Sealing performance of resin cements before andafter thermal cycling: Evaluation by optical coherence tomography

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 9931004

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jo ur nal home p ag e: www.int l .e lsev ierhea l th .com/ journa ls /dema

Sealing performance of resin cements before andafter tcoher

Alaa TuYasunora Operative King Abdulab Cariology aUniversity, 1c Global COEDental Univd Division ofGerontology,

a r t i c

Article histor

Received 25

Received in

4 August 20

Accepted 21

Keywords:

Resin inlay

Resin cemen

Resin coatin

Adaptation

Optical cohe

CorresponE-mail a

http://dx.do0109-5641/hermal cycling: Evaluation by opticalence tomography

rkistania,b,c, Alireza Sadrc,, Yasushi Shimadab, Toru Nikaidob,i Sumid, Junji Tagamib,c

Dentistry Division, Conservative Dental Sciences Department, Faculty of Dentistry,ziz University, Jeddah, Saudi Arabiand Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan, International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo Medical and

ersity, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan Oral and Dental Surgery, Department of Advanced Medicine, National Center for Geriatrics and

National Hospital for Geriatric Medicine, 36-3, Gengo, Morioka, Obu, Aichi 474-8511, Japan

l e i n f o

y:

December 2012

revised form

13

May 2014

t

g

rence tomography

a b s t r a c t

Objectives. Self-adhesive resin cements have been recently introduced; however, there is

little data available on their long-term performance. In this in vitro study, swept-source

optical coherence tomography (OCT) at 1310 nm center wavelength was used for monitoring

adaptation of indirect resin restorations after thermal cycling.

Methods. Resin inlays were luted to class-I cavities of extracted human teeth using three

resin cements; Clearl SA Luting (SA; Kuraray), Bistite II DC or Multibond II (Tokuyama Den-

tal). Each cement was applied with or without pre-coating of dentin by a self-etch adhesive

(Clearl SE Bond) and a low-viscosity microlled resin. OCT imaging was performed after

24 h, after 2000 and after 10,000 thermocycles (n = 5). Selected samples were sectioned for

interfacial observation by confocal laser scanning microscope (CLSM). Floor adaptation (per-

centage) was analyzed by software on 20 B-scans throughout each specimen, and subjected

to statistical analysis by three-way ANOVA test at a signicance level of 0.05.

Results. Resin cement type, resin coating and thermal aging all signicantly affected

adaptation (p < 0.05). Initially, SA showed the highest adaptation; however, thermal aging sig-

nicantly affected its sealing. The best results for all the cements were consistently achieved

when the resin coating technique was applied where no deterioration of interfacial integrity

was observed in the coated groups. CLSM closely conrmed OCT ndings in all groups.

Signicance. OCT could be used for monitoring of composite inlays with several interfa-

cial resin layers. The application of a direct bonding agent in the resin-coating technique

improved interfacial sealing and durability of all resin cements.

2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

ding author. Tel.: +81 3 5803 2483; fax: +81 3 5803 0195.ddress: [email protected] (A. Sadr).i.org/10.1016/j.dental.2014.05.010

2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

994 d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 9931004

1. Introduction

The aestheingly popudevelopmeusing comption techniits placemelarge cavititechniquestour, fractuextra-oral fensures thaare conne

On the cements mdentin-bonThis may ato lower peing performcoating tecwhich DBSto seal deirritation astrength [6for the neself-adhesiself-adhesitation procneed of con[10,11].

Adhesioevaluation a restoratiothe dental are convenand sealindetecting dscope and/these meththey requirrecently, thhave beendental com(OCT) can pimages forlight backsposites andcan be suirestorationinvestigateare few rep

Thermative meanstheir interfimaging of aging appethe aim of thermal cyc

of indirect composite inlays luted with resin cements underOCT, and conrmation of OCT ndings by cross-sectional con-

aser wereealints; (2tegritty of

Ma

Sp

is stcks, ts in

Boach Eas reo exped by

the t. Roues byair tgraiere u, Kyplacy 4 mandoing t, dencoatchinental Proing d rsd waa conA, U

on tured

cavting ith Kura

usinwere

Thetatio.

prepn grgenoredte thAftertic aspect of dental treatment has become increas-lar in the recent years, especially with thent of improved materials and adhesive techniquesosite resins. The indirect composite resin restora-que involves extra-oral fabrication of an inlay andnt with a resin cement. It has been reported that fores, indirect restorations bear advantages over direct

such as improvements in anatomic form, con-re resistance and wear resistance [1]. Furthermore,abrication aids in the relief of residual stresses andt the negative effects of polymerization shrinkaged to the thin layer of resin cement [2].other hand, it is believed that the viscous resinay not provide dentin bonding comparable toding system (DBS) used for direct composite [35].ffect the sealing ability of these cements and leadnetration to tooth substrate and hence, lower bond-ances in comparison to DBS. Therefore, a resin

