Effect of loading mode on bond strength of orthodontic brackets bonded with 2 systems

doi:10.1016/j.ajodo.2004.09.020

American Journal of Orthodontics and Dentofacial Orthopedics

Volume 129, Issue 1, January 2006, Pages 60-64

https://doi.org/10.1016/j.ajodo.2004.09.020 Get rights and content

Introduction: A new orthodontic bracket bonding method or material invariably spawns bond strength studies examining the efficacy of the innovation. The primary purpose of this project was to ascertain whether the mode of in-vitro bracket debonding used in a study affects the measured bond strength. The secondary aim was to compare the bond strengths of 2 different bonding systems. Methods: Flattened stainless steel orthodontic brackets were bonded to flattened bovine enamel with a resin composite bonding agent (Transbond XT, 3M Unitek, Monrovia, Calif). The enamel was prepared with traditional acid etching and priming (37% phosphoric acid gel and Transbond XT Primer, 3M Unitek) or a single-step method (Transbond Plus, 3M Unitek) that combined etching and priming. Cement thickness was kept constant, and bonding was done under controlled temperature and humidity. Brackets were debonded in shear-peel, tension, or torsion. Results: When tested in shear-peel mode, traditional etching and priming produced a stronger bond than the single-step self-etch system. When tested in tension, the traditional bond was weaker than the single-step bond, and when tested in torsion, the bond strengths were similar. Conclusions: Bond strength can vary depending on the method of testing. Claims of clinical efficacy might not be valid.

Section snippets

Material and methods

One hundred-fifty bovine incisors free of obvious defects were obtained from the Oral Health Research Institute, Indiana University School of Dentistry. To control bacterial growth, the teeth had been stored in 0.1% thymol solution. The teeth were rinsed thoroughly and stored in room-temperature distilled water. Using a hacksaw, we sectioned the teeth at the cementoenamel junction. Each crown was partially embedded in self-curing acrylic resin (Coe tray plastic, GC America, Alsip, Ill) in an

Results

Under a stereomicroscope, it became apparent that some brackets had been bonded to dentin or hypomineralized areas. Therefore, from the initial 25 specimens in each group, 2 were removed from the shear-peel PE, shear-peel SS, tensile PE, and torque PE groups. One specimen was deleted from the SS torque group.

Summary statistics are given in the Table. These data show that brackets bonded to SS prepared enamel were statistically (P < .00001) weaker in shear-peel than brackets bonded to

Discussion

The data demonstrate the most obfuscating outcome that is possible—the 3 loading modes generate all 3 mutually exclusive outcomes. Neither hypothesis can be accepted. With regard to hypothesis 1, the single-step method produces a weaker joint when tested in shear-peel, stronger in tension, and the same in torsion. Thus, hypothesis 2 can only be accepted for torsion; in shear-peel and tension, the 2 bonding systems result not only in different, but also opposite, relative bond strengths.

It can

Conclusions

When brackets bonded with 2 different systems were debonded with shear-peel load, 1 method exhibited a greater bond strength than the other. The reverse was true when the brackets were debonded in tension, and the bond strengths were the same when tested in torsion. These inconsistencies are intrinsic to the testing protocol, and the specific results are unique to this particular pair of bonding methods. This outcome underscores the necessity for further systematic studies into this phenomenon

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Cited by (31)

