DENTAL MATERIALS
Original Articles SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS:
EFFECT OF FILLER AMOUNT AND CHEMICAL COMPOSITION OF THE
ORGANIC MATRIX
Nicoleta Ilie1b * , Eva-Maria Plenk2b
1
Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilians University Munich, Goethestr. 70, D-80336
Munich, Germany
2Privat clinic, Bahnhofsweg 6, D-82008 Unterhaching, Germany
Dipl Eng, PhD, Professor
a
DMD, private practitioner
b
ABSTRACT DOI: https://doi.org/10.25241/stomaeduj.2019.6(2).art.2
Introduction: The study aims to quantify the impact of various curing conditions on the
micro-mechanical properties of methacrylate and silorane resin-based composites (RBCs) in OPEN ACCESS This is
an Open Access article under
order to determine the threshold for sufficient polymerization. the CC BY-NC 4.0 license.
Methodology: The Analyzed RBCs have either a similar filler volume amount (55%) but a Peer-Reviewed
different monomer matrix composition (methacrylate or silorane) or a similar monomer Article
matrix but a different filler volume amount (63.3% vs. 55%). Twenty-four different curing Citation: Ilie N, Plenk E-M.
conditions were simulated. A blue-violet LED curing unit was applied in different curing Susceptibility of RBC to various
clinical relevant curing conditions:
modes, exposure times and distances (0-mm and 7-mm). Measurements (Vickers hardness, Effect of filler amount and chemical
composition of the organic matrix.
HV, and Indentation modulus, E) were performed after 24 hrs of storage in distilled water Stoma Edu J. 2019;6(2): 100-110
at 37 °C at the top and bottom of 2-mm thick specimens (360 specimens in total). Received: June 03 2019
One and multiple-way ANOVA and Tukey HSD post hoc-test (α =0.05) was used. A Revised: June 13, 2019
Accepted: June 24, 2019
multivariate analysis (general linear model) assessed the effect strength of the parameters Published: June 25, 2019
exposure time, location of measurement (top-bottom), incident irradiance, radiant *Corresponding author:
exposure (ranging from 1.0 to 47.0 J/cm²) and exposure distance on HV and E. Nicoleta Ilie, Dipl Eng, PhD,
Professor at the Department
Results: In all materials, the highest effect on HV and E was exerted by the exposure time of Operative Dentistry and
and location of measurement. The susceptibility to various curing conditions is material Periodontology, University
Hospital, Ludwig-Maximilians
dependent, while less filled methacrylate-based as well as the silorane micro-hybrid University Munich Goethestr. 70
are more robust to these variations. Fast polymerization (3s) with high irradiance is not D-80336 Munich, Germany
Phone: +49-89-44005-9412
recommended. Fax: +49-89-44005-9302
Conclusions: The best micro-mechanical properties at the top and bottom of 2-mm thick e-mail: nilie@dent.med.uni-
muenchen.de
specimens are generated with a curing time of at least 20s at moderate irradiance.
Copyright: © 2019 the Editorial
Keywords: Resin-based composites; Hardness; Modulus of elasticity; Light curing unit; Council for the Stomatology Edu
Radiant exposure. Journal.
1. Introduction curing quality in various modern RBCs, indicate
Incremental layering technique is accepted as radiant exposure values in the range of [21-24]
a golden standard for the placement of regular J/cm2 [4,5] as sufficient for adequate polymerization.
