US2010273129
Atmospheric Non-Thermal Gas Plasma
Method for Dental Surface Treatment
Inventor(s): YU QINGSONG [US]; LI HAO [US]; CHEN
MENG [US] + (YU QINGSONG, ; LI HAO, ; CHEN MENG)
Applicant(s): UNIV MISSOURI [US]; NANOVA INC [US] +
(CURATORS OF THE UNIVERSITY OF MISSOURI OFFICE OF INTELLECTUAL PROPERTY
ADMIN, ; NANOVA, INC)
Classification: - international: A61C5/00 - European: A61C5/00
Abstract -- The provision
of dental restorations can be improved by generating a cold atmospheric
plasma inside the mouth of the patient and then applying that cold
atmospheric plasma onto a dental restoration site. The dental
restoration site can be composed of either or both of dentin and
enamel. Further, the provision of dental restorations can also be
improved by introducing a dental adhesive onto a dental restoration
site and treating it with a cold atmospheric plasma.
BACKGROUND OF THE INVENTION
[0003] The present disclosure relates to dental cavity repair and
treatment. More specifically, the present disclosure relates to a
surface treatment method for targeted dentin and dental materials using
a cold atmospheric discharge plasma technique to improve the clinical
performance and durability of dental restorations.
[0004] Dental fillings are commonly used to treat dental cavities
resulting from caries. Caries is the formal name for the disease that
causes tooth decay or the formation of what are commonly referred to as
cavities. Caries causes tooth decay resulting in decayed matter forming
in the tooth, the location of the decayed matter often being referred
to as a cavity. As many know, the tooth has an enamel outer layer that
covers a thicker layer of dentin. The enamel protects the dentin, and
in turn, the dentin protects the pulp of the tooth that contains flesh,
including sensitive nerves. Failure of the enamel and the dentin to
protect the pulp, whether from accident or caries, is a toothache.
[0005] To treat caries, the decayed matter in the cavities needs be
removed and the cavities are disinfected and filled. The removal of the
decayed matter is usually performed by a dental drill. The materials
for the filling are most commonly dental amalgam or composite material.
Conventionally, an adhesive is used to firmly connect the tooth to the
filling. Adhesives are also used for crowns and caps. A generic term
that encompasses fillings, crowns, caps and other structures installed
in a tooth to remedy a defect in the tooth is restorations.
[0006] Also, one restoration is being replaced with another restoration
can be performed. Such replacement is sometimes, but not always,
accompanied by the presence of additional decay that needs removal. The
prior restoration will usually be removed in the course of this work,
sometimes by drilling, but also by other means in situations such as
where a crown or a cap is being removed.
[0007] The tooth may be formed to have a recess in the tooth, as is
common for dental fillings. But the tooth may also be formed into a
post or the like, such as when caps are installed.
[0008] Where the surfaces of the tooth, adhesive and filling meet each
other are called interfaces. For a properly installed filling there is
an interface between tooth and adhesive and an interface between
adhesive and filling. Fillings have high failure rates at these
interfaces and often need to be replaced later.
[0009] Failure is particularly prominent in composite dental materials.
Composite restoration has become the preferred form of restorative
material because of patients' aesthetic requirements and the aversion
of patients and dentists to the potential health risk of mercury
release from dental amalgams. But composite restorations do not last as
long as dental amalgams. Some of the reasons for premature failures of
composite restoration include dental composite shrinkage, inadequate
bonding of the adhesive to dentin, and formation of a second cavity at
the edges of or under the restoration.
[0010] Recent studies show that many recorded filling failures occur at
the tooth-adhesive interface. These failures are caused by the failure
of the adhesive bonding attaching the filling material/composite to the
dentin of the tooth. One study has reported that about 70% of composite
restoration failures at the back of the mouth occur at the
dentin-composite interface. The failure of the adhesive to maintain
bonding results in the separation of the composite restoration from
dentin. The resulting gaps lead to staining at the margins of the
restoration, sensitivity, and recurrent caries, which cause a
significant portion of composite restoration removal and replacements.
[0011] Studies also show that adhesion between enamel and composite is
generally adequate for clinical applications, while adhesive/dentin
bonds are the weak link and the interfacial bond strength in the
composite restoration deteriorates significantly over time. The
disruption of the bonded interface can develop as a consequence of
long-term thermal and mechanical stresses, or during the restorative
procedure itself, due to stresses generated by composite polymer
shrinkage.
