Comparative Evaluation of Shear Bond Strength, Enamel Microfracture, and Adhesive Remnant Index of APC Flash-Free System Versus Traditional Bonding: An In-Vitro Study

INTRODUCTION

In orthodontics, shear bond strength plays an important role because it provides a good bond between the brackets and tooth surface; it avoids fracture of the tooth surface and prevents debonding of brackets from the tooth surface. All of these allow sufficient treatment time. Many factors, including the adhesive, its thickness, its strength, the bonding procedure, the clinician's ability, the base design, the geometry of the bracket, the material, and the kind of bracket all contribute to the shear bond strength. Brackets joined using conventional adhesive and adhesive pre-coated (APC) flash-free glue were the subjects of this comparison and evaluation research, which aimed to measure shear bond strength, enamel microfracture, and adhesive residual index.

METHOD

60 recently removed premolars from humans were used in this investigation. Before mounting on the acrylic block, the teeth were meticulously cleaned and preserved in artificial saliva. Two groups were formed from the collected premolars the control group and the experimental group. For the control group, we used American Orthodontics (AO) Master/Mini Master series brackets glued with resin composite kits. To make sure the adhesive was uniformly thick, we flashed extra adhesive around the brackets. In the meantime, samples were bonded using 3M Unitek APC flash-free technology in the experimental group.

RESULTS

The research indicated that there was a statistically significant difference between the two groups to the adhesive remnant index (ARI) and mean shear bond strength. The shear bond strength of the experimental group averaged 10.96 megapascals (MPa), whereas the control group's was 5.70 MPa. The control group's ARI score was 2.97, whereas the experimental group's score was 2.4. There was no statistically significant change seen in enamel microfracture.

CONCLUSION

A more robust shear bond may be possible using APC flash-free brackets. Compared to conventional bonding techniques and brackets, APC flash-free brackets have a lower adhesive residual index. The APC flash-free bracket technology also causes more enamel microfracture than conventional bonding and bracketing methods.

Influence of the orthodontic bonding procedure on biofilm formation

INTRODUCTION

In orthodontics, white spot lesions are a persistent and widespread problem caused by the demineralization of buccal tooth surfaces around bonded brackets. The remaining adhesive around the brackets leads to surface roughness, which might contribute to demineralization. The present in vitro study aimed to compare a conventional and a modern adhesive system (APC Flash-Free technology) for orthodontic brackets with regard to the adhesion of Streptococcus sobrinus, a leading caries pathogen.

METHODS

This in vitro study included 20 premolar teeth and compared 10 APC Flash-Free adhesive-coated ceramic brackets (FF)with 10 conventionally bonded (CB) ceramic clarity brackets. Specimens were incubated in an S. sobrinus suspension for 3 h. To evaluate the bacterial formation, samples were analysed with a scanning electron microscope (SEM). Imaging software was used to quantify and statistically compare percentage values of colonization (PVC) in both groups' adhesion and transition areas.

RESULTS

We found a significant difference in biofilm formation between the groups for the adhesive and transition areas. PVC in the adhesive area was approximately 10.3-fold greater for the CB group compared with the FF group (median: 3.2 vs 0.31; P < 0.0001). For the transition area, median PVC was approximately 2.4-fold greater for the CB group compared with the FF group (median: 53.17 vs 22.11; P < 0.01).

CONCLUSIONS

There was a significantly lower level of S. sobrinus formation around the FF bracket system than there was surrounding the conventionally bonded group. This study suggests that the FF adhesive bracket system can help reduce the occurrence of bacterial growth around orthodontic brackets.

Effects of reducing excess dental adhesive on bacterial adhesion in the bracket periphery

OBJECTIVES

White spot lesions are one of the most common side effects of orthodontic therapy with a multibracket appliance and may indicate a preliminary stage of caries, also known as initial caries. Several approaches may be utilized to prevent these lesions, such as reducing bacterial adhesion in the area surrounding the bracket. This bacterial colonization can be adversely affected by a number of local characteristics. In this context, the effects of excess dental adhesive in the bracket periphery were investigated by comparing a conventional bracket system with the APC flash-free bracket system.

MATERIALS AND METHODS

Both bracket systems were applied to 24 extracted human premolars, and bacterial adhesion with Streptoccocus sobrinus (S. sobrinus) was performed for 24 h, 48 h, 7 d, and 14 d. After incubation, bacterial colonization was examined in specific areas by electron microscopy.

