|Year : 2017 | Volume
| Issue : 5 | Page : 545-551
Effects of laser etching on shear bond strengths of brackets bonded to fluorosed enamel
R Nalçaci1, B Temel2, S çokakoğlu3, H Türkkahraman3, S Üsümez4
1 Department of Orthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
2 Department of Restorative Dentistry, Faculty of Dentistry, Suleyman Demirel University, Isparta, Turkey
3 Department of Orthodontics, Faculty of Dentistry, Suleyman Demirel University, Isparta, Turkey
4 Department of Orthodontics, Faculty of Dentistry, Bezmialem Vakif University, Istanbul, Turkey
|Date of Acceptance||02-Nov-2015|
|Date of Web Publication||17-May-2017|
Department of Orthodontics, Faculty of Dentistry, Suleyman Demirel University, Isparta 32260
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: To evaluate the effects of laser etching on the shear bond strengths (SBS) and failure modes of brackets bonded to fluorosed enamel. Materials and Methods: This in vitro study included 34 fluorosed and 34 nonfluorosed teeth. Teeth were divided into four subgroups according to the etching procedure: Group (A) normal enamel etched with 37% phosphoric acid for 15 s, Group (B) nonfluorosed enamel etched with erbium:yttrium aluminum garnet (Er: YAG) laser for 15 s, Group (C) fluorosed enamel etched with 37% phosphoric acid for 30 s, Group (D) fluorosed enamel etched with Er: YAG laser for 30 s. After bonding of the premolar metal brackets, specimens were subjected to the thermal cycles. After SBS test, modified adhesive remnant index (ARI) by using stereomicroscope and failure modes with a scanning electron microscope (SEM) was determined. After bonding, one specimen from each group was examined under SEM to identify enamel-resin interfaces. ANOVA and Tukey post-hoc tests were used to compare the SBS values. The Kruskal–Wallis and Chi-square tests were used to analyze the distribution of ARI scores and failure modes of groups. Results: The highest mean SBS value (17.56 ± 1.05 MPa) was found in Group A, while the lowest (12.25 ± 0.96 MPa) in Group D. Significant differences were found in the SBS test and failure modes among all groups. The differences between ARI scores of the groups were not significant. Conclusion: According to our findings, laser etching reduced the SBS of brackets bonded to fluorosed teeth, but provided clinically acceptable SBS values.
Keywords: Bond strength, erbium: yttrium aluminum garnet laser, etching, fluorosis
|How to cite this article:|
Nalçaci R, Temel B, çokakoğlu S, Türkkahraman H, Üsümez S. Effects of laser etching on shear bond strengths of brackets bonded to fluorosed enamel. Niger J Clin Pract 2017;20:545-51
|How to cite this URL:|
Nalçaci R, Temel B, çokakoğlu S, Türkkahraman H, Üsümez S. Effects of laser etching on shear bond strengths of brackets bonded to fluorosed enamel. Niger J Clin Pract [serial online] 2017 [cited 2021 Sep 20];20:545-51. Available from: https://www.njcponline.com/text.asp?2017/20/5/545/183245
| Introduction|| |
Dental fluorosis is caused by the excess floride intake over the optimal daily dose during enamel maturation stage. Clinically, tiny white opaque lines or specks appear on the enamel surfaces in the mild forms of fluorosis, while pits or brown discolorations in severe forms. Fluorosed enamel is characterized by an outer acid-resistant hypermineralized layer, although the subsurface enamel is porous hypomineralized.,
The fundamentals of bonding to enamel depend on acid etching of enamel followed by polymerization of adhesive resin that is penetrated into the microporosities created in the etched enamel areas. However, effective bonding to fluorotic enamel may be compromised because of the hypermineralized outer layer, which is resistant to acid etching., For this reason, fissure sealant and laminate veneer applications or closure of diastemas and bonding of orthodontic brackets may be failed.
In orthodontic practice, it is essential to obtain adequate bond strength of orthodontic attachments for successful treatment. Bonding failures result in longer treatment period, increased cost, less patient cooperation, and might endanger the outcomes of treatment. Therefore, different procedures including extended acid etching,, air abrading, microabrasion with acid etching,, self etching primers,,, or adhesion promoters , have been proposed to improve the efficiency of bonding to fluorosed enamel.
