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Year : 2020  |  Volume : 23  |  Issue : 1  |  Page : 110-115

Effect of surface flattening and phototherapy on shear bond strength immediately after bleaching with different modes of universal adhesive

Department of Restorative Dentistry, Dentistry Faculty, Gaziantep University, Gaziantep, Turkey

Date of Submission27-Jun-2019
Date of Acceptance09-Sep-2019
Date of Web Publication10-Jan-2020

Correspondence Address:
Dr. D Surmelioglu
Gaziantep University, Dentistry Faculty, Sehitkamil 27060, Gaziantep
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njcp.njcp_337_19

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Objective: The aim of this study was to compare to effect of phototherapy and surface flattening after immediately bleaching on the shear bond strength to bleached enamel. Methods: Ninety-six human upper incisors were divided into 4 groups (n = 24). Group NB: no bleached, group P: phototherapy with YSGG laser, group F: 0.5 mm surface flattening, group PF: 0.5 mm surface flattening and phototherapy with Er;Cr:YSGG laser. Then, each group was assigned to 2 subgroups according to adhesive mode (n = 12) as; subgroup S (self-etching mode), subgroup T (total-etching mode) which are universal adhesives. All surface conditionings and restorations were performed with composite resin materials immediately after bleaching. Shear bond strength test was performed by using universal testing machine. The surfaces were also evaluated with SEM. The data were statistically analyzed with one-way ANOVA post-hoc Tukey tests. Results: The lowest SBS values were achieved in FS (13.72 ± 2.29) while the highest ones in PT (28.01 ± 6.81). However, the differences were not significant (P > 0.05). All surface conditioning methods provided SBS values similar to the control (P > 0.05). All subgroups of self-etching mode were significantly lower than their total-etching counterparts (P < 0.05). Conclusions: The present study showed that surface removal and phototherapy have a potential clinical application for eliminate to undesirable effect of bleaching treatment. Surface conditioning with either flattening and/or phototherapy may provide clinicians to restore bleached teeth at the same visit with bleaching and reduce chair-time.

Keywords: Bleaching, flattening, phototherapy, shear bond strength, universal adhesive

How to cite this article:
Surmelioglu D, Ozdemir Z M, Atilan S, Yeniceri N E. Effect of surface flattening and phototherapy on shear bond strength immediately after bleaching with different modes of universal adhesive. Niger J Clin Pract 2020;23:110-5

How to cite this URL:
Surmelioglu D, Ozdemir Z M, Atilan S, Yeniceri N E. Effect of surface flattening and phototherapy on shear bond strength immediately after bleaching with different modes of universal adhesive. Niger J Clin Pract [serial online] 2020 [cited 2022 May 16];23:110-5. Available from:

   Introduction Top

Bleaching which is a common cosmetic dental application plays a major role in dental aesthetics.[1] For in-office bleaching treatment, the most preferred bleaching agents are hydrogen peroxide (HP) and carbamide peroxide.[2] Despite the effectiveness and safety of bleaching were proven,[3] a number of previous studies reported some undesirable effects of bleaching procedures. These undesirable side effects include alterations in structure/composition of enamel and residual oxygen formation.[4],[5],[6] The major clinical problem resulting from these ultrastructural changes is decrease in bond strength of adhesives to bleached enamel.[7],[8] This phenomena is an important concern in esthetic dentistry because vital bleaching is the first phase of dental esthetic which is applied before adhesive restorations including composite resins, porcelain laminate veneers.[9]

There are numerous techniques conversing the reduced bonding strength of bleached enamel. These are delayed bonding 24 hours to 2 weeks following bleaching,[5] 0.5–1.0 mm flattening (surface removal) of the bleached surface,[10] application of antioxidants,[11] and laser systems.[12]

Furthermore, the bonding system to be used on bleached enamel may also affect the degree of adhesion.[13] With time improved adhesive technology has directed to the progress of multimode adhesives.[14] These products can be used in 3 different modes as self-etching, selective-etch, and total-etching. Some in vitro studies[15],[16] evaluated the bond strength of universal adhesives, however studies on effects of bleaching treatments to the bonding strength of universal bonding systems in different modes are limited.

