Morphological Analysis of the Resin–Dentin Interface in Cavities Prepared with Er,Cr:YSGG Laser or Bur in Primary Teeth

Abstract

Objective: The purpose of this study was to analyze the resin–dentin interface in cavities prepared with laser or bur in primary teeth. Background data: Erbium, chromium:yttrium–scandium–gallium–garnet (Er,Cr:YSGG) laser was expected to be an alternative cavity preparation method, enhancing surface alterations and producing morphological changes. Methods: Twenty extracted primary molar teeth were divided to four groups according to one of four cavity preparation and pretreatment regimens: Er,Cr:YSGG laser (G1), Er,Cr:YSGG laser+acid-etching (G2), bur (G3), and bur+acid-etching (G4). After applying composite resin to the cavities, the teeth were sectioned. The resin–dentin interface was analyzed under scanning electron microscopy (SEM) and ion analysis was performd with SEM-energy-dispersive X-ray spectroscopy (EDX) after immersion in ammoniacal silver nitrate solution. Results: In G1 and 2, the surfaces were wavy, and in G3 and 4, the surfaces were smooth. Microcracks were seen in some of the lased cavities. In G1 and 2, dentin tubules were exposed and there was lack of a smear layer. In G3, there were gaps and a smear layer in the resin–dentin interface, but no gaps or smear layer were observed in G4. In G2, the resin tags were increased, and some resin tags were broken in cavities, which were prepared with laser (G1 and 2). Conclusions: According to the results of this study, acid-etching was recommended after laser preparations, to have a better adhesion.

Introduction

C aries removal and the preparation of cavities with a high speed handpiece has some disadvantages. Drilling with high speed handpiece can cause thermal and pressure effects on the pulp, and these effects can lead to pain. The use of local anesthetics can solve these kinds of problems, but patients can have fears about the use of anesthetics. Also, when cavities are prepared with a high speed handpiece, excessive loss of enamel and dentin can be seen.^1,2

Laser is now established as a suitable device for the selective and precise removal of caries. Enamel and dentin can easily be removed by using lasers with different wavelengths.³ When lasers are compared with the high speed drill, they are shown to reduce the loss of healthy enamel and dentin, and present a painless and less fear-producing dental treatment for patients.^4

–8

Erbium-based lasers have been used in dental treatments, and the energy levels of these lasers have made some changes in the structure of the teeth. The changes in the structure of the teeth could help in the mechanical bond, in removing the smear layer, and in opening the dentin tubules. The Erbium-based lasers are able to cut enamel and dentin with the same efficiency and speed as the high speed drills. Another advantage of these lasers is that they stimulate the formation of a secondary dentin, have an antibacterial effect, and allow pain-free cavity preparation and caries removal without the need for anesthetics.^4,5,9

The Erbium, chromium:yttrium–scandium–gallium–garnet (Er,Cr:YSGG) laser system can be used for cutting both enamel and dentin, soft tissue procedures, hemostasis, and coagulation. It has been used for endodontic treatments, removal of the carious lesions, cavity preparation, increasing acid resistance of the enamel, removal of smear layer and debris, and root canal sealing. Some studies have suggested that the Er,Cr:YSGG laser allows a sufficient cutting and ablation with minimal or no thermal damage to adjacent tissue, and does not cause pulpal inflammations.^{10

–18} Compared with the conventional high speed drill, a similar Ca/P ratio and Knoop hardness number of the cavity floor were reported when lasers were used in cavity preparations.^{10

–18}

To date, there have been many investigations aiming to examine the morphology of the resin–dentin interface of various adhesive systems on flat dentin surfaces or cavities prepared with high speed drills in permanent teeth. However, a small number of studies have been made to determine the quality of Er,Cr:YSGG laser-prepared dentin surfaces for composite resin bonding in primary teeth. Therefore, the purpose of this study was to analyze and compare the resin–dentin interface in cavities prepared with Er,Cr:YSGG laser or bur in primary teeth. The tested null hypothesis was that there was no difference between Er,Cr:YSGG and bur preparation in terms of interfacial micromorphology, with or without acid-etching procedure.

Materials and Methods

Extracted human primary molars (n=20) were used in this study. The teeth were stored in distillated water and used within 1 month.