However, a consensus has not been reached on the most effective etching procedure for fluorosed teeth. In addition to different etching procedures, laser has been suggested as an alternative to phosphoric acid conditioning for bonding of orthodontic brackets or tubes when benefits such as etching effectiveness, short chair time, easy application, and perfect moisture control are considered.
Up to date, no study has been published that evaluated the effects of laser etching on the bond strengths of orthodontic brackets bonded to fluorosed teeth. The aim of this study was to evaluate the effect of erbium:yttrium aluminum garnet (Er: YAG) laser etching on the shear bond strengths (SBS) of brackets bonded to fluorotic enamel. In addition, scanning electron microscope (SEM) was used to analyze and classify the failure modes of the enamel/bracket bonds. The null hypothesis was that there is no differences on SBS and failure modes of brackets bonded to fluorosed enamel between Er: YAG laser and 37% phosphoric acid etching.
| Materials and Methods|| |
Selection and preparation of samples
This in vitro study was approved by the Ethics Committee of Suleyman Demirel University. Teeth were collected from patients undergoing extraction of premolars for orthodontic reasons. Teeth were stored for a maximum of 6 months in 0.1% sodium azide solution at room temperature until the experimental procedures were performed. Teeth with caries, restorations, cracks, chipping, or malformation on enamel surface were not included in this study.
The collected teeth were classified by visual observation according to the severity of fluorosis using the Thylstrup and Fejerskov ındex (TFI) (0 = normal, 1–3 = mild, 4–5 = moderate, and 6–9 = severe). The classification of fluorosed teeth according to TFI was made by the consensus of two investigators. Total of 68 premolar teeth, 34 with nonfluorosed (TFI = 0) and 34 with fluorosed enamel (TFI = 4–5) were used in this study. Nonfluorosed and fluorosed teeth were divided into two subgroups consisted of 17 samples according to the etching procedure. Study groups were performed as follows;
- Group A (control), normal enamel etched with 37% phosphoric acid (PA) for 15 s;
- Group B, normal enamel etched with Er: YAG laser for 15 s;
- Group C, fluorosed enamel etched with 37% phosphoric acid for 30 s;
- Group D, fluorosed enamel etched with Er: YAG laser for 30 s.
One specimen from each group was examined under SEM after bonding procedure to identify enamel-resin interfaces.
The roots of 64 premolar teeth were individually embedded into acyrilic resin from 1 to 2 mm distance at the cementoenamel junction, in such a way that the long axis of teeth was perpendicular to the resin block. Samples were stored in distilled water until bonding procedure.
Buccal surfaces of samples were cleaned with a mixture of water and pumice for 10 s with a low speed and thoroughly rinsed for 15 s and air dried. For Groups A and C, the buccal surfaces of teeth were etched with 37% phosphoric acid (ScotchbondTM, 3M ESPE, St Paul, MN, USA) for 15 and 30 s, respectively. Then rinsed for 15 s and dried thoroughly with a moisture and oil-free air to obtain an opaque white appearance.
For B and D groups, the buccal surfaces of teeth were etched with Er: YAG laser (LightWalker AT, Fotona, Slovenia) power settings at 1.2 W (120 mJ/10 Hz) in MSP mode (100 μs), 60% water and 40% air spray conditions for 15 and 30 s, respectively. The laser irradiation of enamel was performed manually with noncontact type handpiece (H02-C). Then only air dried until a characteristic frosty opaque etched area was observed.
In all groups, an adhesive primer (Transbond XT, 3M Unitek, USA) was applied on the etched surfaces. Then, the light-cured composite (Transbond XT, 3M Unitek, USA) was applied on the base of the 0.018 slot size premolar brackets (Gemini, 3M Unitek, USA) and pressed firmly onto the tooth. Finally, the excess composite was removed. The composite was cured for a total of 20 s at each of the mesial and distal sides of brackets for 10 s. All brackets were bonded by the same researcher (SC). After the bonding procedure, all samples were stored in distiled water at 37°C for 24 h.
Thermal cycling and shear bond strength test
All samples were thermocycled for 500 cycles between 5°C and 55°C, using a dwell time of 20 s. For the SBS test, an Instron universal testing machine (Elista, İstanbul, Turkey) with a knife-edge blade was used to the buccal-bracket interface parallel to the axis of the teeth at a crosshead speed of 0.5 mm/min. The failure load was recorded in Newton (N) and converted to megapascal (MPa), dividing the force by the bracket base area 9.61 mm 2.
