Dental Materials Journal 2020;
:
–
The influence of resin composite with high fiber aspect ratio on fracture
resistance of severely damaged bovine incisors
Lippo LASSILA1, Viivi OKSANEN1, Márk FRÁTER2, Pekka K.VALLITTU1,3 and Sufyan GAROUSHI1
1
Department of Biomaterials Science and Turku Clinical Biomaterials Center-TCBC Institute of Dentistry, University of Turku, Finland
Department of Operative and Esthetic Dentistry, Faculty of Dentistry, University of Szeged, Szeged, Hungary
3
City of Turku Welfare Division, Oral Health Care, Turku, Finland
Corresponding author, Sufyan GAROUSHI; E-mail: sufgar@utu.fi
2
The aim was to determine the fracture-behavior of incisors restored with different post-core foundations and crown made of
conventional composite (PFC, G-aenial Anterior). Forty bovine-incisors were cut and divided into 5 groups. Group A had teeth restored
using fiber-post and Gradia Core as core build-up and crown of PFC. Group B contained teeth restored with fiber-post and core made
of everX Flow and crown of PFC. In Group C, the teeth were restored with everX Flow as post-core and crown of PFC. Group D, postcore-crown restorations were indirectly made from CERASMART. Group E, teeth were restored with Gradia Core as post-core and
crown of PFC. Restored teeth were statically-loaded until fracture. ANOVA revealed that restoration technique significantly affected
load-bearing capacity (p<0.05). Restored incisors (Group B) had the highest load-bearing capacity (443 N) among all groups. Using
everX Flow as core material with fiber-post is promising to strengthen structurally compromised incisors.
Keywords: Load-bearing capacity, Fiber composite, Anterior crown, EverX Flow
INTRODUCTION
Endodontically treated teeth often require substantial
build-up with varying post-core foundation materials
to retain a complete crown restoration. In recent years
various types of fiber-reinforced composite (FRC) posts
have been introduced in order to provide the dental
profession an alternative to cast or prefabricated
metal posts for restoring endodontically treated teeth,
as the elastic moduli of these fiber posts are closer to
that of dentine than that of metal posts1). In restoring
severely damaged dentition, it is important to restore
strategically important teeth even though they may be
severely damaged. By using adhesive techniques and
particulate filler composite (PFC), as both core and
veneering material, root filled teeth can in some instances
be restored without conventional crown coverage2). A
complete crown with a 2 mm ferrule on a sound tooth
structure changed the distribution of forces to the root
and the post-core complex3). One previous study reported
that when bonded composite was used on structurally
weakened roots, there was no statistical difference in
strength between post-core restorations that used a
ferrule and those without a ferrule4). Many studies on the
mechanical strength of pulpless incisors restored with
fiber posts and PFC cores have shown lower incidences
of root fractures in comparison with other types of postcore systems5-7). Although some clinical reports suggest
that PFC core is a promising alternative to conventional
treatment modalities2,8), fracture of the composite core
has also been reported as a reason for failure9,10). Due
to failures of this type, using restorative composites
Color figures can be viewed in the online issue, which is available at J-STAGE.
Received Feb 22, 2019: Accepted May 13, 2019
doi:10.4012/dmj.2019-051 JOI JST.JSTAGE/dmj/2019-051
in large high-stress bearing applications such as core
structure remains controversial. The relatively high
brittleness and low fracture toughness of current core
composites still restrict their use in these large stressbearing foundations11,12).
The requirement to strengthen composite has led
to an ever increasing research effort into reinforcement
techniques. Several former approaches dealt with
incorporation of ceramic particle reinforced (random
orientation), whisker (single or multi-layer) or fiberreinforced (long or short fibers in various orientations)13-15).
A number of manufacturers have developed short fiberreinforced composites (SFRCs) which claimed to overcome
the weakness of conventional PFC. These SFRCs are
interesting materials because of their close resemblance
to dentine at the level of microstructure and mechanical
properties and some of them are recommended to use as
bulk base or core build-up materials in large cavities of
either vital or non-vital teeth16-19).
Previous studies by Garoushi and co-workers found
that the restoration of anterior endodontically treated
teeth with SFRC yielded a better load-bearing capacity
as opposed to the application of FRC post20,21). This was
partly confirmed by Forster et al., and Fráter et al.,
in endodontically treated premolar teeth with class I
cavity. In those studies, the directly layered SFRC post
and core groups displayed promising performance in
matter of fracture behavior22,23).
