An ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems

Contrary to an old belief, four corner curing does not provide more bond strength or polymerization in bonding of orthodontic metal brackets

Objectives:

The study aimed to investigate the effect of the direction of light curing on bond strength and adhesive polymerization of orthodontic metal brackets.

Material and Methods:

In this in vitro investigation, 75 extracted human upper premolars were randomly divided into three groups according to the curing direction: Group A (20 s curing from the occlusal side of the bracket), Group B (10 s from occlusal and 10 s from gingival), and Group C (5 s from four corners of the bracket). After bonding, the brackets were subjected to a shear bond strength (SBS) test performed with a universal testing machine. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis was used to find the polymerization ratio of the adhesives in each group. Kruskal–Wallis test was to statistical analysis of SBS and FTIR data, respectively, at the 0.05 level of significance.

Results:

The difference in SBS of metal brackets was not statistically significant between the groups (P > 0.05). However, the difference in polymerization ratio was significant between all groups where the highest and lowest ratio belonged to Groups A and B, respectively (P < 0.05).

Conclusion:

Curing metal brackets from four corners do not increase their bond strength and/or polymerization.

Shear bond strength after using sealant before bonding: a systematic review and meta-analysis of in vitro studies

OBJECTIVES

Decalcification during orthodontic treatment is significantly increased. To prevent this negative impact, new treatments with sealants before bonding brackets are commonly been used. This systematic review discusses current knowledge on shear bond strength when using sealant before bonding.

MATERIALS AND METHODS

A systematic review and meta-analysis were performed to identify studies that address shear bond strength after using a sealant before bonding brackets. The search was carried out using common electronic databases in addition to individual searches. Both screening and study eligibility analysis were performed according to PRISMA and Cochrane Guidelines for systematic reviews. Several terms describing shear bond strength after using a sealant before bonding brackets were searched. Particular attention was paid to bond failure and bracket loss. For the statistical outcome, all results were shown in a forest plot based on standardized mean differences (SMD) with a random-effects model to respect heterogeneity of these studies. To assess the heterogeneity of the different trials, I2-value and the Q-Test were performed.

RESULTS

The initial search identified 416 studies. After a thorough selection process, a total of 15 articles met the inclusion criteria. All 15 articles reported results of in vitro studies. Papers were divided into four subgroups according to their used product: ProSeal, Transbond bonding, the combination of Transbond bonding and ProSeal and Clearfil Protect Bond. The results of this review demonstrate a high heterogeneity of the studies. The SMD of the examined 15 articles show nearly no difference between the control and the intervention groups in shear bond strength (p < 0.0001; OR - 0.12; Cl - 0.47-0.23). Forest plots for comparison of the subgroups depict no difference in shear bond strength as well.

CONCLUSIONS

This meta-analysis concludes that there is no additive benefit for shear bond strength when using sealant before bonding. However, additional randomized controlled studies should be performed to analyze impact of sealants on bonding strength and bracket loss in more detail.

CLINICAL RELEVANCE

Using sealants before orthodontic bonding does not reduce shear bond strength.

Comparing orthodontic bond failures of light-cured composite resin with chemical-cured composite resin: A 12-month clinical trial

INTRODUCTION

In this clinical trial, we evaluated and compared bond failure rates of light-cured composite resin vs chemical-cured composite resin for 12 months.

METHODS

Twenty-two subjects (356 stainless steel brackets) were included in this study, and a split-mouth design was used to randomly allocate diagonally opposite quadrants to either chemical-cured (178 brackets) or light-cured (178 brackets) composite resin; the brackets came from the same manufacturer. The survival and failure rates of the brackets were evaluated by the mode of polymerization. The overall bracket survival rates were estimated using the Kaplan-Meier product limit estimate.

RESULTS

There were no significant differences in the bond failure rates between the chemical-cured and the light-cured composites (P = 0.52). Bond failures were greater in posterior teeth (6.7%) than in anterior teeth (1.2%). The highest failure rate was observed in the second premolars (7.7%).

CONCLUSIONS

The overall failure rate of brackets with the 2 bonding systems was 2.8%, which is acceptable for clinical use. The polymerization mode did not influence the bracket survival rate significantly.

