The effect of fibre insertion on fracture resistance
of root filled molar teeth with MOD preparations
restored with composite
S. Bellil, A. Erdemir2,M. Ozcopurr& G. Eskitascioglu3
rDepartment
of Endodontics,Faculty ol Dentistry, Selcuk University, Konya; 2Departmento[ Endodontics,Faculty of Dentistry,
I(irikl<aleUniversity,I(irild<ale;and 3DepartmentofProsthodontics,Faculty ofDentistry, Selcuk University, Konya, Turkey
Abstract
ing, the specimenswere stored in 10001,humidity at
37 "C for 1 day. Compressiveloading of the teeth was
performed using a universal testing machine at a
BelliS, ErdemirA. OzcopurM, Eskitascioglu
G. Theeffect
of fibreinsertion
onfracture
resistance
of rootfilledmolarteeth
crosshead speed of 0.5 mm min-r. The mean load
with MODpreparations
restoredwith composite.
lnternational
necessaryto fracture the samples were recorded in
EndodonticJournal,38,73-80,2005.
newtons (N) and were subjectedto analysisof variance
Aim To evaluatethe effectof using flowablecomposite
(anova) and Tukey post-hoc test.
with or without leno woven ultra high modulus
Results The mean load necessary to fracture the
polyethylenefibre reinforcementon fracture resistance
samplesin eachgroup were (in N): group I: 1676.75 t
of root fllled mandibular molars with mesio-occluso- 1 5 4 . 6 3 " , g r o u p 2 : 3 7 6 . 5 I + 3 7 3 6 b . g r o u p 3 :
distal (MOD) preparations.
7 3 3 . 2 3 + 1 3 3 . 3 3 ' 'g, r o u p4 : 7 8 6 . 4 8 + 1 4 5 . 3 4 " ,g r o u p
Methodology
Sixty sound extracted human man5: 943.63 + 121.I5d. There were statisticallysignifidibular molars were randomly assignedto five groups
cant differencesbetween the/groups annotated with
(n: I2). Group 1 did not receive any preparation.
different letters.
From groups 2 to 5, the teeth were root filled and MOD
(i) Use of flowable composite resin
Conclusions
preparations were created. Group 2 remained unreunder compositerestorationshad no effect on fracture
stored, Group 3 was restored with a dentine bonding
resistanceof root filled molar teeth with MOD prepasystem (DBS;SE Bond, Kuraray, fapan) and composite
rations, (ii) use of polyethylene ribbon fibre under
resin (CR) (AP-X; I(uraray). In group 4, flowable
composite restorations in root filled teeth with MOD
composite resin (Protect Liner F; Kuraray) was used
preparationssignificantly increasedfracture strength.
beforerestoringteeth with CR. in group 5, leno woven
Keywords: flowable compositeresin, fracture resistultra high modulus polyethyleneribbon libre (Ribbond,
ance, polyethyleneribbon fibre.
Seattle,WA, USA) was inserted into the cavities in a
buccal to lingual direction and the teeth were then
restoredwith DBS and CR. After finishing and polishReceived
73 May 2004; acceptetl
13 September
20O4
Introduction
Comparedto teeth with healthy pulps, root filled teeth
are consideredmore susceptibleto fracture as they
possess reduced dentinal elasticity (Johnson et al,
Correspondence:
Dr Sema Belli, Department of Endodontics,
Faculty of Dentistry, Selcuk University, Campus, 42079
I(onya, Turkey (Tel.; +90 332 2231234; fax: +90 332
24100 62; e-mail: [email protected]).
@2 0 0 5I n t e r n a t i oEnnadl o d o nJt iocu r n a l
1976),lower water content (Rosen1961, Heller et aL
1972), deepercavities (Madison & Wilcox 1988) and
substantialloss of dentine (Johnsonet al. 1976, Assif &
Gorfil 1994, Linn & Messer 1994, Assif et aL 2003).
