Comparative evaluation of shear bond strength and debonding properties of GC Ortho Connect composite and Transbond XT composite
Online veröffentlicht: 22. Dez. 2023
Seitenbereich: 35 - 41
Eingereicht: 01. Aug. 2022
Akzeptiert: 01. Dez. 2022
DOI: https://doi.org/10.2478/aoj-2023-0004
© 2023 Somayeh Bahrami et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
Brackets are used to transfer orthodontic forces to the teeth, and so reliable bracket bonding plays a key role in the success of fixed appliance treatment.1 The bond strength of orthodontic attachments should be sufficient to withstand the forces of mastication and stresses exerted by the appliance arch wires while allowing for controlled tooth movement in the three dimensions. At the same time, the bond strength of brackets should allow bracket debonding without damage to the enamel surface.2 At present, light-cure composite resins are the most commonly used materials for bonding orthodontic brackets. However, traditional methods of bracket attachment (using adhesive composites) require multiple steps of etching, rinsing, drying, and the application of a primer before applying the adhesive resins.3–5 Despite the established long-term success of traditional methods, their time-consuming nature is their main drawback, which may negatively affect bond strength, especially in the posterior regions of the dental arch due to limited vision, poor accessibility, and difficult moisture control.5,6 Attempts have been made to simplify the bonding process, and self-etch primers,7 self-adhesive cements,6,8 laser irradiation,1 and the elimination of the priming step9 have been recommended. To enhance wetting and the penetration of resin into the enamel surface, the application of a primer is an essential part of the resin bonding procedure. Traditionally, the mechanical interlocking of resin in between the etched enamel prisms has been considered as the main mechanism of enamel adhesion;10,11 therefore, the use of unfilled resin bonding agents is an imperative part of the bonding process which allows optimal wetting and ensures more reliable resin penetration into the etched enamel surface. Therefore, the elimination of the priming step during resin bonding may create concerns regarding the attainment of optimal bond strength.
The elimination of the priming step may speed up the bonding process and produce greater comfort for the patient and clinician, there is the additional benefit of a decrease in the risk of contamination by oral fluids. In addition, a previous study has shown that bonding resin (unfilled resin) has high cytotoxicity against gingival fibroblasts.12 A review of several studies has revealed that there is no consensus regarding bracket bond strength following the elimination of primer from conventional adhesives.9,13,14 A novel concept to accelerate the bonding process is to use no-primer orthodontic adhesives, such as GC Ortho Connect whose composition eliminates the need for a primer.15 Limited data are available regarding the shear bond strength (SBS) and failure mode of different types of no-primer adhesives, especially GC Ortho Connect composite resin16,17 and whether the priming step can be eliminated when other conventional adhesive systems are used. Therefore, the aim of the present study was to evaluate the SBS and failure mode of GC Ortho Connect composite and compare the material to Transbond XT adhesive with and without its primer.
After obtaining written informed consent from the patients, sixty sound human maxillary and mandibular premolars that had been extracted for orthodontic purposes, were collected. After rinsing, the teeth were placed in distilled water containing thymol crystals (0.1% wt/vol) to inhibit bacterial growth and stored at room temperature (for no longer than 6 months).
The criteria for tooth selection included teeth with an intact buccal enamel surface without caries, restoration, attrition, fracture, congenital anomalies or defects, cracks caused by extraction, or cement remnants as a result of previous orthodontic treatment. Teeth exposed to the application of chemical agents (bleaching treatment) or those with a history of previous orthodontic/endodontic treatment were excluded. The teeth were selected after ensuring their soundness under a stereomicroscope (HP, Palo Alto, USA) at ×20 magnification.
Before bracket bonding, the buccal surface of each tooth crown was polished with a fluoride-free pumice slurry (Kimia Co., Tehran, Iran) and rubber cups in a low-speed hand-piece for 10 sec. Subsequently, the surfaces were thoroughly rinsed with air/water spray for 10 seconds and air-dried for 10 sec. For the purpose of standardisation, each rubber cup was replaced after being used on 5 teeth.
The specimens were randomly assigned to three groups (
Experimental groups (n=20).
| Groups | Etchant | Primer | Composite resin |
|---|---|---|---|
| I | 37% phosphoric acid | Transbond XT | Transbond XT |
| II | 37% phosphoric acid | – | GC Ortho Connect |
| III | 37% phosphoric acid | – | Transbond XT |
Group II (GC Ortho Connect adhesive): In this group, the samples were similarly prepared, except that the brackets were loaded with GC Ortho Connect adhesive (GC Orthodontics, Tokyo, Japan) but no primer was used.
Group III (Transbond XT adhesive without primer): In this group, the samples were similarly prepared, except that the primer was not applied during the bracket bonding procedure.
