Hyunhee Park
5th year, group14Comparison of erbium-doped yttrium aluminum garnet(Er:YAG)
laser etching and conventional acid etching
for orthodontic bracket bonding: A systematic review
Master thesisWork Supervisor PhD, Julija Urbone
Kaunas, 2018
LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY
FACULTY OF ODONTOLOGY THE CLINIC OF ORTHODONTICS
Comparison of erbium-doped yttrium aluminum garnet(Er:YAG)
laser etching and conventional acid etching
for orthodontic bracket bonding: A systematic review
Master thesis
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Summary thesis content and requirements?
2 (0.5 point) Are keywords in compliance with the thesis 0.2 0.1 0 essence?
3 Introduc- Are the novelty, relevance and significance of the 0.4 0.2 0 work justified in the introduction of the thesis?
tion, aim
Are the problem, hypothesis, aim and tasks formed
4 and tasks 0.4 0.2 0
clearly and properly? (1 point)
5 Are the aim and tasks interrelated? 0.2 0.1 0 6 Selection Is the protocol of systemic review present? 0.6 0.3 0
criteria of Were the eligibility criteria of articles for the
7 the studies, selected protocol determined (e.g., year, language, 0.4 0.2 0 search publication condition, etc.)
methods and Are all the information sources (databases with
8 strategy dates of coverage, contact with study authors to 0.2 0.1 0 (3.4 points) identify additional studies) described and is the last
search day indicated?
Is the electronic search strategy described in such a way that it could be repeated (year of search, the
9 last search day; keywords and their combinations; 0.4 0.1 0 number of found and selected articles according to
the combinations of keywords)?
Is the selection process of studies (screening,
10 eligibility, included in systemic review or, if 0.4 0.2 0 applicable, included in the meta-analysis)
described?
Is the data extraction method from the articles
11 (types of investigations, participants, interventions, 0.4 0.2 0 analysed factors, indexes) described?
Are all the variables (for which data were sought
12 and any assumptions and simplifications made) 0.4 0.2 0 listed and defined?
information is to be used in data synthesis, described?
14 Were the principal summary measures (risk ratio, 0.4 0.2 0 difference in means) stated?
Is the number of studies screened: included upon
15 assessment for eligibility and excluded upon giving 0.6 0.3 0 the reasons in each stage of exclusion presented?
Are the characteristics of studies presented in the
16 Systemiza- included articles, according to which the data were 0.6 0.3 0 extracted (e.g., study size, follow-up period, type of
tion and
respondents) presented? analysis of
Are the evaluations of beneficial or harmful data
outcomes for each study presented? (a) simple
17 (2.2 points) 0.4 0.2 0
summary data for each intervention group; b) effect estimates and confidence intervals)
Are the extracted and systemized data from studies
18 presented in the tables according to individual 0.6 0.3 0 tasks?
19 Are the main findings summarized and is their 0.4 0.2 0 relevance indicated?
20 Discussion Are the limitations of the performed systemic 0.4 0.2 0 (1.4 points) review discussed?
21 Does author present the interpretation of the 0.4 0.2 0 results?
22 Do the conclusions reflect the topic, aim and tasks 0.2 0.1 0 Conclusions of the Master’s thesis?
23 (0.5 points) Are the conclusions based on the analysed material? 0.2 0.1 0 24 Are the conclusions clear and laconic? 0.1 0.1 0 25 Is the references list formed according to the 0.4 0.2 0
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26 Are the literature sources cited correctly and 0.2 0.1 0 References precisely?
27 (1 point) Is the scientific level of references suitable for Master’s thesis? 0.2 0.1 0 Do the cited sources not older than 10 years old
28 form at least 70% of sources, and the not older than 0.2 0.1 0 5 years – at least 40%?
Additional sections, which may increase the collected number of points
29 Annexes Do the presented annexes help to understand the +0.2 +0.1 0 analysed topic?
Practical
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30 recommen- +0.4 +0.2 0
are they related to the received results? dations
Were additional methods of data analysis and their
31 results used and described (sensitivity analyses, +1 +0.5 0 meta-regression)?
Was meta-analysis applied? Are the selected
32 statistical methods indicated? Are the results of +2 +1 0 each meta-analysis presented?
General requirements, non-compliance with which reduce the number of points
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35 Does the thesis structure satisfy the requirements of Master’s thesis? -1 point -2 points 36 Is the thesis written in correct language, -0.5 point -1 points
scientifically, logically and laconically?
37 Are there any grammatical, style or -2 points -1 points computer literacy-related mistakes?
38 Is text consistent, integral, and are the -0.2 point -0.5 points volumes of its structural parts balanced?
General
39 Amount of plagiarism in the thesis. >20%
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ments Is the content (names of sections and sub-
40 sections and enumeration of pages) in -0.2 point -0.5 points compliance with the thesis structure and
aims?
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41 compliance with the text? Are the titles of -0.2 point -0.5 points sections and sub-sections distinguished
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42 Are there explanations of the key terms -0.2 point -0.5 points and abbreviations (if needed)?
Is the quality of the thesis typography
43 (quality of printing, visual aids, binding) -0.2 point -0.5 points good?
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CONTENT
ABSTRACT………... 1
INTRODUCTION……….. 2-3
1
SELECTION CRITERIA OF THE STUDIES.
SEARCH METHODS AND STRADEGY……….... 4-7
1.1 Protocol of systematic review……….... 4
1.2 Information sources……….…... 4
1.3 Electronic strategy of the search for data………... 4
1.4 Inclusion and exclusion criteria……….…. 4-5
1.5 Focus questions ………. 5
1.6 Risk of bias assessment………... 6-7
2
SYSTEMATIZATION AND ANALYSIS OF DATA……. 8-2
5
2.1 Explanation of abbreviations ……….… 8
2.2 Characteristics of included studies………....…. 8-2
5
DISCUSSION……….... 2
6-29
CONCLUSION………..
30
REFERENCES……… 3
1-33
ABSTRACT
Objectives: The purpose of present study was to compare the efficiency of erbium-doped yttrium aluminum garnet (Er:YAG) laser etching and conventional acid etching for orthodontic bracket bonding.
Material and methods: included literature were identified by searching the PubMed and ScienceDirect electronic database from February 1st 2008 to February 28th 2018 with these key words and their combinations: laser etching, Er:YAG laser, acid etching, bracket bonding, orthodontics. Inclusion criteria were in English language, including comparison of Er:YAG laser etching and phosphoric acid etching on human teeth and studies with shear bond strength(SBS) test, scanning electron microscopy(SEM) and adhesive remnant index(ARI) scores. Risk of bias assessment was performed using Cochrane Risk of bias Tool.