Root canal treatment should not be consideredcomplete
until the coronal restoration has been placed (Wagnild
& Mueller 2002). Previous studies indicated that
complete cast coverage(Goerig & Mueninghoff 1983,
Hudis & Goldstein 1986), an indirect cast restoration
covering the cusps (Reeh et n/. 1989a), complex
International
EndodonticJournal,38, 73-80, 2005
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Fracture resistance of endodonticallv treated molars Belli et al.
amalgam restorations (Starr f 990, Smales &
Hawthorne 1997) or composite materials (Hernandez
et aL 1994) can be used for final restorations. With
recent advancementsin adhesivetechnology and new
and strongercompositematerials,it is possibleto create
conservative, highly aesthetic restorations that are
bonded directly to teeth. However, polymerization
shrinkage remains a problem for extensive direct
compositerestorations (de Gee et aI. 1993). As polymerization shrinkage is compensatedby flow of composite(Davidsonet aI. 1984), a rigid bond betweenresin
compositeand tooth structures generatescontraction
stressesat the bonding interfaces (Feilzeret al. 1987,
Kemp-Scholte& Davidson 1990). Thesestressescan be
reduced by several methods. Dentine bonding agents
are assumedto resistthe contraction forcesby forming a
continuous hybrid layer between the restoration and
tooth structure (Davidson 1996). Van Meerbeeket aI.
(1993) reportedthe hardnessand elasticityofthe resindentine bonding area using nanoindentation and concluded that the layer of collagen fibrils denselypacked
with resin may act as an inherent elastic buffering
mechanism to compensatefor the polymerizationcontraction of the restorative resin. One of the methods
suggestedfor reducing debonding during polymerization shrinkage is the application of a low viscosity,low
modulus intermediateresin between the bonding agent
and restorativeresin to act as an 'elasticbuffer' or 'stress
breaker' that can relieve contraction stresses and
improve marginal integrity (Kemp-Scholte& Davidson
1990, Van Meerbeeket aI. 1992). However, flowable
composite did not produce gap-free resin margins in
BIackII slot cavities(Belliet al, 2001).
The developmentof fibre-reinforcedcomposite(FRC)
technologyhas increaseduse of compositeresin materials in extensivepreparations.FRChas beenusedin the
laboratory for fabrication of single crowns, full and
partial coveragefixedpartial dentures(Valittu & Sevelius
2000, Edelhoffet aL 2O0I), fabrication of periodontal
splintsand chairsidefixed partial dentures(Meierset al,
1998, Belli & Ozer2000, Meiers& Freilich2001). FRC
hasbeenshown to possess
adequateflexuremodulus and
flexural strength to function successfullyin the mouth
(Vallittu 1998, Freilich et al. 1999). A finite elemental
stressanalysisstudy alsoreportedthat FRCpostand core
systemsprovidedmore adequaterestorationby protecting the remaining tooth tissue with its elasticmodulus
closeto dentine when comparedwith the conventional
rigid post-coresystems(Eskitasciogluet aL 2OO2).
These new materials and techniques enable the
practitioner to approach old problems from a different
@
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EndodonticJournal,38, 73-80. 2005
perspectiveand thereby achieveunique and innovative
solutions.Although there are many studieswith FRCin
the literature, the effect of fibre insertion as a stress
breaker within an extensivecompositerestoration has
not been studied.In this study, it was hypothesizedthat
creating an elastic layer under a compositerestoration
using a leno woven ultra high molecular weight
(LWUHMW) polyethylene fibre ribbon and/or flowable
composite would increase the fracture strength of
endodontically treated teeth with mesio-occluso-distal
(MOD) cavity preparations.
Materials
and methods
Sixty freshly extracted human mature mandibular
molar teeth with similar dimensions and without
caries, abrasion cavities and injury from forceps or
fractures were used. The teeth were cleaned of debris
and soft tissue remnants and were stored in physiological saline at *4 "C until required. The 60 teeth were
randomly assignedinto five groups of 12 teeth each
and were preparedas follows:
Group I
This group did not receive cavity preparation or root
canal treatment and were used as a control.
From groups 2 to 5: Access cavities were prepared
using a high-speedbur and water spray and the canals
were instrumentedwith K filesto an apicalsize3 5 using
the stepbacktechnique. Irrigation with 2 mL ol 5.25o/o
NaOCI preceded each file introduced into the canal.
