microleakage evaluation of bonded amalgam restorations ... · restorations to the prepared cavity....

Dental Research

Microleakage evaluation of bonded amalgam restorations:Confocal microscopy versus radioisotope

Jirasak TangsgoolwatanaVMichael A. CochranVB, Keilli Moore-^^/Yiming Li***

Abstract The purpose ol this study was to compare the degree and pathway of microleakagein bonded amalgam restorations utilizing fluorescent dyes with .wanning laserconfocal microscopy and''-'Ca radioisotope with autoradiographs. Mesial slotpreparations with enamel cen-ical margins and distal preparations with dentinmargins were prepared in extracted human molars. Four liners. Copallte i control).Alt-Bond 2/Resinomer. Amalcoden. and Panavia 21, were used Teeth wererestored with Dispersalloy or Tytin. After therinocycllng. 7 days' storage, andstaining, the degree of microieakage was measured on an ordinal scale. Dentaladhesive liners minimized microleakage; the ranking was. from most to ¡easteffective. All-Bond 2, Panavia 21. and Amalcoden. The control exhibited thegreatest microieakage. Microleakage occurred niost frequently at the liner-toothinterface. No significant difference was ob.served between atnaigams. The highcorrelation between the results of the fluorescent and radioisotope studies indicatedthat these nvo microleakage tests can be directiy compared.(Ouiniessence Int l997:2S:467-477,)

Clinical relevance

The dental adhesive materials tested in this studyeffectively minimized cervical microleakage of btjthspherical and admixed amalgam restorations atenamel and dentin cavosurface margins. However,none ofthe materials completely eliminated micro-leakage in all specimens. When leakage did occur, itwas most frequently found al the adhesive-loothinterface.

Í Deceased.

' Professor of Operative Dentistry and Director of PostgraduateOperative Dentistry, Department of Restorative Dentistry, IndianaUniversity, School of Dentistry, Indianapolis, Indiana.

•"• Professor of Dental Materialsand Direetor of Postgraduate DentalMaterials, Department ol Restorative Dentistry, IndiaFia University,School of Dentistry, Indianapolis. Indiana.

*** Director ofCdl Culture Laboratory, Oral Health Rescarcli Institute,Indiana University, School of Dentistry, Indianapolis, Indiana.

Reprint requests: Dr Michael A. Cochran, Professor of OperativeDentistry, Department of Restorative Dentistry. Indiana University,School of Dentistry, 1121 West Michigan Street, Indianapolis, Indiana46302,

Introduction

Adhesion between restorations and the cavity wall is ofprimary importance for ciinical success of restorativematerials. Because dental amalgam neither adheres norbonds to tooth structure, an interfacial gap may existbetween the cavity wall and the amalgam restoration.Conseguenl microleakage at the tooth-restorationInterface could cause postoperative hypersensitivity,demineralization of tooth structure, and, eventually,pulpal inflammation. Although amalgam will producecorrosion products lo seal the amalgam-tooth inter-facial gap and minimize microleakage, the corrosionprocess occurs slowly and may lead to tooth discolora-tion. To overcome these drawbacks, copal varnishes,resin dentin adhesive, and glass-ionomer cement havebeen used to coat the prepared cavily prior to amalgamplacement to provide an improved marginal seal.

The ability to prevent iTiicroleakage is one of theparameters used to assess the adaptation of dentalrestorations to the prepared cavity. The evaluation ofmicroleakage has been conducted both in vivo and invitro. The measurement of in vitro microleakagebeneath bonded amalgam restorations has been con-dticted by the following techniques: caries inhibition';

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Tangsgoolwatana et al

Table I Materials used in lhe study

Prodtict Type Batch number Manufacturer

Copalite (CO)

All-Bond 2/Resinomer (Al)All-EtchAII-Bond 2

Resinomer

Amalcodeti (AM)

Panavia 21 (Pa)

Dispersalloy (Ds)

Tytin (Ty)

Copal varnish

10% phosphoric acidDentin primer

Resin composite cement

Glass-ionomer cernent

Resin composite cemetit

High-copper, admixedamalgam alloy

High-copper, sphericalamalgam alloy

HJ Bosworth

Bisco Dental059204Primer A: 049274.Primer B; 049284Base: 089304, 089034Catalyst: 089294. 089054

Liquid: 1085Powder: ARBM

11121

140990A-OJ590

41159

MION International

J Morita

LD Caulk/Dentsply

Kerr/Sybron

penetration of '"Ca radioactive tracer-; and penetra-tion of various dyes, such as 0.5% basic ñichsin. '"*' 2%fluorescein,- and 0.5% méthylène blue,^"'-'

