|Year : 2012 | Volume
| Issue : 2 | Page : 46-50
Alternate way of etching enamel for effective clinical management during practice
Krishna Arora1, Pradeep Chandra Shetty2, CS Ramachandra2, SM Laxmikanth2, NB Sham2
1 Department of Orthodontics, D.J College of Dental Sciences, Modinagar, Uttar Pradesh, India
2 A.E.C.S Maaruti Dental College, Bangalore, Karnataka, India
|Date of Web Publication||31-Jan-2013|
Department of Orthodontics, D.J College of Dental Sciences, Ajit Mahal Niwari Road Modinagar, Ghaziabad - 201 204
Source of Support: None, Conflict of Interest: None
Objectives: To test the shear bond strength of brackets bonded to enamel etched with Erbium: Yttrium-aluminium-garnet laser (Er YAG) at different power outputs of 1, 2, and 2.5 W and to check the surface characteristics of enamel using scanning electron microscope. Materials and Methods: Human premolars that had been extracted for orthodontic reason were used. Enamel was then etched using conventional acid etch technique and Er:YAG laser at three different power outputs. Few teeth did not undergo shear test but prepared for scanning electron microscope (SEM) evaluation. Results: The shear bond strength associated with the 1 W laser irradiation was significantly less than the strengths obtained with the other groups. Both the 2 and 2.5 W laser irradiations were capable of etching enamel in the same manner like with acid etching. Conclusion: The mean shear bond strength and enamel surface etching obtained with an Er:YAG laser is comparable to that obtained with acid etching and an alternate to acid etching.
Keywords: Acid etching, Er:Yttrium-aluminium-garnet laser, scanning electron microscope evaluation, shear bond strength
|How to cite this article:|
Arora K, Shetty PC, Ramachandra C S, Laxmikanth S M, Sham N B. Alternate way of etching enamel for effective clinical management during practice. J Dent Lasers 2012;6:46-50
|How to cite this URL:|
Arora K, Shetty PC, Ramachandra C S, Laxmikanth S M, Sham N B. Alternate way of etching enamel for effective clinical management during practice. J Dent Lasers [serial online] 2012 [cited 2017 Jul 21];6:46-50. Available from: http://www.jdentlasers.org/text.asp?2012/6/2/46/106646
| Introduction|| |
Fixed orthodontic treatment necessitates bonding of brackets to the enamel surface. Effective bonding of brackets to enamel surface is extremely critical in orthodontics.
The biomechanical importance of bracket adhesive interface to transfer the load generated from the engagement of an arch wire to the tooth necessitates satisfactory bonding.
Since the report of Buonocuore in 1955, the standard protocol to treat enamel for successful bonding has been etching with 37% phosphoric acid.  The enamel tags created by dissolving hydroxyapatite crystals permit penetration of the fluid adhesive components, and this provides micromechanical retention. Although conventional acid etching is time consuming, a high level of bracket bond strength is achieved. The effects of etching time , and phosphoric acid concentration  have been investigated to seek the most suitable method of enamel preparation.
In contrast, the loss of mineral crystals, essentially the acid protecting barrier, is inevitable.  Hence, enamel decalcification around the orthodontic brackets is a serious problem that the clinicians are still facing, particularly in patients with less than optimal oral hygiene. Because of this mineral loss, the etched enamel may be vulnerable to successive acid attacks in the oral environment.
Among different treatment for surface conditioning/treatment like sandblasting, acid etching, self etching primer, etc. The literature proves that except for acid etching, the bracket-enamel bond strength of rest of the method is not significant. Hence the use of laser for enamel treatment is important in clinical as well as patient point of view, which provide advantages like: It offers high precision, enamel found to be more resistant to acid attack,  and it is time saving in clinical practice.
