Journal of Oral Rehabilitation, 1981, Volume 8, pages 121-129

The interaction between lining materials andcomposite resin restorative materials

G. L. LINGARD, E. H. DAVIES a/7c/J. A. VON FRAUNHOFERInstitute of Dental Surgery, University of London

SummaryThe effects of four lining materials, Dycal, Procal, Cavitec and Poly F cement onAdaptic and Concise have been investigated in vitro. The parameters studied weresurface roughness, hardness and colour both with and without an intermediate(or bonding) resin being present between the restorative material and the liner.

The effects of the four liners on the composites varied both between the liningmaterials themselves and with the composite resin. Two materials, Procal and Dycal,had little interaction with the composites, provided an intermediate resin was usedwith the latter. Cavitec appeared to have an adverse reaction with the compositesand Poly F, whilst having no effect on the colour of the composites, did increasesurface roughness. The adverse effects of lining materials were ascribed to minorconstituents, particularly methyl salicylate, present in the formulation.

IntroductionIt has been suggested that there is a degree of incompatability between compositeresins and certain hning materials resulting in an alteration in surface hardness andsome discolouration in the former (Bow, 1976). Eugenol-based linings have longbeen known to have a deleterious effect on composite resins (Reisbeck& Brodsky,1971; Griffin & Cannon, 1973; Peyton & Craig, 1971; Civjan, Huget & de Simon,1973). This was felt to be due to an inhibition of the resin polymerization by theeugenol constituent although dissolution effects are probably also operative. Calciumhydroxide-based linings are widely used in clinical practice and whilst the absenceof eugenol was hitherto thought to have eliminated this interaction, there is someevidence to suggest these materials may also react with the composite resins.

Messing (1971) reported that staining of the poly (methylmethacrylate) compositeTD71 was found to occur over Dycal, a widely used commercial preparation contain-ing a calcium hydroxide base. He suggested that this discolouration may be due to atrace constituent, namely methyl salicylate.

Adaptic, when exposed to Dycal, was found to show increased surface roughnessand a yellow discolouration of its surface layer. These changes were interpreted byGrajower, Hirschfeld & Zalkind (1974) in a scanning electron microscopy study asCorrespondence: Dr J. A. von Fraunhofer, School of Dentistry, University of Louisville, P.O. Box35360, Louisville, Kentucky 40232, U.S.A.

0305-182X/81/0300-0121 $02.00 1981 Blackwell Scientific Publications121

122 G. L. Lingard, E. H. Davies and J. A. von Fraunhofer

indicating that interaction had occurred between the two materials. Civjan et al.(1973) observed a 10% decrease in hardness with Concise and Blendant, when placedin contact with Pulpdent, a calcium hydroxide-based paste. In contrast, Adaptic andD.F.R. did not show this effect.

There is an increasing use of composite resins for restoring fractured incisorsand in such cases, a large area of dentine is often exposed with the concomitant needfor adequate lining. Clearly, it is important that there should be no intrinsic discoloura-tion of the composite resin due to interaction with the lining since this could leadto impaired aesthetics. In fact, it has been suggested (Bow, 1976) that carboxylatecements might be used as linings to obviate any deleterious effects on the compositerestoration.

This study was undertaken to determine the following:(1) Whether interaction does occur between linings such as Dycal, Procal, Cavitec

and Poly F cement and composite resins;(2) whether the interposing of an unfilled resin between the composite material

and the lining material reduces or prevents such interaction.

Materials and methodsFour lining materials, Dycal, Procal, Cavitec and Poly F cement, and two compositeresin restorative materials, Adaptic and Concise, were used in this study. Details ofthese materials are shown in Table 1.

Table 1. Details of lining materials used

Material Manufacturer Principal ingredient

Dycal L.D. Caulk Company, Calcium hydroxideDelware, U.S.A.

Procal Minnesota Mining and Calcium hydroxideManufacturing Company,Minnesota, U.S.A.

Cavitec Kerr Europe, Zinc oxide andScafati, Italy eugenol

Poly F Amalgamated Dental Poly carboxylateCompany, London, cement with fluorideEngland

A test jig was devised that permitted interaction between a composite resin and alining material over one half of the specimen with the other half remaining in itsas-set state so that it could be used as a control.

