Operative Dentistry, 2012, 38-2, 000-000

Fiber-Reinforced Resin
Coating for Endocrown
Preparations: A Technical
Report
GT Rocca  N Rizcalla  I Krejci

Clinical Relevance
The presented clinical technique using fiber-reinforced composite as a resin-coating layer
was developed for adhesive endocrown restorations. This may reduce the risk of
catastrophic fractures and thus improve the success rate of this type of restoration on
nonvital teeth.

SUMMARY
Coronal rehabilitation of endodontically treated posterior teeth is still a controversial issue.
Although the use of classical crowns supported
by radicular metal posts remains widespread
in dentistry, their invasiveness has been largely criticized. New materials and therapeutic
options based entirely on adhesion are available nowadays, from direct composite resins to
indirect endocrowns. They allow for a more
*Giovanni Tommaso Rocca, Dr Med dent, Geneva School of
Dentistry, Department of Cariology and Endodontology,
Geneva, Switzerland
Nicolas Rizcalla, Dr Med dent, Geneva School of Dentistry,
Department of Cariology and Endodontology, Geneva, Switzerland
Ivo Krejci, Prof Dr Med Dent, Geneva School of Dentistry,
Department of Cariology and Endodontology, Geneva, Switzerland
*Corresponding author: Rue Barthelemy-Menn 19, Geneva,
1205 Switzerland; E-mail: Giovanni.Rocca@unige.ch
DOI: 10.2341/12-139-TR

conservative, faster, and less expensive dental

treatment. However, the absence of a metal or
high-strength ceramic substructure as in fullcrown restorations can expose this kind of
restoration to a higher risk of irreversible
fracture in case of crack propagation. The
aim of this case report is to present a technique to reinforce the cavity of an endodontically treated tooth by incorporating a fiberreinforced composite (FRC) layer into the
resin coating of the tooth preparation, before
the final impressions of the cavity. This technique allows the use of FRCs in combination
with any kind of restorative material for an
adhesive overlay/endocrown.
INTRODUCTION
The tendency of endodontically treated teeth (ETT)
to fracture is still a highly debated issue.1 The
biomechanics of an ETT are principally altered by
the tissue loss due to prior pathologies (caries,
fracture, cavity excavation), endodontic treatment
(access cavity, root canal shaping), and invasive

Operative Dentistry

Figure 1. Initial view of the endodontically treated first maxillary

molar after the removing of the provisional restoration.

Figure 2. Isolation of the cavity.

restorative procedures (post placement, crown fabrication).2 All of these factors may contribute to a
consistent elimination of coronal and radicular
tissues, which increases the fragility and thus the
fracture risk of an ETT.3 Recently, the restoration of
ETT with adhesive techniques has been advocated
both in the root and in the crown to prevent further
loss of sound tissues as adhesion ensures sufficient
material retention without the need for aggressive
macroretentive preparation.46 In particular, the use
of bonded overlays, such as endocrowns, for the
coronal restoration of an ETT is becoming more
common than classic full-crown restorations. The
reason for this change of paradigm is to achieve a
more conservative approach, which preserves tooth
tissues and allows reintervention in case of failure.
Furthermore, endocrowns eliminate many technical
steps during the fabrication, such as post cementation, core buildup, temporary crown, and potential
crown lengthening, which increase treatment time
and costs. Several in vitro studies and some in vivo
trials have confirmed the validity of this adhesive
approach, especially for molars.4,712

replacing restoration.15,17,18 Beside improving the

strength of the restoration, results of these studies
demonstrate that the incorporation of glass fibers
into composite resin materials usually leads to more
favorable fracture patternsabove the CEJbecause the fiber layer acts as a stress breaker and
stops the crack propagation. For classic lab-made
indirect composite restorations, FRCs are commonly
incorporated during the laboratory fabrication into
the base of the work piece.15,19 Unfortunately, this
technique is not possible when the composite
restoration is milled from a CAD/CAM block or with
any kind of ceramic material. The aim of this case
report is to present a technique that will allow the
reinforcement of the cavity of an ETT, as opposed to
the restoration.

However, even with conservative overlays/endocrowns, drastic failuresbelow the cementoenamel

junction (CEJ)are possible, and they have been
reported.1214 In case of crack propagation, the
absence of a metal or high-strength ceramic substructure as in full crowns can expose this type of
restoration to higher risk. To improve toughness,
leucite and lithium-disilicate reinforced ceramics
have been proposed. 15,16 As an alternative to
ceramics, composite resins have been suggested
because of their superior stress-absorbing properties
and high degree of toughness.8,10 In some in vitro
studies, fiber-reinforced composites (FRCs) have
been also employed to reinforce this kind of cusp-

The case reported is an endodontically treated

maxillary first molar in need of a restoration (Figure
1). A conventional indirect technique to fabricate an
endocrown is accomplished by programming two
appointments. During the first appointment,20 the
cavity is cut under local anesthesia. Once the cavity
is properly isolated (Figure 2), an adhesive system is
applied to the entire dentin and to the mesial thin
subgingival portions of enamel margins and then
light cured.21 Then, an adequate amount of composite resin is applied on the dentin and into the mesial
box and light cured. The goal is to fill the pulp
chamber eliminating the undercuts, cover all the
dentin, and relocate the cervical margins 1 mm

Before taking the final impressions of the cavity,

the FRC layer is incorporated on the surface of the
tooth preparation. This technique allows for the use
of FRCs in combination with any kind of restorative
material for an adhesive overlay/endocrown.
METHODS AND MATERIALS

Rocca, Rizcalla & Krejci: Fiber-Reinforced Endocrowns

Figure 5. The customized transparent silicon key.