hnique for indirect restorations was introduced in and a low viscosity microlled resin are appliedntin surface after preparation, decreasing pulpnd postoperative sensitivity and improving bond9]. Meanwhile, the effectiveness of this techniquewly introduced resin cement products (such asve resin cements) has not been investigated. Theve resin cement is proposed to simplify the cemen-edure; it bonds to dentin in one step without theditioning or pre-treatment (priming) of the surface

n tests have been routinely used for laboratoryof these biomaterials. However, the success ofn also greatly depends on its sealing ability oftissue in an actual cavity [12]. Different methodstionally used to evaluate the marginal integrityg of restorations. The most common method isye penetration depth under a stereoscopic micro-or scanning electron microscope (SEM). However,ods are considered as destructive methods sincee sample sectioning, and may be subjective. Moreree-dimensional and in-depth imaging methods

introduced and utilized for characterization ofposites [1318]. Optical coherence tomographyrovide noninvasive, high resolution cross-sectional

biologic microstructures and materials based oncattering from within the structure. Dental com-

hard tissues are scattering media and thereforetable substrates for OCT imaging [1624]. Tooth-

interface under direct resin restorations has beend using this technique [18,19,21,25]; however, thereorts on evaluation of indirect restorations.l cycling procedure has been accepted as an effec-

of articially aging composite restorations to studyacial characteristics in the long-term. In this regard,resin restorations by OCT before and after thermalars to be an attractive research method. Therefore,this laboratory study was to evaluate the effect ofling and resin coating technique on the adaptation

focal ltestedfacial scemencial inintegri

2.

2.1.

For thof crapatienReviewResearture worder tremovaxis ofJapan)surfacspeed 50 m burs wSHOFUwas reimatelthen raccordgroup)(resin-self-ettake D(ClearAccordapplieSE bonusing Kerr, Cplacedlight c

Theseparalled wterior, for 40 sinlays for t.cemenricated

Thefaces inon-euand stsimulations. scanning microscopy (CLSM). The null hypotheses as follows: (1) there was no difference in the inter-g of the composites inlays between different resin) the resin coating could not improve the interfa-y; and (3) There were no changes in the interfacial

different test groups after thermal aging.

terials and method

ecimen preparation

udy, thirty extracted human third molars, freecaries and restorations were selected after theformed consent, as approved by the Institutionalrd of Tokyo Medical and Dental University, Humanthics Committee, protocol no. 725. The root struc-moved below the cement-enamel junction and inose a at dentin substrate; the occlusal thirds were

trimming the crowns at right angles to the longeeth using a model trimmer (Y-230; Yoshida, Tokyo,nd class I cavities were prepared on the at occlusal

using a cylindrical diamond bur attached to a high-urbine under water coolant (carborundum points,n size, SHOFU, Kyoto, Japan). Finishing diamondsed afterward to have a ne surface nish (SF114,oto, Japan). To maintain cutting efcacy, the bured every ve preparations. The cavity was approx-m in width and 2 mm in depth. The teeth weremly divided into two groups of fteen teeth eacho the surface treatment. For the rst group (controltin surface was kept untreated. In the second grouped group), the cavity surface was prepared using theg bonding system, Clearl SE Bond (Kuraray Nori-l, Tokyo, Japan) and a low viscosity microlled resintect Liner F, Kuraray Noritake Dental, Tokyo, Japan).to the manufacturers instructions, SE primer wast to the cavity for 20 s and gently air dried. Then,s applied; mildly air dried and light cured for 20 sventional halogen light curing unit (Optilux 501,SA; 550 mW/cm2). After that, Protect Liner F washe already cured adhesive surface with a brush and

for 20 s.ities in both groups were then lined (covered) with alm (Pechiney Plastic Packaging, Chicago, IL, USA),one increment of composite (Clearl Majesty Pos-ray Noritake Dental, Tokyo, Japan), and light curedg the light curing unit. After curing, the composite

carefully removed from the cavities and checked resin inlays were monitored under OCT prior ton and the defective ones were excluded and refab-

ared cavity surfaces in group 1 and the coated sur-oup 2 were both temporized with a water-settingol temporary lling material (Caviton EX, GC, Japan)

in an incubator at 37 C in a humid condition toe clinical situation for indirect composite restora-

24 h, the temporary lling material was carefully

d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 9931004 995

removed with a spoon excavator and surface was wiped witha cotton pellet containing ethanol for 10 s. The coated sur-faces weregel, rinsed

The tti37% phosphair dried. Twas applieair-dried.

Specimesubgroups Table 1 listsschematic

The resiwith self-ethe self-adtake Dentachemicallythree cemeinstruction

2.2. Th

All specimefor 24 h primens wereestimated tmately [26]dwell time 2 s betweenato Scientito OCT evathe resin re10,000 cycle

2.3. OC

A swept-soKomaki, Japof the optic20 kHz swedened by tivity of thi106 and 119is 11 m in a refractivedepends onthis study. microstructem, digitizdomain to system analight from 2-D image.

