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KJO Korean Journal of Orthodontics

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Original Article

Korean J Orthod 2025; 55(1): 15-25   https://doi.org/10.4041/kjod24.073

First Published Date October 11, 2024, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

Scanning electron microscopy analysis of metallic and aesthetic bracket meshes before and after debonding

Jacqueline Adelina Rodríguez-Cháveza , Hugo Marcelo Flores-Ruizb , Abigailt Flores-Ledesmac , Alvaro García-Pérezd , Lourdes Bazán-Diaze

aInstitute of Dental Research, Department of Integral Dental Clinics, University Center for Health Sciences, University of Guadalajara, Guadalajara, Mexico
bDepartment of Natural and Exact Sciences, CUValles, University of Guadalajara, Ameca, Mexico
cLaboratory of Dental Materials and Biomaterials, Meritorious Autonomous University of Puebla, Puebla, Mexico
dLaboratory of Public Health Research, National Autonomous University of Mexico (UNAM), Tlalnepantla, Mexico
eMaterials Research Institute, National Autonomous University of Mexico, Mexico City, Mexico

Correspondence to:Jacqueline Adelina Rodríguez-Chávez.
Professor, Institute of Dental Research, Department of Integral Dental Clinics, University Center for Health Sciences, University of Guadalajara, Salvador Quevedo y Zubieta street 228, building B, second floor, Independencia Oriente colony, Guadalajara 44340, Mexico.
Tel +52-3310585200 (ext. 33866) e-mail jacqueline.rchavez@academicos.udg.mx

How to cite this article: Rodríguez-Chávez JA, Flores-Ruiz HM, Flores-Ledesma A, García-Pérez A, Bazán-Diaz L. Scanning electron microscopy analysis of metallic and aesthetic bracket meshes before and after debonding. Korean J Orthod 2025;55(1):15-25. https://doi.org/10.4041/kjod24.073

Received: April 9, 2024; Revised: September 10, 2024; Accepted: October 9, 2024

Abstract

Objective: To study the influence of bracket base meshes on shear bond strength and observe them using a scanning electron microscopy (SEM) before and after debonding. Methods: Ninety brackets were divided into nine groups of 10 samples each: G1-Alexander, G2-Mini Sprint® Brackets, G3-In-Ovation R CCO, G4-Gemini SL Self-Ligating Bracket, G5-Classic mini 2G Stylus®, G6-Gemini Metal Brackets, G7-ClarityTM Advanced, G8-Crystall-Ize®, and G9-Ceramic Series Flexx 2G®. Groups G1 to G6 and G7 to G9 consisted of metallic and aesthetic brackets, respectively. Initial photographs of all brackets were taken through SEM at 25X magnification. The brackets were then bonded to premolars using TransbondTM XT, and a shear bond strength test was conducted after 24 hours using an Instron machine at 1 mm/min. After debonding, the bracket meshes were observed using SEM. Results: Before bonding, 72.22% of brackets didn’t present mesh defects, while 27.77% did. SEM analysis revealed that G4 and G5 presented defects in 100%, G7 in 40%, and G8 in 10%. The average shear bond strength of 9.67 ± 2.84 MPa and 11.21 ± 4.99 MPa were obtained for both metallic and aesthetic brackets, respectively. A Pairwise–Wilcoxon test with Benjamini–Hochberg correction was conducted to determine specific statistical differences between the groups, revealing significant differences based on bracket type and shear bond strength (P < 0.009). Conclusions: This study suggested that the shape of bracket meshes influenced shear bond strength.

Keywords: Bracket, Adhesive, Shear bond strength, Scanning electron microscopy

INTRODUCTION

Bracket base designs vary to optimize adhesion between the bracket’s mechanical retention and the adhesive.1,2 This variability includes factors such as bracket material, prescription, base size, ligation type, and retentive base design.3 Among these, the bracket retentive base design is a significant factor influencing shear bond strength (SBS).2 Currently, orthodontic brackets are fabricated from several types of materials with varying degrees of roughness, including metal, ceramic, plastic, titanium, and composite.4 Innovative approaches to improve retention include laser treatments, metal plasma-coated bases, and fusing metallic or ceramic particles to the base.5 For ceramic brackets, retention mechanisms include mechanically retentive bases, chemically retentive bases with silane treatment, and mechanically chemically treated bases.6

The design of the bracket base can improve adhesive penetration or the penetration of the curing light.7 Variables such as points, solder spurs, solder points on the joint surface, and the resin curing light penetration can affect the adhesion of the bracket.8

During debonding, adhesion failure can occur between the bracket and the adhesive interface, between the adhesive interface and the tooth enamel, or within the adhesive. When bond failure occurs at the adhesive-enamel interface, the risk of enamel damage increases due to the micromechanical bond between the adhesive and the tooth,9-11 which could lead to tooth enamel cracks or tooth enamel loss. The bond strength of orthodontic brackets should be high enough to keep the brackets securely in place throughout the treatment and withstand occlusal loads. However, very high bond strengths are unfavorable, as they increase the risk of enamel fractures and subsequent pulp injury after debonding.12,13 Therefore, bond strengths must allow for bracket debonding without damaging the tooth enamel.

The SBSs observed in an in vitro study may be higher than those observed clinically; however, they provide a guide for selecting the appropriate bracket and adhesive.14 Keizer et al.15 suggested SBS values of 6 to 10 MPa as clinically appropriate. In conventional metallic brackets using Transbond XT adhesive, SBS values of 7.24 MPa to 13.20 MPa are suggested.16-19 In aesthetic brackets with the same adhesive, SBS ranges from 14.62 MPa to 47.2 MPa.12,20-22 Mahmoud et al.23 reported an SBS of 9.66 MPa when the same commercial brackets and adhesive brands are used and 7.10 MPa when a different bracket brand is used.

In this in vitro study, we examined the meshes of nine different types of brackets using scanning electron microscopy (SEM), both before and after debonding. We also compared the SBS and the adhesive remnant index (ARI) among the different types of brackets.

MATERIALS AND METHODS

The study was approved by the Institutional Review Board of the Comités de Ética en Investigación, Investigación y Bioseguridad of the Centro Universitario de Ciencias de la Salud of the Universidad de Guadalajara (IRB no. CI-01822). Written informed consent was obtained from all participants who agreed to donate their teeth.

Ninety upper and lower premolars extracted from patients aged 13 to 15 years old for orthodontic treatment were used in this study. The samples were refrigerated at a constant temperature of 4°C, with water changed weekly to prevent bacterial growth in accordance with the International Organization for Standardization/Technical Specification (ISO/TS) 11405:2003 standard.24 Sample size “n” was determined in each section using Molina et al. method,1 based on an 80% power analysis and 95% confidence intervals.

Brackets

Ninety brackets were used for upper and lower right and left first premolars, representing nine bracket brands, with 10 brackets from each brand analyzed. The study included 60 metallic (G1-G6) and 30 aesthetic brackets (G7-G9), organized into nine groups of 10 brackets each, as follows:

  • G1: Alexander, American Orthodontics (LOT A37056, Sheboygan, WI, USA)

  • G2: Mini Sprint® Brackets, Forestadent (REF 706-1056, LOT 257, Pforzheim, Germany)

  • G3: In-Ovation R Complete Clinical Orthodontics (CCO), Dentsply Gac International (LOT 8327, Tokyo, Japan)

  • G4: Gemini SL Self-Ligating Brackets, 3M Unitek TM (REF 027-110, LOT 1631300722, Monrovia, CA, USA)

  • G5: Classic mini 2G Stylus® (LOT 041213, CDMX, Mexico)

  • G6: Gemini Metal Brackets, 3M UnitekTM (REF 119-144, LOT HW5KP, Monrovia, CA, USA)

  • G7: ClarityTM Advanced, 3M UnitekTM (REF 006-110, LOT GS1-128, Monrovia, CA, USA)

  • G8: Crystall-Ize® Stylus® (LOT 150320R1822, CDMEX, Mexico)

  • G9: Ceramic Series Flexx 2G® (LOT 091872, CDMEX, Mexico)