Effect of experimental silane-based primers with various contents of 2-hydroxyethyl methacrylate on the bond strength of orthodontic adhesives

AIM

To evaluate in vitro the effect of different concentrations of 2-hydroxyethyl methacrylate (HEMA) in experimental silane-based primers on shear bond strength of orthodontic adhesives.

METHODS

Different volume percentages of HEMA were tested in four experimental silane-based primer solutions (additions of HEMA: 0, 5.0 vol%, 25.0 vol% and 50.0 vol%). An experimental silane blend (primer) of 1.0 vol% 3-isocyanatopropyltrimethoxysilane (ICMS) + 0.5% bis-1,2-(triethoxysilyl) ethane (BTSE) was prepared and used. The experimental primers together with the control group were applied onto acid-etched premolars for attachment of orthodontic brackets. After artificial aging by thermocycling the shear-bond strength was measured. The fractured surfaces of all specimens were examined under scanning electron microscopy (SEM) to evaluate the failure mode on the enamel surface.

RESULTS

The experimental primers showed the highest shear-bond strength of 21.15 MPa (SD ± 2.70 MPa) and with 25 vol% showed a highly significant increase (P < 0.05) in bond strength. The SEM images showed full penetration of adhesive agents when using silane-based primers. In addition, the SEM images suggested that the predominant failure type was not necessarily the same as for the failure propagation.

CONCLUSIONS

This preliminary study suggested that nonacidic silane-based primers with HEMA addition might be an alternative to for use as adhesion promoting primers.

Evaluation of shear bond strength of orthodontic brackets using trans-illumination technique with different curing profiles of LED light-curing unit in posterior teeth

Background

Although using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. Limited access and poor direct sight may be a problem in the posterior teeth. Meanwhile, effectiveness of the trans-illumination technique is questionable due to increased bucco-lingual thickness of the posterior teeth. Light-emitting diode (LED) light-curing units cause less temperature rise and lower risk to the pulpal tissue. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit.

Methods

Sixty premolars were randomly divided into six groups. Bonding of brackets was done with 40- and 80-s light curing from the buccal or lingual aspect with different intensities. Shear bond strengths of brackets were measured using a universal testing machine. Data were analyzed by one-way analysis of variance test and Duncan's post hoc test.

Results

The highest shear bond belonged to group 2 (high intensity, 40 s, buccal) and the lowest belonged to group 3 (low intensity, 40 s, lingual). Bond strength means in control groups were significantly higher than those in experimental groups.

Conclusions

In all experimental groups except group 6 (80 s, high intensity, lingual), shear bond strength was below the clinically accepted values. In clinical limitations where light curing from the same side of the bracket is not possible, doubling the curing time and increasing the light intensity during trans-illumination are recommended for achieving acceptable bond strengths.

Comparison of shear bond strength of hydrophilic bonding materials: an in vitro study

AIM

The aim of this study was to evaluate and compare the shear bond strength of hydrophilic materials like Transbond MIP with Assure-fluoride releasing light cure sealant paste system (Reliance orthodontic product), Enhance Lc-adhesion booster (Reliance Orthodontics) Prime and Bond NT-one step adhesive with nanotechnology (Dentsply Product India) with Transbond XT as the control group.

MATERIALS AND METHODS

The study was conducted on 180 extracted human premolar teeth which were divided into five main groups. Each group contained 36 teeth, which were further subdivided into three subgroups containing 12 teeth. The teeth were bonded in three different surface environments namely dry, contaminated with artificial saliva and reprimed after contamination with artificial salvia. The brackets were bonded and cured. The shear bond strength was tested using Instron universal testing machine (4501).

RESULTS

The results were subjected to statistical analysis like 3 factorial ANOVA and compared to post-hoc using the Student Newman levels test. The residual resin on the tooth surface after debonding was evaluated with adhesive remnant index.

CLINICAL SIGNIFICANCE

The results revealed that in situations in which moisture contamination is critical there is distinct advantage in using hydrophilic primers.

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.

LED vs Halogen Light-Curing of Adhesive-Precoated Brackets

Objective: To test the hypothesis that bonding with a blue light-emitting diode (LED) curing unit produces no more failures in adhesive-precoated (APC) orthodontic brackets than bonding carried out by a conventional halogen lamp.

