Orthodontic bracket bonding: Enamel bond strength vs time

Experimental study of brackets adhesion with a novel enamel-protective material compared with conventional etching

INTRODUCTION

A reliable adhesion between fixed devices and dental surfaces is a key factor for the clinical success of any orthodontic treatment. Adhesion preparation is associated with damages related to abrasive cleaning, enamel structure defacing caused by etching, enamel loss when removing resin remnants at orthodontic treatment finishing stage or when conditioning surface for adhesive failure and fractures at bracket removal.

AIM

The objective of this study was to compare the shear bond strength of metallic brackets to enamel adhered with a novel non-damaging and remineralizing material for enamel versus the traditional 37% phosphoric acid etching.

MATERIAL AND METHODS

75 Premolars collected from 15- to 40-years old healthy donors requiring extraction were collected. The teeth were then randomly divided into three groups (n = 25). One group was used for the experimental new method (EX), the second for the conventional phosphoric acid etching (PA) method and the third group was left without any treatment (NT). The metallic brackets were fixed with Transbond® XT adhesive and composite resin polymerized for 40 s with a halogen photocuring lamp. The shear bond strength was quantified by means of a universal testing machine at 1 mm/min crosshead speed and a load cell of 1 kN.

STATISTICAL ANALYSIS USED

Tests of normality, adjustment of the data to a root square, a one-way ANOVA and Tukey tests were performed.

RESULTS

Statistically significant differences between the NT (1.4 MPa), PA (32.1 MPa) and EX (9.7 MPa) groups were observed.

CONCLUSIONS

The experimental material for conditioning human enamel induces calcium phosphates crystals on the enamel surface and improves the bond strength in comparison to the NT group.

Effect of nanotechnology in self-etch bonding systems on the shear bond strength of stainless steel orthodontic brackets

OBJECTIVE

To evaluate the effect of silica dioxide (SiO2) nanofillers in different bonding systems on shear bond strength (SBS) and mode of failure of orthodontic brackets at two experimental times.

METHODS

Ninety-six intact premolars were divided into four groups: A) Conventional acid-etch and primer Transbond XT; B) Transbond Plus self-etch primer; and two self-etch bonding systems reinforced with silica dioxide nanofiller at different concentrations: C) Futurabond DC at 1%; D) Optibond All-in-One at 7%. Each group was allocated into two subgroups (n = 12) according to experimental time (12 and 24 hours). SBS test was performed using a universal testing machine. ARI scores were determined under a stereomicroscope. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to determine the size and distribution of nanofillers. One-way ANOVA was used to compare SBS followed by the post-hoc Tukey test. The chi-square test was used to evaluate ARI scores.

RESULTS

Mean SBS of Futurabond DC and Optibond All-in-One were significantly lower than conventional system, and there were no significant differences between means SBS obtained with all self-etch bonding systems used in the study. Lower ARI scores were found for Futurabond DC and Optibond All-in-One. There was no significant difference of SBS and ARI obtained at either time points for all bonding systems. Relative homogeneous distribution of the fillers was observed with the bonding systems.

CONCLUSION

Two nanofilled systems revealed the lowest bond strengths, but still clinically acceptable and less adhesive was left on enamel. It is advisable not to load the brackets immediately to the maximum.

Comparison of enamel-bracket bond strength using direct- and indirect-bonding techniques with a self-etching ion releasing S-PRG filler

This in vitro study compared the shear bond strength (SBS) and adhesive remnant index (ARI) of two systems for bonding orthodontic brackets to enamel. The first system involved a self-etching primer (Beauty Ortho Bond, BO) containing surface pre-reacted glass filler. The second involved a primer applied with phosphoric acid etching (Transbond XT, TX). Ninety-six extracted human premolars were divided into eight groups: Group I (TX/direct bonding), Group II (TX/indirect bonding), Group III (BO/direct bonding), and Group IV (BO/indirect bonding). Groups V-VIII were identical to Groups I-IV, respectively, but were also subjected to 1,500 thermal cycles between 5 and 55°C. ARI was scored by binocular microscopy. SBS was analyzed by three-way ANOVA and the Bonferroni test. ARI was analyzed by the chi-squared test. The BO groups showed lower SBS and ARI results than the TX groups. SBS was significantly influenced by the primer material, bonding technique, and thermal cycling.

