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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 8  |  Issue : 4  |  Page : 238-241

Comparative study of the shear bond strength of composite resin bonded to enamel treated with acid etchant and erbium, chromium: Yttrium, scandium, gallium, garnet laser


1 Department of Preventive Dental Sciences, Division of Periodontics, College of Dentistry, University of Dammam, Dammam, Kingdom of Saudi Arabia
2 Department of Preventive Dental Sciences, Division of Pediatric Dentistry, College of Dentistry, University of Dammam, Dammam, Kingdom of Saudi Arabia

Date of Web Publication27-Dec-2016

Correspondence Address:
Sumit Bedi
Department of Preventive Dental Sciences, Division of Pediatric Dentistry, College of Dentistry, University of Dammam, P. O. Box. 1982, Dammam 31441
Kingdom of Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0976-4003.196807

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  Abstract 

Aim: The purpose of this investigation is in vitro comparison of the shear bond strength (SBS) of composite resin bonded to enamel pretreated with an acid etchant against enamel etched with erbium, chromium: yttrium, scandium, gallium, garnet (Er, Cr:YSGG) laser. Materials and Methods: Sixty premolars were sectioned mesiodistally and these 120 specimens were separated into two groups of 60 each (Groups A and B). In Group A (buccal surfaces), enamel surface was etched using 37% phosphoric acid for 15 s. In Group B (lingual surfaces), enamel was laser-etched at 2W for 10 s by Er, Cr:YSGG laser operational at 2780 nm with pulse duration of 140 μs and a frequency of 20 Hz. After application of bonding agent on all test samples, a transparent plastic cylinder of 1.5 mm × 3 mm was loaded with composite and bonded by light curing for 20 s. All the samples were subjected to SBS analysis using Instron Universal testing machine. Failure modes were observed under light microscope and grouped as adhesive, cohesive, and mixed. Failure mode distributions were compared using the Chi-square test. Results: SBS values obtained for acid-etched enamel were in the range of 7.12–28.36 megapascals (MPa) and for laser-etched enamel were in the range of 6.23–23.35 MPa. Mean SBS for acid-etched enamel was 15.77 ± 4.38 MPa, which was considerably greater (P < 0.01) than laser-etched enamel 11.24 ± 3.76 MPa. The Chi-square test revealed that the groups showed no statistically significant differences in bond failure modes. Conclusions: We concluded that the mean SBS of composite with acid etching is significantly higher as compared to Er, Cr: YSGG (operated at 2W for 10 s) laser-etched enamel.

Keywords: Acid etching, enamel bonding, erbium; chromium:yttrium; scandium; gallium; garnet, laser etching, shear bond strength


How to cite this article:
Alagl AS, Bedi S, Hassan KS. Comparative study of the shear bond strength of composite resin bonded to enamel treated with acid etchant and erbium, chromium: Yttrium, scandium, gallium, garnet laser. Indian J Dent Sci 2016;8:238-41

How to cite this URL:
Alagl AS, Bedi S, Hassan KS. Comparative study of the shear bond strength of composite resin bonded to enamel treated with acid etchant and erbium, chromium: Yttrium, scandium, gallium, garnet laser. Indian J Dent Sci [serial online] 2016 [cited 2019 Aug 23];8:238-41. Available from: http://www.ijds.in/text.asp?2016/8/4/238/196807


  Introduction Top


Adhesion in restorative dentistry is founded on two concepts, first is chemical adhesion, unfolding intermolecular forces at the border and the second concept is centered on micromechanical retention; ascribing adhesion to the penetrability of each of the components.[1] The low surface energy of smear layer, which remains postcavity preparation; hinders the penetration of the tissue with the bonding agent preventing sufficient adhesion and the key of choice to this is acid etching.[2]

Enamel acid etching seems to increase the retention by selective wear down of hydroxyapatite crystals and enabling the penetration of bonding agent resulting in resin tags formation of about 6–12 mm in length.[3] The most extensively used protocol for enamel acid etching is 37% phosphoric acid for 15 s.[4]

The ensuing surface texture although useful for retention of bonding agent, this structure also makes it prone to caries initiation. Acid etching eradicates and demineralizes the outermost shielding enamel layer and makes it vulnerable to long-term acid attack.[5]

