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ORIGINAL ARTICLES
Comparison of shear bond strength of reattached incisor fragment using Er,Cr:YSGG laser etching and conventional acid etching: An in vitro study Ferah Rehman, Gyanendra Kumar, Mridula Goswami, Jatinder Kaur Dhillon
Department of Pedodontics and Preventive Dentistry, Maulana Azad Institute of Dental Sciences, New Delhi
Aim: The aim of this invitro study is to evaluate the shear bond strength of reattached fractured incisor fragments using Er,Cr:YSGG laser and conventional acid etching without additional tooth preparation. Materials and methods: Forty extracted human teeth were divided in two groups of 20 each (Groups A and B). In Group A, fractured surface was treated by an Er, Cr: YSGG laser system (Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA) operating at a wavelength of 2,780 nm and frequency of 20 Hz. In Group B, fractured surface was etched using 37% phosphoric acid (Scotchbond, 3M). In both the groups, further subdivision with 10 sample each was made based on horizontal and oblique fracture. After laser or acid etching, all the samples were reattached using flowable composite resin and light cured. The samples were tested for shear bond strength. Results: Mean shear bond strength for Group A (94.70±39.158) was lower as compared to Group B (121.25±49.937), although the difference was not statistically significant(p value=0.121). Similarly no statistical significant difference was observed amongst the subgroups. (p>0.05) Conclusion: Er,Cr:YSGG laser etching in reattachment of fractured incisor fragment is a good alternative to conventional acid etching. Er,Cr:YSGG showed comparable efficiency in rebonding of fractured teeth fragment as acid etching.
Introduction The majority of dental injuries involve the anterior teeth, especially the maxillary central incisors, because of its position in the arch. 1, 2) The fractured teeth are generally restored using composite resin or complex ceramic restorations. With advancements in acid etching and adhesive resins, the reattachment of tooth fragment has become a commonly used procedure for fractured teeth. This treatment may offer several advantages over conventional composite restoration such as improved esthetics as original shape, color, brightness and surface texture of enamel are maintained. In addition, the incisal edge will wear at a similar rate to adjacent teeth. 3, 4) Furthermore, this technique can be less Addressee for Correspondence: Ferah Rehman, Research Associate, Department of Pedodontics and Preventive Dentistry, Maulana Azad Institute of Dental Sciences, New Delhi. Email id: [email protected] Mobile no: 08826246696 ©2016 JMLL, Tokyo, Japan
time consuming which reduces the cost of the treatment. Many techniques have been proposed for reattaching the fragment to the remaining tooth viz. using a circumferential bevel before reattaching, 5, 6) placing a chamfer at the fracture line after bonding, 7, 8) using a V-shaped enamel notch, 9) placing an internal groove or a superficial over contour over the fracture line. Some authors have also indicated bonding with no additional preparation, however still no consensus has been reached as to which method has an edge over the other method. 10, 11) Development of laser technology has enabled its use in multiple dental procedures, such as soft tissue operations, composite restorations, tooth bleaching, caries removal, and tooth preparations with minimal pain and discomfort as it does not involve either vibration or heat of airotor handpiece. 12) Laser etching has become an alternative to acid etching of enamel and Received date: December 15th, 2015 Accepted date: April 8th, 2016
Laser Therapy 25.2: 115-120
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dentin as it has been reported to yield an anfractuous surface and open dentin tubules, both suitable for adhesion. 13) Er, Cr:YSGG laser of wavelength 2780 nm is effective in cutting the tissue and preparing the cavity. 14) There is no or little (2°C) temperature rise in the dental pulp when the laser is used along with a waterair spray. 15) Enamel preparation using the Er, Cr:YSGG laser produces chalky surface. Scanning electron microscope (SEM) evaluation shows that the laser irradiation produces the surface with high retention for restorative material, making it suitable for composite restoration. 16) A study by C. Fornaini et al. (2012) analysed the effects of Er:YAG laser on enamel and dentin in case of reattachment of fractured fragment and concluded that Er:YAG alone or in combination with phosphoric acid gives better results than acid alone. 17) Re-bonding of a broken tooth fragment, following trauma, with an Er,Cr:YSGG laser was found to be very successful, maintaining stability and vitality of the affected tooth. 18) Various studies have been reported on the use of Er,Cr:YSGG laser in bonding of orthodontic brackets with success, however to the best of our knowledge no study has been reported on Er,Cr:YSGG laser assisted incisor fragment reattachment except one case report. 18) The purpose of this study is to compare the shear bond strength (SBS) of reattached incisor fragment using laser etching and conventional acid etching.
