J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 13

The Effect of Different Light Cure Systems on
Microhardness of Bulk Fill Composite Materials

Linz A. Shalan, B.D.S., M.Sc. (1)
Samer Awn Thiab, B.D.S., M.Sc. (2)

ABSTRACT
Background: The aim of this study was to evaluate the effect of three types of light curing devices QTH, LED and
Flashmax on the surface microhardness of three types of bulkfill composite resins; Filtek Bulkfill posterior composite
( 3M), Tetric Evo Ceram ( Ivoclar Vivadent) and Sonicfill composite ( Kerr)
Materials and methods: Total number of 90 samples was prepared, 30 samples for each type of bulkfill composite,
were divided into three main groups, group A: Filtek posterior bulkfil (3M), group B: Tetric Evo Ceram (Ivoclar
Vivadent) and group C: contain Sonicfill composite (kerr). Which then divided into three subgroups (n= 10) (1)
Samples cured by QTH system (2) Samples cured by LED system and (3) samples cured by Flashmax system then all
samples were subjected for microhardness test (by Vickers hardness tester). The data were recorded and statistically
analyzed, by the ANOVA and the Tukey test.
Results: the data was subjected to statistical analysis using one way ANOVA and Tukey test, the result revealed that
there was a high significant difference among the tested units with LED had high VHN values followed by QTH while
Flashmax had lowest VHN values, also there was high significant difference among the tested materials in which
Sonicfill composite had higher VHN value followed by Tetric EvoCeram while Filtek bulkfill posterior composite had
the lowest VHN.
Conclusions: microhardness of the composite resin materials depend upon energy of the curing device, time of
exposure, composition of the composite material.
Key word: microhardness, bulkfill composite, Flashmax, Sonicfill. . (J Bagh Coll Dentistry 2017; 29(2):13-20)

INTRODUCTION

Bulk-fill composites are popular restorative
materials that have been in the market for several
years, unlike traditional composites, which
typically are placed in maximum increments of 2
mm, bulk-fill composites are designed to be
placed in 4 mm, or sometimes greater increments.
Restoring a tooth in one step certainly appears to
save time, there are some concerns. For example,
manufacturers claim that bulk-fill materials have
greater depth of cure and lower polymerization-
induced shrinkage stress. One proposed rationale
for limiting composite increments to 2 mm is to
allow the curing light to penetrate to the resin
farthest away from the light source (1).

A second reason for using 2-mm increments is
to minimize the shrinkage and shrinkage-induced
stress associated with composite polymerization.
Contraction stresses that exceed the adhesive
strength of the composite may result in gaps
between composite and cavity walls. It is widely
believed that these marginal gaps may lead to
microleakage, sensitivity and secondary caries,
although there is little clinical evidence to support
that secondary caries are caused by this gap
formation (2).

(1) Assist. Professor,. Department of Conservative Dentistry,
College of Dentistry, University of Baghdad.
(2) Lecturer. Depart ment of Conservative Dentistry, College of
Dentistry, University of Baghdad.

Polymerization of the core of the restoration is
directly related to the material's chemical
composition, the organic (type of matrix) or
inorganic portion (type and morphology of filler
contents).

Moreover, it is influenced by the thickness of
the increment inserted into the cavity, intensity
and irradiation time, light spectrum, and distance
of the tip of the light curing unit to the material to
be activated (3). Factors affecting resin-based
composites’ depth of cure have been identified
mainly as curing source intensity and light
exposure duration, filler size and content,
interactions at the filler-matrix interface, shade
and translucency (2).

However, the polymerization reaction cannot
be considered finished after exposure to light due
to the presence of what is called "dark
polymerization" (4). It can be explained by the
presence of a temporary excess of free volume of
monomers with enough mobility that allows
molecules to still interact at lower rates. It has
been reported that the values of resin conversion
for most of the commercial dental composites
vary from 40-75% (4).