[0012] Foods and saliva are perpetually in the mouth, and further,
bacteria are always present. These can cause problems for the adhesive
working to maintain bonding at the restoration-dentin interface.
Unsuccessful dentin bonding also means that there are sites at the
tooth restoration interface that are vulnerable to hydrolytic breakdown
and susceptible to attack by bacterial enzymes. Clinical performance
needs to improve when polymer-based dental composites are to be
considered viable alternative to dental amalgam. The desired
improvements include enhancing the bonding strength at the
adhesive/dentin interface to resist polymerization shrinkage and to
make it impervious to oral fluids.
[0013] Currently, the preparation and disinfection of dental cavities
(dentin surfaces) prior to filling relies on mechanical drilling or
laser techniques to remove dead (synonymous with necrotic), infected,
and non-remineralizable tissue. Both methods are often destructive and
can be painful for patients due to mechanical stimulation (vibration)
and heating of the dental nerve. To ensure sufficient disinfection, an
excess healthy tissue must be removed using the current methods, since
dentine contains many small channels in which bacteria can hide.
Moreover, the disinfection process itself, with the current methods,
can also lead to fracture of dentin.
[0014] Several studies and techniques for the preparation/disinfection
process have been attempted to improve the interface bonding strength,
but with only limited success. For example, U.S. Pat. No. 6,172,130
describes surface treatment of dental prosthesis composed of polymers
containing hydrogen atoms using gas phase plasma in a vacuumed reactor
vessel operated at 13.56 MHz. The plasma treated polymers are
characterized by the hydrogen atoms on the surface of the polymer being
partially replaced by fluorine atoms. The type of modified polymers is
claimed to be able to improve the retention of the prosthesis and/or
limit the development of dental plaque. However, this plasma process,
due to its requirement of reduced-pressure environment, is not suitable
for surface treatment of the dentin of living subjects in dental
clinics.
[0015] Therefore, there is a need to develop a new and improved
preparation/disinfection method employing the cold atmospheric plasma
technology, which can chemically activate dentin surface to implement
chemical bonding and enhance adhesion strength at dentin-composite
interfaces, and consequently to increase the longevity of dental
restorations, as well as to be more cost-effective and less painful to
patients.
SUMMARY OF INVENTION
[0016] A method of surface treatment for providing a dental restoration
can include generating a cold atmospheric plasma inside the mouth of
the patient and then applying that cold atmospheric plasma onto a
dental restoration site. The dental restoration site can be composed of
either or both of dentin and enamel. Also, the surface of dental
adhesive present after introducing a dental adhesive onto a tooth can
also constitute a dental restoration site that can be beneficially
treated with a cold atmospheric plasma.
[0017] The dental restoration can also have a surface of dental
composite layers. The temperature of the cold atmospheric plasma can
range from about 10[deg.] C. to about 50[deg.] C. with temperatures of
about 35[deg.] C. to about 39[deg.] C. being preferred for patient
comfort in most applications. The gas that is excited into the cold
atmospheric plasma can be helium, argon, nitrogen, oxygen, nitrous
oxide, ammonia, carbon dioxide, water vapor, air, gaseous hydrocarbons,
gaseous silicon-carbons, gaseous fluorocarbons or mixtures thereof.
[0018] Also, the atmospheric plasma can be applied to the restoration
site for a period of about 10 seconds to a period of about 2 minutes.
In addition to measuring exposure by a fixed time interval, the method
contemplates the atmospheric plasma being applied to the restoration
site for a period of time that enhances the strength of the
adhesive-site interface.
[0019] The cold atmospheric plasma appears to be most beneficial to the
periphery of a dental restoration site.
[0020] This disclosure also contemplates a method of installing a
dental restoration on a tooth inside of a patient's mouth where
material is removed from a tooth to expose a surface comprising dentin
or enamel. The exposed surface is then treated with a dentally
acceptable acid to clean it, and then the acid is removed to stop the
acid-tooth reaction. Then cold atmospheric plasma is generated inside
the mouth of the patient and applied onto the exposed surface. Then a
dental adhesive is applied to the surface. Optionally the cold
atmospheric plasma can be applied to the adhesive-coated surface. Then
a dental restoration can be installed on the adhesive coated surface.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a schematic of the
apparatus to generate a cold atmospheric plasma.
