Original Article

Effect of Er,Cr:YSGG and Nd:YAG Lasers on Microleakage of Composite Resin Restorations Using Universal Adhesives

Please cite this article as follows: Khamverdi Z, Rezaei-Soufi L, Sobhi Poor J, Ahmadi A, Javanrouh N. Effect of Er,Cr:YSGG and Nd:YAG lasers on microleakage of composite resin restorations using universal adhesives. Avicenna J Dent Res. 2023;15(3):81-86. doi: 10.34172/ajdr.487.

Background

Composite resins are widely used for tooth restoration due to their more conservative technique and high aesthetic. However, polymerization shrinkage, which is still their most important problem (1), can lead to debond the composite-tooth interface, thus causing microleakage in the restoration margins (2). If this process continues, it can be the main cause of composite resin restoration failure because of secondary caries, hypersensitivity, and pulp irritation/necrosis (3,4).

The presence of dentin bonding systems can provide sufficient bonding in the composite resin-tooth tissue interface. Nowadays, new types of bonding have been introduced, which are named universal adhesive systems based on the method of application and bonding strategy, which can act as both self-etching and total etching. Moreover, such bonding systems can be applied to enamel, surface and deep dentin, porcelain, amalgam, and metal (5,6). Regarding the versatility of these adhesives, clinical and laboratory studies on their clinical use and other aspects are increasing (7,8).

In recent years, lasers have found increasing applications in dentistry due to their many capabilities. Nd:YAG (wavelength = 1064 nm) and Er,Cr:YSGG (wavelength = 2780 nm) lasers are among the lasers that are commonly employed in dentistry. Due to the good absorption of these lasers by water and hydroxyapatite, their application on the tooth structure is highly useful because of the presence of water in dental tissues (9).

Several studies have evaluated the microleakage effect and adhesive nature of these lasers due to the change in the dentin surface, and most of them have focused on the bonding resistance of dentin adhesives, while fewer studies have been conducted on the rate of the marginal microleakage of composite materials using laser irradiation (10), reporting contradictory results. In their study, Subramaniam et al observed no significant differences between the microleakage rate of Class III cavities prepared by milling and cavities that were prepared by the Er,Cr:YSGG laser (11). In another study by Kawaguchi et al, laser radiation on the dentin surface did not affect the rate of the marginal microleakage of composite restoration (12). Likewise, Wen et al showed that the use of the Nd:YAG pulsed laser on the dentin surface, before the application of resin bonding, can significantly increase the tensile bond strength and reduce the microleakage (13). Obeidi et al also found that the use of the Nd:YAG laser can reduce composite resin restorations microleakage (14).

Universal bonding systems are versatile and have the ability to be used in different cavity conditions. Working on the best technique for the application of universal adhesives is still in its early stages (15). Due to limited information about the effect of laser application on universal adhesives, the present study sought to evaluate the effect of Nd:YAG and Er,Cr:YSGG lasers on the microleakage of composite resin Class V restorations using several universal bonding systems. The null hypothesis of this study indicated that laser application does not affect the microleakage of composite resin Class V restorations, regardless of the applied universal adhesives.

Materials and Methods

Specimen Preparation

For this in vitro study, 72 healthy human premolars that were extracted up to 3 months ago, were collected and kept in 10% formalin solution. The residual of soft tissues was removed with a scaler from the teeth. The teeth were placed into distilled water 24 hours before the test at room temperature. On the buccal and lingual surfaces, standard Class V cavities were prepared with 3 mm of mesiodistal width, 2 mm of height, and 1.5 mm of depth using a cylindrical diamond bur (Teeskavan, Tehran, Iran) and high-speed handpiece (SK, Fukushima, Japan). As a result, the margin of incisal and gingival was 1 mm above and 1 mm below the CEJ, respectively. Finally, the enamel margin of the samples was beveled using a taper diamond bur (Teeskavan, Tehran, Iran) with a 45-degree angle. Each bur was replaced after 5 cavity preparation processes. The dimensions of the prepared cavities were standardized using a periodontal probe. Each lingual or buccal cavity was considered as a specimen.

