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A COMPARISON OF THE ENAMEL DEMINERALIZATION INHIBITION AND SHEAR BOND STRENGTH OF TWO ORTHODONTIC RESINS
by
JAMES HENRY ALLEN
JOHN O. BURGESS, COMMITTEE CHAIR ANDRE’ FERREIRA
P. LIONEL SADOWSKY
A THESIS
Submitted to the graduate faculty of the University of Alabama at Birmingham, in partial fulfillment of the requirements for the degree of
Master of Science
BIRMINGHAM, ALABAMA
2009
ii
A COMPARISON OF THE ENAMEL DEMINERALIZATION INHIBITION AND SHEAR BOND STRENGTH OF TWO ORTHODONTIC RESINS
JAMES HENRY ALLEN
DENTISTRY
ABSTRACT
White spot lesions (WSLs) left on the teeth after orthodontic treatment are a huge
compromise to the esthetic outcome of a treated case. Patient compliance with oral
hygiene instruction is often low and thus WSLs occur in a large proportion of finished
cases. Amorphous calcium phosphate (ACP) has recently emerged as a viable alternative
to fluoride therapy in preventing enamel demineralization by promoting remineralization.
ACP has been added as filler in an orthodontic bracket adhesive with the expectation of
preventing WSLs in poorly compliant patients. The purpose of this study was to compare
the enamel demineralization inhibition and shear bond strength of an ACP filled
orthodontic bracket adhesive and a conventional adhesive.
Ninety previously extracted human 3rd molar teeth were divided into three groups
of thirty. Within each group, half the teeth were bonded with brackets using the ACP
filled adhesive and the other half were bonded with brackets using the conventional
adhesive. After creating a 2mm window around the bracket, Group 1 was submerged in
an acidic gel for ten days. Demineralization depth and shear bond strength were
recorded. Groups 2 and 3 were stored in distilled water for ten days and 24 hours
respectively after which the brackets were fractured and the shear bond strengths were
recorded. The study found that teeth bonded with the ACP filled adhesive had a 29.8%
reduction in demineralization depth when compared to the conventional adhesive. The
average shear bond strength of the ACP filled adhesive (5.5 MPa) was significantly less
iii
than the conventional adhesive (18.5 MPa) in all three treatment groups. In conclusion,
there was significantly less demineralization with the ACP filled adhesive but the low
bond strengths greatly increase the risk of clinical bond failures.
Keywords: WHITE SPOT LESIONS, AMORPHOUS CALCIUM PHOSPHATE, ORTHODONTICS, SHEAR BOND STRENGTH, ESTHETICS
iv
ACKNOWLEDGMENTS
I would like to thank Dr. John Burgess, Dr. Lionel Sadowsky, Dr. Andre Ferreira,
and Ms. Sandre McNeal for their guidance during the thesis process. I would like to
thank 3M Unitek for supplying the brackets and Bosworth Company for providing the
Aegis Ortho used in the study. A special thanks to Dr. Deniz Cakir, Preston Beck, and
Ian Mugisa for all their help in the lab during the project. Finally, I would like to thank
my fellow 3rd year residents for all of your support and friendship. Although I am
looking forward to graduating, I will miss our time together immensely.
v
TABLE OF CONTENTS
Page
ABSTRACT ........................................................................................................................ ii
ACKNOWLEDGMENTS ................................................................................................. iv
LIST OF TABLES ............................................................................................................. vi
LITERATURE REVIEW ....................................................................................................1
White Spot Lesions and Orthodontics .......................................................................1 Compliance Dependant Modalities for White Spot Lesion Prevention ....................4 Manual Products ............................................................................................4 Fluoride Products ...........................................................................................5 ADA Foundation Amorphous Calcium Phosphate (ACP) ............................6 CPP-ACP (Recaldent) ....................................................................................7 Non-Compliant Modalities for White Spot Lesion Prevention ................................8 Fluoride Products ...........................................................................................8 Development of ACP Filled Composites .....................................................11 Aegis Ortho Studies ...............................................................................................12 Present Study .........................................................................................................14 A COMPARISON OF THE ENAMEL DEMINERALIZATION INHIBITION AND SHEAR BOND STRENGTH OF TWO ORTHODONTIC RESINS ......................15 GENERAL CONCLUSIONS ............................................................................................38 GENERAL LIST OF REFERENCES ...............................................................................39
vi
LIST OF TABLES
Table Page 1 Study Design ..........................................................................................................23
2 Mean Lesion Depths (µm) .....................................................................................26 3 Shear Bond Strengths (MPa) .................................................................................27 4 Mode of Failure......................................................................................................28
1
LITERATURE REVIEW
White Spot Lesions and Orthodontics
The traditional goals of orthodontic treatment have always been function,
esthetics, stability and longevity, but not necessarily in that order. In our society, great
emphasis is placed on appearance. Orthodontists play a significant role in assisting
patients in achieving their esthetic goals. An attractive appearance gives individuals an
advantage in life.1 This is important in our ever increasing competitive world where first
impressions are all important. Tooth shape, tooth proportionality, gingival heights,
incisal edge relationships, smile arc and buccal corridors are some of the smile
components that create optimal esthetics.2 Discolorations on the tooth surface known as
“white spot lesions” detract from the optimal esthetic goals of treatment outcomes.
White spot lesions have a white frosty appearance that often appear in the shape of a ring
circling the position the bracket occupied on the tooth during orthodontic treatment. As
the demineralization producing these lesions occurs slowly, white spots lesions are often
not noticed by the patient until the orthodontic appliances have been removed from their
teeth. These white marks left behind on the teeth compromise the esthetic expectations
of both the orthodontist and more importantly the patient.
2
White spot lesions (WSLs) have been defined as a subsurface enamel porosity
from carious demineralization that presents as a milky white opacity when located on
smooth surfaces.3 Since enamel translucency is directly related to its mineral content, the
optical properties of demineralized enamel are different from adjacent sound enamel.
The porous enamel scatters light differently and clinically results in a frosty white
appearance. White spot lesions occur frequently and can be found in 50% to 96% of
orthodontic patients compared to 11% to 24% of untreated controls.3,4,5 WSLs are more
often seen on maxillary lateral, mandibular canine and premolar, and fist molar teeth and
are often found on the gingival aspect of the bracket and under loose fitting bands where
oral hygiene is more difficult.6,7 In a scanning microscope study, Gwinnett and Ceen 8
showed that bacterial accumulation was greatest at the resin/enamel interface and the
most important factor in plaque accumulation was the surface area of composite resin
exposed. Gwinnett and Ceen stated that normal wear of the resin matrix constantly
exposes filler particles which contribute to a persistently roughened surface, and this
predisposes the resin surface to a rapid attachment and growth of oral microorganisms.
Lim et al. 9 studied bacterial adhesion to various orthodontic raw materials and reported
that bacteria adhered most to orthodontic adhesives because the roughened surface
provides protective niches for bacterial colonization. Another scanning microscope study
revealed that bacterial accumulation was constantly detected in a ten micrometer gap at
the resin enamel interface due to the polymerztion shrinkage of the composite.10
Auxiliaries such as Class II correctors, power chains, underlaces, o-ties and intrusion
arches can also increase the number of potential plaque harboring areas. Studies have
shown that fixed orthodontic appliances not only induce a rapid increase in the volume of
3
dental plaque, but such plaque has a lower pH than that in non-orthodontic patients.8,11
There is a rapid shift in the composition of the bacterial flora of the plaque following the
introduction of orthodontic appliances with an increase in the amount of Streptococci
mutans.12 A rigorous oral hygiene regimen is needed to overcome this new environment
challenge. Most orthodontic offices take great care in instructing the patient on proper
oral hygiene home care. This usually consists of proper brushing and flossing techniques
and frequencies along with the use of a fluoride toothpaste and mouth rinse. Often an
anti-cariogenic diet is recommended to reduce the intake of fermentable carbohydrates.