A light-retlecting binocular microscope and astereomicroscopc have been used to observe thedegree of dye penetration. Furthermore, autoradiogra-phy has been utilized to measure leakage using ''^Ca asa tracer. Recent applications of confocal scanningoptical microscopy have been made to operativedentistry. The subsurface structure of translucentsubstances, such as the interface between tooth andtooth-colored restoration, can be observed.'"*''

The purpose ofthe present study was to compare thein vitro microleakage of bonded amalgam restorationsusing fluorescent dyes with a laser scanning confocalmicroscope to examine the natural tooth-restorationinterface, while the specimen was maintained in anormal hydrated condition. A dual fluorescent tech-nique used in conjunction with confoca! microscopypermitted determination ofthe location ofthe leakageprocess in the interface between tooth and amalgam.Because this was the first use ofthe dual fluorescenttechnique with confocal microscopy to evaluate micro-leakage, the results obtained with this new techniquewere compared with the results of a conventionalradioisotopc C' Ca) leakage study.

Method and materials

Tooth preparation

A total of 160 recently extracted human molars werecollected, stored in distilled water, and refrigerated,Uncoalesced pits and fissures in these collected teethwere sealed with Delton pit and fissure sealant(Ash/Dentsply).

Mesial Class 11 slot preparations with enamelcervical margins and distal preparations with dentinalmargins were prepared in each tooth with a No. 57tungsten carbide bur used in a high-speed handpiecewith copious water. Each proximal box had a 1,5-mmbuccolingual width and a 1,00-mm-deep gingival wall.These two proximal slot preparations were separatewith no occlusal connection. Tlie gingival margin ofthe mesial cavity was placed at least 1.0 mm occlusal tothe cementoenamel junction {CEJ). and the gingivalmargin ofthe distal cavity was placed at least 0.5 mmapical to the CEJ, Retetition grooves were placed atthe axiobuccal and axiolingual line angles with a No.329 pear-shaped carbide bur and extended from thecervical floor to 1,0 mm from the occlusal surface. Allmargins were smoothed with an enamel hatchet.

Restorative procedures

All ofthe materials tested (Table 1 ) were manipulatedfollowing their manufacturer's instructions (Table 2),

468 Quintessence International Volume 28, Number 7/1997


Four groups of 40 teeth each were treated with otte ofthe following four liners: Copalite, All-Bond 2/Resinomer, Amalcoden, or Panavia 21. The combina-tion of All-Bond 2 and Resinomer represented theresin dentin adhesive systems that include an acidconditioner. Panavia 21 represented the resin dentinadhesive systems that preserve a smear layer, whileAmalcoden represented glass-ionomer cements. Co-palite was included as a control material.

Half of each group was treated with liners labeledwith rhodamine B. Based on a pilot study, the variouscomponents of the lining materials were labeled withdifferent amounts of rhodamine B to enable theirdistributions to be observed in tbe confocal micro-scope:

1. 0.005 jimol (2.385 ig) was included in each mix ofthe adhesives" primer liquid.

2. 0.01 iimol (4.79 ^g) was included in eachapplication of Copalite.

3. 0.1 (imol {47,9 |jg) was included in each mix ofeither Resinomer or Panavia 21 pastes.

4. 0.15 iimol (71.85 |ig) was included in each mix ofAitialcoden. This amount is 15 times greater thanthe amount used for Copalite, because rhodamineB is relatively slow to dissolve into and can leachout of Amalcoden.

Ten teeth in each subgroup were restored withDispersalloy and the other 10 with Tytin. The restora-tions were carved with a No. 15 Bard-Parker surgicalblade but not burnished or polished. All restorativeprocedures were performed by one operator. Within24 hours, the whole tooth was wrapped with tinfoil,and a coat of nail polish was applied to seal the edges ofthe tinfoil prior to thermocycling. This was done toprevent rhodamine B from leaching out of Amalcoden.A pilot study showed no evidence of rhodamine B inthe thermocycling baths when the teeth were sealed intinfoil. The specimens were subjected to 2,500 ther-mocycles between an 8°C ± 2°C bath and a 48°C ±2°C bath. The dwell time in each bath was 30 seconds,and the transfer time was 10 seconds.

Microleakage tests

Following thermocycling, the protective tinfoil wasremoved. The apices ofthe specimens were sealed withcompound. The unprepared coronal and root surfaceswere painted with one coat of biack fingernail polish towithin 1 mm ofthe restoration margin to prevent dyepenetration anywhere other than the restoration margin.Tinfoil was adapted over the teeth. The foil covering

Table 2 Material manipulation

Product Procedures

Copalite Apply two coats with blotted cot-ton pellet; dry 30 seconds for eachlayer.