Cavity preparations

Ten teeth were selected randomly and class V cavities (3×2×1.5 mm) were prepared with Er,Cr:YSGG laser (Waterlase MD, Biolase Technology Inc., San Clemente, CA) on buccal and palatinal/lingual surfaces (Fig. 1A). The power output was set at 6.0 W (85–90% air and 80–85% water) for enamel and 3.5 W (70% air and 65% water) for dentine preparation. Therefore, 10 primary molar teeth were used and 20 cavities were obtained. Laser was used in a defocused mode with a working distance of 1.5–2 mm.

FIG. 1.

(A) Buccal and palatinal/lingual cavities. (B) Section types of the teeth (mesiodistally [1], buccolingually [2]). (C) Black arrow shows the analyzed area under scanning electron microscopy (SEM).

The remaining 10 teeth were used for the bur-preparation group; class V cavities were prepared with diamond bur (Shofu Inc., Kyoto, Japan) as in the laser group. Then, all palatinal/lingual cavities were acid etched, rinsed, and gently dried. Acid etching procedure was not performed on buccal cavities. Therefore, four groups were made.

Group 1 (G1): Er,Cr:YSGG laser

Group 2 (G2): Er,Cr:YSGG laser and acid etching

Group 3 (G3): Bur

Group 4 (G4): Bur and acid etching

Adhesive system and bonding procedures

Single Bond (Adper^™ 3M ESPE, St. Paul, MN) was applied to the cavities and light-cured with Hilux Ultra Dental Curing Light (600 mW cm², 450–520 nm, Benlioglu, Turkey), then a composite resin (Filtek^™ Z250, 3M ESPE, St. Paul, MN) were placed to the cavities according to the manufacturer's instructions. The composites were light cured for 20 sec and stored in distilled water for 24 h. The teeth were polished with flexible polishing disks, embedded into acrylic resin. All teeth was sectioned in the x and y direction with a slow speed saw (Mecatome T201 Presi, France) under water cooling to obtain 1×1 mm sticks from the center of the cavities (Fig. 1A–C). The sticks were immersed in ammoniacal silver nitrate solution for 24 h in a dark chamber. At the end of 24 h, the sticks were washed under water for 5 min and placed in photodeveloping solution for 8 h. The sticks were washed with running water for 5 min and stored in distilled water for 1 month at room temperature.

Scanning electron microscopy/ energy dispersive X-ray spectroscopy preparation (SEM-EDX)

After being embedded into acrylic resin, the sticks were polished with wet silicon carbide papers and finished with a diamond paste. After being conditioned with 5% phosphoric acid for 5 sec, the sticks were immersed in ethanol solution for 10 sec, coated with a thin layer of gold, and analyzed in SEM (Jeol 6060, Japan).

Results

In G1 and G2, the surfaces were wavy (Fig. 2), whereas the surfaces were smooth in G3 and G4 (Fig. 3). Microcracks were observed in some of the lased cavities (Fig. 2). In G1 and 2, the dentin tubules were exposed, and the lack of smear layer and gaps was noticeable in the resin–dentin interface (Fig. 4). In G3, there were gaps and a smear layer (Fig. 5), but in G4, there were no smear layer or gaps (Fig. 6).

FIG. 2.

Rugged surface and microcracks were observed in laser cavities (×250). CR, composite resin; D, dentin. Black arrow shows a microcrack.

FIG. 3.

A smooth surface was observed in a bur cavity (×250). CR, composite resin; D, dentin.

FIG. 4.

Note the exposed tubules. No smear or gap were observed (×2000). D, dentin; CR, composite resin.

FIG. 5.

Gaps and smear layer were observed in G3 (×2000). D, dentin; CR, composite resin.

FIG. 6.

No gaps or smear layer were seen in G4 (×3000). D, dentin; CR, composite resin.

In G2, there were increased resin tags (Fig. 7). In G1, there was a thinner hybrid layer, and in some parts, the absence of the hybrid layer was observed. The hybrid layer was thicker in G2 than in G4. Some resin tags were broken in cavities that were prepared with laser (with or without acid etching) (Fig. 8). In the acid-etched groups (2 and 4), the silver ions were seen not only in the hybrid layer but also in dentin tubules (Fig. 9).