New formulations of flowable SFRC (everX Flow)
with high fiber aspect ratio (micrometer scale) and
isotropic reinforcement effect was launched globally in
2019. The effectiveness of fiber reinforcement is strongly
dependent on microstructural parameters such as resin
matrix, fiber diameter, fiber length, fiber orientation
2
Dent Mater J 2020;
and fiber loading18,24). Based on this knowledge, it can be
assumed that SFRC (with high fiber aspect ratio) could
sustain the loads required for complete anterior crown
restorations. Thus, the first aim of this study was to
investigate the load-bearing capacity and failure mode
of post-core restorations made of flowable SFRC. The
second aim was to investigate the curing performance
assessed by surface microhardness at different depths
within the root canal for each used composite. The null
hypotheses were that (1) the incisors restored with the
tested restorative techniques would show similar load
bearing capacity, and that (2) the failure mode would
not depend on the applied restorative technique.
MATERIALS AND METHODS
All materials used in this study were listed in Table 1.
Totally 40 intact and caries-free bovine incisors
were used. All teeth were prepared by the same trained
operator. The clinical crowns were removed from the
CEJ using 1000-grit (FEPA) silicon carbide abrasive
paper at 300 rpm under water cooling using an automatic
grinding machine (Struers Rotopol-11, Struers,
Copenhagen, Denmark). The pulp and periodontal tissue
were removed and cleaned. Then the root length was
adjusted to 15 mm from the root apex. After that, root
was embedded in plastic tube with acrylic resin except
for 2 mm of the cervical area (Fig. 1). Next, they were
divided into 5 groups (n=8/group) and stored in water
until further processing. The mean of root diameter
(SD) is 7.18 (0.4) mm and that of root canal diameter
is 2.37 (0.33) mm. There were no significant differences
in the each diameter of root and root canals. Post space
Table 1
:
–
preparations were made with post drills (Parapost
stainless drills, Coltène/Whaledent, Mahwah, NJ, USA)
using low speed hand piece under water cooling. Postcore and composite crowns were fabricated according to
the groups they belonged (Fig. 2).
Post and core fabrication
The coronal surface of the teeth was etched for 20 s using
a 37% phosphoric acid etch-gel (Scotchbond, 3M ESPE,
St. Paul, MN, USA), rinsed and gently air-dried. Dentine
adhesive were applied according to the manufacturer’s
instructions (Scotchbond Universal, 3M ESPE).
For Groups A (control) and B, dual-cure self-adhesive
luting material (G-CEM LinkAce) was mixed according
to manufacturer’s instruction, and delivered it into root
canal using automix tips. Prefabricated (Ø 1.6 mm) glass
fiber post (MI Core Fiber Post, GC, Tokyo, Japan) after
surface treatment with a primer (G-Multi Primer, GC)
was slowly inserted into luting-filled root canal. After
the post reached at the regulated length (10 mm), excess
luting material removed at level of sectioning. The
cement was light cured for at least 40 s (Elipar TM S10,
3M ESPE, Landsberg am Lech, Germany) in 45° angle,
close to the root of the post. The wavelength of the light
was between 430 and 480 nm and light intensity was
1,600 mW/cm2. The posts were extending 4 mm above the
coronal surface of the prepared teeth. Composite cores
(Group A: CBC, Gradia Core & Group B: SFRC, everX
Flow, fiber length 100–300 µm & Ø6 µm) extending 5.5
mm incisal to the sectioned tooth surfaces were build-up
and polymerized incrementally (20 s per layer), thus the
post will be covered with the core build-up material.
For Group C, posts and cores were fabricated from
Materials used in the study
Brand (code)
Manufacturer
G-aenial
Anterior
(PFC)
GC,
Tokyo, Japan
Hybrid microfilled
composite
UDMA, dimethacrylate co-monomers, prepolymrized silica
and strontium fluoride containing fillers 76 wt%
everX Flow
(SFRC)
GC
Flowable fiber
reinforced composite
(bulk shade)
Bis-EMA, TEGDMA, UDMA, micrometer scale
glass fiber filler (100–300 µm & Ø7 µm),
Barium glass 70 wt%, 46 vol%
Gradia Core
(CBC)
GC
Dual-cured core
build-up composite
Methacrylic acid ester 20–30 wt%, fluoro-alumino-silicate
glass 70–75 wt%, silicon dioxide 1–5 wt%.
