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Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
International Orthodontics 2019; 17: 80–88
Original Article
Websites: www.em-consulte.com www.sciencedirect.com
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations Hooman Zarif Najafi 1, Mohammad Mousavi 2, Nadia Nouri 3, Sepideh Torkan 4
Available online: 11 February 2019
1. Orthodontic Research Center, Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran 2. Department of Orthodontics, School of Dentistry, Kerman University of Medical Sciences, Kerman, Iran 3. Department of Prosthodontics, School of Dentistry, Kerman University of Medical Sciences, Kerman, Iran 4. Department of Orthodontics, University of Washington, Seattle, Washington, USA
Correspondence: Mohammad Mousavi, Department of Orthodontics, School of Dentistry, Kerman University of medical sciences, Kerman, Iran. [email protected]
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Keywords Composite Electron microscope Shear bond strength CO2 Laser Sandblasting Grinding Laboratory research
Summary Introduction > There are controversies regarding the most reliable conditioning method of the aged composite surface to ensure optimum bond strength. The purpose of this study was to evaluate the shear bond strength of metal brackets to microhybrid composite restorations after different surface preparation techniques. Materials and methods > A total of sixty microhybrid composite samples were prepared using upper right central incisor celluloid crown as a mold. Samples were treated with 4 different surface conditioning methods: (1) etching, (2) sandblasting, (3) grinding, and (4) CO2 laser irradiation. Samples were then bonded with metal brackets and underwent shear bond strength testing. A scanning electron microscope was carried out and the data was analysed by one-way ANOVA and post-hoc Tukey test. Bond failure was examined by stereomicroscope and scored based on adhesive remnant index (ARI). Kruskal–Wallis test was used to compare ARI values (a = 0.05). Results > Shear bond strength values in the sandblasting group (17.18 1.53 MPa) were significantly higher than the other groups. There was no significant difference between the grinding (12.87 3.38 MPa) and laser (11.08 1.37 MPa) groups (P = 0.09). The lowest values were recorded in the etching group (6.78 1.69 MPa). There was a significant difference in ARI scores among the four groups (P < 0.001). ARI scores were mostly 2 and 3 in the sandblasting and grinding group, while in the etching and laser groups ARI was mostly 0 and 1. Conclusions > Surface preparation by sandblasting and CO2 laser provides clinically acceptable results with regards to bond strength and ARI score, however grinding and acid etching failed to produce the same results.
tome 17 > n81 > March 2019 https://doi.org/10.1016/j.ortho.2019.01.009 © 2019 CEO. Published by Elsevier Masson SAS. All rights reserved.
Résumé Évaluation de différentes méthodes de préparation de surface sur la résistance au cisaillement du collage des attaches métalliques sur des restaurations composites anciennes Introduction > Il existe des controverses concernant la méthode de conditionnement d'une surface composite ancienne qui soit la plus fiable pour assurer une adhérence optimale. Le but de cette étude était d'évaluer la résistance au cisaillement du collage des attaches métalliques aux restaurations composites micro-hybrides après différentes techniques de préparation de surface. Matériels et méthodes > Au total, 60 échantillons composites micro-hybrides ont été préparés en utilisant la couronne en celluloïd de l'incisive centrale supérieure droite comme moule. Les échantillons ont été traités avec 4 méthodes différentes de conditionnement de surface : (1) mordançage, (2) sablage, (3) meulage, (4) irradiation laser CO2. Des attaches métalliques ont ensuite été collées aux échantillons qui ont été soumis à des essais de résistance au cisaillement. Un microscope électronique à balayage a été réalisé et les données ont été analysées par Anova unidirectionnelle et test de Tukey post-hoc. La rupture adhésive a été examinée au stéréomicroscope et notée en fonction de l'indice des résidus adhésifs (ARI). Le test de Kruskal–Wallis a été utilisé pour comparer les valeurs de l'ARI (a = 0,05). Résultats > Les valeurs de résistance au cisaillement dans le groupe de sablage (17,18 1,53 MPa) ont été significativement plus élevées que dans les autres groupes. Il n'y a pas eu de différence significative entre les groupes de meulage (12,87 3,38 MPa) et les groupes laser (11,08 1,37 MPa) (p = 0,09). Les valeurs les plus basses ont été enregistrées dans le groupe de mordançage (6,78 1,69 MPa). Il y a eu une différence significative dans les scores d'ARI entre quatre groupes (p < 0,001). Les scores ARI ont été principalement de 2 et 3 dans le groupe de sablage et de meulage, tandis que dans les groupes de mordançage et de laser, les scores ARI ont été principalement de 0 et 1. Conclusions > La préparation de surface par sablage et laser CO2 donnent des résultats cliniquement acceptables en ce qui concerne l'adhérence et le score ARI, mais le meulage et le mordançage acide n'ont pas donné les mêmes résultats.
Introduction Many patients have restored teeth with various restorative materials, such as composite resin, amalgam, and porcelain, orthodontists are, therefore, more likely to face difficulty in bonding orthodontic attachments to these materials [1–3]. It has been shown that the bond strength of composite resin to an aged composite restoration is frequently reduced and leads to early failure of the added resin [4–6]. As composites continue to mature after placement, there is a reduction in the number of available vinyl groups (C = C) available for cross polymerization to the new composite layer, so chemical bonding between fresh and aged resin composite is not reliable [7]. It has been proven that Orthophosphoric acid etching cannot change the surface topography of a composite resin and only cleanses the composite resin surface [8,9]. So, enhancement of bond strength between new and old composite usually requires increased
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surface roughness of old composite to promote mechanical interlocking and subsequent coating with bonding agents to improve surface wetting and chemical bonding [10]. Consequently mechanical and chemical surface treatment methods have been attempted [6,8,11–17]. Previous researchers [18–20] reported that mechanical interlocking was the most significant factor contributing to the strength between old and new composites. A low bond failure rate should be a high priority, since replacing loose brackets is inefficient, time-consuming, and costly [21]. There are controversies regarding the most reliable conditioning method of the aged composite surface to ensure optimum bond strength [7,10,22,23]. Some of the previous studies [1,6,12] have recommended roughening with bur and some others [9,10,24], and sandblasting as the best conditioning method. In a study conducted by Zarif Najafi et al. [25]. The effect of CO2
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Mots clés Composite Microscope électronique Résistance au cisaillement Laser CO2 Sablage Meulage Recherche en laboratoire
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Original Article
H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
laser etching on the repair bond strength of silorane composite restorations to the fresh composite was evaluated and it was concluded that surface treatment of silorane-based composite resin with CO2 lasers provides a favourable bond strength. To the best of our knowledge, no studies have evaluated the effect of CO2 laser as a conditioning method on the shear bond strength of orthodontic bracket to the aged composite. On the other hand, in the previous studies [25–27], the effect of CO2 laser on artificial surface conditioning such as porcelain has been investigated. So, this study was designed to evaluate the effect of different surface treatment methods on the bond strength of metal orthodontic brackets to aged microhybrid composite.
Materials and methods Specimen preparation Seventy-six upper right central incisors were made from microhybrid resin composite (Diafil; Diadent group®, Korea) using celluloid crowns (crown refills, 3M ESPE Dental Products®, USA). The advantage of using these crowns is that samples will have a smooth and glossy surface and inhibition of surface polymerization with oxygen during curing will not occur [17]. The composite resin was condensed in the celluloid crowns of upper right central incisors and cured from labial and lingual surfaces for 20 s using a curing light (BluephaseH, Ivoclar Vivadent®, NY, USA) with a light intensity of 600–800 mW/cm2. The specimens that had void or deformation were excluded from the study.