2.4. OC

Specimenstation, andrepeatabilit

holes were drilled on the specimen surface to make sure thatspecimens were placed at the same orientation as accurately

siblerder

on e reair dion [th susionst 20000

datagitalf Heavelos preure dicatal cg inte

adap

Con

rm ce, rectioluff, I0 A,(Sankze din OH/W

(632ion le

Sta

e staicallympaoc. Term

at e (ve

Re

entaand T siin th

and then cleaned for 10 s using 37% phosphoric acidand dried in order to remove any debris.ng surfaces of the resin inlays were treated withoric acid gel for 15 s, rinsed with water and gentlyhen, Tokuso Ceramic Primer (Tokuyama Dental)d as a silane coupling agent to the surface and

ns from each group were further divided into threeaccording to the type of luting resin cement used.

the materials used in this study while Fig. 1 showsdrawing for the sample preparation.n cements used in this study were the dual-curetching primer Bistite II DC (Tokuyama Dental),hesive Clearl SA Luting cement (Kuraray Nori-l, Tokyo, Japan) and the MMA-based self-etching-cured Multibond II (Tokuyama Dental). Each of thents was applied according to the manufacturerss.

ermocycling procedure

ns were then stored at 37 C in humid conditionor to the initial OCT imaging. Then, all the speci-

thermocycled for 10,000 cycles, which was roughlyo represent one year of clinical function approxi-. They were fatigued between 5 C and 55 C with aof 30 s in each temperature, and a transfer time of

baths (Cool Line CL200 and Cool Mate TE200, Yam-c Co., Tokyo, Japan). The specimens were subjectedluation to detect any changes in the adaptation ofstorations after 2000 cycles and after completings.

T system

urce OCT system (Santec OCT-2000, Santec Co.,an), was used in this study. The spectral bandwidthal source is over 100 nm centered at 1310 nm at aep rate. The probe power is within the safety limitsAmerican National Standard Institute. The sensi-s system and the shot-noise limited sensitivity are

dB, respectively. The axial resolution of the systemair, which corresponds to 7 m in tissue assuming

index of approximately 1.5. The lateral resolution the objective lens at the probe and was 17 m inBackscattered light carrying information about theture of the sample is collected, returned to the sys-ed in time scale and then analyzed in the Fourierreveal the depth information of the subject. Thelyzes the frequency components of backscatteredthe sample and creates real-time high resolution

T imaging and analysis

were subjected to serial 2D scans 24 h after cemen- after 2000 and 10,000 thermal cycles. To ensure they of the OCT scans for the same specimen, small

as posIn o

itionedsurfacusing conditthe toodimentions awas 20For thewas ditutes owas deprocesprocedness inThe tocoatin

Cavity

=(1

2.5.

To coninterfawere sLake B(ML-16paper ticle sia certa(1LM21sourcenicat

2.6.

For thstatisttiple copost-hand thformedpackag

3.

Represaging (SS-OCareas BT, SA. to capture OCT image, the specimen was pos-a metal stage with a 35 tilt to avoid peculiarections. The surface of the specimen was blot drieduster to standardize the tooth surface hydration22]. Then, the focus light beam was projected ontorface at 90 and scanned across the cavity in three

using OCT probe. In this manner, 20 serial 2D sec- m interval were obtained. The size of each image

1019 pixels corresponding to 5 mm 6.6 mm (x, z). analysis purpose, each of the 20 serial 2D sections

ly analyzed using ImageJ (ver. 1.42q, National Insti-lth, Bethesda, MD, USA). A custom computer codeped as a plugin for ImageJ based on a binarizationviously reported [13,21], to facilitate image analysisand distinguish pixel clusters with higher bright-ting gap or unsealed interface at the cavity oor.avity adaptation (including resin cement and/orrface) was calculated as

tation%gap length at all cross-sections

cavity oor length at all cross-sections

) 100

focal laser scanning microscopy (CLSM)

the presence or absence of gap at tooth-restorationandomly selected specimens after thermal cyclingned with low-speed diamond saw (Isomet, Buehler,L, USA) and then polished using polishing machine

Maruto, Tokyo, Japan) with silicone carbide (SiC)yo, Saitama, Japan) and diamond pastes with par-own to 0.25 m. The same interfacial location inCT cross-sectional slice was observed under CLSM, Lasertec Co., Yokohama, Japan) with a He-Ne laser.8 nm) and 0.1 mW maximum output power at mag-vels of 5001250.

tistical analysis

tistical analysis of the adaptation, the data were analyzed with three-way ANOVA followed by mul-risons using t-tests with Bonferroni corrections ashe factors were resin cement type, resin coatingal cycling. All the statistical procedures were per-signicance level of = 0.05 with using Statisticsr. 16 for windows; SPSS, Chicago, IL, USA).

sults

tive OCT images from each group after thermaltheir conrmatory CLSM images with A-scan

gnal intensity) proles plotted against selectede same cross-sections are shown in Figs. 24 for

MB respectively. There was a considerable loss of


Table 1 Materials used in this study.

Material(AbbreviaManufactLot no.

