|Year : 2017 | Volume
| Issue : 10 | Page : 1277-1282
Effect of different modes of erbium:yttrium aluminum garnet laser on shear bond strength to dentin
E Kucukyilmaz1, MS Botsali2, E Korkut3, Y Sener3, T Sari4
1 Department of Pediatric Dentistry, Faculty of Dentistry, Izmir Katip Celebi University, Cigli, Izmir, Turkey
2 Department of Pediatric Dentistry, Faculty of Dentistry, Selcuk University, Selcuklu, Turkey
3 Department of Pediatric Dentistry, Faculty of Dentistry, Necmettin Erbakan University, Karatay, Konya, Turkey
4 Department of Prosthodontics, Faculty of Dentistry, Bezmialem Vakif University, Istanbul, Turkey
|Date of Acceptance||29-Mar-2016|
|Date of Web Publication||1-Dec-2017|
Department of Pediatric Dentistry, Faculty of Dentistry, Necmettin Erbakan University, Karatay, Konya
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: The aim of this study was to evaluate the effect of different surface treatments on the shear bond strength (SBS) of resin composites to dentin using total etch dentin bonding adhesives. Materials and Methods: Sixty extracted human molars were flattened to obtain dentin surfaces. The samples were divided into three groups (n = 20): Group I: 37% phosphoric acid + optibond FL + resin composite; Group II: Erbium:yttrium aluminum garnet (Er:YAG) laser (medium short pulse [MSP] mode, 120 mJ/10 Hz) + optibond FL + resin composite; Group III: Er:YAG laser (quantum square pulse [QSP] mode, 120 mJ/10 Hz) + optibond FL + resin composite. After the specimens were prepared, the SBS test was performed at a crosshead speed of 0.5 mm/min. The fractured specimens were examined under a stereomicroscope to evaluate the fracture pattern. Statistical analyses were performed with one-way ANOVA and Tukey's honestly significant difference tests. One sample of treated dentin surface from each group was sputter-coated with gold, and scanning electron microscope (SEM) images were captured. Results: Acid etching showed significantly higher SBS than the other groups (P < 0.05). However, the difference between Er:YAG MSP and QSP mode groups was not statistically significant (P > 0.05). SEM images of the acid-etched dentin surface showed opened dentinal tubule with a regular surface, but Er:YAG MSP mode treated surface was irregular. The surface treated with Er:YAG QSP mode represented wide dentinal tubules with a clean and flat surface. Conclusion: Using different modes (MSP and QSP) of Er:YAG laser for dentin surface treatment before application of total etch adhesives is still not an sufficient alternative compared to acid etching.
Keywords: Acid etching, dentin conditioning, erbium:yttrium aluminum garnet laser, quantum square pulse mode
|How to cite this article:|
Kucukyilmaz E, Botsali M S, Korkut E, Sener Y, Sari T. Effect of different modes of erbium:yttrium aluminum garnet laser on shear bond strength to dentin. Niger J Clin Pract 2017;20:1277-82
|How to cite this URL:|
Kucukyilmaz E, Botsali M S, Korkut E, Sener Y, Sari T. Effect of different modes of erbium:yttrium aluminum garnet laser on shear bond strength to dentin. Niger J Clin Pract [serial online] 2017 [cited 2019 Nov 11];20:1277-82. Available from: http://www.njcponline.com/text.asp?2017/20/10/1277/181402
| Introduction|| |
Many recent studies in the field of restorative dentistry aim to investigate the reliability of bonding between dental materials and dental hard tissues., Restorative materials must provide a fully integrated and strong adhesion to dental hard tissues to ensure the success of clinical treatment and long-term retention of adhesive restorations., The most efficient mechanism for adhesion is thought to be micromechanical retention.,,
The enamel is mainly composed of an inorganic substance called hydroxyapatite, which sufficiently bonds to composite resins owing to the anchoring effect produced by acid etching.,, On the other hand, dentin is composed of more than 50% organic substances, mainly collagen and water, which may consequently decrease the bonding ability of composite resins to dentin. The key to achieving sufficient adhesion to dentin is the method of preparation before application of an adhesive to the dentin surface.,, There are several studies concerning the pretreatment of the dentin surfaces in the literature. Different types of acids have been often used for conditioning prior to the application of adhesive materials., Moreover, new dentin conditioning methods have been developed to obtain higher bond strengths in the field of adhesive dentistry.,,,