All-Bond 2/ResinonierAll-Etch Apply 15 seconds and rinse; dry

I second,All-Bond 2 Apply five coats and dry 5 seconds;

(Primers A&B) light cure 20 secondsResinomer Mix 15 seconds, apply with brush,

and thin with compressed air.

Amalcoden

Panavia 21ED Primers A&B

Mix 30 seconds and apply withbrush.

Mix 5 seconds, apply 60 seconds,and then dry with compressed air.

Universal & Catalyst Mix 30 seconds and apply thinpastes layer with brush.

Oxyguard II Apply i minutes to cover marginafter amalgam placement; re-move with cotton roll andwater spray.

the amalgam filling and 1 mm adjacent to therestoration margin was cut out with a No. 11 Bard-Parker surgical blade. After the varnish was dry, thefoil was burnished. A second coat of nail polish wasthen applied to seal the edges of tinfoil. The polish wasallowed to air dry.

To eliminate individual variations in the teeth, cavitypreparations, and restorations, both microleakagetests were done on the same tooth by using radioactivecalcium chloride C' CaCl.,) prior to immersion in thefluorescein dye. At 7 days, the specimens wereimmersed for 2 hours at room temperature in anaqueous solution (pH 5.5) of''^CaCl^ having radio-activity of 0,1 mCi/mL. After that, the teeth wererinsed for 1 liourunder running water. Specimens werethen scrubbed with a toothbrush and liquid soap.

The next day, the specimens were immersed in a0.5% (5 mg/mL) aqueous solution of fiuorescein dyefor 5 minutes at room temperature. The teeth were thenremoved from the solution and cleaned by scrubbingwith a stainless steel brush and toothpaste. Theprotective tinfoil was removed, and the teeth wererescrubbed.

Each tooth was transversely sectioned undercopious water irrigation. First they were sectioned

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Tangsgoolwatana et ai

midbuccally through the longitudinal axis and thenmesiodistally along the longitudinal axis through thecenter of the restorations. A O..18-mm-thick diamondblade was used. To remove the Hash resulting (romplastic deformation of amalgam during sectioning, thecut surtaces of the specimens were polished on2.000-gril wet silicon carbide papers. The specimenswere kept in humidified storage vials and inspectedwithin 24 hours.

Fluorescent technique

The Laser Scanning Confocal Microscope (Odyssey,Noran Instruments) was used to examine the speci-mens at x40 magnification. The low concentrations offluorescent dye were excited by intense laser light toemit fluorescent light. A 529 nm green excitation filterand a 540- to 560-nm yellow-green high-pass filterwere used to observe the rhodamine B-labeled compo-nents at the emission wavelength of approximately 600nm (reddish orange). To detect fiuorescein. a blueexcitation filter (4S8 nm) and a green high-pass filter(515 nm) were incorporated into the system.

Subsurface images at least 20 |im from the specimensurface were obtained by serial optical sectioning at theresolution of 50 nm per section. Each image wasadjusted and focused until both amaigam-liner andliner-cavity wall interfaces became visible to providegood-quality images. The contrast was standardized bydetermining the optima! contrast for the labeledbonding materials in a preliminary experiment. Allimages were obtained using this predetermined con-trast. The contrast should not have significantlyinfluenced the results because the intensity of thefluorescence was not measured or compared. Thereflected white-light image was also recorded. The twolabeled images (rhodamine and fiuorescein) and thereflection image were then merged to produce the finalred/green/blue composite image.

The microleakage was assessed by observing thedistance of fiuorescein penetration ai the interfaces ofamalgam-liner and liner-gingival cavity wall using thefollowing criteria; I = no dye penetration; 2 =penetration up to one half of the gingival wall; i -penetration from more than one half of the gingivalmargin up to the axial wall: 4 = penetration along theaxial wall. Both halves of each sectioned restorationwere examined. The higher microleakage score fromthe two halves of each restoration was chosen to obtainonly one set of data per restoration.

Radioisotope technique

Tooth sections were placed, cut surface down, directlyon intraoral radiographie film and kept in a lightproofcontainer for 17 hours. The exposed films weredeveloped in an automatic film processor (Peri-Pro;Air Techniques), Microleakage at the gingival matginwas scored on the basis of the following criteria: 1 = nodye penetration; 2 = penetrationalong the gingival walland short oi'the axial wall; 3 = penetration to the axialwall: 4 = penetration along the axial wall.