RESULTS

Overall, significantly fewer bacterial colonies were found in the adhesive area around the APC flash-free brackets (n = 507 ± 13 bacteria) than the conventionally bonded bracket systems (n = 850 ± 56 bacteria). This is a significant difference (**p = 0.004). However, APC flash-free brackets tend to create marginal gaps with more bacterial adhesion in this area than conventional bracket systems (n = 265 ± 31 bacteria). This bacterial accumulation in the marginal-gap area is also significant (*p = 0.029).

CONCLUSION

A smooth adhesive surface with minimal adhesive excess is beneficial for reducing bacterial adhesion but also poses a risk of marginal gap formation with subsequent bacterial colonization, which can potentially trigger carious lesions.

CLINICAL RELEVANCE

To reduce bacterial adhesion, the APC flash-free bracket adhesive system with low adhesive excess might be beneficial. APC flash-free brackets reduce the bacterial colonization in the bracket environment. A lower number of bacteria can minimize white spot lesions in the bracket environment. APC flash-free brackets tend to form marginal gaps between the bracket adhesive and the tooth.

Effects of a flash-free system on dental plaque accumulation and bonding-debonding process: A clinical study

INTRODUCTION

The objectives of this study were to evaluate the effects of a flash-free (FF) System on (1) the amount of plaque accumulation around the braces on buccal surfaces of the teeth, (2) the time required for the placement of brackets, including the clean-up of the flash, (3) the amount of adhesive left on the tooth after debonding, and (4) time required for adhesive remnant clean-up.

METHODS

Thirty-six patients (aged 19.96 ± 5.74 years) were randomly distributed to receive adhesive precoat (APC)-FF and APC-Plus ceramic brackets on the maxillary right or left anterior 6 teeth. Bonding and debonding time were measured per segment in milliseconds. A plaque revealer agent was applied to discolor the dental plaque, and a modified plaque accumulation index was used to evaluate the amount of plaque at 2 different time points. An adhesive residue index was used after the debonding.

RESULTS

The mean bonding times were 138.87 seconds (8332.47 milliseconds) and 77.82 seconds (4669.31 milliseconds) for APC-Plus and APC-FF, respectively. The difference was statistically significant (P ≤0.001). The difference between the mean debonding times was not statistically significant. A significant difference was found between the adhesive residue index scores of the 2 systems (P ≤0.001). There was no statistically significant difference between plaque accumulation scores at first- and second-time points for both adhesive systems. APC-Plus score (0.94 ± 0.98) was higher than the APC-FF score (0.50 ± 0.91) on the incisal side at the second time point (P ≤0.05).

CONCLUSIONS

FF adhesives can be a good alternative to reduce chair time in bonding appointments.

Evaluation of shear bond strength and adhesive remnant index of metal APC™ Flash-Free adhesive system: A comparative in vitro study with APC™ II and uncoated metal brackets

OBJECTIVE

The aim of this in vitro study was to compare the shear bond strength (SBS) and the adhesive remnant index (ARI) of the metal APC™ Flash-Free adhesive system, the APC™ pre-coated adhesive system and a conventional uncoated system.

MATERIALS AND METHODS

One hundred eighty-six freshly extracted human premolars were randomly divided into 3 groups and bonded by a single operator. Group A/Control Group (60 teeth): the manual bonding group treated with Transbond™ XT Light Cure Adhesive Paste (3M™ Unitek). Group B (60 teeth): treated with APC™II metal maxillary premolar precoated brackets. Group C (66 teeth): treated with metal maxillary premolar APC Flash-Free brackets. The teeth were then stored in distilled water at 37̊C for 24hours, and five hundred cycles of thermocycling were performed. The Shear Bond Strength (SBS) test was performed using an Instron Universal Testing Machine, and the adhesive remnant index (ARI) was determined using a dental optical microscope at ×25 magnification.

RESULTS

The mean shear bond strength values showed differences between the three types of brackets (P=0.016; Anova). It was significantly higher with APC™II and lower with APC Flash-Free brackets; however, no significant differences were found between conventional and APC Flash-Free brackets (P-value=0.574). The distribution of the dichotomized ARI score was significantly different between the three brackets (P-value=0.049). The ARI score for APC Flash-Free brackets was higher with no significant difference between the conventional system and APC brackets (P-value=0.361).

