Sys Rev Pharm 2021; 12(11): 594-603
Research Article
A multifaceted review journal in the field of pharmacy
E-ISSN 0976-2779 P-ISSN 0975-8453
Fracture Resistance of Anterior Endocrown vs. Post Crown
Restoration an In- vitro Study
Manar al-Fadhli 1*, Cherif Mohsen1, Hesham Katamich2
1
Department of Prosthodontics, Minia University, Minia, Egypt
2
Department of Prosthodontics, Cairo University, Minia, Egypt
Article History:
Submitted: 10.08.2021
ABSTRACT
Objective: The purpose of this study is to study the
fracture resistance of anterior endocrown versus post
crown restoration.
Materials and methods: Thirty caries free of extracted human maxillary canine with complete root formation were selected for this study. Also two types of
ceramics were used: IPS Emax press and Celtra Press.
Thirty samples were fabricated and divided into 2
groups (15 samples each) according to the type of ceramic used. Then each subgroup was subdivided into
3 subgroups (5 samples each) according to the type
of restorations: Endocrown 6 mm, Endocrown 10 mm,
post+core+crown. All specimens were subjected to a
thermocycling procedure in automated thermocycling
machine. Samples were thermocycled for 5000 cycles,
between 5°C-55°C with a dwell time 15 seconds. All
samples were individually mounted on a computer controlled materials testing machine for a fracture resistance test. After fracture resistance test, all specimens
in the test groups were viewed using a USB digital-microscope, magnification × 35, and the images were
captured and transferred to a IBM personal computer
equipped with the Image-tool software (Image J 1.43
U, National Institute of Health, USA) to determine fail-
INTRODUCTION
Endodontically treated teeth restoration is compromised primarily
because increased risk of coronal destruction that results in tooth
fracture during function. Before the introduction of adhesion in
dentistry, the coronal restoration endodontially treated teeth has
been mainly performed with metallic and macro mechanically
retained posts. In the past, a length of post equal to three fourths
of the root canal or at least equal to the crown length (Goodacre
CJ, Spolnik KJ, 1995; Abramovitz L, et al., 2001). A restorative
option for endodontically treatment an endocrown is. It consists
of a full crown that extends a post into the pulp chamber and/
or pulp canals as one unit (Lander E and Dietschi D, 2008). One
of option to restore severe destructed, supragingival structure of
posterior teeth (Stockton L, et al., 1998) endocrown. These restorations are the most prevalent in case of damaged molars crowns,
narrow and short roots, obturated canals or limited interocclusal
space (Güngör MB, et al., 2017). The endocrown are mechanically
anchored in pulp chambers (3-4 mm element) (Güngör MB, et
al., 2017; Reich S, et al., 2004; Mannocci F and Cowie J, 2014) and
strongly adhesively bonded with hard dental tissues using resin
cements (Reich S, et al., 2004). The little dental structures preparation when compared with conventional post and cores (Mannocci
F and Cowie J, 2014), as well as lack of intervention in the root
canals (Edelhoff D, Sorensen J, 2002). They need less time to be
made and less interfaces between part of the restorations and the
teeth Compared to traditional methods.
One of ZLS classes, celtra press (Dentsply Sirona) is a new material that can deliver the highest level of esthetics mimicking
natural teeth based on having an amazing chameleon effect, perfect balance of translucency and natural like opalescence only
594
Accepted: 24.08.2021
Published: 31.08.2021
ure mode pattern according to the following categorization.
Results: Regarding the fracture resistance testing, the
results of the present study revealed that there was no
statistically significant difference between mean fracture resistance values of IPS Emax press (235.54 N)
and Celtra press; (244.98 N) where both showed statistically non-significant highest mean fracture resistance.
Conclusion: The results obtained in this study revealed
a non-significant difference between the endocrown
restorations and the post and core and crown. Although endocrown showed higher fracture resistance
values compared to the post and core and crown. Also
the results showed non-significant difference between
the endocrown restorations with different designs. Although endocrown (10 mm) showed higher fracture resistance values than endocrown (6 mm) which may be
due to an increase in surface area.