Following biomechanicalpreparation,canalsweredried
with absorbentpaper points (Diadent Group International Inc., Chongfu City, Korea) and obturated with
gutta-percha(DiadentGroup International Inc) and AH
Plussealer(DentsplyDe Trey, Konstanz,Germany)using
coldlateral condensation.MOD cavitieswere preparedin
the teeth down to the canal orificesso that the thickness
of the buccal wall of the teeth measured2 mm at the
buccal occlusalsurface.2.5 mm at the cemento-enamel
junction and 1.5 mm lingual occlusalsurface,1.5 mm
at the cemento-enameljunction (Fig. 1). The teeth were
then embeddedin self-curing polymethylmethacrylate
resin (Vertex;DentimexDental,Zeist,the Netherlands)to
the level of the cemento-enameliunction.
Group 2
This group remained unrestored after MOD cavity
preparation (Fig. 1).
O 2005 International
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Belli et al. Fracture resistance of endodonticallv treated molars
l.smm
viscosity resin composite (flowable composite resin,
FCR) (Protect Liner F; Kuraray) and cured for 20 s.
This low modulus liner was then covered with the same
resin compositeusing a bulk technique as describedin
group 3 (Fig. 3).
Group 5
1 smm
After priming and bonding proceduresas in group 3,
the cavity surfaceswere coated with flowable composite as in group 4. Beforecuring, a piece of LWUHMW
polyethylenefibre (8 mm long, 3 mm width) (Ribbond;
Ribbond Inc., Seattle,WA, USA) was cut and coated
Figure 1 The schematic representation of MOD cavity
molar teeth.
Group 3
The cavitieswere cleaned and dried. After priming for
20 s (SEPrimer; Kuraray, Tokyo, Japan) cavity surfaceswere gently dried. SEBond (l(uraray) was appliedto
the cavity surfaces and cured for 20 s. The cavities
were then restored with a resin composite (Clearfil
AP-X; I(uraray) using a bulk technique and cured for
4 0 s ( F i g ,2 ) .
Group 4
After priming and bonding proceduresas in group 3,
the cavity surfaceswere coated with a layer of low
Figure 2 The restorationof teeth in group 3 with DBS and CR
Endodontic
Journal
O 2005International
Figure3 The restorationof teethin group4 with FCR,DBS
and CR,
with adhesiveresin. Excessmaterial was removed and
the fibre embeddedinside the flowable compositein a
buccal to lingual direction (Fig. 4). After curing for
20 s, the cavities were restored with composite as
describedabove (Fig. 5).
After storing in an incubator at 37 "C in 100%
humidity [or 24 h, the specimenswere placed into a
UniversalTestingMachine (Instron, Canton, MA, USA)
and loadedcompressivelyat 0.5 mm min-r. Compressive force was appliedwith a 5-mm diameter stainless
steel bar. In all cases the force was applied to the
occlusalsurfaceof the restoration touching buccal and
lingual cusps of the teeth. The force necessary to
fracture each tooth was recorded in newtons (N) and
the data were subjected to a one-way analysis of
variance (,tNova) and posf hoc Tukey HSD test for the
five experimentalconditions.
International
EndodonticJournal,38, 73-80, 2005
Fracture resistanceof endodonticallv treated molars Belli et al.
Figure 4 The applicationof 3-mm width
polyethyleneffbre with flowable composite resin from buccal to lingual
direction.
One-way aNovn indicated that the fracture strength
of group 1 was significantly higher than the other
groups (P < 0.05). Restoring teeth with resin composite with or without a flowable compositelining (groups
3 and 4) increasedfracture strength when compared
with the nonrestoredgroup (group 2) (P < 0.05). Use
of flowable compositeresin under the compositeresin
(group 4) did not increase fracture resistancein root
filled teeth (P > 0.05). Inserting a piece of LWUHMW
polyethylenefibre in a buccal to lingual direction under
resin composite restoration (group 5) significantly
increasedfracture strength of molar teeth with MOD
preparations(P < 0.05).
3t4-
214-
1t4-
Figure 5 The schematic representation of teeth restored in
group 5.
Results
The minimum, maximum and mean fracture resistance
(N) and the standard deviation for each of the five
experimental conditions are presented in Table 1.
G r o u p s C a v i t y R e s t o r a t i o tny p e
G r o u p1
G r o u p2
G r o u p3
G r o u p4
G r o u p5
Intact
MOD
MOD
MOD
MOD
i n t a c tt e e t h
nonrestored
D B S+ C R
F C R+ D B S + C R
polyethylene
fibre+
FCR+DBS+CR
n
Discussion
Restorationof root filled molars is a challenge,Sound
tooth structure removed during cavity preparation
influences its strength and ability to resist loading
(Mondelli et al. 19B0, Larson et al. 19B1, Reeh et nl.