Bonding procedure

The teeth were polished with a rubber prophylaxis cup for 10 seconds, rinsed, and cleaned. Bracket bonding followed the manufacturer’s instructions. After rinsing with water, 3M ESPE ScotchbondTM Etching Gel at 37% (LOT 612-602, Neuss, Germany) was applied for 15 seconds and then rinsed off with water. The teeth were dried with oil-free air until a chalky white appearance was visible. A thin layer of TransbondTM XT Light Cure Adhesive Primer (LOT N642767, Monrovia, CA, USA) was applied. The brackets were bonded to the teeth using TransbondTM XT 3M Unitek (LOT N642767) with a positioner (Caliber Boone MASEL 4000-900). Excess bonding adhesive was removed with a small dental scaler. The adhesive was then light-cured for 20 seconds on the distal and mesial sides at a 2 mm distance using a light-curing unit (Bluephase C5, Ivoclar Vivadent AG, Schaan, Liechtenstein) with an output intensity of 600 mW/cm2. To bond the bracket to the tooth, a force of 10 N was applied for 10 seconds. All brackets were placed by a single operator, who had been calibrated using an analytical balance to consistently exert a force of 10 N, in accordance with ISO/TS 11405:2003 standard.24

Shear bond strength test

Each tooth was mounted in acrylic resin and stored in water at 37°C. The SBS test was conducted 24 hours after bracket placement using an Instron universal mechanical testing machine (Instron, model 5567, Norwood, MA, USA) with a loading speed of 1 mm/min.

Adhesive remnant index evaluation of Årtun and Bergland

The tooth surface was examined with an optical microscope at 32× magnification (Axiotech 25 HD, ZEISS, Jena, Germany) to assess the adhesive interface. The ARI scale, which ranges from 0 to 3, indicated the following: 0, no remnant adhesive on tooth enamel; 1, less than 50% remnant adhesive on tooth enamel; 2, more than 50% remnant adhesive on tooth enamel; and 3, 100% remnant adhesive on tooth enamel.25 All examinations were conducted blindly by a single, properly calibrated researcher (Kappa = 0.91).

Mesh observations through SEM

All the brackets, before and after debonding, were observed at 25×, 27×, and 30×. A low vacuum microscope (LV-SEM; Hitachi brand, model SU1510, Tokyo, Japan), with a spatial resolution of 4 nm, operating in low vacuum mode at 20 Pa, was used before bonding. After debonding, observations were made with another LV-SEM (Jeol, model JSM5600LV, Tokyo, Japan) with a spatial resolution of 3 nm. The images of the brackets before and after debonding were obtained in backscatter and shadow modes. Before bonding, the brackets were placed on the SEM sample holder using carbon tape and observed at 30 kV. After the SBS test, the brackets were coated with gold using a Cressington Sputter Coater 108 at 0.5 kV for 2 minutes and observed at 20 kV. No additional preparation techniques were used for the brackets. Since the brackets were observed using a low vacuum microscope and were gold-coated, surface charging was not an issue. Defects in the mesh and enamel loss were evaluated using SEM micrographs. For metal brackets, mesh weld points were inspected for defects, while for aesthetic brackets, the uniformity of surface aggregates was assessed. Brackets with enamel loss after debonding were further analyzed at 250× to identify the presence of enamel prisms.

Statistical analysis

Data were analyzed using R statistical software. Measurement values were assessed using a Shapiro–Wilk test to determine if the data followed a normal distribution. A Kruskal–Wallis test was conducted to identify statistically significant differences in the study groups, followed by a Pairwise–Wilcoxon test to determine differences between groups explicitly. All hypothesis tests were performed with a significance level of P < 0.05, and the P value for intergroup differences was 0.009. For ARI, a descriptive statistical analysis of frequency was performed.

RESULTS

In total, 90 brackets from different brands were examined, comprising 60 metallic (66.66%) and 30 aesthetic (33.33%) brackets, organized into nine groups of 10 brackets each. When analyzing the mesh and its factory defects, 65 of the 90 brackets showed no defects (72.22%), while 25 brackets (27.77%) exhibited defects. Among the metallic brackets, 66.66% had no defects, while 33.33% had defects. In contrast, 83.33% of the aesthetic brackets showed no defects, while 16.66% presented defects, as summarized in Table 1.

Table 1 . Mesh defects percentage of the study groups

GroupWith defect
(%)
Faultless
(%)
Total
(%)
G1. Alexander0100.0100.0
G2. Mini Sprint® Brackets0100.0100.0
G3. In-Ovation R CCO0100.0100.0
G4. Gemini SL Self-Ligating Brackets100.00100.0
G5. Classic mini 2G Stylus®100.00100.0
G6. Gemini Metal Brackets0100.0100.0
G7. ClarityTM Advanced40.060.0100.0
G8. Crystall-Ize®10.090.0100.0
G9. Ceramic Series Flexx 2G®0100.0100.0
Total27.7772.22100.0


In Figure 1, the meshes of the metallic brackets are displayed by brand at 27×. It is noticeable that images G1, G2, G3, and G6 show meshes without defects, while images G4 and G5 exhibit meshes with defects. In images G4A and G5A, which are a magnification of G4 and G5 at 90×, the defects in the junctions of their rods to the center of the brackets are visible.

Figure 1. Mesh images of the different metallic brackets. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus®; and G6, Gemini Metal Brackets. In G4A, a magnification of G4 at 90×, it is observed that a greater detail of the failure in the union of its rods is in the center of the bracket. In G5A, a magnification of G5 at 100×, the failure in the union of the rods can be seen.

In image G1, the double mesh design of the Alexander brand is observed, whereas image G2 illustrates 3D motifs on the base of the Mini Sprint® Brackets. Images G3, G5, and G6 display very regular meshes on the bases of these metallic brackets, in contrast to image G4, which shows an irregular mesh border.

In Figure 2, subfigures G7, G8, and G9 correspond to the meshes of the aesthetic brackets by brand at 25×. Image G7 in Figure 2 displays a smaller grain size on the bracket base than that displayed in G8. Subfigure G9 features 3D motifs similar to those in image G2 (Figure 1), which is reflected in the large surface contact area between the adhesive and the bracket base.

Figure 2. Mesh images of the different aesthetic brackets. In G7, ClarityTM Advanced, it is possible to see a defect, where G7A, at a higher magnification of 80×, shows it; meanwhile, in G7B, at 160×, the size of the aggregate can be seen. In G8, Crystall-Ize®, it is observed that the aggregates are not homogeneous, and G8A at 160× shows them in detail. Finally, in G9, Ceramic Series Flexx 2G®, the mesh without defects can be observed.

The meshes with defects are shown at higher magnifications: in subfigure G7A, which is a magnified view of G7 at 80×, a circular depth defect is noticeable, and in subfigure G7B, this same defect is visible at 160×, where smaller aggregate sizes in the mesh can also be observed. Image G8 reveals inhomogeneous aggregates, while G8A, a magnification of G8 at 160×, shows the aggregates in detail, indicating that they are larger than those in image G7. In subfigure G9, the mesh is displayed without defects.

In Table 2, the mean SBS of the nine groups is presented in MPa and N. Relevant SBS values are reported per group, including the median, maximum, minimum, and interquartile range. Among the metallic brackets, the Gemini SL Self-Ligating Brackets exhibited the highest average SBS at 11.93 MPa, while the In-Ovation R CCO group had the lowest average at 8.5 MPa. For the aesthetic brackets, the ClarityTM Advanced demonstrated the higher average SBS at 14.73 MPa, in contrast to the Crystall-Ize® group, which recorded the lowest value of 8.0 MPa.

Table 2 . Shear bond strength values per group in Mega-Pascals (MPa) and Newtons (N)

GroupnMean ± SD (MPa)Mean ± SD
(N)
Median (MPa)Min
(MPa)
Max
(MPa)
IQR
(MPa)
G1. Alexander1010.32 ± 2.35109.17 ± 24.869.508.3715.030.93
G2. Mini Sprint® Brackets109.41 ± 1.2890.43 ± 12.339.337.2312.051.56
G3. In-Ovation R CCO108.53 ± 2.70103.26 ± 32.727.335.7412.454.28
G4. Gemini SL Self-Ligating Brackets1011.93 ± 3.63123.80 ± 37.7111.417.7921.404.04
G5. Classic mini 2G Stylus®108.65 ± 2.2198.55 ± 25.187.805.9911.913.37
G6. Gemini Metal Brackets109.18 ± 3.3999.26 ± 36.698.603.7113.425.35
G7. ClarityTM Advanced1014.73 ± 1.82202.13 ± 25.0315.3512.6017.533.15
G8. Crystall-Ize®108.00 ± 1.4596.87 ± 17.637.905.5110.083.69
G9. Ceramic Series Flexx 2G®1010.91 ± 7.05125.30 ± 80.986.724.2620.6712.69

Standard deviation (SD), minimum (min), maximum (max), and interquartile range (IQR) per group are reported.