SonicFillTM composite (Kerr Corp., USA) is a
nanohybrid, low-shrink, resin-based, radiopaque,
sonic-activated, bulkfill composite material
designed for direct placement for all cavity classes
in posterior teeth without additional capping layer.
It allows a depth of cure of 5mm, incorporates a
highly-filled proprietary resin with special
rheological modifiers that react to sonic energy.
As sonic energy is applied through the hand piece,

J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 14

the modifier causes the viscosity to drop (up to
87%), increasing the flow ability of the composite
and enabling quick replacement and precise
adaptation to the cavity walls. When the sonic
energy is stopped, the composite returns to a more
viscous, non-slumping state for curving and
contouring (5).

The light-curing unit plays a more influential
role in the basic properties of resin-based
composites. Quartz-tungsten-halogen (QTH) units
have been widely used for polymerizing resin-
based dental materials for decades. QTH units
exhibit several shortcomings, so, as an alternative,
light-emitting diode (LED) light curing units were
introduced for polymerizing resin-based
composites. However, conflicting results have
often been observed in the literature as related to
the effects of both light curing units (5).

Recently, resin-based composite curing lights
have been developed that have higher intensities
and shorter curing cycles which help speed the
resin-based curing (4). One of these new high
intensity light curing units is the Flash Max
P3(CMS Co., Denmark) whose light intensity
ranges from 4000-5000 mW/cm2 and supposed to
give 6 mm curing depth in only three seconds as
claimed by the manufacturer (6).

The relative importance of a microhardness
test lies in the fact that it throws a light on the
mechanical properties of a material. The higher
the degree of conversion, the better the
mechanical properties, hardness, biocompatibility,
water sorption, color stability and wear resistance
of the resin composite (7). Microhardness is often
traditionally used as indirect measurement of
effectiveness of composite cure or the degree of
conversion, so the aim of this study was to
evaluate and compare the influence of different
light curing system (conventional QTH, soft start
LED and Flashmax) on micro hardness of three
types of Bulkfill composite (Filtek Bulkfill
posterior composite, Tetric Evo Ceram bulkfill,
sonic fill composite).

MATERIALS AND METHODS

Three types of bulkfill composite were used in
this study 1. Filtek Bulkfill posterior composite
(3M). 2. Tetric Evo Ceram (Ivoclar Vivadent), 3.
Sonic fill composite (Kerr). Their composition
and shade presented in table (1) three light curing
device were used 1. QTH, 2. LED, 3. Flashmax
their intensity and exposure times presented in
table (2), Sonicfill composite and Filtek bulkfill
posterior composite comes in universal shade,
while Tertic Evo Ceram comes in three shades
IVA, IVB and IVW. In this study we use the
lighter shade IVA.

Grouping
Group A: contain 30 samples made from Filtek
Bulkfill posterior composite (3M) subdivided into
3 subgroup
Group A1: contain 10 samples of Filtek Bulkfill
posterior composite cured by QTH.
Group A2: Contain 10 samples of Filtek Bulkfill
posterior composite cured by LED.
Group A3: Contain 10 samples of Filtek Bulkfill
posterior composite cured by Flashmax.
Group B: contain 30 samples made from Tetric
Evo Ceram composite (Ivoclar Vivadent)
subdivided into 3 subgroup
Group B1: contain 10 samples of Tetric Evo
Ceram composite cured by QTH.
Group B2: Contain 10 samples of Tetric Evo
Ceram composite cured by LED.
Group B3: contain 10 samples of Tetric Evo
Ceram composite cured by Flashmax.
Group C: contain 30 samples made from
Sonicfill composite (Kerr) subdivided into 3
subgroup
Group C1: contain 10 samples of Sonicfill
composite cured by QTH.
Group C2: contain 10 samples of Sonicfill
composite cured by LED.
Group C3: contain 10 samples of Sonicfill
composite cured by Flashmax.

