EGYPTIAN
DENTAL JOURNAL
Vol. 61, 3203:3210, July, 2015
I.S.S.N 0070-9484
w w w. e d a - e g y p t. o r g
EFFECT OF ENDOCROWNS AND GLASS FIBER POST-RETAINED
CROWNS ON THE FRACTURE RESISTANCE OF ENDODONTICALLY
TREATED PREMOLARS
Mohamed Abdel-Aziz * and Amal Abdallah A. Abo-Elmagd *
ABSTRACT
Purpose: The purpose of this in vitro study was to compare the effect of endocrowns and glass
fiber post-retained crowns on the fracture resistance of endodontically treated premolars prepared
with or without ferrule.
Materials and Methods: Twenty sound mandibular premolars were endodontically treated.
They were randomly assigned into 4 groups (n=5), in which, teeth were prepared to receive allceramic restorations. Group 1: Endocrown without ferrule. Group 2: Endocrown with (1 mm
wide shoulders and 2 mm axial wall heights) ferrule. Group 3: Glass fiber post and resin core and
conventional crown without ferrule. Group 4: Glass fiber post and resin core and conventional crown
with ferrule. The lithium disilicate all-ceramic restorations (IPS E-max press, Ivoclar-Vivadent)
were made by injection technique and adhesively cemented (Variolink N, Ivoclar Vivadent).
Specimens were mounted in a universal testing machine (Model LRX-plus; Lloyd Instrument Ltd.,
Fareham, UK). Each specimen was loaded to failure at a crosshead speed of 1.0 mm / min. Mode of
failure was also examined. Data were analyzed using one way analysis of variance (ANOVA) and
Tukey’s post hoc significance difference tests. Differences were considered significant at P<0.05.
Results: One way ANOVA test showed that group (4) recorded statistically significant (p <0.05)
highest mean value (1262.71±277.8 N) followed by group (2) (1139.7±227.94 N) then group (1)
(725.73±137.89 N). Group (3) recorded the lowest statistically significant (p <0.05) mean value
(588.17±94.11 N). Pair-wise Tukey’s post-hoc test showed non-significant (P>0.05) difference
between 2 and 4 groups.
Conclusions: Within the limitations of this study, the presence of ferrule increased the fracture
resistance of endodontically treated premolars restored with either endocrown or glass fiber postand core and all-ceramic crown than those without ferrule.
* Lecturer, Department of Fixed Prosthodontics, Faculty of Dental Surgery, Misr University for Science and
Technology.
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E.D.J. Vol. 61, No. 3
INTRODUCTION
Usually the mutilated tooth is structurally
weakened due to caries, repeated restorations and/
or fracture. It is also weakened by the endodontic
steps including the access cavity and the restorative
techniques required to rebuild the missing tooth
structure. Due to the substantial loss of tooth
structure in an endodontically treated tooth,
it requires special considerations for the final
restoration. These considerations involve; ensuring
adequate restoration retention, maximum tooth
fracture resistance and esthetic needs in some cases.
To restore such a tooth, a post and core foundation
is needed onto which a full crown is retained and
cemented 23, 25. Glass fiber posts were introduced
to bond to both the composite core and root canal
and provide a natural esthetics. As regard to the
modulus of elasticity compared with the dentin, the
glass fiber post has a better performance than other
metallic posts in terms of stress distribution, which
minimizes the risk of root fracture 1, 17. However, the
placement of posts inside the root canals dictates
the removal of additional dental structure and may
involve a risk of root perforation 8, 9.
In clinical cases for instance; an excessive loss
of coronal hard tissue, limited inter-arch space, and
dilacerated or short roots, traditional post-and-core
rehabilitation is impossible 24. Nowadays, the field
of adhesive dentistry promotes a ceramic coronal
restoration of these cases by onlay and overlay
using the pulp chamber extension as a retention
foundation without the needs of for intra-radicular
posts 11, 20, 26, as is the case of endocrowns.