Mounting and grouping of specimens
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In order to reproduce the ageing process, the specimens were stored in deionized water at 37 8C, for 1 week before bonding [6]. To facilitate the debonding procedure, the specimens were mounted in acrylic resin blocks (Acropars 200, Marlic Medical Industries Co®, Tehran-Iran) such that the buccal surfaces were close to parallel with the debonding blade. A mounting jig was used to align the direction of debonding force parallel to the buccal surfaces during the measurement of shear bond strength. Sixty samples were divided randomly into four groups based on the surface preparation technique: group 1 (control): coated with a thin layer of 38% phosphoric acid (Pulpdent®, Watertown, Massachusetts, USA) for 60 seconds, then rinsed with water for 60 seconds, and dried with compressed oil-free air [1,9,12,24]; group 2 (sandblast): sandblasted with micro-etcher (MicroEtcher ERC II, Danville Engineering®, San Ramon, California, USA), using 5 mm aluminum oxide particles at 65 pound per square inch (psi) for 7 seconds. The distance between the nozzle of the instrument and the composite surface during sandblasting was 10 mm for all samples [2,28]; group 3 (diamond bur): abrasion with a coarse tapered diamond bur (G850, 016, D6, Edenta®, AU/SG, Switzerland, 151grit) with a high-speed dental handpiece (BienAir BORA®, Bienne, Switzerland) from two directions perpendicular to
each other, using constant water spray. All samples were grinded by one operator to ensure the same level of pressure is applied to each specimen. The rotating bur was passed over the composite surface three times [12]; group 4 (laser): a pilot study was designed to determine the CO2 laser treatment parameters. Sixteen specimens were prepared and were treated using pulsed CO2 laser with pulse duration of 10 ms, total exposure time of 7 s. The output powers of 1, 3, 5 and 7 watts (W) with frequency modes [5 and 10 hertz (Hz)] were tested on the samples. After laser treatment, a shear bond strength test was carried out on the pilot samples and the combination of the power and frequency that produced the highest shear bond strength (power = 3 W, frequency = 10 Hz) was selected for this study. The laser was held manually and was set according to the parameters resulted from the pilot study. The beam was irradiated in a focused non-contact mode at a distance of 5 mm and perpendicular to the composite surface. The bonding area was treated for 7 seconds using scanning movements.
Bonding procedure Metal standard Edgewise maxillary central incisor brackets with 0.02200 slot (Mini Master Series; American Orthodontics®, Sheboygan, Wisconsin, USA) and surface area of 10.88 mm2 were bonded to the treated composite specimen surfaces, using orthodontic adhesive. A thin film of adhesive primer (Transbond XT, 3M Unitek®, Monrovia, Calif, USA) was applied to the etched surface in all groups. The adhesive paste primer was applied to the bracket base and the bracket was positioned at the centre of the buccal surface and was seated with firm pressure to minimize the thickness of the resin film. An explorer was used to remove excess resin from around the brackets. The adhesive was then light-cured for 20 seconds from mesial and 20 seconds from distal surface. All specimens were stored in distilled water for 48 hours at 37 8C prior to shear bond strength testing.
Measurement of bond strength The shear bond strength test was carried out on a universal testing machine (Instron Corp®, Canton, Massachusetts, USA). A shear load was applied via a mono-beveled chisel blade to the edge of the bracket base and parallel to the resin composite/ adhesive/bracket base interfaces, with a crosshead speed of 0.5 mm/min. The force required to dislodge the bracket was recorded electronically and measured in Newton. The obtained values were converted into Mega-Pascal units (MPa), according to the following equation: shear bond strength = F/A (N/mm2 or MPa), where F is the debonding force in Newton, and A is the cross-sectional surface area of the bracket base in square millimetres.
The bond failure site After the shear test, the brackets and restorations were analysed to examine bond failure mode under a light stereomicroscope at 10 magnifications. The adhesive remnant index (ARI) was
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used to characterize bond failure sites on the composite surfaces, adhesive surface and the bracket bases. According to the ARI system stated by Artun and Bergland [29], scores range from 0 to 3: 0: no adhesive left on the crown surface; 1: less than half of the adhesive left on the crown surface; 2: more than half of the adhesive left on the crown surface; 3: the entire adhesive left on the crown surface.
Scanning electron microscope Two samples from each test group were examined under a scanning electron microscope to evaluate the effects of the different surface preparation methods on the aged composite surfaces. The conditioned surfaces were rinsed with acetone for 10 minutes under ultrasonic movement to remove any debris. Then, samples were stored in an incubator for 24 hours to be completely dried. Finally, the surfaces were coated with a layer of gold and were examined under scanning electron microscope (KYKY, EM3200®, China) under 500 magnification.
Statistical analysis Descriptive statistics including the mean, standard deviation, and minimum and maximum values were calculated for all test groups. One-way analysis of variance (ANOVA) was used to compare shear bond strength among groups and a post-hoc Tukey test was used to do the pair-wise comparison between the groups. The Kruskal–Wallis test was used to determine significant differences in the ARI scores among the four groups.
However, there were statistically significant differences among other groups (P < 0.001). Modes of bond failure are summarized in table III. The Kruskal– Wallis test revealed a significant difference in bond failure among groups (P < 0.001). In the sandblasting and grinding groups, the most commonly recorded ARI scores were 2 and 3. But in the CO2 laser and acid etching groups, ARI scores were mostly 0 and 1. Since cohesive failure cannot be classified in the ARI system, 20% of the samples that showed cohesive failure in the grinding group were excluded from ARI distribution.
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Discussion Currently, an increased number of adults seek orthodontic treatment. This leads to an increased demand for placing orthodontic appliances on already restored teeth with either composite resin restorations or composite laminate veneers [8]. Clinically, optimum bond between two composite layers is achieved in the presence of an oxygen inhibited layer of unpolymerized resin [30]. However, aged restorations do not contain an unpolymerized surface layer [31]. The unreactive methacrylate groups, which allow for adhesion of intermediate adhesive agents, are reduced over time, thereby reducing adhesion compared to a fresh composite [32]. Therefore, it can be concluded that
Results The descriptive statistics for the shear bond strengths of the four surface treatment groups are shown in table I. The mean shear bond strength ranged from 6.78 MPa (Acid etching group) to 17.18 MPa (sandblasting group) (figure 1). One-way ANOVA analysis showed significant differences among the four surface treatment groups for aged microhybrid composite resin (P < 0.001). The results of the post-hoc Tukey test indicated that there were no significant differences between the grinding group and CO2 laser group (P = 0.09) (table II).
Figure 1 Mean SBS in the study groups (MPa)
TABLE I Study groups
n
Mean
SD
Minimum
Maximum
Acid etch
15
6.78
1.69
4.43
9.93
CO2 laser
15
11.08
1.37
9.15
14.45
Sandblasting
15
12.87
1.53
15.46
20.82
Grinding
15
17.18
3.38
6.09
18.89
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Descriptive statistics of shear bond strengths in Mega-Pascal (MPa) in study groups.
Original Article
H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
TABLE II Summary of Tukey post-hoc test. Method
Method
P-value
Grinding
Sandblasting
0.001
Acid etch
0.001
CO2 laser
0.09
Grinding
0.001
Acid etch
0.001
CO2 laser
0.001
Sandblasting
0.001
Grinding
0.001
CO2 laser
0.001
Figure 2
Sandblasting
0.001
Grinding
0.09
Acid etch
0.001
Scanning electron microscope of acid etch group showed a homogeneous pattern on the treated surface and a smoother surface (under 500 magnification)
Sandblasting
Acid etch
CO2 laser
1
Shows statistically significant difference (P < 0.001) among the groups.
bonding brackets to aged composite resin restorations using conventional bonding methods, results in a more frequent bond failure of the brackets [24]. In this context, we evaluated the effect of four surface conditioning methods on the shear bond strength of orthodontic brackets to the aged microhybrid resin composite restorations. Our study showed that sandblasting the resin composite restorations with alumina particles results in the highest shear bond strength (17.18 1.69 MPa), followed by grinding (12.87 3.24 MPa). There was no significant difference between the mean shear bond strength of surfaces treated by grinding and CO2 laser (11.08 MPa, P = 0.09). The lowest shear bond
strength values were observed in the acid etched group (6.78 1.35 MPa). Application of 38 percent orthophosphoric acid is not an effective method for bonding brackets to a composite surface [33], because it does not affect the organic component except its cleaning effect on a composite resin surface [8]. Our scanning electron microscope observations confirmed the results; the acid etched group showed a more homogeneous, smooth surface with shallower irregularities (figure 2). Our result regarding the higher bond strength of composite surfaces treated by sandblasting compared to other groups is in agreement with studies of Viwattanatipa et al. [9] and Demirtas et al. [24]. According to Viwattanatipa et al. [9] the higher bond strength in the sandblasting group can be related to the deep and irregular craters that are created in composite
TABLE III Distribution of adhesive remnant index (ARI) scores in the study groups.