Materials and methods The study sample comprised 40 intact human maxillary central incisor teeth freshly extracted for periodontal
reasons. The teeth that were within 1mm difference of their mesio-distal widths, with incisal edges intact, free from cracks, caries or any other kind of structural defect were included in the study. The teeth were rinsed under tap water in order to remove blood and tissue debris and disinfected using 5% sodium hypochlorite for half an hour and then stored in 0.1% thymol at room temperature until use. 7) All specimens were mounted in standardized self-cure acrylic resin mould. After mounting, the teeth were randomly divided into two groups by simple random technique of flipping a coin, Group A and Group B (Figure 1), each comprising 20 teeth. Each group was further subdivided into two subgroups viz. A1, A2 and B1, B2 depending upon the fracture line as shown in flowchart below. The incisal third was sectioned with a water-cooled low-speed diamond disc according to the subgroup allocated. In Group A, laser etching was done with an Er, Cr:YSGG laser system (Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA) operating at a wavelength of 2780 nm and frequency of 20 Hz. Laser energy was delivered through a fiberoptic system to a sapphire tip terminal that was 600 µm in diameter and 6 mm in length. The power output was set at 1.5 W for 10 s of exposure time. Air and water spray from the handpiece was adjusted to a level of 60% air and 40% water. In Group B, samples were etched with a 37% phosphoric acid gel (3M Scotchbond etchant, 3M Dental Products, St. Paul, MN, USA) for 15 s followed by 15 s of washing with distilled water and air dried
Sample N=40
Group A Laser etching
Group B Acid etching
(N=20)
(N=20)
Subgroup A1 Horizontal fracture
Subgroup A2 Oblique fracture
Subgroup B1 Horizontal fracture
Subgroup B2 Oblique fracture
(N=10)
(N=10)
(N=10)
(N=10)
Figure 1: Distribution of sample
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for 10 s. After laser or acid etching, the samples were dried with oil-free air for 20 s; the light-cured bonding resin (Scotchbond Multipurpose, 3M Dental Products, St. Paul, MN, USA) was then applied immediately with a brush, and cured as per manufacturer’s instructions. The fragments were then reattached using flowable resin composite (Tetric flow, Ivoclar Vivadent, Schaan, Liechtenstein) and polymerized. The reattached teeth were finished and polished using Sof-Lex polishing discs (3M ESPE). All the specimens were transferred to the Instron universal machine individually and subjected to Shear Bond Strength (SBS) analysis at constant crosshead speed of 1.0 mm/min. Shear bond strength was recorded in Newtons.
Statistical analysis For SBS analysis, data were expressed as means ± standard deviation. All data was processed by SPSS software version 19.0 (SPSS Inc., Chicago, IL, USA). To investigate whether SBS was significantly affected by
Table 1: Comparison of mean Shear bond strength between Group A and Group B Groups
SBS (mean±SD)
Group A
94.70±39.158
Group B
121.25±49.937
p-value 0.121
Figure 2: Comparison of mean Shear bond strength between Group A and Group B
Shear bond strength with Er, Cr: YSGG laser
ORIGINAL ARTICLES treatment options, Mann Whitney U test was used for both inter-group and intra-group comparison. Differences were considered significant for a value of p< 0.01.
Results Results were evaluated by a blinded evaluator not involved in the experiment. Mean shear bond strength (SBS) for Group B was higher as compared to Group A, however the difference was not statistically significant as revealed by Mann Whitney U test (p=0.121). The values are depicted in Table 1 and Figure 2. Mean shear bond strength (SBS) values in subgroups of A and B are shown in Table 2 and Figure 3. No statistically significant difference was observed between the subgroups.