Keywords: Canine teeth, Endocrown, Endodontically
treated teeth, Fiber post, Emax, Celtra
*
Correspondence: Manar al-fadhli, Department of
Prosthodontics, Minia University, Minia, Egypt, E-mail:
dr.almanar2012@gmail.com
by polishing the material after pressing it (Celtra press Fact File,
2017). Feld spathic ceramic is the most material for Endocrown
(e.g. Vitablocs Mark II, Vita Zahnfabirk, Bad Säckingen, Germany
and Cerec Blocks, Sirona Dental Systems, Bensheim, Germany),
leucite ceramic (e.g. IPS Empress CAD, Ivoclar Vivadent Schaan/
Liechtenstein), lithium disilicate ceramic (e.g. IPS Emax Press,
Ivoclar/Vivadent, Schaan/Liechtenstein) or resin composite (e.g.
Lava Ultimate, 3 M ESPE, St Paul, MN, USA) (Dietschi D, et al.,
2007). Ceramic endocrown are made by sintering, pressing or
more often CAD/CAM technology. The restorations are aesthetically attractive.
The fracture resistance of ETT has been reported to be mainly
dependent on the amount of adhesive surface, the amount of the
remaining tooth structure and the quality of adhesion (Garbin
CA, et al., 2010). The way of a post in the retention of the core
material is relevant for posterior teeth where masticatory loads are
essentially compressive (Reeh ES, et al., 1989). In vitro studies on
adhesive restoration tested to analyse fracture strength and mode
of failure of cuspid endodontically treated teeth (Zarow M, et al.,
2009).
MATERIALS AND METHODS
The Thirty caries free of extracted human maxillary canine with
complete root formation no crack or fracture. Teeth were cleansed
of calculus and soft tissues, with dental scalers, nylon bristle
brushes, and pumice with low speed hand piece. They were stored
in 5% sodium hypochlorite for 15 minutes at room temperature
for sterilization of extracted teeth.
All teeth were mounted in epoxy resin block using a custom-made
round Teflon shape sample holder (2 cm length, 2 cm internal
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Vol 12, Issue 11, Oct Nov, 2021
al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
diameters) in a vertical direction using centralizing device. The amount of
mixed material that the application requires was determined according to
manufacture structure.
fiber post was reduced to a length of 12.0 mm by cutting the coronal end
with a diamond separating disc under copious coolant, resulting in a dowel
extending 2 mm above the coronal surface of the trimmed crown.
The crowns of teeth were cut perpendicular to the long axis 2 mm above
the cemento-enamel junction from the proximal surface using a super
coarse diamond disc and copious irrigation to avoid dryness (Figure 1).
The root canal was etched with 35% phosphoric acid** (Where ** is Scotch
bond etchant, 3m ESPE Dental products) for 15 seconds, washed with
water spray, and then the excess water was removed from the post space
using paper points.
The access cavity preparation was done including completely pulp chamber de-roofing and orifice was exposed. Then the radicular pulp was extirpated with a barbed broach.
The working length of the canal was determined by inserting a size 10
K-type file into the root canal terminus. Then a glide path was performed
with a size 15 K-type file. The working length was demonstrated by the
initial peri-apical x-ray and kept 0.5 to 1 mm away from the apical constriction. The filling process is continued by using 20 then 25 sized files
respectively. The root canal was instrumented with Pro-Taper Universal
instruments in a sequence of (SX, S1, S2, F1, F2) with an adjustable-torque
motor* (NSK, Japan). The root canal was irrigated with 2 ml 1% sodium
hypochlorite solution after each instrument change. After the instrumentation, the canal was flushed with 5 ml 17% EDTA and 5 ml sodium hypochlorite and then dried with paper points.
The master gutta percha cone inserted into the canal for proper working
length insurance. The obturation process was done in the help of Adseal
sealer. Adseal is resin based root canal sealer which is a paste type of dual
syringe. It provided easy and standard mix of quit volume units (2:1 wt.