Adhesive Application and Laser Irradiation

Using True Random Number Service software (www.random.org), the samples were randomly divided into 9 groups (G1-9) based on the adhesive system and used laser (n=15):

G1 [GP]: G-Premio Bond; G2 [SU]: Scotchbond Universal; G3 [AB]: All Bond Universal

In each of these control groups, the adhesive was applied, according to the manufacturer’s instructions, to the prepared cavities and light cured for 10 seconds by a light cure LED device (Woodpecker, Guangxi, China) with a power of 850 MW/cm².

G4 [GP+Nd:YAG], G5 [SU+Nd:YAG], and G6 [AB+Nd:YAG]

In these groups, after the application of universal adhesives on the specimens, the Nd:YAG laser (Fotona, Ljubljana, Slovenia) was irradiated for 10 seconds on the entire surface of the cavities with a sweeping movement, and then light cured for another 10 seconds. The irradiation was performed in the noncontact mode with an optic fiber of 300 µm diameter tip in a perpendicular position to the target tissue and 5 mm distance from the tooth surface. The characteristics of Nd:YAG were wavelength of 1064 nm, extremely short pulse duration of 100 μs, frequency of 15 Hz, and power of 1 W (16).

G7 [GP+Er,Cr:YSGG], G8 [SU+Er,Cr:YSGG], and G9 [AB+Er,Cr:YSGG]

In these groups, samples were prepared and irradiated as in groups 4-6, except that Er,Cr:YSGG laser (Biolase, San Clemente, CA, USA) was used for these groups. The irradiation parameters of the Er,Cr:YSGG laser included wavelength of 2780 nm, frequency of 10 Hz, “H” Mode, pulse duration of 140 µs, power of 0.1 W, and spot size of 600 µm (17). Water spray was not used during laser irradiations.

Eventually, two layers of Filtek Z250 composite resin were placed in each cavity, and each layer was light cured for 20 seconds. Information on all three types of used adhesives and composite resin is presented in Table 1.

Microleakage Test

After completing the restoration, all groups were placed in a thermocycler (Nemo, Mashhad, Iran) under 3000 thermal cycles (between 55±2°C and 5± 2°C, 20 seconds), and then the apex of the teeth was covered with adhesive wax. Next, two coats of varnish were used to cover the teeth up to 1 mm beyond the margins of the restoration, and finally, all groups (1-9) were placed in a 2% methylene blue solution for 72 hours (11). Subsequently, the specimens were removed from the solution, rinsed with water, and dried for 2 minutes. Afterward, the teeth were mounted in a self-cured acryl (Kaveh, Tehran, Iran) and buccolingually sectioned by a cutting machine (Nemo, Mashhad, Iran) from the center of each restoration. Each section was observed by a stereo-microscope (Olympus, Tokyo, Japan) with 20x magnification. The rate of microleakage in gingival and occlusal margins was determined based on the following rating:

0 - No dye penetration

1 - Dye penetration to 1/3 of gingival/occlusal wall length

2 - Dye penetration to 2/3 of gingival/occlusal wall length

3 - Dye penetration along the whole gingival/occlusal wall length

Statistical Analysis

The data were statistically analyzed using SPSS software (version 21). Non-parametric Kruskal-Wallis and Mann-Whitney U tests were used for comparing the rates of microleakage. The level of significance was set at P<0.05.

Results

In the studied groups, the results related to the rate of microleakage are presented in Table 2. The lowest microleakage rate in the gingival margin was observed in group 6 [AB+Nd:YAG]. However, in the occlusal margin, the lowest microleakage rate was observed in group 8 [SU+Er,Cr:YSGG]. The results of the Kruskal-Wallis test demonstrated a statistically significant difference between the control groups, who received no laser, and the groups that used laser, in the rate of microleakage at both gingival and occlusal margins (P<0.001).