Cerasmart
GC
CAD/CAM block
Bis-MEPP, UDMA, dimethacrylate co-monomers,
silica and barium nano glass 71 wt%
G-CEM
LinkAce
GC
Dual-cured, selfadhesive cement
Paste A: fluoroalumino silicate glass, initiator, UDMA,
dimethacrylate, silicon dioxide Paste B: silicon dioxide,
UDMA, dimethacrylate, initiator, inhibitor
MI Core
Fiber Post
GC
Regular fiber post
UDMA, PMMA, glass fibers
Type
Composition
UDMA, urethane dimethacrylate; TEGDMA, triethyleneglycol dimethacrylate; Bis-EMA, Ethoxylated bisphenol-Adimethacrylate; Bis-MEPP, 2,2-bis(4 methacryloxypolyethoxyphenyl) propane; PMMA, polymethyl methacrylate; wt%,
weight percentage.
Dent Mater J 2020;
:
–
Fig. 1
A photograph showing test specimen before (A) and after restoration (B
and C) and the static load test setup (D).
Fig. 2
Schematic figure representing the test groups with different post-core
foundations.
Group A: fiber-post and Gradia Core as core build-up and crown of PFC.
Group B: fiber-post and core made of everX Flow and crown of PFC.
Group C: everX Flow as post-core and crown of PFC. Group D: postcore-crown made from Cerasmart. Group E: Gradia Core as post-core
and crown of PFC.
SFRC (everX Flow). Posts were made by applying and
polymerizing the SFRC into the prepared canals in bulk
and cores were fabricated and polymerized as described
previously.
For Group D, a photoimpression was taken of the
post-core-crown model using dental CAD/CAM device
(CEREC, Sirona Dental Systems, Long Island City, NY,
USA). A single-structure of post-core-crown restorations
were indirectly made from CAD/CAM composite block
(Cerasmart) and cemented using dual-cure self-adhesive
luting material (G-CEM LinkAce).
For Group E, posts and cores were fabricated from
CBC (Gradia Core). Posts were made by applying and
polymerizing the CBC into the prepared canals in bulk
and cores were fabricated and polymerized as described
previously.
In order to have the same core dimensions,
transparent template matrix (Memosil 2, Heraeus
3
Kulzer, Hanau, Germany) of well-constructed core was
used to aid core fabrication.
Crown fabrication
Crown fabrication was designed in order to simulate
chair-side fabricated technique with light-cured PFC
(G-aenial Anterior) except for Group D. In order to
minimize variations in specimens, a transparent
template matrix of an ideally contoured crown was used
to aid crown fabrication. Fabricated mold of crown was
filled with PFC, then press and place it over the build-up
core, and light cured from outside. The light source was
placed in close contact (1–2 mm) with crown surface.
After polymerization, crown mold was removed. Prior
to the incline-loading test, excess composite around the
cervical area was removed and polished using abrasive
polishing points (Jiffy Polishers, Ultradent, South Jordan,
UT, USA) so that the margin of root and crown material
4
Dent Mater J 2020;
appeared clearly (Fig. 1). All fabricated specimens were
stored in distilled water at room temperature for 48 h.
Fracture load test
A static load was applied to the restored teeth with a
universal testing machine (Lloyd model LRX, Lloyd
Instruments, Fareham, UK) at a speed of 1 mm/min. The
acrylic block containing the restored tooth was tightly
fixed to the inclined metal base to provide a 45-degree
angle between the palatal surface of the incisal edge and
the loading tip (spherical Ø 2 mm) (Fig. 1). The loading
event was registered until fracture for each restored
tooth and the fracture patterns for each specimen was
visually analyzed by two investigators and categorized
to 3 typical types of failures.
Microhardness test
Restored teeth (n=3) from Groups (C and E) were sectioned
mid-sagitally in the mesio-distal plane using a ceramic
cutting disc operating at a speed of 100 rpm (Secotom-50,
Struers) under water cooling. Then, sectioned tooth was
gently polish using #4000-grit silicon carbide papers at
300 rpm under water cooling using an automatic grinding
machine (Rotopol-1, Struers). Surface microhardness
(VH) of composites (SFRC and CBC) inside the canal
was measured using a Vickers indenter (Duramin 40,
Struers) with a 40 objective lens and a load of 1.96 N
applied for 15 s. Each tested sectioned restoration (n=3)
was subjected to 6 indentations, starting from the top
(coronal part, 0 mm) and moving on each 2 mm towards
the bottom (apical part, 10 mm) of the canal. The
diagonal length impressions were measured and Vickers
values were converted into microhardness values by the
machine. Surface microhardness was obtained using the
following equation:
VH=
:
–
bearing capacity (443±143 N) among all the groups
tested. ANOVA showed that restorations reinforced by
post and core made of SFRC (Group C) had a statistically
significantly higher load-bearing capacity (300±98 N)
than incisors restored with CBC as post and core (Group
E, 153±55 N) (p<0.05). Whereas restorations made from
plain CAD/CAM composite (Group D) gave higher load
values (236±89 N) than those with plain CBC (Group E)
(p>0.05).
