|Year : 2015 | Volume
| Issue : 2 | Page : 69-74
The effect of 808 nm diode laser irradiation on shear bond strength of composite bonded to dentin before and after bonding
Mohammadreza Malekipour1, Farnoosh Alizadeh1, Farzaneh Shirani2, Shahram Amini3
1 Department of Operative Dentistry, School of Dentistry, Islamic Azad University, Khorasgan, Iran
2 Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Science, Khorasgan, Isfahan, Iran, India
3 Department of Periodontics, School of Dentistry, Islamic Azad University, Khorasgan, Isfahan, Iran, India
|Date of Web Publication||26-Nov-2015|
Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Science, Isfahan
Source of Support: None, Conflict of Interest: None
Objectives: As bonding ability to tooth surface is an important factor in durability of composite restorations, the aim of this in vitro study was to evaluate the effect of 808 nm diode laser irradiation with different power outputs on the shear bond strength of composite bonded to the dentin before and after applying the bonding agent.
Materials and Methods: A total of 35 healthy third molars were mounted in acrylic resin in a way that each molar had two test sites and divided into seven groups of 10 each. In the control group, the bonding agent was used without laser application. An 808 nm diode laser with different power outputs of 0.5, 1 and 1.5 W for a duration of 20 s was irradiated perpendicularly to the dentin surfaces in three of the experimental groups before and in the other three groups after applying the bonding agent. After composite cylinders had been adhered, they were examined to determine their shear bond strength. Results: According to the least significant difference test, the bond strength mean significantly higher in the control group (P < 0.001) and in all laser power outputs, the mean bond strength was significantly higher in the groups for which laser was irradiated before applying the bonding agent than the groups for which laser was irradiated after applying the adhesive (P < 0.05). Conclusion: Considering the higher bond strength in the control group, it seems that applying laser does not increase the bond strength of composite to the dentin.
Keywords: Bond strength, dentin sensitivity, laser
|How to cite this article:|
Malekipour M, Alizadeh F, Shirani F, Amini S. The effect of 808 nm diode laser irradiation on shear bond strength of composite bonded to dentin before and after bonding. J Dent Lasers 2015;9:69-74
|How to cite this URL:|
Malekipour M, Alizadeh F, Shirani F, Amini S. The effect of 808 nm diode laser irradiation on shear bond strength of composite bonded to dentin before and after bonding. J Dent Lasers [serial online] 2015 [cited 2021 Dec 5];9:69-74. Available from: https://www.jdentlasers.org/text.asp?2015/9/2/69/158465
| Introduction|| |
Adhesion is the process of the interaction of a solid or liquid adhesive substance with the underlying substance on their intermediate surface. Adhesion strength is also a measure of load bearing capacity in a connected link.
Despite significant advances in dentinal adhesives, adhesion to the dentin is known as a matter which requires precision and has a sensitivity to methods in restorative dentistry. For achieving higher strength of dentin-resin, in addition to making newer dentinal adhesives, clinical methods such as applying several layers of adhesive, increasing curing time, increasing the application time of bonding agents on the surface and polymerizing delay have been applied where most results show the creation of a hybrid layer with better quality and stronger polymer.
Temperature appears to be a factor affecting the bond strength of composites to the Tooth structure. In various studies, the effect of this factor has been investigated such as change in the temperature of drying, bonding agent, washing water, restorative substance, and environment.,,
Semiconductor lasers such as diode are considered as the smallest, cheapest, lightest, most durable and the newest generation of lasers. The laser creates many wavelengths continuously produced in visible and infrared areas. All wavelengths of diode laser are absorbed in pigmented tissues. The dental tissue has a low capacity in absorbing diode lasers; consequently, soft tissue surgeries can even be conducted in adjacent to the enamel and dentin and cementum with high levels of safety. Laser beams used in dentistry are a part of nonionizing beams of the electromagnetic spectrum; depending on their wave length, power and also type of the target tissue, they can cause to stimulate or cut the tissue.
According to the study by Sulieman et al. on using diode laser in upper and lower anterior teeth bleaching, diode lasers with a power level of up to 2 W are not dangerous for vitality of the pulp while by increasing the critical temperature to 5.5° it is thought to create irreversible pulpal injury. The results of Klunboot et al.'s study on temperature effects of diode laser on pulpal tissues during bleaching of the teeth revealed that in diode lasers with a wavelength of 808 nm, a power of 1.5 W is the highest power in which change in the pulp temperature still remains below the safety range of 5.6°C and also can be effective for bleaching the teeth.