FIG. 7.

Increased resin tags were noticeable in laser and acid etch group (×3000).

FIG. 8.

Some of resin tags were broken in G1 and 2. D, dentin; CR, composite resin.

FIG. 9.

Ag ions were in dentin tubules. D, dentin; H, hybrid layer; DT, dentin tubule; CR, composite resin.

Discussion

The null hypothesis was rejected. There were differences among the groups. Er,Cr:YSGG and bur preparation created differences in interfacial micromorphology regardless of acid etching procedure.

The elapsed time for cavity preparations in the use of the laser was longer than for the high speed drill, which corresponded to other studies.^17,19

The mechanism of Er,Cr:YSGG laser's ablation effect was attributed to the violent microexpansion of water droplets after efficiently absorbing the laser energy, subsequently forming hydrokinetic forces that could quickly ablate the dental hard tissues.²⁰ The reasons for the energy parameters that were used in this study were based on case studies. When dentin surfaces were irradiated >3.5 W (i.e., 4 or 4.5 W) microcracks were seen under SEM and a frequency of 20 Hz was set prefabricated and could not be changed, which were the reasons for selecting 3.5 W and 20 Hz energy parameters. Second, the roughest surface and the highest ablation efficiency were seen at the 80% air pressure level under SEM, and flattened surfaces were seen in other air pressure levels; therefore, 80% air pressure level was selected. Third, maximal water pressure level was selected to avoid charred or carbonated dentin surfaces. A scaly, irregular and rugged appearance of dentin was observed in G1 and G2 (Fig. 2). Absence of smear layer and exposed dentinal tubules were seen, and melting or carbonation was not seen in the selected energy parameters under SEM. The peritubular dentin protruding from the surrounding intertubular dentin was possibly the result of the higher mineral content and the lower water content of peritubular dentin.^18,21,22 Widened dentin tubule orifices were seen when acid was applied after Er,Cr:YSGG laser irradiation, because of removing the mineral content of the dentin. Flat surfaces were seen after acid etching.^18,23

Previous research has shown that Er,Cr:YSGG laser is an effective device for cutting dental hard tissues,^{3,4,7,14,15,17,20} and that the dentin surfaces prepared by Erbium-based lasers are similar in micromorphology.¹³ These surfaces were rough, irregular, and there is a lack of smear layer. In agreement with the authors, there was no smear layer, and opened dentin tubules were observed in the lased cavities; the resin–dentin interface was rugged in the laser groups because of the microexplosions produced by the laser.^18,24,25 The irradiation effect of the laser was affected by various factors, such as variations in the energy level, frequency, and time of application, all of which might have caused microcracks in the dentin surfaces.²⁶

In G3, gaps and a smear layer were seen. However, no gaps or smear layer was observed in G4, possibly related to acid etching.

When single bond was applied to lased cavities, wider, shorter, funnel-shaped resin tags were seen, and they were greater in number when compared with the bur groups.

In the present study, gap formation was observed in the laser groups, and the reason for these gaps could be a result of collagen alteration. Benazzato and Stefani²⁷ reported that when air–water spray was used after laser ablation, it denatured dentinal collagen fibers in deep regions of dentin, and modified dentinal collagen structurally in the intertubular area. However, in the first portion of the dentinal tubules, collagen seemed to indicate a possible hybrid layer formation. On the other hand, De Munck et al.²⁸ observed that the adhesives bonded significantly less effectively to lased than to bur-cut enamel/dentin. The authors stated that the laser irradiation could inhibit hybridization, and had negative effects on the dentin/adhesive systems interface. Acid etching hampers the hybridization of dentin because applying acid after laser irradiation inhibits the provision of sufficient exposure of collagen fibers.^{24,29

–33}

Conclusions

In the present study, laser and bur cavities were performed in primary teeth. Based on the findings of this research, it may be concluded that acid etching was recommended after laser preparations, to have better adhesion.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

References

Hosoya

, Shinkawa

, Marshall

G.W.