1989b). Preservationoftooth structlrre is important tor
protection against fracture under occlusalloads and for
M i n i m u m M a x i m u m M e a nr S D
12 1472.80
12 334,70
12 513.80
12 568.30
12 733.70
1932.50
431.30
886.00
1064.60
1097.20
1 6 7 6 . 7 t5
3 7 6 . 5 1t
7 3 3 . 2 3t
7 8 6 . 4 8t
9 4 3 . 6 3r
1 5 4 . 6 3a
3 7 . 3 6b
1 3 3 . 3 3c
1 4 5 . 3 4c
121.15
d
Table 1 Minimum, maximum and mean
fracture resistance(N) and the standarcl
deviation for each of the five experimental conditions
D B S ,d e n t i n eb o n d i n gs y s t e m ;C R ,c o m p o s i t er e s i n ;F C R f, l o w a b l ec o m p o s i t er e s i n .
S i m i l a rl e t t e r si n d i c a t es t a t i s t i c a l lsyi m i l a rv a l u e s( P > 0 . 0 5 ) .
E
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Belli et al. Fracture resistance of endodonticallV treated molars
its survival. The main factor endangering the survival of
pulpless teeth is loss of dentine (Helfer et aI. 1972,
Carteret aL 1983, Greenfeld& Marshall 1983). During
root canal treatment, there can be appreciableloss of
dentine including anatomic structures such as cusps,
ridges and the arched roof of the pulpal chamber.
Dentine provides the solid base required for tooth
restoration and so the fundamental problem is the
increasedquantity of sound dentine remaining to retain
and support the restoration (Johnsonet aL I976, Assif
& Gorfil 1994, Linn & Messer1994, Assifet al.2OO3).
Restorationof teeth is an important final step of root
canal treatment.The purposeof a restorationis not only
to repair the tooth, but also to strengthenthe tooth and
provide an effectivesealbetween the canal system and
mouth. In the presentstudy, the strength of teeth was
reducedsignificantlyafter cavity preparation,as shown
in most previousstudies(Mondelliet aI. 1980, Gelbet aI.
1986,Joyntet al, 1987,El-Sherifetal. 1988, Jagadish&
Yogesh 1990). Reinforcement of the cavity with a
restorativematerial is necessaryto support the remaining tooth structure. Some studies have found that
bonded compositerestorationswill strengthen a tooth
when comparedwith amalgam (Tropeet ai, 1986, Reeh
et aL I989a, Hurmuzlu et aL 2OO3a)whereas others
have beenunableto show a difference(Joyntet aI.1987,
Steele& fohnson 1999). Adhesive restorations better
transmit and distribute functional stressesacross the
bonding interface to the tooth with the potential to
reinforce weal<enedtooth structure (Hansen 1988).
Tropeef al. ( 19 8 6) showedthat the resistanceto fracture
of teeth increasedsignificantlywhen MOD preparations
were acid-etchedbefore restoration with a composite
resin, Hurmuzlu et aL (2003a) reported that teeth
restoredwith packablecompositeresin had the highest
resistanceto fracturewhen comparedwith amalgam-or
ormocer-based
composite.
Polymeric adhesivesfor bonding to dentine are used
in dentistry for a wide range of purposes. Applying
most adhesivesystemsinvolves removing or modifying
the smear layer and demineralizing the dentine surface.
Current methods of dentine bonding use acids to
demineralizethe surfacefollowed by the use of hydrophilic low molecular weight primers to penetrate the
remaining collagen network. With the application of
adhesive a resin-impregnated dentine hybrid layer
results, and a micromechanical bond is formed with
the dentine surface(Nakabayashi1982, Duke 1993,
Inokoshi et al, 1993).
