Comparison of Er,Cr:YSGG Laser Handpieces for Class II Preparation and Microleakage of Silorane- or Methacrylate-Based Composite Restorations

Abstract

Objective: The aim of this study was to evaluate the influence of cavity preparation with different Er,Cr:YSGG laser handpieces on microleakage of different posterior composite restorations. Methods: Fifty-four extracted intact human premolars were randomly assigned to three groups according to cavity preparation method: Bur Group: high-speed diamond bur (Diatech), MD Group: Er,Cr:YSGG laser Waterlase MD handpiece (Biolase Millennium II), and Turbo Group: Er,Cr:YSGG laser Waterlase MD TURBO handpiece (Biolase Millennium II). One hundred eight Class II slot cavities were prepared on the mesial and distal proximal surfaces of each tooth, and the cavity preparation times required were determined. The groups were then subdivided according to the restorative systems used (n = 12): a conventional methacrylate-based microhybrid composite (Filtek P60+Adper Single Bond 2/3M); a silorane-based resin composite (Filtek Silorane+Silorane System Adhesive/3M); and a nanohybrid methacrylate-based composite (Kalore+G-Bond/GC). The restorative systems were applied according to the manufacturers' recommendations. Following thermocycling (X5000; 5°C–55°C), the teeth were coated with nail varnish except the restoration margins, immersed in 0.5% basic fuchsin dye solution, and sectioned in a mesiodistal direction. Dye penetration was evaluated under a light microscope for occlusal and cervical margins. Data were analyzed with one-way ANOVA and chi-square tests (p < 0.05). Results: The cavity preparation time (mean ± SD) required for Bur, MD, and Turbo group was 31.25 ± 3.82, 222.94 ± 15.85, and 92.5 ± 7.42 sec, respectively, and the differences among the groups were statistically significant (p < 0.05). Comparing the occlusal and cervical microleakage scores, no statistically significant differences were found among the groups and subgroups (p > 0.05). Conclusions: Er;Cr:YSGG laser cavity preparation with the Turbo handpiece needed shorter time than the MD handpiece, although it needed longer time than the conventional diamond bur. The use of different handpieces of Er,Cr:YSGG laser did not differ from conventional preparation with diamond bur in terms of microleakage with the tested methacrylate- and silorane-based posterior composite restorative systems.

Introduction

With the advance of modern technology, new equipment and esthetic restorative materials have been developed, leading to increased quality, more comfort, and patient acceptance of the dental treatments. During the past 15 years, the clinical applications of lasers have been a special focus of interest in dentistry.^1
–3 Although at the beginning, lasers were regarded as complex devices of limited use in dental applications, in time, researchers and clinicians have accepted the benefits of laser technology in modern dentistry, where they can be used as an adjunct or alternative to conventional methods.⁴

After the discovery of the erbium laser family (Er:YAG and Er,Cr:YSGG), these lasers have been approved by the Food and Drug Administration (FDA), and since then they were accepted as the optimal dental lasers for safe and effective preparation of dental hard tissues.⁵ When the Er,Cr: YSGG laser (2780 nm) is operated with air/water cooling, it has been shown that it cuts dental hard tissues effectively and clearly without thermal damage, due to this wavelength's high absorption both in water and hydroxyapatite. Surface modifications of the tooth tissues after Er,Cr:YSGG laser preparation exhibited an irregular and rough topography without smear layer.⁶ In addition to these surface properties that may be beneficial for further bonding procedures, cavity preparation with ErCr:YSGG laser has some clinical advantages in comparison with conventional high-speed handpieces, such as minimal vibration, minimal or no need for local anesthesia, and bactericidal effect that eliminates the need for cavity disinfection and selective caries removal.⁷

Although the Er,Cr:YSGG laser is reported to remove hard tooth tissues comparable with the conventional diamond burs,⁸ its ablation effectiveness needs to be improved to enable faster and more precise cavity preparations. The ablation capacity of the Er,Cr:YSGG laser depends on various factors such as energy density on the surface, spot size, focal distance, pulse duration, emission mode, frequency, structural properties of the tissue, and amount of water during irradiation.⁶ Besides the tuning of proper laser parameters, laser handpieces and tips used with the laser system directly affect the spot size, focal distance, and output energy density of the laser beam. The transportation rate of laser power also depends on the laser tips, which can affect the efficiency of the reduction.⁹ Thus, appropriate handpiece and tip selection is of great importance to achieve a successful (faster, precise, less thermal side effect) cavity preparation with lasers.

