Fatima.doc
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 22
Fracture resistance of weakened premolars restored with
sonically-activated composite, bulk-filled and
incrementally-filled composites
(A comparative in vitro study )
Fatima Fahad, B.D.S. (1)
Manhal Abdul-Rahman Majeed, B.D.S., M.Sc., Ph.D. (2)
ABSTRACT
Background: This study was conducted to assess the effect of sonic activation and bulk placement of resin
composite in comparison to horizontal incremental placement on the fracture resistance of weakened premolar
teeth.
Materials and method: Sixty sound human single-rooted maxillary premolars extracted for orthodontic purposes were
used in this study. Teeth were divided into six groups of ten teeth each: Group 1 (sound unprepared teeth as a
control group), Group 2 (teeth prepared with MOD cavity and left unrestored), Group 3 (restored with SonicFill™
composite), Group 4 (restored with Quixfil™ composite), Group 5 (restored with Tertic EvoCeram® Bulk Fill composite)
and Group 6 (restored with Universal Tetric EvoCeram® composite using horizontal incremental layering technique).
Standardized class II MOD cavity was prepared in all teeth except (group 1).After finishing the restorative procedure
of each group according to the manufacturer's instructions, all teeth were stored in deionized distilled water in an
incubator at 37°C for seven days.All specimens were subjected to compressive axial loading until fracturein a
universal testingmachine.Specimens were examined by a stereomicroscope at a magnification of (20X) to evaluate
the mode of fracture .
Results: The results of this study revealed that the control group exhibited the highest fracture resistance compared to
all prepared teeth groups (restored or unrestored) and the differences were statistically highly significant (P<0.01),
except with group 3 (which was restored with SonicFill™ composite) where the difference was statistically significant
only (P < 0.05).Additionally the results of this study revealed that the prepared unrestored teeth (Group 2) exhibited
the lowest fracture resistance compared to all restored groups and the differences were statistically highly significant
(P<0.01). Meanwhile, among the restored teeth groups, teeth restored with SonicFill™ composite (group 3) exhibited
the highest fracture resistance as compared with all other restored groups and the difference was statistically highly
significant (P<0.01) .On the other hand, no statistically significant differences in fracture resistance were found among
groups 4, 5 and 6, which were restored with Quixfil™ composite, Tetric EvoCeram® Bulk Fill composite and Universal
Tetric EvoCeram® composite, respectively (P > 0.05). Group 3and Group 5 showed mostly mixed mode of failure,
while Group 4 showed mostly adhesive mode of failure. On the other hand Group 6 teeth showed different modes of
failure.
Conclusions: SonicFill™ composite can be considered as a viable treatment modality for the restoration of weakened
maxillary premolar teeth. On the other hand, the time-consuming incremental layering technique can be substituted
with bulk filling, using bulk fill materials (Quixfil™ and Tetric EvoCeram® Bulk Fill) for reinforcement ofweakened
maxillary premolars.
Key words: Fracture resistance, SonicFill™, bulk fill technique, incremental layering technique. (J Bagh Coll Dentistry
2014; 26(4):22-27).
INTRODUCTION
`````Unresolved controversy exists concerning the
preferred restorative materials and techniques
used to restore weakened maxillary premolars to
improve their resistance to fracture under occlusal
load (1).The evolution of composite materials and
adhesive techniques has considerably changed the
approach to restorations in the posterior area.
The advantages of adhesive restorations are
not only of an aesthetic nature, but, above all,
relate to the possibilities of conserving a greater
amountofhealthy tissue and “reinforcing” the
residual dental structure (2).It is obvious that
dentists have always been looking for a fast and
reliable filling technique allowing the reduction of
layers, effort and time.
(1) Master student, Department of Conservative Dentistry,
College of Dentistry, University of Baghdad.
(2)Assist.Prof., Department of Conservative Dentistry, College of
Dentistry, University of Baghdad.
In an attempt to reduce some of the time and
effort needed for layering and adaptation when
placing posterior composites, new materials have
been introduced and termed "bulk fill" materials
(3).