Metallic brackets had an average SBS value of 9.67 ± 2.84 MPa, while the aesthetic brackets had an average SBS value of 11.21 ± 4.99 MPa. The overall average SBS obtained from the total samples was 10.18 ± 3.74 MPa. To analyze general statistically significant differences between metallic and aesthetic brackets, the SBS values were grouped accordingly.

A Shapiro–Wilk test was conducted on each group, and in both cases, the data did not follow a normal distribution (P = 0.003 for metallic brackets and P = 0.047 for aesthetic brackets). Therefore, a Wilcoxon test was used, which indicated no statistically significant differences between metallic and aesthetic brackets (P = 0.33).

To determine the statistical differences between the nine groups, a multivariable Shapiro–Wilk test was conducted, revealing that the data did not follow a normal distribution (P < 0.05). Consequently, a Kruskal–Willis test was done with a resulting P = 0.0004, indicating statistical differences between the groups. To identify which specific groups differed, a Pairwise–Wilcoxon test was performed with a Benjamini–Hochberg correction, revealing significant differences based on the type of bracket and the SBS (P < 0.009). Table 3 summarizes the statistically significant differences in SBS based on the type of bracket.

Table 3 . Differences between the nine groups; an analysis was based on the brand of brackets and shear bond strength values

G1.
Alexander
G2.
Mini Sprint® Brackets
G3.
In-Ovation
R CCO
G4.
Gemini SL Self-Ligating Brackets
G5.
Classic mini
2G Stylus®
G6.
Gemini Metal Brackets
G7.
ClarityTM Advanced
G8.
Crystall-Ize®
G9. Ceramic Series
Flexx 2G®
G1. Alexander------0.0087*--
G2. Mini Sprint® Brackets------0.0016*--
G3. In-Ovation R CCO------0.0016*--
G4. Gemini SL Self-Ligating Brackets-------0.0052*-
G5. Classic mini 2G Stylus®------0.0016*--
G6. Gemini Metal Brackets------0.0087*--
G7. ClarityTM Advanced0.0087*0.0016*0.0016*-0.0016*0.0087*-0.0016*-
G8. Crystall-Ize®---0.0052*--0.0016*--
G9. Ceramic Series Flexx 2G®---------

The symbol “-” represents the cases where the statistical differences are not significant.

*Statistically significant differences at P < 0.009.



The distribution of the ARI Index values by bracket brand group is shown in Figure 3. The ARI scores for all groups were as follows: 51% presented a value of 2, 39% a value of 1, and 10% a value of 3. In the group of metallic brackets, 50% presented a value of 1, 48.33% value of 2, and 1.66% a value of 3. In contrast, for the group of aesthetic brackets, 56.66% presented a value of 2, 26.67% a value of 3, and 16.66% a value of 1.

Figure 3. Adhesive remnant index by bracket group.

The percentage of bracket meshes associated with tooth enamel (teeth with enamel loss) by group is illustrated in Figure 4. The samples with tooth enamel were quantified through an analysis of the bracket meshes using SEM. Of the total samples (100%), only 6.66% presented tooth enamel; in the metallic bracket group, 5% presented tooth enamel, while 95% did not. In contrast, the aesthetic bracket group showed that 10% presented tooth enamel, and 90% had no tooth enamel.

Figure 4. Percentage of bracket meshes with or absence of tooth enamel, namely percentage of teeth with or absence of enamel loss, respectively.

A contingency table for all groups incorporating ARI and enamel loss could not be analyzed because more than 20% of the cells presented a value of 0. The ARI was recategorized into two variables: those corresponding to < 50% of the remaining adhesive on the enamel and those > 50% of the remaining adhesive in the enamel (Table 4). The global results of the two ARI categories and enamel loss were analyzed with a 2 × 2 contingency table; the chi-square test indicated that more than 20% of the expected counts were less than 5; therefore, Fisher’s exact test was applied, revealing a relationship between enamel loss and the remaining adhesive (P = 0.004). However, Spearman’s rank correlation value of 0.34 indicates a weak association between the two ranked variables.

Table 4 . Global contingency table for enamel loss and recategorized ARI

ARIEnamel lossTotal
YesNot
< 50% of adhesive remaining on enamel6 (6.7)29 (32.2)35 (38.9)
> 50% of adhesive remaining on enamel0 (0)55 (61.1)55 (61.1)
Total6 (6.7)84 (93.3)90 (100.0)
Fisher’s exact testP = 0.004
Spearman’s rank correlation0.34

The frequencies and the percentage of the frequencies (in brackets) are presented.

ARI, adhesive remnant index.



Figure 5 displays the group of metallic brackets after debonding. In subfigures G1 and G2, the meshes are observed at 30× without any tooth enamel. In images G3 at 25× and G5 at 30×, the presence of tooth enamel (indicating enamel loss) is highlighted with a yellow circle. Images G3A and G5A, which are magnifications of G3 and G5 at 250×, show the structure of the enamel prisms. Finally, images G4 at 30× and G6 at 25× illustrate the metallic bracket mesh after debonding; however, tooth enamel is not visible in these images.

Figure 5. Mesh images at 25× and 30× of metallic brackets after debonding. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus® and G6, Gemini Metal Brackets. In G3A, a higher magnification (250×) of figure G3 is marked with a circle highlighting a fragment of tooth enamel (enamel loss), where the presence of enamel prisms is visible. In image G5A, a 250× magnification of figure G5 shows the failure in the union of the rods.

Figure 6 presents the group of aesthetic brackets at 25× after debonding. Image G7 shows the bracket mesh without any tooth enamel loss. The presence of tooth enamel on the bracket bases, highlighted in yellow circles in subfigures G8 and G9, corresponds to teeth where enamel loss occurred. In images G8A and G9A, which are magnifications of G8 and G9 at 250×, the structure of the enamel prisms is clearly visible.

Figure 6. Mesh images at 25× of aesthetic brackets. G7, ClarityTM Advanced; G8, Crystall-Ize®; and G9, Ceramic Series Flexx 2G®. G7 shows the bracket mesh with the absence of tooth enamel. G8 and G9 show a tooth enamel fragment marked in a yellow circle, and then in G8A and G9A, which are magnifications of G8 and G9 at 250×, the presence of tooth enamel prisms can be observed.

DISCUSSION

The results indicated a clear influence of bracket base shape on adhesion. In the metallic bracket groups, the highest SBS mean value was presented in group G4, comprising Gemini SL Self-Ligating Brackets. This trend can be understood by comparing the mesh designs of the other metallic brackets. The irregular bonding mesh of the G4 samples increased the contact surface area between the bracket base and the adhesive, enhancing the adhesion process on the tooth enamel. A similar phenomenon was observed with aesthetic brackets. Group G7, which included ClarityTM Advanced brackets, recorded the highest mean SBS among all groups. This could be attributed to the smaller grain size on the surface of the G7 samples, leading to a more porous surface that facilitated better adhesion between the bracket mesh and the tooth enamel. It is suggested that this process contributed to the elevated SBS mean value observed in group G7 compared to the other groups.

When comparing aesthetic bracket groups through SBS, statistically significant differences were observed between groups G7 and G8 (Table 3), which is reinforced by the notable differences in surface design and SBS mean values among these types of brackets. However, when comparing groups G7 and G9 or G8 and G9, no statistically significant differences were found, although the bracket meshes and the mean SBS varied. Another important point arose when comparing metallic and aesthetic brackets. As shown in Table 3, group G7 exhibited statistically significant differences compared to groups G1, G2, G3, G5, and G6, primarily due to the influence of bracket mesh shape. A similar trend occurred in groups G4 and G8. The aesthetic brackets in groups G7 and G8 featured a bracket mesh shape distinctly different from the other bracket meshes, highlighting the influence of the bracket mesh shape on mean SBS.