Restoration of the caries cavities and damaged tooth tissues in a minimally invasive manner with strong, esthetic, reliable, and long-lasting restorative materials is one of the main goals of today's dentistry. In the past decade, a dramatic improvement in newer generation adhesive systems and composite resin formulations has occurred. The improved physical properties of composite resins and the increasing demand for esthetics are encouraging more clinicians to select these materials for posterior restorations as well as anterior regions. Despite their popularity and improvements, conventional composite resins still have several shortcomings that limit their performance. Their major disadvantage is polymerization shrinkage and its associated stresses.¹⁰

Polymerization shrinkage stresses that occur at the cavity wall and restoration interface may cause cuspal deflection, microfractures in the tooth, and marginal gap formation, which may result in marginal leakage, bacterial invasion, pulpal irritation, postoperative sensitivity, and secondary caries and decrease the longevity of restoration. To overcome shrinkage stresses, new resin composite formulations have been introduced. Among those low shrinking materials, a cationic ring opening monomer system, the so-called silorane-based resin composite, and a methacrylate-based nanosized hybrid resin composite, containing high-density radiopaque prepolymerized fillers with a recently developed polymer technology (DX-511), have gained special interest because of their unique chemical properties.^11,12 Therefore, the purpose of this study was to evaluate the influence of cavity preparation with different Er,Cr:YSGG laser handpieces on microleakage of low shrinking silorane-based or methacrylate-based nanohybrid posterior composite resin restoration systems in Class II cavities.

Materials and Methods

Fifty-four intact human premolars extracted for orthodontic reasons at Hacettepe University, School of Dentistry, Department of Maxillofacial Surgery, were collected and cleaned with pumice under water cooling. Following the disinfection in aqueous-buffered formalin solution for 2 h, the teeth were stored in distilled water at room temperature until use. They were then randomly assigned to three groups according to cavity preparation methods (n = 18 teeth and 36 slot cavities). Minimally invasive Class II slot cavities were prepared on both the proximal surfaces of each tooth. Preparation time needed for each cavity was recorded.

Bur group

Cavity preparations were made using a conventional high-speed handpiece in combination with #836R cylinder diamond burs (Diatech Dental AG, Heerbrugg, Switzerland), which have 1 mm head diameter and 6 mm head length under water cooling. After every five preparations a new bur was used.

MD group

Cavity preparations were made using an Er,Cr:YSGG laser (Biolase Millennium II; Biolase Technologies, San Clemente, CA) Waterlase MD handpiece in combination with an MG6 sapphire tip 6 mm long and 600 μm diameter. The beam with a spot size of 600 μm diameter was aligned vertically to the target tissue at a distance of 1–1, 5 mm and moved in a sweeping motion using a noncontact focus mode. The parameters used for cavity preparation were 5 W, 20 Hz, 140 μs, 60% water, and 70% air.

Turbo group

Cavity preparations in this group were made using an Er,Cr:YSGG laser (Biolase Millennium II, Biolase Technologies) Waterlase MD TURBO handpiece in combination with an MX5 fiber tip with a spot diameter of 500 μm in focus distance. The laser beam was aligned vertically to the target tissue at a distance of 3–5 mm and moved in a sweeping motion using a noncontact focus mode. The parameters used for cavity preparation were 5 W, 20 Hz, 140 μs, 60% water, and 70% air.

The buccolingual width of all cavities was 2.5 mm and the gingival margins were located on the cementoenamel junction (CEJ). The buccal and lingual walls were prepared approximately parallel and their connections to the gingival floor were rounded. The axial depth of the cavities was 1.5 mm and there were no bevel preparations on the margins.^13,14 The cavity standardization was performed by measuring the cavity dimensions with the help of a millimeter-scale periodontal probe.

A Tofflemire matrix was placed to allow building up of the proximal walls. Then the groups were subdivided according to the restorative systems used (n = 12).