Umana et al. studied dentinal tubules sealing by means of diode lasers (810 and 980 nm) with powers of 0.8, 1, 1.6, and 2 W for irradiating 24 third molars, from a distance of 1 mm for 10 s. Their results revealed that applied lasers with powers of 0.8 and 1 W both could be used for sealing dentinal tubules and were harmless to the health of the pulp. According to a study done by Liu et al. on the treatment of dentin hypersensitivity by 980 nm diode laser, lasers with power outputs of 2 W sealed the exposed dentinal tubules effectively without creating any significant morphological change in the pulp and odontoblasts.
Since a major factor in the durability of composite restorations is the power of their bonding to the tooth structure, methods which let resin penetrate more in the tooth structure can help in this connection. Given that in previous studies, the effect of various methods of increasing substrate temperature, washing water temperature, and warming of adhesives and composites have been investigated and so far, no study has been done on heating teeth and bonding agents with laser for increasing the penetration of bonding agents, we decided to evaluate the effect of diode lasers with various powers on the shear bond strength of composite to dentin in an in vitro study. The null hypothesis in this study was using 808 nm diode laser before and after applying a bonding agent does not have an effect on shear bond strength of composite to dentin.
| Materials and Methods|| |
In the present study, 35 healthy human third molars extracted in a time period of 3 months before the onset of the study were selected, and study performed after obtaining consent form from the patients. The teeth had no decay, restoration, crack and specific erosion on the occlusal surface.
After extraction, they were immediately kept in thymol 0.2% solution at room temperature (23°C) for 1-week. Then, the crown and root surfaces of teeth were cleaned from any plaque and soft and hard tissue and kept in distilled water until the testing time. The sample teeth were placed in orthodontic acrylic resin (Orthoresin, Dentsply, England) in a way that a small area of the middle third of the buccal and lingual surface enamel was out of acryl so that the dentin surface would not be contaminated by resin during grinding of buccal and lingual surface. After uniform removal of the enamel using water-cooled Abrasive Wheel (Ecomet III Grinder, Lake Bluff, IL, USA), the exposed dentin surface was ground flat with 600 grit silicon carbide paper below the water flow to create standard smear layer.
The prepared samples were randomly divided into seven groups of 10 each and after tagging were stored in distilled water at room temperature. In the first group, the tooth surface was first etched by acid etch (ultra-etch 35%, Ultradent, USA) for 15 s. Then, each tooth was rinsed with water for 15 s, and the moist surface was blotted with tissue paper so that without accumulation of water, a surface of moist dentin remains for bonding. Then, the dentin bonding system of Prime and Bond NT (Caulk/Dentsply, England) with Acetone solvent was used, as recommended by the manufacture. The bonding was placed on the dentin surface with an applicator tip and the surface remained wet for 20 s. Then, the surface was air dried for 5 s and the bonding agent was placed on the surface in the same form for the second time and after air drying, it was exposed to LED light cure (Litex 695c, Dent America, Taiwan) with an output of 600–800 mW/cm 2 for 20 s. Then, a plastic cylinder (Sinateb, Iran) with a height of 3 mm and diameter of 2 mm which had been convexly prefilled with A2-shade composite (Filtek Z250, 3M ESPE, USA), to prevent bubble accumulation, was placed on the middle third of the dentin. The surface of the tooth was then cured for 40 s. In second and third group, one dental surface of the teeth were etched, washed, and dried with tissue paper and the desired area tagged. Then, gallium-aluminum-arsenide diode laser (doctor smile, pulse duration: 10 ms, pulse mode: Continuous wave, Italy) with a wavelength of 808 nm, fiber diameter of 600 μm, power of 0.5 W and from the distance of 1 mm from dentin surface was rotationally radiated after installing the laser hand-piece on the specific base and adjusting it perpendicularly on the surface for 20 s [Figure 1] and the bonding agent of Prime and Bond NT was used the same way as for group I, and the cylinder which was filled with composite, was bonded and cured.
On the other surface of the teeth, after etching, washing and drying, the bonding agent was applied similar to group I, with the difference that before its curing, diode laser of 808 nm with the power of 0.5 W and distance of 1 mm from the dentin surface was perpendicularly radiated on the surface for 20 s and then, the bonding agent was exposed to light and the cylinder which was filled with composite, was bonded and cured.