Despite these efforts, patient compliance remains an issue. Weinstein et al.13 studied 70
dental patients with a high plaque index and instructed them in proper oral hygiene
procedures. At 24 weeks only 13 percent had reduced plaque levels compared to their
starting values. If patient compliance is poor, the accumulation of plaque soon triggers
the demineralization process which ultimately results in WSLs.
Enamel is the most highly mineralized and hardest substance in the body. The
primary mineral component is hydroxyapatite (HAP) which is a crystalline calcium
phosphate with the formula Ca10(PO4)6(OH)2. Naturally, enamel is in a constant flux of
demineralization and remineralization depending on the pH of the oral environment.
Bacterial plaque accumulating around orthodontic appliances metabolize fermentable
carbohydrates and produce lactic acid that lowers the pH of the local environment.
Arneberg and coworkers 14 showed that the plaque pH in orthodontic patients following a
sucrose challenge could fall as low as 4 in the upper incisor region. When the pH dips
below the critical pH (5.5) of the enamel, calcium and phosphate ions dissolve out the
enamel and flow into the plaque fluid and saliva. This demineralization occurs until the
4
plaque fluid becomes saturated with respect to calcium and phosphate. If this frequently
occurs, the demineralization/remineralization balance is interrupted and net
demineralization is seen. Demineralization can occur and become clinically evident
within four weeks after appliance placement which is typically the length of time
between orthodontic appointments.15 White spot lesions development is considered an
iatrogenic effect of fixed orthodontic treatment and can be subject to litigation.
Recognizing and documenting poor oral hygiene before irreversible changes occur and
instituting an effective remedy, which may very well result in termination of treatment, is
the orthodontists responsibility. Continuing treatment under unfavorable conditions, such
as poor oral hygiene, can leave oneself open to charges of supervised neglect.16
Orthodontists, therefore, must monitor and take the responsibility of WSL prevention.
Compliance Dependant Based Modalities for White Spot Lesion Prevention
Manual Products
Proper patient education is the first step in preventing enamel demineralization.
The patient must understand that daily plaque removal is required to control WSLs. The
easiest and least expensive method of plaque removal is mechanical debridment with
toothbrushes and dental floss. Patients must be trained in proper brushing and flossing
techniques. Patients may be spending adequate time, yet still achieving unsatisfactory
results with poor oral hygiene technique. Electric toothbrushes can be utilized and have
been shown to help patients become more proficient at removing plaque.17 Sharma and
5
Barnes have shown that water jets are an effective adjunct to toothbrushes and result in
better plaque removal in orthodontic patients.18,19
Fluoride Products
In addition to mechanical plaque removal, there are products available which
require patient compliance that can be recommended for home use such as fluoride
dentifrice and fluoride mouthwash. Fluoride is effective in preventing dental caries.
Addition of fluoride to the public water system was one of the great public health
successes of the 20th century and is considered the single most effective public health
measure for preventing tooth decay. Fluoride incorporates into the surface enamel to
form fluoroapatite which makes the enamel less soluble and more resistant to acid attack.
Sodium fluoride, sodium monofluorophosphate, stannous fluoride, amine fluoride or
acidulated phosphate fluoride are the different forms of fluoride that are incorporated into
the topical fluoride products. It is not recommended that the fluoride concentration be
below 0.1% for orthodontic patients.20 Antiplaque fluoridated dentifrice has been shown
to be more effective than fluoride only dentifrice at preventing demineralization around
appliances bonded with composite material.21 O’Rielly and Featherstone 22 found that
fluoride dentifrices alone were not able to stop enamel demineralization in non-compliant
orthodontic patients. Arneberg et al. 14 discovered that the plaque pH and plaque
fluoride levels are proportional in orthodontic patients with the fluoride reservoir quickly
becoming depleted at low pH. Thus the fluoride effect is limited when the pH drops
below 4.5 and the solubility product of fluoroapatite is exceeded. A systematic review of
the literature by Chadwick 6 concluded that the use of topical fluorides in addition to
6
fluoride toothpaste should reduce the incidence of decalcification in orthodontic patients.
Another systematic review of the literature from the Cochrane Clinical Trials Register
(Jan 2004), MEDLINE (1966 to December 2004), and EMBASE (1974 to December
2004) concluded that there is little evidence as to which method or combination of
methods is most effective to deliver fluoride and recommended the best practice for
orthodontic patients is daily rinsing with 0.05% sodium fluoride mouth rinse.23
However, Geiger and coworkers 24 showed that less than 15% of patients rinsed with
fluoride mouth rinse as they were instructed.
ADA Foundation Amorphous Calcium Phosphate (ACP)
Although fluoride has been the mainstay in caries prevention, calcium phosphates
provide an alternate approach to preventing enamel demineralization by promoting
remineralization. Calcium phosphates have a significant medical and dental history since
they are components of normal hard tissues such as enamel, dentin and bone and are
therefore very biocompatible. In 1920 Albee reported that a ‘triple calcium phosphate’
compound used in a bony defect promoted new bone formation. In 1963, Posner was
credited with first discovering a precipitate that formed an amorphous pattern in his
laboratory when trying to make apatite. A year later, investigators under the direction of
Posner first reported amorphous calcium phosphate (ACP) as a component of human hard
tissues.25 ACP is one of many calcium phosphates and has gained attention in dental
research. ACP, because of its high solubility and rapid conversion to HAP in aqueous
environments, possesses characteristics suitable for enamel remineralization. The
American Dental Association Foundation’s Paffenbarger Research Center (PRC) is
7
leading many research efforts in developing ACP and licensing it for commercial use.
The PRC’s formulation of ACP has demonstrated remineralized enamel lesions.26 The
first product on the market utilizing this technology was Enamelon toothpaste which was
introduced in 1999. It consisted of a dual compartment container where calcium and
phosphate were kept separated until squeezed out of the tube at which time they reacted
to form ACP which precipitated onto the tooth surface. Currently this technology has
been added to several products such as toothpastes and whitening agents. Unfortunately
these products require patient compliance. Since the PRC’s ACP is highly soluble, it
quickly washes away and must be frequently reapplied to provide benefit. This low
substantivity has lead to the development of other technologies with the aim of providing
a delivery vehicle that will provide a sustained release of ACP to the tooth.
CPP-ACP (Recaldent)
Recaldent (Bonlac Bioscience International Pty Ltd, Melbourne, Australia) is a
technology that uses casein phosphopeptides (CPP), a milk protein, to stabilize ACP in
solution. The multiple phosphoseryl residues of CPP bind to forming nanoclusters of
ACP, preventing growth to the critical size requiring phase transformations to HAP.
Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is incorporated into
supragingival dental plaque by binding onto the surfaces of bacteria cells and the
intercellular plaque matrix causing significant increases in plaque levels of calcium and
phosphate. This increased level of calcium and phosphate helps maintain a
supersaturated enamel interphase with the tooth surface depressing enamel
demineralization and enhancing enamel remineralization.27 CPP-ACP solutions, when
8
applied to molar teeth of rats, reduced caries by 55% compared to controls.28 In a
human in situ enamel demineralization study, a 1.0% CPP-ACP solution used twice daily
produced a 51% reduction in enamel mineral loss.29 The addition CPP-ACP to sugar
free chewing gums, resulted in a dose related increase in enamel remineralization. At the
high end, 56.4mg of CPP-ACP produced a 152% increase in enamel remineralization
relative to the control gum.30 A chewing gum and mouthrinse study demonstrated that
CPP-ACP increased plaque levels of calcium and phosphate and that significant levels
remained 3 hours after application.31 Although CPP-ACP has demonstrated
substantivity and positive results with respect to enamel remineralization, patient
compliance remains an issue in the success of these products.