The data showed that crowns additionally reinforced
with fiber post (Groups A and B), have higher loadbearing capacity (p<0.05) than crowns without fiber post
(Groups E and C) respectively.
Visual inspection revealed three types of fracture
patterns (Figs. 4 and 5) according to the materials used:
debonding of crowns without tooth fracture was the
main type and found in all groups, debonding with tooth
fracture was found only in groups without fiber post
(Groups C, D, E), and delamination of surface PFC from
underlying SFRC core in crowns additionally reinforced
with fiber post (Group B).
The surface microhardness (VH) of the composite
core materials (CBC and SFRC) decreased gradually
within a limited range with increasing depth (Fig. 6).
1854.4×P
d2
where VH is Vickers hardness in kg/mm2, P is the load
in grams and d is the length of the diagonals in µm.
Fig. 3
Mean values of load-bearing capacity (N) and
standard deviation (SD) of tested groups.
The same letters inside the bars represent nonstatistically significant differences (p>0.05) among
the groups.
Fig. 4
Percentage of various fracture patterns of the test
specimens.
Statistical analysis
The data were statistically analyzed with SPSS software
(SPSS ver. 23, IBM, Somers, NJ, USA) using one-way
analysis of variance (ANOVA) at the p<0.05 significance
level followed by a Levene’s test of equality and Tukey
HSD post hoc test to determine the differences between
the groups.
RESULTS
The load-bearing capacity of the teeth restored with
different techniques is shown in Fig. 3. ANOVA
revealed that the restoration technique significantly
affected load-bearing capacity (p<0.05), however, some
interaction existed between the groups. Levene’s test of
equality of error variances confirmed that test is valid
with p=0.312.
Restored incisors (Group B) had the highest load-
Dent Mater J 2020;
:
5
–
Data showed no difference in VH values between the
tested core composites at 6 mm depth. However, after 6
mm SFRC presented the most drastic decrease along the
VH values. There was a significance difference between
the surface microhardness of SFRC measured at 8 and
10 mm depth in the root canal but not for CBC (Fig. 6).
DISCUSSION
Fig. 5
(A) Debonding without tooth fracture; (B)
Debonding with tooth fracture; (C) Delamination
of PFC.
Fig. 6
Surface microhardness (VH) mean values of tested
flowable core materials at different depths inside
the root canal.
The crown restorations in this study were designed to
evaluate the failure mode and load-bearing capacity
of incisors restored with biomimetic approach for the
fabrication of direct composite crown. This design
reproduced the scenario of major loss of tooth structure.
In this series an attempt was made by using flowable
SFRC as core material with or without prefabricated
glass fiber post under surface layer of PFC, i.e. biomimetic
composite restorations, in order to emulate a more
natural fracture behavior of composite restorations.
The new micrometer scale SFRC (everX Flow) used in
this study has previously been reported to exhibit high
fracture toughness and flexural strength18,25). To our
knowledge there are no other dental composites with
fracture toughness values above 2.6 MPa m1/2. Thus,
we assumed that flowable SFRC core could sustain the
loads required for complete anterior crown restorations.
The results of the fracture test support our assumption
because SFRC core restorations (Groups B and C) showed
a substantial improvement in load-bearing capacity and
failure mode when compared with conventional direct
CBC core restorations (Groups A and E) and indirect
composite restoration (Group D).
Data available in the literature regarding fracture
toughness values of different conventional (direct/
indirect) (light/dual-cured) composites are in range of 1.1
to 1.8 MPa m1/2 which are inferior values in comparisons
with SFRC26,27).
Short fibers enhanced the ability of the material
to resist the crack propagation, as well as to reduce
the stress intensity at the crack tip from which a crack
propagates in an unstable manner. As a consequence, an
increased fracture toughness can be expected. A recent
systematic review by Heintze et al., showed that fracture
toughness being mostly correlated with clinical fracture
of dental composites and no correlations were observed
between clinical outcomes and flexural modulus or
flexural strength of these materials28). Furthermore,
several in vitro studies have revealed a strong
correlation between fracture toughness of a material
and fracture behavior of the corresponding dental
restoration. In particular for biomimetic or bilayered
restorations made of a dentine-replacing SFRC core and
an enamel-replacing PFC veneer a more nature-like
fracture behavior and fewer catastrophic failures were
observed if the SFRC had a more dentine-like fracture
toughness29-36).