Dentin bonClearl SE

(SE)Kuraray N011595

rylateuidin

idal

Low-viscosProtect Lin

(PLF)Kuraray N0074DA

Resin cemeBistite II DC

(BT)Tokuyam028012

Clearl SA (SA)Kuraray N0141AA

Multibond (MB)Tokuyam0780Z1

Indirect resClearl Ma

(MP)Kuraray N00111A

Abbreviatioether dimelate, PMMA

signal intein the A-scwhich werean area of by interfaciwhile in ot(Figs. 2f, 3findicates grestorativeto light reOCT imageFigs. 2c, 3cimately 10tion)urer

Composition

ding systemBond

oritake Dental

Primer: MDP, HEMA, hydrophilic dimethacdl-camphorquinone, N,N-diethanol-p-tolwater.Bond: MDP, Bis-GMA, HEMA, hydrophobicdimethacrylate, dl-camphorquinone,N,N-diethanol-p-toluidine, silanated collosilica.

ity microlled resiner F Bis-GMA, TEGDMA, uoride-methyloritake Dentalmethacrylate, camphorquinone, silanizedcolloidal silica, pre-polymerized organic ller.

nts

a Dental

Primer 1 (A and B): phosphoric acid monomer,acetone, alcohol, water, initiator.Primer 2: HEMA, acetone, initiator.Resin cement pastes:Paste-A: NPGDMA, Bis-MPEPP, silica-zirconialler.Paste-B: MAC-10, silica-zirconia ller,benzoylperoxide, photo-initiator.

Luting

oritake Dental

Paste A: Bis-GMA, TEGDEMA, MDP, hydrophobicaromatic dimethacrylate, silanated barium glaller, silanated colloidal silica,dl-camphorquinone, benzoyl peroxide, initiatoPaste B: Bis-GMA, hydrophobic aromaticdimethacrylate, hydrophobic aliphaticdimethacrylate, silanated barium glass ller,silanated colloidal silica, surface treated sodiumuoride, accelerators, pigments.

II

a Dental

Primer: phosphoric acid monomer, water,acetone, UDMA, co-activator.liquid: MMA, UDMA, HEMA, MTU-6, boratecatalyst.powder: PMMA, co-activator.

in compositejesty Posterior

oritake Dental

Silanated glass ceramics, silanted silica ller,surface treated alumina microller, Bis-GMA,TEGDMA, hydrophobic aromatic dimethacrylatdl-camphorquinone.

ns: MDP: 10-methacryloyloxydecyl dihydrogen phosphate, HEMA: 2-hydrothacrylate, TEGDMA: triethyleneglycol dimethacrylate, MAC-10: methacryloy: poly methyl methacrylate, UDMA: urethane dimethacrylate, MTU-6: 6-me

nsity through the composite inlay as clearly seenan proles in Figs. 2e and f, 3e and f and 4e and f,

drawn by averaging the OCT signal intensity over150 m. Despite this attenuation, the peak causedal gaps was easily detectable in Figs. 2e, 3e and 4e;her areas (with no gap), no such peak was seen

and 4e and f). A bright area in the OCT imageap due to the presence of optical variation between

material, air in the gap and tooth structure leadingection [16]; areas with increased brightness ons were conrmed as gap by CLSM examination in

and 4c. Resin coating resulted in a layer approx-0 m in thickness and improved adaptation as

conrmed thermal cyhigh backscof the typespecimensbottom indothers, the(Fig. 4a). Oresin-coatefrom the in

The meresin cemestandard dProcedure

,e,

Apply the primer for 20 s.Mild air blow.Apply adhesive and air blow gently.Light cure for 10 s.

Apply in a thin layer, light cure for 20 s.Apply primer 1A + 1B, leave for 30 s, air dry, applyprimer 2, leave for 20 s, air-dry, place mixedpaste A + B, light cure for 20 s.

ss

r.

Apply the cement paste mix to the restoration,place the restoration.Light cure for 25 s, and then remove the excesscement.Light cure for 20 s.

Apply primer for 20 s and gently air dry for 10 s.Powder: liquid: 1:3Mix for 5 s, apply to dentin surface.

e,

Bulk lling and light cure for 40 s.

xyethyl methacrylate, Bis-GMA: bisphenol-A diglycidylloxundecane dicarboxylic acid, MMA: methyl methacry-thacryloxyhexyl 2-thiouracil-5-carboxylate.

by the CLSM images in Figs. 2d, 3d and 4d. Aftercling, most of the non-coated specimens showedattering from the resin-dentin interface regardless

of cement as shown in Figs. 2a, 3a and 4a. In some, the bright area extended throughout the cavityicating complete loss of seal (Fig. 3a); while in

gap was formed only at a part of the specimenn the other hand, most of the specimens in thed groups showed little or no detectable reectionterface (Figs. 2b, 3b and 4b).an adaptation percentage of the three differentnts to dentin with or without resin coating andeviation for each group are listed in Table 2 and