S ta tis I ka/ a na h w is

The experimental design for this investigation con-tained four variables: cervical margin location, liningmaterial, labeling in lining material, and amalgamalloy. Because significant interactions were observedbetween the marginal location and the other variables,the degrees of microleakage for enamel and dentinmargins were analyzed separately. The fiuorescent andradioisotope measurements were ranked, and a three-way analysis of variance was perlbrmed on the rankeddata (resulting in a nonparametric test) at the .05 levelof significance. Then multiple comparisons were madeusing posthoc Fisher's Protected Least SignificantDifference to compare microleakage for the liningmaterials on all variables. The intraclass correlationwas used to test agreement between the results of thefiuorescent and radioisotope techniques.

Results

Degree of tnicroleakage

Table 3 compares the degrees of ttiicroleakage amoi^lining materials tested. The results of ICruskal-Watlisthree-way analysis of variance revealed that liningmaterials significantly differed in the degrees ofmicroleakage in both the fiuorescent and radioisotopestudies.

Fluorescent study with confocal microscopy

In both enamel and dentina! margins, the restorationswith All-Bond 2/Resinomer exhibited the least micro-leakage. Microleakage was significantly lower for therestorations with Panavia 21 than for those withAmalcoden in both types of cervical margin, and thanfor restorations with Copalite in enamel margins. Nosignificant difference was observed in the degree ofmicroleakage between the restorations with Amal-coden and those with Copalite in either group.

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Tangsgoolwatana el al

Table 3 Comparison of microieakage among lining materials

Cervical margin location

Fluorescent study Radioisotope study

Lining materials

AlPaAmCo

AlPaCoAm

Mean (SD)

1,88 + 0,942.88± 1,163,78 + 0,703,88 + 0,52

2,50 ±0 .963,68 ±0 .573.75 ±0 ,783.90 ±0 ,38

Lining materials

AlPaAmCo

AlAmPaCo

Mean(SD)

1,97 ±0,852,30 ± 1,203,28 ±0,723,50 ±0,93

2,55 + 0,933,28 ±0.753,33 ± 0-893.90 ± 0.44

Enamel

Dentin

Materials coiListed in inc

cted by tical lines are not significantly different (Fisher's Protected Least Significant Difference!.of the mean from Lhe original measurements ( n = 401.

Table 4 Effect of rhodamine B on microieakage


Fluorescent study Radioisotope study

Label in liner Mean (SD) Label in liner Mean(SD)

Enamel

Dentin

YesNo

YesNo

2,96+ 1,293,24 ± L05

3,38 ± 1.063,54 ±0 .69

YesNo

YesNo

2,77± 1,142,78 ± 1,14

3,21 ±0,953,31 +0.87

Tbere were rListed in inc

.ignificant diñérences among groups,sing order of the mean from the original i asurements (n = 80).

The addition of rhodamine B into lining materialsdid not significantly affect the sealing ability of thelining materials tested (Table 4)- The degrees ofmicroieakage in Tytin restorations were not signifi-cantly different from those in Dispersalloy restorations(Table 5),

Radioisotope study

The restorations with All-Bond 2/Resinomer exhib-ited the least microieakage in both groups, either withenamel or with dentinal gingival margins (Table 3)-However. there was a significant difference betweenAll-Bond 2/Resinomer and Panavia 21 only forrestorations with dentinal gingival margins. Significantdifferences were found between the group with All-Bond 2/Resinomer and groups with either Amalcodenor Copalite,

The degree of microieakage was significantly lowerfor the restorations with Panavia 21 and enamelgingival margins than for restorations with Amal-coden, However, no significant difference was foundbetween the same groups at dentinalal gingival mar-gins. The microieakage ofrestorations with Panavia 21was significantly lower than that of those with Copa-lite, with either enamel or dentinal gingival margins. Inthe group with dentinal gingival margins, a significantdifference was observed in microieakage betweenrestorations with Amalcoden and those with Copalite.The mieroleakage allowed by Copalite was the greatestfor both enamel and dentinal gingival margins.

No significant difference was found between liningmaterials with rhodamine B and those without rhoda-mine B (Table 4), The microieakage of Dispersalloyrestorations was significantly lower than that of Tytin

, Number 7/1997 471


Table 5 Comparison of microleakage helween Dispersailoy and Tytin amalgam restorations


Enamel

Dentin

Huorescent study

Amalgam

TyDs

TyDs

Mean (SD)

2,93 ± 1,333,28 + 0.98

3,45 ± 0,933,46 + 0.87

Radioisotope study

Amalgam

DsTy

TyDs

Mean (SD)

2,59+ 1,232,95 ± 1.01

3,21 + 0.903,31 + 0,92

Groups connected by vertical Inies arc not significantiy different.Listed in increasing order ofthe mean from the original mea bu re ments (n = SO),

Table 6study

Pathways of microleakage from fluorescent

Pathway of leakage

Liningmaterials

No. ofspecimens

with leakage(n = 80)

Liner-amalgaminterface

Liner-tooth

interface

AlAmPa

547873

62,69%5,13%,5,48%

83,3 3X98,72'i',98,63%

restorations in the groups with enamel gingival margins(Table 5 ). Tytin and Dispersalloy restorations were notsignificantly different in the groups with dentinalgingival margins.