Non-Compliant Modalities for White Spot Lesion Prevention
Fluoride Products
There are several modalities available to help protect the patient from white spot
lesions that require much less patient compliance. These products come in the form of
topical applications applied by the dental professional or adhesive materials used to bond
orthodontic appliances. Fluoride varnish can be applied by the orthodontist and results
in prolonged contact and subsequent release of fluoride to the tooth structure. Ogaard et
al. 32 showed a 48% reduction in the depth of naturally occuring enamel lesions treated
with the fluoride varnish Duraphat (Colgate Oral Pharmaceuticals Inc., Canton, MA).
Todd et al. 7 reported 50% less enamel demineralization with a single application of
Duraflor (Pharmascience Inc., Montreal Canada) to teeth bonded with orthodontic
9
appliances. Demito 33 showed that two applications of Duraflor promoted a 38%
reduction in the mean lesion depth adjacent to orthodontic brackets. Although varnishes
are effective in reducing demineralization, they require repeated applications and discolor
teeth which is often objectionable to the patient. A prospective trial comparing a fluoride
releasing sealant (Reliance M5 Protection Plus) with a control showed no significant
difference in the amount of enamel demineralizaton.34 Another fluoride releasing sealant
(ProSeal; Reliance Orthodontic Products, Itasca, IL) released fluoride ions for 17 weeks
in an in vitro study. In addition, it had the ability to be recharged with topical
applications of acidulated phosphate fluoride.35 An in-vitro study conducted by Hu and
Featherstone 36 demonstrated that enamel demineralization was significantly less in teeth
treated with ProSeal than in teeth treated with fluoride varnish or unfilled sealants. A
more recent study showed that ProSeal reduced enamel demineralizaiton by 92% over
untreated controls and provided significantly more protection than a fluoride varnish or
unfilled sealant.37 Although ProSeal has been shown to protect against WSLs, the resin
has to be removed with a bur when orthodontic appliances are removed and resin tags
remain in the enamel which can cause unesthetic staining and compromise future
whitening results.
Glass ionomer cements (GIC) release fluoride and have been used as orthodontic
adhesives for their demineralizaiton preventative affects.38 Although GICs provide a
fluoride reservior capable of sustained release with the ability to be recharged with
fluoride, their lower bond strength compared to composite resins produced more clinical
debonds which limited their polularity.39,40,41 To improve the physical characteristics of
GICs, light-activated resins were incorporated into the mix to give it added strength.
10
Resin-modified glass ionomer cements (RMGI) have improved bond strengths while
providing the fluoride release of GICs, and thus are more widely used as orthodontic
adhesives.42,43,44 Gorton et al. 45conducted an in vivo study comparing the
demineralization around orthodontic brackets bonded with a RMGI with the
demineralization around brackets bonded with a conventional composite resin. Subjects
in the study also used a fluoridated toothpaste. The conclusion reached after a 4 week
period was that the RMGI significantly reduced the prevalance and severity of enamel
demineralization. Sudjalim et al. 46 bonded twenty extracted human 3rd molar teeth with a
RMGI and twenty extracted human 3rd molar teeth with a light-cured resin control. Each
group was subjected to topical applications of either CPP-ACP (TM with Recaldent),
NaF 9000 ppm gel, or a combination of CPP-ACP and NaF gel. The test specimens were
immersed in a demineralizing solution for 96 hours and removed for additional topical
treatments every 4 hours. Sudjalim concluded that the use of RMGI would significantly
reduce the development of enamel demineralizaton. Further, he found that the topical
application of both the CPP-ACP and NaF in combination with the RMGIC provided the
most protection against enamel demineralization and recommended this protocol for at
risk orthodontic patients.
Fluoride releasing composite resins and compomers, a hybrid of glass ionomer
and composite resin, have the ability to prevent enamel decalcification. In a in-vivo
study, Millet et al. 47 reported that 20% of fluoride releasing compomer bonded teeth
were affected by decalcification while 26% of control teeth were affected. Sonis et al. 48
demonstrated in a prospective clinical trial no decalcifacation on teeth bonded with a
fluoride releasing composite resin while the 12.6% of the control teeth experienced
11
decalcifications. Similarly, Underwood et al. 49 following a split mouth clinical study
concluded that an experimental fluoride-exchanging resin held promise as a clinically
useful orthodontic adhesive as it demonstrated significantly less demineralization
compared with a control. Conversely, a systematic review by Derks et al. 50 reported that
fluoride-releasing bonding materials have no significant effect in the preventing WSL
demineralizations.
Development of ACP Filled Composites
Amorphous calcium phosphate has been incorporated as fillers into dental
resin-based resorative materials to take advantage of its ability to remineralize dental hard
tissues. ACP has been marketed as a “smart” material because it has been shown to
release higher levels of calcium and phosphate under acidic conditions.51,52 However,
ACPs high solubility weakens the resin in which it is filled due to the voids left behind
after the ACP leaches out of the polymer matrix.53 Mechanical properties were improved
by introducing glass-forming elements during the preparation of the ACP filler which
permitted a stronger interaction with the surrounding resin matrix. These modified ACP
fillers not only improved the mechanical properties, they also produced a more sustained
release of calcium and phosphate at levels required for HAP formation.54,55 Artificial
lesions created on bovine incisors recovered 38% of lost mineral when covered with an
ACP-containing composite.26 Langhorst et al. 56 created artificial enamel lesions by
submersing teeth for 72 hours in a 4 pH demineralizing solution at 37 ۫C. The teeth were
then cycled through a demineralization and remineralization scheme for 1 month.
12
Quantitative digital image analysis of matched areas from contact microradiographs taken
before and after treatment indicated higher mineral recovery with ACP composites
compared to a commercial orthodontic F-releasing cement (14.4% vs. 4.3%,
respectively), while the control specimens showed an average of 55.4% further
demineralization. Park et al. 57 demonstrated similar mechanical improvements with
glass modified ACP and suggested its use as a base and liner material under dental
restorations. Skrtic et al. 58 studied the effect of combinations of seven different resin
matrices and three types of ACP fillers on the release rates of calcium and phosphate.
Skrtic concluded that UDMA, a urethane di-methacrylate resin, appears to have
advantages over Bis-GMA and highly carboxylated monomer systems such as
PMGDMA in producing higher ion release rates. UDMA also has reduced water sorption
and polymerization shrinkage thus enhancing the strength of the resin matrix.59 With the
systematic improvements in mechanical and ion release properties, Skrtic advocated
ACP-filled composite resins for use as orthodontic bracket adhesives. Now the
orthodontic profession had a potential non-compliant WSL prevention product that
offered an alternative to fluoride therapy.
Aegis Ortho Studies
In March 2004, Aegis Ortho became the first available ACP-containing
orthodontic adhesive to receive Food and Drug Aministration approval. The proprietary
formula of Aegis Ortho utilizes a UDMA resin base along with a mix of various fillers
including ACP. To date, no published studies on the ability of Aegis Ortho to prevent
13
enamel demineralization. The studies involving Aegis Ortho have been more concerned
with its mechanical properties in order to establish its validity as an orthodontic adhesive.