Results: In total 229 studies were identified which were related to keywords used during the search. Finally ten articles are included in this systematic review filtered by inclusion criteria. Our hypothesis is that Er:YAG laser etching can be a proper alternative to conventional acid etching for orthodontic bracket bonding. Er:YAG laser etching was gained some acceptable and comparable SBS values and ARI scores although the results was not remarkable compared to conventional phosphoric acid etching. However, in general SEM evaluation, acid-etched enamel showed regularly with honeycomb appearance but Er:YAG laser-etched showed irregular coarse enamel surface moreover has potential rick for crack on the enamel.
Conclusion: Through this systematic review, our hypothesis could not be confirmed that Er:YAG laser etching on human enamel surfaces can be proper alternative to conventional acid etching for orthodontic bracket bonding.
INTRODUCTION
In orthodontic practice, a minimum of bond strength between the enamel surface and bracket base is essential for the retention of brackets to dental surfaces and bracket base must be enough to withstand the mechanical and thermal effects of the oral environment. Bonding of brackets is based on alteration of the enamel surface, and the standard protocol for this procedure is an acid etching[1]. The bonding between the bracket and the enamel is based on mechanical interlocking of the adhesive into the micro-porosities of the enamel surface. Therefore, surface conditioning is essential to increase bond strength to enamel. Phosphoric acid etching has been using as standard practice and 30% to 50% phosphoric acid gel, applied for 30 to 60 seconds, is commonly used to remove smear layer for successful bonding and presented as the gold standard method of enamel preparation. Enamel etching modifies the tooth surface from being of low-energy and hydrophobic to being of high-energy and hydrophilic, increasing the surface area for bonding[2-5].
Recently, laser irradiation have been proposed as alternative methods for preparing dental hard tissue. Laser enamel abrasion to enhance bond strength of orthodontic brackets is a minimally invasive technique. Especially, erbium lasers have been used for this purpose and resulted in optimal bond strength to natural tooth structure and restorative materials such as composite resins. Laser etching is painless and has been suggested as an alternative to acid etching procedure due to time consuming nature of acid etching, short shelf life of acids, and technical sensitivity.
Er:YAG lasers are one of the most popular among laser etching. This laser causes microexplosions inside the material and creates craters. They cause evaporation of tissue fluids and hydroxyapatite crystals. Er:YAG lasers with a moderate level of energy create a strong bond and do not cause melting or changing the orientation of crystalline structure of enamel in contrast to Nd:YAG and CO2 lasers[6].
The shear bond strength (SBS) of orthodontic brackets should be high enough to prevent bonding failure and should offer adequate resistance against chewing forces and stresses from arch wires . The SBS between the bracket and enamel surface depends on three factors: the design of the bracket base, the adhesive material or bonding resin itself, and the preparation of the tooth surface. Although outcome of acid etching results in high bond strength, its great negative element is the potential for caries formation. Acid etching eliminates and demineralizes the most superficial layer of enamel and makes the teeth more sensitive to long-term acid attacks.[7]
The aim of this study was to compare the efficiency of Er:YAG laser etching and conventional phosphoric acid etching on human enamel surface before orthodontic bracket bonding, this study compared the result of shear bond strength(SBS), enamel morphology after etching by scanning electron microscopy(SEM) examination after etching and adhesive remnant index(ARI) scores after debonding bracket.
Our hypothesis is that Er:YAG laser etching can be a proper alternative to conventional acid etching for orthodontic bracket bonding.
Task of this study:
- To evaluate the shear bond strength (SBS), scanning electron microscopy (SEM) and adhesive remnant index (ARI) scores of Er:YAG etched and phosphoric acid etched enamel. - To compare two etching methods with result from those analysis methods
1. SELECTION CRITERIA OF THE STUDIES
SEARCH METHODS AND STRATEGY
1.1 Protocol of systematic review
The articles review and data extraction were performed according to the protocol of the PRISMA(Prefferd Reporting Items for Systematic Reviews and Meta-analysis) statement [8].
1.2 Information sources
This systematic review is based on a selection of main information source as literature studies was identified by searching the Pubmed and ScienceDirect electronic databases.
1.3 Electronic strategy of the search for data
This systematic review is based on a selection of main information source as literature studies was identified by searching the Pubmed and ScienceDirect electronic databases. The literatures are searched in February 20th 2018 and last searching was February 28th 2018. The literatures which is selected are in the English language, performed on human tooth, studies that published in the years from Feburary 2008 till Feburary 2018 and included the keywords that were used in the search are laser etching, Er:YAG laser, acid etching, bracket bonding, orthodontics and their combinations. In total of 229 scientific studies were identified and were related to key words used during the search. Then duplicated articles were removed.
Irrelevant publications were independently screened by their titles and abstracts
The last stage of screening involved reading the full texts to confirm each study's eligibility based on inclusion and exclusion criteria.
Finally, ten articles were selected in this study.
1.4 Inclusion and exclusion criteria
Inclusion criteria are:
1. Etching perfomed on human enamel surface.
2. Comparison between Er:YAG laser etching and phosphoric acid etching. 3. Studies with used stainless steel bracket.
4. Studies with performed scanning electron microscopy (SEM) evaluation. 5. Studies with performed adhesive remnant index (ARI) scores.
6. Studies with performed shear bond strength (SBS) testing.
7. Years of articles publication were chosen from Feburary 1st 2008 till Feburary 28th 2018. 8. In vitro studies.
Exclusion criteria are: 1. Non human studies.
2. Studies with used rebonded bracket .
3. Laser etching performed on amalgam, composite, or porcelain surface. 4. Literature review, single case reports, editorials, commentaries.
1.5 Focus questions
The focus questions were developed according to the problem, intervention, comparison, and outcome (PICO) is presented in Table 1.
Table 1. PICO table
Component Description
Population Human extracted teeth included in the clinical studies that were etched with Er:YAG
laser and phosphoric acid
Intervention Enamel etching with Er:YAG laser and phosphoric acid on human tooth
Comparison Er:YAG laser etching and conventional acid etching according to results from SBS test,
SEM and ARI scores.