Aspect ratio, critical fiber length, fiber loading and
fiber orientation are the main factors that could improve
or impair the mechanical properties of SFRC24). Aspect
ratio is the fiber length to fiber diameter ratio (l/d). It
6
Dent Mater J 2020;
affects the tensile strength, flexural modulus and the
reinforcing efficiency of the FRC24). Microfibers used in
this study have aspect ratio of more than 30. In order for
a fiber to act as an effective reinforcement for polymers,
stress transfer from the polymer matrix to the fibers is
essential37). This is achieved by having a fiber length
equal to or greater than the critical fiber length and
the given fiber aspect ratio in range of 30–9424). It has
been also concluded that for advanced FRCs, the critical
fiber length could be as much as 50 times the diameter
of the fiber. The diameter of microglass fibers used in
this study is 6 µm and the critical fiber length should be,
therefore, around 300 µm.
Regarding the fracture patterns, the restored groups
produced predominantly favorable fracture patterns (i.e.
fracture above the CEJ). However, crown specimens that
have reinforced core material of SFRC with prefabricated
glass fiber post (Group B) revealed some delaminating
of PFC from the SFRC substructure layer. This finding
is in accordance with previous studies which showed
that SFRC core improves the failure mode of restored
damaged incisors to be more repairable11,20,21). Results
indicated that SFRC substructure supports the PFC
layer and serve as a crack prevention and redirection
layer. Previous studies demonstrated that mechanism
of arresting the crack propagation is greatly influenced
by the distance between the SFRC substructure and
the surface where the stress initiates36,38). Thus, highly
important is how thick SFRC and PFC layers are
applied. In laboratory studies it was observed that
optimal thickness of the veneering PFC composite over
the SFRC substructure is between 1–1.5 mm36,38).
The results of the present study is in agreement with
previous studies with regard to reinforcing effect of fiber
post on anterior composite restorations39,40). Whereas
others showed that fiber posts do not strengthen the teeth
and increase the incidence of catastrophic fractures41,42).
Glass fiber posts with a close elastic modulus to dentine
improve the stress distribution along the root. The
adhesion of fiber posts to the root dentine determines
their resistance to dislodgement43). So, the fundamental
requirement is to achieve an effective bond among luting
materials, composite resin matrix of fiber posts, and root
canal dentine by providing high retention. Because of the
semi-interpenetrating polymer network (-IPN) polymer
matrix structure, the MI glass fiber posts used in this
study have good bonding ability with luting material
and direct composite core\restorations enabling reliable
surface retained applications43). This is in accordance
with many researchers, who concluded in their studies
that the ability of bonding resins to penetrate into
fiber post with semi-IPN polymer matrix may give the
opportunity to establish a good link between fiber posts,
luting cements and composite cores39,40,44,45).
Interestingly, the fracture load of the CAD/CAM
composite restorations (Group D) was lower than that
of the direct composite restorations reinforced by SFRC
or prefabricated glass fiber post (Groups A, B, C). This
finding could be explained partially by the difference in
brittleness between the direct and indirect composites
:
–
used in the present study. While the CAD/CAM blocks
were well polymerized with photo-curing and heatcuring, the veneered PFC was polymerized by photocuring without heat-curing. Consequently, the CAD/
CAM composite restorations were more brittle than the
directly made restorations.
In the literature, the maximum incisal forces of
anterior teeth varies, but the amount was most often
around 200 N, which is lower than the failure loads of
SFRC post-core (Group C) restorations (300 N) found
in this study46). Therefore, it may be suggested that
anterior teeth with a 2 mm ferrule, restored with SFRC
post-core complex, would resist normal occlusal forces.
However, this study did not consider the influence of
parafunctional habits such as bruxism.