Using 30 freshly extracted human third molars, Dunn et al. 60 compared the shear bond
strength (SBS) of Aegis Ortho and a conventional resin-based composite adhesive
(Transbond XT, 3M Unitek). Each tooth was bonded with two brackets - one bonded
with Transbond XT and the other bonded with Aegis Otho. After bonding, the specimens
were stored in water at 37 degrees C for 24 hours and then tested for shear bond strength.
The results showed that Aegis Ortho failed at significantly weaker SBS values than did
Transbond XT, 1.2 MPa and 10 MPa respectively. Foster et al. 61 compared the SBS of
Aegis Ortho with a conventional composite resin (Transbond XT, 3M Unitek) and a
resin-modified glass ionomer cement (Fuji Ortho LC, GC America Inc, Alsip, III). Each
adhesive was used according to manufacturers’ instructions to bond brackets on 20
premolars. The teeth were mounted in acrylic and stored at 370 C for 40 hours prior to
debonding. Foster’s results showed that there was a statistically significant difference in
SBS values between Aegis Ortho and Transbond XT, 6.6 MPa and 15.2 MPa
respectively. There was no statistical difference between Aegis Ortho and Fuji Ortho LC
although Aegis Ortho values were lower, 6.6 MPa and 8.3 MPa respectively. Uysal et al.
62 tested the shear bond strength of lingual retainers bonded with Aegis Ortho and a
conventional lingual retainer composite (Transbond-LR, 3M Unitek). Uysal concluded
that Aegis Ortho had a significantly reduced bond strength when compared to
conventional composite resin cements. Although the shear bond strengths were
significantly lower than the composite resin controls, they were in the range of what has
been reported as being clinically acceptable.63,64,60 Tavas et al. 63 reported that shear/peel
14
strengths of orthodontic brackets should be 5.9 MPa within 24 hours. In another study
Reynolds 64 determined that the clinically acceptable minimum bond strength values for
direct orthodontic bonding systems are 5.9-7.8 MPa.
Present Study
Bosworth Company’s bonding protocol for previous studies 60,61,62 did not include
the use of a primer. Bosworth Company has since changed the bonding protocol for
Aegis Ortho to include their self-etching primer, Aqua Bond. The present study was
designed to test the SBS of orthodontic brackets bonded with Bosworth Company’s new
bonding protocol for Aegis Ortho and compare the values to the SBS values of the
industry standard, Transbond XT. Due to the “smart” characteristics of the ACP
containing products, the bond strength after submersion in a low pH demineralizing
solution was also tested to determine if an acidic environment deteriorated the bond
strength. Since there have been no published studies of the demineralizing inhibition
capabilities of Aegis Ortho, this study compared enamel lesion depth adjacent to
orthodontic brackets bonded with Aegis Ortho and Transbond XT after a demineralizing
treatment. The intensions of this study were to test the bond strength and
demineralization prevention capability of a relatively new product that has the potential
to be a tool for combating white spot lesions in non-compliant patients.
15
A COMPARISON OF THE ENAMEL DEMINERALIZATION INHIBITION AND SHEAR BOND STRENGTH OF TWO ORTHODONTIC RESINS
by
JAMES HENRY ALLEN
In preparation for The Angle Orthodontist
Format adapted for thesis
16
ABSTRACT
White spot lesions (WSLs) left on the teeth after orthodontic treatment are a huge
compromise to the esthetic outcome of a treated case. Patient compliance with oral
hygiene instruction is often low and thus WSLs occur in a large proportion of finished
cases. Amorphous calcium phosphate (ACP) has recently emerged as a viable alternative
to fluoride therapy in preventing enamel demineralization by promoting remineralization.
ACP has been added as filler in an orthodontic bracket adhesive with the expectation of
preventing WSLs in poorly compliant patients. The purpose of this study was to compare
the enamel demineralization inhibition and shear bond strength of an ACP filled
orthodontic bracket adhesive and a conventional adhesive.
Ninety previously extracted human 3rd molar teeth were divided into three groups
of thirty. Within each group, half the teeth were bonded with brackets using the ACP
filled adhesive and the other half were bonded with brackets using the conventional
adhesive. After creating a 2mm window around the bracket, Group 1 was submerged in
an acidic gel for ten days. Demineralization depth and shear bond strength were
recorded. Groups 2 and 3 were stored in distilled water for ten days and 24 hours
respectively after which the brackets were fractured and the shear bond strengths were
recorded. The study found that teeth bonded with the ACP filled adhesive had a 29.8%
reduction in demineralization depth when compared to the conventional adhesive. The
average shear bond strength of the ACP filled adhesive (5.5 MPa) was significantly less
than the conventional adhesive (18.5 MPa) in all three treatment groups. In conclusion,
there was significantly less demineralization with the ACP filled adhesive but the low
bond strengths greatly increase the risk of clinical bond failures.
17
INTRODUCTION
In today’s society, esthetics is probably the most important reason patients seek
orthodontic treatment. Much emphasis has been placed on identifying esthetic smile
components to aid the orthodontist in delivering a beautiful smile. Sarver et al. 1
advocates identifying and recording the positive attributes of a patient’s smile during the
initial exam so that treatment planning will not negatively affect those attributes. The
natural translucency of the patient’s enamel is a characteristic that should not worsen
with orthodontic treatment. However, white spot lesions (WSLs) often develop around
orthodontic appliances during the treatment period resulting in un-esthetic opacities that
lead to patient dissatisfaction. WSLs have been defined as a subsurface enamel porosity
from carious demineralization that presents as a milky white opacity when located on
smooth surfaces.2 Since enamel translucency is directly related to its mineral content, the
optical properties of demineralized enamel are different from adjacent sound enamel.
The porous enamel scatters light differently and clinically results in a frosty white
appearance. It has been reported that anywhere from 50% to 96% of orthodontic patients
get WSLs during treatment.2,3,4 WSLs are more often seen on maxillary lateral,
mandibular canine and premolar, and first molar teeth.5,6 They are often found on the
gingival aspect of the bracket and under loose fitting bands where oral hygiene is more
difficult. Studies have shown that there is a rapid shift in the composition of the bacterial
flora of plaque following the introduction of orthodontic appliances resulting in an
increase in the amount of acidogenic Streptococci mutans which are strongly associated
with enamel demineralization.7 It has also been demonstrated that there is a rapid
increase in the volume of dental plaque after the placement of fixed orthodontic
18
appliances and this plaque has a lower pH than plaque found in non-orthodontic
patients.8,9 Naturally, enamel is in a constant flux of demineralization and
remineralization depending on the balance of the oral environment. Net demineralization
results when poor oral hygiene efforts fail to remove the plaque that has accumulated
around the orthodontic appliances. Each time fermentable carbohydrates are consumed,
the acidogenic plaque around the appliances produce lactic acid that causes a dip in pH
below the solubility threshold of enamel. When this occurs, calcium and phosphate
diffuse out of the enamel disrupting the ordered arrangement of enamel crystals which
produce enamel translucency. This process can occur with WSLs becoming clinically
evident within four weeks, a typical orthodontic appointment interval.10
Patient compliance with proper oral hygiene and a low cariogenic diet is crucial in
preventing white spot lesions. It is the responsibility of the orthodontist to teach the
patient how to effectively clean around the appliances and to monitor the patient’s oral
hygiene at each office visit. Fluoride therapy has been the predominant treatment utilized
in caries prevention and is incorporated in many products such as toothpastes, gels and
mouth rinses designed for at home use by the patient. Fluoride incorporates into the
surface enamel to form fluoroapatite which makes enamel less soluble and more resistant
to acid attack. The recommended fluoride concentration is above 0.1% for orthodontic
patients and the best daily practice for preventing enamel demineralization is using a
fluoride dentifrice along with a fluoride mouth rinse.5,10,11 However, Geiger and
coworkers 12 showed that less than 15% of patients rinsed with fluoride mouth rinse as
they were instructed. O’Rielly and Featherstone 13 concluded that fluoride dentifrices
19
alone were not able to stop enamel demineralization in non-compliant orthodontic
patients.