resin-based composite (RBC) restorations [1]. The These values are often not met in a clinical situation,
increments are limited to a thickness of 2 mm to allow due to a number of factors that are related either
for adequate polymerization in a clinically reasonable to the technique sensitivity of the polymerization
time. In spite of decades of expert knowledge in process [6,7] or to erroneously chosen curing
light curing, the amount of light needed to cure strategies. Particularly in posterior cavities that are
adequately a regular 2-mm thick RBC increment is difficult to access, the light curing unit (LCU) may
still debatable. This is justified in the observation of not be placed perpendicularly to the restoration, the
a material- dependent susceptibility to variation in exposure distance may vary from an ideal position,
radiant emittance (= radiant flux emitted by a surface the exposure time may be chosen too short or the
per unit area) under simulated clinical conditions LCU be contaminated with resins. The total amount
[2,3]. In addition, calculations based on the total of light received by the material may be further
energy delivered to guide irradiation protocols were reduced by using curing strategies involving a pre-
shown to be invalid and not to recognize product curing of the lowest increment when incrementally
behavior [2]. Nonetheless, there is a high demand to reconstructing a deep cavity, based on the wrong
set a general limit for adequate curing, in order to estimate [8] that the lowest increment will receive
support clinicians choosing a proper curing strategy. enough light when curing the upper increments or
Literature data, based on direct evaluation of the when curing through the tooth structure [9]. A very
100 Stoma Edu J. 2019;6(2): 100-110 http://www.stomaeduj.com
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Resin based composites
Original Articles
FiltekTM Supreme XTE FiltekTM Supreme
XTE flow FiltekTM Silorane
Exposure distance Exposure distance
0 mm 7 mm
LCU mode Exposure time [s] LCU mode Exposure time [s]
Standard 5 Standard 5
10 10
15 15
20 20
40 40
High Power 1 High Power 1
2 2
3 3
4 4
12 12
Plasma Emulation 3 Plasma Emulation 3
6 6
Figure 1. Design of the curing conditions.
low transmitted irradiance was identified through [4,5]. An initially improper cured lower increment
2-mm thick layers of various RBCs as well as through will consequently receive low light during curing the
the tooth structure [8,9]. In a nano RBC (Filtek upper ones, which is insufficient to compensate the
Supreme XTE), the transmitted light through 2-mm initial deficits [8]. The aim of this study was to evaluate
thick increments amounted only 1.4% to 2.1% of the the effect of simulating clinically relevant curing
incident light and was merely slightly higher (4.2% to conditions on the micro-mechanical properties
7.4%) in the more translucent, low viscous version of of RBCs with various fillers content and similar
the same material (flowable nano RBC Filtek Supreme chemical composition of the organic matrix (regular
XTE flow) [8]. The same applies for RBCs with a non- vs. flowable methacrylate-based RBCs), as well as
methacrylate polymer matrix, such as the micro- similar volume filler content but different chemical
hybrid Filtek Silorane (4.2% to 6.5%) [8]. Note that a composition of the organic matrix (methacrylate vs.
variety of clinically relevant irradiances (= radiant flux silorane monomers). Therefore, 24 different radiant
or power received by a surface per unit area; 656.4 exposures were simulated by varying the irradiance
mW/cm² to 3361.5 mW/cm²), radiant exposures (656.4 mW/cm² to 3361.5 mW/cm²), the radiant
(46.96 to 0.99 J/cm2) and exposure distances (0 to exposure (0.99 and 47.0 J/cm²) and the exposure
7 mm) were considered in these calculations. The distance (0 to 7 mm) [8]. Moreover, the study aims
indicated % limits for the light transmittance through to determine the bandwidth for adequate curing in
the various materials are related to the irradiance response to the application of light.
while the lower the irradiance, the higher the % The tested null hypothesis were: i) the impact of the
transmitted light in the above indicated interval curing conditions would be similar in all materials;
[8]. Based on these calculations, it was assumed ii) there would be no difference within one material
that the low light transmittance will be directly among the assessed curing conditions; iii) there
reflected in the mechanical properties of the RBCs would be no difference in the mechanical properties
[8]. When transferring the transmitted irradiance to among the analysed materials.
the more clinically relevant term of radiant exposure,
the transmitted light at the bottom of 2-mm thick 2. Material and Methods
increments is quantified as to not exceed 4 J/ The micro-mechanical properties of three regular
cm² at an ideal exposure distance. This involved RBCs (Table 1) were analyzed under different curing
the application of the LCU in close contact and conditions at a specimen thickness of 2 mm. The
perpendicularly to the material. The transmitted light violet-blue LED LCU VALO (Ultradent, South Jordan,
is lowered to < 2 J/cm² when the exposure distance is USA, serial number VO 7710) was used in three
elevated at 7 mm [8]. The values shown above are far different exposure modes (Standard, High Power
below the radiant exposure values indicated in the and Plasma Emulation), at various exposure times
literature for adequate polymerization [21-24] J/cm2 (5s, 10s, 15s, 20s and 40s (=2x20s with no delay in-
Stomatology Edu Journal 101
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Original Articles Table 1. Resin composite brand, type, chemical composition of matrix and filler as well as filler content by weight (wt.)
and volume (vol.) %.