Table 3 provides data on the pairwise comparison of the studied groups. The pairwise comparison of groups in terms of the rate of microleakage revealed a statistically significant difference between the control group and the Nd:YAG and Er,Cr:YSGG laser groups regarding gingival and occlusal margins (Nd: YAG laser at the gingival margin P<0.019 and the occlusal margin P<0.001 and for the Er,Cr:YSGG laser at the gingival margin P<0.001 and the occlusal margin P=0.004). However, no significant difference was observed between the Er,Cr:YSGG and Nd:YAG laser groups in terms of the rate of microleakage at gingival and occlusal margins (P=0.092 and P=0.342, respectively).

Regarding the “bonding” factor, Kruskal-Wallis test results showed that the rate of microleakage using different adhesives was not significantly different at gingival and occlusal margins (P=0.989 and P=0.064, respectively). Based on the results of the Mann-Whitney test for the pairwise comparison of different groups in terms of the rate of microleakage, the microleakage rates at the gingival margin were statistically significant between G1 and G6, G2 and G6, G3 and G4-9, and G4 and G8 (P<0.05). Moreover, the microleakage rates at the occlusal margin significantly differed between G1 and G8, G3 and G5-9, and G4 and G8 (P<0.05). A general comparison between different groups with regard to the microleakage rate at gingival and occlusal margins revealed a statistically significant difference between the two margins (P< 0.001).

Discussion

As far as it is known, little information is available on the microleakage of composite restorations using universal adhesives. Accordingly, the present study was conducted to compare the two Nd:YAG and Er,Cr:YSGG lasers in terms of their effect on the microleakage rate of Class V composite resin restorations using universal adhesives.

There are various methods for assessing the rate of microleakage, including chemical detectors, organic tracer dye penetration, thermocycling, color-producing microorganism, radio-active isotopes, air pressure, neutron activation, scanning electron microscopy, and electrical conductivity (18). The dye penetration is the most widely used method for investigating the microleakage of composite restorations and adhesives. This method is economical, convenient, and safe, requires no special tools, and the depth of dye penetration can be easily observed with a stereo-microscope. In this method, colored materials such as methylene blue, Indian ink, purple crystal, eosin, fuchsin, erythrosine, fluorescein, and rhodamine B can be applied to assess the microleakage (19). Accordingly, 2% methylene blue was employed in this study, which has been previously used by Subramaniam et al (11) and Kapoor et al (20).

As high thermal changes occurred in the oral environment, a total of 3000 thermal cycles were utilized (according to ISO TR40 11405: 1994) for the simulation of clinical conditions in experimental situations (21). The effect of the Nd:YAG laser has been evaluated by numerous studies with different irradiation protocols (12-14,22,23). Thus, this laser was used as an available and efficient laser in restorative dentistry. Additionally, the Er,Cr:YSGG laser was employed with regard to its novelty and little information available in this respect. This laser has high absorption by hydroxyapatite and water and is proper for removing hard tooth tissues or preparing cavities on teeth (24).

According to the results of a study by Raskin, approximately 62.5% of microleakage assessment studies used Class V cavities (25). In microleakage studies, these cavities are often applied due to their high C factor and the possibility of the synchronous evaluation of enamel and dentin margins. On the other hand, universal bonding systems take advantage of new technology. These adhesives have facilitated the application process, leading to saving time and reduced errors in various application steps. Thus, universal adhesives (Scotchbond, all-bond, and G-Premio) were employed in the present study according to some previous studies (26,27).

The findings of the study demonstrated that the application of Er,Cr:YSGG and Nd:YAG lasers reduced microleakage in the studied groups. A significant difference was observed between the two laser groups and the group that was not exposed to lasers (control), and both laser groups had the same role in reducing microleakage. Therefore, this finding led to the rejection of the null hypothesis of the study. It seems that the use of laser causes a slight increase in reaction by an enhancement in the temperature of the bonding agent, increasing its penetration. Moreover, it reduces the microleakage by producing chemical and mechanical changes in the tooth structure (28).