The endocrown is an acid etchable ceramic
crown (such as lithium disilicate-based ceramics)
anchored to the pulp chamber and cavity margins
of endodontically treated posterior tooth obtaining a
macro mechanical retention by the pulpal walls and
micro retention using an adhesive resin cement 10, 24.
The preparation design for endocrown comprises a
cervical circumferential butt margin and a central
retention cavity inside the pulp chamber with or
Mohamed Abdel-Aziz and Amal Abdallah A. Abo-Elmagd
without a ferrule and constructs both the crown and
core as a single unit 7, 14.
Performing the clinical procedures of endocrown
is simpler and faster than the traditional single crown
with post and core and have been reported clinically
a successful restoration for endodontically treated
molars 3, 4.
However, a controversy exists concerning the
restoration of endodontically treated premolars.
Some findings observed that the premolars
compromised the mechanical properties of the
endocrown and presented more failures 4. Others
recommended that, the endocrown should be
considered as an alternative approach for restoring
endodontically treated premolars as the findings
revealed similar performance with conventional
crown 14.
The purpose of this current study was to
compare the fracture resistance of endodontically
treated premolars prepared with or without ferrule
and restored with laboratory manufactured lithium
disilicate endocrowns and glass fiber post-retained
conventional crowns.
MATERIAL AND METHODS
Preparation of tooth specimens
Twenty caries free of recently extracted human
mandibular premolars were selected for the study.
The dimensions of the teeth were measured with a
calibre. The average values were measured at the
level of cemento-enamel junction; (15 mm root
length, 8 mm bucco-lingual, and 5 mm mesiodistal). The teeth were cleaned and stored in saline
solution at room temperature immediately after
extraction.
All teeth were prepared endodontically
using rotary files (Protaper, Dentsply, Maillefer,
Switzerland). After intermittent irrigation, the
root canals were dried with paper points (Spident,
Incheon, Korea). All canals were restored by a
lateral compaction technique with gutta-percha
EFFECT OF ENDOCROWNS AND GLASS FIBER POST-RETAINED CROWNS
cones (Protaper, Dentsply, Maillefer, Switzerland)
and eugenol-free root canal sealer (AH Plus,
Dentsply, De tray, Germany).
The teeth samples were divided randomly into
four groups of five specimens each (n=5). All
teeth were sectioned 3 mm coronal to the cementoenamel junction and then assigned to receive one
of the selected preparation designs and all-ceramic
restorations; (figure 1)
Group 1: Endocrown without ferrule preparation.
Group 2: Endocrown with ferrule preparation.
Group 3: Glass fiber post and resin core and allceramic crown without ferrule preparation.
Group 4: Glass fiber post and resin core and allceramic crown with ferrule preparation.
Fig. (1) Schematic representation of the different groups 1) No
ferrule with endocrown, 2) A ferrule with endocrown,
3) No ferrule with glass fiber post and resin core and
all-ceramic crown. 4) A ferrule with glass fiber post and
resin core and all-ceramic crown.
Preparation for endocrown:
All ten teeth of group (1) & (2) were prepared for
endocrown restorations. After coronal sectioning to
prepare a circular butt margin, a central retention
inlay-type cavity was prepared in the pulp chamber
with an oval anti-rotational shape and a depth of
5 mm from the cavo-surface margin14. The internal
line angles were rounded and smoothed.
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Post-space preparation, cementation and corebuild up:
The ten teeth of group (3) & (4) were received
glass fiber posts size no.1 (Glassix+plus, Nordin,
Switzerland) and a resin composite filling core
(Tetric Ceram, Ivoclar Vivadent, Liechtenstein).
After coronal sectioning, the gutta percha was
removed using a pilot reamer of the post system to
the length of 12 mm from the preparation margins.