Filler
RBCs RBC-Type Batch Shade Resin Matrix Filler
wt%/vol%
FiltekTM A3 Bis-GMA, Bis-EMA, UDMA, TEGDMA, ZrO2, SiO2
Nano N229448 78.5/63.3
Supremee XTE Dentin PEGDMA ZrO2/SiO2
FiltekTM
flowable Bis-GMA, Bis-EMA, TEGDMA, ZrO2, SiO2
Supremee XTE N236527 A3 65/55
Nano PEGDMA ZrO2/SiO2
flow
3,4-Epoxycyclo-
FiltekTM hexylethylcyclopolymethylsiloxane SiO2, YF3
Microhybrid N225426 A3 76/55
Silorane Bis-3,4-epoxycyclo-hexylethylphenyl-
methylsilane
Abbreviations: Bis-GMA, bisphenol-A diglycidyl ether dimethacrylate; Bis-EMA, ethoxylated Bisphenol-A-dimethacrylate;
UDMA, Urethane dimethacrylate; TEGDMA, Triethyleneglycol dimethacrylate, PEGDMA, polyethylene glycol
dimethacrylate. Data are provided by manufacturer (3M).
Table 2. Incident irradiance and radiant exposure as function of exposure distance, LCU’s curing mode, and exposure
time as determined in [8].
Radiant Radiant
Time Irradiance Time Irradiance
Distance Mode exposure Distance Mode exposure
[s] [mW/cm2] [s] [mW/cm2]
[J/cm2] [J/cm2]
0 mm Standard 5 1174.1 5.87 7 mm Standard 5 656.4 3.28
10 1174.1 11.74 10 656.4 6.57
15 1174.1 17.61 15 656.4 9.85
20 1174.1 23.48 20 656.4 13.13
40 1174.1 46.96 40 656.4 26.26
High 1 1760.3 1.76 High 1 986.3 0.99
Power 2 1760.3 3.52 Power 2 986.3 1.97
3 1760.3 5.28 3 986.3 2.96
4 1760.3 7.04 4 986.3 3.95
12 1760.3 21.12 12 986.3 11.84
Plasma 3 3361.5 10.09 Plasma 3 1917.8 5.75
Emulation 6 3361.5 20.17 Emulation 6 1917.8 11.51
between exposures) the Standard mode; 1s, 2s, removed from the mould and stored in distilled
3s, 4s and 12s (=3x4s with no delay in-between water for 24 hours at 37°C. Thereafter, specimens
exposures) in the High Power mode and 3s and 6s were ground and polished under water with
(=2x3s with no delay in-between exposures) in the diamond abrasive paper (mean grain sizes: 20 µm,
Plasma Emulation mode) and exposure distances 13 µm, 6 µm) in a grinding system (EXAKT 400CS,
(0 mm and 7 mm). This resulted in 24 different curing Exakt, Norderstedt, Germany) and transfered to an
conditions, that have been quantified previously [8]. automatic universal testing device (Fischerscope
H100C, Fischer, Sindelfingen, Germany).
2.1. Micro-mechanical properties:
Measurements (n=6 per specimen and side) were
The micro-mechanical properties (Vickers Hardness performed at the top and bottom of each specimen.
HV and Indentation modulus, E) were assessed on The test procedure was carried out force-controlled,
cylindrical specimens (diameter 6 mm, thickness 2 where the test load increased (within 20s) and
mm, n = 5) according to DIN 50359-1:1997-10 [10]. decreased (within 20s) with constant speed between
For specimen preparation, a white Teflon mould 0.4 mN and 500 mN. The load and penetration depth
was used. Immediately after curing, specimens were of the indenter (Vickers pyramid: diamond right
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SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Original Articles
Figure 2. Variation in Vickers Hardness as a function of radiant exposure measured on top and bottom of 2-mm thick specimens made out by the RBC:
a) Filtek Supreme XTE; b) Filtek Supreme XTE flow and c) Filtek Silorane; corresponding irradiance, exposure time and distance are presented in Table 2.