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Method
ARI
Total
0
1
2
3
Grinding
0
1
2
9
12
Sandblasting
0
0
7
8
15
Acid etch
11
4
0
0
15
CO2 laser
8
6
1
15
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Figure 3
Figure 4
Scanning electron microscope of sandblasting group showed pitting irregularities with no particular pattern (under 500 magnification)
Scanning electron microscope of grinding group (under 500 magnification)
restorations. Our scanning electron microscope analysis showed pitting irregularities with no particular pattern. Aluminum oxide particles also created some micro porosities on the resin composite surface that was not observed in other groups (figure 3). So, a bigger surface of resin matrix and filler particles will be ready to be bonded with adhesive compared to other groups. The bond strength values in the study of Demirtas et al. [24] and Viwattanatipa et al. [9] were lower than those of our study in all groups. It may be related to different ageing procedures which cause a gradual decrease in bond strength [6]. Demirtas et al. [24]. thermocycled their samples but we did not. It might also be due to a different type of composite used as restoration. Viwattanatipa et al. [9] used nanofill composite, while Demirtas et al. studied on nanohybrid composite. In the present study, microhybrid composite was used. In hybrid composites (microhybrid and nanohybrid), large filler particles are detached during surface conditioning which leaves a rougher surface. However, in nanofill composites, nanocluster particles of filler are abraded at the same rate as surrounding matrix. Thus, a relatively smoother surface is created that leads to less micromechanical retention and lower shear bond strength [17]. In contrary to the aforementioned studies [9,24], results of the studies conducted by Bishara et al. [12] and Eslamian et al. [6] showed that grinding caused the highest shear bond strength values in comparison to other methods. No quantifiable method is provided in the previous studies regarding surface preparation method with bur and thus it is subject to operator bias [9]. It can be concluded that as grinding is not accurately controlled and measured; the results can vary widely. Another reason for this controversy may be related to what is used for grinding the surface. For instance, Bishara et al. [12] used carbide bur for
surface conditioning but we used diamond bur. According to Bayram et al. [1] and Demirtas et al. [24], grinding is contraindicated for preparation of composite surface because of its uncontrollable abrasive effect and destruction of resin-based composite restoration integrity, which would result in further staining and plaque accumulation in clinical cases. Our results revealed that CO2 laser conditioning could produce acceptable bond strength (11.08 MPa) that is comparable to grinding (12.87 3.24 MPa, P = 0.09). Scanning electron microscope analysis could not clarify a difference in the ablation pattern of the bur group (figure 4) and surface irregularities in the Laser group (figure 5), so it reinforced the results of the shear bond strength measurements between these two groups. However, the material deterioration and re-solidified melting materials could be observed in some areas on the surface of lased composite at 1000 magnification (figure 6). Oskoee et al. [34] found that the shear bond strength of silorane-based composite resin was acceptable (12.36 1.82) when treated with laser. Mirzaie et al. [35] compared the scanning electron microscope of indirect composite conditioned by Er; YAG, Nd:YAG, and CO2 laser. They showed surface treatment by CO2 laser can lead to melting of superficial layer, which is similar to our scanning electron microscope observation. It can be concluded that the residual thermal energy after laser irradiation could change the structure of the surface by melting and packing of components and lead to a decrease in depth of irregularities made by laser [36]. It might justify the lower shear bond strength values in the CO2 laser group compared with the sandblasting and grinding group in our study. Besides the type of laser, Composite type can play an important role in the bond strength of surface treated by laser. Dental
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Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Original Article
H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
Figure 5 Scanning electron microscope of laser group (under 500 magnification)
Figure 6 Scanning electron microscope of laser group showed material deterioration and re-solidified melting materials (under 1000 magnification)
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composite filler particles scatter the energy of the laser beam, whereas various components of the resin-based compartment absorb laser energy [22]. Since the ratio of resin matrix to total volume of composite is lower in hybrid composite than microfilled type, it is expected that laser affects microfilled composite more than hybrid composite. This is in agreement with the result of Lizarelli et al.'s study [37]. They found that the surface of ablated region in a hybrid composite is smoother than microfilled composite. We used ARI scores to evaluate the amount of adhesive remaining on the surface of resin composite restorations after
debonding. The results showed that in the sandblasting and grinding groups, ARI scores of 2 and 3 were the most frequent (table III). It showed that most of the adhesive remained on composite resin restorations, which is a sign of high bond strength and proper adhesion of adhesive to composite restorations [38,39]. The main problem with this mode of bond failure is the additional step required to clean the residual adhesive and polish the surface to regain a smooth and glossy surface. This increases chair time and if not well accomplished, would cause staining and plaque accumulation [1]. In the grinding group, though shear bond strength values were not very high, there was a noticeable amount of cohesive failure (20%) (which could not be classified in the ARI system). It seems the reason for cohesive failure in some samples is the macro retentive areas and irregularities that destroyed surface integrity and decreased cohesive strength to a less amount compared to the cohesive strength of a smooth bulk of composite [10]. Cohesive mode of failure damages the resin-based composite restoration integrity and imposes unnecessary costs for repair or replacement of the restoration [40]. On the other hand, it has been proven that samples, which had cohesive fracture showed higher bond strength [10] and it can be attributed to the wide range of shear bond strength values in the grinding group. Finally, it should be noted that our results were all above the minimum clinically acceptable (5.9–7.8 MPa) [41,42]. Sandblasting was shown to be an effective and controllable method, resulting in sufficient bond strength. CO2 laser irradiation can also be recommended, as it is a controllable method once power, frequency and time is set and results in adequate bond strength. Although the bond strength of the laser group was lower than the sandblasted samples, lower ARI scores show that removal of remnant adhesive from the surface of composite restorations is easier in the laser group. Grinding should be used cautiously, due to the uncontrollable abrasive effect of diamond bur, the risk of cohesive failure during debonding and the possibility of damage to the integrity of the restoration. Besides, bond strength of a grinded surface is not as predictable as there was a variable range of shear bond strength in this group. The use of phosphoric acid cannot be recommended for conditioning the resin composite restorations. Because the bond strength in etching group was much lower than other surface treatments and clinical bond failure may happen frequently when composite restorations are prepared by conventional etching method. The main limitation of the study is that it is in vitro. The results may not have been the same in in vivo conditions. For future studies, we recommend the evaluation of survival bond strength in clinical condition.
Conclusions Based on the results of this study, the shear bond strength of all groups was higher than the minimum acceptable bond strength
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defined by Reynolds. Sandblasting resulted in the highest shear bond strength, while etching was the lowest. Shear bond strength of the CO2 laser and grinding was not significantly different. Grinding showed the risk of cohesive failure in the debonding process and possible damage to the integrity of restoration in some samples. ARI evaluation showed that in the sandblast and grinding samples, most of the adhesive remained on the composite surface, while in the etched and laser samples, adhesive was mostly detached from composite surface.
Clinical significance The conventional etching method is not recommended for conditioning aged composite restorations. Sandblasting and
CO2 laser are effective and controllable methods for treatment of aged composite surface in orthodontic bonding. According to ARI scores, removal of the remnant adhesive from the surface of composite restorations is easier in the laser group. Grinding is an uncontrollable method, which results in unpredictable bond strength values.
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Acknowledgement: The authors thank the Vice-Chancellery of Shiraz University of Medical Sciences for supporting this research (Grant# 1720). This manuscript stems from the relevant doctoral thesis of Dr Mousavi and Dr Nouri. The authors thank Dr. Mehrdad Vosoughi of the Dental Research Development Center and of the School of Dentistry for the statistical analysis. Disclosure of interest: the authors declare that they have no competing interest.