CONCLUSIONS

The mean SBS values were not significantly different between APC Flash-Free metal brackets and uncoated metal brackets. The APC Flash-Free metal system's bond failure occurred at the bracket-adhesive interface, with the highest percentage of teeth having more than 50% of the residual composite on the enamel after debonding.

The effect of beer and milk tea on the shear bond strength of adhesive precoated brackets: An in vitro comparative study

Objectives

The objectives of this study were to evaluate the long-term effects of beer and milk tea on the shear bond strength (SBS) of adhesive precoated brackets and conventional adhesive on brackets.

Methods

The 150 metal brackets were bonded to maxillary permanent premolars and divided into two groups based on adhesive type: (1) Transbond PLUS Color Change Adhesive (TP) and (2) Flash-Free adhesive precoated (APC FF). The bonding processes were carried out exactly as recommended by the manufacturer. Each group’s samples were randomly divided into five subgroups with different immersion solutions and thermal cycles (n = 15): (1) at 24 h after bonding, (2) milk tea at 6 months, (3) milk tea at 1 year, (4) beer at 6 months and (5) beer at 1 year. The SBS differences between groups were analyzed using an independent-sample T test and one-way ANOVA with Dunnett’s T3 as a post hoc analysis.

Results

The SBS of TP were 20.66 ± 4.88 (X ± SD MPa), 23.14 ± 2.33, 17.54 ± 5.12, 24.64 ± 2.26, and 20.91 ± 6.19 for subgroups 1 to 5, respectively. The SBS of APC FF were 13.86 ± 4.14, 17.02 ± 4.04, 13.74 ± 4.40, 15.77 ± 4.11, and 16.21 ± 3.51 for subgroups 1 to 5 respectively. However, the SBS of APC FF was significantly lower than TP for all subgroups (p < 0.05). Beer showed a minor influence on the SBS (p > 0.05). The TP milk tea subgroup increased significantly throughout the 1-year thermal age period (p = 0.028). Both TP and APC FF showed higher values in the milk tea subgroups after 6 months of thermal age than in the beer subgroups (p < 0.05).

Significance

The APC FF group showed significantly lower SBS than the TP group. We found that milk tea increased the SBS in both the TP and the APC FF groups. However, beer had no significant effect on either group.

Comparison of flash-free and conventional bonding systems: A systematic review and meta-analysis

OBJECTIVES

To review the literature systematically to compare the performance of adhesive precoated flash-free bonding systems with conventional adhesive precoated (APC) and operator-coated (OPC) bonding systems.

MATERIALS AND METHODS

PubMed, Cochrane Library, Web of Science, and Embase were searched for potential eligible studies. Study selection and data collection were conducted independently. Statistical analysis was performed by Review Manager 5.3. The Cochran Q test was used to test heterogeneity in the included studies. Risk of bias was evaluated using Cochrane RoB 2.0 tool for randomized controlled trials.

RESULTS

Six studies were included and the overall risk-of-bias judgment was low risk of bias to some concerns. The results of the meta-analyses showed that flash-free required significantly less bonding time than APC (mean difference [MD]: -1.56; 95% confidence intervals [CIs]: -2.56 to -0.56), and no significant differences were found in bond failure rates (risk ratio [RR]: 1.54; 95% Cis: 0.27 to 8.89) and adhesive remnant index (ARI) (MD: -0.50; 95% CIs: -1.14 to 0.14) between them. Qualitative analysis showed that flash-free might have a positive effect on enamel demineralization compared to APC but the quantity of plaque did not differ between them.

CONCLUSIONS

The flash-free bonding system significantly reduced bonding time and it had comparable bond failure rates with APC. So far, there is not enough evidence to support its positive effect on reducing enamel demineralization and the pathogenic bacteria around brackets. In summary, flash-free might be a better choice for clinical bracket bonding.

Adhesive Precoated Bracket: Is It Worth Using? Long-term Shear Bond Strength: An In Vitro Study

OBJECTIVES

 The objectives of this study were to compare the long-term shear bond strength of conventional adhesive on metal brackets with that of adhesive precoated brackets in vitro and to evaluate the amount of adhesive remnant on the tooth surface after debonding.