Discussion Maxillary central incisors were included for the present study as these are more frequently involved in traumat-
Table 2: Comparison of mean Shear bond strength among different subgroups of Group A and Group B Sub- Groups
SBS (mean±SD)
Sub- Group A1
91.70±36.157
Sub- Group A2
97.70±43.701
Sub- Group B1
128.20±34.438
Sub- Group B2
114.30±63.017
p-value 0.631
0.393
Figure 3: Comparison of mean Shear bond strength among different subgroups of Group A and Group B
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ORIGINAL ARTICLES ic dental injuries. 2) According to a recent survey, overall prevalence of traumatic dental injuries was found to be 10.4%, and maxillary central incisors were the most commonly affected teeth (85.2%). The results of this survey also showed almost equal frequency of horizontal and oblique dentinal fractures. 19) The fractured teeth are generally restored using composite resin or complex ceramic restorations. With advancements in acid etching and adhesive resins, the reattachment of tooth fragment became a commonly used procedure for fractured teeth. During rebonding of fractured segment, acid etching results in chemical changes that can modify the organic matter and decalcify the organic component. As a result of this demineralization, enamel becomes more susceptible to caries attack and sensitivity. 20) In order to avoid this demineralization, the present study aimed at utilizing laser for etching the fractured surfaces and the results were comparable to acid etch in terms of resistance to debond the fragments. Er; Cr:YSGG laser was utilized in the present study as it is well-absorbed by water and dental hard tissue. As water absorbs laser radiation better than dental hard tissue, it reduces the increasing temperature of the tissue during the preparation. In addition it provide a smear-free surface, good adhesion, lack of vibration and lack of need for local analgesia in most cases. 21) It had been reported that the use of a bur preparation, with an insufficient cooling, may lead to a temperature rise of over 15°C when the critical temperature rise lies at about or above 5.5°C, at which a high percentage of the pulp cells are killed. But for Er; Cr:YSGG laser preparations, with the suggested cooling settings, a decrease in the temperature of the pulp has been recorded. 21) Laser prepared enamel has a chalk-like appearance that is similar to the acid etched characteristic of enamel and enamel rods. 22) The parameters of laser used in the present study are as per the literature findings for etching procedure. 23, 24) The mean shear bond strength of bonded brackets and enamel surface etching pattern obtained with an Er,Cr:YSGG laser (operated at 1W or 2W for 15 seconds) is comparable to that obtained with acid etching. 23) Similarly, Berk (2008) 24) observed by means of a SEM analysis that 1 W, 1.5 W, and 2 W Er, Cr:YSGG laser irradiation produced etching patterns similar to those of acid etching. The etching effect of Er, Cr:YSGG laser has been studied for various purposes in dentistry like pit and fissure sealant application, orthodontic brackets placement and others, however only a single case is reported for its use in bonding an incisal fragment with success over a period of four years follow up. 18) Various stud-
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ies have evaluated the effect of different materials and type of tooth preparation on shear bond strength of reattached tooth fragment. 1, 6, 7) Although, in clinical practice we do come across both horizontal and oblique teeth fracture with equal frequency but to the best of our knowledge, no study reported regarding the type of fracture and its effect on bond strength. So, in the present study, the effect of type of fracture on shear bond strength was also evaluated. Bond strength values are gross assessing tools for evaluating the efficacy of bonding restorative materials to dentin. Of the various tests, the shear bond strength is less technique sensitive to perform, highlighting the strength at the bonded interface. 25) The cross-head speed used to fracture the specimens in this study was 1mm/min as recommended by ISO standard (ISO/ TS 11405:2003Dental Materials-Testing of adhesion to tooth structure). The results of the present study showed that the shear bond strength of acid etched bonded surfaces was more as compared to laser etched surfaces, however, the difference was not statistically significant. (Table 1, Figure 2) The use of lasers for enamel etching shows contradictory reports. Some researchers stated that laser irradiation was not capable of etching enamel. Martinez-Insua (2000) found weaker adhesion forces in an Er:YAG laser-etched enamel surface than an acid etched enamel surface. 20) This was related to sub-surface cracks observed in (SEM) images. Tarcin et al. (2009) found that the microtensile bond strength was significantly lower in the acid-etched group than the Er, Cr:YSGG and Nd:YAG laser-etched enamel group for two types of bonding agents used. 26) In contrast, some studies reported that laser applications give similar results to acid-etching techniques. Basaran et al. (2007) compared the SBS of brackets using an Er, Cr:YSGG laser in 0.5 W, 0.75 W, 1 W, 1.5 W, 1.75 W, and 2 W. They stated that 1.5 W, 1.75 W and 2 W etching yielded similar success rates as 38% phosphoric acid etching. 23) Ozer et al.(2008) investigated the SBS of brackets that they applied on enamel prepared with 0.75 W Er, Cr:YSGG, 1.5 W Er, Cr:YSGG, 37% orthophosphoric acid or self-etching primer. They found that the 0.75 W laser-applied groups was significantly less in regard to SBS than all other groups, although there was no statistically significant difference among the other groups. 27) Baygin et al. (2011) found no statistical difference between SBS values between 2 W, 20 Hz laser and 40 Hz laser. 28) Acid etching typically produced a repeating surface pattern, with cracks and fissures no deeper than 12 mm that are readily filled with resin. 12) In contrast
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to acid etch treatment, laser etching produced extensive surface fissuring and less regular and less homogeneous surface patterns arising from the union of different craters and microexplosion. Fissuring may be related to the orientation of enamel rods, because enamel is an anisotropic material. One of the potential disadvantages of enamel acid etching is that the acid causes demineralization of the most superficial layer. As a result, this surface becomes more susceptible to longterm acid attack and caries, especially when resin impregnation is defective because of air bubbles or saliva contamination. In view of potential advantages and similar bond strength, lasers can serve as an alternative to acid etching for bonding the fractured incisor fragments. Our results showed no statistically significant difference between horizontal and oblique fracture as far as the technique of bonding is similar in both types.