Disc specimens were produced using a metal ring, 2 cm internal diameter and2 mm deep, one end of which was sealed with tin foil. The hning materials wereinserted into the cavity to half fill it and allowed to set under hand pressure againsta tin foil covered disc to give a smooth as-set surface. When set, one half of thelining was covered with a single thickness of tin foil and the composite material,mixed in accordance with the manufacturer's recommendations, was inserted againstthe lining and the exposed surface was allowed to set against a glass slab coveredwith tin foil for 5 min. When a bonding agent was used, it was painted onto thehning and allowed to set for 2 min before the composite material was inserted.

.;Y; Interaction of restorative materials and liners 123

After setting the lining-composite resin disc specimens were stored at 37C for1 month under one of the following conditions: dry, 100% humidity or immersedin distilled water. Three specimens of each lining-composite system were prepared.

After testing, the discs were separated and the surfaces of composite resins thatwere set against the lining were examined for changes in surface roughness, hardnessand colour followed exposure to the test conditions. Alteration in surface roughnessof the test surface compared to that of the control was assessed visually and witha hand-held probe. At the same time, any discolouration was also noted, the changesbeing designated as slight, moderate or severe. A more detailed colorimetric analysiswas performed with a Lovibond Flexible Optic Tintometer, the procedure havingbeen described previously (von Fraunhofer & Davies, 1973) and discolourationwas assessed in terms of changes in the chromaticity values.

Surface hardness changes were assessed with a Vickers pyramidal hardness(V.P.N.) indentor, the surfaces being lightly polished with water-lubricated 800 grit(17 /xm) silicon carbide paper and chamois cloth impregnated with 6 /xm diamondpaste to facilitate accuracy in measurement.

Table 2. Dycal: visual assessment of surface discolouration roughness andhardness

Material

Adaptic

Adaptic

Concise

Concise

Medium

No bond

Bond*

No bond

Bond*

Condition

Dry100%WetDry100%WetDry100%WetDry100%Wet

No change

DRHDRHDRH

DDDR

Slight

DRHDRHDR

DHDH

RHRHH

Moderate Severe

H

R R DHR

D: surface discolouration.R: surface roughness.H: decrease in surface hardness.^Denotes presence of intermediate unfilled resin layer.

ResultsThe visual assessment of surface roughness, hardness and discolouration is representedin Tables 2-5, while Tables 6 and 7 show the colourimetric analysis and Table 8 thevariation in Vicker's hardness.

All specimens showed some variation in one or all of these factors. The alterationin surface roughness and surface hardness when Dycal, Cavitec and Poly F were setagainst Adaptic and Concise was modified by the bonding medium. This caused areduction in the observed discolouration of the compositeDycal and compositeCavitec specimens. There was no discolouration in those specimens exposed to Poly Fcement, whether or not an intermediate resin layer was present but a decrease insurface hardness and an increase in surface roughness occurred.

124 G. L. Lingard, E. H. Davies andJ. A. von Fraunhofer

Table 3. Cavitec: visual assessment of surface discolouration roughnessand hardness

Material Medium Condition No change Slight Moderate Severe

Adaptic

Adaptic

Concise

Concise

No bond

Bond

No bond

Bond

Dry100%WetDry100%WetDry100%WetDry100%Wet

D

DDD

DD

DD

DDDD

RHRH

RHRHRHRHRHRHRHRHRH

RH

Table 4. Poly F: visual assessment of changes in surface discolouration,roughness and hardness

Material Medium Condition No change Slight Moderate Severe

Adaptic

Adaptic

Concise

Concise

No bond

Bond

No bond

Bond

Dry100%WetDry100%WetDry100%WetDry100%Wet

DHDHDHDHDHDHDHDHDHDHDHDH

RRR

RRR

R R R

,

R R R

DiscussionThe interaction between the two composites and the four lining materials variedwith the nature of the individual materials, the presence or absence of an unfilledresin intermediate or bonding layer and the storage conditions. In the absence of thebonding intermediate, Dycal affected the colour, roughness and surface hardness ofboth Adaptic and Concise but not when it was present (see Table 2). Procal, however,caused less alteration in surface roughness and hardness and almost no change incolour, except under dry conditions with Concise.