Stomatology Edu Journal 103
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Original Articles pyramid with a square base and an angle of α = exposure was significant as well (p<0.05, ηP² = 0.248
136° between the opposite faces at the vertex) were for E and 0.182 for HV).
continuously measured during the load-unload In Filtek Silorane, the impact of the above mentioned
hysteresis. Universal hardness is defined as the test factors follows the same sequence as above:
force divided by the apparent area of indentation exposure time (p<0.05, ηP² = 0.932 for E and 0.903
under the applied test force. From a multiplicity of for HV), location of measurement (top-bottom)
measurements stored in a database supplied by the (p<0.05, ηP² = 0.903 for E and 0.932 for HV), incident
manufacturer, a conversion factor (0.0945) between irradiance (p<0.05, ηP² = 0.760 for E and 0.637 for
Universal hardness and HV was calculated by the HV) and exposure distance (p<0.05, ηP² = 0.033 for E
manufacturer and entered into the software, so that and 0.041 for HV). The impact of the incident radiant
the measurement results were indicated in the more exposure was significant as well (p<0.05, ηP² = 0.476
familiar HV units. E was calculated from the slope of for E and 0.401 for HV).
the tangent adapted at the beginning (at maximum Considering all curing conditions and both specimen
force) of the non-linear indentation depth curve sides (both top and bottom), the micro-mechanical
upon unloading. parameters, HV and E, were lower in Filtek Supreme
2.2. Statistical Analysis Flow (p<0.05; E = 8.09 GPa, HV = 54.34 N/mm²),
while Filtek Silorane and Filtek Supreme showed
A Shapiro–Wilk test verified the normal distribution statistically similar values (p = 0.138 for E (11.18 GPa
of the data. The results were compared using one and 10.47 GPa) and 0.283 for HV (75.34 N/mm² and
and multiple-way ANOVA and Tukey HSD post 79.95 N/mm²). Considering the specimen surfaces
hoc-test (α = 0.05). A multivariate analysis (general individually, the material sequence for the top
linear model) assessed the effect of the parameters surface was the following in statistically significant
exposure time, incident irradiance, incident radiant decreasing order of the measured micro-mechanical
exposure (varying among 0.99 and 47.0 J/cm² [8], properties (Filtek Supreme > Filtek Silorane > Filtek
exposure distance (0 mm and 7 mm) and measuring Supreme Flow, with E = 15.11 GPa; 13.22 GPa; 9.19
position (top-bottom) on HV and E. The partial eta- GPa; and HV = 124.03 N/mm²; 93.71 N/mm²; 64.59
squared statistic reports the practical significance N/mm²). For the bottom surface, significant higher
of each term, based on the ratio of the variation values were identified in Filtek Silorane specimens
accounted for by the effect. Larger values of partial (p<0.05), while both methacrylate RBCs performed
eta-squared indicate a greater amount of variation statistically similar (p = 0.078 for E and 0.065 for HV).
accounted for by the model effect, to a maximum The values measured at the bottom of the specimens
of 1. A correlation analysis (Pearson correlation) in the sequence Filtek Silorane, Filtek Supreme Flow
between HV and E was performed within each RBC. and Filtek Supreme were E = 9.15 GPa; 7.00 GPa and
In all statistical tests, p-values < 0.05 were considered 5.83 GPa; HV = 56.98 N/mm²; 44.08 N/mm²; 35.87
statistically significant when using SPSS Inc. (Version N/mm²). The individual values for all materials and
24.0, Chicago, IL, USA). curing conditions are summarized in Table 2 and
illustrated in Fig 1.
3. Results An excellent correlation was calculated between
The exposure time (p<0.05, ηP² = 0.899 for E and HV and E within each material (Pearson correlation
0.872 for HV) and the location of measurement (top- coefficient = 0.985 for Filtek Supreme XTE, 0.977 in
bottom; p<0.05, ηP² = 0.849 for E and 0.867 for HV) Filtek Silorane and 0.973 in Filtek Supreme XTE Flow).