Outcome Er:YAG laser etching can be an alternative to conventional acid etching for orthodontic
bracket bonding. Focus
questions
- Is there significant difference between laser etched and acid etched group according to result derived from each examination methods?
1.6 Risk of bias assessment
The risk of bias was evaluated by The Cochrane Risk of Bias Tool [9] that include 6 processes: random sequence generation, allocation concealment, blinding of participants and personnel, incomplete outcome data, selective reporting and other sources bias are presented in Table 2. Potential risk of bias was categorized into low risk of bias(+), high risk of bias(-) and unclear risk of bias(?).
Table 2. Risk of bias (from earlies to most recent) Random Sequence Generation Allocatio n Concealm ent Blinding of Participants and Personnel Blinding of Outcome Assessment Incomplete Outcome Data Selective Reporting Other Sources Bias Serkan Sag ̆ır et al., 2013 [1] ? ? + + + + - G. Ierardo et al., 2014 [3] ? ? + + + ? - Güvenç Başaran et al., 2011 [10] ? ? + + + + - Çagrı Türköz et al., 2012 [11] ? ? + + + + - Fulya Ozdemir et al., 2013 [12] ? ? + + + + - Sogra Yassaei et al., 2014 [13] ? ? + + + +
-Serpil Cxokakog ̆l u et al., 2015 [14] ? ? + + + + - Cahide Aglarci et al., 2016 [15] ? ? + + + + - Mohamma d Sadegh Ahmad Akhoundi et al., 2017 [16] ? ? + + + + - R Nalçacı et al., 2018 [17] ? ? + + + + -
Categories as follows: low risk of bias (+), high risk of bias (-), or unclear risk of bias (?).
All of the included studies showed an unclear risk of bias because they were unclearly described in the articles and a high risk of other bias in most of the articles because the population of studies was controlled.
2. SYSTEMIZATION AND ANALYSIS OF DATA
2.1 Explanation of abbreviations
Abbreviations are included in this study to compare efficiency of conventional acid etching and Er:YAG laser etching.
Er:YAG: erbium-doped yttrium aluminum garnet; SBS: shear bond strength; ARI: adhesive remnant index; SEM: scanning electronic microscopy; EDI: enamel damage index; MPa: megapascals; MSP: medium-short pulse mode; QSP: quantum-square pulse mode; ANOVA: analysis of variance.
2.2 Characteristics of included studies
The articles review and data extraction were performed according to the PRISMA diagram (figure 1.)[18]. The initial database search displayed 229 results. The preliminary 47 duplicates articles and title was removed and 162 articles are excluded by relevancy. 7 articles are excluded cause no access for full text and 1 article, had no acid etching control group exist in the study ,was excluded and 2 articles, no assessment of Er:YAG laser etching alone but only exist with acid etching together, were excluded. Finally, In total 10 most relevant articles were included in this systematic review and 330 samples were examined in total. All of the included articles were performed in vitro.
In the summary of included studies (Table 3.) were compared regarding the sample size, method of enamel etching, included assessment and result. The ten included articles were investigate SBS test, SEM or/and ARI index to compare efficiency and bonding failure phosphoric acid etching and Er:YAG laser etching to enamel. All used indices in this systematic review about the following categories are explained under the each table or explained with first mention of the index.
Figure 1. PRISMA flow diagram
The 6 included articles among the total included articles, each study were performed with one acid etching control group and single Er:YAG laser etching group. The other 4 included articles were performed with one acid etching control group and not only one but also another setting of Er:YAG
Table 3. Summary of included studies
Author/Year of publication
Sample Volume of included
Method of enamel surface etching Type of
assessment
Result
Serkan Sag ̆ır et al., 2013 [1] 36 extracted human premolars Group A: n=12 Group B: n=12 Group C: n=12 Inclusion criteria: Intact enamel and no caries, cracks,
restorations, or infections
Group A: etched with 37% phosphoric acid gel for 20 s, rinsed with air-water spray for 15 s, and dried to a chalky-white appearance
Group B: etched with an Er:YAG dental laser (2970-nm wavelength; LightWalker, Fotona, Slovenia) for 15 seconds (120 mj, 10 Hz, 1.2 W, water [50 ml/ min]) in MSP mode, 1mm distance
Group C: etched with the same dental laser and same power settings, but in QSP mode
SBS SEM (after etching) ARI
Er:YAG laser etching with MSP and GSP modes presents a successful alternative to acid etching
G. Ierardo et al., 2014 [3]
33 extracted human third molars
Group A: n=11 Group B: n=11 Group C: n=11
Inclusion criteria:
Group A: with 37% orthophosphoric acid (etching solution, ORMCO, USA) for 30 s.
Group B: with Er:YAG laser irradiation (Fidelius III, Fotona, Slovenia) at 80 mJ and 4 Hz.
SEM (after debonding)
Modified ARI
The use of Er:YAG laser alone showed no significant
advantages over phosphoric acid etching in the bonding procedure for orthodontic brackets
Without caries lesion or
enamel defects Group C: with Er:YAG laser at 40 mJ
and 10 Hz. Güvenç Başaran et al.,
2011 [10] 55 extracted human premolars Group A: n=10 Group B: n=10 Group C: n=10 Group D: n=10 Group E: n=10 SEM: n=5 Inclusion criteria: Etching on crowns that without caries,
restorations, or fractures
Group A: Enamel etched with 38% orthophosphoric acid (Pulpdent Corporation,
Watertown, MA), for 15s, rinsed with water and air-sprayed for 15s, and dried for 15s
Group B: Enamel irradiated with the Er:YAG laser at a distance of 1 mm
Group C: Enamel irradiated with the Er:YAG laser at a distance of 2 mm
Group D: Enamel irradiated with the Er:YAG laser at a distance of 4 mm
Group E: Enamel irradiated with the Er:YAG laser at a distance of 6 mm
SBS SEM (after etching) ARI
No statistically significant difference between phosphoric acid etching and Er:YAG laser etching with 1mm distance and laser irradiaton distance did influence on bond strength
ConBio, Fremont, CA) wavelength: 2940 nm; pulse duration: 250 μs; frequency: 20 Hz; wavelength: 2940 nm, power: 0–8 W; the power output used for the four
different distance settings was constant at 1.75 W for 15 s. Çagrı Türköz et al., 2012 [11] 30 extracted human premolars Group A: n=15 Group B: n=15 Inclusion criteria: Teeth without caries, restorations, and surface abnormalities
Group A: Phosphoric acid (35%) gel (Gel Etch; 3M Unitek, Monrovia, CA, USA), for 15 s, rinsed with water infused from a 3-in-1 syringe for 15 s and dried with an oil- and moisture-free source for 10 s.