[0022] FIGS. 2(a) and 2(b) are
drawings of the cold atmospheric plasma source suitable for dental
applications, according to one embodiment of the invention.
[0023] FIG. 3 shows the various plasma
temperatures at different plasma operating conditions, including power
input and argon flow rate.
[0024] FIG. 4 shows the Fourier
Transform Infrared (FTIR) spectrum change of dentin at surface before
and after plasma treatment.
[0025] FIG. 5 shows the plasma
treatment effects on cell survival curves of Streptococcus mutans,
which is the most common bacterium causing dental cavity.
[0026] FIG. 6 illustrates the bonding
strength improvement for dental composite restoration induced by plasma
treatment of dentin/composite interfaces.
[0027] FIGS. 7(a)-(d) is a drawing of
SEMs taken of fracture surfaces where the fracture occurs at different
interfaces depending on plasma treatment time.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. All
publications, patent applications, patents, and other references
mentioned herein are incorporated by reference in their entirety.
[0029] The present disclosure reveals a new and improved surface
treatment method using cold atmospheric plasma brush technology that
can be used in dental restoration for dental cavity treatment,
preparation, and surface modification of related dental fillings. The
disclosed treatments can be safely used inside the mouth of a patient
without causing more pain than is common to standard dental work. The
surface treatment method can be employed in any surface to activate
chemical bonding effect, particularly the surfaces of a dental filling
site in a dental restoration, such as dentin surface, dental enamel
surface, dental-adhesive surface, and dental-filling surface. The
method for surface treatment at a dental restoration site during a
dental restoration can include generating cold atmospheric plasma at an
appropriate temperature and directing the plasma jet onto a desired
surface at the dental restoration site for duration sufficient to
change the surface characteristics in ways that facilitate bonding of
the treated site with adhesives.
[0030] Cold plasmas, or low-temperature gas plasmas, are partially
ionized gases that contain highly reactive particles including
electronically excited atoms, molecules, ionic and free radical
species, while the gas phase remains near room temperature. Depending
on the plasma chemistry or gas composition, these highly reactive
plasma species clean, and etch surface materials, bond to various
substrates, or combine to form a nanoscale thin layer of plasma
coating, and consequently alter the surface characteristics. These
non-equilibrium plasmas combine exceptional chemical activity with
relatively mild, non-destructive characteristics due to the
room-temperature gas phase.
[0031] The cold atmospheric plasma can comprise plasma gases of helium,
argon, nitrogen, oxygen, nitrous oxide, ammonia, carbon dioxide, water
vapor, air, gaseous hydrocarbons, gaseous fluorocarbons, gaseous
silicon-carbons, and mixtures of them. Desirably, the temperature of
the plasma can range from about 20 to about 50[deg.] C., with about
37+-2[deg.] C. as preferred. The surface of the desired dental filling
site can be the surface of a dentin, the surface of dental enamel, the
surface of a dental adhesive, or the surface of a dental filling. The
term, "adhesive" or "dental adhesive" refers to a composition used on a
dental structure (e.g., a tooth) to adhere a restoration material to
it. Non-limiting examples of such products are listed in Table 1.
