Top PDF Effect of remineralizing agents on bond strength of orthodontic brackets: an in vitro study

One hundred and twenty-six extracted human premolars (66 maxillary premolars and 60 mandibular premolars) were collected from the Oral and Maxillofacial Surgery Department, S.M.B.T. Dental College and Hospital, Sangamner, India. The teeth extracted were from the patients whose treatment plan needed orthodontic extrac- tions and were collected with the informed consent of the patients. The exclusion criteria for selection of the samples were the teeth with caries, cracks, erosion, fluorosis or hypo-calcification, and restored teeth. One hundred twenty teeth were used for SBS testing, and six teeth were used for SEM examination. One hundred twenty selected teeth were randomly divided into three main groups: group A, group B, and group C (n = 40), which were further sub-divided into two groups (n = 20) each, depending on the bonding adhesive used, that is, light cure and chemical cure.

enamel surface as etchant. The enamel surface is then rinsed and dried before applying the adhesive. Self-etching adhesive systems are more recent and their manufacturers have combined the etching and priming steps into one step to decrease the chair time of bonding procedure [7]. These systems are less technique sensitive than total-etch systems due to the necessity of proper moisture control in the latter [8]. The etching pattern in self-etch bonding systems is similar to that in total-etch systems and provides acceptable bond strength [9,10]. However, during debonding procedures, self- etch bonding agents are less likely to cause enamel fracture [11]. Due to their periodic nature and creating fatigue, masticatory forces can affect the bond strength and/or mode of failure of bonded brackets, even when their magnitude is less than the bond strength [1-3]. Since there is limited understanding about the effects of cyclic loads on bond strength and mode of failure of bonded brackets, this study aimed to evaluate and compare the effect of cyclic loading on shear bond strength (SBS) of metal brackets bonded to enamel surfaces using total-etch and self-etch bonding systems.

In addition to fluoride, a casein phosphopeptide- amorphous calcium phosphate (CPP-ACP) and fluoride- containing-CPP-ACP pastes have also been recommended for caries prevention and enamel remineralization [16-18]. It involves the incorporation of the nano-complexes into dental plaque and onto the tooth surface, thereby acting as a calcium and phosphate reservoir [16]. Topically administered CPP-ACP buffers free calcium and phosphate ion activity, maintaining a state of supersaturation with respect to tooth enamel which in turn helps in preventing demineralization and facilitates remineralization [19]. Therefore, the application of CPP-ACP preparations for prevention and treatment of initial caries lesions in orthodontics has been projected [16,20,21]. However, similar to fluoride, enamel treated with topical application of CPP-ACP has been shown to be more resistant to subsequent acid-etching [20], and consequently may lead to brackets failure. Contradicting results have been reported recently concerning the effects of CPP-ACP preparations on the bond strength of orthodontic brackets. Some studies showed significant reduction in bond strength values when CPP-ACP agents were applied before acid-etching [22,23]. However, other studies revealed that the topical application of CPP-ACP agents to enamel surfaces before acid-etching did not harmfully influence the bracket bond strength [12,24-27]. Conversely, significant increase in shear bond strength was reported after application of CPP-ACP before acid-etching process [28].

Richard et al in 1988 12 , evaluated the bond strength and failure location between indirect bonding and direct bonding techniques by bonding orthodontic brackets having foil-mesh bonding pads on extracted human premolars. In indirect bonding technique, one part of the unfilled resin was applied to the teeth and the other part to the composite which was already bonded to the brackets, and the silicone positioner with brackets was then placed onto the teeth. There were marginal voids in two-thirds of indirect bonds among which one third were left defective. Direct, void-free indirect and sealed indirect bonds showed no significant difference in strength whereas indirect bonds with voids were only half as strong indicating that sealing around the brackets immediately after positioned removal may be required. They concluded that, indirect bonding provides bond strength and easier debonding similar to direct bonding.

In an earlier study conducted by Dunn it was suggested that Orthodontic brackets bonded to teeth with an ACP containing composite material failed at significantly lower forces than brackets bonded to teeth with conventional resin-based composite Ortho- dontic cements. So the question that arises is whether the dis- advantage of low bond strength due to the effect of the material outweighs its advantage as a protector against demineralization. Recent studies however show that CPP-ACP application can cause increased shear bond strength of brackets when light-cured adhesive is used. In this in vitro study the effects of pretreatment of CPP-ACP on Shear bond strength (SBS) of Orthodontic brackets was examined.