Group B: Er:YAG laser (KaVo Key 3, hand-piece 2060TM; KaVo Dental GmbH, Biberach, Germany); pulse energy: 350 mJ/pulse; frequency: 4 Hz, from a distance of 1 mm, with water-spray cooling (7 ml/min)
SBS SEM (after debonding) ARI
Although laser conditioning afforded high SBS, the procedure resulted in
considerable damage to teeth. Therefore, the acid etching were found to be safer for orthodontic bracket bonding
Fulya Ozdemir et al., 2013 [12]
26 extracted human upper premolars
Group A: n=13 Group B: n=13
Group A: 38% phosphoric acid gel (Etch-Rite; PulpDent, Watertown, MA, USA) for 30 s, washed with distilled water and dried with oil-free compressed air for 10 s.
SBS ARI
Statistically significant difference in SBS between acid- and laser etched group
Inclusion criteria: Sound, human, upper premolar teeth
Group B: irradiated with Er:YAG (VersaWave; HOYA Photonics Inc., Fremont, CA, USA)
laser with a wavelength: 2.94 mm; pulse energy: 300 mJ/pulse; frequency: 10 Hz; operated for 10 s in a focused, noncontact mode under water spray; 1mm distance Sogra Yassaei et al.,
2014 [13] 40 extracted human premolars Group A: n=20 Group B: n=20 Inclusion criteria: Human premolar without caries, fractrures and enamel surface defects
Group A: conditioned with a 37% phosphoric acid gel for 30 s, rinsed completely for 20 s, and dried with oil and moisture free air until the frosty white appearance was achieved
Group B: etched with Er:YAG laser (KEY Laser 3+, KaVo Dental
Corporation, Biberach , Germany) pulse energy: 80 mJ; frequency: 15Hz for 10 s; power: 1.2 W; The 2060 handpiece (KaVo Dental Corporation, Biberach, Germany); distance of 20 mm; with water spray cooling; dried with oil and moisture free air for 20 s.
SBS SEM (after etching)
Modified ARI
Mean SBS of phosphoric acid etching is significantly higher than Er:YAG laser etching
2015 [14] Group A: n=12 Group B: n=12 Group C: n=12
Inclusion criteria: Teeth without
hypoplastic areas, cracks, and irregularities of enamel structure
sec, then rinsed for 15 sec, and dried in moisture- and oil-free air to obtain an opaque white appearance.
Group B: were etched with Er:YAG laser (LightWalker AT, Fotona, Ljubljana-Slovenia) for 15 s; wavelength: 2940 nm; pulse energy: 100 mJ; frequency:10 Hz; power of 1; pulse duration of 100 ls (MSP mode); energy density:15.72 J/cm2; water/air: 60%/40%; using a noncontact hand piece (H02-C), sweeping motion perpendicular to the enamel surface; diameter of the tip; 0.9 mm.
Group C: same as group B except pulse energy: 200 mJ; power: 2W; energy density: 31.44 J/cm2
Modified ARI
different irradiation power of laser
Cahide Aglarci et al., 2016 [15]
34 extracted human maxillary premolars Group A: n=17 Group B: n=17
Group A: etched with 37 % orthophosphoric acid gel (3MTM ESPETM ScotchbondTM, 3M ESPE, St. Paul, MN, USA) for
20 s, rinsed for 10 s, and dried for 10 s until they appeared frosty white
SBS SEM (after etching) ARI
Laser conditioning with an Er:YAG system results in successful etching, similar to that obtained with acid
Inclusion criteria: Teeth with intact enamel without pretreatment with chemical agents and presence of cracks, restorations, infections and/or enamel defects
Group B: etched with an Er:YAG dental laser (2940 nm wavelength; LightWalker, Fotona, Slovenia); power: 1.2 W;
frequency: 10 Hz for 15 s in the MSP mode (pulse length 100 μs); Energy density: 9.04 J/cm2. The tip diameter was 1.3 mm; air/water: 90%/80 %; single direction, scanned only once, 1mm distance Mohammad Sadegh Ahmad Akhoundi et al., 2017 [16] 6 freshly extracted human premolars Group A: n=3 Group B: n=3
Group A: etched with
37% phosphoric acid gel for 15 s (3M Unitek, Monrovia, CA, USA), rinsed for 10 s and air-dried
Group B: Er:YAG laser (PLUSER, Doctor Smile, LAMBDASPA, Italy), with the following specifications: power: 2W; energy: 200mJ; frequency: 10Hz; time: 10 s; distance: 2mm, water: 70%, air: 90%.
SEM (after etching)
Enamel surface preparation with Er:YAG laser produces irregular and indistinct morphorlogic changes,
completely different from after acid etching
R Nalçacı et al., 2018 [17]
34 extracted human premolars
Group A: etched with 37% phosphoric acid (ScotchbondTM, 3M ESPE, St Paul,
SBS SEM (after
Er:YAG laser etching can be an alternative to acid etching
Inclusion criteria: Teeth without caries, restorations, cracks, chipping, or
malformation on enamel surface
oil-free air to obtain an opaque white appearance
Group B: etched with Er: YAG laser (LightWalker AT, Fotona, Slovenia); power :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. With noncontact type handpiece (H02‐C), only air dried until a characteristic frosty opaque etched area was observed.
Modified ARI
Çagrı Türköz et al.[11] compared a total of 30 extracted human premolars randomly divided into two groups; A group is a 35% orthophosphoric acid-etched group and B group is Er:YAG laser-etched group. After enamel etching of all the groups, the stainless steel premolar brackets (Mini Master Roth; American Orthodontics, Sheboygan, WI, USA) were bonded to the teeth with using an orthodontic adhesive (Transbond XT; 3M Unitek). One-way ANOVA was used for multiple comparisons of the shear bond strengths for the different etching methods. The average bond strength forces and their standard deviations are shown in Table 4. Çagrı Türköz et al.[11] shows that laser-etched group gained the bond strength of of 9.45 ± 0.92 MPa, which was close to that achieved in the acid-etched group (10.55±0.84 MPa). After debonding the brackets, adhesive remnant index was performed and the teeth in group A and B showed similar result from ARI scores; 80% of group A and 86.7% of group B had ARI score 1(Table 5.) In both of group, debonding the bracket showed differences in the surface characteristics of the teeth in two groups according to the SEM evaluation of the samples. For groups A, the whole enamel surface was covered with resin, thereby suggesting good enamel-resin bonding. In Group B, ablation of enamel surfaces and enamel rods were existed. The ablated enamel surface may have potential to fracture during debonding; this may bring about a result in the separation of the enamel surface from the resin material and the formation of roughened area.
