Top PDF Factors Affecting the Shear Bond Strength of Orthodontic Brackets – a Review of In Vitro Studies

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.

The caries infiltration product ICON; a new virtually painless method, was introduced in Germany in 2009. This product utilized a special resin to seal and fill demineralized enamel without causing the loss of healthy hard tissue 29 . Icon can be used for the microinvasive treatment of initial carious lesions in the vestibular and approximal regions. The vestibular version is particularly developed for orthodontic patients after removal of braces 29 . To our knowledge, only a few studies have been conducted regarding ICON, and those have shown promising results 30 . Most studies were testing the effect on the orthodontic brackets 31-33 , other studies were investigating using the resin infiltrant for treatment of the incipient carious lesion and white spots development 34,35 .

A previous study showed that addition of QAS to composite resin caused no change in shear bond strength of brackets after one month [8]. This finding was in agreement with our results since we found no significant difference in shear bond strength of the groups containing QAS and the control group. No standard method exists for assessment of bracket bond strength to tooth structure because in the clinical setting, loads applied to brackets are complex and include a mixture of shear and tensile loads, which cannot be well simulated in vitro. However, shear bond strength test is often performed for this purpose [15] and was adopted in the current study as well. The results showed that by an increase in concentration of QAS, no significant reduction occurred in shear bond strength. Several factors affect the bracket bond strength to tooth structure including the type of adhesive, type of bracket, clinician’s expertise and patient’s cooperation [16].

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.

Finally, a large variability is seen in the fracture sites according to ARI index analysis in this study. G2 and G4 showed 70% and 40%, respectively, bond failures located at the enamel- adhesive interface (ARI 0) and 30-50% were having mixed fractures (ARI 1). There was no ARI 2 or ARI 3 score present for G2. This result is similar to previous study.[20] This seems to be a confirmation of the high retention of these bracket bases but there are high chances of enamel damage. Previous studies evaluated the shear bond strength of self-ligating brackets 24 h after immersion in water found higher frequencies of ARI score 3 [37,38]. Other study [31,39] stated that under moisture contamination water and saliva, there is a higher frequency of ARI score 0. In general, ARI results are very subjective and they should be evaluated carefully [40].

Arabia. Approval was taken from institutional review board of Qassim University. The study comprised non- carious, sound maxillary and mandibular premolars extracted for therapeutic orthodontic purposes. Teeth with hypoplastic areas, fluorosis or gross irregularities of the enamel structures were excluded. No pre-treatment with chemical agents such as alcohol, formalin, or hydrogen peroxide, or any other form of bleaching was allowed. The teeth were cleaned of blood and tissue debris and stored under refrigeration at 4°C in artificial saliva solution. The artificial saliva was refreshed daily to avoid bacterial contamination.

Therefore, this method may be able to simulate the clinical setting [3]. However, Mojtahedzadeh et al. [21] showed that the wire loop method resulted in less dispersed SBS data. Since cyclic loading is similar to the blade technique, this method was used in our study. Despite the general assumption that cyclic loading would decrease the SBS [2, 9, 14, 22], the present results showed that SBS was not affected by cycling loading. In most studies in this field, the staircase or up and down method was employed to evaluate the effect of cyclic fatigue on bond strength [2, 9, 14, 22]. This method characterizes the total fatigue life of a material for a predefined number of cycles. The staircase method creates an experimental group for comparison with non- fatigued control group. In the present study, an effort was made to evaluate the effect of masticatory forces on bond strength of brackets to tooth surface in order to simulate intraoral conditions. In fatigue tests, cycles and loads would be applied such that they would increase the possibility of crack formation, and the results are presented as material durability. However, the present study aimed at finding whether intraoral (mastication) forces would affect the SBS of brackets.

The study and evaluation of the adhesive potential of a specific bonding system are complicated, as there are multiple variables that can influence the survival or longevity of the bracket-enamel interphase [1]. The two primary tests used for evaluating the strength of the orthodontic adhesives measure shear and tensile bond strengths. In the shear test, the force is directed parallel to the long axis of the tooth and as closely as possible to the bracket-tooth interface [2-4]. In vitro studies have shown that orthodontic brackets must be able to sustain loads from 5.9 to 7.8 mega-Pascals (MPa) of shear bond strength (SBS) to be considered clinically successful for orthodontic purposes [5].