When restoring with composite,many factors may
effectthe resistanceof a tooth to vertical and/or cuspal
EndodonticJournal
O 2005 International
fracture,such ascavity dimension(Mondelliet aL I98O,
Purk et aL 199O) or restorative system utilized (Morin
et aL 1984, Eakle 1986). An extensive cavity can be
restoredusing a dentine bonding system (DBS) and a
resin composite,however, the polymerization reaction
of light cured compositesleads to the developmentof
higher stresseswhen the compositeresin is bonded to
the cavity walls. Joynt et aI. (\987) suggestedthat the
fracture resistance of premolar teeth with MOD cavity
preparationsrestoredwith compositeresin may increase
if an incrementalresin placementand curing method is
used.Against the widely acceptedbelief that incremental compositeplacementresults in reducedstressbuildup at the tooth-restorationinterface(Kreici et al, 1987).
Versluis et aL (7996) reported that theoretically bulk
flllings generatelessvolumetric shrinkage within identical cavity shapes.Although layering concepts have
beendescribedas mandatory when working with resinbasedcomposites,the effect of layering technique was
eliminatedand bulk techniquewas usedin this study to
evaluatethe stressmodifying effectof flowable composite lining with or without fibre insertion.
High viscosity bonding agents may also provide a
layer of substantial thickness that acts as a stress
absorber(Alhadainy & Abdalla 1996) and flow of the
composite may release contraction stresses(Takada
et aL 1994,Uno et aL 1994). An advantageofbonding,
coupledwith compositecore build-up, is the high bond
strength to tooth structure and increasedresistanceto
fracture (Hernandez et aL 1994). Hurmuzlu et aL
(2003b) compared the effect of six different DBS on
fracture resistanceof teeth and showed that the type of
DBShad no influencein the fracture resistanceof teeth,
In the presentstudy, it was hypothesizedthat covering
the surfacewith flowable compositeor the addition of
an LWUHMW polyethylenefibre before restoring teeth
with resin composite would provide an increase in
fracture strength. This was theorized on the concept
that the presenceof the glassor polyethylenenetwork
would create a change in the stressdynamics at the
restoration/adhesiveresin interface. This hypothesis
was demonstrated in the LWUHMW polyethylene fibre
group as inserting a pieceoffibre in a buccal to lingual
direction significantly increased fracture strength of
root fllled molar teeth with MOD preparations. The
elastic modulus of polyethylene fibre with adhesive
systemswas previouslymeasuredby Eskitasciogluet al.
(2OO2). The higher modulus of elasticity and lower
flexural modulus of the polyethylene fibre might have a
modifying effect on how the interfacial stressesare
developedalong the restoration/tooth interface.
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EndodonticJournal,38. 73-80. 2005
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Fracture resistanceof endodonticallV treated molarc Belli et al.
With the concept that the presenceof the glass or
polyethylene network would create a change in the
stressdynamicsat the enamel/composite/adhesive
interface,Meiers et aL (2OO3)testedshear bond strength of
composite to flat bovine enamel surfaces with four
differentfibrereinforcementmaterials.Although three of
the lbur materialshad no effecton shear bond strength,
one of the materials tested(Connect;Kerr, Orange,CA,
USA) improved shear bond strength. As a result they
concluded that the higher modulus of elasticity and
lower flexural modulus of the polyethylene flbre may
have a modifying effecton how the interfacial stressesare
developed along the etched enamel/resin boundary.
Haller et aL (I99I) reported a reduction of the bond
strength to dentine of some adhesive systems when
appliedto 3D cavitiesin comparisonwith flat surfaces.In
the present study, MOD preparations were used. The
resultsmay be differentif flat surfaceswere used.On the
contrary, lining the cavity surfaceswith flowable composite did not change the fracture strength. The thicknessof the elastic layer created by flowable composite
might not be enough to compensatecontraction stresses
insidean MOD preparation or the physical propertieso[
an LWUHMW polyethylenefibre might have a positive
effecton distributing stressalong the restoration-tooth
interface.
This study was carried out in in yifro conditions and
the test was performed 24h after restoration. The
thermal, chemical and physical stresses that the
restoration could be subjectedto over a longer period
in vivo may adversely affect the results, therefore
further investigation is necessaryto predict the in vivo
behaviour of this type of restoration,
Conclusions
Within the limits of this study, it can be concludedthat:
1 MOD cavity preparation reduced fracture resistance
of root filled teeth.
2 Useof flowablecompositeunder compositerestoration
had no effecton fracture resistanceof root filled molar
teeth that had been restoredwith compositeresin.
3 Inserting an LWUHMW polyethyleneribbon fibre in
root fllled molar teeth with MOD preparationssignificantly increasedfracture strength.
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