Erbium, chromium-doped yttrium, scandium, gallium and garnet (Er, Cr:YSGG) has become a commonly used system in dentistry with promising results.[17] Er, Cr:YSGG laser which has a wavelength of 2780 nm is well absorbed by water and hydroxy apatite crystals in enamel and dentin.[18],[19] Thus, the authors of the present study questioned whether application of this system on bleached enamel may aid to overcome the adhesion limitations following bleaching and eliminate the necessity of delaying adhesive restorations after bleaching. Furthermore, we aimed to match the correct mode (either self or total) of universal adhesives with Er, Cr:YSGG laser to improve the adhesion to bleached enamel.

Due to lack of conclusive evidence concerning the effect of phototherapy and flatting with different bond system modes on the shear bond strength (SBS) of resin composite materials to enamel after bleaching, the aims of this scientific present study were to explore:

*the influence of phototherapy (Er, Cr:YSGG) and enamel flatting on the SBS of a restorative system to enamel after tooth bleaching.

*the comparable outcomes related to different application mode of universal bond system will exhibit.

   Materials And Methods Top

The ethic of research protocol was confirmed by the Research Ethics Committee of Gaziantep University (2019/207).

Selection and preparation of teeth

Ninety-six human upper incisors free of caries and restorations were collected. All teeth were cleaned with an ultrasonic scaler, polished. They were stored in Chloramine T hydrate 95% (Sigma-Aldrich) for 5 days and at 4°C until the beginning of the SBS test. Specimens were mounted vertically into the section of polyvinyl pipes (7 mm diameter) filled with acrylic resin up to cemento-enamel junction (CEJ) exposing only the clinical crown.


The selected teeth were randomly assigned to 4 groups (n = 24). Three groups other than control group were bleached with bleaching agent Whiteness HP Blue (FGM Prod. Odont. Ltd., Joinville, SC, Brazil) containing 35% HP. Bleaching gel was applied as a thin coating to the buccal surfaces for fifteen minutes, three times (45 minutes) in a session (2 mm). The process to be used for these groups is as follows:

Group NB (No Bleached): The specimens in this group did not bleach and no surface flattening, phototherapy.

Group P (Phototherapy): Twenty-four bleached teeth were immediately exposed to Biolase, Waterlase I-Plus (Biolase, Irvine, CA, USA). The device was set to frequency of 30 Hz, output power of 4.5 W. The tip (MZ = 8) was used at a distance of 2 mm from the enamel surface with no contact for 1 minute.

Group F (Flattening): Buccal surfaces of 24 bleached teeth were immediately removed up to 0.5 mm using a grit machine (Isomed saw, Buehler, Illinois, USA).

Group PF (Phototherapy + Flattening): The buccal surface of twenty four bleached teeth were removed up to 0.5 mm using a grit machine and then, irradiated with Er;Cr:YSGG laser within the same manner.

According to the adhesive mode, teeth were further divided into eight subgroups [Figure 1];
Figure 1: Study design (n denotes the number of enamel specimens in a group)

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  • Subgroup NBS (control group + self-etching mode)
  • Subgroup NBT (control group + total-etching mode)
  • Subgroup PS (bleached + phototherapy + self-etching mode)
  • Subgroup PT (bleached + phototherapy + total-etching mode)
  • Subgroup FS (bleached + flattening + self-etching mode)
  • Subgroup FT (bleached + flattening + total-etching mode)
  • Subgroup PFS (bleached + flattening + phototherapy + self-etching mode)
  • Subgroup PFT (bleached + flattening + phototherapy + total-etching mode).