Cahide Aglarci et al. [15] a total of 34 extracted premolars randomly divided in to two groups depending on the etching procedure used. Group A was a 37% phosphoric acid etching as control group and Group B was the Er:YAG laser etching group (Table 3.). After the etching procedures, one specimen from each group was selected for the observation of enamel surfaces under a scanning electron microscopy (SEM). Stainless steel, pre-adjusted, edgewise maxillary premolar brackets (0.22-in. slot; Mini Master Series Brackets, American Orthodontics, Sheboygan, WI, USA) were bonded with Transbond XT (3M Unitek, Monrovia, CA, USA) to the conditioned surfaces in all groups. SBS test and ARI score was performed after bracket bonding. SBS data for the two groups were subjected to normality testing using the Kolmogorov–Smirnov test. The SBS values for the three groups are shown in Table 4. There was no significant difference between the Er:YAG laser (7.49 ± 3.4 MPa) and acid etching groups (7.55 ± 2.8 MPa). Bond failure modes are shown in
interaction with the enamel in the Er:YAG laser etching group. In the acid etching group, numerous and continuous enamel tags were observed.
R Nalçacı et al.[17] compared a total of 34 extracted human premolars randomly divided into two groups; group A was etched with 37% phosphoric acid as control group and group B was etched with Er:YAG laser. Both of 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). ANOVA tests were used to compare SBS values among the groups. The mean shear bond strength values and the standard deviation were shown in Table 4. There were no significant differences in the mean SBS values among groups A (17.56±1.05 MPa) and B (16.38±0.82 MPa). 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)[19]. The comparison of ARI scores of study groups were shown in Table 6. Both of 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. After debonding , SEM evaluation were performed. There were distinct features in the enamel-resin interface to differentiate between laser- and acid-etched groups. The homogen and regular hybrid layer was observed in acid-etched groups while irregular hybrid layer was in laser-etched groups.
Fulya Ozdemir et al.[12] compared a total of 26 extracted human upper premolars randomly divided into two groups; group A was 38% phosphoric acid etching and group B was Er:YAG laser etching. Stainless steel, standard edgewise, upper premolar brackets (Standard Edgewise Dynalock; 3M Unitek, Monrovia, CA, USA) were used for this study. After surface conditioning, the liquid primer Transbond XT (3M Unitek) was applied to the etched surfaces, and the brackets were bonded on the teeth with Transbond XT adhesive. Debonding was performed with a shearing force using a testing machine (Table 3.) Welch test was used to evaluate SBS of the groups. The mean and standard deviation values of SBS for both groups are presented in Table 4. In evaluations with the Welch test, there was a statistically significant difference in bond strength between group A and B (p < 0.001). A comparison of SBSs for the acid- (25.27±5.12 MPa) and laser-etched (7.73±2.45 MPa) groups revealed that the laser group showed significantly lower values (p < 0.001). After debonding procedure, all enamel surfaces and brackets were examined under ×40 microscopy and classified according to the adhesive remnant index (ARI). Show the ARI scores of both groups, all of 13
samples of group A had an ARI scores of 1, all of 13 samples of group B had an ARI scores of 0 (Table 5.).
Sogra Yassaei et al. [13] compared a total 40 extracted human premolars randomly divided into two groups each 20 samples, group A was with a 37% phosphoric acid etching and group B was Er:YAG laser etching. An evenly thin layer of adhesive resin (Resilience Ortho Technology, Tampa, Florida, USA) was laid on the etched teeth surfaces. The metal brackets were placed on the center of teeth surfaces and bonded with composite resin (Resilience Ortho Technology, Tampa, Florida, USA). Dartec testing machine was used for SBS evaluation with a crosshead speed of 1 mm per minute until bracket debonding. There were significant differences between each mean SBS values of group A and B (P < 0.05) according to the ANOVA test. Acid-etched (30.45±1.63 MPa) group had significantly higher SBS values compared to laser-etched (18.32±3.00 MPa) group (Table 4.). After bracket debonding, all samples of both groups were observed using a stereomicroscope at ×10 magnification for observation of residual adhesive remnant on the enamel surface and the bond failure sites between the enamel, resin and bracket base. The modified ARI which was introduced by bishara and Trulove[19] was used in this study. The result from ARI scores indicated 65% of group A had ARI scores of 3 and 25% of group A had ARI scores of 4 (Table 6.). ARI scores of 2 in 40% and score of 1 in 35% of group B (Table 6.). Two additional teeth were etched with acid for one tooth and laser for the other tooth in accordance with the protocol described in Table 3. The teeth were performed SEM evaluation using an electron microscope (VEGA, TESCAN Co. Czech Republic) to observe the enamel pattern of etching. SEM examination shows an enamel surface after the Er:YAG laser etching is in accordance with type 3 pattern of etching and conventional phosphoric acid etching technique produced enamel surface resembled type 1 pattern of etching (Annex 1.). There were no crack or fracture was noticed on the laser-etched enamel surface, whereas acid etched enamel shows cracks in some regions.
Mohammad Sadegh Ahmad Akhoundi et al. [16] compared a total of 6 freshly extracted human premolars randomly divided into two group 3 premolars each; group A were conditioned with 37% phosphoric acid gel and group B were conditioned with Er:YAG laser. The samples were sent to a special laboratory for SEM analysis by a blinded operator. The acid-etched enamel surface
the laser-etched samples indicated a completely irregular and rough structure without obvious patterns in any region that could be explained by micro-explosions generated by laser irradiation which have a destructive effect on the enamel.