A post space was prepared with the corresponding
calibrating drill (size no.1) included in the post
system. The canals were etched with 36% phosphoric
acid (Total Etch, Ivoclar Vivadent, Liechtenstein)
for 15 seconds. The canals were thoroughly rinsed
with sterile water, dried with compressed air and
paper points. A light cure, adhesive agent (Tetric
N-Bond, Ivoclar Vivadent, Liechtenstein) was
applied inside the root canal using a micro brush.
The adhesive was rubbed to canal walls for 10
seconds and the excess solvent was removed with
gentle oil free compressed air for 1-3 seconds and
light cured for 20 seconds according to manufacturer
instructions.
A silane coupling agent (Silane, Ultradent, South
Jordan, Utah, USA) was applied on the post surface
for one minute and then gently air dried for 5
seconds. The post was luted with the same bonding
agent using the brush, the excess solvent was
removed and the adhesive was cured for 20 seconds.
The base and catalyst of dual cure resin cement
(Variolink N, Ivoclar Vivadent, Liechtenstein) were
mixed properly and applied for post cementation.
Each post was cut to 4 mm from the cemntoenamel margin. The core build up was made
incrementally till the predetermined dimensions.
The final layer was placed using a transparent
matrix to allow for shape standardisation between
samples. The core height was adjusted to 3 mm.
All the margins and the angle of convergence were
adjusted and standardized for conventional crown
preparation.
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E.D.J. Vol. 61, No. 3
In group (2) & (4), the teeth were further
prepared for 1 mm shoulder finish line and 2 mm
circumferential ferrule axial wall heights using a
rotary diamond stone 7.
Laboratory procedures:
For each prepared sample of endocrowns and
conventional crowns, an individual impression was
made by poly-vinyl siloxane impression material
(Virtual, Ivoclar-vivadent) and stone die (type IV)
was fabricated. All the crowns were constructed
from wax (GEO, Renfert GmbH, Germany) with
the same heights and dimensions and prepared for
ceramic crown pressing by the injection technique
according to the manufacturer’s instructions
and materials. The ceramic material for crowns
fabrication was IPS E-max (Ivoclar-Vivadent).
Bonding procedure
The fitting surface of the all-ceramic crowns,
either conventional crowns or endocrowns were
etched with 9.5% buffered hydrofluoric acid gel
(Porcelain etch, Ultradent South Jordan, Utah, USA)
for one minute, washed thoroughly and dried. The
etched surface of each crown was silanized (Silane,
Ultradent, South Jordan, Utah, USA) for one minute
and then dried followed by adhesive agent (Tetric
N-Bond, Ivoclar Vivadent, Liechtenstein) and light
curing for 20 seconds. The adhesive system was
applied on the prepared surface of teeth. Then, each
crown was cemented to its corresponding tooth
sample using dual cure resin cement (Variolink N,
Ivoclar Vivadent, Liechtenstein). Excess cement
was removed immediately with a microbrush and
light cured.
Mohamed Abdel-Aziz and Amal Abdallah A. Abo-Elmagd
Teflon square mould was constructed with 15 mm
width and 20 mm length to accommodate the acrylic
resin block. An auto polymerizing resin powder
(Acrostone, Acrostone dental factory, Industrial
zone, Cairo, Egypt) was mixed with monomer
and poured inside the mould. Each specimen was
embedded into the filled mould along its long axis
using a surveyor (Ney Surveyor, Dentsply, USA)
and 2 mm below the cervical line of the root was left
exposed. After complete hardening of the acrylic
resin, the block was removed from the mould.
Fracture resistance testing
Each specimen along with the acrylic resin block
was mounted into a custom-made carrier with an
inclination of 45 degrees 2 and then loaded to failure
using a universal testing machine (Model LRX-plus;
Lloyd Instrument Ltd., Fareham, UK) (figure 2).