Effect of orthodontic adhesive thickness on force required by debonding pliers

This in vitro study evaluated the relationship between removal force and the thickness of three orthodontic adhesives, namely, light- and chemical-cured resin cements and a resin-modified glass ionomer cement. The thickness of each adhesive was 50, 100, 150, or 200 µm, and all adhesives were bonded on bovine incisors. Removal force was measured before (TC-0) and after 1,000 thermal cycles (TC-1000), and values were compared. At TC-0, the removal strengths for adhesive thicknesses of 50 and 100 µm were significantly lower than those for thicknesses of 150 and 200 µm (P < 0.05). At TC-1000, removal strengths for adhesive thicknesses of 50 and 100 µm were also significantly lower than those for 150 and 200 µm. Superbond Orthomite specimens showed a significant difference in removal strength between TC-0 and TC-1000 (P < 0.05) at all thicknesses. There was no significant difference in the distribution of adhesive remnant index scores at any thickness. These findings indicate that decreasing the thickness of applied orthodontic adhesive reduces the removal strength required.

Effects of surface treatment and artificial aging on the shear bond strength of orthodontic brackets bonded to four different provisional restorations

OBJECTIVE

To evaluate the combined effects of material type, surface treatment, and thermocycling on the bond strength of orthodontic brackets to materials used for the fabrication of provisional crowns.

MATERIALS AND METHODS

Four materials were included in this study (ProTemp, Trim Plus, Trim II, and Superpont C+B). Sixty cylindrical specimens (1 × 3 cm) were prepared from each material and equally divided into three groups. The first group was ground with silica carbide paper, the second was polished with pumice, and the last group was sandblasted with 50-µm aluminum oxide particles. Stainless-steel maxillary central incisor brackets (Victory Series, 3M) were bonded to the provisional material specimens with Transbond XT light-cured composite resin, and half of the specimens from each group were thermocycled 500 times in 5°C and 55°C water baths. Then the brackets were debonded with shear testing, and the results were statistically analyzed by three-way analysis of variance and Tukey's multiple-comparison tests at α  =  0.05. Adhesive Remnant Index (ARI) was also identified.

RESULTS

Before and after thermocycling, ProTemp materials showed the highest shear bond strength with orthodontic brackets (10.3 and 13.1 MPa, respectively). The statistical analysis indicated an interaction among the three independent variables (P < .05) and statistically significant differences in bond strength among provisional materials (P < .001), surface treatments (P < .001), and thermocycling (P < .05). According to the ARI, most groups demonstrated adhesive failure.

CONCLUSIONS

The provisional material type, surface treatment, and artificial aging have a significant effect on bond strength. Sandblasting treatment exerts a beneficial effect on shear bond strength.

Influence of four systems for dental bleaching on the bond strength of orthodontic brackets

OBJECTIVE

To compare the influence of four systems for dental bleaching on the shear bond strength (SBS) of orthodontic brackets.

MATERIALS AND METHODS

One-hundred and fifty freshly extracted bovine teeth were randomly divided into five groups. In group I the teeth were untreated (control). In the remaining groups the teeth were bleached, as follows: group II: 38% hydrogen peroxide; group III: 10% carbamide peroxide; group IV: resin-based coating material (RBCM), Beauty Coat; and group V: RBCM, White Coat. In all groups the enamel was conditioned with a self-etching primer and brackets were bonded with composite resin. Samples were stored (37°C, 24 hours), tested, and statistically analyzed, with significance predetermined at P ≤ .05. The adhesive remnant index (ARI) was also evaluated and analyzed.

RESULTS

The SBS of group V (22.49 ± 5.34 MPa) was significantly higher than that of all other groups (I: 17.1 ± 5.11 MPa; II: 14.72 ± 5.42 MPa; III: 12.04 ± 5.29 MPa; and IV: 18.23 ± 5.58 MPa). In contrast, the SBS of group III was significantly lower than that of all groups (except group II). Significant differences in the ARI scores were present between groups.

CONCLUSIONS

The use of RBCM for dental bleaching before bonding orthodontic brackets did not reduce the SBS. In contrast, hydrogen and carbamide peroxides negatively affected the SBS. The SBS yielded after bleaching with carbamide peroxide was significantly lower.