Fig. 1 Schematic view of study method; resin inlays were cemented in round cavities using a resin cement with or withoutresin coating, and subjected to OCT observation at baseline and after thermal cycling. CLSM was used for conrmation ofOCT ndings after cutting the specimens. SE: dentin-bonding system Clearl SE Bond; PLF: Protect liner F; BT: Bistite II DC;BT-NC: Non-Coated Bistite II DC; BT-C: Coated Bistite II DC; SA: Clearl SA Luting; SA-NC: Non-Coated SA Luting; SA-C:Coated SA Luting; MB; Multibond II; MB-NC: Non-Coated Multi bond II; MB-C: Coated Multibond II.

presented as bar graphs in Fig. 5. ANOVA test demonstrateda signicant effect of resin coating, cement type and thermalcycling on gap formation in the cavity oor (p < 0.05). Theinteraction between these three factors was also signicant

(p < 0.05). The application of resin coating of SE and PLFsignicantly improved the adaptation of resin inlays todentin (p < 0.05) regardless the type of cement or sampleage. Without resin coating, SA signicantly showed better

Fig. 2 Repthermal cyresin inlayfrom BT-C same sectito have occplotted ovecaused by while in (f)cement; RCresentative cross-sectional OCT images and signal intensity procles and corresponding CLSM images of the same cross-sections

cemented with BT showing an increase in the signal intensity agroup showing an improved adaptation of the resin inlay after reons at 500 and 1250 magnication conrming the OCT ndinurred at the resin cement primer and dentin interface (blank arrr selected areas (indicated by lines) in the same cross-sections. NFresnel reection due to contrast in refractive index between res, no detectable change in signal intensity can be observed when: resin coat; D: dentin.les of BT-NC and BT-C groups after 10,000. (a) B-scan and binary image of the interface of at the cavity oor. (b) B-scan and its binarizationsin coating. (c and d) CLSM images from thegs. The gap under BT-NC specimen in (c) appearsow). (e and f) A-scans (SS-OCT signal intensity)ote the peak in backscatter signal (arrow) in (e)

torative material and air at the interfacial gap the interface is sealed. In: resin inlay; Ce: resin


Fig. 3 ImB-scan andcavity oorsection as CLSM imagArrow in (eresin ceme

sealing comsignicant MB (p > 0.05regimens cadaptation

Table 2

Gro

Non-coatedBistite II DCMulti bondSA Luting (

CoatedBistite II DCMultibond SA Luting (

In each coletters are comparisoages obtained from specimens luted using SA with and without binary image of the selected interface from a SA-NC sample sh. (b) No gap was detected in B-scan and binary image of this SA-in (a) at 500 and 1250 magnication showing gap between SAe of the same section presented in (b). (e and f) A-scans plotted ) indicates the high intensity in backscatter signal caused by airnt; RC: resin coat; D: dentin.

pared to BT and MB. However, there was nodifference in the adaptation between BT and). In the non-coated specimens, thermal cyclingaused signicant decrease (p < 0.05) in the cavity

percentage of BT and SA only after 2000 cycles.

However, wpercentagehand, the change in materials.

Cavity adaptation percentage (standard deviation) in each group

up Baseline 2,000 The

(BT-NC) 72.4 (14.6)aA 65.5 (1 II (MB-NC) 68.0 (17.1) aC 74.5 (1SA-NC) 85.2 (14.1) bD* 71.3 (2

(BT-C) 92.3 (7.5)cG 91.1 (7II (MB-C) 88.8 (8.5) cH 90.4 (1SA-C) 99.4 (2.0)bI* 98.1 (2

lumn, values marked by similar lowercase letters are not signicantly diffenot signicantly different. (*) indicates no signicant difference between coans by Bonferroni post-hoc).resin coating after 10,000 thermal cycles. (a)owing an increase in the signal intensity at theC specimen. (c) CLSM images from the same

and dentin in the cavity oor. (d) Conrmatoryalong the designated lines shown in (a and b).

lled gap in the interface. In: resin inlay; Ce:

hen MB was used as a cement, the adaptation increased non-signicantly (p > 0.05). On the othercoated specimens showed no signicant (p < 0.05)adaptation after thermal cycling with all cement

.

rmocycles 10,000 Thermocycles

6.7) dA 56.5 (17.0) hB

5.5) eC 75.0 (15.7) iC

0.0) eE 58.5 (20.0) hF

.05) fG 89.0 (8.0) jG

1.7) fH 90.5 (9.0) jH

.3) gI 97.5 (2.8) kI

rent. In each row, values marked by similar uppercaseted and non-coated groups (three-way ANOVA multiple


Fig. 4 SS-from MB-Nspecimen sspecimen sin (a). (d) Clocations o(solid line).attenuationindicated bresin ceme

4. Di

In this studinterface. Onique that a safe broain various bous dental margins of or using ionthat allowsin a long-te

During tent interfaccoat-cemenples and dnon-coatedface was noOCT 2D images, signal proles and conrmatory CLSM images oC and MB-C groups after 10,000 thermal cycles. (a) B-scan and bhowing some microgaps at the cavity oor indicated by bright phowing good adaptation. (c) CLSM under 500 and 1250 magnLSM of the same section as in (b) shows good sealing in the resinn the same cross-section to show the difference in backscatter s