In-office applications of fluoride releasing products have been utilized in an
attempt to reduce the effects of poor patient compliance. These products include
elastomerics, varnishes, sealants, resin modified glass ionomer cements and adhesives
that are applied to or adjacent to the enamel and have shown the ability to reduce enamel
demineralization.6,14,15,16,17,18,19,20,21,22 These products are designed to provide a constant
source of fluoride to the tooth; however, Arneberg et al. 23 reported that plaque pH and
plaque fluoride levels are proportional in orthodontic patients with the fluoride reservoir
quickly becoming depleted at low pH. Arneberg showed that the plaque pH in
orthodontic patients following a sucrose challenge could fall as low as 4 in the upper
incisor region. The fluoride effect becomes limited when the pH drops below 4.5 and the
solubility of fluoroapatite is exceeded.24
Amorphous calcium phosphate (ACP) provides an alternative to fluoride in
regards to preventing enamel demineralization and has gained much attention in the
dental research community over the past decade. ACP is an important intermediate in the
formation of the main mineral component of enamel, hydroxyapatite (HAP). ACP
possesses characteristics suitable for enamel remineralization because of its high
solubility and rapid conversion to hydroxyapatite in aqueous environments.25 ACP has
been incorporated in many desensitizing and whitening products with the unofficial claim
of reducing enamel demineralization. To increase ACP’s substantivity it has been
packaged with casein phosphopeptides (CPP) which are milk proteins that stabilizes ACP
in solution by slowing its conversion to HAP. This CPP-ACP combination is marketed
20
as Recaldent (Bonlac Bioscience International Pty Ltd, Melbourne, Australia). CPP-ACP
is incorporated into supragingival dental plaque by binding to the surfaces of bacteria and
various components of the intercellular plaque matrix causing significant increases in
plaque levels of calcium and phosphate. This increased level of calcium and phosphate
helps to maintain a state of supersaturation with respect to enamel mineral, thereby
depressing enamel demineralization and enhancing enamel remineralization.26,27,28,29,30
Although CPP-ACP has a clinical history of success when used frequently, patient
compliance is still an integral part of its clinical effectiveness.
Amorphous calcium phosphate has been incorporated as a filler in dental resin-
based resorative materials to take advantage of its ability to remineralize dental hard
tissues.31,32 ACP has also been marketed as a “smart” material because it releases higher
levels of calcium and phosphate ions under acidic conditions.33,34 This property, in
theory, makes an ACP filled resin a great choice in dental applications where poor oral
hygiene persists. However, ACPs high solubility results in voids in the resin after the
ACP dissolves out of the polymer matrix leading to weakening of the resin.35 Initially,
ACP filled resins were advocated in non-stess bearing conditions such as bases or liners
under dental restorations.36 ACP filled resins were recommended for use as orthodontic
adhesives to prevent enamel demineralization adjacent to orthodontic brackets after
improvements in mechanical properties were made.25,37,38
In March 2004, Aegis Ortho (Harry J. Bosworth Co., Skokie, Ill) became the first
available ACP-containing orthodontic adhesive to receive Food and Drug Aministration
approval. The proprietary formula of Aegis Ortho utilizes a UDMA resin base along
with a mix of various fillers including ACP. To date, there have been no published
21
studies on the ability of Aegis Ortho to prevent enamel demineralization. The studies
involving Aegis Ortho have been more concerned with its mechanical properties in order
to establish its validity as an orthodontic adhesive. Dunn et al. 39 compared the shear
bond strength (SBS) of Aegis Ortho and a conventional resin-based composite adhesive
(Transbond XT, 3M Unitek). They reported that Aegis Ortho had significantly lower
shear bond strength than did Transbond XT, 1.2 MPa and 10 MPa respectively. Dunn
concluded that Aegis Ortho did not have suitable mechanical strength for use as an
orthodontic bracket adhesive. Foster et al. 40 compared the SBS of Aegis Ortho with a
conventional composite resin (Transbond XT, 3M Unitek) and a resin-modified glass
ionomer cement (Fuji Ortho LC, GC America Inc, Alsip, III). Foster’s results concluded
that Transbond XT with a 15.2 MPa bracket bond strength was statistically greater than
the 6.6 MPa produced by Aegis Ortho. There was no statistical difference between
Aegis Ortho and Fuji Ortho LC although Aegis Ortho values were lower, 6.6 MPa and
8.3 MPa respectively. Although the shear bond strengths of Aegis Ortho were
significantly lower than the composite resin controls, they were in the range (5.9-7.8
MPa) of bonds that are clinically acceptable.39,41,42 The original bonding protocol for
Aegis Ortho did not call for the use of a priming agent. After low SBS were reported for
Aegis Ortho, the Bosworth Company changed the bonding protocol for Aegis Ortho by
adding their self etching primer, Aqua Bond.
Patient compliance remains a hinderance to the effectiveness of proven techniques
and products in preventing white spot lesions. The present in vitro study is designed to
evaluate a new orthodontic product intended to prevent white spot lesions with little or no
patient compliance. For the purposes of the present study, the null hypotheses assumed
22
that there were no statistically significant differences in (1) the depth of demineralization
adjacent to orthodontic brackets bonded with Aegis Ortho and Transbond XT and 2) the
mean shear bond strengths of orthodontic brackets bonded with Aegis Ortho and
Transbond XT under various treatment conditions. Therefore, the specific aims of the
present in vitro study were 1) to bond brackets following manufacturer’s instructions to
human third molar teeth using either an ACP-filled resin (Aegis Ortho) or a traditional
composite (Transbond™ XT), fracturing them at 24 hours and 10 days to compare
bracket shear bond strengths and modes of failure, 2) to demineralize enamel in a 2 mm
unprotected window around the bracket for 10 days and measure the lesion depth at
0.5mm from the bracket base, comparing Aegis Ortho and Transbond™ XT, and 3) to
determine if the increased release of ACP-filler at low pH decreases bond strength.
MATERIALS AND METHODS
Study Design
Ninety extracted human third molar teeth were collected. The teeth were
inspected under 10x magnification and were free of visible opacities, decalcifications,
fractures, or peculiar morphology. The teeth were stored in 10% sodium hypochlorite for
approximately two months prior to the study. Three groups of thirty teeth were
established based on the treatment conditions under which the teeth were to be tested.
The three groups were further randomly assigned to two groups of fifteen teeth each
depending on the bonding adhesive to be used for adhering the brackets (.018-in MBT
Victory Series, 3M Unitek, Monrovia, CA) (Table 1).
23
Table 1
Study design
Treatment Condition Groups Aegis Ortho Transbond XT
Group 1: 10 Day Demineralization (n = 30)
n = 15 n = 15
Group 2: 10 Day H2O Storage (n = 30)
n = 14 n = 15
Group 3: 24 Hour H2O Storage (n = 30)
n = 15 n = 15
In group 1, the thirty teeth were cleaned and the mesiobuccal cusp of each tooth was
pumiced with fluoride free flour pumice for 10 seconds, rinsed with sterile water, and
dried with oil/moisture free air. A two millimeter by seven millimeter piece of protective
barrier tape was placed on the tooth at the approximate occlusal aspect of the bracket
position. The purpose of the tape was to eliminate any variables due to the different
bonding protocols that might affect the demineralization study. In the order of random
assignment, the brackets were bonded to the extracted teeth according to manufacturer’s
instructions. The teeth bonded with Transbond XT were conditioned with 37%
phosphoric acid for 30 seconds, rinsed with sterile water for 10 seconds, and dried with
oil/moisture free air until the enamel had a frosty appearance. A thin coat of Transbond
XT primer (3M Unitek) was applied and photopolymerized for 10 seconds. Transbond
XT light-cured adhesive paste (3M Unitek) was then applied to the base of the bracket
and the bracket was placed on the mesiobuccal cusp parallel to the long axis of the tooth.