strongly influenced the micro-mechanical properties
measured in Filtek Supreme XTE flow specimens. 4. Discussion
With a lower, but significant, influence followed the Although constantly improving in the last decades,
factor incident irradiance (p<0.05, ηP² = 0.399 for the demand for shortening the exposure time for
E and 0.251 for HV), while the impact of exposure curing dental RBCs, to allow for a faster and more
distance was very low (p<0.05, ηP² = 0.038 for E and economical clinical work, is still valid nowadays. For
0.030 for HV). The impact of the incident radiant this purpose manufacturers are not straying from
exposure was significant as well (p<0.05, ηP²= 0.607 the development of LCUs with continuously higher
for E and 0.498 for HV), but lower compared to the radiant emittance. This trend was motivated in the
individual effect of exposure time. concept of “exposure reciprocity” that is based on
The impact of the above-mentioned factors was the opinion that a RBC needs a certain amount of
even stronger in the higher filled methacrylate- energy to be cured adequately, while the way in
based nano RBC Filtek Supreme XTE. It follows the which photons are supplied is supposed to be of
sequence: exposure time (p<0.05, ηP² = 0.972 for E minor importance. The term radiant exposure (J/
and 0.973 for HV), location of measurement (top- cm²) characterizes the amount of energy supplied
bottom) (p<0.05, ηP² = 0.993 for E and 0.996 for HV), by the LCU and is calculated as the product of the
irradiance (p<0.05, ηP² = 0.126 for E and 0.128 for radiant emittance (mW/cm²) and exposure time (s).
HV) and exposure distance (p<0.05, ηP² = 0.037 for E The “exposure reciprocity” concept assumes a similar
and 0.031 for HV). The impact of the incident radiant effect when exposing the RBC to a given radiant
104 Stoma Edu J. 2019;6(2): 100-110 http://www.stomaeduj.com
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Table 3. Vickers hardness [N/mm²] and Indentation modulus (GPa) measured on specimen’s top and bottom at 0 mm
Original Articles
and 7 mm exposure distance. Superscripts indicate statistically homogeneous subgroups within a column (Tukey’s HSD
test, α = 0.05).
a) FiltekTM Supreme XTE
Vickers hardness HV [N/mm²]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 126.6 CD
(2.1) 33.1 CD
(2.7) 117.9 c
(1.2) 0.0 a
(0.0)
10 126.6 CD
(3.5) 38.1 D
(2.5) 120.8 cdef
(2.5) 19.7 b
(2.7)
15 130.8 DEF
(2.6) 69.0 E
(5.7) 124.1 efg
(2.1) 27.4 c
(2.7)
20 137.2 F
(2.8) 81.4 F
(5.0) 129.4 hi
(2.4) 35.9 d
(2.3)
40 155.9 G
(3.8) 99.8 G
(2.9) 133.1 i
(1.1) 85.1 f
(4.5)
High 1 107.7 A
(3.7) 0.0 A
(0.0) 85.7 a
(3.5) 0.0 a
(0.0)
Power 2 115.1 B
(4.5) 0.0 A
(0.0) 110.5 b
(3.6) 0.0 a
(0.0)
3 125.2 CD
(3.4) 23.5 B
(2.7) 118.4 cd
(2.2) 0.0 a
(0.0)
4 124.4 C
(2.1) 26.9 BC
(4.0) 119.7 cde
(3.2) 0.0 a
(0.0)
12 129.8 CDE
(4.6) 96.2 G
(5.6) 128.6 ghi
(2.1) 43.7 e
(1.1)
Plasma 3 124.7 CD
(1.8) 38.3 D
(3.4) 123.2 def
(2.9) 0.0 a
(0.0)
Emulation 6 135.9 EF
(3.2) 86.4 F
(4.9) 125.5 fgh
(2.8) 42.8 e
(2.1)
0 = not measurable, material was not cured
Indentation Modulus, E [GPa]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 14.6 BC
(0.7) 6.2 BC
(0.3) 14.3 c
(0.5) 0.0 a
(0,3)
10 15.0 BC
(0.2) 6.4 BC
(0.5) 14.9 cde
(0.6) 4.8 b
(0,3)
15 16.0 DEF
(0.4) 10.5 D
(0.6) 15.8 def
(0.5) 5.4 c
(0,5)
20 16.7 F