When the results of this study were compared with studies of other authors, some differences and similarities were found. Mitwally et al.21 reported high SBS in metallic brackets bonded with Transbond XT, indicating that these strengths could complicate the orthodontic bracket debonding process, potentially leading to cracks or even enamel fractures due to cohesive failures of 22.38 ± 6.08 MPa. This study’s findings align with their findings regarding the appearance of enamel cracks and fractures in some samples, even though the values reported here were lower (9.67 ± 2.84 MPa). They also reported an ARI score of 1; however, in our study, a value of 2 was obtained. Conversely, Alencar et al.26 observed that up to 6.94 mm2 of adhesive adhered to the tooth, i.e., less than half of the adhesive remained on the bracket base, which is consistent with the results of this study, as most samples showed less than 50% adhesive remaining on the brackets. This difference in outcomes may be attributed to variations in methodology and the application of thermocycling in their study.

Other authors, such as Delavarian et al.12 reported an average SBS of 13.71 ± 3.54 MPa for metallic brackets and 14.62 ± 4.30 MPa for ceramic brackets using the Transbond XT system, which aligns with the values reported in this study. They did not identify statistically significant differences in SBS values between metallic and ceramic brackets. In SEM, they observed the presence of cracks in metallic brackets across two samples from each group. However, the small sample sizes hindered their ability to draw definitive conclusions. In contrast, this study involved the examination of all brackets before and after debonding. Meanwhile, Mahmoud et al.23 reported an average SBS of 9.667 MPa in metallic brackets with the Transbond XT adhesive system and an ARI index value of 1, which corresponds with the findings for the group of metallic brackets reported here. They also reported that as SBS values increased, the ARI index decreased. Furthermore, Hellak et al.27 reported an average SBS of 15.49 ± 3.28 MPa for metallic brackets using Transbond XT and an ARI index value of 0. This study does not agree with those values, and the differences can likely be attributed to variations in methodology and the preparation methods used.

Furthermore, Zanarini et al.28 reported percentages of tooth enamel present on and within the resin. Specifically, they found that 83% of the samples exhibited a thin enamel coat over the resin surface, 7% contained sizable enamel fragments attached to the composite resin, and 10% had a smooth surface with no evidence of enamel presence. In the present study, only two samples presented enamel fragments, and in four, a small layer of prisms was evident through SEM. However, this finding was not statistically significant since it only appeared in 6.66% of the total samples, which may be attributed to methodological differences.

In addition, Ferreira et al.29 concluded that dental enamel was lost during each step of the bonding and debonding procedures evaluated, with the greatest loss occurring after acid conditioning. However, they only examined seven samples, while in the present study, all brackets were observed, revealing enamel loss in only six samples.

CONCLUSIONS

The present study concluded that the bracket mesh shapes influence SBS because some mesh shapes increase the contact surface area between the adhesive and tooth enamel. The meshes of the aesthetic brackets ClarityTM Advanced and Crystall-Ize® exemplified this. Due to the significant differences in bracket meshes, some statistically significant differences were found in the SBS values between metallic and aesthetic brackets. For example, there were statistically significant differences between the aesthetic bracket brand, ClarityTM Advanced, and several metallic bracket brands, including Alexander, Mini Sprint® Brackets, In-Ovation R CCO, Classic mini 2G Stylus®, and Gemini Metal Brackets. Notably, no statistically significant differences were found in the SBS values between the metallic bracket groups, as their bracket mesh shapes were not fundamentally different.

It is also worth mentioning that although the findings of this study align with clinically acceptable average SBS values, tooth enamel was found in 6.66% of brackets analyzed, indicating that 6.66% of the teeth had enamel loss. However, this enamel loss is unlikely to cause significant clinical consequences such as lesions or erosion since enamel loss during bracket removal is almost inevitable. Furthermore, no clear association was found between SBS values, bracket mesh shape, and the presence of tooth enamel on the bracket base after debonding. In fact, most samples showed less than 50% of adhesive remaining on the bracket base.

ACKNOWLEDGEMENTS

The authors extend their gratitude to the Central Electron Microscopy Laboratory IF-UNAM for providing the facilities and to M. Monroy, J. Cañetas-Ortega, S. Tehuacanero-Cuapa, M. Aguilar-Franco, and C. Zorrilla for their technical assistance; to Biomaterials Dental Laboratory at the Research Division of Dentistry Faculty at UNAM and to J. Gerrero-Ibarra and T. Baeza-Kingston for technical assistance; to students C. S. Andrade-Martinez, D. Fisher-Martínez, M. C. Soto-Mata, and J. Collins-Cordero for their comments.

AUTHOR CONTRIBUTIONS

Conceptualization: JARC. Data curation: HMFR, AFL. Formal analysis: HMFR, AFL. Investigation: JARC, AGP, LBD. Writing–original draft: JARC. Writing–review & editing: HMFR, AFL.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

None to declare.

References

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  22. Hofmann E, Elsner L, Hirschfelder U, Ebert T, Hanke S. Effects of enamel sealing on shear bond strength and the adhesive remnant index: study of three fluoride-releasing adhesives in combination with metal and ceramic brackets. J Orofac Orthop 2017;78:1-10. https://doi.org/10.1007/s00056-016-0065-x
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  23. Mahmoud E, Pacurar M, Bechir ES, Maris M, Olteanu C, Dascalu IT, et al. Comparison of shear bond strength and adhesive remnant index of brackets bonded with two types of orthodontic adhesives. Mater Plast 2017;54:141-4. https://doi.org/10.37358/MP.17.1.4805
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  26. Alencar EQ, Nobrega ML, Dametto FR, Santos PB, Pinheiro FH. Comparison of two methods of visual magnification for removal of adhesive flash during bracket placement using two types of orthodontic bonding agents. Dental Press J Orthod 2016;21:43-50. https://doi.org/10.1590/2177-6709.21.6.043-050.oar
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Article

Original Article

Korean J Orthod 2025; 55(1): 15-25   https://doi.org/10.4041/kjod24.073

First Published Date October 11, 2024, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

Scanning electron microscopy analysis of metallic and aesthetic bracket meshes before and after debonding

Jacqueline Adelina Rodríguez-Cháveza , Hugo Marcelo Flores-Ruizb , Abigailt Flores-Ledesmac , Alvaro García-Pérezd , Lourdes Bazán-Diaze

aInstitute of Dental Research, Department of Integral Dental Clinics, University Center for Health Sciences, University of Guadalajara, Guadalajara, Mexico
bDepartment of Natural and Exact Sciences, CUValles, University of Guadalajara, Ameca, Mexico
cLaboratory of Dental Materials and Biomaterials, Meritorious Autonomous University of Puebla, Puebla, Mexico
dLaboratory of Public Health Research, National Autonomous University of Mexico (UNAM), Tlalnepantla, Mexico
eMaterials Research Institute, National Autonomous University of Mexico, Mexico City, Mexico

Correspondence to:Jacqueline Adelina Rodríguez-Chávez.
Professor, Institute of Dental Research, Department of Integral Dental Clinics, University Center for Health Sciences, University of Guadalajara, Salvador Quevedo y Zubieta street 228, building B, second floor, Independencia Oriente colony, Guadalajara 44340, Mexico.
Tel +52-3310585200 (ext. 33866) e-mail jacqueline.rchavez@academicos.udg.mx

How to cite this article: Rodríguez-Chávez JA, Flores-Ruiz HM, Flores-Ledesma A, García-Pérez A, Bazán-Diaz L. Scanning electron microscopy analysis of metallic and aesthetic bracket meshes before and after debonding. Korean J Orthod 2025;55(1):15-25. https://doi.org/10.4041/kjod24.073

Received: April 9, 2024; Revised: September 10, 2024; Accepted: October 9, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective: To study the influence of bracket base meshes on shear bond strength and observe them using a scanning electron microscopy (SEM) before and after debonding. Methods: Ninety brackets were divided into nine groups of 10 samples each: G1-Alexander, G2-Mini Sprint® Brackets, G3-In-Ovation R CCO, G4-Gemini SL Self-Ligating Bracket, G5-Classic mini 2G Stylus®, G6-Gemini Metal Brackets, G7-ClarityTM Advanced, G8-Crystall-Ize®, and G9-Ceramic Series Flexx 2G®. Groups G1 to G6 and G7 to G9 consisted of metallic and aesthetic brackets, respectively. Initial photographs of all brackets were taken through SEM at 25X magnification. The brackets were then bonded to premolars using TransbondTM XT, and a shear bond strength test was conducted after 24 hours using an Instron machine at 1 mm/min. After debonding, the bracket meshes were observed using SEM. Results: Before bonding, 72.22% of brackets didn’t present mesh defects, while 27.77% did. SEM analysis revealed that G4 and G5 presented defects in 100%, G7 in 40%, and G8 in 10%. The average shear bond strength of 9.67 ± 2.84 MPa and 11.21 ± 4.99 MPa were obtained for both metallic and aesthetic brackets, respectively. A Pairwise–Wilcoxon test with Benjamini–Hochberg correction was conducted to determine specific statistical differences between the groups, revealing significant differences based on bracket type and shear bond strength (P < 0.009). Conclusions: This study suggested that the shape of bracket meshes influenced shear bond strength.