Comparison between fluorescent and radioisotope

Studies

The intraclass correlation coefficient between theresults from the fluorescent and radioisotope tech-niqties was .858, which indicated that the distributionsfor fluorescent and radioisotope studies were in highagreement.

Pathway of tnicroleakage

The data for the microleakage pathways from thefluorescent study were presented as a percentage(Table 6), Microleakage with All-Bond 2/Resinomerspecimens occurred at the liner-tooth interface in83,33% ofthe specimens and at the liner-amalgam

interface in 62.96%, Simultaneous leakage at bothinterfaces could occur. Microleakage at the liner-amalgam interface (Fig 1 ) was detected more often inDispersalloy restorations than in Tytin restorations,whether cervical margins were placed on enamel ordentin.

For the restorations with Amalcoden, microleakageoccurred at the liner-tooth interface (Fig 2) in 98,72Xof the restorations, Microleakage along the liner-amalgam interface was detected in 5,13% of therestorations. For the restorations with Panavia 21,microleakage occurred at the liner-tooth interface ( Fig3) in 98,63% ofthe restorations. The percentage ofmicroleakage observed at the liner-amalgam interfacewas 5,48%,

It was almost impossible to identify the pathway ofmicroleakage in most ofthe restorations with Copaliteat x40 magnification (Fig 4) because the varnish layerv»as discontinuous and very thin. This problem per-sisted even with higher magnification (x200) (Fig 5),In all specimens, the Copalite appeared to be attachedto the amalgam (Fig 5). Almost all ofthe Copalitespecimens exhibited severe microleakage with fluores-cein dye penetration into dentinal tubules.

Discussion

Copallte

it is well established that the penetration of micro-leakage tracer into the underlying dentin can bediminished with the application of cavity varnish,"^The restorations with Copalite in this study generallyexhibited the greatest microleakage compared to therestorations with the other materials (see Table 3),This finding agrees with the results of the study by

472 Ouiniessence International Volume 28, Number 7/1997


F¡g 1 Mtcroleakage (green) occurs al both inlerfaces,liner-amalgam and liner-tooth, in a Dispersalloy restoration(Ds) with All-Bond 2/Resinomer lAI) labeled with rhodamineBiyellowi iDi Denlin (Bar- 100 jim. ongmal magniftcalionx40 I

Fig 2 Microleakage occurs at the liner-tooth inlertace in aDispersalloy restoration (Ds) with Amalcoden (Am) labeledwith rhodamine B (red). Fjuorescein dye (yellowish green)appears in (be liner, and rhodamine B is seen penetratingdentin iD.i (Bar = 100 |im, original magnilicaiion x40.)

Fig 3 Fluorescein dye (yellowish green) penetrates theliner-looth interface in a Dispersalloy restoration (Ds) withPanauia 21 (Pa) labeled witb rhodamine B (red). (D) Dentin.(Bar= 100 \im: original magnification x40 1

Fig 4 Microleakage occurs at the liner-tooth interface in aDispersalloy restoration (Ds) with Copalite (Co) labeled withrhodamine B (red). The layer of Copalite appears lo bediscontinuous and fhin. Fluorescetn dye (yellowish green) isseen only j t the Copalite-dentin interface (D) Dentin: (E)enamel. (Bar - 100 lam: original magnification x40 }

Fig 5 Higher magnificafion of lhe amalgam-dentin inter-face area in a Tyfin restoration (Ty) lined wifh Copalitelabeled with rhodamtne B Ired). It is impossible fo verify Ibepafhway of microleakage because the layer of Copahleappears lo be discontinuous and thin However, Copaliteseems io attach fo amalgam. (D) Dentin (Bar - 10 ^im;original magnification x200.)

jrne28. Number 7/1997 473


Charlton et al,''' who found that Copalite is lesseffective in reducing microleakage of amalgam restora-tions than is adhesive resin.