In contrast, Cavitec affected both materials irrespective of whether the intermediatelayer was present or not except that under dry storage, this material had no discolour-ing effect on Adaptic. Poly F, under all conditions, had no effect on the colour andsurface hardness of the two composites although the degree of roughness increasedfrom slight to moderate in the absence of the bonding intermediate. This rougheningeffect on the composites is probably a consequence of the inherent surface roughnessof Poly F itself. When a bonding medium is present, it might provide a slight 'cushion-ing' and smoothing effect so that the effect of the surface irregularity of the liningis reduced and, consequently the composite roughness is less marked.

Interaction of restorative materials and liners 125Table 5. Procal: visual assessment of changes in surface discolouration,roughness and hardness

Material Medium Condition No change Slight Moderate Severe

Adaptic

Adaptic

Concise

Concise

No bond

Bond

No bond

Bond

Dry100%WetDry100%WetDry100%WetDry100%Wet

DDDDRHDRHDRH

DDDDDR

DRH RH RH

DR HRH RH RH RH H

Table 6. Colorimetric studies with Adaptic

No bond Bond

Liningmaterial

Procal

Cavitec

PolyF

Dycal

37C

Dry100%WetDry100%WetDry100%WetDry100%Wet

&

&

&

&

H

H

H

H

L

25-725-723-425-325-723-425-726-325-725-725-723-4

Control

A

580580580577577577580580580580580580

Pe

141414141414141414141414

L

25-725-725-718-218-217-322-320 919-023-421-321-3

Test

A

577577577582582582580580580580580580

Pe

141414121212141414141414

L

23-423-423-423-422-322-324-323-723-721-323-419 5

Control

A

580580580577577577580580580577577577

Pe

141414141414141414141414

L

22-322-322-322-322-322-322-923-323-321-324-521-3

Test

A

577577577577577582580580579577577577

Pe

141414141412131313141414

L=luminance.A=dominant wave length (nm).Pe=spectral purity.

The yellow discolouring effect of the liners of the composites was most apparentunder moist conditions. Using the system described previously for measurement ofthe colour change (von Fraunhofer & Davies, 1973), a pattern emerged wherebyalteration in the luminance values was detected with all systems. Overall, there wasa decrease in luminance when Dycal, Cavitec and Poly F were set against Adaptic andConcise but an increase or little change occurred with Procal. This alteration in lumin-ance is indicative of changes in the composite surface topography, Procal causing theleast disruption. There was little alteration in the spectral purity and dominantwavelength for the Adaptic systems except when exposed to Cavitec. Here, a shift indominant wavelength of 5 fxm occurred, a definite alteration in colour. However, these

126 G. L. Lingard, E. H. Davies andJ. A. von Fraunhofer

Table 7. Colorimetric studies with Concise

Liningmaterial

Procal

Cavitec

PolyF

Dycal

37C

Dry100%WetDry100%WetDry100%WetDry100%Wet

&

&

&

&

H

H

H

H

24232424242425242423

L

-5-4-5-5-5-5-3-3-5-4

23-424-5

Control

A

579579579579579579578578578579579579

Pe

181818181818191919181818

No

L

26-926-928-819-520-821-827-826-221-519-526-923-4

bond

Test

A

578578578579578578578578578577578578

Pe

191919182121191819201919

L

26-926-926-924-524-524-524-125-324-524-526-524-5

Control

A

579579579580580580578578578578578578

Pe

181818181818222122191919

L

26-923-426-520-420-420-428-314-227-725-926-521-8

Bond

Test

A

580579579580579579578578578577578578

Pe

18IB18181818181818171921

L = luminanceA = dominant wave length (nm).Pe = spectral purity

Table 8. Indentation hardness (V.P.N.)

Adaptic Concise

No bond* Bondt No bond* Bondt

Control Test Control Test Control Test Control Test

Dycal Dry100% & HWet

Cavitec Dry100% & HWet

Poly F Dry100% & HWet

Procal Dry100% & HWet

97-6 68-691 8 86 990-0 77-297-6 79-89 0 8 8 6 190-0 68-198-5 91-691 6 82-591-6 81-298-5 97-691-6 9 4 690 0 94 6

99-4 68-1861 95-194-1 94-199-4 79-292-4 78-587-6 90-899-4 95-291 6 90-087-6 70-299 4 98-587-6 91-691 6 91 6

89-2 65-5101 0 100-0101-0 83-290-0 80-399-4 82-5

103-0 84-090-8

103-0101-090-8

100-0101-0

90-089-281-692-497-699-4

91-6 98-595-1 105-094-1 84-792-495-893-291-594-693-2

81-294-187-681-694-190-8

91-6 91-695-1 94-293-2 94-2

* No bonding medium (unfilled resin layer) present.t Unfilled resin intermediate applied to the lining material.

factors showed greater variance when the Concise systems were examined, Caviteccausing an alteration in spectral purity of 3% and all three linings, viz. Cavitec,Dycal and Procal, caused a 1-2 /xm shift in dominant wavelength.