Studies have examined the physical alteration after bleaching to find a possible explanation for decrease in enamel bond strength caused by bleaching agents. Titley KC et al also suggested that the reduction in bond strength might be related to the presence of residual hydrogen peroxide at or near the enamel surface which interfered with resin attachment and inhibited resin polymerization. (28) There are more studies that have described this effect. (29,85) The loss of calcium and alterations in the organic substance might be important factors to cause a decrease in enamel bond strengths. (37) Rotstein I et al suggested that bleaching agents changed the original ratio between the organic and inorganic components of the tissues and increased their solubility. (41) Also, Bistey T et al reported that at-home and in-office peroxide- containing bleaching agents are capable of causing structural alteration in enamel at low and high concentrations as well. (62) These studies probably explains the reduction in shear bond strength after office bleaching.

Very limited studies have been found to be conducted to evaluate the effect of fluoride and CPP-ACP on the bond strength. Also, studies conducted have shown con- troversial results. In a study conducted by Damon et al. [11] and Bishara et al. [12], the shear bond strength was not affected by various concentrations and methods of application of fluoride. However, the study conducted by Tabrizi and Cakirer [13] concluded that no significant difference was seen between control, CPP-ACP, and CPP-ACP with fluoride group, while fluoride application caused a significant decrease in the tensile bond strength of etch and rinse bonding technique. Kecik et al. [14] compared the effects of CPP-ACP and acidulated phos- phate fluoride on SBS values and found higher SBS values for all test groups. Xiaojun et al. [15] reported higher SBS in the CPP-ACP applied group when light-cure adhesives were used. In a study conducted on demineralized en- amel by Uysal et al. [16], fluoride and CPP-ACP en- hanced the bond strength of the orthodontic brackets compared to the control group in demineralized en- amel. In contradiction to this, Ekizer et al. [17] showed no significant difference in fluoride group and control group, while CPP-ACP enhanced the bond strength of the orthodontic brackets.

The LED can be considered as useful tool for ortho- dontist to save bonding time. The LED light units are cordless, smaller, and lighter with estimated lifetimes of over 10,000 hours, and they do not require a noisy cooling fan. Therefore, it seems that they are a better choice as compared with halogen sources. Further investigation under clinical conditions is suggested to compare the results to previous in vitro studies.

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.

Reynolds 65 suggested that at the minimum, a bond strength of 6-8 MPa would be clinically acceptable. This value is often used as a benchmark in orthodontic bonding studies to enamel and non-tooth surfaces. The use of this minimum value as a reference for in vitro bond strengths has been criticized. 43,66 It has never been tested whether 6-8 MPa in vitro is clinically acceptable. It is known that bond strengths achieved in vitro are approximately 40% higher than that found in vivo. 67 Finnemore 43 recommends that extrapolation of bond strength data and comparison to a minimum reference value should be avoided. Furthermore, comparison of bond strength data between different studies is inappropriate, due to wide variation in methodology. Rather, bond strength data should only be used to assess the relative effectiveness of the adhesives within the study.

Our investigation showed that decontamination consisting of thorough rinsing with air and water, and drying with air can be used successfully on surfaces contaminated with blood or saliva after priming. Our study also concludes that application of primer significantly increases the bond strength of the flowable composites and the bond strength of the flowable composites increases with the filler content. Transbond XTTM adhesive, which is a conventional orthodontic composite, has superior shear bond strength than the flowable composites used in this study. Esthet X Flow, which is micro hybrid restorative flowable composite, exhibited highest bond strength among the flowable composites used in this study. Heliosit Orthodontic, a composite designed for bonding the orthodontic brackets produced the lowest bond strengths among the flowable composites used in this study. But the shear bond strength produced by this composite were above the minimum values recommended for orthodontic bracket bonding. Admira Flow which is a Ormocer, and Restofil N Flow Nano which is a nano hybrid restorative composite, can be used for bonding the orthodontic brackets. Contamination with blood during orthodontic procedures significantly decreases the shear bond strength of the adhesives. The bond failure for both conventional and flowable composites appeared to be same. Clinical management of contaminated bonding surfaces can be recommended as follows: renewed etching and priming is not necessary. Simple decontamination with water air spray and air drying the surface gives sufficient bond strength if contamination occurs after the application of the primer.