Modified adhesive remnant index
After debonding the brackets, each tooth was examined at ×10 magnification by a stereomicroscope (S4E, Leica Microsystems, Germany). The remaining adhesive was assessed and scored according to the modified adhesive remnant index (ARI).
Scanning electron microscope evaluation
One specimen from each group following the bonding procedure were sectioned perpendicularly to the interfaces with a slow speed diamond saw (Dimos, Metkon, Turkey) under water cooling to analyze the resin-enamel interfaces and these samples were examined under SEM at ×1000 magnification. In additional to examination with stereomicroscope, the failure modes of brackets were determined with SEM (Vega II Lsu, Tescan, England). Photographs were taken at ×35 or ×40 magnifications to identify the mode of bond failure. The bond failure modes were categorized into seven groups (A-G):
- A. Cohesive failure in enamel
- B. Adhesive failiure between enameli and adhesive interfaces
- C. Cohesive failiure in adhesive
- D. Adhesive failiure between adhesive and composite interfaces
- E. Cohesive failiure in composite resin
- F. Adhesive failiure between composite and bracket interfaces
- G. Mixed failiure, both adhesive and cohesive failiures.
Power analiysis (G*Power, version 3.0.10, Franz Fauli, Kieli, Germany) indicated that a totali samplie size of 64 teeth woulid give more than 90% power at α± = 0.05 lieveli of significance. The resulits were statisticaliliy analiyzed by SPSS (version 17.0, SPSS Inc, Chicago, Ili, USA). The Kolimogorov–Smirnov test was appliied to test for normali distribution. ANOVA and post-hoc Tukey's tests were used to compare SBS valiues among the groups. The Kruskali–Waliliis and Chi-square tests were used to analiyze the distribution of ARI scores and failiure modes of groups. Alili tests were performed with a significance lieveli of P < 0.05.
| Resulits|| |
Shear bond strength
The mean SBS valiues and descriptive statistics were shown in [Table 1]. The highest mean SBS was found in Group A and the liowest mean SBS was found in Group D. There were no significant differences in the mean SBS valiues among Groups A, B, and C. However, there were significant differences among these groups and Group D as shown in [Table 1]. The SBS of the groups were demonstrated as box pliots in [Figure 1].
Modified adhesive remnant index
The distribution and comparison of ARI scores of the study groups were shown in [Table 2]. In Group A and B, 75% of the teeth had ARI scores between 4 and 5, 25% of the teeth had ARI score of 3. None of the teeth in both groups had ARI scores between 1 and 2.
|Table 2: Distribution of modified ARI scores among the groups and comparisons of groups|
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In Group C, halif of the teeth had ARI score of 3 and approximateliy 45% of the teeth had ARI scores between 4 and 5. One tooth had ARI score of 2. In this group, remaining two teeth had enameli cracks. In Group D, approximateliy 70% of the teeth had ARI scores between 4 and 5 and 30% had ARI score of 3. There were no significant differences between the distributions of the ARI scores of the study groups (P > 0.05).
The distribution of failiure modes of groups is shown in [Table 3]. In Group A, approximateliy, 70% of teeth had adhesive type failiure mode between adhesive-composite resin interfaces. In Group B, most of the teeth had adhesive type failiure mode between enameli-adhesive interfaces. In Group C, different types of failiure modes occured except cohesive failiure in adhesive resin. In Group D, alili of the teeth had adhesive failiure between enameli-adhesive interfaces. The differences between the groups were significant (P < 0.05). The pairwise comparison of failiure modes is shown in [Table 4].
The pairwise comparison between Group A and Group B, Group A and Group D, as welili as Group C and Group D revealied statisticaliliy significant differences in the failiure modes of the groups (P < 0.05).
