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.