References Bayram M, Yesilyurt C, Kusgoz A, Ulker M, Nur M. Shear bond strength of orthodontic brackets to aged resin composite surfaces: effect of surface conditioning. Eur J Orthod 2011;33:174–9. [2] Espinar-Escalona E, Barrera-Mora JM, LlamasCarreras JM, et al. Improvement in adhesion of the brackets to the tooth by sandblasting treatment. J Mater Sci Mater Med 2012;23:605–11. [3] Ebert T, Elsner L, Hirschfelder U, Hanke S. Shear bond strength of brackets on restorative materials. J Orofac Orthop 2016;77:73–84. [4] Boyer D, Chan KC, Reinhardt J. Build-up and repair of light-cured composites: bond strength. J Dent Res 1984;63:1241–4. [5] Chiba K, Hosoda H, Fusayama T. The addition of an adhesive composite resin to the same material: bond strength and clinical techniques. J Prosthet Dent 1989;61:669–75. [6] Eslamian L, Borzabadi-Farahani A, Mousavi N, Ghasemi A. The effects of various surface treatments on the shear bond strengths of stainless steel brackets to artificially-aged composite restorations. Aust Orthod J 2011;27:28–32. [7] Padipatvuthikul P, Mair LH. Bonding of composite to water aged composite with surface treatments. Dent Mater 2007;23:519–25. [8] Hammad SM, El Banna MS. Effects of cyclic loading on the shear bond strength of metal orthodontic brackets bonded to resin composite veneer surface using different conditioning protocols. Prog Orthod 2013;14:14. [9] Viwattanatipa N, Jermwiwatkul W, Chintavalakorn R, Nanthavanich N. The effect of different surface preparation techniques on the survival probabilities of orthodontic brackets bonded to nanofill composite resin. J Orthod 2010;37:162–73. [10] Hemadri M, Saritha G, Rajasekhar V, et al. Shear bond strength of repaired composites using surface treatments and repair
tome 17 > n81 > March 2019
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
materials: an in vitro study. J Int Oral Health 2014;6:22. Abdelnaby YL. Effects of cyclic loading on the bond strength of metal orthodontic brackets bonded to a porcelain surface using different conditioning protocols. Angle Orthod 2011;81:1064–9. Bishara SE, Ajlouni R, Oonsombat C. Bonding orthodontic brackets to composite using different surface preparations and adhesive/primers: a comparative study. World J Orthod 2003;4:343–7. Eslamian L, Ghassemi A, Amini F, Jafari A, Afrand M. Should silane coupling agents be used when bonding brackets to composite restorations? An in vitro study. Eur J Orthod 2009;31:266–70. Kao E, Eliades T, Rezvan E, Johnston W. Torsional bond strength and failure pattern of ceramic brackets bonded to composite resin laminate veneers. Eur J Orthod 1995;17:533–40. Newman SM, Dressler KB, Grenadier MR. Direct bonding of orthodontic brackets to esthetic restorative materials using a silane. Am J Orthod Dentofacial Orthop 1984;86:503– 6. Schwartz RE, Tyas M, West V. The bonding of orthodontic brackets to composite resin surfaces. Aust Dent J 1990;35:472–3. Viwattanatipa N, Prasertsangwal J, Juntavee N. Weibull analysis of shear/peel bond strength of orthodontic buccal tubes bonded to five resin composites. Orthod Waves 2008;67:120–7. Brosh T, Pilo R, Bichacho N, Blutstein R. Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites. J Prosthet Dent 1997;77:122–6. Kimyai S, Mohammadi N, Navimipour EJ, Rikhtegaran S. Comparison of the effect of three mechanical surface treatments on the
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
repair bond strength of a laboratory composite. Photomed Laser Surg 2010;28:25–30. Söderholm KJM, Roberts MJ. Variables influencing the repair strength of dental composites. Eur J Oral Sci 1991;99:173–80. Maryanchik I, Brendlinger EJ, Fallis DW, Vandewalle KS. Shear bond strength of orthodontic brackets bonded to various esthetic pontic materials. Am J Orthod Dentofacial Orthop 2010;137:684–9. € O, € Eren D, Siso SH, Akin GE. Effect of Bektas O thermocycling on the bond strength of composite resin to bur and laser treated composite resin. Lasers Med Sci 2012;27:723–8. € Rinastiti M, Ozcan M, Siswomihardjo W, Busscher HJ. Effects of surface conditioning on repair bond strengths of non-aged and aged microhybrid, nanohybrid, and nanofilled composite resins. Clin Oral Investig 2011;15:625–33. Demirtas HK, Akin M, Ileri Z, Basciftci FA. Shear bond strength of orthodontic brackets to aged nanohybrid compositeresin surfaces using different surface preparation. Dent Mater J 2015;34:86–90. Zarif Najafi H, Oshagh M, Torkan S, Yousefipour B, Salehi R. Evaluation of the effect of four surface conditioning methods on the shear bond strength of metal bracket to porcelain surface. Photomed Laser Surg 2014;32:694–9. Ahrari F, Heravi F, Hosseini M. CO2 laser conditioning of porcelain surfaces for bonding metal orthodontic brackets. Lasers Med Sci 2013;28:1091–7. Akova T, Yoldas O, Toroglu MS, Uysal H. Porcelain surface treatment by laser for bracket-porcelain bonding. Am J Orthod Dentofacial Orthop 2005;128:630–7. Ozer M, Arici S. Sandblasted metal brackets bonded with resin-modified glass ionomer cement in vivo. Angle Orthod 2005;75:406–9.
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[1]
88
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[29] Årtun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid etch enamel pretreatment. Am J Orthod Dentofacial Orthop 1984;85:333–40. [30] Li J. Effects of surface properties on bond strength between layers of newly cured dental composites. J Oral Rehabil 1997;24:358– 60. [31] Kupiec K, Barkmeier W. Laboratory evaluation of surface treatments for composite repair. Oper Dent 1995;21:59–62. € [32] Ozcan M, Barbosa SH, Melo RM, Galhano GAP, Bottino MA. Effect of surface conditioning methods on the microtensile bond strength of resin composite to composite after aging conditions. Dent Mater 2007;23: 1276–82. [33] Charles A, Senkutvan R, Ramya R, Jacob S. Evaluation of shear bond strength with different enamel pretreatments: an in vitro study. Indian J Dent Res 2014;25:470–4.
[34] Oskoee PA, Mohammadi N, Chaharom MEE, et al. Effect of surface treatment with Er; Cr: YSSG, Nd: YAG, and CO2 lasers on repair shear bond strength of a silorane-based composite resin. J Dent Res 2013;7:61–6. [35] Mirzaie M, Garshasbzadeh NZ, Yassini E, Shahabi S, Chiniforush N. Effect of laser treatment on surface morphology of indirect composite resin: scanning electron microscope (SEM) evaluation. Lasers Med Sci 2013;4:92–5. [36] Ferreira LS, Apel C, Francci C, et al. Influence of etching time on bond strength in dentin irradiated with erbium lasers. Lasers Med Sci 2010;25:849–54. [37] Lizarelli RdF, Moriyama LT, Pelino JEP, Bagnato VS. Ablation rate and morphological aspects of composite resins exposed to Er: YAG laser. J Oral Laser App 2005;5:151–60. [38] Carstensen W. Effect of reduction of phosphoric acid concentration on the shear bond
[39]
[40]
[41] [42]
strength of brackets. Am J Orthod Dentofacial Orthop 1995;108:274–7. Lippitz SJ, Staley RN, Jakobsen JR. In vitro study of 24-hour and 30-day shear bond strengths of three resin–glass ionomer cements used to bond orthodontic brackets. Am J Orthod Dentofacial Orthop 1998;113: 620–4. Eslamian L, Borzabadi-Farahani A, Mosavia N, Ghasemi A. A comparative study of shear bond strength between metal and ceramic brackets and artificially-aged composite restorations using different surface treatments. Eur J Orthod 2011;34:610–7. Reynolds I. A review of direct orthodontic bonding. Br J Orthod 1975;2:171–8. Richter C, Jost-Brinkmann P-G. Shear bond strength of different adhesives tested in accordance with DIN 13990-1/-2 and using various methods of enamel conditioning. J Orofac Orthop 2015;76:175–87.