2005. Influence of Carisolv on resin adhesion for two different adhesive systems to sound human primary dentin and young permanent dentin. J. Dent., 33:283–291.

Nor

J.E.

, Feigal

R.J.

, Dennison

J.B.

, Edwards

C.A.

1996. Dentin bonding: SEM comparison of the resin–dentin interface in primary and permanent teeth. J. Dent. Res., 75:1396–1403.

Marraccini

T.M.

, Wigdor

H.A.

, Walsh

J.T

Jr. , Stabholtz

, Zezell

D.M.

2005. Morphological evaluation of enamel and dentin irradiated with 9.6μm CO2 and 2.94μm Er:YAG lasers. Laser Phys. Lett, 11:551–555. onlinelibrary-wiley-com.web.bisu.edu.cn.

Jacboson

, Berger

, Kravitz

, Ko

2004. Laser pediatric Class II composites utilizing no anesthesia. J. Clin. Pediatr. Dent., 28:99–101.

Jacboson

, Berger

, Kravitz

, Patel

2003. Laser pediatric crowns performed without anesthesia: a contemporary technique. J. Clin. Pediatr. Dent., 28:11–2.

de FZ Lizarelli

, Moriyama

L.T.

, Bagnato

V.S.

2002. Ablation rate and micromorphological aspects with Nd:YAG picosecond pulsed laser on primary teeth. Lasers Surg. Med., 31:177–185.

Hadley

, Young

D.A.

, Eversole

L.R.

, Gornbein

J.A.

2000. A laser-powered hydrokinetic system for caries removal and cavity preparation. J. Am. Dent. Assoc., 131:777–785.

Yamada

, Hossain

, Suzuki

, Kinoshita

J.I.

, Nakamura

, Matsumoto

2001. Removal of carious dentin by Er:YAG laser irradiation with and without carisolv. J. Clin. Laser Med. Surg., 19:127–131.

Araujo

R.M.

, Eduardo

C.P.

, Duarte Junior

S.L.

, Araujo

M.A.

, Loffredo

L.C.

2001. Microleakage and nanoleakage: influence of laser in cavity preparation and dentin pretreatment. J. Clin. Laser Med. Surg., 19:325–332.

10.

Toomarian

, Fekrazad

, Sharifi

, Baghaei

, Rahimi

, Eslami

2008. Histopathological evaluation of pulpotomy with Er,Cr:YSGG laser vs formocresol. Lasers Med. Sci., 23:443–450.

11.

Hibst

, Keller

1989. Experimental studies of the application of the Er:YAG laser on dental hard substances: I Measurement of the ablation rate. Lasers Surg. Med, 9:338–344.

12.

Keller

, Hibst

. 1989. Experimental studies of the application of the Er:YAG laser on dental hard substances: II Light microscopic and SEM investigations. Lasers Surg. Med, 9:345–351.

13.

Harashima

, Kinoshita

, Kimura

, Brugnera

, Zanin

, Pecora

J.D.

, Matsumoto

2005. Morphological comparative study on ablation of dental hard tissues at cavity preparation by Er:YAG and Er,Cr:YSGG lasers. Photomed. Laser Surg., 23:52–55.

14.

Wang

, Zhang

, Matsumoto

2005. In vivo study of the healing processes that occur in the jaws of rabbits following perforation by an Er,Cr:YSGG laser. Lasers Med. Sci., 20:21–27.

15.

Eversole

L.R.

, Rizoiu

, Kimmel

A.I.

1997. Pulpal response to cavity preparation by an erbium, chromium:YSGG laser-powered hydrokinetic system. J. Am. Dent. Assoc., 128:1099–1106.

16.

Matsuoka

, Jayawardena

J.A.

, Matsumoto

2005. Morphological study of the Er,Cr:YSGG laser for root canal preparation in mandibular incisors with curved root canals. Photomed. Laser Surg., 23:480–484.

17.

Hossain

, Nakamura

, Tamaki

, Yamada

, Murakami

, Matsumoto

2003. Atomic analysis and knoop hardness measurement of the cavity floor prepared by Er,Cr:YSGG laser irradiation in vitro. J. Oral Rehabil, 30:515–521.

18.

Lee

B.S.

, Lin

P.Y.

, Chen

M.H.