Figure 3. The composite resin coating.

supragingivally. For that purpose, a low shrinking

nano-hybrid composite is applied (Tetric EvoCeram,
Ivoclar-Vivadent AG, Schaan, Liechtenstein). Considering the thickness of the future restoration, at
least 1.5 mm is recommended.9, Although adhesive
luting does not require any particular taper of the
cavity or a macro-retentive geometry, the fabrication
of a concavity in the middle of the pulpal chamber
will help with the positioning of the restoration
during insertion (Figure 3). The next step is the
insertion of the frame of resin preimpregnated
bidirectional glass fibers (Dentapreg UFM, ADM
A.S., Brno, Czech Republic) on top of the cavity
preparation. The suitable mesiodistal length of the
fiber network can be measured in the oral cavity
with a periodontal probe (Figure 4). Fibers are then
cut and left under light protection outside the
mouth. Then, a transparent silicon key (Elite

Figure 4. The suitable length of the fiber-reinforced composite sheet

is measured in the mouth with a periodontal probe.

transparent, Zhermack SpA, Badia Polesine, Italy)

is made to replicate the molar cavity and the occlusal
part of adjacent teeth (Figure 5). A layer of about 0.5
mm of flowable composite (Tetric EvoFlow, IvoclarVivadent AG), just enough to accommodate the
FRCs, is spread into the cavity and left uncured.
The fiber network is then inserted into the cavity
over the flowable composite film, and its mesh is
slightly opened (Figure 6). Thereafter, the FRC is
completely adapted to the cavity with the customized
silicon key and light cured (Figure 7). A second layer
of flowable composite is applied over the FRC and
light cured to cover all the exposed fibers (Figure 8).
The enamel margins are finished with fine diamond
burs (Composhape, Intensiv SA, Grancia, Switzerland) to obtain well-defined and sharp margins
before the impression of the cavity (Figure 9). The

Figure 6. The fiber frame embedded in a flowable resin is inserted

into the cavity.

Operative Dentistry

Figure 7. The fiber-reinforced composite layer is polymerized

through the transparent key with a powerful LED lamp.

Figure 9. Enamel is refurbished before the impressions.

indirect restoration is then fabricated. In the case

mentioned, the endocrown was milled from a CAD/
CAM composite resin block (LAVA Ultimate, 3M
ESPE AG, Seefeld, Germany; Figure 10). During the
following appointment, the intaglio surface of the
restoration and the cavity are adhesively treated,
and the restoration is luted with a conventional
light-cured micro-hybrid resin composite.22

based on adhesion are available nowadays.3,2325 In

the case of small to medium cavities, direct composite resins and indirect inlay/onlay restorations have
almost replaced metallic restorations.2629 In the
case of large cavities, or whenever a cuspal coverage
is needed, bonded endocrowns made of ceramic or
composite currently represent a valid alternative to
classical full crowns to restore the esthetics and
function of ETT.4,8,1012,15

DISCUSSION
In the past 30 years, the optimal performances
achieved by modern adhesive systems and the
growing emphasis on minimal invasive principles
in all fields of dentistry have finally promoted
adhesive strategies for ETT. Although metallic
restorations and classic PFM crowns supported by
radicular metal posts remain widespread, their
invasiveness in the root as well as in the crown has
been largely criticized, and new therapeutic options

Figure 8. A further thin layer of flowable resin is applied on fibers to

isolate and protect them.

In the clinical case presented, the large amount of

tissue lost due to pathology and to the endodontic
treatment supports the use of a minimally invasive
adhesive endocrown restoration instead of a full
crown. This technique allows for the conservation of
sound dentin and, above all, peripheral enamel,
maintaining the possibility of bonding margins of
the future restorations to it, which is known to have a
beneficial effect on marginal stability.30 The adhesive
procedure also eliminates the need for the use of a
post and a core, which would be otherwise necessary

Figure 10. The CAD/CAM composite restoration one month after the
luting.