ORIGINAL ARTICLES (Table 2, Figure 3) This can be explained by the improved adhesive systems and composite resins in the last decades. Andreason et al. (1995) reported their results on reattachment after acid etching alone and after acid etching together with dentin bonding agent. The rate of survival of restored teeth that had been etched with acid only was 50% at 1year, whereas that of teeth restored with acid etching and a dentin bonding agent was 50% at 3 years. 8)
Conclusion Within the limits of an in vitro study, the use of Er,Cr:YSGG laser in reattachment of fractured incisor fragment is acceptable. However, larger sample size and in vivo studies are required to further enhance this finding.
References 1: Macedo GV, Diaz PI, De O Fernandes CA, Ritter AV. Reattachment of anterior teeth fragments: A conservative approach. J Esthet Restor Dent 2008;20:5-18 2: Andreasen JO, Andreasen FM. Textbook and color atlas of traumatic injuries to the teeth. 3rd ed. St. Louis: Mosby- Year Book, Inc; 1994. p. 216-56 3: Leinfelder KF. Composite resin systems of posterior restorations. Pract Periodontics Aesthet Dent 1993;5(3 Suppl 1):23-7 4: Lutz FU, Krejci I,Oddera M. Advanced adhesive restorations: The post-amalgam age. Pract Periodontics Aesthet Dent 1996;8:385-94 5: Simonsen RJ. Traumatic fracture restoration: An alternative use of the acid etch technique. Quintessence Int Dent Dig 1979;10:15-22 6: Amir E, Bar-Gil B, Sarnat H. Restoration of fractured immature maxillary central incisors using the crown fragments. Pediatr Dent 1996;8:285-8 7: Davis MJ, Roth J, Levi M. Marginal integrity of adhesive fracture restorations: Chamfer versus bevel. Quintessence Int Dent Dig 1983;14:1135-46 8: Andreasen FM, Norèn JG, Andreasen JO, Engelhartsen S, Lindh-Strömberg U. Long-term survival of fragment bonding in the treatment of fractured crowns: A multicenter clinical study. Quintessence Int 1995;26:669-81. 9: Diangelis AJ, Jungbluth M. Reattaching fractured tooth segments: An esthetic alternative. J Am Dent Assoc 1992;123:58-63
Shear bond strength with Er, Cr: YSGG laser
10: Martens LC, Beyls HM, deCraene LG, D’Hauwers RF. Reattachment of the original fragment after vertical crown fracture of a permanent central incisor. J Pedod 1988;13:53-62 11: Reis A, Francci C, Loguercio AD, Carrilho MR, Rodrigues Filho LE. Re-attachment of anterior fractured teeth: Fracture strength using different techniques. Oper Dent 2001;26:287-94 12: Turkmen C, Sazak-Ovecoglu H, Gunday M, Gungor G, Durkan M, Oksuz M. Shear bond strength of composite bonded with three adhesives to Er,Cr:YSGG laser-prepared enamel. Quintessence Int. 2010;41:e119-24 13: 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 14: 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 15: 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 16: Hibst R. Laser for caries removal and cavity preparation: State of art and future direction. J Oral Laser Appl. 2002;2:203-12 17: C. Fornaini, S. Petruzzella, R. Podda, E. Merigo, S.