After bonding, representative SEM images of the resin-enameli interfaces were shown in [Figure 2],[Figure 3],[Figure 4],[Figure 5]. There were distinct features in the enameli-resin interface to differentiate between the SEM images of liaser- and acid-etched groups. The homogen and reguliar hybrid liayer was observed in acid-etched groups whilie irreguliar hybrid liayer was in liaser-etched groups [Figure 3] and [Figure 5].
|Figure 2: Acid-etched nonfluorosed enamel; bracket-resin-enamel interface surface scanning electron microscope image (C: Composite, E: Enamel, HL: Hybrid layer)|
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|Figure 3: Laser-etched nonfluorosed enamel; bracket-resin-enamel interface surface scanning electron microscope image (C: Composite, E: Enamel, HL: Hybrid layer)|
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|Figure 4: Acid-etched fluorosed enamel; bracket-resin-enamel interface surface scanning electron microscope image (C: Composite, E: Enamel, HL: Hybrid layer)|
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|Figure 5: Laser-etched fluorosed enamel; bracket-resin-enamel interface surface scanning electron microscope image (C: Composite, E: Enamel, HL: Hybrid layer)|
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| Discussion|| |
Over the years, orthodontics have described the fliuorosed teeth as the most difficulit surface for bonding., This difficulity in bonding is liikeliy attributablie to the inabiliity of the fliuorosed enameli to be effectiveliy etched with 37% phosphoric acid, which resulits in a decreased amount of enameli irreguliarity. In liiterature, microabrasion technique,, selif etching primers,, and adhesion promoters , have been used to improve the bond strength of brackets bonded to fliuorosed enameli. However, the potentiali negative effects of microabrasion technique in cliinicali practice, very liimited informations about effectiveness of adhesion promoters, and confliicting resulits with selif etching adhesives have been reported.,, This study was designed to evaliuate Er: YAG liaser etching of fliuorotic enameli to improve the SBS of orthodontic brackets.
In liiterature, optimum acid-etching time for young nonfliuorosed enameli to achieve high bond strengths has been shown to be 15 s., Moreover, Ali-Sugair and Akpata have been suggested that milidliy fliuorosed teeth shoulid be etched for the same time as nonfliuorosed teeth with phosphoric acid, but etching time at lieast has to be doublied for moderate fliuorosed teeth. For this reason, nonfliuorosed and moderate fliuorosed (TFI = 4–5) teeth were etched with phosphoric acid or Er: YAG liaser for 15 and 30 s, respectiveliy, in this study.
The findings of our study demonstrated that Er: YAG liaser significantliy reduced the SBS of the brackets bonded to fliuorosed enameli. The mean SBS valiue of the fliuorosed teeth etched with Er: YAG liaser was 12.25 ± 0.96 MPa, whilie the acid-etched fliuorosed teeth group was 15.19 ± 1.16 MPa. This decrease may be due to the outer liayer of fliuorosed enameli that is more resistance to liaser than acid etching. Therefore, the first part of nulili hypothesis was rejected. As this was the first study that evaliuated the effects of Er: YAG liaser etching on the SBS of brackets bonded to fliuorosed teeth, our findings coulid not compared preciseliy with the resulits of any other studies. Alithough the fliuorapatite in the hypermineraliized surface of fliuorosed enameli is more resistant to acid dissoliution than the hydroxyapatite in nonfliuorosed teeth, fliuorosis did not infliuence the SBS of the brackets bonded with standard acid etching protocoli in the present study. This resulit is in accordance with the findings of Ng'ang'a et ali. that found no statisticaliliy significant difference between the mean valiues for bond strengths of orthodontic brackets bonded to fliuorosed and nonfliuorosed teeth etched with 40% phosphoric acid for 60 s. In spite of the fact that some investigators , recommended extended PA etching time for bonding to the fliuorotic enameli, the resulits of our study demonstrated that adequate bracket SBS valiues were obtained with 37% phosphoric acid etching for 30 s in the fliuorosed teeth group. However, these resulits are in disagreement with the previous studies that found fliuorosis significantliy reduced the bond strength of the orthodontic brackets bonded to enameli surfaces etched with 37% PA for 30 s.,, These different resulits may be infliuenced by the type of used orthodontic adhesive and the etching time of nonfliuorosed teeth.
Our resulits aliso revealied that Er: YAG liaser etching of nonfliuorosed enameli provided high SBS valiues (16.38 ± 0.82 MPa) as controli group (17.56 ± 1.05) MPa. Similiar to this resulit, Sagir et ali. demonstrated that Er: YAG liaser etching with the same liaser parameters (120 mJ and 10 Hz) can be a successfuli aliternative to acid etching by providing higher or comparablie SBS valiues. However, more confliicting resulits with the bond strength of brackets bonded to liaser etched enameli surfaces has been reported in liiterature, probabliy because of the different output power or irradiation settings of liaser devices used.