Ratio) of base and catalyst according to manufacture instructions. They
were mixed together on a mixing pad using spatula for 15-20 seconds until
creamy homogenous mix was gained. The sealer was applied to the cone
size F2 and inserted into the canal. A hot burnisher was used to remove the
protruded gutta percha.
Classification of samples
Thirteen were divided into two main groups according to the type of
restoration and three subgroups according to the designs of preparation
(Table 1):
Conventional post and core supported crowns group preparation
For each tooth, post space preparation began with the removal of gutta
percha to a depth of 10 mm from the coronal tooth structure using gates
glidden drills, then Glassix radiopaque glass fiber composite post drill*
was used to remove any residual root filling and complete canal preparation with water spray coolant and at a low speed (30000 R.P.M). Each glass
RelyX unicem dual-cure self-adhesive resin cement* (Where * is Nordon,
swiss dental products of distinction) was used for luting of glass-fiber
poste.
After post cementation the remaining tooth structure was etched followed
by the application of adhesive bonding agent according to manufactures
instruction. Composite was applied with increments to the tooth structure
and polyester crown forms for standardizing the core height, then light
activated for 40 seconds for each surface. Axial walls were prepared with
a circumferential 90° shoulder margin 1 mm wide with rounded internal
line angles, located on sound tooth structure 1 mm from the cemento-enamel junction. And with a 10° convergence angle using diamond stone.
A special milling machine was used for teeth preparation. The assembly
incorporate a conventional-speed 30.000 rpm straight hand-piece perpendicular to the surveyor platform.
Preparation design of endocrown: The entrance to the pulpal canal was
opened and gutta percha is removed to a depth 6 mm and without undercuts in the access cavity. A cylindrical-conical diamond bur was used to
make the coronal pulp chamber and endodontic access cavity continuous.
It has a total occlusal convergence of 7°. The width and thickness of the enamel strip should be maintained by preserving as much tissue as possible
from the root canal walls. The depth of the cavity should be 6 mm.
The pulp chamber was cleaned with ultrasound and its floor thoroughly.
Orifice and undercuts of mesial and distal were protected using an adhesive system and flowable resin.
The butt joint, or cervical sidewalk, was the base of the restoration, and
it provided a stable surface that could withstand the compressive stresses. The prepared surface was made parallel to the occlusal plane so that
the stress resistance was ensured along the major axis of the tooth. The
pulp chamber cavity ensured retention and stability. Extracoronally, the remaining vertical portion of the crown was prepared with a bevel labial and
palatal and rounded internal line angles, located on sound tooth structure
(Akkayan B and Gulmez T, 2002) (Figures 2-4).
Figure 1: Decapitation of the tooth in the epoxy resin block
Table 1: Classification of the samples
Group (A)
LDS (15 samples)
Accuracy: 91%
Accuracy: 91%
Group (B)
ZN+LDS (15 samples)
595
Subgroup (A1)
Post+core+crown
Samples
Subgroup (A2)
Subgroup (A3)
Subgroup (B1)
Subgroup (B2)
Subgroup (B3)
Endocrown 6 mm
Endocrown 10 mm
Post+core+crown
Endocrown 6 mm
Endocrown 10 mm
5 samples
5 samples
5 samples
5 samples
5 samples
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Vol 12, Issue 11, Oct Nov, 2021
al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
Figure 2: Lateral view for preparation of endocrown
Figure 3: Endocrown preparation without ferrule
Figure 4: Facial and lateral view of cemented endocrown
Specimen's classification
The specimens will be divided into 6 sub-groupsa) The first subgroup consisted of 5 specimens involved endodontically
treated maxillary canine restored with glass fiber posts cemented with rely
x cement, composite filling cores and conventional IPS Emax press crowns
following the manufacture instructions.
b) The second subgroup consisted of 5 specimens involved endodontically
treated maxillary canine and restored with IPS Emax endocrown according to design with 6 mm preparation.
c) Third subgroup consisted of 5 specimen involved endodontically treated maxillary canine and restored with IPS Emax Endocrown according to
design with 10 mm preparation.
d) The forth subgroup consisted of 5 specimens involved endodontically
treated maxillary canine and restored with glass fiber posts cemented with
rely x cement, composite filling cores and celtra press ceramic crowns following the manufacture instructions (Mannocci F, et al., 1999).
e) The five subgroup consisted of 5 specimens involved endodontically
treated maxillary canine and restored with celtra press Endocrown according to design with 6 mm preparation
596
f) The six subgroup consisted of 5 specimen involved endodontically treated maxillary canine and restored with celtra press Endocrown according
to design with 10 mm preparation.