The upper plate of the machine included a steel rode
with a round tip with a diameter of 3.6 mm placed
at the centre of the occlusal surface of the crown of
each specimen. A 0.5 mm tin foil sheet was placed
between the rode and crown to ensure even stress
distribution and minimize the transmission of local
force peaks on the ceramic surface. The samples
were subjected to a slowly increasing compressive
load at a constant crosshead speed of 1.0 mm per
minute until an audible crack or fracture occurred.
Load was automatically recorded in Newton (N).
The root of each tooth was thinly covered with
a layer of a light body silicone based impression
material (Speedex, Coltene whaledent, Switzerland)
to simulate the thickness of periodontal ligament 16.
In order to mount the root of each sample in the
universal testing machine, an acrylic resin block
was made. A specially designed longitudinally split
Fig. (2) Fracture resistance testing using a universal testing
machine.
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EFFECT OF ENDOCROWNS AND GLASS FIBER POST-RETAINED CROWNS
Data were recorded using computer software
(Nexygen-MT- 4.6; Lloyd Instruments) and
analyzed statistically with one way analysis
of variance (ANOVA) and Tukey’s post hoc
significance difference tests. Differences were
considered significant at P<0.05.
TABLE (1) Comparison of fracture resistance
results (Mean±SD) between all groups in
Newton (N)
Mean
SD
Tukey's
rank
1 Endocrown
without ferrule
725.73
137.89
B
2 Endocrown with
ferrule
1139.7
227.94
A
I] Debonding of all ceramic restoration without
fracture.
3 Fiber post
without ferrule
588.17
94.11
C
II] Fracture of the restoration without fracture of the
tooth (favourable failure).
4 Fiber post with
ferrule
1262.71 277.80
A
Different
indicating
After loading, mode of fracture for each specimen
was examined using a digital microscope (Scope
Capture Digital Microscope, Guangdong, China) at
× 25 magnifications and classified according to the
following descriptions 5:
III] Fracture of the restoration/tooth complex above
the level of tooth root embedded in the resin
block (acceptable failure).
Group
letter
*; significant (p<0.05)
significance
ANOVA
P value
<0.0001*
(p<0.05)
IV] Fracture of the restoration/tooth complex
iwnside tooth root embedded in the resin block
(catastrophic failure).
RESULTS
Mean fracture resistance and standard deviations
(SD) of the tested groups are recorded and displayed
in table (1) and graphically drawn (figure 3).
As indicated by one way ANOVA test, it was
found that group 4 (Fiber post and conventional
crown with ferrule) recorded statistically significant
(p <0.05) highest mean value (1262.71±277.8 N)
followed by group 2 (endocrown with ferrule)
(1139.7±227.94 N) then group 1 (endocrown
without ferrule) (725.73±137.89 N). Group 3
(Fiber post and conventional crown without ferrule)
recorded the lowest statistically significant (p <0.05)
mean value (588.17±94.11 N).
Pair-wise Tukey’s post-hoc test showed nonsignificant (P>0.05) difference between (2) and (4)
groups.
Fig. (3) A column chart of fracture resistance mean values for
all groups.
The favourable (type II) and acceptable (type
III) failure modes were predominant in this study.
While, debonding of all ceramic restoration without
fracture (type I) and catastrophic failure (type IV)
were not occurred (figure 4).
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E.D.J. Vol. 61, No. 3
Mohamed Abdel-Aziz and Amal Abdallah A. Abo-Elmagd
premolars. They concluded that the restoration of
endodontically treated mandibular premolars with
endocrowns cannot be recommended over treatment
using post-and- core foundations.
Fig. (4) Type of fracture for all groups; 1) Fracture of
endocrown without ferrule (type II). 2) Fracture of
endocrown/tooth complex (type III). 3) Fracture of
tooth in conventional crown without ferrule (type III).
4) Fracture of all ceramic crown (type II).
DISCUSSION
Glass fiber post system became popular because
of its esthetic properties, and simple technique.
However, the ceramic endocrown restoration
is considered to some clinician an alternative
treatment to post-and-core and conventional crown
in endodontically treated posterior teeth. It can
conserve the remaining tooth structure, reduce the
need for macro-retentive geometry, and provide a
more esthetic result being constructed from ceramic.