Subgroup NBS, PS, FS and PFS (n = 12) were applied with Single Bond Universal (3M ESPE, St. Paul, MN, USA) as self-etching mode. Other subgroups NBT, PT, FT and PFT (n = 12) were etched with 37% phosphoric acid (3M ESPE, St. Paul, MN, USA) for 30 s, rinsed for 30 s and after that with air spray. Afterwards, Single Bond Universal was applied to specimens as total-etching mode. Following all these bonding procedures the bonding agent was rubbed on the buccal surface of the teeth for 15 s, spread with air spray and polymerized with VALO LED (Ultradent Products, Inc. USA) light device for 20 s.

Restoration procedure

After bonding process was completed, the buccal surfaces of teeth were restored using teflon mold (3 mm inside diameter, 4 mm height) to obtain cylinder composite resin. For the restoration G-aenial anterior composite (GC Europe, Inc. Leuven, Belgium) was used and polymerized for 20 s in each increment using VALO LED. Finally, all prepared teeth were stored in artificial saliva (NeutraSal) at 37°C for 24 h. Before undergoing the SBS test, thermocycling was performed between 5°C and 55°C for 5000 cycles with a dwell time 30 s. All the materials were applied on the teeth surface according to manufacturer's instructions [Table 1].
Table 1: Materials used in the study

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Shear bond strength (SBS) test

For SBS test, universal testing machine (AGS-X, Shimadzu, Kyoto, Japan) with a knife-edge blade was used. The blade was positioned to the resin enamel interface as close as possible. A shear load was applied to each specimen until failure at a crosshead speed of 1.0 mm/min. Values were recorded in Newton (N) and were converted in Megapascals (MPa) by dividing the load in Newton to composite cylinder surface area in mm.

SEM observation

Samples were covered with gold (Bal-Tec, SCD 050 Sputter Coater, Fürstentum, Liechtenstein) and examined under scanning electron microscope (SEM) (GeminiSEM 300, Zeiss, Oberkochen, Germany) in order to visualize ultrastructural changes with a magnification of × 1000. [Figure 2] demonstrates SEM images of 8 different surfaces.
Figure 2: Scanning electron microscope images of the enamel surface (a) no bleached (b) no bleached + acid (c) bleached (d) bleached + flattening (e) bleached + flattening + acid (f) bleached + phototherapy (g) bleached + phototherapy + acid (h) bleached + flattening + phototherapy + acid

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Statistical analyses

Data was analyzed by using SPSS 22 for Windows (Chicago, IL, USA). The significance level for SBS was set at P < 0.05. SBS values were compared using one-way ANOVA among the study groups and Tukey's post-hoc test for multiple crosscheck.

   Results Top

[Table 2] and [Figure 3] present the mean and standard deviations (SD) of the SBS test values for eight subgroups in MPa. Among the groups, the lowest bond strength was observed in FS (13.72 ± 2.29) while highest bond strength was achieved in subgroup NBT (28.01 ± 6.81).
Table 2: Mean bond strength values (N) and standard deviation of adhesive systems on enamel

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Figure 3: Overall shear bond strength values (MPa)

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SBS values ofP (phototheray), F (flattening), PF (phototheray + flattening) groups were similar with NB (control group) (P > 0.05) for both total and self-etching groups. Application of the total – etching mode with all of the surface pretreatment showed higher the highest bond strength values compared to self-etching immediately after bleaching (P < 0.05).

   Discussion Top

Following bleaching treatment, restorations are generally required to be changed due to color disparities. However, this is not indicated until ultrastructural composition of dental hard tissues return to normal because bleaching processes may cause damage in organic and inorganic components of enamel structures such as prism core and lead to the obstruction of inter-prismatic spaces with free oxygen radicals. Accordingly, this makes formation of resin tags difficult and interferes with bond strength between the tooth and restoration interface.[20],[21] Within this limited knowledge, this experimental in-vitro study objected to compare the bond strength of both bleached and no bleached enamel by using universal bonding systems with different modes following different surface conditioning techniques including; (i) flattening from buccal surface up to 0.5 mm, (ii) Er, Cr:YSGG laser phototherapy, (iii) combination of both, prior to pre-restoration processes for laminate, composite veneers, composite fillings.

