RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,
BANGALORE, KARNATAKA
ANNEXURE - II
2010
PROFORMA FOR THE REGISTRATION
OF
SUBJECT FOR DISSERTATION
BY:
Dr. SHWETA ASWAL
Postgraduate Student
DEPARTMENT OF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS
Krishnadevaraya College of Dental Sciences and Hospital, Bangalore – 562 157
RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, BANGALORE, KARNATAKA
ANNEXURE-II
Proforma For Registration Of Subject For Dissertation
01 / NAME OF THE CANDIDATE AND ADDRESS / Dr. Aswal ShwetaPostgraduate student in Orthodontics
Krishnadevaraya College Of Dental Sciences,Krishnadevaraya nagar,
via Yelahanka Hunasamaranahalli
Bangalore- 562157
02. / Name of the institution / Krishnadevaraya College Of Dental Sciences & Hospital, Bangalore
03. / Course of study & Subject / Master Of Dental Surgery In Orthodontics And Dentofacial Orthopaedics
04. / Date of admission / 26-05-2010
05. / Title of topic / “Effect of early orthodontic force on shear bond strength of orthodontic brackets bonded with different adhesive systems. – an invitro study”
6. Brief resume of the intended work
6.1: Need for the study:
In clinical orthodontic practice , bonding of the brackets and placement of arch wires might be done in the same visit. Hence force could be applied to the bracket within the first hour after bonding , and it could have an adverse effect on bond strength.
Therefore polymerization of the adhesive should reach a minimum value to enable the adhesive to resist bonding failure when tying in the initial arch wire.
The purpose of this study is to evaluate the effect of applying early orthodontic force on the shear bond strength of orthodontic brackets bonded with different adhesive systems.
6.2:Review of literature
A study was conducted to evaluate the effect of applying early orthodontic force on the shear bond strength (SBS) of orthodontic brackets bonded with 4 adhesive systems. Eighty stainless steel brackets were bonded to the enamel surfaces of extracted premolars with 4 adhesive systems.
For each adhesive,10 brackets were bonded without application of force (groups 1, 3, 5, and 7), and another 10 were subjected to a 120-g force with a coil spring (groups 2, 4, 6, and 8). This force was applied 30 minutes after bonding and maintained for 24 hours.
Groups 1 and 2 had Rely-a-bond primer and Rely-a-bond adhesive. Groups 3 and 4 had Transbond XT primer and Transbond XT adhesive. Groups 5 and 6 had Transbond Plus Self Etching Primer and Transbond XT adhesive . Groups 7 and 8 had Rely X unicem bonding system. After thermocycling, SBS testing was performed by using a universal testing machine.Application of force yielded nonsignificant reductions in SBS for all adhesives. For all studied adhesive systems, orthodontic force up to 120 g can be applied within the first hour after bonding with no deleterious effects on bond strength1.
A study performed evaluated the effect of loading bonded brackets for 2 weeks prior to measuring shear debonding force in vitro, and compared the results with in vivo bond failure rates for two groups of patients whose brackets were loaded by the archwire either immediately after bonding, or not less than 1 week later.
Shear testing and survival analysis indicated in vitro loading prior to testing had no significant effect on the shear debonding force.
When the in vivo data were studied there was no significant difference in the rate of bond failure between those patients whose archwires were placed at the time of fitting the appliance, and those whose archwires were placed no less than 1 week after bracket placement2
The study addressed the question of whether shear and tensile loads applied 15 minutes after bonding metal brackets to enamel affected the shear/peel bond strength of the adhesive.
Ninety standard 0.022-inch stainless steel edgewise premolar mesh-backed brackets were bonded using a no-mix chemical-cured adhesive to 90 teeth, which had been prepared in a standardized manner.
After 15 minutes three groups of 30 teeth were subjected to the following regimes: no applied load, tensile static load of 0.77 N (78 g), and shear static load of 0.77 N. After 14 days storage in 100 per cent relative humidity at 370 C, the shear/peel strength of the adhesive bond was measured using a purpose built jig mounted on a universal testing machine. Shear/peel bond strengths were analysed using Weibull statistics.
The findings indicate that static loads (such as tying in of archwires) can be placed on brackets 15 minutes after cementation, without a clinically significant reduction in bond strength of the tested adhesive3.
A study investigated the rate of bond strength development for orthodontic adhesives in bracket bonding. Four orthodontic adhesive systems were examined.
Bovine incisors were mounted in self-curing acrylic resin, and the facial surfaces were wet-ground to expose flat enamel. Orthodontic brackets were bonded according to the manufacturers’ instructions.
Shear bond strengths were measured after storage in water for 5, 10, and 60 minutes, and 24 hours. Differences between bond strengths at 24 hours and the other test periods were statistically analyzed. All materials tested had the highest bond strengths at 24 hours, and bond strength increased with storage time. The earliest time point at which there was no significant difference in bond strength compared with that at 24 hours was defined as the initial stable time.
Differences in this value might have clinical implications for the assessment of orthodontic adhesives, which can incur high stresses immediately after placement. The rate of development of enamel bond strength must be considered to ensure sufficient maturation of orthodontic adhesives before functional loading4.
A study conducted compared the effects of time on the shear bond strength of a resin reinforced glass ionomer and a composite adhesive system specifically (1) within half an hour after bonding the bracket to the tooth and (2) at least 24 hours from the time of bonding when the adhesive has achieved most of its bond strength.