Developments in arena of lasers enable its use in numerous soft tissue and hard tissue operations, with insignificant pain and anxiety.[5],[6],[7] Laser etching is a viable alternative to acid etching of enamel as the procedure is painless with no vibration or heat.[7],[8] It also results in a circuitous surface and exposed dentin tubules, which play a vital role in bonding.[8],[9] Different lasers are used in restorative dentistry such as CO2 laser and neodymium-doped yttrium aluminium garnet (Nd:YAG) laser; however, Nd:YAG laser is not well-absorbed by dental hard tissue and CO2 laser though well-absorbed by dental tissue is not suitable because it can cause an upsurge in the temperature of the vital dental pulp.[7],[9],[10] Thus, to avoid these disadvantages, erbium (Er) lasers with two different wavelengths were introduced. Er-doped yttrium aluminum garnet laser (Er:YAG wavelength 2940 nm) and Er, chromium:yttrium, scandium, gallium, garnet (Er, Cr:YSGG wavelength 2780 nm) are presently the most effective in cutting the hard dental tissue and preparing the cavity.[11] There is no or little (2°C) temperature increase in the dental pulp when used along with a water-air spray.[7] Enamel etched with Er, Cr:YSGG laser produces chalky surface. Scanning electron microscope (SEM) evaluation shows that laser irradiation results in a surface with high retention for restorative material, making it suitable for composite filling.[7],[9],[11],[12] Er:YAG laser radiation evaporates the water content of hard instantly, which results in irregular surface. These irregularities work as a mechanical retention increasing adhesion of restoration to tooth hard tissue, which can be a replacement for acid etching technique, not only in microscopic dimensions but also in macroscopic and clinical presence.[9],[13],[14]


  Materials and Methods Top


Sixty sound, noncarious recently extracted human premolars were collected and sectioned mesiodistally to get 120 surfaces. Fractured teeth were rejected. All samples were kept in a phosphate-buffered 5% solution of formalin at 4°C to diminish growth of bacteria.

All the specimens were fixed in a resin block leaving the coronal portion exposed. 120 surfaces were assessed for composite bonding to enamel, after acid etching (Group A: n = 60) and after laser etching (Group B: n = 60).

Group A - Acid etch, the sixty buccal surfaces were thoroughly cleaned for 30 s and air dried for 20 s. Later, the samples were etched with a 37% phosphoric acid for 15 s followed by 15 s of washing with distilled water and air dried for 10 s.

Group B - Laser etch, the sixty lingual surfaces were thoroughly cleaned for 30 s and air dried for 20 s. Later, the samples were etched with an Er, Cr:YSGG laser (Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA) [Figure 1] functioning with a wavelength of 2780 nm, pulse of 140 µs, and a repetition rate of 20 Hz along with an air-water spray (80% and 60%, respectively, as recommended by manufacturer) to prevent the enamel surfaces from overheating. Laser energy was delivered using sapphire tip recommended by manufacturer for etching MC6 (600 µm in diameter and 6 mm in length) with power output set at 2W and enamel surfaces were lased for 10 s in a sweeping motion with energy density of 80 J/cm [2],[15],[16],[17],[18] achieving approximately 3 mm × 3 mm laser-etched enamel surface area [Figure 2].
Figure 1: Erbium, chromium:yttrium, scandium, gallium, garnet laser (Waterlase iPlus, Biolase Technology, Inc., CA, USA).

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Figure 2: Enamel surface of specimen etched with erbium, chromium:yttrium, scandium, gallium, garnet laser.

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After etching, all the samples were glazed with adhesive agent (Scotchbond Multipurpose, 3M) for 15 s followed by air-drying of surface for 5 s, and light curing for 10 s. A transparent plastic cylinder of 1.5 mm × 3 mm was loaded with composite (Filtek Z350 XT, 3M ESPE, USA) and bonded by light curing for 20 s.

Shear bond strength testing

Specimens were stored in distilled water at 37°C for 48 h to prevent desiccation and cracking. Later, all the samples were subjected for shear bond strength (SBS) testing using Universal Instron testing machine [Figure 3], loaded to failure at a cross-head speed of 1 mm/min. After recording maximum load for all samples, SBS was expressed in megapascals (MPa). Failure modes were evaluated by a single operator under an optical microscope (Nikon type 102, Tokyo, Japan) at ×40 magnification, and classified as cohesive within the substrate (enamel or composite resin), adhesive (between adhesive and enamel), or mixed (if adhesive and cohesive fractures occurred simultaneously).
Figure 3: Enamel shear bond strength testing with Instron Universal testing machine.

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Statistical analysis

For SBS analysis, data were expressed as means ± standard deviation. To investigate whether SBS was significantly affected by treatment option, a Student's t-test with the Bonferroni correction was used. The level of significance was set at P < 0.01.


  Results Top


Mean SBS for acid-etched enamel was 15.77 ± 4.38 MPa, which was considerably greater (P < 0.01) than for laser-etched enamel 11.24 ± 3.76 MPa [Table 1]. The Chi-square test revealed that the groups showed no statistically significant differences in bond failure modes [Table 2].
Table 1: Mean shear bond strength for acid-etched enamel and for laser-etched enamel

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Table 2: Failure mode distribution in the groups (%)

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Shear bond strength analysis

By applying Student's unpaired t-test, it was found that there is a highly significant statistical difference between mean values of SBS in acid-etch enamel and laser etch enamel group (i.e., P < 0.01).


  Discussion Top


Acid etching restructures the surface by removing the smear layer and selective removal of inter-prismatic mineral structure, thereby enhancing the surface energy and roughness while organic materials are less affected. Mostly, 10%–37% phosphoric acid is applied to etch enamel.[19] In our study, 37% phosphoric acid gel was used and found that acid etching commanded the increase in SBS to enamel.