Keywords: Bracket, Adhesive, Shear bond strength, Scanning electron microscopy

INTRODUCTION

Bracket base designs vary to optimize adhesion between the bracket’s mechanical retention and the adhesive.1,2 This variability includes factors such as bracket material, prescription, base size, ligation type, and retentive base design.3 Among these, the bracket retentive base design is a significant factor influencing shear bond strength (SBS).2 Currently, orthodontic brackets are fabricated from several types of materials with varying degrees of roughness, including metal, ceramic, plastic, titanium, and composite.4 Innovative approaches to improve retention include laser treatments, metal plasma-coated bases, and fusing metallic or ceramic particles to the base.5 For ceramic brackets, retention mechanisms include mechanically retentive bases, chemically retentive bases with silane treatment, and mechanically chemically treated bases.6

The design of the bracket base can improve adhesive penetration or the penetration of the curing light.7 Variables such as points, solder spurs, solder points on the joint surface, and the resin curing light penetration can affect the adhesion of the bracket.8

During debonding, adhesion failure can occur between the bracket and the adhesive interface, between the adhesive interface and the tooth enamel, or within the adhesive. When bond failure occurs at the adhesive-enamel interface, the risk of enamel damage increases due to the micromechanical bond between the adhesive and the tooth,9-11 which could lead to tooth enamel cracks or tooth enamel loss. The bond strength of orthodontic brackets should be high enough to keep the brackets securely in place throughout the treatment and withstand occlusal loads. However, very high bond strengths are unfavorable, as they increase the risk of enamel fractures and subsequent pulp injury after debonding.12,13 Therefore, bond strengths must allow for bracket debonding without damaging the tooth enamel.

The SBSs observed in an in vitro study may be higher than those observed clinically; however, they provide a guide for selecting the appropriate bracket and adhesive.14 Keizer et al.15 suggested SBS values of 6 to 10 MPa as clinically appropriate. In conventional metallic brackets using Transbond XT adhesive, SBS values of 7.24 MPa to 13.20 MPa are suggested.16-19 In aesthetic brackets with the same adhesive, SBS ranges from 14.62 MPa to 47.2 MPa.12,20-22 Mahmoud et al.23 reported an SBS of 9.66 MPa when the same commercial brackets and adhesive brands are used and 7.10 MPa when a different bracket brand is used.

In this in vitro study, we examined the meshes of nine different types of brackets using scanning electron microscopy (SEM), both before and after debonding. We also compared the SBS and the adhesive remnant index (ARI) among the different types of brackets.

MATERIALS AND METHODS

The study was approved by the Institutional Review Board of the Comités de Ética en Investigación, Investigación y Bioseguridad of the Centro Universitario de Ciencias de la Salud of the Universidad de Guadalajara (IRB no. CI-01822). Written informed consent was obtained from all participants who agreed to donate their teeth.

Ninety upper and lower premolars extracted from patients aged 13 to 15 years old for orthodontic treatment were used in this study. The samples were refrigerated at a constant temperature of 4°C, with water changed weekly to prevent bacterial growth in accordance with the International Organization for Standardization/Technical Specification (ISO/TS) 11405:2003 standard.24 Sample size “n” was determined in each section using Molina et al. method,1 based on an 80% power analysis and 95% confidence intervals.

Brackets

Ninety brackets were used for upper and lower right and left first premolars, representing nine bracket brands, with 10 brackets from each brand analyzed. The study included 60 metallic (G1-G6) and 30 aesthetic brackets (G7-G9), organized into nine groups of 10 brackets each, as follows:

  • G1: Alexander, American Orthodontics (LOT A37056, Sheboygan, WI, USA)

  • G2: Mini Sprint® Brackets, Forestadent (REF 706-1056, LOT 257, Pforzheim, Germany)

  • G3: In-Ovation R Complete Clinical Orthodontics (CCO), Dentsply Gac International (LOT 8327, Tokyo, Japan)

  • G4: Gemini SL Self-Ligating Brackets, 3M Unitek TM (REF 027-110, LOT 1631300722, Monrovia, CA, USA)

  • G5: Classic mini 2G Stylus® (LOT 041213, CDMX, Mexico)

  • G6: Gemini Metal Brackets, 3M UnitekTM (REF 119-144, LOT HW5KP, Monrovia, CA, USA)

  • G7: ClarityTM Advanced, 3M UnitekTM (REF 006-110, LOT GS1-128, Monrovia, CA, USA)

  • G8: Crystall-Ize® Stylus® (LOT 150320R1822, CDMEX, Mexico)

  • G9: Ceramic Series Flexx 2G® (LOT 091872, CDMEX, Mexico)

Bonding procedure

The teeth were polished with a rubber prophylaxis cup for 10 seconds, rinsed, and cleaned. Bracket bonding followed the manufacturer’s instructions. After rinsing with water, 3M ESPE ScotchbondTM Etching Gel at 37% (LOT 612-602, Neuss, Germany) was applied for 15 seconds and then rinsed off with water. The teeth were dried with oil-free air until a chalky white appearance was visible. A thin layer of TransbondTM XT Light Cure Adhesive Primer (LOT N642767, Monrovia, CA, USA) was applied. The brackets were bonded to the teeth using TransbondTM XT 3M Unitek (LOT N642767) with a positioner (Caliber Boone MASEL 4000-900). Excess bonding adhesive was removed with a small dental scaler. The adhesive was then light-cured for 20 seconds on the distal and mesial sides at a 2 mm distance using a light-curing unit (Bluephase C5, Ivoclar Vivadent AG, Schaan, Liechtenstein) with an output intensity of 600 mW/cm2. To bond the bracket to the tooth, a force of 10 N was applied for 10 seconds. All brackets were placed by a single operator, who had been calibrated using an analytical balance to consistently exert a force of 10 N, in accordance with ISO/TS 11405:2003 standard.24

Shear bond strength test

Each tooth was mounted in acrylic resin and stored in water at 37°C. The SBS test was conducted 24 hours after bracket placement using an Instron universal mechanical testing machine (Instron, model 5567, Norwood, MA, USA) with a loading speed of 1 mm/min.

Adhesive remnant index evaluation of Årtun and Bergland

The tooth surface was examined with an optical microscope at 32× magnification (Axiotech 25 HD, ZEISS, Jena, Germany) to assess the adhesive interface. The ARI scale, which ranges from 0 to 3, indicated the following: 0, no remnant adhesive on tooth enamel; 1, less than 50% remnant adhesive on tooth enamel; 2, more than 50% remnant adhesive on tooth enamel; and 3, 100% remnant adhesive on tooth enamel.25 All examinations were conducted blindly by a single, properly calibrated researcher (Kappa = 0.91).