The question then arises whether the light-cure
SFRC material could have an adequate polymerization
also inside the root canal. The surface microhardness
(VH) of composites could help indirectly to evaluate the
degree of the conversion of the monomer at different
depth within the same composite23,47). In this study, the
maximum VH of each tested core composites at the 0 mm
depth (top surface layer) was considered as the baseline,
which represented the best degree of conversion of each
composite. The ratio of VH at the 10 mm depth (apical
portion) compared with the baseline could be used to
judge the polymerization capability of each composite
and a ratio above 80% has often been used as a minimum
acceptable threshold value48). Based on this calculated
method, flowable light-cure SFRC could be used up to
8 mm depth in side canal while dual-cure CBC could
be used safely up to 10 mm depth (Fig. 6). This is
interesting and could be attributed to the potential light
transmitting capacity of the short glass fibers inside the
canal as well as the greater transparency observed in
SFRC material. This finding is in line with the result
of curing depth performed in the study by Shouha and
Ellakwa, which showed that SFRC exhibited the deepest
cure (6.7 mm) in comparison with different conventional
PFC composites49). Previous studies have also shown
that FRCs conduct and scatter the light better than
conventional PFC composites47,50).
Several studies have been conducted on the
fracture resistance of endodontically treated incisor
teeth restored with different esthetic posts including
zirconia and fiber posts9,12,39-42). However, direct
comparison of fracture resistance values and failure
modes obtained from these studies is improper because
of several variations in the study designs such as
using human teeth or bovine teeth or artificial teeth,
luting procedure of the post, tooth preparation, crown
restoration, artificial aging, or loading conditions.
The fracture resistance values determined by the
various investigators were recorded under different
measurement criteria. These criteria were either initial
cracking that was interpreted as crack development
or a reduction in the load by an absolute or relative
amount26,36,40). For this study, the maximum static force
on the final fracture was determined. Stress applied to
the teeth and dental restorations is generally low and
Dent Mater J 2020;
repetitive rather than being isolated and impactive
in nature. However, because of a linear relationship
between fatigue and static loading, the compressive
static test also gives valuable information concerning
the fracture behavior and load-bearing capacity31).
It is important to emphasize that a valuable
advantage of using flowable SFRC is that it enable
restoration of the extensively destroyed tooth using
composite, and this approach reduces the number of
sessions required to end the restorative procedure as
well as the cost of treatment. Further research and
clinical trials are needed for detailed information on
this flowable SFRC material and to validate this in vitro
study.
CONCLUSIONS
The restoration of structurally compromised incisor
teeth with the use of flowable SFRC as core material
with regular fiber post displayed promising performance
in matter of load bearing capacity and failure mode.
:
8)
9)
10)
11)
12)
13)
14)
15)
ACKNOWLEDGMENTS
This study belongs to the research activity of BioCity
Turku Biomaterials Research Program (www.
biomaterials.utu.fi) and it was supported by Stick Tech
Ltd. Member of the GC Group.
16)
CONFLICTS OF INTERESTS
18)
Authors LL, VO and MF declare to have no conflict of
interests. Author PV consults for Stick Tech-Member of
the GC Group in R & D and training. Author SG has
received consultancy fees from StickTech/GC.
REFERENCES
1) Qualtrough AJ, Mannocci F. Tooth-colored post system: a
review. Oper Dent 2003; 28: 86-91.
2) Grandini S, Goracci C, Tay FR, Grandini R, Ferrari M.
Clinical evaluation of the use of fiber posts and direct
resin restorations for endodontically treated teeth. Int J
Prosthodont 2005; 18: 399-404.
3) Figueiredo FE, Santos RC, Silva AS, Valdívia AD, OliveiraNeto LA, Griza S, et al. Ferrule design does not affect the
biomechanical behavior of anterior teeth under mechanical
fatigue: An in vitro evaluation. Oper Dent 2019; 44: 273-280.
4) Saupe WA, Gluskin AH, Radke RA. A comparative study of
fracture resistance between morophological dowel and cores
and a resin-reinforced dowel system in the intraradicular
restoration of structurally compromised roots. Quintessence
Int 1996; 27: 483-491.
5) Sirimai S, Riis DN, Morgano SM. An in vitro study of the
fracture resistance and the incidence of vertical root fracture
of pulpless teeth restored with post-and-core systems. J
Prosthet Dent 1999; 81: 262-269.
6) Fokkinga WA, Kreulen CM, Vallittu PK, Creugers NH. A
structured analysis of in vitro failure loads and failure modes
of fiber, metal, and ceramic post-and-core systems. Int J
Prosthodont 2004; 17: 476-482.
7) Fokkinga WA, Kreulen CM, LeBell- Rönnlöf AM, Lassila LV,
Vallittu PK, Creugers NH. Fracture behavior of structurally
compromised non-vital maxillary premolars restored using
17)
19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
–
7
experimental fiber reinforced composite crowns. Am J Dent
2006; 19: 326-332.