Materials and Methods: Sixty-five patients were selected for this randomized clinical trial, in which a total of 1152 stainless steel APC brackets were employed. In order to carry out a valid comparison of the bracket failure rate following use of each type of curing unit, each patient's mouth was divided into four quadrants. In 34 of the randomly selected patients, designated group A, the APC brackets of the right maxillary and left mandibular quadrants were bonded using a halogen light, while the remaining quadrants were treated with an LED curing unit. In the other 31 patients, designated group B, halogen light was used to cure the left maxillary and right mandibular quadrants, whereas the APC brackets in the remaining quadrants were bonded using an LED dental curing light. The bonding date, the type of light used for curing, and the date of any bracket failures over a mean period of 8.9 months were recorded for each bracket and, subsequently, the chi-square test, the Yates-corrected chi-square test, the Fisher exact test, Kaplan-Meier survival estimates, and the log-rank test were employed in statistical analyses of the results.

Results: No statistically significant difference in bond failure rate was found between APC brackets bonded with the halogen light-curing unit and those cured with LED light. However, significantly fewer bonding failures were noted in the maxillary arch (1.67%) than in the mandibular arch (4.35%) after each light-curing technique.

Conclusions: The hypothesis cannot be rejected since use of an LED curing unit produces similar APC bracket failure rates to use of conventional halogen light, with the advantage of a far shorter curing time (10 seconds).

A comparison of three light curing units for bonding adhesive pre-coated brackets

OBJECTIVE

To compare the effectiveness of three curing lights of different types.

DESIGN

Prospective randomized laboratory investigations.

MATERIALS AND METHOD

Adhesive pre-coated orthodontic brackets were bonded to 9 groups of extracted premolars and the adhesive was cured using three different curing lights, each at three different times. Bond strength was tested using a shear/peel method.

RESULTS

The plasma light had 3 times the light intensity of the standard quartz halogen light. The curing times recommended by the manufacturers were 2 seconds for the plasma light, 10 seconds for the high intensity quartz halogen light and 20 seconds for the standard one. Mean debond stresses with these cure times were 9.36, 11.77 and 12.00 MPa, respectively, p<0.04. Increasing the plasma light cure to 4 seconds increased the mean debond stress to 11.19 MPa, similar to that for the other lights, p=0.62.

CONCLUSIONS

Use of a plasma light confers worthwhile time savings when bonding orthodontic brackets, whilst producing bonds of equivalent strength to those found with quartz halogen lights.

Plasma arc versus halogen light-curing of adhesive-precoated orthodontic brackets: A 12-month clinical study of bond failures

The purpose of this randomized clinical trial was to evaluate the performance of adhesive-precoated brackets cured with 2 different light-curing units (conventional halogen light and plasma arc light). Thirty patients treated with fixed appliances were included in the investigation. Each patient's mouth was divided by the split-mouth design into 4 quadrants. In 15 randomly selected patients, the maxillary left and mandibular right quadrants were cured with the halogen light, and the remaining quadrants were cured with the plasma arc light. In the other 15 patients, the quadrants were inverted. A total of 600 adhesive precoated stainless steel brackets were examined: 300 were cured with a conventional halogen light for 20 seconds, and the others were cured with the plasma arc light for 5 seconds. The number, cause, and date of bracket failures were recorded for each light-curing unit over 12 months. Statistical analysis was performed with the Fisher exact test, Kaplan-Meier survival estimates, and the log-rank test. No statistically significant differences in bond failure rates were found between the adhesive-precoated brackets cured with the halogen light and those cured with the plasma arc light; neither were any significant differences in performance found with each light-curing unit between the maxillary and mandibular arches. Plasma arc lights can be considered an advantageous alternative to conventional light curing, because they enable the clinician to reduce the curing time of adhesive-precoated orthodontic brackets without significantly affecting their bond failure rate.

Clinical bond failure of pre-coated and operator-coated orthodontic brackets

OBJECTIVES

To test the hypothesis that there is no significant difference in clinical bracket failure between the 3M APC Mini Twin bracket system and the Transbond XT adhesive during orthodontic treatment.