Recently, endocrown restoration became the
subject of many studies. It has been considered a
restorative option for posterior endodontically
treated and badly damaged molars 6. Some clinicians
suggested the concept of endocrown restoration for
restoring the endodontically treated premolars 13.
The results of this study showed that group 4
(fiber post with ferrule) recorded the highest fracture
resistance of all groups and there was no significant
difference with group 2 (endocrown with ferrule).
This result was in agreement with the study of
Forberger and Göhring 7. They also evaluated the
marginal continuity and fracture behavior of both
lithium disilicate crowns with different types of post
and core and endocrown in endodontically treated
Lin CL et al 12 observed the favourable
performance of endocrown restorations in premolars
by using the finite element method. In other in vitro
studies14, 15, they found that the endocrown and
conventional crown restorations for endodontically
treated premolars did not significantly differ from
each other. They explained that the endocrown
restorations recorded the low stress values because
endocrown include both the crown and core as a
single unit which decrease the effect of multiple
interfaces. As well, thickening of the ceramic
occlusal portion compared to the conventional
crown.
On the other hand, Bindl and Mörmann4
evaluated the clinical performance of 208
endocrowns cemented to premolars and molars and
observed that the premolars presented more failures
than the molars. They referred this to the smaller
surface area of premolars for adhesion compared
with molars. Moreover, premolars have greater
crown height, which compromises the mechanical
properties of the endocrown.
In groups; 2 and 4, a ferrule effect was attained
by extending the future restoration margin 2.0
mm below the foundation limit according to the
recommendation of Sorensen and Engelman 22.
Sometimes, in many clinical cases, the extensive
loss of tooth structure of endodontically treated
tooth may preclude the use of ferrule. In group 1, the
premolars were restored with endocrowns without
ferrule to simulate the restorative approaches for
badly damaged teeth, which do not allow the use of
ferrule. However, the fracture resistance of group 4
(fiber post with ferrule) was significantly higher than
group 1 (endocrown without ferrule). This result was
in accordance with Schmidlin et al 21 who indicated
the importance of ferrule in increasing the fracture
EFFECT OF ENDOCROWNS AND GLASS FIBER POST-RETAINED CROWNS
resistance of the endodontically treated tooth. Also,
Ma OS et al 18 reported the value of ferrule which
increases fracture strength and minimizes loss of
bond of prosthetic restorations. This also explained
the result of group 4 (fiber post with ferrule) which
recorded a higher significant fracture resistance
than group 3 (fiber post without ferrule).
REFERENCES
In this study, Lithium disilicate – based ceramics
was used for construction of both conventional
crowns and endocrowns due to its high mechanical
strength and being acid etched; it can promote
micromechanical interlocking with resin cement
and bonded to the tooth interface 2. The adhesive
property of this kind of ceramic material explained
the absence of failure mode type (I); debonding of
either endocrown or conventional crown without
restoration fracture.
All samples restored with glass fiber posts
showed favourable or acceptable fracture patterns.
This might be due to the modulus of elasticity of
fiber-reinforced posts which close to that of dentin,
resulting in a better stress distribution at the post–
dentin interface 19. Also, the same results occurred
in the samples of endocrown. Since the stresses
were concentrated at the cervical area and the outer
root surface, a cohesive fracture of the endocrown
ceramic material, which remained attached to the
fractured segment of cervical root, thus indicating
good bond strength between lithium disilicate
material and tooth structure. As well, this explains
why samples did not show catastrophic failures.
CONCLUSIONS
Within the limitations of this study we can
conclude that: Both endocrown and glass fiber
post-and core and all-ceramic crown with ferrule
increases the fracture resistance of endodontically
treated mandibular premolars more than that without
ferrule and the endodontically treated mandibular
premolars should not be restored with endocrown in
the absence of ferrule.
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