, Hsieh

T.T.

, Lin

C.P.

, Lai

J.Y.

, Lan

W.H.

2007. Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin–resin interface. Dent. Mater., 23:570–578.

19.

Aoki

, Ishikawa

, Yamada

, Otsuki

, Watanabe

, Tagami

, Ando

, Yamamoto

1998. Comparison between Er:YAG laser and conventional technique for root caries treatment in vitro. J. Dent. Res., 77:1404–1414.

20.

Dederich

D.N.

, Bushick

R.D.

2004. Lasers in dentistry: separating science from hype. J. Am. Dent. Assoc, 135:204–212quiz 229.

21.

Lee

B.S.

, Lin

C.P.

, Hung

Y.L.

, Lan

W.H.

2004. Structural changes of Er:YAG laser–irradiated human dentin. Photomed. Laser Surg., 22:330–344.

22.

Lee

B.S.

, Lin

C.P.

, Lin

F.H.

, Lan

W.H.

2002. Ultrastructural changes of human dentin after irradiation by Nd:YAG laser. Lasers Surg. Med., 30:246–252.

23.

Fried

, Ashouri

, Breunig

, Shori

2002. Mechanism of water augmentation during IR laser ablation of dental enamel. Lasers Surg. Med., 31:186–193.

24.

Aranha

A.C.

, De Paula Eduardo

, Gutknecht

, Marques

M.M.

, Ramalho

K.M.

, Apel

2007. Analysis of the interfacial micromorphology of adhesive systems in cavities prepared with Er,Cr:YSGG, Er:YAG laser and bur. Microsc. Res. Tech., 70:745–751.

25.

Ekworapoj

, Sidhu

S.K.

, McCabe

J.F.

2007. Effect of different power parameters of Er,Cr:YSGG laser on human dentine. Lasers Med. Sci., 22:175–82.

26.

Delfino

C.S.

, Souza-Zaroni

W.C.

, Corona

S.A.M.

, Pecora

J.D.

, Palma–Dibb

R.G.

2006. Effect of Er:YAG laser energy on the morphology of enamel/adhesive system interface. Appl. Surface Sci, 252:8476–8481. www.journals.elsevier.com.

27.

Benazzato

, Stefani

2003. The effect of ER:YAG laser treatment on dentin collagen: an SEM investigation. J. Oral Laser Appl, 3:79–81. www.quintpub.com.

28.

De Munck

, Van Meerbeek

, Yudhira

, Lambrechts

, Vanherle

2002. Micro-tensile bond strength of two adhesives to Erbium:YAG-lased vs bur-cut enamel and dentin. Eur. J. Oral Sci, 110:322–329.

29.

Sassi

J.F.

, Chimello

D.T.

, Borsatto

M.C.

, Corona

S.A.

, Pecora

J.D.

, Palma–Dibb

R.G.

2004. Comparative study of the dentin/adhesive systems interface after treatment with Er:YAG laser and acid etching using scanning electron microscope. Lasers Surg. Med., 34:385–390.

30.

Barceleiro Mde

, de Mello

J.B.

, de Mello

G.S.

, Dias

K.R.

, de Miranda

M.S.

, Sampaio Filho

H.R.

2005. Hybrid layer thickness and morphology: the influence of cavity preparation with Er:YAG laser. Oper. Dent., 30:304–310.

31.

Bertrand

M.F.

, Hessleyer

, Muller–Bolla

, Nammour

, Rocca

J.P.

2004. Scanning electron microscopic evaluation of resin–dentin interface after Er:YAG laser preparation. Lasers Surg. Med., 35:51–57.

32.

Dunn

W.J.

, Davis

J.T.

, Bush

A.C.

2005. Shear bond strength and SEM evaluation of composite bonded to Er:YAG laser-prepared dentin and enamel. Dent. Mater., 21:616–624.

33.

Malta

C.M.

, Pelino

J.E.P.

, de Andrade

M.F.

, Lizarelli

R.F.Z.

2008. Bond strength of an adhesive system irradiated with Nd:YAG laser in dentin treated with Er:YAG laser. Laser Phys. Lett, 5:144–150. www.onlinelibrary.wiley.com.