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Original Article
Websites: www.em-consulte.com www.sciencedirect.com
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations Hooman Zarif Najafi 1, Mohammad Mousavi 2, Nadia Nouri 3, Sepideh Torkan 4
Available online: 11 February 2019
1. Orthodontic Research Center, Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran 2. Department of Orthodontics, School of Dentistry, Kerman University of Medical Sciences, Kerman, Iran 3. Department of Prosthodontics, School of Dentistry, Kerman University of Medical Sciences, Kerman, Iran 4. Department of Orthodontics, University of Washington, Seattle, Washington, USA
Correspondence: Mohammad Mousavi, Department of Orthodontics, School of Dentistry, Kerman University of medical sciences, Kerman, Iran. [email protected]
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Keywords Composite Electron microscope Shear bond strength CO2 Laser Sandblasting Grinding Laboratory research
Summary Introduction > There are controversies regarding the most reliable conditioning method of the aged composite surface to ensure optimum bond strength. The purpose of this study was to evaluate the shear bond strength of metal brackets to microhybrid composite restorations after different surface preparation techniques. Materials and methods > A total of sixty microhybrid composite samples were prepared using upper right central incisor celluloid crown as a mold. Samples were treated with 4 different surface conditioning methods: (1) etching, (2) sandblasting, (3) grinding, and (4) CO2 laser irradiation. Samples were then bonded with metal brackets and underwent shear bond strength testing. A scanning electron microscope was carried out and the data was analysed by one-way ANOVA and post-hoc Tukey test. Bond failure was examined by stereomicroscope and scored based on adhesive remnant index (ARI). Kruskal–Wallis test was used to compare ARI values (a = 0.05). Results > Shear bond strength values in the sandblasting group (17.18 1.53 MPa) were significantly higher than the other groups. There was no significant difference between the grinding (12.87 3.38 MPa) and laser (11.08 1.37 MPa) groups (P = 0.09). The lowest values were recorded in the etching group (6.78 1.69 MPa). There was a significant difference in ARI scores among the four groups (P < 0.001). ARI scores were mostly 2 and 3 in the sandblasting and grinding group, while in the etching and laser groups ARI was mostly 0 and 1. Conclusions > Surface preparation by sandblasting and CO2 laser provides clinically acceptable results with regards to bond strength and ARI score, however grinding and acid etching failed to produce the same results.
tome 17 > n81 > March 2019 https://doi.org/10.1016/j.ortho.2019.01.009 © 2019 CEO. Published by Elsevier Masson SAS. All rights reserved.
Résumé Évaluation de différentes méthodes de préparation de surface sur la résistance au cisaillement du collage des attaches métalliques sur des restaurations composites anciennes Introduction > Il existe des controverses concernant la méthode de conditionnement d'une surface composite ancienne qui soit la plus fiable pour assurer une adhérence optimale. Le but de cette étude était d'évaluer la résistance au cisaillement du collage des attaches métalliques aux restaurations composites micro-hybrides après différentes techniques de préparation de surface. Matériels et méthodes > Au total, 60 échantillons composites micro-hybrides ont été préparés en utilisant la couronne en celluloïd de l'incisive centrale supérieure droite comme moule. Les échantillons ont été traités avec 4 méthodes différentes de conditionnement de surface : (1) mordançage, (2) sablage, (3) meulage, (4) irradiation laser CO2. Des attaches métalliques ont ensuite été collées aux échantillons qui ont été soumis à des essais de résistance au cisaillement. Un microscope électronique à balayage a été réalisé et les données ont été analysées par Anova unidirectionnelle et test de Tukey post-hoc. La rupture adhésive a été examinée au stéréomicroscope et notée en fonction de l'indice des résidus adhésifs (ARI). Le test de Kruskal–Wallis a été utilisé pour comparer les valeurs de l'ARI (a = 0,05). Résultats > Les valeurs de résistance au cisaillement dans le groupe de sablage (17,18 1,53 MPa) ont été significativement plus élevées que dans les autres groupes. Il n'y a pas eu de différence significative entre les groupes de meulage (12,87 3,38 MPa) et les groupes laser (11,08 1,37 MPa) (p = 0,09). Les valeurs les plus basses ont été enregistrées dans le groupe de mordançage (6,78 1,69 MPa). Il y a eu une différence significative dans les scores d'ARI entre quatre groupes (p < 0,001). Les scores ARI ont été principalement de 2 et 3 dans le groupe de sablage et de meulage, tandis que dans les groupes de mordançage et de laser, les scores ARI ont été principalement de 0 et 1. Conclusions > La préparation de surface par sablage et laser CO2 donnent des résultats cliniquement acceptables en ce qui concerne l'adhérence et le score ARI, mais le meulage et le mordançage acide n'ont pas donné les mêmes résultats.
Introduction Many patients have restored teeth with various restorative materials, such as composite resin, amalgam, and porcelain, orthodontists are, therefore, more likely to face difficulty in bonding orthodontic attachments to these materials [1–3]. It has been shown that the bond strength of composite resin to an aged composite restoration is frequently reduced and leads to early failure of the added resin [4–6]. As composites continue to mature after placement, there is a reduction in the number of available vinyl groups (C = C) available for cross polymerization to the new composite layer, so chemical bonding between fresh and aged resin composite is not reliable [7]. It has been proven that Orthophosphoric acid etching cannot change the surface topography of a composite resin and only cleanses the composite resin surface [8,9]. So, enhancement of bond strength between new and old composite usually requires increased
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surface roughness of old composite to promote mechanical interlocking and subsequent coating with bonding agents to improve surface wetting and chemical bonding [10]. Consequently mechanical and chemical surface treatment methods have been attempted [6,8,11–17]. Previous researchers [18–20] reported that mechanical interlocking was the most significant factor contributing to the strength between old and new composites. A low bond failure rate should be a high priority, since replacing loose brackets is inefficient, time-consuming, and costly [21]. There are controversies regarding the most reliable conditioning method of the aged composite surface to ensure optimum bond strength [7,10,22,23]. Some of the previous studies [1,6,12] have recommended roughening with bur and some others [9,10,24], and sandblasting as the best conditioning method. In a study conducted by Zarif Najafi et al. [25]. The effect of CO2
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Mots clés Composite Microscope électronique Résistance au cisaillement Laser CO2 Sablage Meulage Recherche en laboratoire
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Original Article
H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
laser etching on the repair bond strength of silorane composite restorations to the fresh composite was evaluated and it was concluded that surface treatment of silorane-based composite resin with CO2 lasers provides a favourable bond strength. To the best of our knowledge, no studies have evaluated the effect of CO2 laser as a conditioning method on the shear bond strength of orthodontic bracket to the aged composite. On the other hand, in the previous studies [25–27], the effect of CO2 laser on artificial surface conditioning such as porcelain has been investigated. So, this study was designed to evaluate the effect of different surface treatment methods on the bond strength of metal orthodontic brackets to aged microhybrid composite.
Materials and methods Specimen preparation Seventy-six upper right central incisors were made from microhybrid resin composite (Diafil; Diadent group®, Korea) using celluloid crowns (crown refills, 3M ESPE Dental Products®, USA). The advantage of using these crowns is that samples will have a smooth and glossy surface and inhibition of surface polymerization with oxygen during curing will not occur [17]. The composite resin was condensed in the celluloid crowns of upper right central incisors and cured from labial and lingual surfaces for 20 s using a curing light (BluephaseH, Ivoclar Vivadent®, NY, USA) with a light intensity of 600–800 mW/cm2. The specimens that had void or deformation were excluded from the study.