In recent years, lasers are being increasingly applied in the field of dentistry, and their use for preparing the dental hard tissues prior to restoration has been suggested., The microscopic and macroscopic irregularities resulting from laser therapy do not cause demineralization of the dentin surface and also open dentin tubules without creating a smear layer. This suggests that the combined use of the laser therapy with adhesive materials may be useful in increasing bond strength.,,, Studies have shown that erbium:yttrium aluminum garnet (Er:YAG) lasers form a microretentive surface, leading to increased bonding strength when used on enamel and dentin.,,, Parameters such as pulse duration and pulse energy can be adjusted to ensure a higher bond strength on the surface where the laser is applied. Current studies are investigating the optimal parameters for Er:YAG laser use to eliminate the acid-etching step on different surfaces.,,,, Recently developed quantum square pulse (QSP) mode provides short low-energy Er:YAG laser pulses delivered at an optimal rate, which results in both higher efficiency and precision with minimal thermal adverse effects.,,, Dentin surfaces conditioned with QSP mode Er:YAG laser have been shown to be sharp and well-defined with higher surface quality, required for high bond strength.,, In addition, it has been claimed that QSP mode significantly reduces the undesirable effects of laser beam scattering and absorption in the debris cloud during hard tissue ablation.,
In literature, there are many studies concerning the surface conditioning effect of Er:YAG laser, but only few studies have mentioned the effects of the medium short pulse (MSP) and QSP modes. Therefore, this study aims to evaluate the effect of different modes of the Er:YAG laser on shear bond strength (SBS) of adhesive resins to dentin. In addition, the treated dentin surfaces were evaluated morphologically under a scanning electron microscope (SEM). The null hypothesis tested was that there is no difference between SBS values of the dentin irradiated with different pulse settings of the Er:YAG laser and the acid-etched surface, followed by the application of a total etch adhesive.
| Materials and Methods|| |
xsPreparation of the specimens
A power analysis established by G*Power Version 3.1.3 (Franz Faul, Universität Kiel, Germany) software, based on an equal ratio among groups and a sample size of 60 teeth would provide over 85% (actual power = 0.86528) power to detect significant differences with 0.60 effect size and at the α = 0.05 significance level (critical F = 2.5279439; noncentrality parameter λ = 14.6000).
Sixty extracted sound human mandibular molars were collected and stored in chloramine solution at 4°C. The teeth were cleaned with a scaler and water/pumice slurry and were embedded in polyester resin. The occlusal enamel was completely removed to obtain a flat dentin surface. Prepared dentin surfaces were polished with 600-grit paper for 60 s to create a standard and clinically relevant smear layer. A smooth surface of dentin was obtained for all specimens, and teeth were randomly divided into three groups (n = 20), representing the three different surface treatments to be investigated [Table 1].
|Table 1: Dentin surface pretreatment and adhesive material applied to the specimens|
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A contact hand piece (H14 C, Fotona d.d, Ljubljana, Slovenia) with a sapphire tip (8 mm long, 1.3 mm diameter) was used to treat dentin surfaces with laser irradiation. The Er:YAG laser (LightWalker, Fotona, Ljubiana, Slovenia) with MSP and QSP modes was used with settings of 120 mJ, 10 Hz, and 1.20 Watts for 4 s. During irradiation, the level of water spray level was 6 and the distance between the sapphire tip and the target surface was 2 mm. The distance of the sapphire tip was standardized by a custom-made apparatus with a holder, and the whole surface was scanned for 30 s with the tip perpendicular to the dentin surface.