Güvenç Başaran et al. [10] investigated the shear bond strength of bonding to enamel following 38% phosphoric acid etching and Er:YAG laser etching using same properties of laser setting but 4 different irradiation distances which is 1, 2, 4 and 6mm(Table 3.). One-way ANOVA was used for multiple comparisons of the shear bond strength for the different etching methods. A total of 50 extracted human premolars were compared according to shear bond strength test and also scanning electron microscopy (SEM) evalutation performed on 5 premolars after each different surface treatment. After all the etchings had been performed, stainless-steel standard edgewise premolar brackets (DynaLock; 3M Unitek, Seefeld, Germany) were bonded to the teeth. After the bonding material (Transbond XT; 3M Unitek, Monrovia, CA) had been applied, the bracket was placed onto the tooth surface. After debonding, ARI were evaluated and shown in Table 5. Descriptive statistics for the comparison of shear bond strengths for the five groups are given in Table 4. The acid-etched group indicated the highest mean shear bond strength (19.42±6.13 MPa). The mean shear bond strengths for the Er:YAG laser at 1, 2, 4 and 6 mm were 14.87±4.38, 10.68±2.98, 5.73±2.28 and 5.72±3.65 MPa. One-way ANOVA revealed a statistically significant difference in shear bond strength between all the laser-etched groups and the acid-etched group (p<0.001). The shear bond strength in the acid-etched group was not significantly different from that in the Er:YAG 1mm group (p>0.05), but was significantly different from that in all the other laser irradiation distances groups (p<0.001). According to SEM, the enamel surface etching pattern with phosphoric acid-etched was a type 3 acid-acid-etched pattern with a regular rough surface and spaces (Annex 1.). Laser irradiation in group B and C (Er:YAG laser etching with distances of 1 and 2mm) was enough to etch the enamel with a type 3 pattern as acid-etched group (Annex 1.). However, In group D and E the laser irradiation was not enough to etch the enamel sufficiently producing a type 4 pattern (Annex 1.). The ARI values showed statistically significant differences between all groups but when the Er:YAG 4 and 6mm groups were excluded (Table 5.).
Serkan Sag ̆ır et al.[1] compared acid etching and Er:YAG laser etching according to different pulse modes; a total 36 human premolars randomly divided into 3 groups 12 samples each; group A were etched with 37% phosphoric acid gel, group B were etched with an Er:YAG dental laser in medium-short pulse mode (MSP) and group C were etched with an Er:YAG demtal laser in quantum-square pulse mode (QSP). Scanning electron microscope (SEM) photographs of one tooth
from each group were taken (10003; JSM-5310; JEOL, Peabody, Mass) to observe alterations in enamel surfaces. The enamel damage index (EDI)[20] were used to evaluate the enamel surfaces. The EDI includes the following categories: grade 0, smooth surface without scratches, and perikymata might be visible; grade 1, acceptable surface, with fine scattered scratches; grade 2, rough surface, with numerous coarse scratches or slight grooves visible; and grade 3, surface with coarse scratches, wide grooves, and enamel damage visible to the naked eye. On the remaining 10 premolars in each group, stainless steel brackets (American Orthodontics, Sheboygan, Wis) were bonded to upper premolars using Transbond XT primer and resin (3M Unitek, Monrovia, Calif) according to the manufacturer’s instructions. The SBS test was using a universal testing machine (Shimadzu AG-X, Tokyo, Japan) operating at speed of 0.5 mm per minute. The mean SBS values were presented in Table 4. The obtained data were analyzed by one-way ANOVA. There were statistically significant differences between the SBS values of the groups (P , .01). The QSP group indicated the highest SBS values among the MSP and then acid-etched groups (Table 4.). The QSP group demonstrated significantly higher SBS values compared to the acid etching group (P , .01), whereas the differences were not statistically significant between the acid etching and MSP laser etching groups and between the two laser groups (P . .05). In SEM evaluation, the sample from the acid etching group indicated a rough surface, with numerous coarse scratches or slightly visible grooves which is in EDI grade 2. Samples of both laser modes seemed to produce coarse scratches, extensive grooves, and enamel damage visible with the naked eye (EDI grade 3). According to ARI scores (Table 5), both laser-etched groups indicated that the failure rate in general was mixed in nature, with less than 50% of adhesive remaining on the enamel. In the acid-etched group, ARI scores were mainly adhesive in nature, demonstrating less than 50% or no adhesive remaining on enamel.
G. Ierardo et al. [3] compared according to acid etching and Er:YAG etching with different pulse energy and frequency; a total 33 extracted human third molars randomly divided into three groups 11 samples each; group A were conditioned with 37% orthophosphoric acid , group B were conditioned with Er:YAG laser irradiation at 80 mJ and 4 Hz and group C were conditioned with Er:YAG at 40 mJ and 10 Hz. After enamel surface conditioning, a bracket (Damon MX3-UR3, ORMCO) was bonded using the bonding adhesive (ORTHOSOLO, ORMCO) and a composite
the enamel surface demonstrated in the control group were etched with phosphoric acid (Table 6.). No cracks were observed under SEM in any of the 33 samples, comfirming that debonding forces did not damage the enamel surface.
Serpil Cxokakog ̆lu et al.[14] compared with acid etching and Er:YAG etching with different pulse energy. A total of 36 extracted human premolars randomly divided into three groups 12 samples each; group A were etched with 37% phosphoric acid, group B were etched with Er:YAG laser (100 mJ, 10 Hz) and group C were etched with Er:YAG laser (200 mJ, 10 Hz). After etching, all samples were applied with Transbond XT Primer (3M Unitek, California, USA). Then, an Instron universal testing machine (Elista, Turkey) was used with a knife-edge blade located at the buccal–bracket interface parallel to the axis of the teeth at a crosshead speed of 0.5 mm per minute. ANOVA and post-hoc multiple comparison tests were used to compare SBS values among the groups. The mean SBS values and standard deviations were presented in Table 4. There were no sifnificant differences in the mean SBS value between acid-etched (16.74±1.24 MPa) , Er:YAG laser-etched at 100 mJ (16.50±0.97 MPa) and Er:YAG laser-etched at 200 mJ (7.49±3.4 MPa) The remaining adhesive was assessed according to the modified Adhesive Remnant Index (ARI) scores [19]. Results were presented in Table 6. In the control groups, the teeth in group A had ARI scores between 4 and 5. Half of the teeth in group B had ARI scores of 4 and the other half had scores of 5. Half of the teeth in group C had ARI scores of 5, and 25% of the teeth had scores of 4. Additionally, one sample had an enamel crack from group C.