Following the bonding procedure, each sample was mounted such that the root of each tooth was vertically embedded in self-cure acrylic resin (Marlic Medical Ind. Co., Karaj, Iran), using PVC rings (30 mm height × 10 mm internal diameter) in such a way that the buccal surface of each tooth was positioned perpendicular to the resin base. Using a spatula, excess resin was removed up to 1 mm below the cementoenamel junction, so that no resin was left in contact with the crown.
A surveyor and its analyser rod, (Marathon-103, Saeyang Microtech, South Korea) was used to parallel the bracket base, so that the bracket-tooth interface was parallel to the direction of shear force application. By so doing, the point of application and direction of the debonding force were standardised for all samples.
Following bracket attachment, the teeth were immersed in tap water to minimise temperature rise caused by the exothermic polymerisation reactions. All samples were bonded and mounted by the same operator.
After mounting, the samples were coded and stored in distilled water at 37°C for 24 hr to simulate the oral temperature, following which the SBS was measured by a universal testing machine (K-21046 model, Walter + Bai, Löhningen, Switzerland) using a chisel-shaped tip (0.5 mm) at a crosshead speed of 0.5 mm/min.
The chisel tip was positioned at the bracket-tooth interface, and an occluso-gingival load was applied to produce a shear force until fracture occurred. The maximum force causing failure was recorded in Newtons and converted to Megapascals (MPa) by dividing the measured force values by the mean surface area of the brackets (11.85 mm2).
The debonded samples were examined under a stereomicroscope equipped with a video camera (Motic Instruments, Carlsbad, USA) and image analyser software at ×20 magnification to determine the amount of adhesive remaining on the enamel surface. The ARI scores were determined for each sample according to the criteria of Artun and Berglund: Score 0 = No adhesive left on the tooth surface; score 1 = less than half of the adhesive left on the tooth; score 2 = more than half of the adhesive left on the tooth; score 3 = all adhesive left on the tooth, with distinct impression of the bracket mesh. The examiner was blinded to the group allocation of samples.
Statistical analysis was performed using SPSS version 23 (SPSS Inc., Chicago, USA). Descriptive statistics including the mean, standard deviation, median, minimum, and maximum values were calculated for all groups. The normality of the data was assessed by the Kolmogorov–Smirnov test. ANOVA was applied to determine whether significant differences existed in the mean SBS of the groups. The post-hoc Tukey’s test was used for pairwise comparisons. The Kruskal–Wallis test was applied to determine significant differences in ARI scores between the groups.
The normal distribution of data was confirmed by the Kolmogorov-Smirnov test. Table II presents descriptive statistics for the SBS (MPa) of the groups. The highest mean SBS was found in the GC Ortho Connect composite (group II), which was significantly different from the SBS of other groups. The one-way ANOVA showed significant differences in SBS, between the three groups (
Descriptive and analytical statistics of shear bond strength (MPa) of the three groups (
| Group | Composite | Mean | Std. deviation | Minimum | Maximum | Tukey’s Test |
|---|---|---|---|---|---|---|
| I | Transbond XT with primer | 12.66 | 3.3 | 7.18 | 18.21 | A* |
| II | GC Ortho Connect | 15.50 | 3.25 | 10.82 | 20.78 | B |
| III | Transbond XT without primer | 11.18 | 4.94 | 5.50 | 24.28 | A |
Different letters indicate statistically significant differences at
Table III presents the frequency distribution of the ARI scores in each group. As shown, GC Ortho Connect composite demonstrated a higher frequency of score 2 (cohesive fracture); whereas, in both the Transbond XT composite groups (I and III), the ARI score 0 (adhesive fracture) had the highest frequency. Therefore, the failure sites of Transbond XT composite with or without its primer were the same.
Frequency distribution and percentage of the adhesive ARI scores in the three groups(n=20).
| ARI score* | ||||||
|---|---|---|---|---|---|---|
| Groups | Composite | 0 | 1 | 2 | 3 | Mann–Whitney |
| I | Transbond XT with primer | 9 (45%) | 6 (30%) | 4 (20%) | 1 (5%) | A** |
| II | GC Ortho Connect | 5 (25%) | 2 (10%) | 8 (40%) | 5 (25%) | B |
| III | Transbond XT without primer | 11 (55%) | 4 (20%) | 4 (20%) | 1 (5%) | A |
ARI scores: 0 = no adhesive left on the tooth, 1 = less than half of the adhesive left on the tooth, 2 = more than half of the adhesive left on the tooth, and 3 = all adhesive left on the tooth,
Different letters indicate statistically significant differences at
The Kruskal–Wallis test revealed a statistically significant difference in ARI scores between the three groups (
Despite great advancements in orthodontic bracket bonding, it remains a topic of investigation. The field is rapidly evolving to achieve better material performance, less enamel damage, and a stronger bond to restorative materials. In addition, simplifying clinical procedures to achieve better results in a shorter period of time has been the focus of many material manufacturers.6–10,16–18 In the present study, a novel no-primer orthodontic adhesive was compared using Transbond XT composite as the control group.