A multistep, total etch bonding agent (Optibond FL, Kerr Dental, Orange, USA) was used for all groups after application of different surface conditioning methods. The bonding procedures were performed according to the manufacturer's instructions. The primer was applied for 15 s, and then gently air-dried for 5 s. The adhesive was then applied and light cured for 20 s with a light curing unit (Demetron A1, Kerr Dental, Orange, USA). A composite resin restorative material (Filtek Z250, 3M Unitek, California, USA) was bonded to all dentin specimens using a split Teflon mold with an inner diameter and height of 3 mm × 3 mm. The mold was secured to the specimen, and then two 1.5 mm increments of composite were light cured separately for 40 s each. The Teflon mold was removed and specimens were stored in water at 37°C for 24 h.
Shear bond testing
SBSs of the specimens were tested for failure using a universal testing machine (Instron Corp., Canton, MA, USA) with 0.5 mm/min crosshead speed with a knife-edge blade. The load at failure was recorded in Newtons (N) and the bond strength was calculated in MPa by dividing the load at failure by the adhesive surface area (mm 2). The data obtained from SBS tests were analyzed using one-way ANOVA and Tukey's honestly significant difference tests (α = 0.05).
Fractured specimens were examined by a stereomicroscope (CX41, Olympus, Tokyo, Japan) at ×20 magnification to determine failure modes and were classified as cohesive (100% cohesive failure in the tooth substrate), adhesive (100% adhesive failure between the tooth substrate and adhesive resin), or mixed (mixed failure with adhesive failure and cohesive failure in the tooth substrate).
Scanning electron microscope evaluation
A treated dentin surface from each of the three groups was used for the SEM evaluations. Samples were sputter-coated with gold and inspected using a SEM (Evo LS10, Carl Zeiss, Oberkochen, Germany). The whole surface was examined and the most representative areas were photographed at ×1500.
| Results|| |
The mean SBS values and standard deviations (SD) for the groups are presented in [Table 2]. A comparison between the groups revealed that acid-etched group showed significantly higher bond strength than the other groups (P < 0.05). The difference between Er:YAG MSP and QSP-treated groups was not statistically significant (P > 0.05). The modes of failure for the specimens after the SBS test are presented in [Table 3].
|Table 2: Mean shear bond strength values (MPa) and standard deviations of each group|
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|Table 3: Distribution of failure modes within groups for shear bond strength (n=20)|
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Scanning electron microscope observations
The acid-etched dentin specimen showed a regular surface with opened dentinal tubules, without smear layer [Figure 1]. Laser-irradiated dentin surfaces had irregularities caused by laser beam scattering and exhibited a flaky surface appearance without a smear layer [Figure 2] and [Figure 3]. The QSP-mode-treated specimen exhibited a cleaner and flatter dentin surface than did the MSP-mode-treated surfaces. This is thought to be due to the reduced scattering effect of the QSP mode [Figure 2] and [Figure 3].
|Figure 1: Scanning electron microscope images of the dentin surface etched with 37% phosphoric acid: The dentin surface is regular and clean of smear layer, showing wide open dentinal tubules|
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|Figure 2: Scanning electron microscope images of the dentin surface conditioned with erbium:yttrium aluminum garnet laser medium short pulse mode: Surface is irregular and clean of smear layer and the dentinal tubules are opened|
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|Figure 3: Scanning electron microscope images of the dentin surface conditioned with erbium:yttrium aluminum garnet laser quantum square pulse mode: the dentin surface is perfectly clean and flat, showing wide open dentinal tubules|
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| Discussion|| |
Dentin conditioning with acid etching is a commonly used method to create a microretentive dentin surface without a smear layer., It is well known that etching with phosphoric acid increases the bond strength between adhesive materials and dental hard tissues., However, it is also emphasized that acid etching causes demineralization of the enamel and dentin surfaces and could possibly induce secondary caries around the composite restorations., In accordance with the developments in dental laser technology over the years, conditioning of dental hard tissues with Er:YAG lasers has been widely investigated.,,, It was reported that dentin tissue irradiated with Er:YAG laser showed a microscopically rough surface and opened the dentinal tubules and sterilized the dentin surfaces without smear layer production or excessive demineralization.,,, Therefore, it is thought that Er:YAG laser irradiation may be adequate for dentin preparation in the bonding of the adhesive materials.