Most of these products such as Surefil™ SDR
(Dentsply Caulk), X-trafil (VOCO, Cuxhaven,
Germany), Venus® Bulk Fill (HeraeusKulzer)
and Filtek™ Bulk Fill Flowable Restorative (3M
ESPE) are based on a low viscosity composite,
and are applied in a bulk layer of 4mm thickness
and light cured, then another composite is used
to fill the rest of thecavity. This makes the
restorative procedure longer and more complex;
therefore, these materials should not be classified
as true "bulk fill" materials (4). More recently, true
"bulk fill" composite resin materials have been
introduced such as QuixFill™ posterior restorative
(Dentsply) and Tetric EvoCeram® Bulk Fill
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 23
(Ivoclar Vivadent). QuixFill™ posterior restorative
offers an extremely high filler load (66% by
volume and 86% by weight) and it offers a
complete 4mm cure in as little as 10 seconds,
while still offering a prolonged working time to
allow creation of pre-cure anatomy (5).
On the other hand, Tetric EvoCeram® Bulk
Fill material is another bulk fill material which
can also be placed in increments of up to 4 mm
and can achieve high marginal adaptation to the
floor and walls of cavity preparation, eliminating
the need for a flowable liner as reported by the
manufacturer (6).
Very recently, Kerr and KaVo, after three
years of a common development project, launched
the SonicFill™ system for posterior restorations.
The system consists of a hand piece activated
sonically and a special composite formulation,
which contains about 83.5% of fillers by weight,
mainly silica and barium aluminoborosilicate
glass. Upon activation, the sonic energy lowers
the viscosity of the composite and extrudes the
composite that has initially a thick consistency.
The viscosity change of the composite will
ensure a perfect adaptation to the cavity walls and
avoids the stickiness of the composite to the
instrument. It is not necessary to condense the
composite because the high frequency vibration
yields intimate adaptation to the cavity walls
without voids inclusion. Cavities up to 5 mm of
depth are filled in one bulk increment. Upon
deactivation of the sonic energy, the viscosity of
the composite increases and allows easy
adaptation and accurate sculpting morphology of
the composite. SonicFill system is indicated for
posterior restorations in class I and II and as a
buildup material for cusp reconstruction as well as
a base after root canal treatment (4).
MATERIALS AND METHODS
Sample selection
Sixty sound human single-rooted maxillary
premolar teeth, extracted for orthodontic purposes
from patients with agerange from 18-22
yearscollected from different health centers, were
used in this study.Teeth were stored
in0.1%thymol solution for 48 hours (6), then in
deionized distilled water at room temperature (7).
Only sound teeth free from cracks and with
regular occlusal anatomy and approximately
similar crown size were selected (8). For each
tooth, the maximum bucco-lingual and mesio-
distal dimensions and inter-cuspal distance were
measured using a digital caliper (9). The measured
dimensions varied with a maximum deviation of
not more than 10% from the determined mean.
These measurements were used in the distribution
of the teeth among the different groups to provide
uniformity of tooth size in each group (10).
Teeth mounting
To simulate the periodontal ligament, root
surfaces were marked 2 mm below the cemento-
enamel junction CEJ and covered with a 0.6 mm
thick foil (Adapta foil, Bego, Germany)(11). Each
tooth was embedded in a block of self-cured
acrylic resin (Veracril, Colombia) in a rubber
mold cylinder (2.5cm width-3cm height). The
teeth were embedded along their long axes using a
dental surveyor.
After the first signs of polymerization, teeth
were carefully removed manually from the resin
blocks (12).The acrylic covered the roots to within
2 mm of the CEJ, to approximate the support of
alveolar bone in a healthy tooth (13). In order to
simulate the periodontal ligament, the Adapta
(foil) was removed from the root surface and light
body addition silicone impression material
(Express™, 3M ESPE, USA) was injected into the
acrylic resin blocks in the site that was previously
occupied by the tooth root and adapta foil, and the
tooth was reinserted into the resin block. A
standardized silicone layer that simulated
periodontal ligament was thus created taking the
thickness of the foil (11).
Sample grouping
The teeth were randomly divided into six
groups of ten teeth each according to the type of
restorative material used as follows:
Group1: This group comprised ten sound
unprepared teeth that served as a control group.
Group 2: An extensive class II MOD cavity was
prepared, but the cavity was left unrestored.
Group 3: The MOD cavity was restored with
SonicFill™ composite (Kerr Corp., USA).
Group 4: The MOD cavity was restored with
Quixfil™ bulk fill composite restorative material
(Dentsply DETREY GmbH, Germany).
Group 5: The MOD cavity was restored with
Tetric EvoCeram® Bulk Fill composite restorative
material (IvoclarVivadent, Liechtenstein).