Copalite, a hydrophobic varnish, has poor wettingability on moist dentin-"; contact angles on dentinrange from 53 to 106 degrees.-' As a result, themajority of microleakage usually occurred at theinterface between Copalite and dentinal gingival wallsin the present study. Moreover, a two-layer applicationof Copjlite on the dentinal walls, even with the smearlayer intact, can seal only about 80% to 85% ofthetubules.-"-- Pinpoint holes in the varnish film'' areformed during the volatilization ofthe organic solvent,so that tbe layer of Copalite appears to be discontinuousin the cross-sectional view (see Fig 5). Consequently,it was extremely difficult or impossible to identify thepathway of microleakage in many restorations linedwith Copalite.

All-Bond 2/Resinomer

The restorations with All-Bond 2/Resinomer exhibitedsignificantly the least microleakage among the liningmaterials tested. The present results are in agreementwith previous findings in a microleakage study thatused 2% er>Throsin as a microleakage marker and slotpreparations restored with T>iin and Dispersalloy.-'Resinomer used with All-Bond 2 allowed the leastmicroleakage in both amalgams compared to 14 othercorrunercial products for amalgam bonding, includingPanavia 21 and Amalcoden.-' Another investigationdemonstrated significant reduction of microieakage inrestorations with All-Bond 2 adhesive compared withrestorations lined with copal varnish,••*

The adhesion of dentin adhesive systems is im-proved by the applications of an acid conditioner tothe dentinal surtace. The contact angle ofa resin dentinadhesive was reduced from 28 to 12 degrees bypretreating the dentin with ethylenediaminetetraaceticacid.-'' The bonding mechanism of the resin dentinadhesives with dentin conditioning agents is caused bythe impregnation and interpénétration of monomersinto the demineralized dentin.-''-'' The gaps at therestoration-dcntin interface were absent when replicastaken from the restoration-dentin interfaciai area wereviewed under a scanning electron microscope (SEM)(x 120 to x400 magnifications).-^-" This may explainwhy the largest number of specimens without dyepenetration was found in the restorations with All-Bond 2/Resinomer.

The fluorescent markers used in conjunction withconfocal microscopy located the pathway of micro-

leakage. The pathway of microleakage occurred at theliner-tooth interface in 83.33% of specimens withAll-Bond 2/Resinomer. Recent findings showed that,although specimens with All-Bond 2 demonstrated theabsence of gap formation, silver nitrate could migratealong the porous zone at the base ofthe hybrid layer.'"-''Titley and others'- examined the penetrating ability ofa dentin adhesive primer into demineralized dentin.Fractured specimens from shear bond testing wereviewed under SEM with high magnification (x3,000to xll.OOOl. The method of preparing specimens bycritical point drying enabled the SEM to demonstratethe infiltration of resin monomer into the demineral-ized zone of etched dentin. Although primer appearedto facilitate the penetration of unfilled resin, bondingresin failed to infiltrate the total depth of demineral-ized zone. The presence of collagen fibrils on thefractured surfaces of both halves of specimens (dentinhalf and restoration half) implied that the collagenfibrils were not completely enveloped with bondingresin at the base of the demineralized zone."- Thecollapsed collagen on the surface layer of decalcifieddentin may prevent the penetration of the dentinadhesive into the flill depth of demineralized dentin."^

Microleakage at the liner-amalgam interface wasdetected in 62.96% of the specimens with All-Bond2/Resinomer. It is not clear why microleakage at thisinterface occurred in this group more often than withthe other lining materials. Microleakage detected atthis amalgam/Resinomer interface appears to contra-dict the manufacturer's claim that diar>'sulfone di-methacrylate. an active monomer in Resinomer, canform chemical adhesion to amalgam.

A tnalcoden

Amalcoden generally allowed significantly greaterleakage than did All-Bond 2/Resinomer and Panavia21 and showed no significant difference in sealingability for amalgam restorations with either type ofcervical margin. A previous investigation using anautoradiographic technique C' Ca) also reported thatAmalcoden was effective in reducing microieakageunder amalgam restorations.'•* However. Prati et al'^confirmed that the adhesion of type III glass ionomercements is not sufficient to eliminate dye penetrationalong the liner-dentin interface in in vitro compositerestorations.

It is surprising that there is no correlation betweenclinical perfortnance and laboratory' tests of leakage forglass-ionomer cement. In vitro, a gap was seen at thedentin-glass-ionomer cement interface-*''-"^ however.


