact
Acetone C3H6O 56 20 5.1 5000
ppm
Skin
Contact
Skin
Contact,
Eye
Contact,
ingestion,
inhalation
Isopropyl
Alcohol
𝐶3 𝐻8 𝑂 82.5 16.5 3.9 5000
ppm
Ingestion,
Inhalation
Skin,
Eyes

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Table 2: Average Size of Filler Particles
Stage of Powder Preparation Average Particle Diameter (nanometers)
Titanium Oxide before it is silanized or washed 16.84
Titanium Oxide Silanized with MPTMS 24.08
Table 3: Qualitative Results from the Samples
Sample
Number
Solvent Ease of
Stirring
Apparent
Sample
Porosity
Color of
Sample
Ease of
Polishing
FALL 1 Acetic Acid Was easy to
stir. Had
difficulties
with some
agglomerates
Sample has a
high apparent
porosity. Lots
of holes from
the sample
when it
emerged.
Indicates not
all of sample
evaporated in
vacuum.
Sample came
out of the
oven with a
yellow tint.
Hints at
potential
reaction or
hydrolysis
with the
matrix.
A high
percentage of
the sample
comes off
while
polishing.
Most likely
due to high
porosity in
sample.
FALL 2 Isopropyl
Alcohol
Had difficulty
adding
powder to the
samples, even
after usage of
solvent. May
need a high
amount if
used in the
future.
Same has
some
porosity. Not
to the degree
of FALL 1,
but there are
some holes
that are
deeper than
the surface.
Sample came
out of the
oven white.
Not a
significant
amount of
composite
lost while
polishing.
Some holes
from porosity
impossible to
remove.
FALL 3 Acetone Was easy to
stir. Had
difficulties
with some
agglomerates
Least amount
of porosity
visible in the
sample.
Shows a high
degree of
removal from
the sample.
Sample came
out of the
oven white.
Not a
significant
amount of
composite
lost while
polishing.
Was able to
remove most
visible
imperfections.