An analysis of the SBS indicated that all of the adhesive systems tested in the present study provided clinically acceptable bond strength (6–8 MPa) according to Reynolds.19 The current study demonstrated that GC Ortho Connect composite yielded the highest mean SBS value (15.50±3.25 MPa) compared with the Transbond XT composite, which is largely used in studies as the control group.5,20 The result is supported by Elkalza et al.16 who confirmed the reliable bond strength of the adhesive.
In a comparison of other no-primer orthodontic adhesives, Heliosit composite and Ortho Cem composite were evaluated by Scribante et al.18 who reported mean SBS values of 10.64 MPa and 8.31 MPa, respectively. Considering the consistent and similar methodology, it appears that GC Ortho Connect has stronger enamel adhesion compared to Heliosit and Ortho Cem composite resins.
The omission of a bonding agent may simplify the clinical procedure, decrease chair time, minimise the risk of moisture contamination, and lower the costs of the bonding process.9 A comparison of Transbond XT with and without its primer revealed no significant difference in SBS, which indicates that the absence of a priming agent may not compromise the SBS. These findings are consistent with those of Neves et al.,9 Nandhra et al.,13 Shahabi et al.,14 and Rai et al.21 but disagree with the results of Pulido et al.,22 who believed that the application of a primer increases bracket bond strength.
Moreover, previous authors believed that primer application prior to composite bonding has the advantage of immediate obliteration of enamel pores (created by acid etching) that are not covered by the bracket base, thereby, preventing decalcification9; however, a scanning electron microscopic study demonstrated that the length and shape of the resin tags in the etched enamel surface are independent of the materials examined.23,24 The liquid phase of the composite resin is present in sufficient quantities to flow into the conditioned enamel porosities and act independently of the charged particles.25
The ARI score also plays an important role in determining the bonding potential of adhesive systems. The index quantifies the amount of adhesive remaining on the tooth surface after bracket debonding.2 The present results regarding the ARI scores showed that the failure modes of brackets bonded with GC Ortho Connect composite were significantly different from those bonded with Transbond XT. The bond failure in the Transbond XT composite with or without primer occurred at the enamel-adhesive interface (score 0) which indicated that, in both Transbond XT composite groups (I and III), significantly lower amounts of adhesive remnant remained on the enamel surface than in the GC Ortho Connect group. This is contrary to the findings of Vicente et al.8 and Scribante et al.18 who reported a higher frequency of ARI scores of “2” and “3” in the Transbond XT group. Variations in materials (bracket types) and different study designs may explain the contradictory results reported for this composite. The effect of bracket base design on the ARI scores has been previously documented.26 However, low ARI scores (0 and 1) are considered favourable, since there is less adhesive to remove from the tooth surface following debonding which, therefore, reduces the risk of iatrogenic damage during enamel polishing.27
The assessment of the ARI scores also revealed that the GC Ortho Connect composite presented a higher frequency of ARI score “2”. Therefore, debonding mainly occurred within the adhesive (cohesive fracture). The findings are in agreement with those of Scribante et al.,18 and Faltermeier et al.28 and are likely due to the lower filler content of no-primer composites that produces a reduction in cohesive strength. Debonding at the bracket-adhesive interface or within the adhesive is advantageous because it leaves the enamel surface relatively intact; however, considerable chair time is needed to remove the residual adhesive with the added possibility of damaging the enamel surface during the cleaning process.27 Nevertheless, new evidence regarding enamel polishing and adhesive removal after debonding shows that specific finishing burs can safely remove the adhesive without surface damage.29 It is important to note that high ARI scores are valuable when accompanied by high bond strength values (as in GC Ortho Connect composite) as high ARI scores with low bond strength could indicate a weak bond at the adhesive-bracket interface.
In general, although randomised clinical trials are required to assess the clinical performance of the GC Ortho Connect composite adhesive in the oral environment, the in vitro results regarding its performance are promising. In light of the SBS and ARI scores, the results of the GC Ortho Connect composite in the present study showed that this composite could be effectively applied for orthodontic bracket bonding. Henkin27 concluded that adhesives with high ARI scores (2 or 3) associated with high bond strength values are preferred for orthodontic application.
In summary, in order to make the orthodontic bonding process easier and reduce chair time, it is recommended GC Ortho Connect composite is used instead of removing the primer from conventional orthodontic composites (composites that are supplied with primer). In addition to reducing the bond steps and ease of use, GC Ortho Connect composite helps in better isolation while retaining adequate bond strength. Also, the failure mode of this composite reduces the risk of enamel surface damage during debonding process.
The SBS generated by GC Ortho Connect composite was significantly greater than that generated by Transbond XT composite.
The failure mode of GC Ortho Connect composite was mainly within the adhesive (score 2), which was significantly better than the dominant failure mode of Transbond XT.