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ORIGINAL ARTICLES Nammour, and P. Vescovi. Er:YAG Laser and Fractured Incisor Restorations: An In Vitro Study. Int J Dent. 2012;2012:617264 18: N. Berk, G. Berk, S. Ulucam. Case Report: laserassisted rebonding of a central incisor tooth due to a severe trauma - 4 years of follow-up. European archives of Paediatric Dentistry 12 (Issue 2). 2011 19: Bilder L et al. Traumatic dental injuries among 12and 15-year-old adolescents in Georgia: results of the pathfinder study. Dent Traumatol. 2015 Oct 20. [Epub ahead of print] 20: Martinez-Insua A, Da Silva Dominguez L, Rivera FG, Santana-Penín UA. Differences in bonding to acid-etched or Er:YAG-laser-treated enamel and dentin surfaces. J Prosthet Dent. 2000;84:280-8 21: Moritz A. Oral Laser Application. Berlin: Quintessenz Verlag, 2005 22: Trajtenberg CP, Pereira PN, Powers JM. Resin bond strength and micromorphology of human teeth prepared with an Erbium:YAG laser. Amer J Dent. 2004 Oct;17(5):331-6 23: Basaran G, Ozer T, Berk N, Hamamci O. Etching
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enamel for orthodontics with an erbium, chromium:yttrium-scandium-gallium-garnet laser system. Angle Orthod. 2007;77(1):117-23 24: 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 25: Nujella BPS, Choudary MT, Reddy SP, Kumar MK, Gopal T. Comparison of shear bond strength of aesthetic restorative materials. Contemporary Clinical Dentistry. 2012;3(1):22-26 26: Tarcin B et al. Tensile bond strength of dentin adhesives on acid- and laser-etched dentin surfaces. Quintessence Int. 2009;40:865-74 27: Ozer T, Basaran G, Berk N. Laser etching of enamel for orthodontic bonding. Am J Orthod Dentofacial Orthop. 2008;134:193-7 28: Baygin O, Korkmaz FM, Tuzuner T, Tanriver M. The effect of different techniques of enamel etching on shear bond strengths of fissure sealents. Dentistry. 2011;1:109
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ORIGINAL ARTICLES
Comparison of shear bond strength of reattached incisor fragment using Er,Cr:YSGG laser etching and conventional acid etching: An in vitro study Ferah Rehman, Gyanendra Kumar, Mridula Goswami, Jatinder Kaur Dhillon
Department of Pedodontics and Preventive Dentistry, Maulana Azad Institute of Dental Sciences, New Delhi
Aim: The aim of this invitro study is to evaluate the shear bond strength of reattached fractured incisor fragments using Er,Cr:YSGG laser and conventional acid etching without additional tooth preparation. Materials and methods: Forty extracted human teeth were divided in two groups of 20 each (Groups A and B). In Group A, fractured surface was treated by an Er, Cr: YSGG laser system (Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA) operating at a wavelength of 2,780 nm and frequency of 20 Hz. In Group B, fractured surface was etched using 37% phosphoric acid (Scotchbond, 3M). In both the groups, further subdivision with 10 sample each was made based on horizontal and oblique fracture. After laser or acid etching, all the samples were reattached using flowable composite resin and light cured. The samples were tested for shear bond strength. Results: Mean shear bond strength for Group A (94.70±39.158) was lower as compared to Group B (121.25±49.937), although the difference was not statistically significant(p value=0.121). Similarly no statistical significant difference was observed amongst the subgroups. (p>0.05) Conclusion: Er,Cr:YSGG laser etching in reattachment of fractured incisor fragment is a good alternative to conventional acid etching. Er,Cr:YSGG showed comparable efficiency in rebonding of fractured teeth fragment as acid etching.