These findings are consistent with the results of Wen et al (13), Obeidi et al (14), Navarro, and White, confirming the positive role of the Nd:YAG laser in reducing marginal microleakage (29,30). However, the research conducted by Kawaguchi et al (12), Subramaniam & Pandey (11), Matos et al (31), and Malta et al (16) showed that the irradiation of the Nd:YAG laser on dentin surfaces (before or after adhesive application) does not affect reducing the marginal microleakage of composite restorations.

The findings further indicated that the application of different universal bonding systems (SU, AB, and GP) did not have a significant effect on reducing microleakage. The presence of 10-MDP and 4-MET in the composition of all used universal adhesives may be the possible reason for the obtained result. 10-MDP and 4-MET are acidic functional monomers that can etch the dentin surface and chemically bond to the calcium (32). The pairwise comparison of different groups revealed significant differences between some groups, as previously mentioned in the results, in terms of the microleakage rate reduction at the gingival margin. The significant difference among G4 and G8, both of which received laser, seems to be related to the component of silane in the Scotchbond Universal adhesive composition, whereas the G-Premio bond does not contain it. The silane may cause better absorption when the adhesive is exposed to Er,Cr:YSGG laser radiation compared to radiation with the Nd:YAG laser. The rates of microleakage at the occlusal margin were significantly different between G1 and G8, G3 and G5-9, and G4 and G8. A greater reduction of microleakage is reported in the groups exposed to the laser due to the increase in temperature by the laser.

The comparison between the rates of microleakage at gingival and occlusal margins indicated that the rate of microleakage at the gingival margin is greater compared to the occlusal margin. The dentin structure has a heterogeneous nature with high contents of organic and water compared with enamel. Thus, the bond to dentin is not reliable while enamel creates a stronger bond to composite resin. This may be an explanatory reason for this result. However, beveling, which was performed for enamel margins, can reduce the microleakage (33). In this study, a specific protocol was considered for laser application. Different protocols may show a variety of effects. For future studies, it is recommended to apply different laser irradiation protocols with different powers. In this way, it is possible to extend the results of this study to all adhesives and achieve an optimal combination of laser and adhesive for resin composite restorations with a low rate of microleakage and long-term services.

Conclusion

Considering the limitations of this study, the irradiation of Nd:YAG and Er,Cr:YSGG lasers, after using the studied universal adhesives and before placing the composite resin, had a positive effect on reducing the microleakage of Class V restorations. Different adhesive systems and lasers, used in this study, did not affect the rate of microleakage.

Acknowledgments

The authors thank the Vice-chancellor for Research and Technology of Hamedan University of Medical Sciences for supporting this study.

Author’s Contribution

Conceptualization: Zahra Khamverdi.

Data curation: Zahra Khamverdi, Loghman Rezaei-Soufi.

Formal analysis: Niloufar Javanrouh.

Funding acquisition: Zahra Khamverdi.

Investigation: Ali Ahmadi.

Methodology: Zahra Khamverdi, Loghman Rezaei-Soufi.

Project administration: Zahra Khamverdi.

Resources: Ali Ahmadi.

Software: Niloufar Javanrouh.

Supervision: Zahra Khamverdi.

Validation: Zahra Khamverdi.

Visualization: Zahra Khamverdi, Loghman Rezaei-Soufi.

Writing–original draft: Jalil Sobhi Poor

Writing–review & editing: Zahra Khamverdi.

Competing Interests

The authors declare that they have no conflict of interests.

Ethical Approval

The present study was approved by the Medical Ethics Committee of Hamadan University of Medical Sciences, Hamadan, Iran (IR.umsha.REC.1396.128).

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