Thermocycling
All specimens were subjected to a thermocycling procedure in automated
thermocycling machine. Samples of retention test were thermocycled for
5000 cycles, between 5°C-55°C with a dwell time 15 seconds, but specimens of microleakage test the number of cycles used was 500 cycles between 5°C-55°C with a dwell time 25 seconds (Figure 5).
Test procedure (fracture resistance test)
Tests were performed using Bluehill Lite Software from Instron®.
After fracture resistance test, all specimens in the test groups were viewed
using a USB digital-microscope (U500 × Digital Microscope, Guangdong,
China), magnification x35, and the images were capture and transferred to
a IBM personal computer equipped with the Image-tool software (Image J
1.43 U, National Institute of Health, USA) to determine failure mode pattern according to the following categorization (Table 2).
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al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
Figure 5: Thermo-cycling device
Table 2: Classification of failure modes
Failure mode A
Failure mode B
Failure mode C
Failure mode D
The lowest point of fracture line is located above cervical line
The lowest point of fracture line is located between cervical line and tooth root embedded in resin
The lowest point of fracture line is located inside tooth root embedded in resin
More than one fracture lines run vertically and horizontally
Statistical analyses
Data analysis was performed in several steps. Initially, descriptive statistics
for each group results. One-way ANOVA followed by pair-wise Tukey’s
post-hoc tests were performed to detect significance between groups. Student t-test was done between subgroups. Fisher exact test for qualitative
data was done for mode of failure. Statistical analysis was performed using
Grapg-Pad Instat statistics software for Windows (www.graphpad.com). p
values ≤ 0.05 are considered to be statistically significant in all tests.
Data were presented as mean, standard deviation (SD), confidence intervals (low-high) for values. The results were analyzed using Graph Pad Instat (Graph Pad, Inc.) software for windows. A value of p<0.05 was considered statistically significant. After homogeneity of variance and normal
distribution of errors had been confirmed, one-way ANOVA and student
t-test was done for comparison between subgroups and main groups respectively. Two-way was done to detect effect of each variable (material
and restorations). Chi square test was performed between failure patterns.
Sample size (n=5/subgroup) was large enough to detect large effect sizes
for main effects and pair-wise comparisons, with the satisfactory level of
power set at 80% and a 95% confidence level.
RESULTS
Fracture resistance
The mean values and standard deviation of fracture resistance (N) for both
groups as function of restoration types are summarized in Table 3 and
graphically drawn in Figures 6 and 7.
With Gr_A: There was not statistically significant difference (p<0.05) as
Subgr_A3 recorded mean value (253.86 ± 29.59 N) followed by Subgr_
A2 (234.74 ± 42.56 N) while Subgr_A1 recorded the lowest statistically
significant (p<0.05) mean value (218.01 ± 21.13 N) as indicated by one-
way ANOVA test (p=0.002<0.05). Pair-wise Tukey’s post-hoc test showed
non-significant (p>0.05) difference between Subgr_A1, Subgr_A2 and
Subgr_A3 (Table 3 and Figure 6).
Group A vs. Group B
Subgroup 1: It was found that Subgr_B1 recorded statistically non-significant higher fracture resistance mean value (220.02 ± 18.59 N) than Subgr_A1 (218.01 ± 21.13 N) as indicated by student t-test (p=0.8771 >0.05)
(Table 4 and Figure 7).
Subgroup 2: It was found that Subgr_B2 recorded statistically non-significant higher fracture resistance mean value (245.54 ± 35.39 N) than Subgr_A2 (234.74 ± 42.56 N) as indicated by student t-test (p=0.6742>0.05)
(Table 4 and Figure 7).