P60 subgroup

Twelve cavities in six teeth of each group were restored with a standard conventional methacrylate-based microhybrid composite (Filtek P60/3M ESPE) in combination with an etch-and-rinse adhesive (Adper Single Bond 2/3M ESPE). The entire cavities were dried with oil-free air, etched with 37% phosphoric acid (30 sec for enamel, 15 sec for dentin), and rinsed with water for 10 sec. Excess water on the cavities was removed by the help of a tissue paper. Then, 2–3 consecutive coats of adhesive were applied to enamel and dentin for 15 sec with gentle agitation, air thinned for 5 sec, and light cured with a high-intensity LED device emitting 1500 mW/cm² output power (Radii Plus, SDI, Bayswater, Australia) for 10 sec. Consequently, Filtek P60 composite resin was applied as two layers by light curing each layer for 20 sec.

Silorane subgroup

Twelve cavities in each group were restored with a silorane-based resin composite (Filtek Silorane/3M ESPE) in combination with its self-etch adhesive system (Silorane System Adhesive/3M ESPE). Silorane System Adhesive self-etch primer bottle was shaken briefly before use. The primer was applied to all cavity surfaces and massaged for 15 sec. A gentle air flow was used until the primer was spread to an even nonmoving film and light cured for 10 sec. Then, the Silorane System Adhesive-bond bottle was shaken, the bond was applied to the all cavity surfaces, and light cured for 10 sec. Filtek Silorane composite resin was applied as two layers by light curing each layer for 20 sec.

Kalore subgroup

The remaining12 cavities in each group were restored with a nanohybrid methacrylate-based composite (Kalore/GC) in combination with a self-etch adhesive (G-Bond/GC). G-Bond adhesive was applied to the entire dried cavity, left undisturbed for 5–10 sec, dried thoroughly under air pressure for 5 sec, and light cured for 10 sec. Consequently, Kalore composite resin was applied as two layers by light curing each layer for 20 sec.

The restorative systems were applied by strictly following the manufacturers' recommendations (Table 1). After 24 h of storage in distilled water, the restorations were finished and polished using polishing disks (Sof-LexTM; 3M ESPE). The teeth were thermocycled for 5000 cycles (5°C–55°C), with 30-sec dwell time. After covering the apex of each tooth with epoxy resin, the entire tooth surfaces except for the restoration sites, including 1 mm around the restoration margins, were sealed with nail varnish. After being sunk in 0.5% basic fuchsin solution for 24 h, the specimens were washed with running water and sectioned in the mesiodistal direction with the help of a low-speed diamond saw (EXAKT/EXAKT Technologies, Norderstedt, Germany). The specimen sections were observed with a stereomicroscope ( × 20 magnification; Nikon SE, Tokyo, Japan) and the dye penetration levels were scored for occlusal and cervical walls by a single operator.¹³

Table 1.

Materials Used in the Study

Material (manufacturer)	Composition	Application
Adper single bond 2 (3M ESPE)	Bis-GMA,HEMA, dimethacrylates, polyalkenoic acid copolymer, initiator, water, ethanol	Etch with 37% phosphoric acid for 15 sec, rinse with water for 10 sec, and remove excess water with the help of a tissue paper. Apply 2–3 consecutive coats of adhesive to etched enamel and dentin for 15 sec with gentle agitation, gently air thin for 5 sec, and light cure for 10 sec.
Filtek P60 (3M ESPE)	Filler: 61 vol% silica/zirconia filler (mean particle size of 0.6 μm) Polymeric matrix: Bis-GMA, Bis-EMA, UDMA TEGDMA	Apply a maximum layer of 2 mm. Light cure for 20 sec.
Silorane system primer and silorane system adhesive (3M ESPE)	Silorane system adhesive self-etch primer: phosphorylated methacrylates, Vitrebond™ copolymer, BisGMA, HEMA, water, ethanol, silane-treated silica filler, initiators, stabilizers, silorane system adhesive bond: hydrophobic dimethacrylate, phosphorylated methacrylates, TEGDMA, silane-treated silica filler, initiators, stabilizers	Apply the primer to the entire surface of the cavity and massage for 15 sec. Use a gentle stream of air until the primer was spread to an even film and did not move any longer. Light cure for 10 sec. Apply the bond to the entire cavity and light cure for 10 sec.
Filtek silorane (3M ESPE)	Silorane resin, initiating system: camphorquinone, iodonium, salt, electron donor, quartz filler, yttrium fluoride, stabilizers, pigments	Apply a maximum layer of 2 mm. Light cure for 20 sec.
G-Bond (GC)	Acetone, distilled water methacryloxyethyltrimellitate anhydride urethane dimethacrylate, triethyleneglycol dimethacrylate	Apply the adhesive to the prepared enamel and dentin surfaces using the microtip applicator, leave undisturbed for 5–10 sec, dry thoroughly for 5 sec under maximum air pressure. Light cure for 10 sec.
Kalore (GC)	Urethane dimethacrylate, DX-511 co-onomers, dimethacrylate, fluoroaluminosilicate glass, pre-polymerized filler, silicon dioxide, photo initiator, pigment	Apply a maximum layer of 2 mm. Light cure for 20 sec.