MATERIALS AND METHODS

 A total of 90 maxillary permanent premolars were randomly divided into two groups. The samples in the first group were bonded with metal brackets using Transbond PLUS Color Change Adhesive (TP), and the samples in the second group were bonded with Flash-Free adhesive precoated brackets (APC FF). The bonding techniques were performed, according to the manufacturer's instructions. The samples from each group were randomly divided into three subgroups with different thermal cycles (n = 15). The shear bond strength (SBS) and adhesive remnant index (ARI) were measured and calculated.

STATISTICAL ANALYSIS

 Two-way ANOVA and Chi-square test were used to analyze the differences in the SBS and ARI between the groups, respectively.

RESULTS

 The means of the SBS of the APC FF subgroups were significantly lower than those of the TP subgroups, except in the 10,000 thermocycle subgroups. Chi-square test showed no statistically significant differences between the groups and subgroups. An ARI score of 1 was the predominant score in both groups.

CONCLUSIONS

 This study found that the SBS of APC FF gradually increased with time and thermal aging did not affect the failure pattern.

Effects of adhesive flash-free brackets on debonding pain and time: A randomized split-mouth clinical trial

OBJECTIVES

To evaluate the effects of adhesive precoated (APC) flash-free brackets on the level of pain, amount of remnant adhesive, and removal time during the debonding procedure.

MATERIALS AND METHODS

Thirty patients (20 female, 10 male) aged 12 to 18 years undergoing nonextraction fixed orthodontic treatment were included in this study. APC flash-free and conventional ceramic brackets were bonded with a split-mouth study design. Bracket types were randomly allocated to quadrants. During the removal of the brackets, the visual analogue scale (VAS) was used to assess the level of pain for each tooth. The adhesive remnant index (ARI) was used to determine the amount of adhesive remaining on the tooth surface. Adhesive removal times were calculated per quadrant. The data were analyzed using the Wilcoxon test for comparisons between groups.

RESULTS

Pain scores were generally higher for the conventional group than for the flash-free group. There were no differences in VAS scores across most tooth types during debonding. Overall, ARI results showed more adhesive remnants in the conventional bracket group (P < .001). Except for the right maxillary quadrant, the times required to remove the adhesive were significantly longer for the flash-free brackets than the conventional brackets (P ≤ .005).

CONCLUSIONS

Although removal time was slightly longer for the flash-free adhesive than for the conventional adhesive, lower pain scores were generally observed for the flash-free adhesive brackets during the debonding procedure. Both time and pain differences could be considered clinically insignificant.

Enamel around orthodontic brackets coated with flash-free and conventional adhesives

OBJECTIVE

To evaluate enamel roughness and color after debonding flash-free adhesive precoated brackets and brackets coated with conventional orthodontic adhesives using nonbonded enamel as control.

MATERIALS AND METHODS

A total of 80 extracted human premolars were divided into the following four groups: group I: APC^TM Flash-Free adhesive precoated brackets; group II: APC^TM PLUS adhesive precoated brackets; group III: noncoated brackets, which were coated manually at the time of bonding (all three brackets were Clarity^TM Advanced ceramic brackets [3M Unitek, Monrovia, CA, USA]); group IV: nonbonded enamel (control). Bonded premolars were subjected to demineralization, and then brackets were debonded. Each group was then divided into two subgroups to assess enamel around the debonded brackets, and also enamel in the control group, using an atomic force microscope and spectrophotometer. In addition, 12 samples were used to assess the bracket/adhesive/enamel junction with a scanning electron microscope.

RESULTS

Mean values of root mean square roughness (Rq) and maximum profile valley depth (Rv) for APC^TM Flash-Free, APC^TM PLUS, and Clarity^TM Advanced groups were 140 nm and 482 nm, 210 nm and 727 nm, and 447 nm and 1243 nm, respectively. All three groups showed higher roughness and depth values than the control enamel. Spectrophotometer results yielded ∆E* of 3.7 ± 0.6, 5.1 ± 0.4, and 7.1 ± 0.6 for APC™ Flash-Free, APC™ PLUS, and Clarity^TM Advanced groups respectively. Color coordinates showed progressively higher L* and b* values and progressively lower a* values from group I to group III.