In the fourth and fifth groups, the applied method was similar to the previous groups; however, diode laser with the power of 1 W was used. In the sixth and seventh groups, diode laser with the power of 1.5 W was radiated on middle third of dentin before and after applying the bonding agent and the cylinders which were filled with composite were bonded and cured. Plastic cylinders were separated from the composite by making two vertical cuts in the cylinder and effort was made to enforce the least possible stress on the cylinders. After removing plastic cylinders, samples were stored in distilled water and incubator (Behdad, Iran) for 24 h at a temperature of 37°C.
Their shear bond strength was tested with Instron device (Dartec, Series HC10, England). The samples were fixed in the fixed jaw, the device head was placed parallel to the moving jaws in the direction of the force vertex, and perpendicular to the interface of the composite and dentin as far as possible [Figure 2].
Shear force with the loading rate of 0.5 mm/min was applied on samples up to the fracture time of the composite cylinders. The data for each group were recorded in terms of Newton and according to the surface area of the composite cylinder, the rate of applied force was converted in MPa. The obtained data were statistically analyzed by SPSS version 20 (Version 20.0. Armonk, NY: IBM Corp) using ANOVA and least significant difference (LSD) test.
| Results|| |
The results of studying the shear bond strength of composite bonded to dentin without laser irradiation and with three laser power levels before and after applying the bonding agent are provided in [Table 1]. ANOVA results showed that the mean shear bond strength of composite bonded to dentin had a significant difference in various groups (P < 0.001). LSD post-hoc test provided two by two comparisons of groups which are presented in [Table 2].
|Table 1: The mean shear bond strength of composite to dentin in various groups|
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|Table 2: P values of two by two comparisons of the groups with each other|
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According to the LSD test, shear bond strength of composite bonded to dentin in the control group was superior with a significant difference over the other groups (P < 0.001). Furthermore, at each laser power (0.5, 1 and 1.5 W), where it was applied before and after applying the bonding agent, the comparison of the shear bond strength of composite bonded to dentin revealed that in each of the three laser power levels, the shear bond strength of the group with laser radiation before applying the bonding agent was significantly higher than the group with the laser radiation after applying the bonding agent (P < 0.05). On the other hand, the LSD test showed that, the bond strength of composite to dentin with diode laser radiation of 1 W before applying the bonding agent had no significant difference with diode laser radiation of 0.5 W after applying the bonding agent (P = 0.78). Furthermore, comparing the bond strength with laser radiation of 1.5 W before applying the bonding agent and 1 W after applying the bonding agent revealed no significant difference (P = 0.86).
| Discussion|| |
By increasing the use of composite resins as tooth materials in anterior and posterior teeth, in different fields, several studies have been done in various conditions of applying these materials, the results of which lead to a higher bond strength, and lower micro-leakages in composite restorations in clinical conditions.
In the previous studies, the effect of temperature on the dentin bonding agent, the effect of air temperature on evaporating solvent, the effect of environment temperature on bond strength and temperature effect on composites were investigated.,,,
It should be explained that by reviewing databases before doing this study, no record of similar studies with the same methodology were found; it is thus not possible to compare the results with similar studies while compared with studies that are in line with the present study in some respect, the following points are in order: The present study didn't support our null hypothesis. In this study, a diode laser of 808 nm with power levels of 0.5, 1 and 1.5 W was applied on the dentin before and after applying the bonding agent for 20 s assuming that the temperature change created on the surface with the laser is capable of changing the properties of the dentin surface in reaction to the bonding agent.
Meanwhile, each power level was used on the two surfaces of each tooth and at a certain time so that the desired power could be assessed without confounding factors in the substrate. In this study, the shear bond strength test was also used because it is the most common method of evaluation of the bond strength and is easily comparable with other studies. The laser wave length determines the absorption rate and interaction with tissues. While a wavelength of 980 nm is more absorbed by water, a wavelength of 810 nm is more absorbed by melanin. More absorption of the diode laser of 980 nm in the dentin water shows less increase in the pulp temperature, compared to a diode laser of 810 nm.,,
Part of the energy absorbed by the mineral structures of dentin, such as phosphate and carbonate, disarranges the order of crystal alignment, because of thermo-mechanical destruction and thus causes to melt the dentinal tissue., These changes are more severe in using higher power levels.