Shear bond strength of orthodontic brackets to fluorosed enamel
2014, Revista Portuguesa de Estomatologia, Medicina Dentaria e Cirurgia Maxilofacial
Citation Excerpt :
Regardless of the lower bond strength observed with fluorosed teeth when compared with non‐fluorosed teeth, the mean bracket bond values achieved in all experimental groups were higher than those mentioned above. Nonetheless, it is known that several factors may influence the bond values, such as the mechanical test configurations used.39–41 The lack of uniformity in the methodology of previous publications limits the comparability of the bond values between studies and their extrapolation to clinical behavior.
To evaluate the influence of dental fluorosis and etching time on the shear bond strengths (SBSs) of orthodontic brackets to human enamel.
A total of 48 human maxillary central incisors, extracted for periodontal reasons were used. The sample was divided into three experimental groups (n = 16): group H30 with healthy teeth and group F30 and F60 with fluorosed teeth (Thylstrup and Fejerskov Index scores 3–4). After etching the dental enamel with 35% phosphoric acid for 30 s (groups H30 and F30) or for 60 s (group F60), metal orthodontic brackets were bonded with Transbond XT adhesive system and light cured (1200 mW/cm² for 10 s). The specimens were then thermocycled (5–55 °C, 500 cycles), stored in distilled water (37 °C/7 days), and tested in shear (Instron, 1KN, 1 mm/min). Failure mode was classified, with a stereomicroscope (20× magnification), according to the adhesive remnant index (ARI). SBS data were statistically analyzed with 1‐way ANOVA, followed by Tukey post hoc tests (α = 0.05). Kruskal–Wallis and Mann–Whitney nonparametric tests were used to analyze failure data (α = 0.05).
No statistically significant (p = 0.763) differences were found between F30 and F60, but these groups showed a statistically (p < 0.05) lower bond strength values than H30. The non‐fluorosed group showed a significantly (p < 0.05) higher ARI score than the other groups.
Orthodontic brackets adhesion to enamel is negatively influenced by dental fluorosis. Doubling the etching time in fluorosed teeth was not enough to produce similar results to those observed in the healthy ones.
Avaliar a influência da fluorose e do tempo de condicionamento ácido sobre a resistência adesiva ao corte de brackets ortodônticos colados ao esmalte.
48 incisivos centrais maxilares humanos, extraídos por razões periodontais, e divididos em três grupos experimentais (n=16): grupo H30 com dentes sem fluorose e grupos F30 e F60 com dentes com fluorose (Índice de Thylstrup e Fejerskov, classificação 3–4). Após o condicionamento do esmalte com ácido fosfórico a 35% durante 30 segundos (H30 e F30) ou durante 60 segundos (F60), foram cimentados brackets metálicos com o sistema adesivo Transbond XT e fotopolimerizados (1200mW/cm² durante 10 segundos). Os espécimes foram termociclados (5–55°C, 500 ciclos), armazenados em água destilada (37°C/7 dias), e testados ao corte (Instron, 1KN, 1mm/min). A falha foi classificada, com um estereomicroscópio (ampliação 20x), de acordo com o Índice de Adesivo Remanescente (ARI). Os dados de resistência adesiva foram analisados com ANOVA e comparações múltiplas segundo Tukey (α=0,05). Os testes de Kruskal‐Wallis e Mann‐Whitney foram utilizados para analisar os dados da falha (α=0,05).
Não foram encontradas diferenças estatisticamente significativas (p=0,763) entre F30 e F60, mas estes grupos apresentaram valores de resistência adesiva estatisticamente (p<0,05) mais baixos que os obtidos em H30. O grupo H30 apresentou uma classificação ARI estatisticamente (p<0,05) superior aos grupos F30 e F60.
A adesão de brackets ortodônticos ao esmalte é negativamente influenciada pela fluorose dentária. A duplicação do tempo de condicionamento ácido nos dentes com fluorose não foi suficiente para promover resultados similares aos observados nos dentes sem fluorose.
Effect of high-powered LED-curing exposure time on orthodontic bracket shear bond strength
2014, Revista Portuguesa de Estomatologia, Medicina Dentaria e Cirurgia Maxilofacial
Citation Excerpt :
In orthodontic treatment, achieving an appropriate bond strength between the bracket and the tooth surface is essential, in order to minimize accidental debonding that can increase the costs and delay the treatment.6,7 Several factors that could affect the ability to promote proper bracket bond strength have been described.8–11 In spite of this, optimizing the composite resin physical and mechanical properties depends on reaching an adequate degree of cure, and the degree of cure of light-activated resins is directly related to the intensity of light and radiation exposure time.12,13
To evaluate the influence of light exposure time on the adhesive strength and the failure mode of orthodontic brackets bonded to human enamel.