Introduction The majority of dental injuries involve the anterior teeth, especially the maxillary central incisors, because of its position in the arch. 1, 2) The fractured teeth are generally restored using composite resin or complex ceramic restorations. With advancements in acid etching and adhesive resins, the reattachment of tooth fragment has become a commonly used procedure for fractured teeth. This treatment may offer several advantages over conventional composite restoration such as improved esthetics as original shape, color, brightness and surface texture of enamel are maintained. In addition, the incisal edge will wear at a similar rate to adjacent teeth. 3, 4) Furthermore, this technique can be less Addressee for Correspondence: Ferah Rehman, Research Associate, Department of Pedodontics and Preventive Dentistry, Maulana Azad Institute of Dental Sciences, New Delhi. Email id: [email protected] Mobile no: 08826246696 ©2016 JMLL, Tokyo, Japan
time consuming which reduces the cost of the treatment. Many techniques have been proposed for reattaching the fragment to the remaining tooth viz. using a circumferential bevel before reattaching, 5, 6) placing a chamfer at the fracture line after bonding, 7, 8) using a V-shaped enamel notch, 9) placing an internal groove or a superficial over contour over the fracture line. Some authors have also indicated bonding with no additional preparation, however still no consensus has been reached as to which method has an edge over the other method. 10, 11) Development of laser technology has enabled its use in multiple dental procedures, such as soft tissue operations, composite restorations, tooth bleaching, caries removal, and tooth preparations with minimal pain and discomfort as it does not involve either vibration or heat of airotor handpiece. 12) Laser etching has become an alternative to acid etching of enamel and Received date: December 15th, 2015 Accepted date: April 8th, 2016
Laser Therapy 25.2: 115-120
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dentin as it has been reported to yield an anfractuous surface and open dentin tubules, both suitable for adhesion. 13) Er, Cr:YSGG laser of wavelength 2780 nm is effective in cutting the tissue and preparing the cavity. 14) There is no or little (2°C) temperature rise in the dental pulp when the laser is used along with a waterair spray. 15) Enamel preparation using the Er, Cr:YSGG laser produces chalky surface. Scanning electron microscope (SEM) evaluation shows that the laser irradiation produces the surface with high retention for restorative material, making it suitable for composite restoration. 16) A study by C. Fornaini et al. (2012) analysed the effects of Er:YAG laser on enamel and dentin in case of reattachment of fractured fragment and concluded that Er:YAG alone or in combination with phosphoric acid gives better results than acid alone. 17) Re-bonding of a broken tooth fragment, following trauma, with an Er,Cr:YSGG laser was found to be very successful, maintaining stability and vitality of the affected tooth. 18) Various studies have been reported on the use of Er,Cr:YSGG laser in bonding of orthodontic brackets with success, however to the best of our knowledge no study has been reported on Er,Cr:YSGG laser assisted incisor fragment reattachment except one case report. 18) The purpose of this study is to compare the shear bond strength (SBS) of reattached incisor fragment using laser etching and conventional acid etching.
Materials and methods The study sample comprised 40 intact human maxillary central incisor teeth freshly extracted for periodontal
reasons. The teeth that were within 1mm difference of their mesio-distal widths, with incisal edges intact, free from cracks, caries or any other kind of structural defect were included in the study. The teeth were rinsed under tap water in order to remove blood and tissue debris and disinfected using 5% sodium hypochlorite for half an hour and then stored in 0.1% thymol at room temperature until use. 7) All specimens were mounted in standardized self-cure acrylic resin mould. After mounting, the teeth were randomly divided into two groups by simple random technique of flipping a coin, Group A and Group B (Figure 1), each comprising 20 teeth. Each group was further subdivided into two subgroups viz. A1, A2 and B1, B2 depending upon the fracture line as shown in flowchart below. The incisal third was sectioned with a water-cooled low-speed diamond disc according to the subgroup allocated. In Group A, laser etching was done with an Er, Cr:YSGG laser system (Waterlase MD, Biolase Technology Inc., San Clemente, CA, USA) operating at a wavelength of 2780 nm and frequency of 20 Hz. Laser energy was delivered through a fiberoptic system to a sapphire tip terminal that was 600 µm in diameter and 6 mm in length. The power output was set at 1.5 W for 10 s of exposure time. Air and water spray from the handpiece was adjusted to a level of 60% air and 40% water. In Group B, samples were etched with a 37% phosphoric acid gel (3M Scotchbond etchant, 3M Dental Products, St. Paul, MN, USA) for 15 s followed by 15 s of washing with distilled water and air dried
Sample N=40
Group A Laser etching
Group B Acid etching
(N=20)
(N=20)
Subgroup A1 Horizontal fracture
Subgroup A2 Oblique fracture
Subgroup B1 Horizontal fracture
Subgroup B2 Oblique fracture
(N=10)
(N=10)
(N=10)
(N=10)
Figure 1: Distribution of sample
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for 10 s. After laser or acid etching, the samples were dried with oil-free air for 20 s; the light-cured bonding resin (Scotchbond Multipurpose, 3M Dental Products, St. Paul, MN, USA) was then applied immediately with a brush, and cured as per manufacturer’s instructions. The fragments were then reattached using flowable resin composite (Tetric flow, Ivoclar Vivadent, Schaan, Liechtenstein) and polymerized. The reattached teeth were finished and polished using Sof-Lex polishing discs (3M ESPE). All the specimens were transferred to the Instron universal machine individually and subjected to Shear Bond Strength (SBS) analysis at constant crosshead speed of 1.0 mm/min. Shear bond strength was recorded in Newtons.