From the readings it is apparent that Concise is affected to a greater degree bythe lining materials than Adaptic, and of these Cavitec had the most marked effect.

Interaction of restorative materials and liners 111

With the use of a bonding intermediate, the chromaticity values for Adaptic remainedmore or less constant but those for Concise exhibited some variation; in particular,a change in luminance of 2-5 % was found when it was exposed to Procal, Caviteca n d P o l y F . - . , - . , . - - : : . : . ; - - .- , - , . - . , , , , . : , ; : : - , - : - v ^ . . ^ ' : : " . ;

This finding also suggests a smoother surface on placing an intermediate betweenthe lining and composite; Adaptic being less affected than Concise.

It seems that the differences in chromaticity values do not accurately reflect theobserved colour change and this may be due to two factors. A relationship doesexist between luminance, spectral purity and surface roughness (von Fraunhofer &Davies, 1973) although this is little understood. Therefore, as the differences were notin the dominant wavelength, reflecting a true shift in colour, but predominantly inluminance with some alterations in spectral purity the recorded chromaticity assess-ment may merely reflect characteristics of the surface topography rather than anactual shift in colour.

It is possible that the standard head of the colorimeter, measuring light reflectedfrom the sample surface at 45, should be modified. This follows from the fact thatin any measurement of the optical properties of a surface, the geometry of the measur-ing head can be a factor in the results obtained. Thus, in studying a gloss or brightsurface, i.e. one having a specular refiectance greater than 50 %, a 45 or 60 (from thenormal to the surface) measuring head should be used but for a very glossy or brightsurface, a higher angle (20) instrument is required whilst lower angles should beutilized for matt surfaces. In contrast, the sheen of a surface should be measured atlow angles, i.e. greater than 70. Thus with a dental restorative material which isrequired to exhibit both brightness and sheen, the measurement of optical propertiesinevitably requires a compromise to be made, particularly when the surface colour,which is affected by the measuring angle, is required to be characterized. It is possiblethat if a different geometry measuring head were used, any shifts in the dominantwavelength could be more readily detected. A low angle instrument, for example,might be able to detect colour changes arising from surface roughness.

Alterations in surface roughness was visually assessed (Tables 2-5). An overallincrease in surface roughness did occur although inherent in the experimental designwas a smooth setting surface for all the lining materials. The most severe disruptionoccurred with Cavitec and Poly F, although the use of the intermediate bondingagent reduced the roughness in all cases except with Cavitec.

Gross changes in surface hardness (Table 3) were also noted when Cavitec wasset against Adaptic and Concise; while these were less for Dycal, there were stillsome changes. Procal and Poly F caused little effect.

These findings were generally substantiated when the macrohardness was measured.Of all specimens Procal caused the least alteration whether in the unbonded or bondedstate. Contrast this with Dycal where alterations of 5-29 V.P.N. were measuredwith Adaptic and 1-23 V.P.N. with Concise, the greatest of these occurring in drystorage. These were reduced with the application of the intermediate resin wherea slight increase was noted with the exception of Dycal-Adaptic in dry conditions.For Cavitec, on the other hand, macrohardness differences of 5-22 V.P.N. withAdaptic and 7-19 V.P.N. with Concise were noted. The application of an inter-mediate bond allowed only slight reduction, and this was chiefly with Concise. Anunexpected decrease of up to 20 V.P.N. was seen for composites set against Poly Fas this was not anticipated following the visual assessment. The greater decrease

128 G. L. Lingard, E. H. Davies andJ. A. von Fraunhofer

in hardness of Poly F was recorded in moist conditions. When a bonding intermediatewas incorporated into the system, less reduction in hardness occurred which confirmedthe visual characteristics. Since the respective bonding mediums contain no fillerparticles an assumption that this would result in a further decrease in surface hardnesswas not validated. In fact the antithesis occurred, therefore confirming that thereaction at the composite lining interface is modified by the application of a bondingmedium thus allowing the system to achieve greater strength.