Wiltshire et al (2010) mentioned that debonding force is determined from the load drop on the mechanical machine and reported in units of Newtons (N), kilogram (kg), or pounds (lb). Bond strength is defined as the force of debonding divided by the area of the bonded interface measured in units of megapascals (MPa), kilograms per square centimeter (kg/cm 2 ), pounds per square inch (lb/in 2 or psi). It is difficult to estimate the optimal bond strength of an adhesive in the oral environment. This is because the orthodontic brackets are subjected to masticatory forces, which are often a mixture of shear, peel, shear-peel, and tensile force. Rather than focusing on an arbitrary numerical “clinical acceptable bond strength”, they suggested to pay more attention to potential damage to the enamel, especially when the bond strength is too high. They recommended mean bond strength of at least 3 - 4MPa in vitro for minimal reliable clinical bonding. (72)

In this in vitro, experimental study, sample size was calculated to be 12 in each of the four groups for assessment of shear bond strength according to a previous study by Li et al, [9] assuming alpha=0.05, beta=0.2, effect size of 0.57 and standard deviation of 2.5 using one-way ANOVA. The current investigation was approved by the ethics committee of Tehran University of Medical Sciences (IR.TUMS.REC 1395.2909). The QAS compound that was synthesized and used in this study was methacryloxyethyl cetyl dimethyl ammonium chloride, which was added to Transbond XT light-cure adhesive primer (3M Unitek, Monrovia, CA, USA) [10]. Table 1 lists the constituents of primer and composite resin used in this study. A control group of pure primer was also considered.

Scougall–Vilchis et al. [23] compared the influence of four tooth whitening systems on the shear bond strength of orthodontic brackets. The authors found that the use of a whitener containing 38 % hydrogen peroxide did not significantly affect the shear bond strength values. However, the group treated with 10 % carbamide peroxide showed a more significant decrease in strength than the control group (not whitened). These results corroborate those of the present study, as a significant decrease in the values of the negative control group (group 2) with the positive control group (group 1) was observed. These data confirm that home whitening treatment before the completion of bracket bonding negatively influences the bond strength of brackets [3, 7, 24].

Pre-treatment of ceramic surfaces is necessary to obtain sufficient strength to bond orthodontic brackets to all ceramic restorations. Several options have been described which are generally combinations of various mechanical and chemical conditioning methods, such as bonding to glazed ceramic with coupling agent (silane), deglazing the ceramic by roughening the surface (diamond burs; air particle abrasion (APA) with aluminium oxide), and chemical preparation of the ceramic with acids, such as phosphoric, hydrofluoric, acidulated phosphate fluoride. 2 These methods achieved bond

Several chemical methods have also been rec- ommended such as prolonged exposure to phosphoric acid, etching with hydrofluoric acid, silanation, and application of a variety of bonding resins or adhesion promoters. Unlike the tooth enamel, the conventional phosphoric acid etching has no effect on composite restoration surfaces; therefore, creating micromechani- cal retention is difficult in such surfaces [2]. Some studies have shown that hydrofluoric acid etching is effective for producing clinically acceptable bond strength values [3, 9, 12, 14]. Bayram et al. [14] and Viwattanatipa et al. [12] both reported mean shear bond strength values of 7.2 MPa and 13.0 MPa, fol- lowing hydrofluoric acid etching, compared to 2.8 MPa and 6.5 MPa when no surface preparation was performed. However, these values were less than those values achieved following diamond bur preparation or air abrasion. In contrast, Brosh et al. [18] reported that the lowest bond strength was noted following the use of hydrofluoric acid. Hydrofluoric acid is a highly caustic substance and can cause severe damage if it in- advertently contacts the soft tissue. It also increases the chairside time since its use requires placement of a soft tissue barrier. Considering these shortcomings and the controversy regarding its positive effect on bond strength, hydrofluoric acid was not used in our study. It is also believed that silanation is an effective adhe- sion promoter for bonding to porcelain surfaces. How- ever, its efficacy for effective bonding to old compo- site resin restorations is still a matter of debate [19].