Various commercially available laser systems have also been introduced for dental use, the first being reported in 1964.  Among the innovations for substrate treatment, the role of the Erbium: Yttrium-Aluminum-Garnet (Er:YAG) laser has been highlighted.  . Compared with other lasers, the Er:YAG laser has a greater ability to handle dental hard tissue with high efficiency and the ability of laser irradiation to remove the smear layer has been also reported. ,
The Er:YAG laser, which uses a pulsed-beam system, fiber delivery, and a sapphire tip bathed in a mixture of air and water vapor, has been shown to be effective for soft tissue surgery and for cutting enamel, dentine and bone. , After Er:YAG laser irradiation, the surface alteration of enamel and dentine shows microirregularities and the absence of a smear layer.  This suggests that the Er:YAG laser may etch enamel suitably for orthodontic purposes. Therefore, the present study was conducted to test the shear bond strength, surface characteristics, and fracture mode of brackets bonded to enamel etched with an Er:YAG laser operated at different power outputs.
| Materials and Methods|| |
Sixty-four human premolars teeth, which had been extracted for orthodontic purpose, were used in the study. Crowns with caries, restorations, or fractures were discarded. Any remaining soft tissues were removed from tooth surface with a dental scaler. All teeth were stored in 4°C distilled water containing 0.2% thymol to inhibit the bacterial growth until use.
Sixty premolars teeth were mounted horizontally in a self-curing acrylic resin so that at least 2 mm of the buccal enamel was exposed. The surface of the teeth were polished with pumice and rubber prophylactic cups, rinsed with water and dried with air and spray.
The sixty premolars samples were then randomly divided into four treatment groups. The remaining four teeth did not undergo the shear test but were prepared for scanning electron microscope (SEM) evaluation (JEOL/JSM 840 A, Japan) after different surface treatments. The four groups were as follows:
The samples were tested for shear bond strength on Universal Testing machine at a cross head speed of 5 mm/minute and the readings of shear bond strengths were recorded in Newton and converted into Megapascals by following equation:
For acid etching, 37% phosphoric acid was applied to the enamel surface, rinsed with running water and gently dried with dryer. Each procedure was done for 30 seconds, bonding agent was painted on the tooth using the applicator tip, left for 20 seconds, air blown, and light cured for 10 seconds, the adhesive (Transbond XT 3M) was then applied and light cured for 10 seconds for each surface. For laser treatment, the enamel surface was ablated with an Er:YAG laser (Twinlight, Fotona, Ljubljana, Slovenia) [Figure 1] at 2.94 μm wavelength for 15 seconds. The diameter of the treated spot was about 1.2 mm. After ablation, to clear tooth particles and dust, the surface of laser-treated specimens was cleaned with running water without brushing and dried in air.
- Group A: Enamel etched with 37% phosphoric acid
- Group B: Enamel irradiated with the Er:YAG laser at 1 W for 15 seconds
- Group C: Enamel irradiated with the Er:YAG laser at 2 W for 15 seconds
- Group D: Enamel irradiated with the Er:YAG laser at 2.5 W for 15 seconds
The laser etched enamel showed a dull, frosty appearance. For all groups, the adhesive (Transbond XT) was then painted on the tooth using the applicator tip, left for 20 seconds, air blown, and light cured for 10 seconds. After this, the Stainless Steel brackets (Premolar Brackets 0.022 inch slot, from Gemini with mesh bracket base surface area as 10.6 mm 2 ) were bonded.
After the application of the adhesive material (Transbond XT), the bracket was placed on the tooth surface, adjusted to its final position. Each side of the tooth (mesial, distal, occlusal, and gingival) was light cured for 10 seconds, for a total of 40 seconds for each tooth.
Once the bonding protocols were completed the specimens were then subjected to shear bond strength test using Universal Testing machine. The values obtained were recorded.
One specimens in each group was selected, whose surface was conditioned with 37% phosphoric acid, and Er:YAG Laser with 1, 2, and 2.5 W. The crowns were sectioned from the roots with a carborandum disc using water spray at the labial cemento-enamel junction. Each crown was sectioned vertically in labio-lingual direction. The sections of tooth were cleaned with water and dried with compressed air.
The specimens were then examined in JSM-840 scanning electron microscope (JEOL Ltd, Tokyo, Japan) operated at 20 KV. Photographs were taken at the magnification of 1000× to analyze the surface roughness and etching pattern [Figure 2].