Roeters JJ. Extended indications for directly bonded composite
restorations: a clinician’s view. J Adhes Dent 2001; 3: 81-87.
Fraga RC, Chaves BT, Mello GS, Siqueira JF Jr. Fracture
resistance of endodontically treated roots after restoration. J
Oral Rehabil 1998; 25: 809-813.
Nagata K, Garoushi SK, Vallittu PK, Wakabayashi N,
Takahashi H, Lassila LVJ. Fracture behavior of singlestructure fiber-reinforced composite restorations. Acta
Biomater Odontol Scand 2016; 2: 118-124.
Bijelic J, Garoushi S, Vallittu PK, Lassila LV. Short fiber
reinforced composite in restoring severely damaged incisors.
Acta Odontol Scand 2013; 71: 1221-1231.
Bijelic-Donova J, Garoushi S, Vallittu PK, Lassila LVJ.
Mechanical properties, fracture resistance, and fatigue limits
of short fiber reinforced dental composite resin. J Prosthet
Dent 2016; 115: 95-102.
Xu HHK, Quinn JB, Smith DT, Giuseppetti AA, Eichmiller
FC. Effect of different whiskers on the reinforcement of dental
resin composites. Dent Mater 2003; 19: 359-367.
Zandinejad AA, Atai M, Pahlevan A. The effect of ceramic and
porous fillers on the mechanical properties of experimental
dental composites. Dent Mater 2006; 22: 382-387.
Garoushi S, Vallittu PK, Lassila LVJ. Short glass
fiber reinforced restorative composite resin with semiinterpenetrating polymer network matrix. Dent Mater 2007;
23: 1356-1362.
Garoushi S, Säilynoja E, Vallittu P, Lassila L. Physical
properties and depth of cure of a new short fiber reinforced
composite. Dent Mater 2013; 29: 835-841.
Garoushi S, Vallittu PK, Lassila L. Mechanical properties
and wear of five commercial fibre-reinforced filling materials.
Chin J Dent Res 2017; 20: 137-143.
Garoushi S, Gargoum A, Vallittu PK, Lassila L. Short fiberreinforced composite restorations: A review of the current
literature. Investig Clin Dent 2018; 9: e12330.
Lassila L, Säilynoja E, Prinssi R, Vallittu P, Garoushi S.
Characterization of a new fiber-reinforced flowable composite.
Odontology 2019; 107: 342-352.
Garoushi S, Vallittu PK, Lassila LV. Direct restoration
of severely damaged incisors using short fiber-reinforced
composite resin. J Dent 2007; 35: 731-736.
Garoushi S, Vallittu PK, Lassila LV. Continuous and short
fiber reinforced composite in root post-core system of severely
damaged incisors. Open Dent J 2009; 3: 36-41.
Forster A, Sáry T, Braunitzer G, Fráter M. In vitro fracture
resistance of endodontically treated premolar teeth restored
with a direct layered fiber-reinforced composite post and core.
J Adhes Sci Technol 2017; 31: 1454-1466.
Fráter M, Lassila L, Braunitzer G, Vallittu PK, Garoushi S.
Fracture resistance and marginal gap formation of post-core
restorations: influence of different fiber reinforced composites.
Clin Oral Investig 2019 [Epub ahead of print].
Vallittu PK. High-aspect ratio fillers: fiber-reinforced
composites and their anisotropic properties. Dent Mater
2015; 31: 1-7.
Garoushi S, Vallittu P, Lassila L. Mechanical properties
and radiopacity of flowable fiber-reinforced composite. Dent
Mater J 2019; 38: 196-202.
Quinn JB, Quinn GD. Material properties and fractography
of an indirect dental resin composite. Dent Mater 2010; 26:
589-599.
Ilie N, Hickel R, Valceanu AS, Huth, KC. Fracture toughness
of dental restorative materials. Clin Oral Investig 2012; 16:
489-498.
Heintze SD, Ilie N, Hickel R, Reis A, Loguercio A, Rousson
V. Laboratory mechanical parameters of composite resins
and their relation to fractures and wear in clinical trials-A
8
Dent Mater J 2020;
systematic review. Dent Mater 2017; 33: 101-114.
29) Fennis WM, Tezvergil A, Kuijs RH, Lassila LV, Kreulen
CM, Creugers NH, et al. In vitro fracture resistance of fiber
reinforced cusp-replacing composite restorations. Dent Mater
2005; 21: 565-572.
30) Garoushi S, Lassila LVJ, Vallittu PK. Fiber-reinforced
composite substructure: load bearing capacity of an onlay
restoration. Acta Odontol Scand 2006; 64: 281-285.