DESIGN

A randomized, split mouth, prospective clinical trial.

SETTING AND SAMPLE POPULATION

The Department of Orthodontics and Dentofacial Orthopedics at University of Missouri, Kansas City. Twenty-nine subjects who were treatment planned to receive comprehensive orthodontics using 0.018 slot appliances.

EXPERIMENTAL VARIABLE

The adhesive pre-coated brackets (APC) system was randomly assigned to one side of the mouth and the Transbond XT was assigned to the opposite side.

OUTCOME MEASURE

The absence of any of the brackets at the time of a regular or emergency orthodontic appointment.

RESULTS

There was no significant difference (P > 0.05) in bracket failure between the 3M APC Mini Twin bracket system and the Transbond XT adhesive at any time period (90, 180, or 365 days). The failure rate of brackets on premolars was higher than on incisors or canines.

CONCLUSION

APC Mini Twin bracket system and Transbond XT adhesive are equally effective in maintaining brackets clinically. Inexperienced operators had an overall 7.5% bond failure 12 months following bracket placement.

Relationship between enamel etch characteristics and resin-enamel bond strength

OBJECTIVES

The aim of the study was to investigate the relationship between etch patterns produced on surface enamel by phosphoric acid and the corresponding bond strengths achieved.

MATERIALS AND METHODS

Twenty-eight patients had the buccal surface of their teeth etched and replicated for examination under the scanning electron microscope, at the commencement of orthodontic treatment. Histometry was employed to assess the nature and quality of etch patterns using a four-point scale. Twenty of each tooth type (total of 240), were collected and A Company pre-adjusted orthodontic brackets, bonded using Transbond light-cured orthodontic adhesive according to the manufacturer's instructions and 24-hour bond strength testing was undertaken. The Adhesive Remnant Index (ARI) was recorded for the tooth and bracket surface for all specimens.

RESULTS

The type of etch was not significantly affected by the side (left or right) of the mouth assessed (p = 0.532). Overall, there was no significant difference between etch types for upper and lower teeth (p = 0.218); however, there were significant differences between specific teeth in the upper and lower arch. The greatest amount of Type A etch (well-defined etched enamel prisms) was found on the lower incisors, yet in all cases this 'ideal' etch was found to occupy less than 5% of the etched buccal surface enamel. The greatest area of etched enamel surface was occupied by Type C (etched but enamel prisms not evident). The mean bond strength values varied significantly between different tooth types, with the lowest bond strength found on the upper first molar(6.5MPa) and the highest on the lower first molar (13.1 MPa).

CONCLUSIONS

An ideal etch pattern is not essential in order to produce a strong bond.

Halogen versus high-intensity light-curing of uncoated and pre-coated brackets: a shear bond strength study

AIM

To evaluate the shear bond strengths of adhesive pre-coated brackets (APC) and conventional uncoated brackets (Victory) cured with two different light-curing units: a conventional halogen light (Visilux 2) and a micro-xenon light (Aurys).

SETTING

Ex vivo study

MATERIALS AND METHODS

Sixty freshly extracted bovine permanent mandibular incisors were randomly assigned to one of four groups, each group consisting of 15 specimens. Two groups (one for each type of bracket) were exposed to the halogen light for 20 seconds and used as controls. The remaining two groups were cured with the micro-xenon light for 2 seconds. After 24 hours, all samples were tested in a shear mode on an Instron Machine. Analysis was by two-way ANOVA with Scheffé's test for comparisons, Kaplan-Meier survival estimates, and Cox model. The Chi-square (chi(2)) test was used to determine significant differences in the ARI scores.

RESULTS

The mean shear bond strength of the uncoated brackets cured with Visilux 2 was significantly higher than those of all the other groups tested. Both groups cured with Visilux 2 produced significantly higher mean shear bond strengths than those of the corresponding groups cured with Aurys. No statistically significant differences were found between the two groups cured with Aurys.

CONCLUSIONS

Compared to halogen light-curing, the micro-xenon light enables the clinician to reduce significantly the curing time of both APC and uncoated brackets, and although significantly lower, their shear bond strengths may be clinically acceptable.