(0.3) 12.1 E
(0.4) 15.8 ef
(0.4) 6.4 d
(0,2)
40 17.7 G
(0.3) 13.4 F
(0.5) 16.2 f
(0.5) 11.9 g
(0,5)
High 1 12.9 A
(0.4) 0.0 A
(0.0) 10.3 a
(0.3) 0.0 a
(0,0)
Power 2 14.3 B
(0.4) 0.0 A
(0.0) 13.0 b
(0.6) 0.0 a
(0,0)
3 14.8 BC
(0.2) 5.6 B
(0.5) 14.9 cd
(0.4) 0.0 a
(0,0)
4 15.3 CD
(0.2) 6.3 BC
(0.6) 15.2 cde
(0.4) 0.0 a
(0,0)
12 16.2 EF
(0.4) 12.9 EF
(0.4) 15.8 def
(0.2) 8.2 e
(0,1)
Plasma 3 15.8 DE
(0.3) 6.5 C
(0.2) 15.1 cde
(0.7) 0.0 a
(0,0)
Emulation 6 16.4 EF
(0.2) 12.2 E
(0.6) 15.4 def
(0.4) 7.3 f
(0,4)
0 = not measurable, material was not cured
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Original Articles
b) FiltekTM Supreme XTE flow
Vickers hardness, HV [N/mm²]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 64.3 B
(4.6) 53.6 E
(2.8) 67.9 cd
(1,1) 27.5 d
(3.2)
10 66.5 B
(2.6) 60.9 F
(2.1) 67.0 cd
(1.9) 44.9 f
(3.2)
15 67.4 B
(1.0) 61.0 F
(2.1) 67.7 cd
(2.0) 58.4 h
(1.5)
20 68.4 B
(1.5) 64.9 F.G
(1.5) 69.1 cd
(2.1) 62.4 hi
(0.9)
40 69.7 B
(2.0) 67.8 G
(1.2) 71.0 d
(1.6) 67.2 i
(2.8)
High 1 53.1 A
(2.3) 9.8 A
(1.9) 30.6 a
(1.5) 3.9 a
(0.5)
Power 2 64.1 B
(2.9) 23.5 B
(1.4) 59.3 b
(3.2) 13.8 b
(1.4)
3 64.8 B
(4.9) 32.0 C
(3.2) 65.1 c
(4.0) 14.4 b
(2.5)
4 65.7 B
(3.8) 47.7 D
(3.5) 65.0 c
(3.8) 21.6 c
(1.2)
12 67.9 B
(1.6) 65.2 F.G
(0.1) 68.5 cd
(1.6) 52.9 g
(3.1)
Plasma 3 66.5 B
(3.2) 47.3 D
(2.4) 65.2 c
(1.3) 36.8 e
(4.2)
Emulation 6 68.3 B
(2.2) 62.0 F
(2.8) 66.9 cd
(1.5) 58.7 h
(2.5)
Indentation Modulus, E [GPa]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 9.6 CD
(0.3) 8.5 DE
(0.5) 9.0 cd
(0.1) 5.9 d
(0.5)
10 9.7 CD
(0.4) 8.7 EF
(0.2) 9.3 cde
(0.2) 7.6 f
(0.3)
15 9.8 CD
(0.3) 9.3 FG
(0.3) 9.5 def
(0.3) 8.9 gh
(0.2)
20 9.9 D
(0.1) 9.3 FG
(0.3) 9.8 ef
(0.1) 8.8 gh
(0.3)
40 10.1 D
(0.2) 9.9 G
(0.3) 9.9 f
(0.3) 9.4 h
(0.2)
High 1 7.3 A
(0.2) 2.2 A
(0.3) 5.0 a
(0.2) 1.0 a
(0.1)
Power 2 8.5 B
(0.6) 4.6 B
(0.3) 8.2 b
(0.6) 2.8 b
(0.1)
3 9.1 BC
(0.7) 5.9 C
(0.6) 8.8 bc
(0.4) 3.3 b
(0.3)
4 9.4 CD
(0.4) 7.8 D
(0.4) 9.2 cd
(0.3) 4.5 c
(0.1)
12 9.7 CD
(0.5) 8.7 EF
(0.2) 9.5 def
(0.3) 8.4 g
(0.3)
Plasma 3 9.7 CD
(0.2) 7.9 D
(0.5) 9.3 cde
(0.2) 6.6 e
(0.4)
Emulation 6 10.1 D
(0.3) 9.4 FG
(0.4) 9.5 def
(0.3) 9.0 h
(0.4)
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SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
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Original Articles
c) FiltekTM Silorane
Vickers hardness, HV [N/mm²]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 92.5 BC
(4.3) 74.9 BC
(1.9) 91.4 bc
(2.9) 0.0 a
(0.0)
10 93.4 BCD
(2.7) 85.1 DE
(6.3) 92.6 bc
(3.2) 69.0 b
(4.8)
15 98.5 DE
(2.2) 85.3 DE
(3.0) 93.9 bc
(1.7) 73.6 b
(2.3)
20 98.5 DE
(2.2) 86.5 DE
(1.4) 96.2 cd
(2.5) 73.8 b
(3.3)
40 100.0 E
(3.4) 90.3 E
(1.4) 99.7 d
(1.0) 82.9 c
(1.8)
High 1 83.2 A
(4.0) 0.0 A
(0.0) 82.3 a
(5.7) 0.0 a
(0.0)
Power 2 87.6 AB
(4.3) 0.0 A
(0.0) 89.4 b
(2.2) 0.0 a
(0.0)
3 93.4 BCD
(2.1) 69.7 B
(4.8) 89.4 b
(2.1) 0.0 a
(0.0)
4 94.3 CD
(2.7) 76.4 C
(1.9) 94.1 bc
(2.3) 0.0 a
(0.0)
12 98.7 DE
(2.4) 90.0 E
(3.5) 94.2 bcd
(2.4) 82.3 c
(3.1)
Plasma 3 97.6 CDE
(2.2) 83.3 D
(2.8) 95.8 bcd
(3.6) 73.4 b
(4.0)
Emulation 6 98.2 CDE
(2.4) 90.2 E
(3.0) 95.8 cd
(3.6) 80.9 c
(4.1)
0 = not measurable, material was not cured
Indentation Modulus, E [GPa]
Curing Exposure 0mm- exposure distance 7mm-exposure distance
mode time [s] top bottom top bottom