Mesh observations through SEM

All the brackets, before and after debonding, were observed at 25×, 27×, and 30×. A low vacuum microscope (LV-SEM; Hitachi brand, model SU1510, Tokyo, Japan), with a spatial resolution of 4 nm, operating in low vacuum mode at 20 Pa, was used before bonding. After debonding, observations were made with another LV-SEM (Jeol, model JSM5600LV, Tokyo, Japan) with a spatial resolution of 3 nm. The images of the brackets before and after debonding were obtained in backscatter and shadow modes. Before bonding, the brackets were placed on the SEM sample holder using carbon tape and observed at 30 kV. After the SBS test, the brackets were coated with gold using a Cressington Sputter Coater 108 at 0.5 kV for 2 minutes and observed at 20 kV. No additional preparation techniques were used for the brackets. Since the brackets were observed using a low vacuum microscope and were gold-coated, surface charging was not an issue. Defects in the mesh and enamel loss were evaluated using SEM micrographs. For metal brackets, mesh weld points were inspected for defects, while for aesthetic brackets, the uniformity of surface aggregates was assessed. Brackets with enamel loss after debonding were further analyzed at 250× to identify the presence of enamel prisms.

Statistical analysis

Data were analyzed using R statistical software. Measurement values were assessed using a Shapiro–Wilk test to determine if the data followed a normal distribution. A Kruskal–Wallis test was conducted to identify statistically significant differences in the study groups, followed by a Pairwise–Wilcoxon test to determine differences between groups explicitly. All hypothesis tests were performed with a significance level of P < 0.05, and the P value for intergroup differences was 0.009. For ARI, a descriptive statistical analysis of frequency was performed.

RESULTS

In total, 90 brackets from different brands were examined, comprising 60 metallic (66.66%) and 30 aesthetic (33.33%) brackets, organized into nine groups of 10 brackets each. When analyzing the mesh and its factory defects, 65 of the 90 brackets showed no defects (72.22%), while 25 brackets (27.77%) exhibited defects. Among the metallic brackets, 66.66% had no defects, while 33.33% had defects. In contrast, 83.33% of the aesthetic brackets showed no defects, while 16.66% presented defects, as summarized in Table 1.

Table 1 . Mesh defects percentage of the study groups.

GroupWith defect
(%)
Faultless
(%)
Total
(%)
G1. Alexander0100.0100.0
G2. Mini Sprint® Brackets0100.0100.0
G3. In-Ovation R CCO0100.0100.0
G4. Gemini SL Self-Ligating Brackets100.00100.0
G5. Classic mini 2G Stylus®100.00100.0
G6. Gemini Metal Brackets0100.0100.0
G7. ClarityTM Advanced40.060.0100.0
G8. Crystall-Ize®10.090.0100.0
G9. Ceramic Series Flexx 2G®0100.0100.0
Total27.7772.22100.0


In Figure 1, the meshes of the metallic brackets are displayed by brand at 27×. It is noticeable that images G1, G2, G3, and G6 show meshes without defects, while images G4 and G5 exhibit meshes with defects. In images G4A and G5A, which are a magnification of G4 and G5 at 90×, the defects in the junctions of their rods to the center of the brackets are visible.

Figure 1. Mesh images of the different metallic brackets. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus®; and G6, Gemini Metal Brackets. In G4A, a magnification of G4 at 90×, it is observed that a greater detail of the failure in the union of its rods is in the center of the bracket. In G5A, a magnification of G5 at 100×, the failure in the union of the rods can be seen.

In image G1, the double mesh design of the Alexander brand is observed, whereas image G2 illustrates 3D motifs on the base of the Mini Sprint® Brackets. Images G3, G5, and G6 display very regular meshes on the bases of these metallic brackets, in contrast to image G4, which shows an irregular mesh border.

In Figure 2, subfigures G7, G8, and G9 correspond to the meshes of the aesthetic brackets by brand at 25×. Image G7 in Figure 2 displays a smaller grain size on the bracket base than that displayed in G8. Subfigure G9 features 3D motifs similar to those in image G2 (Figure 1), which is reflected in the large surface contact area between the adhesive and the bracket base.

Figure 2. Mesh images of the different aesthetic brackets. In G7, ClarityTM Advanced, it is possible to see a defect, where G7A, at a higher magnification of 80×, shows it; meanwhile, in G7B, at 160×, the size of the aggregate can be seen. In G8, Crystall-Ize®, it is observed that the aggregates are not homogeneous, and G8A at 160× shows them in detail. Finally, in G9, Ceramic Series Flexx 2G®, the mesh without defects can be observed.

The meshes with defects are shown at higher magnifications: in subfigure G7A, which is a magnified view of G7 at 80×, a circular depth defect is noticeable, and in subfigure G7B, this same defect is visible at 160×, where smaller aggregate sizes in the mesh can also be observed. Image G8 reveals inhomogeneous aggregates, while G8A, a magnification of G8 at 160×, shows the aggregates in detail, indicating that they are larger than those in image G7. In subfigure G9, the mesh is displayed without defects.

In Table 2, the mean SBS of the nine groups is presented in MPa and N. Relevant SBS values are reported per group, including the median, maximum, minimum, and interquartile range. Among the metallic brackets, the Gemini SL Self-Ligating Brackets exhibited the highest average SBS at 11.93 MPa, while the In-Ovation R CCO group had the lowest average at 8.5 MPa. For the aesthetic brackets, the ClarityTM Advanced demonstrated the higher average SBS at 14.73 MPa, in contrast to the Crystall-Ize® group, which recorded the lowest value of 8.0 MPa.

Table 2 . Shear bond strength values per group in Mega-Pascals (MPa) and Newtons (N).

GroupnMean ± SD (MPa)Mean ± SD
(N)
Median (MPa)Min
(MPa)
Max
(MPa)
IQR
(MPa)
G1. Alexander1010.32 ± 2.35109.17 ± 24.869.508.3715.030.93
G2. Mini Sprint® Brackets109.41 ± 1.2890.43 ± 12.339.337.2312.051.56
G3. In-Ovation R CCO108.53 ± 2.70103.26 ± 32.727.335.7412.454.28
G4. Gemini SL Self-Ligating Brackets1011.93 ± 3.63123.80 ± 37.7111.417.7921.404.04
G5. Classic mini 2G Stylus®108.65 ± 2.2198.55 ± 25.187.805.9911.913.37
G6. Gemini Metal Brackets109.18 ± 3.3999.26 ± 36.698.603.7113.425.35
G7. ClarityTM Advanced1014.73 ± 1.82202.13 ± 25.0315.3512.6017.533.15
G8. Crystall-Ize®108.00 ± 1.4596.87 ± 17.637.905.5110.083.69
G9. Ceramic Series Flexx 2G®1010.91 ± 7.05125.30 ± 80.986.724.2620.6712.69

Standard deviation (SD), minimum (min), maximum (max), and interquartile range (IQR) per group are reported..



Metallic brackets had an average SBS value of 9.67 ± 2.84 MPa, while the aesthetic brackets had an average SBS value of 11.21 ± 4.99 MPa. The overall average SBS obtained from the total samples was 10.18 ± 3.74 MPa. To analyze general statistically significant differences between metallic and aesthetic brackets, the SBS values were grouped accordingly.

A Shapiro–Wilk test was conducted on each group, and in both cases, the data did not follow a normal distribution (P = 0.003 for metallic brackets and P = 0.047 for aesthetic brackets). Therefore, a Wilcoxon test was used, which indicated no statistically significant differences between metallic and aesthetic brackets (P = 0.33).

To determine the statistical differences between the nine groups, a multivariable Shapiro–Wilk test was conducted, revealing that the data did not follow a normal distribution (P < 0.05). Consequently, a Kruskal–Willis test was done with a resulting P = 0.0004, indicating statistical differences between the groups. To identify which specific groups differed, a Pairwise–Wilcoxon test was performed with a Benjamini–Hochberg correction, revealing significant differences based on the type of bracket and the SBS (P < 0.009). Table 3 summarizes the statistically significant differences in SBS based on the type of bracket.

Table 3 . Differences between the nine groups; an analysis was based on the brand of brackets and shear bond strength values.

G1.
Alexander
G2.
Mini Sprint® Brackets
G3.
In-Ovation
R CCO
G4.
Gemini SL Self-Ligating Brackets
G5.
Classic mini
2G Stylus®
G6.
Gemini Metal Brackets
G7.
ClarityTM Advanced
G8.
Crystall-Ize®
G9. Ceramic Series
Flexx 2G®
G1. Alexander------0.0087*--
G2. Mini Sprint® Brackets------0.0016*--
G3. In-Ovation R CCO------0.0016*--
G4. Gemini SL Self-Ligating Brackets-------0.0052*-
G5. Classic mini 2G Stylus®------0.0016*--
G6. Gemini Metal Brackets------0.0087*--
G7. ClarityTM Advanced0.0087*0.0016*0.0016*-0.0016*0.0087*-0.0016*-
G8. Crystall-Ize®---0.0052*--0.0016*--
G9. Ceramic Series Flexx 2G®---------

The symbol “-” represents the cases where the statistical differences are not significant..