Group 6: The MOD cavity was restored with
Universal Tetric EvoCeram®composite restorative
material (IvoclarVivadent, Liechtenstein), using
horizontal incremental layering technique.
After the random distribution of the teeth into
the six experimental groups, statistical analysis
using one-way ANOVA test was done among the
groups for the bucco-lingual and mesio-distal
dimensions and for the inter-cuspal distance to
assure that there were no statistically significant
differences among the groups concerning crown
dimensions.
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 24
Cavity preparation
Mesio-occluso-distal (MOD) cavities were
prepared in all specimens using a flat-ended
diamond fissure bur (4mm cutting height, 1mm
diameter) in a high speed turbine handpiece with
water coolant that was fixed to a modified dental
surveyor, except for group 1, which served as a
control. The width of the cavity was standardized
3mm, which approximates one half of the inter-
cuspal distance and one third of the bucco-palatal
dimension.
The depth of the cavity was 3mm at the pulpal
floor level and 4mm at the gingival seat level
measured from the palatal cavo-surface margin,
with 1mm depth of the axial wall.The buccal and
palatal walls of the cavity were prepared parallel
to each other(14, 15, 16). The cavity dimensions used
in this study are shown in Figure1.
Figure 1: Diagram showing the dimensions
of the MOD cavity preparation.
Before preparation of the teeth, an outline of
the cavity was drawn with a super color marker
(17). Tooth preparation was carried out with aid of
modified dental surveyor in order to standardize
the cavity preparation.Teeth showing pulpal
exposure after preparation were discarded (10).The
depth of the cavity was checked with a graduated
periodontal probe and the width of the cavity was
checked using a digital caliper (18).
Adhesive procedure
SuperMat® Adapt®SuperCap® Matrix system
(Kerr Corp.)was used in this study and changed
for each restoration.Single Bond Universal
Adhesive (3M ESPE) was usedfor groups 3 to 6
prior to composite resin placementwith the self-
etch technique following the manufacturer's
instructions and light cured with a LED light
curing unit with a light intensity of 600 mw/cm2
(Woodpecker® LED.C Wireless Curing Light) for
10 seconds according to the manufacturer's
instructions.
Restorative procedure
The three bulk fill composite materials
SonicFill™(Kerr Corporation, USA), Quixfil™
compositematerial (Dentsply DETREY GmbH)and
Tetric EvoCeram® Bulk Fill composite material
(IvoclarVivadent, Liechtenstein) were applied to
the cavity in a single bulk increment of 4mm
according to the manufacturer’s instructions.
CompoRoller™ was used to compress the
material, adapting the margins; removing the
excessand sculpting anatomy.
Each restoration was then light cured for 20
seconds according to the manufacturer's
instructions. Additional light curing from the
buccal and palatal sides for 20 seconds was done
according to the manufacturer's recommendation.
Group 6 was restored with Universal Tetric
EvoCeram® composite using horizontal
incremental technique. The cavity was filled with
two increments of 2 mm each since the total depth
of the cavity was 4 mmusing CompoRoller™
instrument, followed by light curing for 20
seconds from occlusal direction according
manufacturer’s instructions.Afterfinishing the
restorative procedure, all teeth were stored in
deionized distilled water in an incubator at 37°C
for seven days before testing (31).
Mechanical testing
All specimens were subjected to compressive
axial loading until fracture in a computer-
controlled universal testing machine (LARYEE,
China) with a crosshead speed of the 0.5
mm/minute. The load was applied parallel to the
long axis of the teeth using a steel bar 8 mm in
diameter, touching the occlusal surface of the
tooth at the slopes of the cusps rather than the
restoration (15).
All samples were loaded until fracture and the
maximum breaking loads were recorded in kN.
The mode of failure was evaluated under a
stereomicroscope (Altay biovision line, Italy) at a
magnification of (20 X).The mode of failure was
recorded and classified as adhesive, cohesive and
mixed modeof failure (13).
RESULTS
The descriptive statistics of fracture resistance
of all groups with the percentage of increase in
fracture resistance are shown in Table 1. One-way
ANOVA test revealed a statistically highly
significant difference among the groups as shown
in Table 2. Further comparisons among groups
were done using the Least Significant Difference
test (LSD test) to see where the significant
difference occurred as shown in Table 3.
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 25
The results of this study revealed that the
control group exhibited the highest fracture
resistance compared to all prepared teeth groups
(restored or unrestored) and the differences were
statistically highly significant (P<0.01), except
with Group 3 (which was restored with SonicFill™
composite) were the difference was statistically
significant only (P < 0.05 .)