[0000]
TABLE 1
Company Name Bonding Products
3M/ESPE Prompt L-Pop, Prompt SE, Scotchbond SE, Scotchbond
Multipurpose Plus, Scotchbond Multipurpose, Easy Bond
SE, Single Bond Plus
ALL DENTAL ComposiRepair
PRODUCTS
BISCO Elitebond, All-Bond 2, All-Bond 3, All-Bond SE, One Step,
One Step Plus, Tyrian SPE
CENTRIX Multibond, Adhere
COLTENE One Coat Bond, One Coat 7.0, One Coat SE, Coltene ART
WHALEDENT Bond
COOLEY & COOLEY Snapbond
COSMEDENT Powerbond, Complete
DE TREY/DENTSPLY PRIME & BOND NT, Xeno III, Xeno IV, XP Bond,
ProBond
DENMAT Tenure Bond, Tenure S, Tenure Uni-Bond, Tenure A&B,
Tenure Quick
DISCUS DENTAL Cabrio
GC AMERICA Fuji Bond LC, Unifil Bond LC
HENRY SCHEIN Dentin Bonding Agent, Natural Elegance Prime Bond,
Sun
Schein Bond
HERAEUS KULZER Gluma Solid Bond, Denthesive II, Gluma Comfort
Bond,
Gluma One Bond, Gluma Gold Bond, i Bond, i Bond SE
IVOCLAR/VIVADENT ExciTE, Heliobond, Syntac Sprint, Syntac Single
Component, Syntac 3, AdheSE
J. MORITA One up Bond F, M-Bond
KERR XR-Bond, Optibond, Optibond FL, Optibond Solo,
Optibond Solo Plus, Self Etching, Optibond All in One
KURARAY Clearfil liner bond 2, Clearfil liner bond 2V, Clearfil
DC Bond, Clearfil SE bond, Clearfil Photobond, S3 Bond, New Bond
L.D. CAULK/ Prime & Bond NR, Probond, Xeno III, Xeno IV, XP
Bond
DENTSPLY
PARKELL Touch & Bond, Easy Bond, C&B Metabond,
Totalbond, Brush & Bond, Etch Free
PENTRON CLINICAL Bond 1, Nano Bond, Bond 1 SF Solvent Free SE,
Bond It,
TECHNOLOGIES Bond 1 C&B
PREMIER Integrabond, Bond Boost SE
PULPDENT Dentastic Uno, Dentastic Uno Duo, Dentastic
SHOFU Imperva Bond, Beautibond, Fl Bond
TOKUYAMA Mac-bond II, Bond Force
ULTRADENT Permaquik, Permagen, PQ1
VOCO Solobond M, Admira Bond
[0032] Cold plasma surface treatments, when employed to modify the
surface of the dentine, can increase adhesive penetration into collagen
fibrils leading to a more effective hybrid layer and increasing
chemical bonding between the collage fibrils and the dental adhesive.
The plasma can also act as a primer for the collagen fibers. Low
temperature plasmas in particular, when modifying polymers for
adhesion, can be tailored to reduce the negative effects seen with
other preparatory methods such as surface roughening, wet chemical
treatments, or exposure to flames.
[0033] Dentin is largely a matrix of hydroxyapatite having fibrils of
collagen distributed within the hydroxyapatite. While not wishing to be
bound by theory, it is believed that when utilized correctly and
efficiently cold plasma is a gentle method used to increase the
wettability of the topmost layer of polymeric surfaces, such as
collagen fibrils, without negatively affecting the underlying material.
Plasma can also uniquely tailor the surface of polymeric materials by
addition of reactive gases in small quantities, which permits the
plasma to easily modify and enhance the surface characteristics of
various types of adhesives. Additionally, cold atmospheric plasma is a
good candidate to sterilize the surface of surgical instrumentation to
prevent bacterial infection, which in turn decreases the chance of the
composite failing because of the formation of secondary caries.
[0034] The inventive surface treatment method for a dental filling site
includes the steps of 1) generating cold atmospheric plasma at a
pre-determined temperature, and 2) directing the plasma onto a desired
surface at the dental filling site for duration sufficient to change
the surface characteristics.
[0035] FIG. 1, is a schematic illustration of a typical dental plasma
brush and related power supply. The plasma brush device 10 contains a
plasma brush generator 12 that includes a walled, narrow gas chamber 14
and two electrodes 16 & 18, which are located inside the gas
chamber 14. The hot wire electrode 16 is connected to an optional
ballasted resistor 20 that can be used to restrain the discharge
current coming from the external power source 22. The grounded
electrode 18 is connected to ground.
[0036] A working gas 24 can be introduced into the gas chamber 14. When
electrical power is applied through the electrodes 16 & 18, the gas
in the gas chamber 14 is excited. A glow discharge plasma 26 of the gas
flowing through the plasma generator will be formed. The discharge
plasma 26 will exit through a nozzle 28, which can be disposable for
control of hygiene.
[0037] The electrodes can be powered by an external power source 22.