Subgroup 3: It was found that Subgr_A3 recorded statistically non-significant higher fracture resistance mean value (253.86 ± 29.59 N) than Subgr_B3 (269.39 ± 45.34 N) as indicated by student t-test (p=0.1924>0.05)
(Table 4 and Figure 7).
Total effect of material on fracture resistance
Regardless to restoration type, totally it was found that Gr_A recorded
statistically non-significant higher bi-axial flexure strength mean value
(235.54 ± 31.09 N) than Gr_B (244.98 ± 33.11 N) as indicated by two way
ANOVA test (p>0.05) (Table 5 and Figure 8). The failure modes of the different groups are listed in (Table 6) and (Figures 9-14).
The difference in the failure modes between Gr_A subgroups was statistically significant as revealed by chi square test (p<0.05).The difference
in the failure modes between Gr_B subgroups was statistically non-significant as revealed by chi square test (p<0.05).The difference in the failure modes of all subgroups was statistically significant as revealed by chi
square test (p<0.05) as shown (Table 6).
Table 3: Mean values ± SDs of fracture resistance (N) results for both groups as function of restoration types
Variable
Gr_A
subgroups
Mean
SD
Subgr_A1
218.01B
21.13
Subgr_A2
234.74B
42.56
Subgr_A3
253.86B
29.59
Gr_B
Subgr_B1
220.02B
18.59
Subgr_B2
245.54B
35.39
Subgr_B3
269.39B
45.34
Note: Different letter in the same column indicating statistically significant difference (p<0.05*: Significant (p<0.05) ns: Non-significant (p>0.05)
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al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
Figure 6: Schematic drawing of failure modes
Figure 7: Column chart of fracture mean values for both groups as function of restoration types
Table 4: Comparison of fracture resistance (N) results (Mean values ± SDs) between both groups as function of restoration types
Variable
Groups
Mean
SD
95% CI
High
244.24
243.09
t-test
p value
0.8771 ns
Subgr_1
Gr_A
Gr_B
218.01
220.02
21.13
18.59
Low
191.77
196.94
Subgr_2
Gr_A
Gr_B
234.74
245.54
42.56
35.39
181.9
201.6
287.57
289.47
0.6742 ns
Subgr_3
Gr_A
Gr_B
253.86
269.39
29.59
45.34
267.12
213.09
340.6
325.68
0.1924 ns
Note: *: Significant (p<0.05); ns: Non-significant (p>0.05)
Table 5: Comparison between total fracture resistance results (Mean values ± SDs) as function of material group
Variables
Material group
Groups
Mean
SD
Tukey’s rank
Statistics (p value)
Gr_A
235.54
31.09
A
0.543 ns
Gr_B
244.98
33.11
A
Note: Different letter in the same column indicating statistically significant difference (p<0.05*: Significant (p<0.05); ns: Non-significant (p>0.05)
Figure 8: Column chart comparing fracture mean values between both groups as function of restoration types
598
Figure 9: A column chart of total fracture resistance mean values as function of material group
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al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
Figure 10: Stacked column chart of failure modes for all subgroups
Figure 11: Representative microscopic image of failure mode A (× 30)
Figure 12: Representative microscopic image of failure mode B (× 30)
Figure 13: Representative microscopic image of failure mode C (× 30)
Figure 14: Representative microscopic image of failure mode D (× 30)
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al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
Table 6: Chi square test comparing between failure modes results for both groups as function of restoration types
Variable
Gr_A
Subgroups
Failure mode
A
60%
60%
0%
60%
60%
20%
B
20%
20%
20%
20%
20%
20%
Subgr_A1
Subgr_A2
Subgr_A3
Gr_B
Subgr_B1
Subgr_B2
Subgr_B3
Chi test
p value
Note: *: significant (p<0.05); ns: non-significant (p>0.05)
DISCUSSION
Ceramics have proven its efficiency as biologically compatible and highly
esthetic material. Lithium disilicate ceramics and its modified class known
as zirconia reinforced lithium silicate have a great popularity owing to their
high superior esthetic and fracture resistance properties making them
strong alternative of clinical situations (Ferrari M, et al., 2001, Krejci I, et
al., 1994; Jindal S, et al., 2004).