Sample preparation:

Two-piece aluminum mold with a diameter of
6mm and a height of 4mm (7) was used for the
preparation of composite specimens for the
evaluation of the depth of cure. A celluloid strip
was placed on a flat glass slide on top of a white
background. The aluminum mold was then placed
on it and slightly over filled in one increment with
one of the composite materials and a second
celluloid strip was then placed on top of the mold
and overlaid with another glass slide with the
application of 100gm load to extrude excess
material. The top slide was then removed and the
composite resin light-cured with either of the
following curing units: (1) quartz tungsten-
halogen (QTH) light curing unit (Ivoclar), (2)
LED light curing unit (USA)(3) FlashMax P3high
intensity LED curing unit (CMS Co., Denmark).
The tip of the light curing unit was placed in
direct contact with the overlaid celluloid strip.

The light guide of QTH light curing unit has a
diameter of 4mm, while the FlashMaxP3 light
curing unit is supplied with two light guides: a
4mm tip and an 8mm tip light guides. The 4mm

J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 15

tip was used in this study for the purpose of
standardization, after completing the light curing
procedure, the over laid celluloid strip was
removed and the aluminum mold was opened.
Then stored for 24hours in a light proof container
with distilled water at 37˚c to complete
polymerization and inhibit any further
polymerization from transient light (7).

Relative microhardness was measured b y
doing the surface microhardness test on both sides

of the samples (top and bottom) to give indication
about the depth of cure by calculating the ratio of
bottom/top hardness. A minimum value of 0.80
have to be reached in order to consider the bottom
microhardness of the samples was determined
using Vickers Microhardness tester (MicroMet
6040 Wilson Microhardness; BUEHLER,
U.S.A.).

Table 1: Composition of the tested composite materials

Product The resin matrix: The filler: Filler size
Filler

loading Manufacture Shade

Filtek Bulk
Fill, Posterior

restorative

AUDMA, UDMA,
and 1, 12-

dodecane-DMA.

Silica filler, a zirconia
fill and ytterbium
trifluoride filler

4-20nm 76.5%- Wt

3M ESPE, St.

Paul, USA

Tetric
EvoCeram
Bulk Fill

Bis-GMA
UDMA

Bis-EMA

Ytterbium fluoride,
barium aluminium

silicate glass

550 nm
(mean) 80% wt

Ivoclar
vivadent

Sonic fill Bis-EMA TEGDMA

Silicon dioxide
Glass, oxide,

chemicals
Zirconium compound
Ytterbium triflouride

0.4µm-
30nm 83% wt Kerr A2

Table 2: curing systems used in this study

Device Intensity Exposure time Wave length Manufacturer
QTH 400 40 S 400-500 Ivoclar, Austeria
LED 460 40 S 440-480 USA

Flashmax 4000 3 s 4000-5000 Denmark

RESULTS
Statistical analysis among groups for the effect
of light curing system on tested materials:

Descriptive analysis for both top and bottom
surfaces:

Means, standard deviation for microhardness
values VHN for the three tested curing systems on
both top and bottom surfaces the result showed
that LED had the highest means followed by QTH

and lowest mean value for Flashmax as shown in
table (3).

Interfacial analysis

ANOVA test was made among tested groups
for both top and bottom surfaces which revealed a
high significant differences (p<0.001) in
microhardness values HV among groups as shown
in table (3).

Table 3: Descriptive & ANOVA for the effect of tested light curing systems on top and bottom

surfaces of the tested materials

M ean
Std.

Deviation F
P-value sig

M ean
St d.

Deviation
F p -value s ig

A1 53.44 7.14 39.11 4.94
B1 56.94 4.41 49.08 3.56
C1 67.04 4.20 32.91 5.71
A2 58.93 5.01 46.79 5.34
B2 59.49 4.04 54.81 4.62
C2 70.36 3.04 43.34 3.53
A3 49.68 3.04 57.06 1.40
B3 52.99 2.71 65.36 4.97
C3 64.50 4.06 51.62 5.40

Descriptive & ANOVA for bottom s urface
groups subgroups

25.736

.000

16.993 0.001

24.557 0.001

54.921 0.001

28.667

16.664

Flashmax

QTH

LED

Des criptive & ANOVA for top s urface

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Restorative Dentistry 16

The data revealed from ANOVA test analyzed
by Tueky's test for all tested material for both top
and bottom surfaces which showed that for (top
surface) the materials which cured by QTH there
was a non-significant difference (p<0.05) between
group A1 and B1, High-significant differences
between group A1 and C1 (p< 0.001), Highly
significant differences between group B1 and C1
(p< 0.001) in microhardness value VHN. For
LED there was non-significant difference (p<
0.05) between group A2 and B2, a High-
significant difference (p< 0.001) between A2 and
C2, high significant differences between B2 and
C2.