The signal from unsealed interface shows sudden increase in th in case of good sealing. (f) A-scan plotted along the line in crosy blank arrow is caused by low backscattering of light from MB cnt; RC: resin coat; D: dentin.

scussion

y, OCT was used to detect gaps in tooth-restorationCT is a non-invasive diagnostic imaging tech-can give real time, high resolution images usingdband light source. Nowadays, OCT is being usediomedical applications including dentistry. Previ-studies had showed the ability of OCT to evaluatecomposite restorations without cutting the sampleizing radiations [21]. OCT is an objective method

evaluation of the same section at different timesrm study.he evaluation of tooth-restoration interface, differ-es were located including dentin-resin coat, resint and cement-inlay interfaces in the coated sam-entin-cement and cement-inlay interfaces in the

samples. Among these, the cement-inlay inter-t included in the process of image analysis in this

study. Occainternal res

In this sto provide Figs. 24. Asthrough ditial reectitwo media result in a bright area ite resin is among diffrelation [20and opticalresin matri82% accordwith a highwith lowerlower refracf the same cross-sections for selected specimensinary image of the interface for a MB-NCixels. (b) B-scan and its binarization for MB-Cication conrm gap locations identied by OCT-coated group. (e) A-scan of two different

ignal of areas with (dashed line) and without gape intensity compared to uniform gradual

s-section (b). The decrease in signal intensityompared to resin composite. In: resin inlay; Ce:

sional gaps at this interface were considered to bein defects.tudy, image analysis was conducted on 2D imagesdata through the whole cavity as presented in

the light propagates through the sample, it passesfferent materials, undergoing refraction and par-on. The reection of light as it passes betweenwith different refractive indices (Fresnel reection)peak in the backscatter signal (A-scan) forming ain 2D OCT image. The refractive index of a compos-dependent on its composition and can be variableerent materials. According to the GladstoneDale], index of refraction can be related to the ratio

constants of the ingredients, which are mainly thex and the llers. For example MP has a ller vol% ofing to manufacturer, and contains alumina llers

refractive index (n = 1.75), while other composites ller load contain barium glass ller that has ative index (n = 1.52). Moreover, methacrylate resins


Fig. 5 Barcementatio

Table 3 in study.

Mate

MP SE + PLF (reBT SA MB

generally htriethylenediglycidyl emethyl meto various t

Refractiwere meadetails else(approximaplaced ovethen calculthrough thresults from1.481.58 asare close to

In orderintensity ative index cindex medcarried out graph representing cavity adaptation percentage and standard n), after 2000 thermal cycles and after 10,000 thermal cycles.

Measured refractive indices for materials used

rial n

1.58sin coat) 1.55

1.501.511.48

ave a refractive index of 1.491.55 (for, TEGDMA:glycol dimethacrylate and Bis-GMA: bisphenol-Ather dimethacrylate, respectively) and PMMA (polythacrylate) has a refractive index of 1.48, accordingechnical reports.ve indices of different materials used in this studysured following the methodology explained inwhere [17,20]. Briey, a thin slice of each materialtely 300 m) is prepared and imaged by OCT whiler a reective metal stage. The refractive index isated by measuring the ratio of optical path lengthe material to the actual thickness of the slice. The

at least 3 measurements were in the range of presented in Table 3. These refractive index values

those of dentin [20]. to conrm the assumption that an increased signalt the interface indicated gap due to the refrac-ontrast between the material and a low-refractiveium such as air (n = 1.0), further investigation was

by imaging the specimens after each step of the

inlay placeafter DBS wshown in Fcoating is is rising froinitial adap

The comity after uscavity. It shstep of an fabricationcement layresin cemeindicated bintermediathe border ance of a dtwo surfacenough. It are resultindefect, the cate the veunder thission correlof the interstudy was cget pixels iby a mediabright clusdeviation of each group at baseline (24 h afterment. Representative OCT images of the specimenas applied and following placement of the PLF areig. 6a and c, that suggest the surface of the appliedhighly reective while little additional reectionm the underlying dentin interface showing goodtation of the resin coating to the surface of dentin.posite inlays were fabricated on the prepared cav-ing a plastic parafn lm separator mold into theould be mentioned that replacing the impressionindirect technique by this method shortened the

time but could also have yielded a thicker resiner. An OCT image of an inlay placed without anynt to check its t is presented in Fig. 6e. As clearlyy the signal intensity prole (Fig. 6f), absence of anyte cement layer leads to high light reection fromof composite and dentin resulting in the appear-ouble-reection peak where the distance betweenes (i.e. inlay bottom and dentin surface) is widewas previously reported that since the reectionsg from the double refraction at the borders of thevertical dimension of the target pixels may not indi-rtical dimension of the gap between two interfaces

experiment setup, while the horizontal dimen-ated well with the extent of the unsealed portionface [21]. Therefore, the percentage of gap in thisalculated as the total horizontal length of the tar-n the selected interface after removing the noisen lter. The custom software was used to detectters indicating increase in the signal intensity in


Fig. 6 (a) plicathe design e thclose to the of lresin coat; n appurpose of ealinbackscatter into check for (f) Dthe bounda ow) (g) In the le tin sintensity p an ncement wa t-cucaused by n ref

restorationdetermine area of inteThe target pimage.