100 metal brackets were bonded with Transbond XT to the enamel bucal surface of human premolars. The sample was randomly divided into 5 experimental groups (n = 20) according to the light exposure time (2, 4, 6, 8 and 10 s) and light cured with an LED-curing device (1600 mW/cm²). The specimens were thermocycled (5–55 °C, 500 cycles), stored in distilled water (37 °C, 7 days) and tested in shear, using an Instron universal machine (1 KN, 1 mm/min). Failure mode was classified according to the Adhesive Remnant Index (ARI) using a stereomicroscope (20× magnification). Shear bond strength (SBS) data were analyzed with one-way ANOVA, followed by Tukey post hoc tests. The failure mode data were submitted to Kruskal–Wallis nonparametric test, followed by Tukey post hoc tests to the ranks. A significance level of 5% was set for all data.
The mean SBS values were 5.5 ± 1.93 MPa (2 s), 7.4 ± 1.95 MPa (4 s), 8.6 ± 1.72 MPa (6 s), 9.3 ± 1.64 MPa (8 s) and 11.6 ± 2.65 MPa (10 s). Failure mode was mainly classified as Score 2. Both the SBS (p < 0.001) and the failure mode (p = 0.002) were statistically influenced by the exposure time.
Reducing the exposure time to less than 10 s decreases the bracket bond strength. The weakest adhesive link was found at the bracket-adhesive interface.
Avaliar a influência do tempo de exposição na resistência adesiva e tipo de falha de brackets aplicados ao esmalte humano.
Cem brackets metálicos foram colados com Transbond XT ao esmalte vestibular de pré-molares humanos. Os espécimes foram divididos aleatoriamente em 5 grupos experimentais (n = 20) de acordo com o tempo de exposição à luz (2, 4, 6, 8 e 10 segundos) e fotopolimerizados com um aparelho LED (1.600 mW/cm²). Após termociclagem (5–55 °C, 500 ciclos) e armazenamento em água destilada (37 °C, 7 dias), foi avaliada a resistência adesiva ao corte (SBS), com Instron (1 KN, 1 mm/min). O tipo de falha foi classificado de acordo com o Índice de Adesivo Remanescente (ARI), utilizando estereomicroscópio (20x). Os dados de SBS foram analisados estatisticamente com ANOVA, seguida de comparações múltiplas segundo Tukey. O tipo de falha foi analisado com teste não paramétrico segundo Kruskal–Wallis seguido de comparações múltiplas às ordens segundo o método de Tukey. O nível de significância estatística foi fixado em 5%.
Os valores médios de SBS foram de 5,5 ± 1,93 MPa (2 segundos), 7,4 ± 1,95 MPa (4 segundos), 8,6 ± 1,72 MPa (6 segundos), 9,3 ± 1,64 MPa (8 segundos) e 11,6 ± 2,65 MPa (10 segundos). O tipo de falha observado foi predominantemente classificado como Índice 2. Tanto a resistência adesiva (p < 0.001) como o tipo de falha (p = 0.002) foram estatisticamente influenciados pela variação do tempo de exposição.
A diminuição do tempo de exposição abaixo dos 10 segundos reduz a resistência adesiva dos brackets. O elo mais fraco da interface adesiva foi a união do adesivo ao bracket.
Evaluation of UDMA's potential as a substitute for Bis-GMA in orthodontic adhesives
2013, Dental Materials
Citation Excerpt :
The mean SBS value for Transbond XT (30 MPa) in this study seems relatively high in comparison to analogous data from other studies; for example Vilchis et al. [34] obtained mean SBS values of 26.5 MPa (SD 8.1 MPa) while Willems et al. [35] obtained a value of 8.4 MPa. These differences can be greatly attributed to the widespread use of various methodologies throughout the literature, which result in an unbalanced distribution of confounding factors (e.g. polymerization time, specimen storage medium, cross-head speed and the directionality of the debonding force) [19,35–40]. As the TEGDMA fraction was sequentially increased the resulting mean bond strength seemed to decrease (Fig. 3).
To investigate the effect of UDMA %, of a range of filled UDMA:TEGDMA resins, on viscosity, degree of conversion and shear bond strength. Furthermore, to compare between model filled and unfilled UDMA adhesives, and clinically used orthodontic adhesives on these properties.
Four filled and four unfilled resins with a UDMA to TEGDMA weight ratio 50:50, 60:40, 70:30, 80:20 were formulated, tested and compared to the Bis-GMA control Transbond XT. The properties investigated were: viscosity (rotational viscometry), degree of conversion (DC) (FT-IR) and bond strength (shear bond strength test). One-way ANOVA and Tukey post hoc test was used to statistically analyze the data for viscosity and DC% while the non-parametric Kruskal–Wallis and Mann–Whitney U-test was used for the shear bond strength values.
For SBS a comparable bond strength was obtained between the U80:T20(F) adhesive and the control Transbond XT (27.1 and 30.1 respectively). There was no significant difference between the U70:T30 adhesive and the control. Transbond XT (43.1%) had a significantly lower DC% than all the UDMA based adhesives. Furthermore, there was no significant difference between the DC% means of the various UDMA resins. There was a significant decrease in the viscosity for both filled and unfilled groups, as the TEGDMA concentration was increased.
The results indicate that adhesives formulated with UDMA and TEGDMA monomers, could produce resins with comparable viscosities to the Bis-GMA control, Transbond XT. Adhesives formulated with high UDMA %, can be used to produce resins with greater viscosity and increased bond strength, potentially without affecting their degree of conversion.
Effect of early orthodontic force on shear bond strength of orthodontic brackets bonded with different adhesive systems
2010, American Journal of Orthodontics and Dentofacial Orthopedics