Ninety-one freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into four groups: Group I, glass ionomer adhesive debonded within 30 minutes from initial bonding; Group II, glass ionomer adhesive debonded after 24 hours immersion in deionized water at 37°C; Group III, composite adhesive debonded within 30 minutes from initial bonding; Group IV, composite adhesive debonded after 24 hours immersion in deionized water at 37°C.
In general, the shear bond strengths were significantly greater in the 2 groups debonded after 24 hours. The present findings indicated that the resin reinforced glass ionomer adhesive has a significantly lower initial bond strength but increased more than 20-fold within 24 hours.
In comparison, the composite adhesive has a significantly larger initial bond strength that doubled within 24 hours. The clinician needs to take these properties into consideration when ligating the initial arch wires5.
6.3: Objectives
· To evaluate the effect of applying a continuous orthodontic force for 24 hours (30 mins after bonding ) on the shear bond strength of orthodontic brackets bonded with 4 adhesive systems.
· The amount of the adhesive on the enamel surface is assessed by using the adhesive remnant index (A R I)
7: METHOD AND METHODOLOGY
7.1:Materials
1. Chemical cured UNITETM primer and adhesive
2. Light cured transbond XT primer and adhesive
3. Light cured fuji orthod LC GIC
4. Light cured Biodinamica(Biofix) flowable composite
5. Standard Edgewise brackets
6. Closed coil spring
7. Force gauge
Inclusion criteria:
1. 80 extracted premolars (from patients requiring orthodontic treatment and advised for extraction of premolars).
Exclusion criteria:
1. Decayed teeth indicated for extraction.
2. Malformed teeth are not included.
3. Supernumerary teeth which are extracted as a part of orthodontic treatment are not included for the study.
4. Fluorosed or mottled teeth are not included for the study
7.2: Method of collection of data:
Eighty freshly extracted maxillary first premolars are collected, cleaned, and stored in a 0.1% aqueous thymol solution. They are embedded in autopolymerizing acrylic resin poured in metal rings with the buccal surface up. The teeth are cleaned and then polished with pumice and rubber cups.
A hook made of 0.9-mm stainless steel round wire is fixed in the acrylic toward the apex of the teeth. Standard edgewise metal orthodontic brackets are used in this study with an average base area of 0.0184 in2 (11.85 mm2).
The teeth are divided randomly into 8 equal groups of 10 premolars each. The brackets are bonded to the teeth by using 1 of 4 adhesive systems.
In groups 1 and 2, a coat of liquid UniteTM primer is applied on the etched enamel surface . UniteTM adhesive is applied to the base of the bracket and pressed firmly onto the tooth. Excess adhesive is removed around the base of the bracket before setting.
In groups 3 and 4, thin coat of Transbond XT primer is applied on the etched enamel. Transbond XT adhesive paste is applied to the base of the bracket and pressed firmly onto the tooth. Excess adhesive is removed around the base of the bracket, and the adhesive is light cured .
In groups 5 and 6, the enamel is treated with biodinamic ( biofix ) flowable composite and light cured.
In groups 7 and 8, the fuji orthod LC GIC is applied on bracket and light cured.
After bonding, the specimens are allowed to bench set for 30 minutes. In groups 2, 4, 6, and 8, a 120-g force is applied to the bonded brackets with a closed titanium coil spring. One end of the coil spring is ligated to the bracket, and the other end is stretched and ligated to the metal hook until the desired force is reached according to the force gauge.
After preparation, all specimens are stored in distilled water at 370 ± 10 for 24 hours. Before testing bond strength, all specimens are thermocycled 500 times between 2 water baths at 50C and 550C with a dwell time of 30 seconds in each bath. SBS testing is carried out for all groups with a universal testing machine (instron).
.
The specimens are fixed horizontally in a specially designed steel base anchored to the fixed member of the testing machine. A knife edged steel rod is fixed to the movable upper member of the machine. The specimens are subjected to a shear load at a crosshead speed of 2 mm per minute until failure.
The load is applied under the incisal wings of each bonded bracket and parallel to the long axis of each mounted tooth. The load required to dislodge each bracket is recorded in newtons, and SBS is calculated in megapascals by dividing the load by the cross-sectional area of the bracket base.
After debonding, the teeth and brackets are examined under 10-times magnification. The amount of the adhesive on the enamel surface of the teeth is assessed by using the adhesive remnant index (ARI).
Mean SBS values and standard deviations are calculated for all groups.
7.3: Does the study require any investigations or interventions to be conducted on
Patients or other humans or animals?
NO.
Has ethical clearance been obtained in your institution in case of 7.3?
Not applicable
8.List of references:
1. Yasser Lofty Abdelnaby, Essam El Saeid Al Wakeel.effect Of early orthodontic force on shear bond strength of orthodontic brackets Bonded with different adhesive systems.Am J Orthod Dentofacial Orthop 2010;138:206-14
2. Ireland AJ, Sherriff M. Effect of timing of archwire placement on of in vivo bond failure. Br J Orthod 1997;24:243-5.
3. Ching E, Cook PA, Bubb NL,Wood DJ. Effect of early static loading on the in vitro shear/peel bond strength of a ‘no mix’ orthodontic adhesive. Eur J Orthod 2000;22:555-9.
4. Yamamoto A, Yoshida T, Tsubota K, Takamizawa T, Kurokawa H, Miyazaki M. Orthodontic bracket bonding: enamel bond strength vs time. Am J Orthod Dentofacial Orthop 2006;130:435.e1-6.
5. Bishara SE, VonWald L, Olsen ME, Laffoon JF. Effect of time on the shear bond strength of glass ionomer and composite orthodontic adhesives. Am J Orthod Dentofacial Orthop 1999;116:616-20.