For Flashmax there was non-significant
difference between A3 and B3, also High-
significant differences between A3 and C3, high

significant differences between B3 and C3 as
shown in table (4) and figure (1). For the (bottom
surfaces) Tukey test revealed that for QTH there
was a High significant differences between group
A1 and B1, a Significant differences between
group A1 and C1(p> 0.01), a High significant
differences between group B1 and C1(p< 0.001).

For LED there were high significant
differences between A2 and B2, significant
differences between A2 and C2, High significant
differences between groups B2 and C2.

For Flashmax there was a high significant
difference between group A3 and B3, significant
differences between A3 and C3, High significant
differences between B3 and C3 as shown in table
(4).

Table 4: Tukey test for the effect of light curing systems on top and bottom surfaces of the tested

materials
Tukey test for top surface Tukey test for bottom surface

Groups sub-groups Mean diff p-value sig Mean diff p-value sig

QTH A1 B1 -3.50 .333 NS -9.97 .000 HS
C1 -13.60 .000 HS 6.20 .021 S

B1 C1 -10.10 .001 HS 16.17 .000 HS
LED A2 B2 -0.56 .950 NS -8.02 .001 HS

C2 -11.43 .000 HS 3.45 .020 S
B2 C2 -10.87 .000 HS 11.47 .000 HS

Flashmax A3 B3 -3.31 .084 NS -8.30 .001 HS
C3 -14.82 .000 HS 5.44 .020 S

B3 C3 -11.51 .000 HS 13.74 .000 HS

Figure 1: A chart show the effect of curing system on VHN for the top surfaces of the tested

materials

Descriptive and interfacial analysis for
microhardness according to the type of
material:
Descriptive statistics for both top and bottom
surfaces:

Means, standard deviation for microhardness
values VHN for the three tested composite
materials for both top and bottom surfaces are
listed in table (3), the result showed that Sonicfill
composite had the highest means followed by

0
10
20
30
40
50
60
70
80

QTH LED FLASHMAX

Filtek bulkfill Tetric evo ceram sonicfill

J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 17

Tetric Evo Ceram and lowest mean value for Filtek Bulkfill composite as shown in table (5).

Table 5: Descriptive and interfacial statistics for top and bottom surfaces for the tested materials

group
Descriptive & ANOVA for top surface

Descriptive & ANOVA for bottom
surface

Groups Subgroup
Mean
Top

surface
SD F P- value sig

Mean
bottom
surface

SD F p-value sig

Filtek
Bulk fill
posterior

A1 53.44 7.13
7.612 0.002 HS

39.01 4.7
26.05 0.000 HS A2 58.93 5.01 48.08 3.73

A3 49.68 3.04 32.91 5.71
Tetric
Evo

Ceram

B1 56.94 4.41
7.46 0.003 HS

46.69 5.05
16.99 0.000 HS B2 59.49 4.04 53.81 3.92

B3 52.99 2.7 43.34 3.53

Sonic fill
C1 67.04 4.2

8.81 0.001 HS
57.03 2.31

24.14 0.000 HS C2 70.36 3.04 64.56 4.39
C3 64.5 4.05 51.62 5.4

Inferential statistics

Statistical analysis of data by using ANOVA
test for all groups of tested composite revealed
that there is a high significant differences (p<
0.001) in microhardness values VHN among the
groups for each composite material after curing
with different light curing systems in both top and
bottom surfaces as shown in table (5).