Tangsgoolwatana et ai

this gap formation was not observed in replicasobtained Irom impressions of in vivo glass-ionomerrestorations.'*^ Although numerous studies,''"' in-cluding the present fiuorescent study, have foundsevere marginal leakage in vitro in glass-ionomerrestorations, a 2.5-year retrospective clinical studyshowed no recurrent caries in 133 cervical glass-ionomer restorations.""' The 3-year clinical study byMatis et al" reported that the percentage of glass-ionomer restorations without marginal discolorationriuigcd from 74'/ñ to l'~)%.

Motint et al"*- proposed that the difierence betweenthe in vitro and in vivo situation for glass-ionomerrestorations may result from the lack of dentinul fiuidHow in Ihe extracted tooth. It is possible thatglass-ionomer cement may be dehydrated during theearly setting phase. This dehydration will interfere withthe ionic exchange that produces the adhesion be-nvcen dentin and glass-ionomer cement. To simulatein vivo conditions, they suggested that microleakagetesting, including thermocycling. for type 111 glass-ionomer materials be performed 2 weeks after place-ment because this lining material needs at least 2 weeksto achieve optimal physical properties.

Microleakage in Amalcoden occurred at 98.72% ofthe liner-tooth interfaces and at 5.13% of the litier-iimalgam interfaces. The use of an aqueous solution ofdye may be inappropriate in microleakage testing forglass-ionomer cement. It may give false results becausediffusion of fiuorescein dye into Amalcoden wasobvious in mosl specimens in the present study. Thisconfirms previously reported problems using an aqueoussolution of dye with glass-ionomer cement."' In thatstudy, the depth of dye penetration around glass-ionomer restorations could not be assessed becausebasic fuchsin dye was absorbed into the bulk of therestorations.

Paiittviii 21

On the whole. Panavia 21 did not reduce microleakageas effectively as did All-Bond 2/Resinomer. This maybe a result ofthe lack of acid conditioning ofthe dentinwith Panavia 21. The results ofthe study by Charlton etal'"'supported this theory. In that sîudy. a resin dentinadhesive with an acid conditioner under amalgamrestoration was more effective in reducing micro-leakage compared to the systems without dentinalconditiííners. Panavia 21 appears more effective inbonding amalgam restorations to enamel margins thanto dentinal margins. The lower Ca'* concentrations indentil!, compared to ename!. itiay result in poorer

adhesion of l()-methacryloxydecyl dihydrogen phos-phate (MDP), a phosphate ester monomer in Panavia21. to dentin.•*' The MDP monomer may depend onpolar interaction between the negatively chargedphnsphate groups and positively charged calcium ionsin enamel and dentin.

If dentin adhesive monomer has high potential todiffuse beyond the smear layer, it is not necessary toremove the smear layer before application of bondingagents."'"' The monomers can penetrate the smear layerand lock with the underlying dentin after polymeri-zation. The ED primer of Panavia 21 contains threemain adhesion promoters: 2-hydroxyethyl methacryl-ate (HLMA), MDP, and N-methacryloyl 5-aminosali-cylic acid (5-NMSA]. Morra"' reported that HEMApossesses a strong affinity toward hydroxyapatite inlooth structure. Another group of investigators be-lieved that HEMA raises the surface energy oftheconditioned dentin by increasing the concentration ofhydroxyl groiipsin that dentinal surface.""' In addition,5-NMSA has carboxylic and hydroxyl radicals in asalicyclic acid group that can increase the wettability ofthe conditioned dentin.""' Although Panavia 21 con-tains these three monomers, microleakage occurred at98.63% ofthe liner-tooth interfaces but only at 5.48%of the liner-amalgam interfaces. The presence of asmear layer may prevent continuous, uniform attach-ment ofthe reactive monomers in Panavia 21. Yu et al""investigated the pathway of microleakage by usingsilver nitrate, a leakage tracer, and an energy dispersivex-ray mapping technique in Class V composite restora-tions with occlusal and gingival margins placed onenamel and root surfaces respectively. The enamel wasetched with 371 phosphoric acid for 15 seconds, andthe cavity was pretreated with a smear layer-mediateddentin bonding agent. Silver was found intensively inthe smear layer and in the dentinal tubules. Thissupports the finding in the present study that thepathway of microleakage may be the smear layer-dentininterface for the resin dentin adhesive without dentinalconditioner.

It is possible that MDP forms a bond with amalgambecause microleakage occurred only at 5.48% of theliner-amalgam interfaces. The actual bonding mecha-nism of this phosphate ester monomer to metal is notfully understood. The phosphate group in MDP maycovalently link to the positively charged metallic ionson the alloy surface."" It is also possible that the unsetadhesive and the plastic amalgam form a strongmechanical interlock as both materials harden. Figure3 shows evidence for Ihe interiocking ofthe amalgam

_ jme 2S, Number 7/1997 475

Tangsgoolwñtana et al

and Panavia 21, Nu piiblishetl arlicle has thorotighiyi.'lucidiilcd Ihc bonding mcclKinism lielwcen freshlycoiulctised aiiialgLini and doiikii aillicsivc matériels.