CONCLUSIONS

Under the same demineralization conditions, enamel around debonded APC™ Flash-Free adhesive precoated brackets showed less roughness and color changes compared to the other two groups.

Effect of different debonding techniques on shear bond strength and enamel cracks in simulated clinical set-ups

OBJECTIVE

The aim of this study was to evaluate the relationship between debonding forces and enamel cracks length change between different debonding techniques.

METHODS

80 extracted premolar teeth with intact buccal enamel were divided into five groups. In each group, enamel cracks were evaluated by stereomicroscope before and after debonding. All teeth were bonded with metal brackets by self-cure adhesive (3M, USA) and then debonded by bracket debonding plier, fixed on the UTM machine, through five methods based on location of plier on brackets: OGwing (occlusogingival), MDwing (mesiodistal), Oblique, OGbase (occlusogingival) and Cusp-base.

RESULTS

Based on non-parametric distribution of data, there was no significant difference between groups in ARI and enamel cracks length change. The highest shear bond strength for debonding presented in OG base method (25.25 ± 8.4) and the difference was statistically significant (P-value = 0.029). There was no linear relationship between shear bond strength and cracks length change and also between ARI and cracks length change.

CONCLUSION

Despite the lower cracks length change in Cusp-base method than other groups, there wasn't significant difference between debonding methods. Also the amount of debonding forces and ARI do not affect the changes of cracks length.

Comparison of clinical bond failure rates and bonding times between two adhesive precoated bracket systems

OBJECTIVE

To compare the clinical bracket failure rate and bonding time differences between Adhesive Precoated Flash-Free (APCF) and Adhesive Precoated Plus (APCP) bracket systems.

METHODS

Thirty-three patients (7 male and 26 female) with a mean age of 17.2 ± 3.6 years and permanent dentition were included in the study. Total of 660 brackets were bonded by 1 operator with the use of a split-mouth design, and bracket failure rates were observed over 6 months. Bracket bonding time of each group was also evaluated. Bracket failure rates were evaluated by means of chi-square test. One-way analysis of variance (ANOVA) and Tukey honestly significant difference tests were used to evaluate the bonding time differences between groups.

RESULTS

The overall, APCF, and APCP bracket failure rates were 1.21%, 1.81%, and 1.51%, respectively. Chi-square test revealed significant differences (P <0.01) between groups in bracket failure rates. The upper left APCP group showed significantly (P <0.05) more failure than the other groups. One-way ANOVA test (P <0.001) showed statistically significant bonding time differences between groups. Bonding time of APCF brackets was significantly shorter than the bonding time of APCP brackets for the same quadrants. Chi-square test did not reveal significant differences (P >0.05) between groups according to adhesive remnant index scores.

CONCLUSIONS

Compared with APCP brackets, APCF brackets can reduce the bonding time without increasing bracket failure rate.

Enamel demineralization around two different orthodontic bracket adhesive systems: An in vivo study

Objective

To compare the enamel demineralization around the two precoated adhesive bracket systems, APC Flash-Free and APC PLUS (3M Unitek, Monrovia, CA, USA), in clinical settings.

Material and method

This prospective experimental in-vivo study included 40 premolar teeth, which were planned for extraction due to orthodontic purposes. They were divided into two groups (Group A; n = 20 teeth were bonded with APC Flash Free ceramic brackets and group B; n = 20 teeth were bonded with APC Plus ceramic bracket). After four weeks, the teeth were extracted, sectioned, and examined under the Scanning Electron Microscope (SEM) to evaluate the amount of demineralization from the enamel surface to the deepest point.

Results

Findings revealed that the mean values of demineralization under SEM were significantly higher in APC Plus compared to APC Flash Free (149.95 µm vs. 112.96 µm, respectively) (P < 0.05). The difference between the two systems was mainly found in the middle part of the facial surfaces, while there were no differences between the two systems in the proximal parts.

Conclusion

The enamel demineralization around APC Flash-Free adhesive bracket system was significantly less than that of APC plus Adhesive bracket system, which can be due to the absence of the caries promoting adhesive flash during tooth bonding using the flash free system.

Shear bond strength of a flash-free orthodontic adhesive system after thermal aging procedure

Background

The aim of this study was to compare the shear bond strength (SBS) of a flash-free and precoated orthodontic adhesive with a compomer orthodontic adhesive before and after thermocycling. The adhesive remnant index (ARI) was also determined for both adhesives.