The data revealed from ANOVA test analyzed
by Tueky test for all tested material for both top
and bottom surfaces which showed that for (top
surface) of Filtek Bulkfill posterior composite
there was anon-significant difference (p< 0.05)

between group A1 and A2, non-significant
differences between group A1 and A3 (p< 0.05),
highly significant differences between group A2
and A3 (p< 0.001) in microhardness value VHN.
For Tetric-Evo Ceram there was non-significant
difference (p< 0.05) between group B1 and B2, a
non-significant difference between B1 and B3,
High significant differences between B2 and B3.

For Sonicfill composite there was non-
significant difference between C1 and C2, also
non-significant differences between C1 and C3,
high significant differences between C2 and C3 as
shown in table (6) and fig (2).

Table 6: Tukey test for the groups of tested materials for both top and bottom surfaces.

Tukey test for top surface Tukey test for bottom surface
Groups Sub-groups Mean diff p-value sig mean diff p-value sig

Filtek
bulkfill

A1
A2 -5.49 0.073 NS -10.07 0.000 HS
A3 3.76 0.273 NS 5.10 0.01 S

A2 A3 9.25 0.002 HS 15.17 0.000 HS

Tetric Evo
ceram

B1
B2 -2.55 0.305 NS -8.12 0.001 HS
B3 3.95 0.069 NS 2.35 0.037 S

B2 B3 6.5 0.002 HS 10.47 0.000 HS

Sonic
fill

C1
C2 -3.32 0.104 NS -8.53 0.000 HS
C3 3.24 0.114 NS 4.41 0.019 S

C2 C3 6.56 0.001 HS 12.94 0.000 HS

J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 18

Figure 2: Chart for the microhardness value for the three tested materials top surfaces

Figure 3: Chart for the microhardness value for the three tested materials bottom surfaces

Tukey test for bottom surface showed that

for Filtek Bulkfill posterior composite there
was a High significant differences among group
A1 and A2, Significant differences among
group A1 and A3, High significant differences
among A2 and A3. For Tetric Evo Ceram High
significant differences between group B1 and
B2, significant differences between B1 and B3,
High significant differences between group B2
and B3. For Sonicfill there was High significant
differences between C1 and C2, Significant

differences between group C1 and C3, High
significant differences between group C2 and
C3 as shown in table (6) and fig(3)

Another analyses were made between top to
bottom for each material following this
equation Bottom/top =Ratio as shown in table
(7).

Form table (7) all tested material reach the
Top/bottom ratio of 0.8 except for Filtek Bulk
fill posterior composite cured with QTH ( group
A1) and cured with Flashmax (group A3).

Table 7: Bottom/ top ratio for all groups

Group Subgroup Top/bottom ratio Top/bottom ratio

Filtek
bulkfill

A1 0.711
A2 0.815
A3 0.662

Tetric Evo
ceram

B1 0.802
B2 0.904
B3 0.817

Sonic
fill

C1 0.835
C2 0.917
C3 0.8

DISCUSSION
Effect of light cure system on microhardness:

If the resin composite does not receive
sufficient total energy various problems may

occur with the final restoration such as the
reduction in the amount of monomer to polymer
conversion an increased cytotoxicity of the
restorative material, reduction in the hardness of

QTH LED Flash max

filtek Bulk fill Tetric Evo Ceram Sonic fill

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Restorative Dentistry 19

the restorative material. Adequate polymerization
of the light cured composite materials depend
upon (1) light activation energy (2) wave length
(3) curing time.

In this study LED show highest microhardness
VHN value for all tested material followed by
QTH and the lowest VHN value for Flashmax as
shown in tables (3), fig (1) for both top and
bottom (4 mm depth) for all tested groups. This
can be explained by analyses of total amount
energy density of the system which is an
important parameter and it is the amount of
energy of appropriate wavelength emitted during
irradiation. This energy is calculated as the
product of the output of the curing light unit and
the time of irradiation which can be calculated
from the equation:

Energy density= Intensity x Time (10)
As a result QTH have energy density 16 J/cm2,

LED has energy density 18.4 J/cm2 and Flashmax
have energy density 12 J/ cm2. This results agree
with findings (11,12).