Amalgam iili<'\

DispersiilKn exhibited signiricaiilly less microleakaiieihan did T> lin btii tmlj for groups wilh enamel marginsin Ihc radioisotopi; sltidy (Table 5), No general trendof iiiicrolcLikage with respect lo amalgam alloy cOLildhe deicrmincd because the microieakage in Tytini-i;sinraiinns WLIS mil significantly diiïereni from that inDispersalkn icsinialioiis in ull olher compared

C'nmpuri'.i'ii ÍH-l\VíVn lluorcsccni and imlion-Hc/ic

The iniraclass corrolaiion indicLiled high agreementbebvceii liie lluurcscent and Ihe radioisolope tech-iiitiuos 111 this present study. This result contradictsearÜLT cinichisions that the results of microieakagetesting from dilferenl conüilions and techniques shouldniHbecompared,- "" "*'' However, comparison betweenthe findings in this study and previous sludies is almosiiüipossiblc. as some materials tesled in this sUidy haveniily rccciilly become commerciLilly available or were(ibiaitied before they were marketed.

The lltiorescent iechnii.|tiein Ihe piesenl study fuilcdlodilferentiatc ihc degree ofmicroleakage between theresiorations with Amalcoden and Copalile in bolhenamel and deniinal gingival margins. In contrast, thistechnique could identify a significant difference be-hveeii lhe resioraiiotis with All-Bond 2/Resinonierand ihosc wilh Panavia 21, These findings indicatedthai ihc lluurcsceni technique appeared to be moresuitable lor differentiating microieakage patterns indenliii adhesives wilh similar good performance. Themajtir advantage of the lluorescent technique withconfocul microscopy is avoiding the use of radioactivematerials.

On the other hand, lhe radioisotope study was ableto dillerenliaie the degree of microieakage between Iherestorations with All-Bond 2/Resinomer and Panavia21 only in the group wilh dentinai gingival margins.Nevertheless, with the use of radioisotope dye in thisstudy. Amulcodcn was shown to reduce microieakagemore than Copalite in restoration;, with dentinalgingival mai^ins. This may imply ihal '' Ca is appropriatefor malcriáis wilh a wider range ol" degree tif leakage.

The díilíi indicuie that the conlocal method iscapable of detecting the microieakage. its indicated bythe compLirison wiih ihe well-acceplcd radioisotope

technique. In addition, iheconfbcal method allows theobservation of the pathway and the location ol themicroieakage at the restoration-bonding agent-dentininterfaces. However, the confocal image is limited tothe ability of (he laser light to penetrate lhe specimen.Therefore, subsurface imaging was possible into thedeniinal tissue and the bonding agent but not inio lheamalgam restoration. The presenl study represents aninitial investigation of the microieakage of bondedamalgam lesiorations using laser scanning confocalmicroscopy, Kurther research is warranted to refine themelhod and to confirm the findings obtained from thepresent investigation.

It IS dilf~icult to correlate the observulions from thisstudy or any other in vitro dye or radioisotopepenetration study with in vivo penetration of eitherbacleria or oral fluid. Moreover, some restorativeniLiieriais exhibit antimicrobial activity that may be ableto inhibit recurrent caries development underneathbonded amalgam restoration^" even though leakagedoes occur. Long-term clinical studies are essential indetermining ihe iull chnicai performance of bondedamalgam restoration because this study represents onlya very early slage of ihc liletimc of this restoration.

Summary

1, The ability of the dental adhesive materials tesled toreduce microieakage ranked, from highest to lowest,as follows: ('/^All-Bond 2/Resinomer, I'J' Panavia21, and ¡3) Amalcoden, Copalite permitied thegreatest microieakage,

2, The incorporation of rhodamine B into the iiningmaterials did not affect iheir sealing properties butdid allow for easy identification of the adhesiveliner,

3, The findings of the fluorescent study indicated thatmicroieakage occurred most frequently at theliner-tooth interface,

4, The study generally failed to demonslrate a differ-ence in the degree of microieakage between Dispers-alloy and Tytin restorations.

5, The high agreement between the resuits of thelluorescent and the radioisotope studies indicatedthat the results of these Iwo microieakage tests canbe compared,

6, While the results of this study supported the use ofdental adhesive materials to line umalgam restora-tions, long-term data are needed lo verify iheirefïlcacy.


Tangagoolwatana et al

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