Introduction: With the introduction of photosensitive (light- cured) restorative materials in dentistry, various methods were suggested to enhance their polymerization and curing time including layering and the use of more powerful light curing devices. The purpose of this study was to comparatively evalu- ate shear bond strength of stainless steel bracket using conven- tional halogen light and light-emitting diode (LED) curing units. Materials and methods: This in vitro study was carried out in the Department of Orthodontics, Pacific Dental College, Debari, Udaipur, India. Sample included 120 freshly extracted human premolars collected and etched by 37% phosphoric acid, washed and dried, and sealent applied. Then preadjusted edgewise upper premolar stainless steel brackets were applied on the teeth. The teeth were divided into groups of six, each group having 20 teeth. Group I was cured by halogen light curing unit by 10 seconds, group II is cured by LED curing unit by 10 seconds, group III is cured by halogen light curing unit by 20 seconds, group IV is cured by LED curing unit by 20 seconds, group V is cured by halogen light curing unit by 40 seconds, group VI is cured by LED curing unit by 40 seconds.

In view of the questions raised, the aim of this study was to evaluate the in vitro bond strength of orthodontic brackets bonded with: total etch, total etch with previous application of Er:YAG laser and the self-etching adhesive systems after thermal-mechanical cycling, simulating 1 year of treatment. The null hypothesis tested was that there would be no statisti- cally significant difference among the bond strength values when the adhesive systems and laser for orthodontic bracket bonding were used.

of the oral environment which causes pH fluctuations, as well as the complex cyclic loading of chewing, alcohol-containing fluids, temperature variations, and food consistency, all of which make it difficult to specif- ically determine the reasons for failure [6-9]. When con- sidering each of these factors, the true effectiveness and performance of any particular bracket-bonding system in in vitro studies become questionable when different studies are compared. However, if studies are performed under standardized testing conditions, they may gener- ate more reliable information that may be useful in future studies.

For the simulation of dental crowns or veneers, blocks (30 mm × 15 mm × 12 mm) of inCoris TZI zirconium oxide sinter ceramic (Dentsply Sirona, York, USA) were sintered and prepared according to the technique work steps in a dental laboratory. Subsequently, the ceramic blocks (n = 20) were randomized and divided into two groups and fixation of Marquis 022 Roth brackets (Or- tho Technology, Tampa, USA) was done either by using the bonding agent Monobond S (Ivoclar Vivadent) or Monobond Etch & Prime (Ivoclar Vivadent). Detailed in- formation about the bonding agents is given in Table 2. A total of 240 brackets were used in this study, 120 for the group of Monobond S and 120 for the group of Monobond Etch & Prime. In each group, half of the brackets were positioned simulating an orthodontic lev- eling phase using a 0.14-nickel titanium wire of specified length and rubber ligatures. To ensure that the wire re- mains in situ, both ends were fixed (Fig. 1, activated). The other half of the brackets was also placed simulating an orthodontic leveling phase; however, no wire was ac- tivated (Fig. 1, non-activated). Individual positions of brackets, end positions A and B, as well as the middle position C were considered in the statistical evaluation. The application of the materials (indicated in Table 1) and the bonding procedure were performed following the manufacturers recommendations. Afterwards, all specimens were subjected to thermocycling (5° Celsius

bonding composite was considered a potential method to reduce white spot lesions during orthodontic treatment even with the general agreement that it is not simple to predict what might occur when the bonding adhesive is used in the demanding environment of the oral cavity [17–19]. Clinpro, a fluoridated varnish, has been intro- duced to the market and supposed to be most beneficial in a neutral pH environment. Sealants were suggested as protective enamel agents that do not require patient co- operation, but sealants on areas adjacent to brackets are subject to physical challenges as tooth brushing and acid attacks that limit their effect [20, 21]. Recently, resin infil- trants were found to decrease the dissolution of enamel and so limit the appearance of white spot lesions. In an in vitro study to compare a conventional adhesive, a caries infiltrant (ICON), and a combination of both in resisting demineralization, it was found that in both sound enamel and artificial caries lesions, the application of the caries infiltrant was effective in protecting the enamel against dissolution [22].

Debonded brackets were prepared by bonding brackets with composite resin Transbond XT (3 M Unitek), to unetched and slightly wet tooth surfaces. Excess bonding material was removed carefully, and the brackets were light-cured for 40 seconds (10 seconds on each of the 4 sides). The brackets were then debonded from the tooth surface with a bracket removing plier with light pressure [1,2]. A total of 40 debonded brackets were prepared. The recycling of the debonded brackets was done using Sandblaster. The debonded brackets were recycled by subjecting the bracket bases to sandblasting with Aluminum oxide particles of size 50 µm, at 5 bars of pressure for 20-40 seconds until bonding resin was no longer visible to the naked eye and the bracket base appeared frosted. Each sandblasted bracket base was then wiped with acetone on a cotton pledget and dried with an air spray [1,3].