Mounting and grouping of specimens
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In order to reproduce the ageing process, the specimens were stored in deionized water at 37 8C, for 1 week before bonding [6]. To facilitate the debonding procedure, the specimens were mounted in acrylic resin blocks (Acropars 200, Marlic Medical Industries Co®, Tehran-Iran) such that the buccal surfaces were close to parallel with the debonding blade. A mounting jig was used to align the direction of debonding force parallel to the buccal surfaces during the measurement of shear bond strength. Sixty samples were divided randomly into four groups based on the surface preparation technique: group 1 (control): coated with a thin layer of 38% phosphoric acid (Pulpdent®, Watertown, Massachusetts, USA) for 60 seconds, then rinsed with water for 60 seconds, and dried with compressed oil-free air [1,9,12,24]; group 2 (sandblast): sandblasted with micro-etcher (MicroEtcher ERC II, Danville Engineering®, San Ramon, California, USA), using 5 mm aluminum oxide particles at 65 pound per square inch (psi) for 7 seconds. The distance between the nozzle of the instrument and the composite surface during sandblasting was 10 mm for all samples [2,28]; group 3 (diamond bur): abrasion with a coarse tapered diamond bur (G850, 016, D6, Edenta®, AU/SG, Switzerland, 151grit) with a high-speed dental handpiece (BienAir BORA®, Bienne, Switzerland) from two directions perpendicular to
each other, using constant water spray. All samples were grinded by one operator to ensure the same level of pressure is applied to each specimen. The rotating bur was passed over the composite surface three times [12]; group 4 (laser): a pilot study was designed to determine the CO2 laser treatment parameters. Sixteen specimens were prepared and were treated using pulsed CO2 laser with pulse duration of 10 ms, total exposure time of 7 s. The output powers of 1, 3, 5 and 7 watts (W) with frequency modes [5 and 10 hertz (Hz)] were tested on the samples. After laser treatment, a shear bond strength test was carried out on the pilot samples and the combination of the power and frequency that produced the highest shear bond strength (power = 3 W, frequency = 10 Hz) was selected for this study. The laser was held manually and was set according to the parameters resulted from the pilot study. The beam was irradiated in a focused non-contact mode at a distance of 5 mm and perpendicular to the composite surface. The bonding area was treated for 7 seconds using scanning movements.
Bonding procedure Metal standard Edgewise maxillary central incisor brackets with 0.02200 slot (Mini Master Series; American Orthodontics®, Sheboygan, Wisconsin, USA) and surface area of 10.88 mm2 were bonded to the treated composite specimen surfaces, using orthodontic adhesive. A thin film of adhesive primer (Transbond XT, 3M Unitek®, Monrovia, Calif, USA) was applied to the etched surface in all groups. The adhesive paste primer was applied to the bracket base and the bracket was positioned at the centre of the buccal surface and was seated with firm pressure to minimize the thickness of the resin film. An explorer was used to remove excess resin from around the brackets. The adhesive was then light-cured for 20 seconds from mesial and 20 seconds from distal surface. All specimens were stored in distilled water for 48 hours at 37 8C prior to shear bond strength testing.
Measurement of bond strength The shear bond strength test was carried out on a universal testing machine (Instron Corp®, Canton, Massachusetts, USA). A shear load was applied via a mono-beveled chisel blade to the edge of the bracket base and parallel to the resin composite/ adhesive/bracket base interfaces, with a crosshead speed of 0.5 mm/min. The force required to dislodge the bracket was recorded electronically and measured in Newton. The obtained values were converted into Mega-Pascal units (MPa), according to the following equation: shear bond strength = F/A (N/mm2 or MPa), where F is the debonding force in Newton, and A is the cross-sectional surface area of the bracket base in square millimetres.
The bond failure site After the shear test, the brackets and restorations were analysed to examine bond failure mode under a light stereomicroscope at 10 magnifications. The adhesive remnant index (ARI) was
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used to characterize bond failure sites on the composite surfaces, adhesive surface and the bracket bases. According to the ARI system stated by Artun and Bergland [29], scores range from 0 to 3: 0: no adhesive left on the crown surface; 1: less than half of the adhesive left on the crown surface; 2: more than half of the adhesive left on the crown surface; 3: the entire adhesive left on the crown surface.
Scanning electron microscope Two samples from each test group were examined under a scanning electron microscope to evaluate the effects of the different surface preparation methods on the aged composite surfaces. The conditioned surfaces were rinsed with acetone for 10 minutes under ultrasonic movement to remove any debris. Then, samples were stored in an incubator for 24 hours to be completely dried. Finally, the surfaces were coated with a layer of gold and were examined under scanning electron microscope (KYKY, EM3200®, China) under 500 magnification.
Statistical analysis Descriptive statistics including the mean, standard deviation, and minimum and maximum values were calculated for all test groups. One-way analysis of variance (ANOVA) was used to compare shear bond strength among groups and a post-hoc Tukey test was used to do the pair-wise comparison between the groups. The Kruskal–Wallis test was used to determine significant differences in the ARI scores among the four groups.
However, there were statistically significant differences among other groups (P < 0.001). Modes of bond failure are summarized in table III. The Kruskal– Wallis test revealed a significant difference in bond failure among groups (P < 0.001). In the sandblasting and grinding groups, the most commonly recorded ARI scores were 2 and 3. But in the CO2 laser and acid etching groups, ARI scores were mostly 0 and 1. Since cohesive failure cannot be classified in the ARI system, 20% of the samples that showed cohesive failure in the grinding group were excluded from ARI distribution.
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Discussion Currently, an increased number of adults seek orthodontic treatment. This leads to an increased demand for placing orthodontic appliances on already restored teeth with either composite resin restorations or composite laminate veneers [8]. Clinically, optimum bond between two composite layers is achieved in the presence of an oxygen inhibited layer of unpolymerized resin [30]. However, aged restorations do not contain an unpolymerized surface layer [31]. The unreactive methacrylate groups, which allow for adhesion of intermediate adhesive agents, are reduced over time, thereby reducing adhesion compared to a fresh composite [32]. Therefore, it can be concluded that
Results The descriptive statistics for the shear bond strengths of the four surface treatment groups are shown in table I. The mean shear bond strength ranged from 6.78 MPa (Acid etching group) to 17.18 MPa (sandblasting group) (figure 1). One-way ANOVA analysis showed significant differences among the four surface treatment groups for aged microhybrid composite resin (P < 0.001). The results of the post-hoc Tukey test indicated that there were no significant differences between the grinding group and CO2 laser group (P = 0.09) (table II).
Figure 1 Mean SBS in the study groups (MPa)
TABLE I Study groups
n
Mean
SD
Minimum
Maximum
Acid etch
15
6.78
1.69
4.43
9.93
CO2 laser
15
11.08
1.37
9.15
14.45
Sandblasting
15
12.87
1.53
15.46
20.82
Grinding
15
17.18
3.38
6.09
18.89
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Descriptive statistics of shear bond strengths in Mega-Pascal (MPa) in study groups.
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H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
TABLE II Summary of Tukey post-hoc test. Method
Method
P-value
Grinding
Sandblasting
0.001
Acid etch
0.001
CO2 laser
0.09
Grinding
0.001
Acid etch
0.001
CO2 laser
0.001
Sandblasting
0.001
Grinding
0.001
CO2 laser
0.001
Figure 2
Sandblasting
0.001
Grinding
0.09
Acid etch
0.001
Scanning electron microscope of acid etch group showed a homogeneous pattern on the treated surface and a smoother surface (under 500 magnification)
Sandblasting
Acid etch
CO2 laser
1
Shows statistically significant difference (P < 0.001) among the groups.
bonding brackets to aged composite resin restorations using conventional bonding methods, results in a more frequent bond failure of the brackets [24]. In this context, we evaluated the effect of four surface conditioning methods on the shear bond strength of orthodontic brackets to the aged microhybrid resin composite restorations. Our study showed that sandblasting the resin composite restorations with alumina particles results in the highest shear bond strength (17.18 1.69 MPa), followed by grinding (12.87 3.24 MPa). There was no significant difference between the mean shear bond strength of surfaces treated by grinding and CO2 laser (11.08 MPa, P = 0.09). The lowest shear bond
strength values were observed in the acid etched group (6.78 1.35 MPa). Application of 38 percent orthophosphoric acid is not an effective method for bonding brackets to a composite surface [33], because it does not affect the organic component except its cleaning effect on a composite resin surface [8]. Our scanning electron microscope observations confirmed the results; the acid etched group showed a more homogeneous, smooth surface with shallower irregularities (figure 2). Our result regarding the higher bond strength of composite surfaces treated by sandblasting compared to other groups is in agreement with studies of Viwattanatipa et al. [9] and Demirtas et al. [24]. According to Viwattanatipa et al. [9] the higher bond strength in the sandblasting group can be related to the deep and irregular craters that are created in composite
TABLE III Distribution of adhesive remnant index (ARI) scores in the study groups.