Under magnification, the bracket was placed on the tooth adjacent to the barrier tape and
excess bonding material was removed with an explorer. The adhesive was
24
photopolymerized for 20 seconds on the mesial aspect of the bracket and 20 seconds on
the distal aspect of the bracket using an Ortholux™ LED curing light (3M Unitek) with a
power density of 1000 mW/cm. The teeth bonded with Aegis Ortho were conditioned
with 35% phosphoric acid (Harry J. Bosworth Co., Skokie, Ill) for 30 seconds, rinsed
with sterile water for 10 seconds, and dried with oil/moisture free air. A self-etching
primer, Aqua Bond (Harry J. Bosworth Co.), was then rubbed onto the enamel surface for
15 seconds. The teeth were rinsed with sterile water for 10 seconds and dried with
oil/moisture free air. Aegis Ortho light-cured adhesive paste (Harry J. Bosworth Co.,
Skokie, Ill) was applied to the base of the bracket and the bracket was placed on the
mesiobuccal cusp parallel to the long axis of the tooth. Under magnification, the bracket
was placed adjacent to the barrier tape and excess bonding material was removed with an
explorer. The adhesive was photopolymerized for 20 seconds on the mesial aspect of the
bracket and 20 seconds on the distal aspect of the bracket using an Ortholux™ LED
curing light (3M Unitek) with a power density of 1000 mW/cm2. The tape was removed
from all 30 teeth in group 1 and any residual adhesive residue removed with alcohol. The
teeth were coated with a clear acid resistant nail varnish (Revlon, New York, NY) leaving
a 2 millimeter circumferential window of unprotected enamel adjacent to the bracket.
The demineralizing solution was prepared by buffering a 1M solution of 85% lactic acid
with a 1M solution of sodium hydroxide to make a stock solution of pH 4.5. A calibrated
sensION2 pH/ISE meter (Hach Company, Loveland, CO) was used to measure the pH.
Thirty grams of medium viscosity Carboxymethyl Cellulose (Sigma-Aldrich Co., St.
Louis, MO) were added to 500 mls of stock solution and stirred with a kitchen mixer
until a gel like consistency was attained. A final pH of 4.5 was confirmed with the pH
25
meter. The bracketed teeth were completely submerged in the demineralizing solution
and stored at 37 ۫ C for 10 days. In groups 2 and 3, the teeth were bonded in random
order similarly to group 1 with the omission of the two millimeter by seven millimeter
piece of protective barrier tape since these groups were not to undergo demineralization
treatment. Group 2 was stored in distilled water at 37 ۫ C for 10 days. Group 3 was stored
in distilled water at 37 ۫ C for 24 hours.
At the conclusion of the respective treatment times, the teeth in all three groups
were mounted in acrylic cylinders and positioned in the Instron testing machine. A shear
force was applied at the bracket/tooth interface using a sharp chisel-shaped rod attached
to the upper platen of the universal testing machine (Model 5565, Instron, Norwood, MA)
at a crosshead speed of 0.5mm per minute until bracket failure. The bracket bond
strengths (N) were recorded for all teeth and after dividing by the cross-sectional area of
the bracket base, the bond strength in MPa was calculated. Each tooth was then
inspected under magnification and the mode of failure recorded.
The teeth in group 1 were then removed from the acrylic cylinders and sectioned
buccolingually through the bonding sites using an Isomet low speed saw (Model 1180,
Buehler, Lake Bluff, IL). The sections were stained with methylene blue dye so that the
enamel lesions could be accurately observed and measured at 300x using a digital
microscope (Keyence, VHX-600 series, Woodcliff Lake, NJ). At a distance of 0.5 mm
from the occlusal aspect of where the bracket was bonded, the depth of each enamel
lesion was measured in µm.
26
Statistical Analysis
A two-way ANOVA analysis was used to compare the shear bond strengths of the
resin groups and treatment groups. A one factor ANOVA analysis was also used to
compare the demineralization depth between the two resin groups. The modes of failure
were analyzed using a Chi-square test. Statistical significance for all tests was
determined at p<.05. All analysis was done using SAS version 9.1 (Cary, NC).
RESULTS
The mean enamel lesion depths from group 1 are listed in Table 2. The mean
lesion depth of enamel bonded with Aegis Ortho at a distance of .5mm from the bracket
base was statistically less than the mean lesion depth of enamel bonded with Transbond
XT (p < .0006). Due to enamel fracture during the shearing of brackets in the Transbond
XT group, five samples were unable to be sectioned and lesion depth accurately
measured.
Table 2
Mean lesion depths (µm)
Resin Group
Mean Lesion Depth (ìm)
Std Dev.
Aegis Ortho (n=15) 51.80 ±13.88 P < .0006Transbond XT (n=10) 73.25 ±12.23
27
There was a statistically significant difference in the mean shear bond strengths
between brackets bonded with Aegis Ortho and brackets bonded with Transbond XT
(Table 3). The Aegis Ortho bonds failed at statistically lower SBS values in every
treatment group than the Transbond XT bonds.
Table 3 Shear Bond Strengths (MPa) Resin Group
Tx Group 1: 10 Day Demineralization (MPa ± Std Dev)
Tx Group 2: 10 Day H2O Storage
(MPa ± Std Dev)
Tx Group 3: 24 Hour H2O Storage
(MPa ± Std Dev)
Aegis Ortho 5.26 ± 3.61 4.64 ± 2.21 6.52 ± 1.68
Transbond XT 17.09 ± 6.05 21.21 ± 7.32 17.28 ± 5.63P‐value < .001 < .001 < .001 There were no statistically significant differences in the bracket SBS values
between the treatment groups in teeth bonded with Aegis Ortho. There was a statistically
significant difference in bracket SBS values between the treatment groups in teeth
bonded with Transbond XT with treatment group 2 SBS producing statistically higher
values than treatment groups 1 or 3 (p-values <.024 and <.031 respectively).
There was a statistically significant difference in the mode of failure between the
two resin groups (p < .0001). The Aegis Ortho group failed 93.18% at the resin/enamel
interface with zero enamel fractures. The Transbond XT group failed 33.33% at the
resin/enamel interface, 31.11% at the resin/bracket interface, and 35.56% within the
enamel.
28
Table 4
Mode of Failure
% failure at resin/enamel
% failure at resin/bracket
% failure within enamel
Aegis Ortho 93.18 6.82 0Transbond XT 33.33 31.11 35.56
DISCUSSION
White spot lesions adjacent to orthodontic brackets are a major concern to the
orthodontist and the patient. These lesions can progress to frank cavitations requiring
dental restorations if left untreated. WSLs naturally regress in size after orthodontic
appliances are removed, but the enamel will never recover its original translucency.43
Therefore, it is most important to prevent WSLs rather than attempt to treat them after
they occur. Unfortunately most currently available methods of preventing WSLs require
patient compliance. Patients with WSLs have proven to be non-compliant and are
unlikely to comply with further preventive methods. Orthodontists therefore seek
methods of preventing WSLs that do not require patient compliance.