Descriptive statistics, including the mean, standard deviation, and minimum and maximum values, were calculated for each group [Table 1]. Multiple comparisons [Table 3] of the shear bond strengths for the different etching types were performed with the analysis of variance (ANOVA) test [Table 2].
| Results|| |
Shear bond strength
Highest mean shear bond strength (SBS) (MPa) was recorded in Group-4 followed by Group-3 and Group-1, respectively. Lowest mean SBS (MPa) is recorded in Group-2 [Table 1]. The difference in mean SBS (MPa) between the groups was found to be statistically significant (P < 0.05). The difference in mean SBS (MPa) was found to be statistically significant between Group-2 and Group-4 (P < 0.01). The difference in mean SBS (MPa) was not statistically significant between Group-1 and Group-2 (P > 0.05), Group-1 and Group-3 (P > 0.05), Group-1 and Group-4 (P > 0.05), Group-2 and Group-3 (P > 0.05) as well as Group-3 and Group-4 (P > 0.05).
Scanning electron microscope examination
Group-1 shows Type-III acid etched pattern with the regular rough surface and spaces as described by Silverstone et al. can be seen [Figure 2]a.
Group-2 with 1 W laser irradiation produced a more preferred type I etching pattern [Figure 2]b. A honeycomb-like appearance was seen with a 1-W laser irradiation.
Group-3 with 2 W laser irradiation produced a type III acid-etching pattern more likely similar to that produced by acid etching [Figure 2]c.
Group-4 Laser irradiation with 2.5 W produced a Type III acid-etching pattern with more micro cracks, and the surface destruction was more prominent [Figure 2]d.
| Discussion|| |
The direct bonding of orthodontic brackets has revolutionized and improved the clinical practice of orthodontics. However, there is a need to further improve the bonding procedure to save time and to minimize enamel loss without jeopardizing the ability to maintain clinically useful bond strength.
Maleic and polyacrylic acids have been used to control the enamel loss as alternatives to phosphoric acid. . The use of polyacrylic acid has resulted in reduced bond strength. So by using Er:YAG laser the demineralization or the loss of enamel can be controlled to some extent by avoiding the acid With the recent advancements in resources and materials, the Er:YAG laser has proved to be effective and as an alternative method to etch the enamel in short duration without compromising the shear bond strengths  therefore laser-induced caries resistance is gaining a lot of importance in orthodontics. .
The ability of Er:YAG laser to effectively ablate dental hard tissues is ascribed to its 2940 nm wavelength emission, which is coincident with the main absorption band of water and hydroxyapatite of enamel.
We also found that laser at 2 W power produced clinically acceptable shear bond strength, which was comparable to the levels achieved with conventional 37% phosphoric acid etching. The shear bond strength of 2.5 W laser was found to be more than acid etching but in scanning electron microscope, we noticed that there is more destruction of the enamel, although we got type-III etching pattern but with more microcracks. Hence, the ideal power setting for etching the enamel to attain acceptable shear bond strength would be of 2 W.
Moreover, Er:YAG laser etching is painless and does not involve either vibration or heat, and the easy handling of the apparatus makes this treatment highly attractive for routine clinical use.  In addition, this laser can be used in wet conditions and the water-cooled system does not cause any untoward thermal effects on the tooth pulp. Moreover, the clinician has more control of the area to be etched with the laser system. Although gel acids are more stable than liquid acids, there is always a shift of acid on the enamel surface.
The required time for acid etching varies from 15 to 60 seconds. Barkmeirer et al. in 1985,  reported that 15 seconds of enamel etching with phosphoric acid is sufficient for successful orthodontic bonding. Fifteen seconds of water spraying and 15 seconds of air drying are also necessary in phosphoric-acid etching. A total of 45 seconds for each tooth is needed with phosphoric acid. The time needed for laser systems is around 25 seconds, 15 seconds for etching and 10 seconds for drying, which is definitely shorter than that required for phosphoric acid.
From a clinical standpoint, saving chair side time also improves adhesion because it reduces the risk of salivary contamination. Because it was not our main purpose, the required time was not recorded, but it was evident that laser saves chair time. The results of the study indicate that laser has the potential to successfully bond orthodontic brackets with clinically acceptable bond strengths as compared with acid etching.
Nevertheless, these putative advantages of laser etching might be outweighed by the capital expenditure associated with current laser units. However, with technological advancements and more usage of lasers, the cost factor is only bound to come down.
| Conclusion|| |
- The mean shear bond strength and enamel surface etching obtained with an Er:YAG laser (operated at 2 and 2.5 W for 15 seconds) is comparable with acid etching and an alternative to acid etching.
- More preferred type-III etching pattern was seen with 2 W laser (Group-3).
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]