Statistical analysis For SBS analysis, data were expressed as means ± standard deviation. All data was processed by SPSS software version 19.0 (SPSS Inc., Chicago, IL, USA). To investigate whether SBS was significantly affected by
Table 1: Comparison of mean Shear bond strength between Group A and Group B Groups
SBS (mean±SD)
Group A
94.70±39.158
Group B
121.25±49.937
p-value 0.121
Figure 2: Comparison of mean Shear bond strength between Group A and Group B
Shear bond strength with Er, Cr: YSGG laser
ORIGINAL ARTICLES treatment options, Mann Whitney U test was used for both inter-group and intra-group comparison. Differences were considered significant for a value of p< 0.01.
Results Results were evaluated by a blinded evaluator not involved in the experiment. Mean shear bond strength (SBS) for Group B was higher as compared to Group A, however the difference was not statistically significant as revealed by Mann Whitney U test (p=0.121). The values are depicted in Table 1 and Figure 2. Mean shear bond strength (SBS) values in subgroups of A and B are shown in Table 2 and Figure 3. No statistically significant difference was observed between the subgroups.
Discussion Maxillary central incisors were included for the present study as these are more frequently involved in traumat-
Table 2: Comparison of mean Shear bond strength among different subgroups of Group A and Group B Sub- Groups
SBS (mean±SD)
Sub- Group A1
91.70±36.157
Sub- Group A2
97.70±43.701
Sub- Group B1
128.20±34.438
Sub- Group B2
114.30±63.017
p-value 0.631
0.393
Figure 3: Comparison of mean Shear bond strength among different subgroups of Group A and Group B
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ORIGINAL ARTICLES ic dental injuries. 2) According to a recent survey, overall prevalence of traumatic dental injuries was found to be 10.4%, and maxillary central incisors were the most commonly affected teeth (85.2%). The results of this survey also showed almost equal frequency of horizontal and oblique dentinal fractures. 19) The fractured teeth are generally restored using composite resin or complex ceramic restorations. With advancements in acid etching and adhesive resins, the reattachment of tooth fragment became a commonly used procedure for fractured teeth. During rebonding of fractured segment, acid etching results in chemical changes that can modify the organic matter and decalcify the organic component. As a result of this demineralization, enamel becomes more susceptible to caries attack and sensitivity. 20) In order to avoid this demineralization, the present study aimed at utilizing laser for etching the fractured surfaces and the results were comparable to acid etch in terms of resistance to debond the fragments. Er; Cr:YSGG laser was utilized in the present study as it is well-absorbed by water and dental hard tissue. As water absorbs laser radiation better than dental hard tissue, it reduces the increasing temperature of the tissue during the preparation. In addition it provide a smear-free surface, good adhesion, lack of vibration and lack of need for local analgesia in most cases. 21) It had been reported that the use of a bur preparation, with an insufficient cooling, may lead to a temperature rise of over 15°C when the critical temperature rise lies at about or above 5.5°C, at which a high percentage of the pulp cells are killed. But for Er; Cr:YSGG laser preparations, with the suggested cooling settings, a decrease in the temperature of the pulp has been recorded. 21) Laser prepared enamel has a chalk-like appearance that is similar to the acid etched characteristic of enamel and enamel rods. 22) The parameters of laser used in the present study are as per the literature findings for etching procedure. 23, 24) The mean shear bond strength of bonded brackets and enamel surface etching pattern obtained with an Er,Cr:YSGG laser (operated at 1W or 2W for 15 seconds) is comparable to that obtained with acid etching. 23) Similarly, Berk (2008) 24) observed by means of a SEM analysis that 1 W, 1.5 W, and 2 W Er, Cr:YSGG laser irradiation produced etching patterns similar to those of acid etching. The etching effect of Er, Cr:YSGG laser has been studied for various purposes in dentistry like pit and fissure sealant application, orthodontic brackets placement and others, however only a single case is reported for its use in bonding an incisal fragment with success over a period of four years follow up. 18) Various stud-