Amorphous calcium phosphate (ACP) has recently been incorporated as a filler
into a composite resin matrix. This product is marketed as the orthodontic adhesive
Aegis Ortho (Harry J. Bosworth Co., Skokie, Ill). There have been no referred
publications reporting the effectiveness of Aegis Ortho in preventing enamel
demineralization adjacent to orthodontic brackets. However previous studies have
shown that ACP filled composite resins have the ability to remineralize artificially
created enamel lesions. Skrtic et al. 31 created artificial enamel lesions and covered them
29
with an experimental ACP composite. After cycling them through a
demineralization/remineralization sequence, measurements showed that 38% of lost
mineral was regained in lesions under the ACP composite. Langhorst et al. 32 created
artificial enamel lesions and covered them with an ACP composite. The teeth were then
cycled through a demineralizaiton/remineralization protocol for 1 month. Quantitative
digital image analysis of matched areas from contact microradiographs taken before and
after treatment indicated higher mineral recovery with ACP composites compared to a
commercial orthodontic F-releasing cement (14.4% vs. 4.3%, respectively), while control
specimens showed an average of 55.4% further demineralization. While these studies
showed positive results, they measure mineral recovery of previously created enamel
lesions that are covered with an ACP composite. This is not what happens in an
orthodontic clinical scenario where the demineralization occurs adjacent to the composite
and the starting point is sound enamel. Clinically the ACP first leaches out of the
composite matrix into the plaque biofilm where it then diffuses into the tooth to form
HAP. In my study, sound enamel adjacent to orthodontic brackets was subjected to 240
continuous hours of demineralization solution at pH 4.5 with no cycling protocol. The
lesion depth was measured 0.5mm from the composite pad which is clinically where most
WSLs occur. The results showed that human molar teeth bonded with Aegis Ortho had a
29.82% reduction in demineralization depth compared to teeth bonded with Transbond
XT (p = .0006). The mean lesion depth of enamel bonded with Aegis Ortho was
51.80µm while the mean lesion depth of enamel bonded with Transbond XT was
73.25µm. This study was not designed to mimic the oral environment, but to detect if
Aegis Ortho could reduce demineralization on adjacent enamel under continuous acid
30
attack. Therefore, the clinical effect of Aegis Ortho in the present study could be
underestimated due to the conditions of the study.
Glass fillers are added to composite resins to increase strength, decrease
polymerization shrinkage, add esthetic properties, and provide a coefficient of thermal
expansion similar to tooth structure. A silane coupling agent is used to chemically bond
the organic resin and the inorganic filler. Poor or no bonding of the filler to the resin
matrix causes the filler to act as porosity in the composite and lowers fracture toughness
and flexural strength of the composite resin.44 The primary purpose of the ACP filler in
Aegis Ortho is to leach out of the polymer matrix so it can provide calcium and
phosphate for enamel remineralization. This makes an ACP filled composite inherently
weaker than conventional glass filled composites. Although many improvements have
been made in the mechanical properties of ACP filled composites leading to the
introduction of Aegis Ortho, initial bond studies of Aegis Ortho showed unfavorable
results compared to conventional composites.39,40 The bonding protocol for Aegis Ortho
during these studies did not include the use of a primer. A self etching primer (SEP),
Aqua Bond (Harry J. Bosworth Co., Skokie, Ill), was added to the bonding protocol of
Aegis Ortho since these study results were published. Unpublished data from Bosworth
Company reported an average bracket shear bond strength value after a two hour water
storage at 37 ۫C that was statistically similar to Transbond XT (3M Unitek) (9.8 MPa vs
10.2 MPa; p>0.05). These results were not confirmed by the results of the present study.
The mean SBS values of Aegis Ortho in all treatment groups were significantly lower
than the mean SBS values of Transbond XT (Table 3). Group 3 (24 hour water storage)
exhibited the most similar test conditions to the previous studies by Dunn and Foster.
31
The 24 hour mean SBS for Aegis Ortho in the present study was 6.5 MPa which was
greater than Dunn’s 1.2 MPa for Aegis Ortho implying that the Aqua Bond primer in the
present study improved the bond numbers. This conflicts with the mean bracket SBS
reported by Foster with Aegis Ortho of 6.6 MPa which implies no additional benefit from
the Aqua Bond. Erickson et al (2008) stated that the acidic monomers in self-etching
primers (SEP) can remove some of the etched enamel structure created by the
conventional etch, and the scrubbing action can also damage the etched enamel rods
resulting in shallower resin tags and weaker bond strengths. SEM images taken at 3000x
of the different etched surfaces in the present study show a more ordered arrangement of
enamel rods in the conventionally etched enamel, whereas the enamel rods appear to be
less orderly in the pre-etch, SEP enamel. This could account for some of the reduced
bond strength of Aegis Ortho. Perhaps Bosworth Company should use a conventional
priming agent as an alternative to the SEP. SEM images taken at 50x and 500x show
cracks in the composite surface of polished Aegis Ortho discs where the filler particles
disrupt the polymer matrix. This results in less available bonding surface and provides
diffusion channels for deeper penetration of water and bacterial enzymes that are known
to degrade the polymeric chain integrity.45 The reduced bonding area available, diffusion
channels for greater water sorption, and etch pattern all contribute to the low SBS values
and the mode of bond failure being 93.2% at the resin/enamel interface.
ACP has been marketed as a “smart” material because it produced increased
levels of calcium and phosphate ions at lower pH levels.33,34 In the present study, there
was no statistical difference in the mean SBS values of Aegis Ortho submerged in
demineralization solution at pH 4.5 for 10 days (group 1) compared to Aegis Ortho stored
32
in water for 10 days (group 2). This suggests that the increased release of ACP filler at
lower pH has no effect on the bond strength of the material. This could be due to the
small amount of exposed surface area of composite around the perimeter of an
orthodontic bracket compared to the surface area of composite under a bracket bonded to
the enamel surface. Perhaps more time is needed see the effects of lost filler on bond
strengths.
Clinical bond failures of orthodontic brackets result in emergency office visits,
extend the overall treatment time, and add to the expense of the orthodontic treatment.
Tavas et al. 41 reported that shear/peel strengths of direct bonded adhesives should
develop 5.9 MPa within 24 hours. Reynolds 42 determined that the minimum bond
strength values in direct orthodontic bonding systems that are clinically acceptable are
5.9-7.8 MPa. While the mean SBS of the Aegis Ortho in groups 1 and 2 were slightly
below these numbers, the group 3 values of Aegis Ortho were within the minimally
acceptable range. Linklater et al. 46 studied patterns of bond failures in vivo and
determined that maxillary anterior teeth had the least amount of bond failures at around
2%. Since the maxillary anterior teeth comprise the esthetic zone where WSLs have the
largest negative esthetic impact, orthodontists should consider using Aegis Ortho in the
maxillary anterior region despite its lower shear bond strengths especially in higher caries
risk patients.
CONCLUSIONS
Under the conditions of the present study, the following conclusions are made:
33
1. Aegis Ortho reduces enamel lesion depth by 29.82% compared to a traditional
composite resin bracket adhesive when subjected to an acid challenge.
2. The mean shear bond strength associated with Aegis Ortho was significantly
lower than the traditional composite resin control.
3. The increased release of ACP-filler at low pH does not significantly reduce the
mean shear bond strength of the material.
4. Orthodontists should consider bonding maxillary anterior teeth with Aegis Ortho
for increased WSL protection on at risk patients where compliance issues are
anticipated.