This 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 (Reliance Orthodontic Products, Itasca, Ill). Groups 3 and 4 had Transbond XT primer and Transbond XT adhesive (3M Unitek, Monrovia, Calif). Groups 5 and 6 had Transbond Plus Self Etching Primer and Transbond XT adhesive (3M Unitek). Groups 7 and 8 had RelyX Unicem (3M ESPE, Seefeld, Germany). After thermocycling, SBS testing was performed by using a universal testing machine (Type 500, Lloyd Instruments Ltd, Fareham Hants, UK). The results of SBS testing for all adhesives were analyzed by 2-way analysis of variance and the Duncan test. The unpaired Student t test was used to compare the effect of force on the SBS of each adhesive.
Transbond XT primer and its adhesive had the highest values (without force, 11.2 ± 3.1 MPa; with force, 10.7 ± 2.7 MPa), and RelyX Unicem had the lowest (without force, 5.8 ± 1.5MPa; with force, 5.7 ± 1.6 MPa). Application of force yielded nonsignificant reductions in SBS for all adhesives; this reduction was less pronounced with RelyX Unicem.
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 strength.
In-vitro orthodontic bond strength testing: A systematic review and meta-analysis
2010, American Journal of Orthodontics and Dentofacial Orthopedics
The aims of this study were to systematically review the available literature regarding in-vitro orthodontic shear bond strength testing and to analyze the influence of test conditions on bond strength.
Our data sources were Embase and Medline. Relevant studies were selected based on predefined criteria. Study test conditions that might influence in-vitro bond strength were independently assessed by 2 observers. Studies reporting a minimum number of test conditions were included for meta-analysis by using a multilevel model with 3 levels, with author as the highest level, study as the second level, and specimens in the study as the lowest level. The primary outcome measure was bond strength.
We identified 121 relevant studies, of which 24 were included in the meta-analysis. Methodologic drawbacks of the excluded studies were generally related to inadequate reporting of test conditions and specimen storage. The meta-analysis demonstrated that 3 experimental conditions significantly affect in-vitro bond strength testing. Although water storage decreased bond strength on average by 10.7 MPa, each second of photopolymerization time and each millimeter per minute of greater crosshead speed increased bond strength by 0.077 and 1.3 MPa, respectively.
Many studies on in-vitro orthodontic bond strength fail to report test conditions that could significantly affect their outcomes.
A comparison of the shear-peel and third-order bond strengths of orthodontic brackets with 2 etch techniques and the role of bracket asymmetry
2006, American Journal of Orthodontics and Dentofacial Orthopedics
Introduction: Innovations in orthodontic bonding are inevitably followed by a flurry of studies to ascertain efficacy. Unfortunately, the published reports are often contradictory or highly variable. The primary purpose of this study was to analyze protocols that measure orthodontic bracket bond strength. The effects of loading mode and the role of bracket asymmetry were examined. The secondary goal was to test a self-etch enamel preparation system. Materials and Methods: Flattened stainless steel orthodontic brackets (.022-in Victory Series, 3M Unitek, Monrovia, Calif) were bonded to a total of 192 flattened bovine incisors with a resin composite bonding agent (Transbond XT, 3M Unitek.) The enamel was prepared with traditional, two-step (TS) acid (37% phosphoric acid gel) etching and priming (Transbond XT Primer, 3M Unitek) or with a single step (SS) self-etch (Transbond Plus, 3M Unitek) material. Cement thickness was held constant and bonding was done under controlled temperature and humidity. The brackets were debonded in the occlusogingival and in the gingivocclusal directions (ie, the 2 senses of shear-peel) and using a new technique in the buccal-root and in the lingual-root directions (ie, the 2 senses of a third-order moment.) Results: Data showed no significant differences between TS and SS regardless of load modality. However, significant differences were revealed between the senses of debonding, indicating bracket asymmetry effects. Conclusions: The wide clinical use of these newer self-etching primers has been supported by these limited findings. A new third-order debonding protocol has been demonstrated to be a useful tool. Bracket asymmetry affects some bond strength values, and there is a need for standardization of testing protocols.

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: Partially supported by the Indiana University School of Dentistry Student Research Fund and the American Association of Orthodontists Foundation.

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Original articleEffect of loading mode on bond strength of orthodontic brackets bonded with 2 systems

Section snippets

Material and methods

Results

Discussion

Conclusions

J Dent

Dent Mater

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Am J Orthod

Am J Orthod Dentofacial Orthop

Original article
Effect of loading mode on bond strength of orthodontic brackets bonded with 2 systems