Table 4. Mean shear bond strength(SBS) and standard deviations
Author Used machine Sample Volume
of tested(N)
Result (MPa) Mean ± standard deviation Acid-etched group(A) Laser-etched group(except A) Serkan Sag ̆ır et al., [1]
Universal testing machine (Shimadzu AG-X, Tokyo, Japan) A: 12 B: 12 C: 12 A: 6.6±2.413 B: 10.1±4.458 C: 11.8±2.7
Güvenç Başaran et al.,[10]
Testing machine (M500-25; Testometric, Rochdale, UK)
A: 10 B: 10 C: 10 D: 10 E: 10 A: 19.42±6.13 B: 14.87±4.38 C: 10.68±2.98 D: 5.73±2.28 E: 5.72±3.65 Çagrı Türköz et al., [11]
Universal testing machine (Instron Co., Canton, MA, USA) A: 15 B: 15 A: 10.55±0.84 B: 9.45±0.92 Fulya Ozdemir et al., [12]
Testing machine (Instron 3345; Instron, Canton, MA, USA) A: 13 B: 13 A: 25.27±5.12 B:7.73±2.45 Sogra Yassaei et al., [13]
Dartec testing machine (Dartec, Zwick Roell Group, UK)
A: 20 B: 20
A: 30.45±1.63 B: 18.32±3.00
Serpil
Cxokakog ̆lu et al., [14]
Instron universal testing machine (Elista, Turkey)
A: 11 B: 11 C: 11 A: 16.74±1.24 B: 16.50±0.97 C: 16.60±1.20 Cahide Aglarci et al., [15]
Universal testing machine (Shimadzu AG-X, Tokyo, Japan) A: 17 B: 17 A: 7.55±2.8 B: 7.49±3.4 R Nalçacı et al., [17]
Instron universal testing machine (Elista, İstanbul, Turkey)
A: 17 B: 17
A: 17.56±1.05 B: 16.38±0.82
Acid etching(group A), laser etching(other group except A) Values are presented as mean ± standard deviation.
MPa= megapascals
Table 5. Adhesive remnant index (ARI) scores among the groups and comparison of groups
C: 10 0 (0) 10 (100) 0 (0) 0 (0) Güvenç Başaran et al.,[10] A: 10 2 (20) 2 (20) 2 (20) 4 (40) B: 10 3 (30) 2 (20) 3 (30) 2 (20) C: 10 4 (40) 3 (30) 2 (20) 1 (10) D: 10 4 (40) 3 (30) 2 (20) 1 (10) E: 10 5 (50) 3 (30) 2 (20) 0 (0) Çagrı Türköz et al., [11] A: 15 2 (13.3) 12 (80) 1 (6.7) 0 (0) B: 15 0 (0) 13 (86.7) 2 (13.3) 0 (0) Fulya Ozdemir et al., [12] A: 13 0 (0) 13 (100) 0 (0) 0 (0) B: 13 13 (100) 0 (0) 0 (0) 0 (0) Cahide Aglarci et al., [15] A: 17 7 (41.2) 10 (58.8) 0 (0) 0 (0) B: 17 1 (5.9) 4 (23.5) 7 (41.2) 5 (29.4)
Acid etching(group A), laser etching(except A)
ARI scores were: 0= no adhesive left on the tooth; 1= less than half of the adhesive left on the tooth; 2= more than half of the adhesive left on the tooth; 3= all adhesive left on the tooth.
Table 6. Modified adhesive remnant index(ARI) scores among the groups and comparison of groups Author Group ARI scores 1 n (%) 2 n (%) 3 n (%) 4 n (%) 5 n (%) G. Ierardo et al., 2014 [3] A: 11 6 (54.5) 5 (45.5) 0 (0) 0 (0) 0 (0) B: 11 4 (36.4) 0 (0) 0 (0) 7 (63.6) 0 (0) C: 11 4 (36.4) 0 (0) 2 (18.2) 0 (0) 5 (45.4) Sogra Yassaei et al., [13] A: 20 0 (0) 1 (5) 13 (65) 5 (25) 1 (5) B: 20 7 (35) 8 (40) 3 (15) 2 (10) 0 (0) Serpil Cxokakog ̆lu A: 12 0 (0) 0 (0) 0 (0) 7 (58.3) 5 (41.7) B: 12 0 (0) 0 (0) 0 (0) 6 (50.0) 6 (50.0)
et al., 2015 [14] C: 12 0 (0) 0 (0) 2 (16.7) 3 (25.0) 6 (50.0) R Nalçacı et al., 2018 [17] A: 16 0 (0) 0 (0) 4 (25) 11 (69) 1 (6) B: 16 0 (0) 0 (0) 4 (25) 10 (62.5) 2 (12.5)
Acid etching(group A), laser etching(except A)
ARI scores were: 1= all the adhesive left on the tooth; 2= more than 90% of the adhesive left on the tooth; 3= between 10-90% of adhesive left on the tooth; 4= less than 10% of the adhesive left on the tooth; 5= no adhesive left on the tooth.
DISCUSSION
For many years, the using of acid-etching systems when bonding brackets to the enamel surface with orthodontic adhesives has been widely accepted by most orthodontists as a routine technique Moreover, enamel changes might have clinical relevance when phosphoric acid-etched[21]. Acid etching was used as control group in all of included studies and described as group A in this review. It is the most popular etching technique for resin tagging on the enamel surface. However, the possibility of enamel decalcification is an important limitation and the main cause of dental caries. Laser technology has been widely used in dental practice since its advent, with studies demonstrating it to be safe for use in bracket bonding procedures in orthodontic practice [1]. This systematic review focused on Er:YAG laser etching as an comparison group with phosphoric acid etching for orthodontic bracket bonding.
Our hypothesis was that Er:YAG laser etching can be proper alternative to conventional acid etching for orthodontic bracket bonding. In the present study, Er:YAG laser etching were compared with conventional acid etching technique with regard to SBS values for bonded bracket, ARI scores, and SEM images. The results demonstrated similarities and differences among the 10 included studies. Clinically acceptable bond strength values in orthodontics range from 6 to 8 MPa[1].
Totally, 330 extracted teeth of ten articles are included in this systematic review. In summary all the articles were comparing efficiency of conventional acid etching and Er:YAG laser etching according to shear bond strength test (SBS), scanning electron microscop (SEM) after etching and/or after debonding to observe enamel surface and adhesive remnant index (ARI).
According to the results from SBS test (Table 4.), in some included articles: Güvenç Başaran et al.[10], Çagrı Türköz et al.[11], Serpil Cxokakog ̆lu et al.[14], Cahide Aglarci et al. [15] and R Nalçacı et al.[16] were similar with no statistical difference between conventional phosphoric acid etching and Er:YAG laser etching groups. Most of articles used ANOVA test for multiple comparison of SBS value[1, 10, 11, 13, 14, 17] but some articles used different test such as Kolonogorov Smirnov test for normality testing in Cahide Aglarci et al. [15] study and Welch test to evaluate the groups in Fulya Ozdemir et al. [12] study.