Effects of a torsion load on the shear bond strength with different bonding techniques

The purpose of this study was to test the hypothesis that a torsional load applied after bracket bonding does not affect the shear bond strength (SBS) with different bonding techniques. Sixty human premolars were divided into two groups (experimental and control) to investigate the effects of a torsion load, and the two groups were further subdivided into three groups of 10 for the evaluation of different adhesive systems (one etch-and-rinse adhesive, Transbond XT; two self-etching primer adhesives, Transbond Plus and Beauty Ortho Bond). A torsion load (1.45 N/cm) was applied by beta-titanium wire at 15 minutes after bracket bonding in the experimental groups. All specimens were then thermocycled between 5 and 55°C for approximately 1 week (6000 cycles). The SBS for each sample was examined with a universal testing machine and the adhesive remnant index (ARI) score was calculated. Data were compared by two-way analysis of variance, Student's t-test, and a chi-square test. The SBS for Transbond XT after thermocycling with a torsion load was significantly lower than that without a torsion load. For Transbond Plus and Beauty Ortho Bond, there was no significant difference in the mean SBS between specimens thermocycled with and without a torsion load. No significant difference in the distribution of frequencies among the ARI categories was observed among the six groups, although the ARI scores for specimens with a torsion load tended to be higher than those without a torsion load. In conclusion, the SBS of the conventional etch-and-rinse adhesive system significantly decreased under a torsion load with thermocycling.

Effect of early orthodontic force on shear bond strength of orthodontic brackets bonded with different adhesive systems

INTRODUCTION

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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

INTRODUCTION

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

Many studies on in-vitro orthodontic bond strength fail to report test conditions that could significantly affect their outcomes.

Shear bond strength of orthodontic brackets bonded with different self-etching adhesives

INTRODUCTION

The purpose of this study was to compare the shear bond strength (SBS) of orthodontic brackets bonded with 4 self-etching adhesives.

METHODS

A total of 175 extracted premolars were randomly divided into 5 groups (n = 35). Group I was the control, in which the enamel was etched with 37% phosphoric acid, and stainless steel brackets were bonded with Transbond XT (3M Unitek, Monrovia, Calif). In the remaining 4 groups, the enamel was conditioned with the following self-etching primers and adhesives: group II, Transbond Plus and Transbond XT (3M Unitek); group III, Clearfil Mega Bond FA and Kurasper F (Kuraray Medical, Tokyo, Japan); group IV, Primers A and B, and BeautyOrtho Bond (Shofu, Kyoto, Japan); and group V, AdheSE and Heliosit Orthodontic (Ivoclar Vivadent AG, Liechtenstein). The teeth were stored in distilled water at 37 degrees C for 24 hours and debonded with a universal testing machine. The adhesive remnant index (ARI) including enamel fracture score was also evaluated. Additionally, the conditioned enamel surfaces were observed under a scanning electron microscope.

RESULTS

The SBS values of groups I (19.0 +/- 6.7 MPa) and II (16.6 +/- 7.3 MPa) were significantly higher than those of groups III (11.0 +/- 3.9 MPa), IV (10.1 +/- 3.7 MPa), and V (11.8 +/- 3.5 MPa). Fluoride-releasing adhesives (Kurasper F and BeautyOrtho Bond) showed clinically acceptable SBS values. Significant differences were found in the ARI and enamel fracture scores between groups I and II.

CONCLUSIONS

The 4 self-etching adhesives yielded SBS values higher than the bond strength (5.9 to 7.8 MPa) suggested for routine clinical treatment, indicating that orthodontic brackets can be successfully bonded with any of these self-etching adhesives.

Use of flowable composites for orthodontic bracket bonding

OBJECTIVE

To test the bonding characteristics of four flowable composites for orthodontic bracket bonding.

MATERIALS AND METHODS

Metal brackets were bonded to acid-etched human enamel using four flowable composites (Grandio Flow, GF; UniFil Flow, UF; UniFil LoFlo Plus, UL; and DenFil Flow, DF), an orthodontic bonding system (Transbond XT, TX), and a restorative composite (Filtek Z250, FZ). After 24 hours of storage in water at 37 degrees C, a shear bond strength (SBS) test was performed. After debonding, the adhesive remnant index (ARI) was assessed. In addition, the flow and flexural strength of the materials were examined.

RESULTS

The SBS for the flowable composites ranged between 7.2 and 8.3 MPa, and TX showed a significantly higher value (mean 10.9 MPa). The flowable composites also demonstrated a significantly superior flowability, yet inferior flexural strength (except for DF) than TX and FZ. Two flowable composites (GF and UL) produced significantly higher ARI scores than TX and FZ, which represented a larger resin remnant on the enamel surfaces after debonding.

CONCLUSION

When considering the SBS and ARI scores obtained in this study, flowable composites with no intermediate bonding resin could be conveniently applied for orthodontic bracket bonding.