The atmospheric pressure plasma can be generated and maintained by
electric power input from a direct current or alternating current,
audio or radio frequency, or pulsed power supplies. The working gas 24
can be helium, argon, nitrogen, oxygen, nitrous oxide, ammonia, carbon
dioxide, water vapor, air, gaseous hydrocarbons, gaseous fluorocarbons,
gaseous silicon-carbons, and mixtures thereof. Argon or air is
preferred in certain dental applications, such as enhancement of
bonding strength in dental restoration, or disinfection of dental
bacteria. The duration of each surface treatment varies depending upon
the particular application, but commonly run less than 60 seconds.
[0038] A nozzle 28 is used to direct the flow of the discharge plasma
out of the gas chamber 14. The nozzle 28 can be in any shape. For
example, the exit from the nozzle 28 can be round, oval or square, or
other desirable shape. Additionally, it is desirable for the shape of
the gas chamber 14 to complement the shape of the nozzle 28.
[0039] One operable shape is a nozzle 28 that is relatively narrow in a
first direction generally perpendicular to the flow of gas and
relatively wide in a second direction transverse to the first direction
but still generally perpendicular to the flow of gas. Such a nozzle 28
forms plasma with a brush-like shape at the exit of the chamber.
Operatively, when the nozzle 28 forms a brush of plasma, the gas
chamber 14 is dimensioned slit-like to complement the nozzle 28.
[0040] While the plasma brush would be operable without a ballasted
resistor 20, glow-to-arc transitions can be prevented by a ballasted
resistor 20 and working gas 24 appropriate to the narrow slit chamber
design. The brush-like shaped plasma extends beyond the exit of the
chamber, and possesses there active features of low-pressure or
non-equilibrium plasmas. The resultant low-pressure or non-equilibrium
gasses can be used to treat surfaces of dentin, enamel, adhesive, or
dental composite layer for dental composite filling.
[0041] Further information on the plasma brush are incorporated by
reference as if fully set forth herein from Y. X. Duan, C. Huang, Q. S.
Yu, 2005, "Low-temperature direct current glow discharges at
atmospheric pressure", IEEE Transactions on Plasma Science, 33, p.
328-329.
[0042] The plasma can be directed to the surface of dentin, enamel,
dental adhesives, or dental fillings. FIG. 2(a) is a side view facing a
broad aspect 30 of the plasma brush 32. The width of the plasma brush
is desirably in the range of 1 to 10 mm. The diagram shows the plasma
to be safe to apply to a human finger 34, which can be readily done.
FIG. 2(b) shows a side view facing the narrow aspect 36 of the plasma
"brush." The narrow aspect 36 of the plasma brush 32 has a thickness of
about 1-5 mm, and is desirable in the range of 1 to 3 mm. A ruler 38 is
also shown indicating a length 40 for the plasma brush 32 of about 5
mm, and is desirable in the range of 5 to 12 mm.
[0043] When employing the atmospheric plasma brush, the size and
temperature of the plasma can be easily controlled by varying the
plasma input power mainly through adjusting the electrical current to
the electrodes and gas flow rate passing the plasma chamber. The
desired temperature of the plasma ranges from about 20 to about
50[deg.] C. A plasma temperature of about 37+-2[deg.] C. is preferred
for work in humans. It should be noted that the temperature can be
adjusted to suit the comfort of a particular patient or other species
of animal.
[0044] FIG. 3 is a graph showing various plasma temperatures under
different generating conditions. Line 42 denotes the thermocouple
temperature (Y-axis) as a function of power source wattage at a
constant flow of argon gas at 2000 standard cubic centimeters per
minute (sccm). Line 44 shows the same at a flow rate of 3000 sccm, line
46 at 4000 sccm, and line 48 at 5000 sccm. Thermocouple, IR imaging,
and thermometers, when used in correlation, can be used to provide a
reasonable range of the plasma temperatures.
[0045] The plasma temperature profile of the described atmospheric
plasma brush was established by taking thermal IR images. In comparison
with the plasma temperatures measured using a thermocouple, it was
noted that an average of 5[deg.] C. higher temperature was recorded
using the IR imaging method. The nerve system of human teeth is very
sensitive to temperature differences. The results of the thermal
imaging study indicate that the plasma temperature of the plasma brush
can be well controlled to be close to human body temperature.