Additionally the results of this study revealed that
the prepared unrestored teeth (Group 2) exhibited
the lowest fracture resistance compared to all
restored groups and the differences were
statistically highly significant (P<0.01).
Among the restored teeth groups, teeth restored
with SonicFill™ composite (Group 3)exhibited the
highest fracture resistance as compared with all
other restored groups and the difference was
statistically highly significant (P<0.01 .)
On the other hand, no statistically significant
differences in fracture resistance were found
among Groups 4, 5 and 6, which were restored
with Quixfil™ composite, Tetric EvoCeram® Bulk
Fill composite and Universal Tetric EvoCeram®
composite, respectively (P>0.05). Concerning the
fracture mode, Group 3 and Group 5 showed
mostly mixed mode of failure, while Group 4
showed mostly adhesive mode of failure. On the
other hand, Group 6 showed different modes of
failure.
Table 1: Descriptive statistics of fracture
resistance of each group in kN
Percentage of
increase in
fracture
resistance
SD Mean Groups
100% 0.094 1.18250 Group1
- 53%* 0.029 0.55633 Group 2
90.7% 0.110 1.0726 Group 3
74.8% 0.079 0.88533 Group 4
72.3% 0.046 0.855 Group 5
75.85% 0.048 0.897 Group 6
*Percentage of decrease in fracture
Table 2: One-way ANOVA test for comparison
of significance among different groups
Sum of
Squares
df
Mean
Square
F Sig.
Between
groups
1.377 5 0.275
50.062
.000
(HS)
Within
groups
0.165 30 0.006
Total 1.543 35
Table 3: LSD test between the different
groups
Groups Mean Difference S.E. Sig.
G 1
G2 .626167* .042829 .000 (HS)
G 3 .109833* .042829 .016 (S)
G 4 .297167* .042829 .000 (HS)
G 5 .327500* .042829 .000 (HS)
G 6 .285500* .042829 .000 (HS)
G 2
G 3 -.516333* .042829 000 (HS)
G4 -.329000* .042829 .000 (HS)
G5 -.298667* .042829 .000 (HS)
G6 -.340667* .042829 .000 (HS)
G 3
G4 .187333* .042829 .000 (HS)
G 5 .217667* .042829 .000 (HS)
G6 .175667* .042829 .000 (HS)
G 4 G5
.030333 .042829 .484 (NS)
G6 -.011667 .042829 .787 (NS)
G 5 G 6 -.042000 .042829 .335 (NS)
* The mean difference is significant at the 0.05
level.
DISCUSSION`````
The highest fracture resistance mean value
presented by the intact teeth (Group 1) could be
attributed to the presence of intact palatal and
buccal cusps with intact mesial and distal
marginal ridges which form a continuous circle of
dental structure, reinforcing the tooth and
maintaining its integrity (19).This is in
agreementwith Santos and Bezzera (20).
In this study, the lowest fracture resistance
mean value presented by the prepared unrestored
teeth which was statistically highly significant
when compared with all other groups could be
attributed to thetype and quality of the remaining
tooth structure after MOD cavity preparationas
teeth with large MOD cavities are severely
weakened due to the loss of the reinforcing tooth
structures,specially the cuspsand marginal ridges,
so become more susceptible to fractureThis is also
in agreement with Santos and Bezzera (20).
In this study, it is clearly seen that all
composite resin restored teeth displayed higher
fracture resistance than the prepared but
unrestored teeth (Group 2) regardless of the type
of composite material used and with varying
percentages of increase in fracture strength as
shown in Table 1.This could be due to the micro-
mechanical bonding between the adhesive system
and the tooth structure and hybrid layer formation
which tend to bind the walls of the cusps together
and strengthen the remaining tooth structure (21).
Among the restored groups, Group 3 (which
was restored with SonicFill™ composite) showed
the highest fracture resistance mean value and the
highest percentage of increase in fracture
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 26
resistancewith statistically highly significant
difference as compared with all other restored
groups. This could be attributed to the followings:
1. Better adaptation of SonicFill™ composite to
the cavity walls owing to its fluctuating viscosity
as a result of sonic activation delivered through
the SonicFill™hand piece. Sonic activation lowers
the viscosity of the SonicFill™ composite
dramatically, up to 87%, which is related to
special rheological modifiers that react to sonic
activation delivered through the SonicFill™ hand
piece during its placement, increasing its
flowability and providing superior adaptation to
the cavity walls, and thus making the frequency
and size of critical voids located at the margin and
along line angles of the cavity less pronounced
compared to conventional putty-like composites
(22).