Occlusal wall dye penetration scores

Dye penetration cannot be observed on the restoration–tooth interface.

Dye penetration observed on the restoration–tooth interface only on enamel.

Dye penetration observed on the restoration–tooth interface beyond the dentino-enamel junction.

Dye penetration observed on the restoration–tooth interface up to the pulpal wall.

Cervical wall dye penetration scores

Dye penetration cannot be observed on the restoration–tooth interface.

Dye penetration observed on the restoration–tooth interface up to half the cervical wall.

Dye penetration observed on the restoration–tooth interface more than half the cervical wall.

Dye penetration observed on the restoration–tooth interface on the entire cervical wall reaching up to the axial wall.

Data were then subjected to one-way ANOVA or chi-square tests for statistical evaluation (p = 0.05) by using the SPSS 12.0 Software for Windows (SPSS, Inc., Chicago, IL).

Results

The cavity preparation times needed for the groups were significantly different (p < 0.05) (Table 2). Cavity preparation time with diamond bur was shorter than the Waterlase Turbo handpiece, whereas cavity preparation time with both diamond bur and Waterlase Turbo was longer than the Waterlase MD handpiece (p < 0.05). Cavity configurations seemed more precise in the bur group, whereas the laser-prepared cavities exhibited irregular outlines. The irregularities were more pronounced in the Turbo group in comparison with the MD group (Fig. 1).

FIG. 1.

Cavity configurations of each group.

Table 2.

Cavity Preparation Time (Mean ± SD) Required for Different Cavity Preparation Groups

Cavity preparation groups	Number of specimens	Cavity preparation time (sec)
Bur	36	31.25 ± 3.83^a
MD	36	222.94 ± 15.85^c
Turbo	36	92.50 ± 7.42^b

Different superscript letters indicate statistically significant difference (p < 0.05).

In the occlusal margin, 1 specimen in Bur-P60 and Bur-Kalore groups showed dye penetration into enamel. The restorations in the other groups did not exhibit any microleakage (Table 3).

Table 3.

Occlusal Wall Microleakage Score Distributions of the Groups

	Bur			MD			TURBO
Groups	P60 (n = 12)	Silorane (n = 12)	Kalore n = 12)	P60 (n = 12)	Silorane (n = 12)	Kalore (n = 12)	P60 (n = 12)	Silorane (n = 12)	Kalore (n = 12)
Microleakage scores	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall	Occlusal wall
0	11	12	11	12	12	12	12	12	12
1	1	0	1	0	0	0	0	0	0
2	0	0	0	0	0	0	0	0	0
3	0	0	0	0	0	0	0	0	0

In the cervical margin, Bur-P60, Bur-Kalore, Turbo-Silorane, and Turbo-Kalore groups were free of microleakage. One specimen in Bur-Silorane, MD-Kalore, and Turbo-P60 groups and two specimens in MD-P60 and MD-Silorane groups showed dye penetration into half the cervical wall. One specimen in the Turbo-P60 group exhibited microleakage on the complete cervical wall (Table 4). However, when the occlusal and cervical microleakage scores were compared, the differences among the groups and subgroups were not statistically significant (p > 0.05) (Fig. 2).

FIG. 2.

Representative photographs of each group after microleakage evaluation.