*Statistically significant differences at P < 0.009..



The distribution of the ARI Index values by bracket brand group is shown in Figure 3. The ARI scores for all groups were as follows: 51% presented a value of 2, 39% a value of 1, and 10% a value of 3. In the group of metallic brackets, 50% presented a value of 1, 48.33% value of 2, and 1.66% a value of 3. In contrast, for the group of aesthetic brackets, 56.66% presented a value of 2, 26.67% a value of 3, and 16.66% a value of 1.

Figure 3. Adhesive remnant index by bracket group.

The percentage of bracket meshes associated with tooth enamel (teeth with enamel loss) by group is illustrated in Figure 4. The samples with tooth enamel were quantified through an analysis of the bracket meshes using SEM. Of the total samples (100%), only 6.66% presented tooth enamel; in the metallic bracket group, 5% presented tooth enamel, while 95% did not. In contrast, the aesthetic bracket group showed that 10% presented tooth enamel, and 90% had no tooth enamel.

Figure 4. Percentage of bracket meshes with or absence of tooth enamel, namely percentage of teeth with or absence of enamel loss, respectively.

A contingency table for all groups incorporating ARI and enamel loss could not be analyzed because more than 20% of the cells presented a value of 0. The ARI was recategorized into two variables: those corresponding to < 50% of the remaining adhesive on the enamel and those > 50% of the remaining adhesive in the enamel (Table 4). The global results of the two ARI categories and enamel loss were analyzed with a 2 × 2 contingency table; the chi-square test indicated that more than 20% of the expected counts were less than 5; therefore, Fisher’s exact test was applied, revealing a relationship between enamel loss and the remaining adhesive (P = 0.004). However, Spearman’s rank correlation value of 0.34 indicates a weak association between the two ranked variables.

Table 4 . Global contingency table for enamel loss and recategorized ARI.

ARIEnamel lossTotal
YesNot
< 50% of adhesive remaining on enamel6 (6.7)29 (32.2)35 (38.9)
> 50% of adhesive remaining on enamel0 (0)55 (61.1)55 (61.1)
Total6 (6.7)84 (93.3)90 (100.0)
Fisher’s exact testP = 0.004
Spearman’s rank correlation0.34

The frequencies and the percentage of the frequencies (in brackets) are presented..

ARI, adhesive remnant index..



Figure 5 displays the group of metallic brackets after debonding. In subfigures G1 and G2, the meshes are observed at 30× without any tooth enamel. In images G3 at 25× and G5 at 30×, the presence of tooth enamel (indicating enamel loss) is highlighted with a yellow circle. Images G3A and G5A, which are magnifications of G3 and G5 at 250×, show the structure of the enamel prisms. Finally, images G4 at 30× and G6 at 25× illustrate the metallic bracket mesh after debonding; however, tooth enamel is not visible in these images.

Figure 5. Mesh images at 25× and 30× of metallic brackets after debonding. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus® and G6, Gemini Metal Brackets. In G3A, a higher magnification (250×) of figure G3 is marked with a circle highlighting a fragment of tooth enamel (enamel loss), where the presence of enamel prisms is visible. In image G5A, a 250× magnification of figure G5 shows the failure in the union of the rods.

Figure 6 presents the group of aesthetic brackets at 25× after debonding. Image G7 shows the bracket mesh without any tooth enamel loss. The presence of tooth enamel on the bracket bases, highlighted in yellow circles in subfigures G8 and G9, corresponds to teeth where enamel loss occurred. In images G8A and G9A, which are magnifications of G8 and G9 at 250×, the structure of the enamel prisms is clearly visible.

Figure 6. Mesh images at 25× of aesthetic brackets. G7, ClarityTM Advanced; G8, Crystall-Ize®; and G9, Ceramic Series Flexx 2G®. G7 shows the bracket mesh with the absence of tooth enamel. G8 and G9 show a tooth enamel fragment marked in a yellow circle, and then in G8A and G9A, which are magnifications of G8 and G9 at 250×, the presence of tooth enamel prisms can be observed.

DISCUSSION

The results indicated a clear influence of bracket base shape on adhesion. In the metallic bracket groups, the highest SBS mean value was presented in group G4, comprising Gemini SL Self-Ligating Brackets. This trend can be understood by comparing the mesh designs of the other metallic brackets. The irregular bonding mesh of the G4 samples increased the contact surface area between the bracket base and the adhesive, enhancing the adhesion process on the tooth enamel. A similar phenomenon was observed with aesthetic brackets. Group G7, which included ClarityTM Advanced brackets, recorded the highest mean SBS among all groups. This could be attributed to the smaller grain size on the surface of the G7 samples, leading to a more porous surface that facilitated better adhesion between the bracket mesh and the tooth enamel. It is suggested that this process contributed to the elevated SBS mean value observed in group G7 compared to the other groups.

When comparing aesthetic bracket groups through SBS, statistically significant differences were observed between groups G7 and G8 (Table 3), which is reinforced by the notable differences in surface design and SBS mean values among these types of brackets. However, when comparing groups G7 and G9 or G8 and G9, no statistically significant differences were found, although the bracket meshes and the mean SBS varied. Another important point arose when comparing metallic and aesthetic brackets. As shown in Table 3, group G7 exhibited statistically significant differences compared to groups G1, G2, G3, G5, and G6, primarily due to the influence of bracket mesh shape. A similar trend occurred in groups G4 and G8. The aesthetic brackets in groups G7 and G8 featured a bracket mesh shape distinctly different from the other bracket meshes, highlighting the influence of the bracket mesh shape on mean SBS.

When the results of this study were compared with studies of other authors, some differences and similarities were found. Mitwally et al.21 reported high SBS in metallic brackets bonded with Transbond XT, indicating that these strengths could complicate the orthodontic bracket debonding process, potentially leading to cracks or even enamel fractures due to cohesive failures of 22.38 ± 6.08 MPa. This study’s findings align with their findings regarding the appearance of enamel cracks and fractures in some samples, even though the values reported here were lower (9.67 ± 2.84 MPa). They also reported an ARI score of 1; however, in our study, a value of 2 was obtained. Conversely, Alencar et al.26 observed that up to 6.94 mm2 of adhesive adhered to the tooth, i.e., less than half of the adhesive remained on the bracket base, which is consistent with the results of this study, as most samples showed less than 50% adhesive remaining on the brackets. This difference in outcomes may be attributed to variations in methodology and the application of thermocycling in their study.

Other authors, such as Delavarian et al.12 reported an average SBS of 13.71 ± 3.54 MPa for metallic brackets and 14.62 ± 4.30 MPa for ceramic brackets using the Transbond XT system, which aligns with the values reported in this study. They did not identify statistically significant differences in SBS values between metallic and ceramic brackets. In SEM, they observed the presence of cracks in metallic brackets across two samples from each group. However, the small sample sizes hindered their ability to draw definitive conclusions. In contrast, this study involved the examination of all brackets before and after debonding. Meanwhile, Mahmoud et al.23 reported an average SBS of 9.667 MPa in metallic brackets with the Transbond XT adhesive system and an ARI index value of 1, which corresponds with the findings for the group of metallic brackets reported here. They also reported that as SBS values increased, the ARI index decreased. Furthermore, Hellak et al.27 reported an average SBS of 15.49 ± 3.28 MPa for metallic brackets using Transbond XT and an ARI index value of 0. This study does not agree with those values, and the differences can likely be attributed to variations in methodology and the preparation methods used.

Furthermore, Zanarini et al.28 reported percentages of tooth enamel present on and within the resin. Specifically, they found that 83% of the samples exhibited a thin enamel coat over the resin surface, 7% contained sizable enamel fragments attached to the composite resin, and 10% had a smooth surface with no evidence of enamel presence. In the present study, only two samples presented enamel fragments, and in four, a small layer of prisms was evident through SEM. However, this finding was not statistically significant since it only appeared in 6.66% of the total samples, which may be attributed to methodological differences.