[0046] The duration of treatment can vary from 5 seconds to 10 minutes.
The preferred treatment time will be in the range of 10 seconds to 2
minutes and the most preferred range will be in the range of 10 seconds
to 60 seconds.
[0047] In a particular application, dentin surfaces were treated by
argon plasma brush at room temperature for 0, 30, 100, and 300 sec.
Adper Single Bond Plus dental adhesive (3M ESPE) and Filtek Z250
composite (3M ESPE) were applied and light cured as directed.
[0048] FIG. 4 shows the Fourier Transform Infrared (FTIR) spectrum
change of dentin surface before plasma treatment 50 and after plasma
treatment 52. The FTIR spectrum change after plasma treatment shows
that there is a significant chemical change on the dentin surface. One
change is the increase of carbonyl groups present at the surface, shown
in area 54, which can contribute, in part, to the enhancement of the
bonding strength at dentin-composite interfaces. While not wishing to
be bound by theory, the formation of more carbonyl groups on the
collagen fibers can increase hydrogen bonding between adhesive and
fiber. These additional functional groups also can permit the collagen
fibers to disaggregate after rewetting because of the electrical
repulsive forces, which can significantly increase the surface area of
the collagen fibers and in turn the bonding strength of the collagen
fibers to adhesives.
[0049] This can be understood in view of the composition of
representative collagens and adhesives. Type I collagen is one type of
collagen present in dentin. Type I collagen is generally about [1/3]
glycine and [1/6] proline or hydroxyproline. Lysine, hydroxylysine, and
histidine are generally involved in cross-linking type I collagen
molecules into fibrils. ADPER SINGLE BOND PLUS is a representative
dental adhesive. ADPER SINGLE BOND PLUS comprises BisGMA,
dimethacrylates, HEMA, VITREBOND polyalkenoic acid copolymer, water,
ethanol, and silica nanoparticles. All of these can have hydrogen
bonding with the recited components of Type I collagen.
[0050] Dentin collagen has 3 times the hydroxylysine as skin collagen.
When treated with HEMA and glutaraldehyde only 18% of the lysine and
15% of the hydroxylysine are cross-linked. Steric hindrance prevents
more than 80% of the free amino acids from interacting with the
adhesive. As a result, opportunities for hydrogen bonding are severely
reduced in a collagen fiber as compared to the separate parts of a
collagen molecule.
[0051] While not wishing to be bound by theory, the plasma is thought
to disaggregate the triple helix. The result of the disaggregation can
be that the amino acids that were held in the interior of the triple
helix are exposed by breaking up the triple helix. Not only does this
result in more amino acids being exposed, it increases the surface area
exposed for adhesion by taking surface area that was on the inside of a
fiber, and making that surface area available for adhesion.
[0052] The techniques of the present disclosure result in an increase
in the ultimate tensile strength for the dentin-composite bond induced
by plasma treatment of dentin-composite interfaces at the margins of
the interfaces. The increase of carbonyl groups on plasma treated
dentin surfaces shown in the FTIR implies the treatment effect is due
to the reactive species in the plasma rather than the heat produced
from the plasma brush. Both heat treated and plasma treated surfaces
show an amide II shift. In other words, plasma treatment did induce
chemical structural changes on the collagen fibrils, which determines
the final interfacial bonding strength of dental composite restorations.
[0053] Furthermore, the plasma treatment at the dental filling site
provides additional disinfection effects besides improving bonding
strength. FIG. 5 shows the plasma treatment effects on cell survival
curves of Streptococcus mutans, the most common bacterium causing
dental cavity. The Y-axis of FIG. 5 is the Y-axis of colony-forming
unit (CFU), a measure of viable bacterial numbers, and the X-axis is
the treatment time with argon at a flow rate of 2000 sccm. Line 56
represents the results at 5 W of power, line 58 at 10 W of power and
line 60 at 15 W of power. The results shown in FIG. 5 demonstrate that
plasma treatment can also effectively and rapidly disinfect bacteria in
the cavity.