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17. Hu, W., & Featherstone, J. (2005). Prevention of enamel demineralization: An in-vitro study using light-cured filled sealant. American Journal of Orthodontics and Dentofacial Orthopedics , 128 (5), 592-600. 18. Soliman, M., Bishara, S. E., Wefel, J., Heilman, J., Warren, J. (2006). Fluoride release from an orthodontic sealant and its clinical implication. Angle Orthodontist , 76 (2), 282-288. 19. Buren, J. L., Staley, R. N., Wefel, J., & Qian, F. (2008). Inhibition of enamel demineralization by an enamel sealant, Pro Seal: An in-vitro study. American Journal of Orthodontics and Dentofacial Orthopedics , 133 (4), S88-S94. 20. Gorton, J., Featherstone, J. (2003). In vivo inhibition of demineralization around orthodontic brackets. American Journal of Orthodontics and Dentofacial Orthopedics , 123 (1), 10-14. 21. Sudjalim, T. R., Woods, M. G., Manton, D. J., & Reynolds, E. C. (2007). Prevention of demineralization around orthodontic brackets in vitro. American Journal of Orthodontics and Dentofacial Orthopedics , 131 (6), 705e1-705e9. 22. Underwood, M. L., Rawis, H. R., Zimmerman, B. F. (1989). Clinical evaluation of a fluoride-exchanging resin as an orthodontic adhesive. American Journal of Orthodontics and Dentofacial Orthopedics , 96 (2), 93-99. 23. Arneberg, P., Giertsen, E., & Emberland, H. (1997). Intra-oral variations in total plaque fluoride related to plaque pH. A study in orthodontic patients. Caries Research , 31, 451-456. 24. Ogaard, B. (2008). White Spot Lesions During Orthodontic Treatment: Mechanisms and Fluoride Preventice Aspects. Seminars in Orthodontics , 14 (3), 183-193. 25. Skrtic, D., Antonucci, J. M., & Eanes, E. D. (2003). Amorphous Calcium Phosphate-Based Bioactive Polymeric Composites for Mineralized Tissue Regeneration. Journal of Research of the National Institute of Standards and Technology , 108 (3), 167-182. 26. Reynolds, E., Cain, C., Webber, E., Black, C., Riley, P., Johnson, I., et al. (1995). Anticariogenicity of Calcium Phosphate Complexes of Tryptic Casein Phosphopeptides in the Rat. Journal of Dental Research , 74, 1272-1279. 27. Reynolds, E. (1997). Remineralizaiton of Enamel Subsurface Lesions by Casein Phosphopeptide-stabilized Calcium Phosphate Solutions. Journal of Dental Research , 76 (9), 1587-1595. 28. Reynolds, E. (1998). Anticariogenic complexes of amorphous calcium phosphate stabilized by casein phosphopeptides. A review. Spec Care Dentist , 18 (1), 8-16.
36
29. Shen, P., Cai, F., Nowicki, A., Vincent, J., & Reynolds, E. (2001). Remineralization of Enamel Subsurface Lesions by Sugar-free Chewing Gum Containing Casein Phosphopeptide-Amorphous Calcium Phospate. Journal of Dental Research , 80 (12), 2066-2070. 30. Reynolds, E., Cai, F., Shen, P., & Walker, G. (2003). Retention in Plaque and Remineralization of Enamel Lesions by Various Forms of Calcium in a Mouthrinse or Sugar-free Chewing Gum. Journal of Dental Research , 82 (3), 206-211. 31. Skrtic, D., Hailer, A., Takagi, S., Antonucci, J., & Eanes, E. (1996). Quantitative Assessment of the Efficacy of Amorphous Calcium Phosphate/Methacrylate Composites in Remineralizing Caries-like Lesions Artificially Produced in Bovine Enamel. Journal of Dental Research , 75 (9), 1679-1686. 32. Langhorst, S., O'Donnell, J., & Skrtic, D. (2009). In vitro remineralization of enamel by polymeric amorphous calcium phosphate composite: Quantitative microradiographic study. Dental Materials , 25 (7), 884-891. 33. Xu, H. H., Weir, M. D., & Sun, L. (2008). Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties. Dental Materials , doi:10.1016/j.dental.2008.10.009. 34. Regnault, W. F., Icenogle, T. B., Antonucci, J. M., & Skrtic, D. (2007). Amorphous calcium phosphate/urethane methacrylate resin composites. Journal of Materials Science: Materials in Medicine , doi:10.1007/s10856-007-3178-3. 35. Skrtic, D., & Antonucci, J. (2007). Dental Composites Based on Amorphous Calcium Phosphate - Resin Composition/Physiochemical Properties Study. J Biomater Appl , 21 (4), 375-393. 36. Park, M. S., Eanes, E. D., Antonucci, J. M., & Skrtic, D. (1998). Mechanical properties of bioactive amorphous calcium phosphate/methacrylate composites. Dental Materials , 14, 137-141. 37. Skrtic, D., Antonucci, J. M., & Eanes, E. D. (1996). Improved properties of amorphous calcium phosphate fillers in remineralizing resin composites. Dental Materials , 12 (5), 295-301. 38. Skrtic, D., Antonucci, J. M., Eanes, E. D., Eichmiller, F. C., & Schumacher, G. E. (2000). Physiochemical Evaluation of Bioactive Polymeric Composites Based on Hybrid Amorphous Calcium Phosphates. J. Biomed. Mat. Res., Applied Biomaterials , 53 (4), 381-391. 39. Dunn, W. (2007). Shear bond strength of an amorphous calcium-phosphate-containing orthodontic resin cement. American Journal of Orthodontics and Dentofacial Orthopedics , 131 (2), 243-247.
37
40. Foster, J. A., Berzins, D. W., & Bradley, T. G. (2008). Bond Strength of an Amorphous Calcium Phosphate-Containing Orthodontic Adhesive. The Angle Orthodontist , 78 (2), 339-344. 41. Tavas, M. A., & Watts, D. C. (1984). A visible light activated direct bonding material: an in vitro comparative study. British Journal of Orthodontics , 11, 33-37. 42. Reynolds, I. R. (1975). A review of direct orthodontic bonding. British Journal of Orthodontics , 2, 171-178. 43. Willmot, D. (2008). White Spot Lesions After Orthodontic Treatment. Seminars in Orthodontics , 14 (3), 209-219. 44. Van Noort, R. (2002). Resin Composites and Polyacid-Modified Resin Composites. In Introduction to Dental Materials (2 ed., pp. 96-106). Elsevier Health Sciences. 45. Brantley, W., & Eliades, T. (2001). Orthodontic Materials. New York: Thieme Stuttgart. 46. Linklater, R., & Gordon, P. (2003). Bond failure patterns in vivo. American Journal of Orthodontics and Dentofacial Orthopedics , 123 (5), 534-539.
38
GENERAL CONCLUSIONS
The aim of the present study was to evaluate the shear bond strength of an
ACP filled composite resin designed to provide protection against
demineralization around orthodontic brackets. The study also measured the depth
of enamel demineralization around an orthodontic bracket when subjected to a
continuous acid assault. The results showed that the enamel lesion depth adjacent
to the ACP filled resin was reduced by 29.82% over the lesion depth adjacent to a
traditional composite resin bracket adhesive. The mean shear bond strength
associated with Aegis Ortho was significantly lower than the traditional
composite resin control. The increased release of ACP-filler at low pH does not
significantly reduce the mean shear bond strength of the material. Since bond
failure rates are typically low in the anterior, orthodontists may consider bonding
maxillary anterior teeth with an ACP filled composite resin for increased WSL
protection on at risk patients where compliance issues are anticipated.
39
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44
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