Material and Methods

The adhesive remnant index (ARI) was also determined for both adhesives. Material and Methods: A total of 120 human premolars were randomly divided into two groups (n=60) according to the orthodontic adhesive used: APC Flash-Free Adhesive Coated Appliance System (APC FF) or Transbond PLUS Color Change Adhesive (TP), as control. A SBS test was performed and ARI value for each specimen was also assessed. Results were analyzed by two-way ANOVA and Tukey's Chi-square test (p<0.05).

Results

SBS values were significantly influenced by thermocycling (p<0.01). Neither the orthodontic adhesive nor the interaction between adhesive and thermocycling statistically affected SBS results (p>0.05).

Conclusions

APC FF and TP showed similar bond strength results. Thermocycling induced a significant decrease in SBS values for the two adhesives tested, without differences between 10,000 and 20,000 thermal cycles. Moreover, APC FF left less adhesive remnants on the enamel compared to TP. Key words:APC Flash-Free, APC cement, aging, orthodontics, resin cements.

A comparative assessment of bracket survival and adhesive removal time using flash-free or conventional adhesive for orthodontic bracket bonding: A split-mouth randomized controlled clinical trial

OBJECTIVES

To compare bracket survival and adhesive removal time between a flash-free and a conventional adhesive for orthodontic bracket bonding.

MATERIALS AND METHODS

Forty-five consecutive patients had their maxillary incisors, canines, and premolars bonded with ceramic brackets using a flash-free adhesive (APC Flash-Free Adhesive, 3M Unitek, Monrovia, Calif) on one side and a conventional adhesive (APCII Adhesive, 3M Unitek) on the other side. The side allocation was randomized. Bracket failure was recorded at 4-week intervals. The adhesive remnant index (ARI) was scored on debond and adhesive removal timed to the nearest second. The primary outcome was adhesive removal time per quadrant. Secondary outcomes were bracket failure rate, time to first-time failure of a bracket, and ARI score on debond. Paired t-tests were used to compare adhesive removal times and ARI scores between the adhesives with P < .05 considered statistically significant.

RESULTS

Bracket failure rates were 4.3% for the flash-free adhesive and 1.9% for the conventional adhesive, with mean times to first-time failure of 31 weeks for the flash-free adhesive and 42 weeks for the conventional adhesive; neither failure rates nor times to first failure were significantly different. Although the flash-free adhesive left significantly more adhesive on the tooth surface after debonding, the adhesive removal times were 22.2% shorter than with the conventional adhesive.

CONCLUSIONS

Bracket survival with the flash-free adhesive was equivalent to the conventional adhesive when ceramic brackets were bonded. Adhesive removal was significantly faster when using the flash-free adhesive, which may result in time savings of more than 20% compared with the conventional adhesive.

[Comparison of adhesive seal morphology between APC™ PLUS and APC™ Flash-Free Adhesive Coated brackets]

INTRODUCTION

Does the new adhesive-coated APC™ Flash-Free bracket from the 3M Unitek^® group simplify the bonding protocol without compromising precision?

OBJECTIVES

The aim of this study was to compare the morphology of the adhesive joint between the classic APC™ PLUS adhesive-coated brackets and APC™ Flash-Free brackets.

MATERIALS AND METHODS

In vitro bonding of esthetic brackets in the CLARITY™ ADVANCED range was performed to compare the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets.

RESULTS

No statistically significant difference was found concerning the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets. A statistically significant difference was found regarding the thickness of the adhesive between the two types of bracket. The adhesive used for the APC™ Flash-Free brackets was significantly thicker than for the APC™ PLUS brackets (P=0.0001). Adhesive thickness was also more homogeneous on the APC™ Flash-Free brackets (P=0.001 for the relative difference).

CONCLUSION

The adhesive is thicker but adhesive homogeneity is greater with APC™ Flash-Free brackets than with APC™ PLUS brackets.