Also the depth of cure of composite resin is
mainly dependent on exposure time of the light
source to the composite resin (9) therefore, the
short curing time for Flashmax unit as
recommended by manufacturer (table 2) led to
low VHN value for the tested materials this can be
explained as the duration of the exposure will
allow the excited camphorquinon (typical
photosensitive agent in light cured dental resin
composites) molecules to diffuse and react with a
mine and it is important to increase exposure
duration and use appropriate light curing device to
maximize the hardness of the resin materials(13).
This result agree with previous studies (9,13,14)

Effect of the material on the microhardness:

Sonicfill composite had the highest
microhardness value VHN among the tested
composite material in all used curing system as
shown tables (5,6) and figure (2,3), From both top
and bottom curing value followed by Tetric Evo
Ceram composite and the lowest microhardness
value VHS for Filtek Bulk fill posterior
composite. This in agreement with previous
studies (12,15). which claimed that Sonicfill system
had the highest score among the tested materials
and can be used as an alternative to regular
composite for posterior teeth (12) .This is related to
several factors (1) the Nano-filling technology
which led to material have better mechanical
properties than other types of composite (12) (2) the
optical properties of resins (optical transmission
coefficient) which vary with material composition
(particle type, contents and size) (16), from table
(1) Sonicfill composite have higher filler loading

(83%) followed by Tetric Evo Ceram (80%) and
Filtek Bulkfill posterior composite (76.5%) this
result in agreement with previous study (15,16) , as
an increase in filler content results in higher
hardness means. As regard the size of the
incorporated fillers, the filler particles in the resin
based composites scatter light, this scattering
effect is increased as the particle size of the fillers
in the composite approaches the wavelength of the
activating light and will reduce the amount of
light that is transmitted through the composite (16).

Material with the smallest filler particles size
(0.19-3.3µm) showed the highest values of overall
light transmittance for all filler contents, where as
those with larger size (0.04-10) µm showed lower
light transmittance for all filler contents (17) from
table (1) the Sonicfill composite had the smaller
size of filler particles and this result in agreement
the previous studies (16). So as regards the particle
type the zirconium is harder than heavy-metal
glass and the crystalline form (zirconium silica) is
harder than non-crystalline (glass) and it diffuse
light as it penetrate (16).

Optical properties of Sonicfill can explain the
higher microhardness of Sonicfill composite as
compared with Tertic Evo Ceram although both of
them are nanohybrid composite this in agreement
with previous studies (5). Also Tetric Evo Ceram
bulk fill composite exhibits a statistical higher
microhardness value than Filtek Bulk fill posterior
composite may be attributed to the presence of
polymerization booster (Ivocerin) which it is
highly reactive photoinitiator system allows a
faster, deeper curing than other composites and it
is allow application larger increments with greater
depth of up 4mm in very short time and light
sensitivity inhibitor which integrated into
photoinitior system and act as a protective shield
against ambient light like operating light (12).

Effect of depth of the material on
microhardness

The microhardness of resin composites are
affected by the resin composite thickness (18), in
the present study the same tendency of the
microhardness decreasing as the resin thickness
increased was observed as shown in table (3).
Previous studies reported that the resin hardness at
the bottom was significantly different from that at
the top when the specimens were 4 to 5 mm
thickness this result in agreement with previous
studies (18,19). This is due to the fact that at top
surface sufficient light energy reach photoinitior,
thus starting the polymerization reaction as light
passes through the body of a composite, it is
intensity is greatly decreased due to absorption
and dispersion of light by filler particles and resin

J Bagh College Dentistry Vol. 29(2), June 2017 The Effect of Different

Restorative Dentistry 20

matrix. This decrease results in a gradation of cure
causing a decrease in hardness level from the top
surface to inwards. This fact explain the
difference between top surface and bottom surface
hardness for all tested materials and tested curing
unites this finding in agreement with previous
studies (20) .

The bottom/top hardness ratio above 80% has
often been used as a minimum acceptable
threshold which means in this study the material
which bottom/top ratio of 80% and above can be
placed and cured properly in the 4 mm bulk in
clinical situations as shown in table (7).

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