Standard 5 12.3 AB
(0.5) 12.0 B
(0.2) 13.1 cde
(0.3) 0.0 a
(0.0)
10 13.7 CDE
(0.4) 12.3 B
(0.8) 13.0 bcd
(0.2) 12.5 b
(0.7)
15 14.1 DE
(0.5) 12.4 B
(0.3) 13.5 def
(0.1) 13.1 bc
(0.3)
20 14.1 DE
(0.5) 13.5 C
(0.4) 13.5 def
(0.3) 13.0 bc
(0.2)
40 14.3 E
(0.5) 13.8 C
(0.5) 14.3 f
(0.5) 13.5 c
(0.3)
High 1 11.7 A
(0.6) 0.0 A
(0.0) 11.2 a
(1.2) 0.0 a
(0.0)
Power 2 13.2 BCD
(0.2) 0.0 A
(0.0) 12.1 abc
(1.0) 0.0 a
(0.0)
3 13.2 BCD
(0.2) 11.8 B
(0.9) 12.0 ab
(0.5) 0.0 a
(0.0)
4 13.6 CD
(0.4) 12.1 B
(0.2) 13.4 de
(0.3) 0.0 a
(0.0)
12 13.7 CDE
(0.8) 13.8 C
(0.5) 14.2 ef
(0.3) 12.7 b
(0.8)
Plasma 3 12.9 BC
(0.5) 13.3 C
(0.3) 13.2 def
(0.7) 12.8 b
(0.4)
Emulation 6 13.5 CDE
(0.4) 13.5 C
(0.2) 13.6 def
(0.4) 13.5 c
(0.2)
0 = not measurable, material was not cured
exposure, irrespective if the radiant emittance is shown that efficient polymerization, especially in
enhanced to the detriment of the exposure time or depth, is achieved with LCUs of a radiant emittance
vice versa. This simple construct sounds useful in about 1200 mW/cm² and exposure times of at least
a clinical situation but it is not universally valid [2]. 20s [11]. The radiant exposure levels required for
Musanje et al. [2] identified no lower limit of radiant a RBC to be polymerized adequately depend to a
emittance for an effective polymerization, up to 25 large extent on the composition of the RBC [2] and
mW/cm², but the very long exposure time needed for consequently each product must be individually
appropriate curing is no longer relevant for practical analyzed. The present study attaches particular
use. Numerous studies in recent years have clearly attention to the effect of the different composition
Stomatology Edu Journal 107
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Original Articles of the organic matrix (silorane vs. methacrylate) at
a comparable filler volume amount (55%). With the
based RBC and unconditionally banned for the
analyzed regular methacrylate-based RBCs. The
limitation of using commercially available materials results confirm the failure recorded earlier with the
with a small difference in their organic matrix P(plasma)A(arc)C(curing)-LCUs, which were advocated for a
(Table 1), the study also analyzed the effect of the rapid, 3-second curing, as being equivalent to that of
filler volume amount at a given composition of the a 40 or 60 s exposure from a QTH (Quartz Tungsten
organic matrix Confirming the data of Musanje et Halogen) light [12]. Numerous studies attested
al. [2,3], the analyzed RBCs reacted differently to the insufficient polymerization [12,13], emphasizing
variation in radiant exposure. The analyzed flowable the need for multiple 3-s exposures to achieve a
RBC (Filtek Supreme XTE flow) showed only minor clinically adequate performance [12, 14]. Enhancing
differences in micro-mechanical properties at a sharp LCU’s radiant emittance alone is thus insufficient in
variation of radiant exposure levels, while the higher curing currently available RBCs. Modern attempts
viscous RBCs (Filtek Supreme XTE and Filtek Silorane) conjunct a fast curing (3-s) at high radiant emittance
reacted with a higher variation in the measured (> 3000 mW/cm²) with altering the polymerization
properties. The present study also identified that mechanism of methacrylate-based RBCs. The latest