The interaction is probably due to air entrapped between the filled resin and thelining material thereby inhibiting the polymerization of the adjacent resin. Thisincomplete polymerization may be due to a reaction of the atmospheric oxygenwithin the chain forming radicals so preventing the chain propogation and crosslinkage to give a highly polymerized structure (von Fraunhofer 1971). The presenceof a bonding medium would effectively reduce the amount of entrapped air so allowinga more complete polymerization of the resin and therefore achieving a smoother,harder surface. An alteration in the surface continuity would in turn modify theoptical properties of the resin; as this disruption would be situated at the lining-composite interface, a greyish discolouration described by Grajower et al (1974)would be evident.

There is no doubt that both Dycal and Cavitec, when set against Adaptic andConcise, cause a yellowish discolouration and that this is almost entirely correctedby the use of an intermediate bond. Dycal and Procal have calcium hydroxide bases,Cavitec a zinc oxide-eugenol base while Poly F is a carboxylate cement containingfiuoride. However, the first three all have a common constituent, the essential oils.A trace of butylene glycol disalicylate being present in Dycal, the eugenol base ofCavitec and methyl salicylate in Procal. It has been suggested that the essential oilsare incompatable with the cornposites (Messing, 1971) and so causing a yellowishor greyish discolouration but if this is so, it is not clear how Procal does not interactas do Dycal and, to a greater degree, Cavitec.

The undersurface of the lining material was also discoloured, this being moreintense than that which occurred in the composites. It is possible the initial reactionis within the lining material and a by-product is the yellow discolouration whichsubsequently penetrates the softened composite, more so in moist or wet conditions.This interaction would of course be masked by an intermediate resin.

ConclusionsIn situations where large areas of dentine are exposed, so requiring a lining prior toplacement of a composite restoration, as in class II fractures seen in anterior teethof children, the result of this study indicates the lining material of choice to be Procal.This lining apparently allows little interaction with either Adaptic or Concise usedwith or without an intermediate bond. Dycal, on the other hand gave good resultsproviding an intermediate bond was used to prevent an interaction between thesematerials and atmospheric oxygen, resulting in a poorly polymerized resin surfacewhich may discolour yellow, have a decreased surface hardness and an increasedsurface roughness.

Alternatively, Poly F can be used although when the pulp is in close proximity, acalcium hydroxide based lining may offer greater protection. There is no discolourationof the composite when set against Poly F, but a marked increase in surface roughnessdoes occur, which in tooth fractures with a large labial component, requiring extensive

Interaction of restorative materials and liners 129

lining, may cause an alteration in the optical properties of the composite resultingin a greyish discolouration. This effect is reduced through the application of anenamel bonding medium.

Cavitec is not recommended as although the interaction is modified by the inter-mediate resin, this is less than for Procal, Dycal and Poly F, and the liner wouldappear to have a greater adverse effect.

AcknowledgmentWe are indebted to Professor G.B. Winter for the motivation and support for thisstudy.

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Association of South Africa, 31, 449.CIVJAN, S., HUGET, E . F . & DE SIMON, L . B . (1973) Compatibility of resin composites with varnishes,

liners and bases. International Association of Dental Research Abstracts, 11, 65 (51st Generalmeeting).

VON FRAUNHOFER, J . A . (1971) The surface hardness of polymeric restorative materials. BritishDental Journal, 130, 243.

VON FRAUNHOFER, J.A. & DAVIES, E . H . (1973) The effect of surface finish and ultra-violet light onthe colour of restorative dental materials. Israeli Journal of Dental Medicine, 11, 8.

GRAJOWER, R . , HIRSCHFELD, Z . & ZALKIND, M . (1974) Compatibility of a composite resin with pulpinsulating materials. A scanning electron microscope study. Journal of Prosthetic Dentistry, 31,70.

GRIFFIN, J.R. & CANNON, R . W . S . (1973) The properties and clinical application of the moderncomposite resin. Australian Dental Journal, 18, 26.

MESSING, J . J . (1971) The use of silicate and composites in practice. Proceedings of the British Societyfor Restorative Dentistry, 1, 33.

PEYTON, R . & CRAIG, R . (1971) Restorative Dental Materials C. Mosby, St Louis, U.S.A.REISBECK, M . H . & BRODSKY, J.F. (1971) Strength parameters of composite resins. Journal of Prosthetic

Dentistry, 26, 178.

Manuscript accepted 25 January 1979