According to Zach and Cohen's study, increasing the pulp temperature to 5.5°C led to irreversible pulp damage in 15% of monkey's teeth. When the pulp temperature increased to 11.1°C, 60% of the teeth developed irreversible pulpitis, and by increasing the temperature to 16.6°C, 100% of the teeth suffered from necrosis. According to Sulieman et al., increasing the pulp temperature to 5.5°C is considered as the threshold value beyond which leads to irreversible pulp damage.
Based on results of Umana's study, a diode laser with wavelengths of 810 and 980 nm and power levels of 0.8 and 1 W can cause closing or narrowing the dentinal tubules without fissures or cracks. Higher energy density (1.6 and 2 W) causes damage to the dentin surface and, therefore, causes pulp damage. Therefore, it seems that using laser for heating the surface decreases the penetration of the bonding agent by creating morphological changes in the dentin more than making useful changes in the surface for increasing the bond strength.
Liu et al. studied the morphological changes created in dentin after the radiation of diode laser of 980 nm with power levels of 2, 3 and 4 W for 5 s by scanning electron microscopy and concluded that more dentinal tubules occluded with increase in power levels of laser. In the present study, to select the safe power levels of laser for the pulp, studies on the effect of the diode laser on desensitizing of dentin were used. Heat, light and laser are often applied to increase the temperature of the bleaching agent on the tooth surface. Heating of whitening agent leads not only to increase the pulp temperature but also to increase the penetration of peroxide of bleaching material to the pulp.,
Buchalla and Attin contend that faster penetration of the heated bleaching agent to the dentin tissue can explain the effect of faster bleaching of activated bleaching methods by heating in a short time span. In fact, light and heat affect the chemical bleaching agent (gel) instead of teeth and its pigment, and thus lead to increased effect of bleaching.
In this study, the idea of heating the bonding agent with laser for deeper penetration in tubules was obtained from evaluating the studies on the activity of bleaching agent (gel) by diode laser. Ceballos proposes that the destruction of dentin due to fusion of collagen fibrils together leads to lack of interfibrillar space and restricts infiltration of the resin in the dentinal interfibrillar spaces.
Based on the results of the present study, the highest shear bond strength of composite to dentin was obtained in the control group (nonlaser radiation) (34.3 MPa) indicating the decrease of shear bond strength of composite to dentin using laser can be due to partial closure of the dentinal tubules or lack of re-hydration of the laser radiated dentinal surface before applying the bonding agent. From among various power levels of the diode laser before bonding, the shear bond strength of composite to dentin in the 0.5 W (25.2 MPa) group was more significant than the 1 W (19.1 MPa) group; and it was more in the 1 W group than in the 1.5 W (12.2 MPa) group (P < 0.05) which is because of the effect of higher powers of the diode laser in blocking more dentinal tubules. Comparing various laser power levels before and after applying the bonding agent, in the group of radiated laser before applying the bonding agent with significant difference, shear bond strength of composite to dentin was more than that in the group of radiated laser after applying the bonding agent. It seems the bonding agent penetrates to acid etched surface and the dentinal tubules and between collagen fibrils as well as the control group. However, after radiating the laser, the surface of the prepared dentin suffers from: (a) Morphological disturbances that impede normal composite and dentin match, (b) a close adaptation of composite with the surface is not created well, and (c) possible presence of more bubbles in the interface may decrease bond strength of this group as compared to groups influenced by the laser before using the bonding agent. At that surface, although the dentinal tubules have relatively been closed, it can be said that better evaporation of the solvent and also a flat and uniform surface of the bonding agent gave the possibility of better bonding interface between composite and dentin with fewer bubbles and higher bond strength compared to the group undergoing laser radiation after applying the bonding agent.
Results of lower bond strength in the laser radiated groups after applying bonding agent compared to the groups in which laser was used before applying bonding agent, despite the wetness of the dentin surface, can be indicative of the insignificant role of lack of rewetting than probability of partial closure of the dentinal tubules in reducing the bond strength in the laser radiated groups before applying the bonding agent compared to the control group. However, application of electronic microscopes is essential to prove this hypothesis. It is also suggested to study factors that affect the increase of bond strength of resin-dentin simultaneously through simulated clinical states such as pulp pressure, inter-tubular fluid flow, and thermo-cycling.
| Conclusion|| |
The bond strength of composite to dentin with laser radiation was significantly lower than that of control.
| Acknowledgment|| |
We thank Akbar Hasanzadeh for his work during data analysis.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]