Table 4.

Cervical Wall Microleakage Score Distributions of the Groups

	Bur			MD			TURBO
Groups Microleakage scores	P60 (n = 12) Cervical wall	Silorane (n = 12) Cervical wall	Kalore (n = 12) Cervical wall	P60 (n = 12) Cervical wall	Silorane (n = 12) Cervical wall	Kalore (n = 12) Cervical wall	P60 (n = 12) Cervical wall	Silorane (n = 12) Cervical wall	Kalore (n = 12) Cervical wall
0	12	11	12	10	10	11	10	12	12
1	0	1	0	2	2	1	1	0	0
2	0	0	0	0	0	0	1	0	0
3	0	0	0	0	0	0	0	0	0

Discussion

Restoring posterior teeth with composite resin systems is a highly sensitive technique and the quality of the restorations can be affected by several factors, including cavity size, surface characteristics of the tooth tissues, properties of the composite and adhesive resin systems, use of incremental techniques, strong adhesion, and good marginal adaptation and seal.¹⁵

In case of insufficient adhesion, polymerization shrinkage may cause the creation of a gap on the adhesive interface. From this viewpoint, the use of low shrinking composite resin systems and handling cavity preparations with lasers have been suggested for more reliable adhesion on posterior region.¹² Therefore, the aim of this study was to evaluate the microleakage of low shrinking silorane-based or methacrylate-based nanohybrid posterior composite resin systems on Class II slot cavities, which were prepared with different Er,Cr:YSGG laser handpieces.

In the present study, minimally invasive Class II slot cavity design was preferred since it enables to effectively remove the caries lesion by preventing the intact tooth tissues from being sacrificed. However, the preparation of these cavities can be challenging due to difficulties in vision and control of moisture and bleeding at the gingival margins. In many instances, the quality of restorations is compromised due to inadequate preparation of the tooth. Besides, there is the risk of damaging the neighboring teeth with conventional diamond burs, as they are side and end cutting instruments. The use of Er,Cr:YSGG laser beam for cavity preparation is advantageous as it does not damage the surrounding tissues for being only end cutting.¹⁶ In addition, it is possible to selectively remove the carious tooth tissues and preserve the intact dentin by using adequate laser parameters, due to the high water content of caries lesion, which presents a strong thermomechanical interaction with Er,Cr:YSGG laser wavelength.¹³

In this study, the visual evaluation of the cavity sections revealed precise cavity shapes in cavities prepared by bur, whereas the cavity outlines were irregular in cavities prepared by laser. This was an expected finding as laser preparation occurs by microexplosions in water particles in the tissues or over the tissues supplied by water spray of the handpiece.¹⁷ This ablation process is typical of laser irradiation and gives the appearance of small circular depression-like cavities, so-called ablation craters, in the prepared surfaces.¹⁸ Comparing the laser handpieces, the ablation craters were deeper and narrower in cavities prepared by Turbo handpiece in comparison with cavities prepared with MD handpiece. This could be explained by the narrower focus diameter (500 μm) of the MX5 fiber tip used with Turbo handpiece, which transports higher energy density to the target tissue, when operated with the same settings (5 W, 20 Hz) in comparison with 600 μm MG6 sapphire tip used with MD handpiece.

There are many quantitative and qualitative methods to evaluate microleakage.^16,19 However, the basic fuchsin dye penetration test was utilized in the present study to assess microleakage, for it has been widely used, easily available, cheap, and nontoxic.²⁰

Surface modifications after Er,Cr:YSGG laser preparation such as irregular tooth surfaces, the absence of smear layer, open dentinal tubules, and intact enamel rods are suggested as positive factors that may improve the adhesion of composite resin systems.¹⁶ However, there are some controversies about the influence of Er,Cr:YSGG laser applications on microleakage in the literature. While some studies reported a decrease on the microleakage after Er,Cr:YSGG laser cavity preparation,^7,21,22 the findings of other studies did not indicate any significant difference on microleakage after Er,Cr:YSGG or conventional diamond bur preparation.^16,23,24 In this study, no significant differences were observed on microleakage in cavities prepared either with Waterlase MD or Waterlase Turbo handpieces, in comparison with conventional diamond bur. Although more irregular surfaces created by Turbo handpiece might be expected to be more suitable for better adhesion, the microleakage of cavities prepared by Turbo handpiece was not different from cavities prepared by MD handpiece.