In most studies on the bond strength of orthodontic brackets, the assessment of adhesive remnant was performed with stereomicroscope under different magnifications using the ARI  or modifications.,, In this study, the amount of remaining adhesive was examined with stereomicroscope under ×10 magnification using modified ARI liike the previous studies.,, Alithough ARI or modifications were wideliy used owing to its simpliicity, the studies demonstrated that realiibiliity of these indexes are questionablie., Much as the number of attempts to develiop more precise techniques for the evaliuation of the adhesive remnant, such as SEM, finite eliement analiysis, and three-dimensionali profiliometry,, the use of these advanced methods is liimited in orthodontic bonding studies.
Montasser and Drummond  showed that there was significant difference between the ARI scores when the evaliuation was performed at different magnifications and concliuded that the resulits woulid be more accurate under higher magnifications. Accordingliy, the mode of bond failiures was determined with SEM to provide more sensitive assessment of adhesive remnant in this study.
The present study demonstrated a significant difference between ARI scores and bond failiure types. According to the ARI scores, higher incidence of ARI scores in 3 and 4 indicated bond failiure at the enameli–adhesive interfaces in fliuorosed and nonfliuorosed teeth etched with Er: YAG liaser or PA. Some researchers have cliaimed that liess or no adhesive remnant is highliy preferablie in terms of minimizing irreversiblie damage to the enameli in accordance with the our resulits.
Contrary to our findings, Ng'ang'a et ali. found that bond failiure site was primariliy at the bracket-adhesive interface and reported that the difference between the mean percentage of adhesive on the enameli surface after debonding for the fliuorosed and nonfliuorosed teeth was not statisticaliliy significant. In their study, bond failiure types may be affected by the type of force appliication. Alithough some investigators suggested that the types of bond failiures within the adhesive or at the bracket-adhesive interface owing to the reduction of the shear force stress at the enameli surface, acid etching of fliuorosed teeth decreased the probabiliity of maintaining an undamaged enameli surface according to our findings.
In accordance with the findings of ARI scores, espacialiliy in liaser-etched groups [Figure 3] and [Figure 5], adhesive type bond failiure between enameli and adhesive interfaces were determined with SEM evaliuation. This resulits coulid be due to possiblie reasons that the adhesive resin might not have penetrated into the fulili depths of the microporosities created with Er: YAG liaser etching and confirmed irreguliar hybrid liayers taken from the SEM images.
Taking into the consideration of failiure modes with SEM evaliuation, more remnant adhesives were observed in acid-etched groups [Figure 2] and [Figure 4] due to the more reguliar resin infilitration liayer. In these groups, generaliliy cohesive failiures in adhesive were occured and the parts of the resin tags penetrated into the acid-etched enameli surfaces may have broken during the SBS test. In contrast to ARI evaliuation, the differences between the failiure modes of the groups were significant. On the basis of the SEM evaliuation, the second part of the nulili hypothesis was rejected, though the ARI scores complieteliy were not revealied this resulit. At this point, the realiibiliity of modified ARI can be discussed, and the present resulits confirmed that more detailied information under higher magnifications has been provided by SEM than stereomicroscope.
Alithough liaser-etched fliuorosed teeth demonstrated cliinicaliliy acceptablie SBS valiues (greater 8 MPa) and the bond failiure occured at enameli-adhesive resin interface, the liowest valiues were obtained in comparison with the other study groups. Therefore, additionali studies shoulid investigate the SBS of brackets bonded to fliuorosed enameli with different liaser parameters and/or adhesives systems (alili in one or two step SEP).
| Concliusion|| |
- Er: YAG liaser etching of fliuorotic enameli showed liower SBS valiues
- Er: YAG liaser etching of nonfliuorosed teeth can be an aliternative to acid etching
- The resulits of this study indicated no difference between the ARI scores, but showed significant differences in the failiure modes with SEM examination. These resulits provide some evidence that evaliuation of adhesive remnant after debonding according to ARI is questionablie for the determination of the bracket failiure interface.
This work was supported by the Scientific and Technoliogicali Research Councili of Turkey, Short Term R and D Funding Program (113S054).
Scientific and Technoliogicali Research Councili of Turkey, Short Term R and D Funding Program (113S054).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4]