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ies have evaluated the effect of different materials and type of tooth preparation on shear bond strength of reattached tooth fragment. 1, 6, 7) Although, in clinical practice we do come across both horizontal and oblique teeth fracture with equal frequency but to the best of our knowledge, no study reported regarding the type of fracture and its effect on bond strength. So, in the present study, the effect of type of fracture on shear bond strength was also evaluated. Bond strength values are gross assessing tools for evaluating the efficacy of bonding restorative materials to dentin. Of the various tests, the shear bond strength is less technique sensitive to perform, highlighting the strength at the bonded interface. 25) The cross-head speed used to fracture the specimens in this study was 1mm/min as recommended by ISO standard (ISO/ TS 11405:2003Dental Materials-Testing of adhesion to tooth structure). The results of the present study showed that the shear bond strength of acid etched bonded surfaces was more as compared to laser etched surfaces, however, the difference was not statistically significant. (Table 1, Figure 2) The use of lasers for enamel etching shows contradictory reports. Some researchers stated that laser irradiation was not capable of etching enamel. Martinez-Insua (2000) found weaker adhesion forces in an Er:YAG laser-etched enamel surface than an acid etched enamel surface. 20) This was related to sub-surface cracks observed in (SEM) images. Tarcin et al. (2009) found that the microtensile bond strength was significantly lower in the acid-etched group than the Er, Cr:YSGG and Nd:YAG laser-etched enamel group for two types of bonding agents used. 26) In contrast, some studies reported that laser applications give similar results to acid-etching techniques. Basaran et al. (2007) compared the SBS of brackets using an Er, Cr:YSGG laser in 0.5 W, 0.75 W, 1 W, 1.5 W, 1.75 W, and 2 W. They stated that 1.5 W, 1.75 W and 2 W etching yielded similar success rates as 38% phosphoric acid etching. 23) Ozer et al.(2008) investigated the SBS of brackets that they applied on enamel prepared with 0.75 W Er, Cr:YSGG, 1.5 W Er, Cr:YSGG, 37% orthophosphoric acid or self-etching primer. They found that the 0.75 W laser-applied groups was significantly less in regard to SBS than all other groups, although there was no statistically significant difference among the other groups. 27) Baygin et al. (2011) found no statistical difference between SBS values between 2 W, 20 Hz laser and 40 Hz laser. 28) Acid etching typically produced a repeating surface pattern, with cracks and fissures no deeper than 12 mm that are readily filled with resin. 12) In contrast
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to acid etch treatment, laser etching produced extensive surface fissuring and less regular and less homogeneous surface patterns arising from the union of different craters and microexplosion. Fissuring may be related to the orientation of enamel rods, because enamel is an anisotropic material. One of the potential disadvantages of enamel acid etching is that the acid causes demineralization of the most superficial layer. As a result, this surface becomes more susceptible to longterm acid attack and caries, especially when resin impregnation is defective because of air bubbles or saliva contamination. In view of potential advantages and similar bond strength, lasers can serve as an alternative to acid etching for bonding the fractured incisor fragments. Our results showed no statistically significant difference between horizontal and oblique fracture as far as the technique of bonding is similar in both types.
ORIGINAL ARTICLES (Table 2, Figure 3) This can be explained by the improved adhesive systems and composite resins in the last decades. Andreason et al. (1995) reported their results on reattachment after acid etching alone and after acid etching together with dentin bonding agent. The rate of survival of restored teeth that had been etched with acid only was 50% at 1year, whereas that of teeth restored with acid etching and a dentin bonding agent was 50% at 3 years. 8)
Conclusion Within the limits of an in vitro study, the use of Er,Cr:YSGG laser in reattachment of fractured incisor fragment is acceptable. However, larger sample size and in vivo studies are required to further enhance this finding.
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