Universal testing machine that is an in-vitro method providing rapid and certain data was preferred for measuring SBS on detailed parameters.[22] The SBS test is a reliable and simple method that measure the bond strengths of the using materials with surface area as to 3–6 mm in diameter.[23] Consequently, in this current study, the SBS test was preferred for measuring the bond strengths values of resin materials with 3 mm diameter.

Single Bond Universal is a bonding agent which contains 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and ethanol. MDP provides chemical bonding to enamel structure and lead to increase long-term bonding performance.[24] Also, ethanol limits the undesirable effects of free oxygen molecules on the tooth surface by reacting with water and oxygen after bleaching treatment.[13] Because its post-bleaching efficiency was proven, we preferred to include this contemporary material in the present study.[25]

Previous studies have been performed using different types of adhesive systems to evaluate the bond strength between composite restoration and tooth surface after the bleaching treatment.[21],[26] An in vitro research evaluated SBS values of a total-etching and a self-etching adhesive systems to the enamel after bleaching treatment and reported the decreasing of bond strength when self-etching adhesive mode was used.[21] Similarly, in another experimental study performed immediately after bleaching, total-etching systems provided higher bond strengths than self-etching adhesives.[26] The last generation of adhesives known as universal adhesives can be used with different modes.[27] Many researchers have investigated the bonding strength of universal bonding systems to tooth surface.[28],[29] Furthermore Oz et al. found that the total-etching system was superior to the self-etching systems in their study which was evaluated in two different universal bond systems.[15] These findings are in accordance of our results. However, to the best of our knowledge, there is no current study performed to evaluate the bond strength to bleached enamel following contemporary methods including phototherapy and/or flattening treatment with different mode of universal adhesive systems.

According to the current study, clinicians can prefer to use universal bonding agents with both of modes immediately after bleaching, if the bleached enamel surface is irritated with Er;Cr:YSGG laser phototherapy. Er, Cr:YSGG laser is absorbed by water composition of enamel and subsequently cause its evaporation with other hydrated components. Also, it lead to enamel microexplosions and microablations.[30] Furthermore, the heat caused during microexplosions removes free oxygen radicals from the buccal surface, providing a convenient adhesion.[31] These statements are the likely reasons for positive effects of Er, Cr:YSGG laser treatment on adhesion to tooth surface after bleaching. In the literature, there are conflicting results for laser phototherapy application to the enamel surface.[32],[33] The outcomes of the present study are related to the selected laser parameters (4.5 W and 30 Hz) and type of bonding systems.[34]

The clinically acceptable composite-to-enamel bond strength values should be between 15 and 30 MPa.[35] However, Cheng et al.[36] found SBS values of bleached enamel after flattening 0.5 mm of the buccal surface was similar to the control group with total etching system which is similar to the results of present study. Thus, although flattening which is a simple and cost-effective method seems a promising application for the adhesion of post-bleaching restorations, results may vary according to the type bonding. For this reason, Er, Cr:YSGG laser phototherapy either in combination with flattening or alone provided further increase of the adhesion in cases of total etching systems are used. These results also indicate the placement of immediate coronal restoration following bleaching removing the necessity of waiting time.

Within the limitations of the present study, Er, Cr:YSGG phototherapy and enamel flattening can be used to eliminate the adverse effects of bleaching agents. This provides the clinicians to restored bleached teeth immediate after bleaching session and by this way reduce chair-time. Flattening is an easy and cheap method for conditioning bleached enamel. Despite the difference was not significant, Er, Cr:YSGG phototherapy provided a slight further increase in SBS of bleached teeth. Further studies are required to better identify this issue.

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]


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