EXAMPLE 1
[0054] An atmospheric cold plasma brush (ACPB), a non-thermal gas
plasma source, was used to treat and prepare dentin surfaces for dental
adhesive and dental composite application. Extracted unerupted human
third molars were used for this investigation. The occlusal one-third
of the crown was sectioned by means of a water-cooled low speed diamond
saw (Buehler, Lake Bluff, Ill.). The exposed dentin surfaces were
polished with 600 grit SiC sand papers under water and then etched
using 36% phosphoric acid. Dentin surfaces were Ar plasma treated for
0, 30, 60, and 300 sec. A flow rate of 2500 sccm and a power of 5 watts
were chosen. The results of these treatments are shown in FIG. 6.
Oxygen additions at various flow rates were also tested. Adper Single
Bond Plus dental adhesive (3M ESPE) and Filtek Z250 composite (3M ESPE)
were applied and light cured as directed. Dentin/composite bars (8-10
mm*1 mm*1 mm) were cut from the prepared teeth for tensile testing and
interface characterization. The chemical structural changes of the
plasma treated dentins were characterized by FTIR. Fracture surfaces
were characterized by SEM (Philips XL30 ESEM-FEG).
[0055] When plasma treatment was not used, the strength of a
dentin-adhesive interface was 36.8+-10.5 Mpa. But 30 seconds of plasma
treatment on the dentin surface increased the tensile strength of the
dentin/adhesive interface of peripheral dentin to 60.4+-15.7 Mpa. These
findings were confirmed with SEM. The notion of peripheral dentin is
understood in the art. One definition is given by viewing the tooth
from above. If the dentin is above pulp, it is central and the
remaining area is peripheral. It can also be understood as being the
most peripheral 1 to 2 mm or so of the tooth. The SEM observations show
increased areas of composite on the fracture surface when compared to
the untreated control samples. It was found that numerous plasma
treated samples failed in locations other than the dentin/adhesive
interface, while most of the control samples failed at the interface.
The periphery is an area that in a particular planned or installed
restoration is most exposed to the contents of the mouth, including,
but not limited to, saliva, bacteria and food.
EXAMPLE 2
[0056] SEM images shown in FIGS. 7(a)-(d) have been taken of the
fracture surfaces that can be generated using methods of this
disclosure. FIGS. 7(a)-(d) represent back scattered SEM images of the
fracture surfaces of the test specimens prepared from: (a) the
untreated controls (0 sec), (b) 30 sec, (c) 100 sec, and (d) 300 sec
plasma treated dentin. The resulting SEM images showed that more
composite remained on dentin surfaces plasma treated for 30 seconds
when compared with controls. This illustrates that rather than the
fissure occurring in the adhesive-dentin interface, the break occurs in
the composite instead, showing that the adhesion of the interface is
stronger than the internal strength of the composite.
[0057] Fracture modes were determined and recorded. Table 2 presents
micro tensile test data and fracture location of the specimens prepared
from plasma treated dentin and the untreated controls (0 sec treatment)
[0000]
TABLE 2
Treatment Time
0 s 30 s
Bonding Strength
Average Stress (MPa) 38.80 60.38
Standard Deviation (MPa) 8.66 15.66
Average Modulus (GPa) 642.49 963.45
Standard Deviation (GPa) 64.48 98.05
Fracture Location (%)
Interface 84.62% 50.00%
Composite 15.38% 50.00%
Dentin 0.00% 0.00%
Zapit 0.00% 0.00%
[0058] More specimens cohesively failed in the composite for plasma
treated specimens compared to controls, except for the specimens
prepared from 300 s plasma treated dentin specimens. Control specimens
had adhesive or mixed failures more frequently than the plasma treated
specimens. SEM examination of the fractured cross sections showed that
large amounts of composite/adhesive were observed on 30 s plasma
treated dentin surfaces, which implies the dentin-adhesive interface is
stronger than the bulk composite. These trends were also observed with
the test specimens that gave higher tensile strength. Plasma treated
specimens cohesively failed within the composite more frequently than
the control specimens which also implies a stronger interface.
[0059] While the invention has been described in connection with
specific embodiments thereof, it will be understood that the inventive
methodology is capable of further modifications. This patent
application is intended to cover any variations, uses, or adaptations
of the invention following, in general, the principles of the invention
and including such departures from the present disclosure as come
within known or customary practice within the art to which the
invention pertains and as can be applied to the essential features
herein before set forth and as follows in scope of the appended claims.
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