In the current study, using the caries infiltrant (ICON) before bonding did not significantly change the bond strength compared to the other groups, although the bond strength was lower when self-etching primer was used than when phosphoric acid was used for enamel preparation before bonding. This was also observed in the control group; shear bond strength was lower when self-etching primer was used than when phosphoric acid was used, but this difference was statistically insignifi- cant. Previous studies found a significant increase in the shear bond strength of Transbond XT adhesive with phosphoric acid and Transbond XT primer when ICON was used before bonding orthodontic brackets to sound enamel [36] or even to demineralized enamel [37]. The shear bond strength was also increased when Transbond Plus Self Etching Primer was used instead of the conven- tional phosphoric acid etching to sound enamel [36]. The shear bond strengths recorded in this study were sufficient for clinical use in all the six groups presenting different combinations of adhesive systems and enamel protective agents as well as control groups. The average range of bond strength was suggested by Reynolds [38] to be 5.9 to 7.8 MPa for clinical and 4.9 MPa for laboratory performances. In vitro and in vivo stud- ies of SBS are both needed; in vitro measurements of shear bond strength provide useful information about the bonding efficiency of different types of materials, but the actual performance of these materials can only be evaluated in the environment where they were intended to function [39]. Unfortunately, no one variable or combination of variables that can be mea- sured in the laboratory is perfectly predictive of what might occur when the bonding adhesive is used in the demanding environment of the oral cavity [40-42]. Therefore; in vitro studies are mainly important as a preliminary guide to the clinician, while in vivo stud- ies are needed for evidence-based practice.

These results are in agreement with Bayram et al 30 , who reported that the bond strength achieved with Transbond alone, was the lowest compared to bond strengths achieved when additional mechanical surface preparation, such as diamond bur or air abrasion, was used. They reported a bond strength of only 2.77 MPa, which was significantly lower than that found in our study. This difference can be explained by differences in methodology. Bayram et al 30 used a longer duration for thermocycling (1000x), faster crosshead speed (1mm/min) during debonding, and flat composite resin disks rather than anatomically shaped composite resin restorations. These results are also in agreement with Viwattanatipa et al 29 , who found that Plastic Conditioner, when used alone, resulted in the lowest bond strengths compared to other groups in which

The sample was randomly divided into three equal groups. Group A (black) was the control group, and the teeth were etched with 37% phosphoric acid gel (Dentsply, York, PA, USA) for 30 seconds. After that, the teeth were rinsed for 20 seconds and then dried with a stream of air for 20 seconds to appear opaque and frosty. For those teeth that did not show a white frosty appearance, the procedure was repeated. Then the pre- adjusted edgewise brackets (Gemini brackets, 3M Unitek, Monorovia, California, USA) of 3.3mm diameter and mesh base were bonded to the etched enamel using light cure composite resin (Megafill MH, Megadenta) as per the manufacturer's instructions. The brackets were seated and positioned firmly in the middle third of the buccal enamel surface.

Several studies have compared the SBS of orthodontic brackets according to acids used for etching, etchant concen- tration, duration of etching and variation in etching pattern. Olsen et al. (12) compared the effects, on SBS and bracket failure location, of two adhesives and two enamel condition- ers (37% Phosphoric acid and 10% Maleic acid). The results showed no significant difference in the mean SBS among the four groups. Carstensen (13) evaluated the effect of differ- ent Phosphoric acid concentrations on the SBS of brackets bonded to enamel. The three concentrations examined were 37%, 2% and 5%. This study reported that, the mean SBS after etching with 37% acid was significantly higher than that after etching with 2% Phosphoric acid. The effect of etch time and debond interval upon the SBS of metallic or- thodontic brackets was studied by Bin Abdullah and Rock (14). The 3 different etching time studied were 15, 30, or 60 seconds and the 3 different debonding time evaluated were 5 or 15 minutes, or 24 hours. The lowest mean SBS was observed in the group of specimens etched for 15 seconds and debonded after 5 minutes. The possible difference in the SBS to acid etched enamel on the different teeth of the dentition was investigated by Hobson et al. (15). The results showed that tooth type had a significant effect on the SBS, with the greatest mean SBS found on the lower first molar teeth and lowest on the upper first molar teeth. Furthermore, the mean SBS was higher on anterior teeth compared to posterior teeth in the upper arch whereas, it was lower on the anterior teeth compared to posterior teeth in the lower arch.