A article by Çagrı Türköz et al.[11], presented that no significantly differences of the bond strength of the laser-etched group were 9.45 ± 0.92 MPa, which was comparable to that achieved in the
acid-etched group (10.55±0.84 MPa). ARI scores after debonding was also no significantly difference between two groups (Table 5.). Cahide Aglarci et al.[15] also indicated SBS values, 7.55±2.8 MPa in acid etched control group and 7.49±3.4 MPa in Er:YAG laser etched group (Table 4.), thus there were no significant differences but ARI score revealed differences, acid etching group showed a greater distribution of scores 2–3 score, whereas the Er:YAG laser etching groups showed a greater distribution of scores 0–1, which means acid-etched group has higher bond failure rate (Table 5). score The result of study by R Nalçacı et al.[17] are presented no significant differences according to both SBS test and modified ARI index between acid etching group (Table 4., 6.) However, there were difference according to SEM examination of enamel surface after debonding, acid-etched group showed homogen and regular hybrid layer of the resin-enamel interfaces but laser-etched group showed irregular hybrid layer.
In SEM examination of some studies [10, 13, 16] showed different etching pattern on the etched enamel which underwent different etching methods. Etching pattern type is presented in Annex 1. Both of studies [13, 16] revealed that the etching pattern of acid-etched groups are type 1 with honeycomb appearance but laser-etched group in Sogra Yassaei et al.[13] study showed a type 3 of etching pattern and another laser-etched group in Mohammad Sadegh Ahmad Akhoundi et al.[16] study showed completely irregular coarse structure without obvious patterns. In Güvenç Başaran et al.[10] study, the enamel surface etching pattern with acid-etched was a type 3 acid-etched pattern with a regular rough surface and spaces also laser irradiation in group B and C (Er:YAG laser etching with distances of 1 and 2mm) was enough to etch the enamel with a type 3 pattern as acid-etched group. However, In group D and E the laser irradiation was not enough to etch the enamel sufficiently producing a type 4 pattern.
The potential risk of enamel crack or damaging was indicated in some studies. According to Türköz et al.[11], SEM, laser etched group exhibited the ablation of enamel surfaces and enamel robs. The ablasted enamel surface may have fractured during debonding and this may resulted in the separation of the enamel surface from the resin material and the formation of roughness. Not only this study but also Mohammad Sadegh Ahmad Akhoundi et al.[16] presented similar result Er:YAG laser-etched group showed coarse structure without pattern while acid-etched group showed typical
Cxokakog ̆lu et al.[14] study, one tooth from laser etching group C (200 mJ, 10 Hz) had enamel crack after etching.
In addition, some studies indicated under different setting of Er:YAG produced different efficiency result of etching [1, 3, 10, 14]. According to Güvenç Başaran et al.[10], the bond strength in Er:YAG laser-etched group was not significantly different from acid-etched group but bond strength following etching decreased as the distance increased however, in SEM evaluation, found no differences in enamel characteristics following laser etching at different distances. SBS value from the test is described in Table 4. SBS values of acid etched-group were 19.42±6.13 MPa and 1mm distance of Er:YAG irradiation were 14.87±4.38 MPa. However, the SBS values in other distance with 2, 4 and 6mm were 10.68±2.98, 5.73±2.28, 5.72±3.65 MPa. As already mentioned previously, clinically acceptable bond strength values are 6 to 8 MPa in orthodontic practice. In other studies [1], suggest Er:YAG laser etching with MSP and QSP modes presents a successful alternative to acid etching by providing higher or comparable SBS values. The SBS values of acid-etched group were 6.6±2.413 MPa, laser-acid-etched group were 10.1±4.458 MPa in MSP and 11.8±2.7 MPa in QSP. In this study, also no significantly differences between acid-etched and laser-etched at different pulse energy and frequency setting according to modified ARI index; at Er:YAG laser irradiation at 80 mJ and 4 Hz were similar to acid-etched group but Er:YAG laser irradiation at 40 mJ and 10 Hz were increased bonding failure [3].
On the other hand, some studies [12, 13] had opposite result from assessment, in Table 4, indicated a significantly difference between conventional acid etching and Er:YAG laser etching. Er:YAG laser etching groups were significantly lower value then conventional acid etching groups in shear bond strength [12,13]. In this study[3], shows that statistically significantly different in shear bond strength which is 25.27±5.12 MPa in acid-etched group and 7.73±2.45 MPa. And also another study [13] presented that mean shear bond strength of acid-etched group were higher than laser-etched group (Table 4.).
Er:YAG laser etching was gained some acceptable and comparable SBS values and ARI scores with conventional phosphoric acid etching although the results was not remarkable. However, in general SEM evaluation, acid-etched enamel showed regularly with honeycomb appearance but Er:YAG laser-etched showed irregular coarse enamel surface moreover has potential rick for crack on the enamel.
In addition, the results derived from all the samples of ten included studies are inconsistent and a large gap between opposite results each other, our hypothesis could not be confirmed through this systematic review.
There are limitation of this systematic review since all 10 included studies with a limited number of samples were performed heterogeneous setting of clinical environment, such as all samples etched with different percentage of phosphoric acid, the use of different technical devices, used different bond adhesive and composite resin for bonding, not performed same evaluation methods and index also the result were not tested under same comparison and evaluation test . Since all of included studies in this systematic review are in vitro study, so far impossible to duplicate the oral environment in vitro, because of the complexity of the system and changing stress, humidity, and acidity of the medium. In vitro studies are performed to overcome limitations by simplifying and controlling the conditions affecting the system; however, these limitations should be kept in mind while interpreting the results.
CONCLUSION
Our hypothesis could not be confirmed that Er:YAG laser etching on human enamel surfaces can be alternative to conventional acid etching for orthodontic bracket bonding. Er:YAG laser etching was gained some acceptable and comparable SBS values and ARI scores although the results was not remarkable compared to conventional phosphoric acid etching. However, in SEM evaluation, acid-etched enamel showed regularly with honeycomb appearance while Er:YAG laser-acid-etched showed irregular coarse enamel surface which has potential risk for crack on the enamel after etching or debonding.
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