Download Original Manuscript Enamel

Effect of laser etching on bonding effectiveness of
orthodontic brackets to enamel using a universal adhesive
Introduction:
Enamel bonding for orthodontic applications was introduced in 1965 and is considered a
significant milestone in orthodontic treatment. (1) This technique has been widely accepted by
most orthodontists. Development of modern adhesive materials has led to the widespread use of
bonded attachment in fixed appliances. Composite resin is the most popular orthodontic adhesive
because of good bond strength.(2)in the beginning, separate chemical components and several
application steps were needed for priming and bonding.(3)Current advances have focused on the
development of delivery systems that simplify the steps involved. This not only lessens clinical
application time, but also significantly reduces the technique-sensitivity or the risk of making
errors during application or manipulation. (4-6)
In the Self etch strategy; there is no need to apply a preliminary phosphoric acid gel on dental
substrates as dentine demineralization and priming occur simultaneously.(7, 8) A clear
disadvantage of the Self etch protocol is the reduction in enamel bonding effectiveness.(9, 10)
The performance of Self etch adhesives has improved when these systems were applied to
phosphoric acid-treated enamel.(11-13)
Lamper et al evaluated the performance of four different adhesives and concluded that Singlecomponent self-etch adhesives showed the lowest bond strengths, caused limited enamel
damage, and generally left less residual composite on the tooth.(14) yuasa et al studied
The effects of 2 years of storage and 6000 thermocycles on the shear bond strength of two selfetching adhesive systems and stated that self-etch systems produced adequate SBS even after 2
years.(15)in
a
study
conducted
by
traditional orthodontic bracket bonding agent
Isman
et
(Transbond
al,
the shear bond strength
XT)
against
of
a
two self-etch, self-
adhesive systems (Maxcem Elite and Vertise Flow) was evaluated and it was showed that no
significant differences were found between Transbond XT and the self-adhesives applied with
etching,
but
self-etch, self-adhesive bonding systems require
additional
phosphoric
acid
application to achieve comparable SBS values as the traditional orthodontic bonding agent. (16)
Considering the differences in professional judgment regarding the selection of the adhesive
strategy and the number of steps, some manufacturers have released more versatile adhesive
systems that give the dentist the opportunity to decide which adhesive strategy to use: etch-andrinse or self-etch. This new family of dental adhesives is known as “universal” or “multi-mode”
and represents the latest generation of adhesives on the market.(17-19)They are designed under
the “all-in-one” concept of the already existing one-step self-etch adhesives but also incorporate
the versatility of being adaptable to the clinical situation.(20)
Recently laser systems have drawn a lot of attention in dentistry as a new method for surface
treatment. Laser etching was introduced into orthodontic bonding in the 1990s. Initially,
Nd:YAG laser was used to etch the enamel surface. The results of using Nd:YAG laser showed
compromised bonding strength, longer bonding time and more discomfort than conventional acid
etching. Nd:YAG laser is more suitable for soft tissue procedures. Application of Nd:YAG laser
on dental hard tissue is ineffective and also has thermal side effect which can cause discomfort to
the patient and is harmful to dental pulp(21-24). After the introduction of Er:YAG and
Er,Cr:YAG lasers, etching by laser has become more effective. The shear bond strength of tooth
surface etched by Er,Cr:YAG laser is comparable to those prepared by acid and reaches an
adequate level.(25-27)However, some researchers disagree with the above findings(28).
Aside from the bond strength, laser etching is useful when applied in immediate bonding on
surgical exposed teeth without acid etching(29). The calcium-phosphate ratio of the enamel can
be modified after laser irradiation leading to the formation of more stable and acid-proof
compounds. It is similar to the effect of fluoride on enamel.(26, 27, 30, 31)
To the best of our knowledge there is not any study regarding shear bond strength of universal
adhesives in bonding of orthodontic brackets. Therefor the aim of this study is to test a universal
adhesive (scotch bond) to determine its efficacy for use in orthodontic bracket bonding to enamel
surfaces and compare the results to conventional bonding methods. Furthermore we will also
investigate the added effectiveness of laser treatment in the clinical performance of bonding
agents for orthodontic purposes.
Materials and Methods:
The sample
Fifty maxillary premolar teeth with intact buccal surfaces which were extracted for orthodontic
purposes were selected for this study. The teeth were stored in distilled water which was changed
weekly to prevent bacterial growth. The premolar teeth were mounted in self-cure acrylic resins
so that at least 2mm of the buccal surface remained exposed. The enamel was then pumiced,
washed and dried. Subsequently the teeth were divided into 5 groups to be prepared for
orthodontic bracket bonding.
Surface treatment
The 65 teeth will be divided into 5 groups (n=13) each receiving a different surface treatment
prior to bracket bonding. The groups will be as follows:
Group A:
Treatment: Acid etching using 37% phosphoric acid, rinsing with water and drying with air.
Bonding: Transbond XT™ primer
Group B:
Treatment: Treated using an Er,Cr:YSGG laser working at a wavelength of 2780 nm and a power
of 2 W (5.6 J/cm2) with an angle of 90 degrees.
Bonding: Transbond XT™ primer
Group C:
Treatment: Acid etching using 37% phosphoric acid, rinsing with water and drying with air.
Bonding: Scotchbond™ Universal Adhesive
Group D:
Treatment: No surface treatment.
Bonding: Scotchbond™ Universal Adhesive
Group E:
Treatment: Treated using an Er,Cr:YSGG laser working at a wavelength of 2780 nm and a power
of 2 W (5.6 J/cm2) with an angle of 90 degrees.
Bonding: Scotchbond™ Universal Adhesive
Bonding of the orthodontic brackets
All 65 teeth will be bonded using right upper incisor brackets (Mini Master Series; American
Orthodontics, Sheboygan, Wisconsin, USA) with a bracket base area of 8.82 mm2. The light-cure
adhesive system which will be used for bonding of the brackets will be Transbond™ XT (3M
Unitek, Monrovia, California, USA). Before application of the adhesive a thin layer of the same
bonding agent used during surface treatment will be added to the bracket base.
Thermocycling
To recreate the oral environment and fatigue the resin composite the bonded samples will be
stored in 37° C distilled water for a day and then subjected to 3000 cycles between 5 °C and 55
°C with a dwelling time of 30 seconds between each cycle.
Shear bond strength testing
For the shear bond strength testing each sample will be placed in a universal testing machine in a
manner that ensures parallel positioning of the bracket base with the loading rod. Shear load will
be applied to the composite bracket interface at a speed of 0.5 mm/min until fracture. The results
will be recorded in Newtons and subsequently converted to Megapascals.
Adhesive remnant index and SEM evaluation
Following the debonding of the brackets from the composite discs, they will be subjected to
microscopic evaluation (×40) to be categorized according to the adhesive remnant index (ARI)
system based on the amount of adhesive material remaining on the composite discs. One sample
from each group will be selected randomly and sent for SEM evaluation (×1000).
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