To furthtion of gapinlay) placegap betweecuring the and then pcase, a strocating the gadequatelycured, no inprevious stcolloids thatrast agent penetrationlic particlesagents [27]research wnot be neceposites inv

The rouIt has also compositesIn the curand used ta low atten2 mm thickobserved wthought to

viscores h thred

truct resge oationCross-sectional OCT image showing prepared cavity after apated line in (a). Note that it may be difcult to characterize th

axial resolution of OCT). (c) OCT image after the applicationblank arrow indicates pulp horn. Note that the resin has bee

OCT imaging. Corresponding A-scan in (d) indicates good s signal intensity. (e) OCT image showing the inlay inserted t. Note the clear reections from the boundary of the cavity.ries of air-lled space, the inlay (top boundary, rst bold arrft image, previously cured layer of the resin placed over deneak indicated by bold arrow in (h) conrms the gap, which cs adequately pushed against the dentin surface prior to lighsurface reection from the resin cement due to its contrast i

interface [13]. This software requires the user toan intensity limit to detect the target pixels in therest that includes the resin interface in this study.ixels are those with high brightness in a binarized

er rule out the possibilities of bias in the detec-s, OCT images of the resin cement layer (withoutd over dentin are presented in Fig. 6g and h. A

highlystructubeneatmonitowith s

Thecoverapreparn the cement and dentin was simply created byresin cement as a separate layer on a glass slidelacing the cured cement layer over dentin. In thisng reection from the interface is evidently indi-ap. On the other hand, when the resin cement was

pushed against the dentin surface and then light-tensity peak was detected at the interface. Someudies have suggested the application of metallict would highly backscatter the OCT light as a con-applied after placement of the restoration (as in dye

tests) [18]. Others have suggested that the metal- should be incorporated into the dentin bonding. However, the results obtained from a series oforks suggest that such an increased contrast mayssary for assessment of a wide range of resin com-estigated under OCT [12,13,1618,21].nd cavities were prepared 2 mm in depth [13,18].been shown that OCT signal attenuation through

depends on various compositional factors [28].rent study, a posterior composite was selectedo fabricate resin inlays; this composite showeduation effect and small signal loss through theness. Nevertheless, bright lines were occasionallyithin composite inlays. These micro defects are

be produced during the manipulation of the

good interfshown thating, a reliaresin coatinite cores to[33]. The colow-viscosicould provi[32,34]. Thesive failurepoints out ing of dentremains pr

In this resulted in of the resintional applDBS from talso enhansion of its foxygen inhlayer in theinteractionual uncureand the arotion of DBS (SE). (b) Signal intensity prole alongin bonding layer (approximately 10 m; which isow viscosity microlled resin (PLF) to form theplied twice to result in a thicker layer for theg of the resin coat with no increase ina prepared cavity with no cement or resin coat toouble peak in signal intensity prole caused byand dentin (lower boundary, second bold arrow).hows a strong reection from the interface; theot be seen in the right image where the resinring. The blank arrow in (h) shows signal peakractive index with air.

us composite [29]. Such scattering in the superiormay affect the penetration depth immediatelyem [30]. Therefore, the fabricated inlays wereusing OCT before cementation to exclude thoseural voids or defects [31].in coating technique allows for protection andf the prepared dentin immediately after cavity

reducing postoperative sensitivity and providing

acial adaptation and marginal seal. It was also

in a mechanism essentially similar to direct bond-ble hybrid layer is produced [8,32]. Furthermore,g enhanced the bond strength of indirect compos-

pulpal oor dentin in endodontically treated teethmbination of the two-step self-etch adhesive and aty resin, which was employed in the current work,de the highest bond strength of cement to dentin

resin coating shifted the failure mode from adhe- to cohesive failure within the cement [33]. Thisthe clinical signicance of resin coating on seal-in; as even if the restoration fractures, the dentinotected in both vital and non-vital teeth [33].study, the application of resin coating on dentina statistically signicant increase in the adaptation

cement to dentin (Table 2 or Fig. 5). The addi-ication of a low-viscosity microlled resin protectsearing during removal of temporary restoration. Itces the adhesive polymerization through the diffu-ree radicals that polymerize uncured resin in theibited layer [32,35]. Moreover, the resin composite

coating technique would prevent possibly adverses that have been reported to occur between resid-d acidic monomers within the self-etch adhesivematic tertiary amine derived from chemical- and


dual-cured resin composites. In addition, the low-viscositymicrolled resin with lower ller content combined with abonding agbreaking recement an[35]. The atoward thecement to PLF in com

Before unsealed aslightly moBT-NC. Hoobserved.