In addition, Ferreira et al.29 concluded that dental enamel was lost during each step of the bonding and debonding procedures evaluated, with the greatest loss occurring after acid conditioning. However, they only examined seven samples, while in the present study, all brackets were observed, revealing enamel loss in only six samples.

CONCLUSIONS

The present study concluded that the bracket mesh shapes influence SBS because some mesh shapes increase the contact surface area between the adhesive and tooth enamel. The meshes of the aesthetic brackets ClarityTM Advanced and Crystall-Ize® exemplified this. Due to the significant differences in bracket meshes, some statistically significant differences were found in the SBS values between metallic and aesthetic brackets. For example, there were statistically significant differences between the aesthetic bracket brand, ClarityTM Advanced, and several metallic bracket brands, including Alexander, Mini Sprint® Brackets, In-Ovation R CCO, Classic mini 2G Stylus®, and Gemini Metal Brackets. Notably, no statistically significant differences were found in the SBS values between the metallic bracket groups, as their bracket mesh shapes were not fundamentally different.

It is also worth mentioning that although the findings of this study align with clinically acceptable average SBS values, tooth enamel was found in 6.66% of brackets analyzed, indicating that 6.66% of the teeth had enamel loss. However, this enamel loss is unlikely to cause significant clinical consequences such as lesions or erosion since enamel loss during bracket removal is almost inevitable. Furthermore, no clear association was found between SBS values, bracket mesh shape, and the presence of tooth enamel on the bracket base after debonding. In fact, most samples showed less than 50% of adhesive remaining on the bracket base.

ACKNOWLEDGEMENTS

The authors extend their gratitude to the Central Electron Microscopy Laboratory IF-UNAM for providing the facilities and to M. Monroy, J. Cañetas-Ortega, S. Tehuacanero-Cuapa, M. Aguilar-Franco, and C. Zorrilla for their technical assistance; to Biomaterials Dental Laboratory at the Research Division of Dentistry Faculty at UNAM and to J. Gerrero-Ibarra and T. Baeza-Kingston for technical assistance; to students C. S. Andrade-Martinez, D. Fisher-Martínez, M. C. Soto-Mata, and J. Collins-Cordero for their comments.

AUTHOR CONTRIBUTIONS

Conceptualization: JARC. Data curation: HMFR, AFL. Formal analysis: HMFR, AFL. Investigation: JARC, AGP, LBD. Writing–original draft: JARC. Writing–review & editing: HMFR, AFL.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

None to declare.

Fig 1.

Figure 1.Mesh images of the different metallic brackets. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus®; and G6, Gemini Metal Brackets. In G4A, a magnification of G4 at 90×, it is observed that a greater detail of the failure in the union of its rods is in the center of the bracket. In G5A, a magnification of G5 at 100×, the failure in the union of the rods can be seen.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Fig 2.

Figure 2.Mesh images of the different aesthetic brackets. In G7, ClarityTM Advanced, it is possible to see a defect, where G7A, at a higher magnification of 80×, shows it; meanwhile, in G7B, at 160×, the size of the aggregate can be seen. In G8, Crystall-Ize®, it is observed that the aggregates are not homogeneous, and G8A at 160× shows them in detail. Finally, in G9, Ceramic Series Flexx 2G®, the mesh without defects can be observed.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Fig 3.

Figure 3.Adhesive remnant index by bracket group.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Fig 4.

Figure 4.Percentage of bracket meshes with or absence of tooth enamel, namely percentage of teeth with or absence of enamel loss, respectively.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Fig 5.

Figure 5.Mesh images at 25× and 30× of metallic brackets after debonding. G1, Alexander; G2, Mini Sprint® Brackets; G3, In-Ovation R CCO; G4, Gemini SL Self-Ligating Brackets; G5, Classic mini 2G Stylus® and G6, Gemini Metal Brackets. In G3A, a higher magnification (250×) of figure G3 is marked with a circle highlighting a fragment of tooth enamel (enamel loss), where the presence of enamel prisms is visible. In image G5A, a 250× magnification of figure G5 shows the failure in the union of the rods.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Fig 6.

Figure 6.Mesh images at 25× of aesthetic brackets. G7, ClarityTM Advanced; G8, Crystall-Ize®; and G9, Ceramic Series Flexx 2G®. G7 shows the bracket mesh with the absence of tooth enamel. G8 and G9 show a tooth enamel fragment marked in a yellow circle, and then in G8A and G9A, which are magnifications of G8 and G9 at 250×, the presence of tooth enamel prisms can be observed.
Korean Journal of Orthodontics 2025; 55: 15-25https://doi.org/10.4041/kjod24.073

Table 1 . Mesh defects percentage of the study groups.

GroupWith defect
(%)
Faultless
(%)
Total
(%)
G1. Alexander0100.0100.0
G2. Mini Sprint® Brackets0100.0100.0
G3. In-Ovation R CCO0100.0100.0
G4. Gemini SL Self-Ligating Brackets100.00100.0
G5. Classic mini 2G Stylus®100.00100.0
G6. Gemini Metal Brackets0100.0100.0
G7. ClarityTM Advanced40.060.0100.0
G8. Crystall-Ize®10.090.0100.0
G9. Ceramic Series Flexx 2G®0100.0100.0
Total27.7772.22100.0

Table 2 . Shear bond strength values per group in Mega-Pascals (MPa) and Newtons (N).

GroupnMean ± SD (MPa)Mean ± SD
(N)
Median (MPa)Min
(MPa)
Max
(MPa)
IQR
(MPa)
G1. Alexander1010.32 ± 2.35109.17 ± 24.869.508.3715.030.93
G2. Mini Sprint® Brackets109.41 ± 1.2890.43 ± 12.339.337.2312.051.56
G3. In-Ovation R CCO108.53 ± 2.70103.26 ± 32.727.335.7412.454.28
G4. Gemini SL Self-Ligating Brackets1011.93 ± 3.63123.80 ± 37.7111.417.7921.404.04
G5. Classic mini 2G Stylus®108.65 ± 2.2198.55 ± 25.187.805.9911.913.37
G6. Gemini Metal Brackets109.18 ± 3.3999.26 ± 36.698.603.7113.425.35
G7. ClarityTM Advanced1014.73 ± 1.82202.13 ± 25.0315.3512.6017.533.15
G8. Crystall-Ize®108.00 ± 1.4596.87 ± 17.637.905.5110.083.69
G9. Ceramic Series Flexx 2G®1010.91 ± 7.05125.30 ± 80.986.724.2620.6712.69

Standard deviation (SD), minimum (min), maximum (max), and interquartile range (IQR) per group are reported..


Table 3 . Differences between the nine groups; an analysis was based on the brand of brackets and shear bond strength values.

G1.
Alexander
G2.
Mini Sprint® Brackets
G3.
In-Ovation
R CCO
G4.
Gemini SL Self-Ligating Brackets
G5.
Classic mini
2G Stylus®
G6.
Gemini Metal Brackets
G7.
ClarityTM Advanced
G8.
Crystall-Ize®
G9. Ceramic Series
Flexx 2G®
G1. Alexander------0.0087*--
G2. Mini Sprint® Brackets------0.0016*--
G3. In-Ovation R CCO------0.0016*--
G4. Gemini SL Self-Ligating Brackets-------0.0052*-
G5. Classic mini 2G Stylus®------0.0016*--
G6. Gemini Metal Brackets------0.0087*--
G7. ClarityTM Advanced0.0087*0.0016*0.0016*-0.0016*0.0087*-0.0016*-
G8. Crystall-Ize®---0.0052*--0.0016*--
G9. Ceramic Series Flexx 2G®---------

The symbol “-” represents the cases where the statistical differences are not significant..

*Statistically significant differences at P < 0.009..


Table 4 . Global contingency table for enamel loss and recategorized ARI.

ARIEnamel lossTotal
YesNot
< 50% of adhesive remaining on enamel6 (6.7)29 (32.2)35 (38.9)
> 50% of adhesive remaining on enamel0 (0)55 (61.1)55 (61.1)
Total6 (6.7)84 (93.3)90 (100.0)
Fisher’s exact testP = 0.004
Spearman’s rank correlation0.34

The frequencies and the percentage of the frequencies (in brackets) are presented..

ARI, adhesive remnant index..


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