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Method
ARI
Total
0
1
2
3
Grinding
0
1
2
9
12
Sandblasting
0
0
7
8
15
Acid etch
11
4
0
0
15
CO2 laser
8
6
1
15
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Figure 3
Figure 4
Scanning electron microscope of sandblasting group showed pitting irregularities with no particular pattern (under 500 magnification)
Scanning electron microscope of grinding group (under 500 magnification)
restorations. Our scanning electron microscope analysis showed pitting irregularities with no particular pattern. Aluminum oxide particles also created some micro porosities on the resin composite surface that was not observed in other groups (figure 3). So, a bigger surface of resin matrix and filler particles will be ready to be bonded with adhesive compared to other groups. The bond strength values in the study of Demirtas et al. [24] and Viwattanatipa et al. [9] were lower than those of our study in all groups. It may be related to different ageing procedures which cause a gradual decrease in bond strength [6]. Demirtas et al. [24]. thermocycled their samples but we did not. It might also be due to a different type of composite used as restoration. Viwattanatipa et al. [9] used nanofill composite, while Demirtas et al. studied on nanohybrid composite. In the present study, microhybrid composite was used. In hybrid composites (microhybrid and nanohybrid), large filler particles are detached during surface conditioning which leaves a rougher surface. However, in nanofill composites, nanocluster particles of filler are abraded at the same rate as surrounding matrix. Thus, a relatively smoother surface is created that leads to less micromechanical retention and lower shear bond strength [17]. In contrary to the aforementioned studies [9,24], results of the studies conducted by Bishara et al. [12] and Eslamian et al. [6] showed that grinding caused the highest shear bond strength values in comparison to other methods. No quantifiable method is provided in the previous studies regarding surface preparation method with bur and thus it is subject to operator bias [9]. It can be concluded that as grinding is not accurately controlled and measured; the results can vary widely. Another reason for this controversy may be related to what is used for grinding the surface. For instance, Bishara et al. [12] used carbide bur for
surface conditioning but we used diamond bur. According to Bayram et al. [1] and Demirtas et al. [24], grinding is contraindicated for preparation of composite surface because of its uncontrollable abrasive effect and destruction of resin-based composite restoration integrity, which would result in further staining and plaque accumulation in clinical cases. Our results revealed that CO2 laser conditioning could produce acceptable bond strength (11.08 MPa) that is comparable to grinding (12.87 3.24 MPa, P = 0.09). Scanning electron microscope analysis could not clarify a difference in the ablation pattern of the bur group (figure 4) and surface irregularities in the Laser group (figure 5), so it reinforced the results of the shear bond strength measurements between these two groups. However, the material deterioration and re-solidified melting materials could be observed in some areas on the surface of lased composite at 1000 magnification (figure 6). Oskoee et al. [34] found that the shear bond strength of silorane-based composite resin was acceptable (12.36 1.82) when treated with laser. Mirzaie et al. [35] compared the scanning electron microscope of indirect composite conditioned by Er; YAG, Nd:YAG, and CO2 laser. They showed surface treatment by CO2 laser can lead to melting of superficial layer, which is similar to our scanning electron microscope observation. It can be concluded that the residual thermal energy after laser irradiation could change the structure of the surface by melting and packing of components and lead to a decrease in depth of irregularities made by laser [36]. It might justify the lower shear bond strength values in the CO2 laser group compared with the sandblasting and grinding group in our study. Besides the type of laser, Composite type can play an important role in the bond strength of surface treated by laser. Dental
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Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Original Article
H. Zarif Najafi, M. Mousavi, N. Nouri, S. Torkan
Figure 5 Scanning electron microscope of laser group (under 500 magnification)
Figure 6 Scanning electron microscope of laser group showed material deterioration and re-solidified melting materials (under 1000 magnification)
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composite filler particles scatter the energy of the laser beam, whereas various components of the resin-based compartment absorb laser energy [22]. Since the ratio of resin matrix to total volume of composite is lower in hybrid composite than microfilled type, it is expected that laser affects microfilled composite more than hybrid composite. This is in agreement with the result of Lizarelli et al.'s study [37]. They found that the surface of ablated region in a hybrid composite is smoother than microfilled composite. We used ARI scores to evaluate the amount of adhesive remaining on the surface of resin composite restorations after
debonding. The results showed that in the sandblasting and grinding groups, ARI scores of 2 and 3 were the most frequent (table III). It showed that most of the adhesive remained on composite resin restorations, which is a sign of high bond strength and proper adhesion of adhesive to composite restorations [38,39]. The main problem with this mode of bond failure is the additional step required to clean the residual adhesive and polish the surface to regain a smooth and glossy surface. This increases chair time and if not well accomplished, would cause staining and plaque accumulation [1]. In the grinding group, though shear bond strength values were not very high, there was a noticeable amount of cohesive failure (20%) (which could not be classified in the ARI system). It seems the reason for cohesive failure in some samples is the macro retentive areas and irregularities that destroyed surface integrity and decreased cohesive strength to a less amount compared to the cohesive strength of a smooth bulk of composite [10]. Cohesive mode of failure damages the resin-based composite restoration integrity and imposes unnecessary costs for repair or replacement of the restoration [40]. On the other hand, it has been proven that samples, which had cohesive fracture showed higher bond strength [10] and it can be attributed to the wide range of shear bond strength values in the grinding group. Finally, it should be noted that our results were all above the minimum clinically acceptable (5.9–7.8 MPa) [41,42]. Sandblasting was shown to be an effective and controllable method, resulting in sufficient bond strength. CO2 laser irradiation can also be recommended, as it is a controllable method once power, frequency and time is set and results in adequate bond strength. Although the bond strength of the laser group was lower than the sandblasted samples, lower ARI scores show that removal of remnant adhesive from the surface of composite restorations is easier in the laser group. Grinding should be used cautiously, due to the uncontrollable abrasive effect of diamond bur, the risk of cohesive failure during debonding and the possibility of damage to the integrity of the restoration. Besides, bond strength of a grinded surface is not as predictable as there was a variable range of shear bond strength in this group. The use of phosphoric acid cannot be recommended for conditioning the resin composite restorations. Because the bond strength in etching group was much lower than other surface treatments and clinical bond failure may happen frequently when composite restorations are prepared by conventional etching method. The main limitation of the study is that it is in vitro. The results may not have been the same in in vivo conditions. For future studies, we recommend the evaluation of survival bond strength in clinical condition.
Conclusions Based on the results of this study, the shear bond strength of all groups was higher than the minimum acceptable bond strength
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defined by Reynolds. Sandblasting resulted in the highest shear bond strength, while etching was the lowest. Shear bond strength of the CO2 laser and grinding was not significantly different. Grinding showed the risk of cohesive failure in the debonding process and possible damage to the integrity of restoration in some samples. ARI evaluation showed that in the sandblast and grinding samples, most of the adhesive remained on the composite surface, while in the etched and laser samples, adhesive was mostly detached from composite surface.
Clinical significance The conventional etching method is not recommended for conditioning aged composite restorations. Sandblasting and
CO2 laser are effective and controllable methods for treatment of aged composite surface in orthodontic bonding. According to ARI scores, removal of the remnant adhesive from the surface of composite restorations is easier in the laser group. Grinding is an uncontrollable method, which results in unpredictable bond strength values.
Original Article
Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations
Acknowledgement: The authors thank the Vice-Chancellery of Shiraz University of Medical Sciences for supporting this research (Grant# 1720). This manuscript stems from the relevant doctoral thesis of Dr Mousavi and Dr Nouri. The authors thank Dr. Mehrdad Vosoughi of the Dental Research Development Center and of the School of Dentistry for the statistical analysis. Disclosure of interest: the authors declare that they have no competing interest.