31) Garoushi S, Lassila LVJ, Tezvergil A, Vallittu PK. Static and
fatigue compression test for particulate filler composite resin
with fiber-reinforced composite substructure. Dent Mater
2007; 23 :17-23.
32) Keulemans F, Lassila LVJ, Garoushi S, Vallittu PK,
Kleverlaan CJ, Feilzer AJ. The influence of framework
design on the load-bearing capacity of laboratory-made inlayretained fibre-reinforced composite fixed dental prostheses. J
Biomech 2009; 42: 844-849.
33) Dere M, Ozcan M, Göhring TN. Marginal quality and fracture
strength of root-canal treated mandibular molars with overlay
restorations after thermocycling and mechanical loading. J
Adhes Dent 2010; 12: 287-294.
34) Keulemans F, Van Dalen A, Kleverlaan CJ, Feilzer AJ. Static
and dynamic failure load of fiber-reinforced composite and
particulate filler composite cantilever resin-bonded fixed
dental prostheses. J Adhes Dent 2010; 12: 207-214.
35) Fráter M, Forster A, Keresztúri M, Braunitzer G, Nagy K. In
vitro fracture resistance of molar teeth restored with a short
fibre-reinforced composite material. J Dent 2014; 42: 11431145.
36) Garoushi S, Hatem M, Lassila L, Vallittu PK. The effect of
short fiber composite base on microleakage and load bearing
capacity of posterior restorations. Acta Biomater Odontol
Scand 2015; 1: 6-12.
37) Bijelic-Donova J, Garoushi S, Lassila L, Keulemans F,
Vallittu PK. Mechanical and structural characterization of
discontinuous fiber-reinforced dental resin composite. J Dent
2016; 52: 70-78.
38) Garoushi S, Lassila LV, Tezvergil A, Vallittu PK. Load
bearing capacity of fibre-reinforced and particulate filler
:
–
composite resin combination. J Dent 2006; 34: 179-184.
39) Le Bell-Rönnlöf AM, Lassila LV, Kangasniemi I, Vallittu PK.
Load-bearing capacity of human incisor restored with various
fiber-reinforced composite posts. Dent Mater 2011; 27: 107115.
40) Hatta M, Shinya A, Vallittu PK, Shinya A, Lassila LV. High
volume individual fiber post versus low volume fiber post: The
fracture load of the restored tooth. J Dent 2011; 39: 65-71.
41) Zicari F, Van Meerbeek B, Scotti R, Naert I. Effect of ferrule
and post placement on fracture resistance of endodontically
treated teeth after fatigue loading. J Dent 2013; 41: 207-215.
42) Lazari PC, de Carvalho MA, Del Bel Cury AA, Magne P.
Survival of extensively damaged endodontically treated
incisors restored with different types of posts-and-core
foundation restoration material. J Prosthet Dent 2018; 119:
769-776.
43) Vallittu PK. Are we misusing fiber posts? Guest editorial.
Dent Mater 2016; 32: 125-126.
44) Le Bell AM, Tanner J, Lassila LV, Kangasniemi I, Vallittu P.
Bonding of composite resin luting cement to fiber-reinforced
composite root canal posts. J Adhes Dent 2004; 6: 319-325.
45) Le Bell AM, Lassila LV, Kangasniemi I, Vallittu PK. Bonding
of fibre-reinforced composite post to root canal dentin. J Dent
2005; 33: 533-539.
46) Anusavice KJ. Phillips’ science of dental materials. 11th ed.
St. Louis: Elsevier; 2003. p. 93-94, 598-603.
47) Garoushi S, Vallittu PK, Lassila LV. Depth of cure and
surface microhardness of experimental short fiber-reinforced
composite. Acta Odontol Scand 2008; 66: 38-42.
48) Flury S, Hayoz S, Peutzfeldt A, Hüsler J, Lussi A. Depth of
cure of resin composites: is the ISO 4049 method suitable for
bulk fill materials. Dent Mater 2012; 28: 521-528.
49) Shouha PSR, Ellakwa AE. Effect of short glass fibers on
the polymerization shrinkage stress of dental composite. J
Biomed Mater Res B Appl Biomater 2017; 105: 1930-1937.
50) Le Bell AM, Tanner J, Lassila LV, Kangsniemi I, Vallittu PK.
Depth of light-initiated polymerization of glass fiber-reinforced
composite in a simulated root canal. Int J Prosthodont 2003;
4: 403-408.