Lithium silicate ceramics reinforced with zirconia fillers have been recently
introduced in an attempt to combine the advantages of both components;
since addition of zirconia filler particles to lithium silicate is supposed to
increase the strength of the material.
Celtra® in its fully crystallized form is introduced material to the dental
market so it is mandatory to study its mechanical properties. Despite the
fact that results from in-vitro testing of fracture resistance of these materials cannot be directly correlated to clinical survival, yet it provides a
valuable insight on the clinical performance of the material.
The use of the post and core and coverage crown has been the classical approach for restoring endodontically treated teeth, the consensus now is the
need to conserve remaining and healthy dental structure which can help to
mechanically stabilize the tooth-restoration complex and increase surface
available for adhesion (Sonkcsriya S, et al., 2015).
The introduction of glass fibre posts changed this concept to some extent;
having lower modulus of elasticity compared to metal posts consequently having the advantage of dissipating stresses along the post length and
through the tooth (Wietske FA, et al., 2004). This feature differs from metal
posts which have higher modulus of elasticity that concentrate stresses in
the apical third of the root.
The current literature stated that the use of glass fibre posts may decrease
the occurrence of root fractures compared to rigid metal posts.
The glass fibre posts are able to improve the bending resistance and that
failures, they are more easily restorable and the modulus of elasticity similar to dentin. They are submitted to loading, the good absorb the forces
concentrated along the root, thus reducing the probability of fracture (Otto
T and Mormann WH, 2015; El-Damanhoury HM, et al., 2015).
Recently introduced endocrown restoration provided a conservative alternative treatment for endodontically treated teeth as it is a relatively easy,
cost effective procedure and less chairside time, supragingival margins, facilitate plaque control and clinical inspection. In addition, endocrown allows strengthens the tooth by minimal tooth reduction and by preserving
sound dental tissue and root canal structures.
Endocrown restorations have proven to be easier on many levels specifically concerning the clinical procedures. It is simpler and faster than the
traditional post, core and crown procedure and has been clinically reported to be successful in the restoration of endodontically treated teeth
and endocrown required minimal tooth reduction leading to strengthening and preserving sound dental tissues. This conservative treatment
600
C
20%
20%
20%
20%
20%
20%
<0.0001*
D
0%
0%
0%
0%
0%
0%
Chi square test
P value
45.34
45.34
45.34
45.34
45.34
45.34
is referred to the recent progress in adhesive systems and recent ceramic
materials (Abdallah A and Abdel-Aziz M, 2015; Guo J, et al., 2016).
Endocrown restorations have been used for the treatment of teeth with
severe damages of crown, in addition to conventional crown restorations
supported by post-core systems.
All teeth were embedded in epoxy resin 2 mm below the cemento enamel
junction to mimic the position of the root in the bone. Epoxy resin was
used as its modulus of elasticity (12 GPa) near to that of human bone (18
GPa).
All canines were sectioned perpendicular to the long axis 2 mm above the
CEJ in order to simulate the compromised condition of severely damaged
endodontically treated teeth 70
The crowns and endocrown were cemented using dual cure adhesive resin
cement. Followed the clinical protocols of Cementation procedures to ensure a close simulation of clinical relevant conditions (Wietske FA, et al.,
2004; Jindal S, et al., 2012).
The strength of the bond between zirconia reinforced lithium silicate restorations and resin adhesives was reported to be dependent on the surface
treatment of the restoration (Biacchi GR and Basting RT, 2012). Internal
surfaces of the restorations were acid etched using hydrofluoric acid for 20
seconds according to the manufacturer instructions to create micro-retentive and active surface. Silane coupling agent was then applied which has a
bi-functional group that serves to achieve a chemical bond between silica
of ceramic and adhesive resin and increase bond strength by improving the
wettability of the restoration surface.