References Bayram M, Yesilyurt C, Kusgoz A, Ulker M, Nur M. Shear bond strength of orthodontic brackets to aged resin composite surfaces: effect of surface conditioning. Eur J Orthod 2011;33:174–9. [2] Espinar-Escalona E, Barrera-Mora JM, LlamasCarreras JM, et al. Improvement in adhesion of the brackets to the tooth by sandblasting treatment. J Mater Sci Mater Med 2012;23:605–11. [3] Ebert T, Elsner L, Hirschfelder U, Hanke S. Shear bond strength of brackets on restorative materials. J Orofac Orthop 2016;77:73–84. [4] Boyer D, Chan KC, Reinhardt J. Build-up and repair of light-cured composites: bond strength. J Dent Res 1984;63:1241–4. [5] Chiba K, Hosoda H, Fusayama T. The addition of an adhesive composite resin to the same material: bond strength and clinical techniques. J Prosthet Dent 1989;61:669–75. [6] Eslamian L, Borzabadi-Farahani A, Mousavi N, Ghasemi A. The effects of various surface treatments on the shear bond strengths of stainless steel brackets to artificially-aged composite restorations. Aust Orthod J 2011;27:28–32. [7] Padipatvuthikul P, Mair LH. Bonding of composite to water aged composite with surface treatments. Dent Mater 2007;23:519–25. [8] Hammad SM, El Banna MS. Effects of cyclic loading on the shear bond strength of metal orthodontic brackets bonded to resin composite veneer surface using different conditioning protocols. Prog Orthod 2013;14:14. [9] Viwattanatipa N, Jermwiwatkul W, Chintavalakorn R, Nanthavanich N. The effect of different surface preparation techniques on the survival probabilities of orthodontic brackets bonded to nanofill composite resin. J Orthod 2010;37:162–73. [10] Hemadri M, Saritha G, Rajasekhar V, et al. Shear bond strength of repaired composites using surface treatments and repair
tome 17 > n81 > March 2019
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
materials: an in vitro study. J Int Oral Health 2014;6:22. Abdelnaby YL. Effects of cyclic loading on the bond strength of metal orthodontic brackets bonded to a porcelain surface using different conditioning protocols. Angle Orthod 2011;81:1064–9. Bishara SE, Ajlouni R, Oonsombat C. Bonding orthodontic brackets to composite using different surface preparations and adhesive/primers: a comparative study. World J Orthod 2003;4:343–7. Eslamian L, Ghassemi A, Amini F, Jafari A, Afrand M. Should silane coupling agents be used when bonding brackets to composite restorations? An in vitro study. Eur J Orthod 2009;31:266–70. Kao E, Eliades T, Rezvan E, Johnston W. Torsional bond strength and failure pattern of ceramic brackets bonded to composite resin laminate veneers. Eur J Orthod 1995;17:533–40. Newman SM, Dressler KB, Grenadier MR. Direct bonding of orthodontic brackets to esthetic restorative materials using a silane. Am J Orthod Dentofacial Orthop 1984;86:503– 6. Schwartz RE, Tyas M, West V. The bonding of orthodontic brackets to composite resin surfaces. Aust Dent J 1990;35:472–3. Viwattanatipa N, Prasertsangwal J, Juntavee N. Weibull analysis of shear/peel bond strength of orthodontic buccal tubes bonded to five resin composites. Orthod Waves 2008;67:120–7. Brosh T, Pilo R, Bichacho N, Blutstein R. Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites. J Prosthet Dent 1997;77:122–6. Kimyai S, Mohammadi N, Navimipour EJ, Rikhtegaran S. Comparison of the effect of three mechanical surface treatments on the
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
repair bond strength of a laboratory composite. Photomed Laser Surg 2010;28:25–30. Söderholm KJM, Roberts MJ. Variables influencing the repair strength of dental composites. Eur J Oral Sci 1991;99:173–80. Maryanchik I, Brendlinger EJ, Fallis DW, Vandewalle KS. Shear bond strength of orthodontic brackets bonded to various esthetic pontic materials. Am J Orthod Dentofacial Orthop 2010;137:684–9. € O, € Eren D, Siso SH, Akin GE. Effect of Bektas O thermocycling on the bond strength of composite resin to bur and laser treated composite resin. Lasers Med Sci 2012;27:723–8. € Rinastiti M, Ozcan M, Siswomihardjo W, Busscher HJ. Effects of surface conditioning on repair bond strengths of non-aged and aged microhybrid, nanohybrid, and nanofilled composite resins. Clin Oral Investig 2011;15:625–33. Demirtas HK, Akin M, Ileri Z, Basciftci FA. Shear bond strength of orthodontic brackets to aged nanohybrid compositeresin surfaces using different surface preparation. Dent Mater J 2015;34:86–90. Zarif Najafi H, Oshagh M, Torkan S, Yousefipour B, Salehi R. Evaluation of the effect of four surface conditioning methods on the shear bond strength of metal bracket to porcelain surface. Photomed Laser Surg 2014;32:694–9. Ahrari F, Heravi F, Hosseini M. CO2 laser conditioning of porcelain surfaces for bonding metal orthodontic brackets. Lasers Med Sci 2013;28:1091–7. Akova T, Yoldas O, Toroglu MS, Uysal H. Porcelain surface treatment by laser for bracket-porcelain bonding. Am J Orthod Dentofacial Orthop 2005;128:630–7. Ozer M, Arici S. Sandblasted metal brackets bonded with resin-modified glass ionomer cement in vivo. Angle Orthod 2005;75:406–9.
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[29] Årtun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid etch enamel pretreatment. Am J Orthod Dentofacial Orthop 1984;85:333–40. [30] Li J. Effects of surface properties on bond strength between layers of newly cured dental composites. J Oral Rehabil 1997;24:358– 60. [31] Kupiec K, Barkmeier W. Laboratory evaluation of surface treatments for composite repair. Oper Dent 1995;21:59–62. € [32] Ozcan M, Barbosa SH, Melo RM, Galhano GAP, Bottino MA. Effect of surface conditioning methods on the microtensile bond strength of resin composite to composite after aging conditions. Dent Mater 2007;23: 1276–82. [33] Charles A, Senkutvan R, Ramya R, Jacob S. Evaluation of shear bond strength with different enamel pretreatments: an in vitro study. Indian J Dent Res 2014;25:470–4.
[34] Oskoee PA, Mohammadi N, Chaharom MEE, et al. Effect of surface treatment with Er; Cr: YSSG, Nd: YAG, and CO2 lasers on repair shear bond strength of a silorane-based composite resin. J Dent Res 2013;7:61–6. [35] Mirzaie M, Garshasbzadeh NZ, Yassini E, Shahabi S, Chiniforush N. Effect of laser treatment on surface morphology of indirect composite resin: scanning electron microscope (SEM) evaluation. Lasers Med Sci 2013;4:92–5. [36] Ferreira LS, Apel C, Francci C, et al. Influence of etching time on bond strength in dentin irradiated with erbium lasers. Lasers Med Sci 2010;25:849–54. [37] Lizarelli RdF, Moriyama LT, Pelino JEP, Bagnato VS. Ablation rate and morphological aspects of composite resins exposed to Er: YAG laser. J Oral Laser App 2005;5:151–60. [38] Carstensen W. Effect of reduction of phosphoric acid concentration on the shear bond
[39]
[40]
[41] [42]
strength of brackets. Am J Orthod Dentofacial Orthop 1995;108:274–7. Lippitz SJ, Staley RN, Jakobsen JR. In vitro study of 24-hour and 30-day shear bond strengths of three resin–glass ionomer cements used to bond orthodontic brackets. Am J Orthod Dentofacial Orthop 1998;113: 620–4. Eslamian L, Borzabadi-Farahani A, Mosavia N, Ghasemi A. A comparative study of shear bond strength between metal and ceramic brackets and artificially-aged composite restorations using different surface treatments. Eur J Orthod 2011;34:610–7. Reynolds I. A review of direct orthodontic bonding. Br J Orthod 1975;2:171–8. Richter C, Jost-Brinkmann P-G. Shear bond strength of different adhesives tested in accordance with DIN 13990-1/-2 and using various methods of enamel conditioning. J Orofac Orthop 2015;76:175–87.
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