SA is a to tooth ssive or etcdihydrogendemineraliknown to hapatite forresistance cium salt inincluded inthe surfacedentin surf

BT is a with two dthan SA. Oncosity of thof penetratto applicatAlso, residuway and inmechanicaAfter the sNC and BT-percentageexpansion leading to eration of t

MB is asingle-bottphoric acidactivator. Imay be copolymerizaprimer [40]tation aftermay enhanstimulate cuptake by layer and clthat the waponents iswith watercompositio

In the cdid not signshould be

system used for resin coating in penetrating into dentin andsealing the interface. SE bond has exhibited good long-term

l resny of

difth a. Themenin cthe t [44ed inereding pplieterfendinmenhniqd.hortre wets. Terfacd tht typ

Co

thecludtoothcule witnterfeme

owl

searnce ciencentach no

Scie

r e n

asselrsusinicaickel eth aikaidsin-cstem03;5:ent with low modulus of elasticity form a stress-sin layer relieving the polymerization stresses ofd leading to better adaptation of the resin inlaysssociation of these factors may have contributed

signicantly higher adaptation percentage of resindentin when the surface was coated with DBS andparison with non-coated samples.thermal cycling, SA-NC showed only scarcereas indicating good initial seal. MB-NC showedre unsealed areas in the interface compared towever, no statistically signicant difference was

self-adhesive resin cement; it is known to adheretructure without the need of a separate adhe-hant. The cement utilizes 10-methacryloxydecyl

phosphate (MDP) functional monomer to achievezation and bonding to the tooth surface. MDP isave a high chemical bonding potential to hydroxy-ming a very stable bond and excellent waterconrmed by the low dissolution rate of its cal-

water [3638]. In fact, the acidic monomer is also the primer agent of the DBS, which conditions

by dissolving the smear layer and demineralizingace.dual-cured resin cement that needs pretreatmentifferent primers. Its optical adaptation was lowere reason may be the high ller content and the vis-e mixed cement, which may decreased the depthion into the primed dentin. Other factors relatedion method should be taken into consideration.al solvents from primer may create leakage path-terfere with monomer polymerization and reducel properties leading to poor bonding performance.pecimens were subjected to thermal cycling, SA-NC showed signicant decrease in the adaptation. This may be related to the difference in thermalcoefcients between cement material and dentingap formation or by accelerated hydrolytic degen-he cement material [39].n MMA-based powder-liquid resin cement with ale self-etching primer. The primer contains phos-

monomer and borate derivative as a surfacet had the lowest adaptation performance whichntributed to the slow rate of its setting chemicaltion, and hydrophilic nature of the water-based. However, MB-NC showed no decrease in adap-

thermal cycling. The heat during thermal agingce the chemical polymerization of the cement andompletion of its setting reaction. In addition, waterthe resin cement may result in expansion of theosure of some microgaps [41,42]. It has been shownter sorption by resin containing hydrophilic com-

intense in the rst days after coming to contact, and then gradually plateaus depending on then of the resin [43].oated groups, on the other hand, thermal cyclingicantly inuence the restoration adaptation. Thisattributed to the reliability of the direct bonding

clinicaover a

Theis worgroupscoat-cthe resunder cemenobservconsidaccordwere amay inand borecoming tecapplie

In sas thecemenall intaffectecemen

5.

Withinbe constudy the difsurfacterm iresin c

Ackn

This reExcelleular Sand Dreseartion of

r e f e

[1] Wvecl

[2] Hte

[3] Nresy20ults and high hydrolytic stability; giving it an edge the resin cements used alone in this study.ference in adaptation among the coated groupsttention, since the same coating was used in alle nding was attributed to the defects at resint interface, which reects the differences among

ements, such as contraction stresses that developconstrained polymerization condition of the resin]. However, since these defects were predominantly

BT-C and MB-C groups, other factors should be. During cementation, each cement was appliedto the manufactures instructions where primersd as well; the application of the water-based primerre with polymerization of the hydrophobic cementg to the resin coat surface. In this context, it isded that for cementation of inlays in the resin coat-ue, a water-free resin cement system should be

, the null hypotheses of the study were rejected,re signicant differences in sealing between resinhe use of resin coating technique improved over-ial sealing of the resin cements. Thermal aginge interfacial integrity depending on the resine and coating.

nclusion

limitation of this in vitro study, the following caned that OCT is a high-speed imaging technique to-indirect composite restoration interface withoutties of common leakage tests. Treatment of dentinh resin coating before cementation improves long-acial sealing of indirect restorations placed withnts.

edgments

ch was supported in part by the Global Center ofProgram, International Research Center for Molec-e in Tooth and Bone Diseases at Tokyo Medicall University, partly by grants-in-aid for scientic. 24792019 from the Japan Society for the Promo-nce and partly by King Abdulaziz University.

c e s

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Sealing performance of resin cements before and after thermal cycling:Evaluation by optical coherence tomography

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Sealing performance of resin cements before andafter thermal cycling: Evaluation by optical coherence tomography