Cementation was done using dual cure self-adhesive resin cement, which
provides a simple bonding procedure and saves time consumed in application of multi-steps adhesive materials. Moreover, according to many authors self-adhesive resin cement achieved micro-leakage values and marginal adaptation comparable to adhesive resin cement.
A strict adherence of the bonding protocols for the ceramic material used
was followed according to the manufacturer’s recommendation in order to
eliminate the variable during bonding procedures.
According to Radovic et al. (Radovic I, et al., 2008) self-adhesive cementation to dentin and various restorative materials was satisfactory and
comparable to other multistep resin cements.
Thermocycling all specimens were subjected to a thermocycling procedures in automated thermocycling machine. Samples of retention test
were thermocycled for 5000 cycles, between 5°C-55°C with a dwell time
15 seconds, but specimens of microleakage test the number of cycles used
was 500 cycles between 5°C-55°C with a dwell time 25 seconds.
Regarding the fracture resistance testing, the results of the present study
revealed that there was no statistically significant difference between mean
fracture resistance values of IPS Emax press (235.54 N) and Celtra press;
(244.98 N) where both showed statistically non-significant highest mean
fracture resistance.
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Vol 12, Issue 11, Oct Nov, 2021
al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
The samples were mounted on a computer controlled materials testing
machine (Model 3345; Instron Industrial Products, Norwood,MA, USA)
with a loadcell of 5 kN and data were recorded using computer software
(Instron® Bluehill Lite Software).
Tightening screws of the lower fixed compartment of testing machine
byto secured the Samples. Fracture test was done by compressive mode
of load applied at the 135° angle (through housing the sample in specially
designed 45° angle jig) using a metallic rod with flat tip (5 mm diameter)
attached to the upper movable compartment of testing machine traveling
at cross-head speed of 1 mm/min placed incisal with tin foil sheet in-between to achieve homogenous distribution of stress and minimization of
the transmission of local force peaks. The angle of the applied load was
selected to simulate the angulation of load in the oral cavity.
The load at failure manifested by an audible crack and confirmed by a
sharp drop at load-deflection curve recorded using computer software (Instron® Bluehill Lite Software). The load required to fracture was recorded
in Newton.
After fracture resistance test, all specimens in the test groups were viewed
using a USB digital-microscope (U500 × Digital Microscope, Guangdong,
China),
The results obtained in this study revealed a no-significant difference between the endocrown restorations and the post and core and crown. Although endocrown showed increase fracture resistance values compared
to the post and core and crown. Also the results showed non-significant
difference between the endocrown restorations with different designs. Although endocrown (10 mm) showed higher fracture resistance values than
endocrown (6 mm) which may be due to an increase in surface area.
Finally, there was no significant difference between the two tested ceramics.
This may be due to the fact that according to the manufacture the zirconia
content in celtra is only about 10% in weight, which didn't result in significant difference increasing in fracture resistance.
(Preis et al. 1995) who examined the fracture resistance of lithium disilicate and zirconia reinforced lithium disilicate and they found that both
have similar values. The high fracture resistance values of e-max CAD
were reasonable due to the development of the high crystalline content of
fine highly-interlocking lithium disilicate crystals embedded in the glassy
matrix after crystallization.
The results of the mean fracture resistance values of e-max press and Celtra
press showed no statistically significant difference. This was in accordance
with Ap et al. (Forberger N and Gohring T, 2008), who concluded that the
addition of zirconia to glass matrix of lithium disilicate did not increase
the flexural strength owing to the increase in viscosity due to ZrO2 content
and the accompanied decrease in crystal growth.
El Sayed and Emam reported that addition of zirconia to lithium disilicate
ceramics did not improve the fracture resistance of all ceramic crowns
Chang et al. (Otto T and Mormann WH, 2015) stated that leucite-reinforced glass ceramic endocrown restorations showed statistically higher
fracture resistance values than all-ceramic crowns supported by glass fibre
post and composite core for premolars. These results were attributed to the
increased thicknesses of the ceramic materials and the reduced number of
interfacial surfaces for endocrown with respect to post-core crowns (Otto
T and Mormann WH, 2015; Magne P, et al., 2014).