2. Better mechanical properties of SonicFill™
composite as compared with the other
compositematerials (Quixfil™composite, Tetric
EvoCeram® Bulk Fill compositeand universal
Tetric EvoCeram®composite) including higher
compressive strength, higher flexural strength and
higher fracture toughness and fracture work, with
an intermediate flexural modulus between
Quixfil™ and Tetric EvoCeram® Bulk
Fill(24,25,26).Such differences in the mechanical
properties among the three different bulk fill
materials used in this study could be attributed to
the differences in the type and size of fillers and
the difference in filler loading.
On the other hand, the statistically non-
significant differencesinfracture resistance among
Group 4, Group 5&Group 6 even though Quixfil™
composite has higher filler loading than the
universal and bulk fill versions of Tetric
EvoCeram® composite could be due to that
Quixfil™ composite is a microhybrid composite,
while the other two composite materials are
nanohybrid composites, and hence
nanotechnology might have compensated the
effect of higher filler loading of Quixfil™ resulting
in statistically non-significant differences in
fracture resistance.
Concerning the fracture mode, Group 3
(SonicFill™Group) showed mostly mixed type of
failure (80%) (Cohesive type in restoration within
the upper part of the restoration and adhesive type
in the remaining part).This could be attributed to
the following:
1. Proper adaptation of the material to cavity
walls without void formation owing to its
fluctuating viscosity combined with the low
shrinkage and contraction stress upon curing of
bonded SonicFill™ composite.Low contraction
stressreduced the possibility of the composite
pulling away from the tooth surface during
polymerization with subsequently low cuspal
deflection.
2.High mechanical properties of SonicFill™
(especially its high fracture toughness and fracture
work), which made the material able to absorb the
applied load and preserve the tooth-
restorationinterface, up to the point at which the
applied load exceeded the fracture toughness limit
of the material, thus underwent cohesive failure in
the upper part of the restoration and lost its ability
to transmit the applied load and preserve the
tooth-restoration interface, hence underwent
adhesive type of failure.
3. Another possible contributing factor for this
finding might be the high bond strength of Single
Bond Universal Adhesive to enamel (28).
Group 4 (Quixfil™Group) showed mostly
adhesive type of failure (90%). This may be
attributed tothe heavy viscosity of Quixfil™
composite, which might hindered the appropriate
adaptation of the material to the cavity walls,
resulting in void formation at the tooth restoration
interface (23). On other hand the high flexural
modulus of Quixfil™ composite as a result of its
high filler loading might not allowed the material
to absorb the applied load and undergo plastic
deformation; instead, the increased stresses from
theapplied load were transferred to the tooth-
restoration interface, resulting in adhesive type
offailure before the material would fail
mechanically (29). Also the resin matrix of
Quixfil™ composite serves to give the resin
mixture a high cohesion (30).
Group 5 (Tertic EvoCeram® Bulk Fill Group)
showed mostly mixed mode of failure (80%). This
could be attributed to the low shrinkage stress of
Tertic EvoCeram® Bulk Fill composite according
to manufacturer's information.This is in
agreement with Van Ende et al. (27), who found
that for materials with low shrinkage stress, mixed
failure was the predominant type of failure rather
than de-bonding with subsequent adhesive failure.
This is also in agreement with El Gezawi et al. (29)
who found that most failures of bulk fill
composites were mixed.
Group 6 showed cohesive type of failure in
50%, adhesive type of failure in 30% and the
other 20% showed mixed type of failure. This
finding might be due to the incorporation of voids
or contamination between composite layers.
Voids developed from resin porosity contain
oxygen and form polymerization inhibiting zone
resulting in bond failures between increments (31).
SonicFill™ composite can be considered as a
viable treatment modality for restoration of
weakened teeth. It is obvious that dentists have
J Bagh College Dentistry Vol. 26(4), December 2014 Fracture resistance
Restorative Dentistry 27
always been looking for a fast and reliable filling
technique allowing the reduction of layers, effort
and time; therefore, the time-consuming
incremental layering technique can be substituted
with the bulk fill technique using bulk fill
materials (Quixfil™ and TetricEvoCeram® Bulk
Fill) for reinforcement of weakened teeth.
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