In the present study, another aim was to compare the microleakage of two common low-shrinking composite resin systems with a conventional methacrylate-based microhybrid composite. It is known that the organic matrix of conventional methacrylate-based composite resins consist basically Bisphenol-A glycidyl methacrylate (BisGMA), as in the Filtek P60 composite resin system, used in this study. BisGMA is a very viscous material that has low conversion degree and high polymerization shrinkage compared with other monomers as a result of having high molecular weight, consisting backbone phenol groups, and high intermolecular reactions caused by hydroxyl groups.^11,25 Most conventional methacrylate-based composites are reported to shrink between 3% and 5% during polymerization.²⁶ To overcome this problem, low shrinking composite resin systems with new chemical properties were developed.^11,26 Filtek Silorane is one of those low shrinking systems unique with its chemical composition and oxirane ring-opening chemistry, also offering the advantage of increased hydrophobicity because of siloxane by which the insolubility of the restoration could be achieved in a humid oral environment.^27,28

GC Kalore is another low shrinking composite resin, which is the only composite resin system containing the special DX-511 monomer, with high-molecular-weight urethane dimethacrylate-based monomer, leading to decreased shrinkage because of having low reactive group concentration.^29,30 The molecular mass of DX-511 is reported to be about twice that of BisGMA, enabling DX-511 to exhibit a lower reactive site density per unit. For this reason, Kalore has lower polymerization shrinkage when compared with the conventional methacrylate-based composites.³¹ In the present study, microleakage evaluation of the tested posterior composites presented a sufficient marginal sealing ability on Er,Cr:YSGG- or bur-prepared minimally invasive Class II slot cavities, even on cervical margin, which is more critical for gap formation.

On clinical conditions, the gingival margins of the Class II cavities are mostly located on or below the CEJ, where the marginal sealing is questionable because of the absence of enamel tissue.³² In addition to weaker adhesion to dentin and cementum, the cervical margin is also more critical for gap formation between composite resin and the cavity walls due to polymerization shrinkage. Therefore, in this study, the cervical margins of the preparations ended on the CEJ, as those are most likely to leakage and there is a greater need for studies to obtain satisfactory restorations.³³ Supporting these concerns, Ozel et al.³³ evaluated the effect of two different restoration techniques on the microleakage of Er:YAG laser- or diamond bur-prepared Class II cavities and reported statistically higher microleakage values on cervical margins versus occlusal margins both in laser and diamond bur groups. On the contrary, Yazici et al.²⁴ compared the effects of Er,Cr:YSGG laser, chemical vapor deposition bur, and diamond bur cavity preparation methods on the microleakage of composite resin restorations and declared no significant differences on the cervical and occlusal microleakage scores neither on laser nor on bur groups. The results of the current study are in line with Yazıcı et al.'s²⁴ findings, as no statistically significant differences were observed when the occlusal and cervical microleakage scores were compared with the Er,Cr:YSGG laser and diamond bur groups. However, it is hard to compare the results of this study with the previous findings, because of the diversity in study designs, materials used, laser systems, and laser parameters.

Research on the best way to utilize Er,Cr:YSGG laser technology for restorative treatments is crucial to optimize the treatment potential and will allow broader usage of lasers. In addition, the efficacy of the current low shrinking composite resin systems has to be validated with further laboratory, scanning electron microscope and in vivo studies.

Conclusions

Depending on the findings of this in vitro study, the following conclusions could be drawn:

Cavity preparation time with Turbo handpiece of ErCr:YSGG laser was less than MD handpiece, although they both required more time than conventional diamond bur.

The use of both Er,Cr:YSGG laser handpieces resulted in similar microleakage trends with conventional diamond bur, when tested with the current composite resin systems.

Silorane-based and nanohybrid methacrylate-based composite systems used in this study revealed a sufficient marginal sealing ability on Class II slot cavities.

Footnotes

Acknowledgments

This work was supported by the Hacettepe University Scientific Research Coordination Unit.

Author Disclosure Statement

No competing financial interests exist.

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