The potential disadvantage of acid etching is that it causes chemical alteration that can change the organic matter and decalcify the organic component, making the enamel more susceptible to caries.[5] Therefore, laser etching of enamel surfaces was looked upon as a viable alternative.

The advantage of Er, Cr:YSGG is its good absorption by water and enamel because of which heat is dissipated and as water reaches the boiling point, it results in a micro-explosion in tooth surface.[7],[14],[15] Hence, this laser is used for etching of enamel surfaces for the purpose of bonding the composite resin to enamel surface. Thus, the aim of our study was to assess the SBS of composite to enamel surface with conventional acid etching versus laser etching.

Previous studies present conflicting conclusions concerning enamel surface and cavity preparations by Er, Cr:YSGG. For enamel, use of radiation outputs ranging from 2.5W to 6W has been recommended by previous researchers. Recently, Berk et al.[15] detected by SEM analysis that varying outputs of 1W, 1.5W, and 2W Er, Cr:YSGG, formed comparable etching patterns to those with acid etching. Moezizadeh et al.[20] in their study found that surface treatment of Signum Plus indirect composite with Er, Cr:YSGG laser showed greater bond strength with 1W irradiation than 2W irradiation output. In our study, we used 2W output to etch the enamel as used and recommended by earlier studies.

The time for laser etching used in our investigation was 10 s and for acid etching 15 s as per recommendations by previous reports in literature. Baygin et al.[21] found that 10 s of 2W laser etching could be a possible alternative to enamel acid etching. The results of our study indicate that SBS values of composite bonded to enamel etched with Er, Cr:YSGG laser (operated at 2W for 10 s) were much lower when compared to acid-etched enamel. The explanation for such observation can be an insufficient laser etching time as reported in a previous study. Obeidi et al.[16] found that increasing the laser etching time to 40 s may increase the bond strength to the level of conventional acid etching.

In our study, it was found that mean SBS values of composite with acid etching are significantly higher as compared to Er, Cr:YSGG (operated at 2W for 10 s) laser-etched enamel. These results corroborate with the previous study by Hoshing et al.[17] The mean SBS for laser etch group (11.24 ± 3.76 MPa) is significantly lower than that for acid etch group (15.77 ± 4.38 MPa). Such variation could be because of hidden weaknesses at the surface or at resin-tissue interface, any variance in surface curving or because of air bubbles trapping within the resin/resin-tissue interface. Furthermore, in the laser-etched enamel, “micro-explosions” result in an increased frequency of cohesive tooth fractures which may further weaken the enamel and make the surface more heterogeneous as compared to that by acid etching. Still, results of our study suggest that advantages of laser etching may be compromised by microfissuring caused by it, leading to decrease in bond strength. More extensive studies including larger samples should further evaluate the bond strength and surface topography by means of SEM in future.


  Conclusions Top


We concluded that the mean SBS values of composite with acid etching are significantly higher as compared to Er, Cr:YSGG (operated at 2W for 10 s) laser-etched enamel.

Financial support and sponsorship

Research reported in this publication was funded by the University of Dammam, Grant Number 2015091.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Preethee T, Kandaswamy D, Arathi G, Hannah R. Bactericidal effect of the 908 nm diode laser on Enterococcus faecalis in infected root canals. J Conserv Dent 2012;15:46-50.  Back to cited text no. 8
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Visuri SR, Gilbert JL, Wright DD, Wigdor HA, Walsh JT Jr. Shear strength of composite bonded to Er:YAG laser-prepared dentin. J Dent Res 1996;75:599-605.  Back to cited text no. 9
    
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Secilmis A, Altintas S, Usumez A, Berk G. Evaluation of mineral content of dentin prepared by erbium, chromium:yttrium scandium gallium garnet laser. Lasers Med Sci 2008;23:421-5.  Back to cited text no. 11
    
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Yamazaki R, Goya C, Yu DG, Kimura Y, Matsumoto K. Effects of erbium, chromium:YSGG laser irradiation on root canal walls: A scanning electron microscopic and thermographic study. J Endod 2001;27:9-12.  Back to cited text no. 12
    
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Santos CR. Application of Er:YAG and Er, Cr:YSGG lasers in cavity preparation for dental tissue: A literature review. World J Dent 2012;3:340-3.  Back to cited text no. 14
    
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Berk N, Basaran G, Ozer T. Comparison of sandblasting, laser irradiation, and conventional acid etching for orthodontic bonding of molar tubes. Eur J Orthod 2008;30:183-9.  Back to cited text no. 15
    
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Obeidi A, McCracken MS, Liu PR, Litaker MS, Beck P, Rahemtulla F. Enhancement of bonding to enamel and dentin prepared by Er, Cr:YSGG laser. Lasers Surg Med 2009;41:454-62.  Back to cited text no. 16
    
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Baygin O, Korkmaz FM, Tüzüner T, Tanriver M. The effect of different enamel surface treatments on the microleakage of fissure sealants. Lasers Med Sci 2012;27:153-60.  Back to cited text no. 18
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

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