Bindl and Mörmann (Bindl A and Mörmann WH, 1999) showed using
finite element analysis studies revealed that endocrown were more resistant to failures than crowns with post-core systems, because of their lower
stress values (Krejci I, et al., 1994; El-Damanhoury HM, et al., 2015). In
light of the literature, in this study, endocrown modified with different materials and designs, and post core systems were tested.
601
Indicates that intracoronal reinforcement did not significantly increase the
clinical success rate of any of the anatomic groups of endodontically treated teeth. On the other side, coronal coverage significantly improved the
clinical success rate of endodontically treated maxillary premolars, maxillary molars, mandibular premolars, and mandibular molars. It did not
significantly affect mandibular anterior or maxillary anterior endodontically treated teeth.
Shaker 2007 (Sherfudhin H, et al., 2011) reported that endocrown had the
least fracture load compared to standard crowns. He suggested that when
restoring endodontically treated premolars, glass fibre posts and composite core supported crowns would be an alternative to endocrown which
show un-repairable.
Ghajghouj and Taşar-Faruk, 2019 determine the effect of design of restoration on the fracture resistance of different (CAD/CAM) ceramics. Ceramics used included lithium disilicate IPS Emax-CAD, Vita Suprinity and
PEEK with intracoronal cavity depth of 2 mm and 3 mm. Cements used
were either PanaviaV5, Relyx Ultimate or GC. Results proved that PEEK
endocrown had higher fracture resistance and that different intracoronal
cavity depths were found to have no effect on the fracture resistance.
Moreover, the results were in agreement with Hamdy, 2015 (Shah RJ, et al.,
2014) that observed the fracture resistance of full crown greater than inlay
and endocrown and reported that the full coverage crown showed the best
mode of failure and inlay showed the worst (Shah RJ, et al., 2014).
The obtained opposed these results of this study by chang et al. 2009
(El-Damanhoury H, et al., 2015) who reported that with the adhesive
technique creating sufficient ferrule might cause the loss of sound tooth
structure and result in bonding strength compromised, because, enamel is
preferred to dentin for bonding, this contradictory finding might be related to the difference in the material and methodology between the studies.
Where chang et al. 2009 used pro CAD to perform their study rather than
IPS emax press in our study.
Forberger and Gohring 2008 concluded that the restoration of endodontically treated mandibular premolars with endocrown cannot be recommended over treatment using post and core foundations.
Ramirez et al. 2014, (Sebastià AR, et al., 2014) evaluated the fracture resistance of anterior teeth endodontically treated and restored with crowns
made of composite or ceramic and retained without the use of a post
(endocrown) or with posts of 5 mm (short) and 10 mm in length (long).
Results revealed that the post, length of post, and crown material had no
significant effect on the fracture resistance.
The hypothesis of this study was completely rejected as there was no significant difference between the endocrown restorations and the traditional
post and core and crown. Also, there was no difference between the endocrown designs tested. Finally, there was no significant difference between
the two tested ceramic materials.
Within the limitation of this study, because the lack of research of canine
endocrown the following conclusions-pressable IPS e-max materials
showed non-significant fracture resistance values than pressable celtra
techniques.
CONCLUSION
Within the limitation of this study, based on the result obtained in this
current research the following conclusion.
• Restoration endodontically treated maxillary canine with endocrown
restorations give rise to higher fracture resistance value than post post and
core and crown. although this increase in fracture resistant is not significant.
• Endocrown (10 mm) give highest fracture resistant than endocrown (6
mm). Yet there was no significant different between the two restorations.
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al-Fadhli M: Fracture Resistance of Anterior Endocrown vs. Post Crown Restoration an In-vitro Study
• The reinforced Lithium silicate (celtra) recorded more significant higher
fracture resistance value than Lithium disilicate (e-max)
• On canine needs further research for being a viable restoration in this
condition. Different materials have no effect on the fracture resistance of
endocrown restorations.
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