Bond strength of pre-coated flash-free adhesive ceramic brackets. An in vitro comparative study on the second mandibular premolars

CONTEXT/OBJECTIVES

Clinical studies show a mean bond failure rate of orthodontic brackets, which ranges between 6% and 8%, with a predominance for the second mandibular premolars. The pre-coated flash-free adhesive ceramic brackets allow to obtain, according to their manufacturer, a low bond failure rate, while ensuring a simplified implementation. The aim of this study was to measure the shear bond strength of ceramic brackets bonded with the direct method using a pre-coated flash-free adhesive system, and to compare it with the shear bond strength of the old generation precoated brackets and that of operator coated brackets to the buccal surface of the second mandibular premolars.

MATERIEL AND METHODS

45-second mandibular premolars extracted for orthodontic purposes were randomly distributed into 3 groups of 15 teeth each. In the first group, the brackets were precoated with the APC™ Flash-Free^® system (3M Unitek; in the second group, with the APC Plus^® system (3M Unitek), and in the third group, the brackets were bonded manually with the Transbond XT^® composite (3M Unitek). The enamel surface was prepared in the same way for the 3 groups: etching using 36% orthophosphoric acid, followed by the application of the Transbond XT^® primer adhesive (3M Unitek). Each sample was submitted to shear bond strength forces using a Universal Testing Machine LRX^® (Lloyd Instruments LTD., Fareham, UK) in shear mode with a crosshead speed of 1.0mm/min. The bond strength values of the brackets were recorded in megapascals (MPa) for each tooth. The mean values were then compared using the one-way ANOVA test.

RESULTS

Although the mean shear bond strength value for the APC Flash-Free^® group was lower than those of the two other groups, this difference was not statistically significant (P=0.276).

CONCLUSION

Given the experimental conditions of this in vitro study, the shear bond strength of the brackets precoated with the APC Flash-Free^® system is comparable to the two other conventional systems.

Microleakage under ceramic flash-free orthodontic brackets after thermal cycling

OBJECTIVE

To compare microleakage under 3M Unitek's APC Flash-Free Adhesive Coated System bracket and the APC PLUS Adhesive Coated System bracket after thermal cycling.

MATERIALS AND METHODS

Forty freshly extracted human maxillary premolars were randomly divided into two groups and bonded with either a Flash-Free bracket or a PLUS bracket. After bonding, the samples were incubated in a water bath at 37°C for 24 hours and thermocycled for 5000 cycles between 5°C and 50°C. All teeth were immersed in a 2% methylene blue solution for 24 hours, embedded in acrylic and sectioned in a buccolingual direction at approximately the center of the bracket. Microleakage was observed at the enamel-adhesive interface from the occlusal and gingival margins of the bracket base. Statistical analysis was conducted using the Mann-Whitney U-test.

RESULTS

The median microleakage was higher in the Flash-Free group, but the difference between the two groups was not statistically significant (P > .05).

CONCLUSION

In a laboratory setting, there is no significant difference between the extent of microleakage under the APC Flash-Free Adhesive Coated System bracket and the APC PLUS Adhesive Coated System bracket after thermal cycling.

Shear bond strength and debonding characteristics of a new premixed self-etching with a reference total-etch adhesive

Background

To determine the shear bond strength and adhesive remnant index of a new premixed self-etching primer and adhesive (Tectosan, BonaDent, Germany) for orthodontic appliances in comparison to a reference total-etch system Transbond XT.

Methods

Bovine incisors were embedded in resin and randomly divided into two groups of 16 samples each. Brackets (Discovery, Dentaurum, Germany) were bonded in group 1 (total-etch-system, Transbond XT) and in group 2 (self-etch-system, Tectosan) with curing light for 40 s. Shear bonding strengths were measured after 24 h of storage in distilled water at 37 °C with a Zwicki 1120 testing machine (Zwick Roell, Germany). A force was applied on the bracket base at the wings in occluso-gingival direction. Then the adhesive remnant index (ARI) was determined.

Results

No statistical differences on SBS were found for both bonding agents (p = 0.63). ARI scores however differed statistically significantly (p = 0.035): in the total-etch group more adhesive remained on the teeth, whereas in the self-etch group more adhesive remained on the brackets. There were no visible enamel damages in both groups.

Conclusions

No differences in the shear bond strength were found between both bonding agents. In our study the self-etch-system shifted the adhesive remnant index from more adhesive on the teeth to more adhesive on the bracket - as other already published self-etch systems did - with the new benefit of not increased enamel damages. Tectosan might therefore be a promising alternative to adhesive systems.