The present study was designed to compare the surface morphology of dentin surfaces conditioned with acid etching, Er:YAG laser with MSP mode, and QSP modes as well as the bonding abilities of composite resins to these prepared surfaces. According to the results, the acid-etched group showed higher bond strength values than the other groups. Therefore, the null hypothesis was rejected.
There are several studies in literature that investigated the bonding strengths of Er:YAG laser-irradiated surfaces.,, However, results were conflicting and even disputable. Some researchers assumed that the characteristics of the flaky laser-irradiated surface made the surface suitable for bonding procedures as it enlarged the surface area available for bonding.,,, Lee et al. claimed that Er:YAG laser irradiation could be an alternative option to conventional acid-etching methods. Similarly, Basaran et al. reported comparable SBS values obtained from Er:YAG laser-irradiated surfaces and acid-etched surfaces. In contrast, many other studies investigating the effects of laser irradiation on bond strengths to dentin showed that acid-etched dentin surfaces produced higher bond strengths, than laser-irradiated dentin surfaces.,, Dunn et al. reported that SBS of the laser-etched dentin and enamel was inferior to that of conventional etching with 37% phosphoric acid. The results of the present study demonstrated that acid-etched dentin surfaces produced higher SBS than did various modes of Er:YAG laser-irradiated dentin surfaces, corroborating the findings of Ceballos et al., Eguro et al., and Ramos et al. SEM images from the present study showed the flaky appearance of laser-irradiated dentin, described by Aoki et al. as the cuff-like appearance of peritubular dentin. This may cause non-infiltration of resins following laser irradiation, resulting in lower bond strengths. The present study demonstrated that the SBS of laser-irradiated dentin was not satisfying compared to that of acid-etched dentin. Furthermore, a higher incidence of adhesive failures was observed in laser groups, indicating poor interaction between the adhesive resin and the tooth substrate.
The power and irradiation settings of the laser devices may have a larger influence on adhesion than what was first assumed. In particular, pulse duration and pulse energy of the Er:YAG laser are the most significant determinants for adhesion to the dentin surface. High-pulse energy, provided by the Er:YAG laser, may cause some thermal deposition and long pulses have undesirable scattering effects on dentin.,, However, using low-pulse energy and short pulse duration is inefficient for conditioning or ablating dentin surfaces.,, With the development of the QSP mode for the Er:YAG laser, it is possible to split each pulse into several shorter pulses without loss of speed and effect., The QSP mode helps avoid unwanted effects such as absorption and scattering of the laser beam in the debris cloud. Shorter pulses also mean less thermal effects on dental hard tissues.,, There are only a limited number of studies in the literature that compare the effects of QSP mode with other surface conditioning methods. Saǧır et al. suggested that Er:YAG laser etching with MSP and QSP modes could be an alternative to acid etching because it provides higher or comparable SBS values. Nevertheless, Altunsoy et al. reported that the highest microtensile bond strength was obtained from acid-etched dentin surfaces, while the MSP-and QSP-mode-treated groups showed weaker bond strength properties. Similarly, the present study demonstrated that dentin conditioning with Er:YAG laser MSP and QSP modes were not as effective as conventional acid-etching methods.
| Conclusion|| |
According to the results of the current study, it can be concluded that using different modes (MSP and QSP) of the Er:YAG laser for the treatment of dentin surfaces prior to the application of total etch adhesives is not an effective alternative to acid etching.
Despite the advances in adhesive dental materials and the achievement of greater bonding to dentin, experts should be careful when using the Er:YAG laser for the pretreatment of dentin prior to bonding procedures. The etching step should not be eliminated until further evidence-based studies report more effective parameters for the conditioning the dentin surfaces using lasers.
Further studies should be conducted to assess the superficial and sub-superficial layers of irradiated dental hard tissues and materials. This would ensure more effective application of new techniques in the field of adhesive dentistry.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]