Rocca, Rizcalla & Krejci: Fiber-Reinforced Endocrowns

in a typical crown preparation. Moreover, the adhesive cavity configuration keeps all margins of the
restoration away from the periodontium, which is
beneficial for hygiene and periodontal health.1,31
Once the tooth is isolated by a rubber dam, a microhybrid composite resin is applied to the cavity.
Regardless of its composition, resin coating aids
elevating cavity margins in slightly subgingival areas
as well as eliminating cavity undercuts, thus saving
sound tooth structure. Besides these structural
functions, the placement of this composite layer on
dentin immediately after cavity preparation provides
optimal cavity sealing and protection of the endodontic treatment during the temporization period.3234
Potential exposure to oral fluids and consequent
water sorption of bonding resin are minimized as
well.35 In addition, a composite base leads to the
fabrication of thinner inlays and onlays. This implies
a better light penetration through the definitive
restoration during light polymerization, introducing
the use of light-cured luting composites above
chemical or dual-cured resins for cementation. Furthermore, and especially for ETT, this composite base
reinforces cavity walls during the temporary phase.12
Thereafter, a frame of resin preimpregnated
bidirectional glass fibers is applied to the cavity
(Dentapreg UFM, ADM A.S.). FRCs have been
largely tested as materials above all in fixed partial
dentures, and they have proved to have superior
mechanical properties compared with conventional
restorative particulate filler composite resins.18,36,37
Their use is growing in cusp-replacing single-tooth
restoration to overcome limitations in terms of
fracture toughness of conventional composite restorative materials in highload-bearing posterior areas.15,1719,38 The FRC layer is positioned between the
tooth cavity and the restoration, in a more tensile
zone.37 In case of a classical indirect technique, this
configuration is achieved by incorporating the fibers
at the base of the composite overlay during the in-lab
fabrication. During function, in case of a vertical
crack inside the restoration, the FRC layer has the
ability to slow or stop the crack propagation through
underlying tissues, thus avoiding irreversible fractures. Considering the fibers orientation, the choice
of bidirectional or woven fibers seems more appropriate than unidirectional ones, as in the mouth the
restoration is submitted to multidirectional chewing
loads.15,18 Although some authors consider that in
single-tooth restorations, the ability of fibers to yield
better failure modes is the most beneficial effect of
FRC incorporation,17 Dere and others15 have recently found that the presence of a multidirectional FRC

layer under cusp-replacing composite restorations

also led to an improvement of fracture strength for
endodontically treated molars.
In the specific case presented, the fiber layer is
applied to the cavity before an impression is taken.
The incorporation of the fiber layer is accomplished
with the help of a layer of flowable composite. The
same highly filled micro-hybrid composite used to
seal the cavity may be the best choice from different
points of view, as flowable composites exhibit high
contraction stress during polymerization and may
not be sufficiently resistant to deformation under
load.39,40 On the other hand, highly filled microhybrid composites are quite difficult to spread in a
thin layer because of their high viscosity. The low
viscosity of the flowable composite guarantees the
diffusion of this resin into the preimpregnated fiber
network and decreases the risk of void incorporation.
The use of a customized transparent silicon key to
push the fiber layer in place during polymerization
improves the adaptation of the FRC sheet to the
geometry of the cavity and limits the thickness of
this intermediate layer. This aspect is of prime
importance when a thin restoration is indicated.,41
Moreover, the customized key simplifies the application and the polymerization of the FRC layer
compared with the use of specific metallic instruments as suggested by the manufacturer (Dentapreg
Fork, ADM A.S.). Once the FRC layer is cured,
further application of flowable composite over the
fibers protects them from an accidental exposure
during the temporary phase.22,37
The incorporation of the FRC layer into the tooth
cavity before the impression gives the operator the
choice between different restorative options. Several
materials can be used to fabricate endocrowns, such
as feldsphatic porcelain or reinforced glass-ceramic,
hybrid composite, or CAD/CAM ceramic and composite blocks. The scientific literature is still not
clear about which material is best indicated for this
kind of restoration. The authors prefer hybrid
composite resins, citing their stress-absorbing properties and their practical benefits such as the
possibility to modify and repair the surface easily.42
In particular, CAD/CAM resin blocks (LAVA Ultimate, 3M ESPE AG) may be used instead of classical
lab-made restorations in order to avoid defects
inherent in a free-hand laboratory technique and
thus improving mechanical properties. The in-lab
insertion of an FRC layer at the base of a milled
CAD/CAM composite restoration, even if theoretically possible, would mean cutting the restoration,
thus compromising its homogeneity.

Operative Dentistry

CONCLUSIONS
Adhesive overlays, often called endocrowns, are
increasingly used as a restorative alternative to full
crowns for nonvital teeth. Their advantages are
minimal invasiveness, simpler preparation, and
optimal coronal seal. The risk associated with these
restorations is rare but may result in a catastrophic
vertical fracture of the tooth-restoration complex,
often leading to the extraction of the tooth. The
presented clinical technique with FRC reinforcement
of the resin-coating layer was developed for use with
CAD/CAM composite or ceramic restorations. It may
reduce this risk of extensive fractures and thus
improve the success rate of this type of restoration
on nonvital teeth.
Acknowledgements
The authors would like to thank Dominique Vinci for the
laboratory work and Izabella Nerushay for the English
revision.
Conflict of Interest
The authors certify that they have no proprietary, financial, or
other personal interest of any nature or kind in any product,
service, and/or company that is presented in this article.

(Accepted 29 June 2012)

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