of 5 kN, and the data were recorded using computer soft- ware (Nexygen-MT; Lloyd Instruments) as previously mentioned in the evaluation of SSBS. The specimens underwent cyclic loading by means of a monobeveled steel chisel that was attached to the upper movable component of the machine. The load was applied at the base of the bracket in the occlusogingival direction. The load profile was in the form of a wave at a rate of 1 Hz. Compressive shear fatigue test for 5,000 load cycles or until bond failure was determined by testing according to the staircase (up-and-down) method [24,25]. The first speci- men was tested at the approximate value of about 25% of the static shear bond strength previously evaluated [26]. Then, the load was raised by a fixed amount of 20 Newton (N) for the next tested specimen. On the other hand, if the bracket did not survive, i.e., the bond failed at some point during the 5,000 cycles, the load was lowered also by the same fixed amount of 20 N for the next specimen. This procedure of raising the maximum load by 20 N following a test where the orthodontic bond has not failed and low- ering the load by the same fixed amount following a bond failure was continued for each following specimen until all ten specimens in each group were evaluated.

Accordingly, the purpose of the present study is to test the efficacy of indirect bonding compared with conven- tional direct bonding, evaluating the number of bond failures which occurred during treatment; the observation period was 15 months for both groups. The null hypoth- esis of the study was that there is no significant difference in bracket failure rates between the two bonding tech- niques, also when comparing the upper and lower arches and the anterior and posterior segments.

SBS measurement, several factors can influence the results. This in vitro study fails to simulate factors such as intraoral aging of resin composites, PH and temperature fluctua- tion based on individual’s dietary intake and oral hygiene, complex cyclic loading, microbial attack and enzymatic degradation. Pickett et al 50 and Murray and Hobson 51 found

A customised jig was suspended from the crosshead of a universal testing machine (TUE-C- 400, Fine Spavy Associated & Engineers Pvt Ltd, Miraj). A gingivo-occlusal load was applied to the bracket, producing shear force at the bracket-facet interface for all the three groups. A computer, electronically connected with the test machine, recorded the results of each test. Shear bond strengths were measured at a crosshead speed of 0.5mm/min (Figure 5 and 6)

An orthodontic resin must be capable of retaining the brackets firmly bonded to the teeth throughout treatment, resisting masticatory forces and those generated by orthodontic mechanics [11] [12]. However, it is important for orthodontists to know the properties and technique used with materials, in order to prevent bond eventual failures that may lead to bracket debonding, causing loss of efficiency in tooth movement, in addition to time and economic loss to the orthodontist. The present results show that all resin presented bond strength to enamel above the acceptable values for the use in cases of orthodontic bracket bonding. Also, the current results rein- force the idea of the individuality of clinical cases.

control 14 . Nanoparticles are clusters of atoms in the size range of 1-100 nm. Nano as a word means one-billionth of a physical quantity. Nanoscale materials have very different new properties which differ from materials in molecular form. Nanomaterials have a much greater surface area to volume ratio than their conventional forms 15 . Recent studies have demonstrated that specially formulated metal oxide nanoparticles have good antibacterial activity, and antimicrobial formulations comprising of nanoparticles could be effective bactericidal materials 16 . The nanoparticles are highly reactive, as it binds to tissue proteins and brings structural changes in the bacterial cell wall and nuclear membrane, leading to cell distortion and death. It is believed that interaction with the three main components of bacterial cells produce the bactericidal effect: the peptidoglycan cell wall and plasma membrane, bacterial DNA, and bacterial proteins, especially enzymes involved in vital cellular processes such as the electron transport chain 17 .The nanoparticles antibacterial property is induction of intracellular reactive oxygen species like hydrogen peroxide, a strong oxidizing agent harmful to bacterial cells 18 .