the exposure time and the irradiance itself, and not involve a reversible addition-fragmentation chain
only their connection as radiant exposure (time x transfer (RAFT) polymerization and have been so far
irradiance), has an influence on the polymerization incorporated in two commercial available bulk-fill
of the analyzed RBC, thus confirming again previous RBCs [15,16]. The proof for the clinical success of a
studies [2,3]. Moreover, the study identified that 3-s curing of materials with a RAFT polymerization is
in all analyzed materials, it was the exposure time missing for the moment. . This is not least due to the
showing the highest impact (higher partial eta- recent launch (2019) of the products. Note, however,
squared values) on the measured properties, while that curing with high radiant emittance increases the
the irradiance played a minor role. In general, the risk to over-heat the pulp or to injure the soft tissues.
best results were identified in all RBCs at the longest Besides, curing fast at high irradiances will leave no
exposure time (40 s) and lowest LCU’s radiant room to relieve internal stresses accumulated during
emittance (1174 mW/cm2). Note, however, that the shrinkage [17].
lowest irradiance used in the present study has a To simulate clinically relevant curing conditions, the
comparatively high value and involves a modern, LCU was placed either directly on or at a distance
well-functioning LCU. of 7 mm from the specimen’s surface. This distance
The highest radiant emittance employed in the was chosen based on the observation of Price at
present study was delivered by the program al.[18] that the distance between the LCU and the
“plasma”, with a value of 3361.5 mW/cm². A 3-s cavity bottom is 6.3 mm (standard deviation 0.7) in
curing in this mode, based on the data of the a standard class II cavity. Note that the irradiance in
present study must be considered as insufficient the simulated curing conditions of the present study
for all analyzed materials and should be avoided amounted at an exposure distance of 7 mm only 43%
clinically. When doubling the exposure time (6-s) to 49% of the values at a direct contact to the surface
in the same curing mode, the properties improved, [8]. It should also be noted that the curing times
but to a different extent. The silorane-based material recommended by the manufacturer are mainly based
showed properties that were statistically similar to on the assumption that the LCU is placed directly and
a 20s or 40s exposure in the standard mode, and perpendicularly on the restoration, which would be
thus similar to the highest achievable properties considered an ideal situation. Compared to the effect
in this material. For the methacrylate-based RBCs, of the exposure time or location of measurement
the 6-s exposure might be considered as sufficient (top-bottom) the effect of the exposure distance
only for the top surface. At the bottom surface, the was low in all materials. This effect corroborates well
recorded values were comparable to a 20-s exposure with the identified low effect of exposure distance
in the standard mode but significantly lower as a on the transmitted irradiance through the same
40s exposure in the same mode. The differentiation materials and specimen geometries [8]. Moreover,
among materials accentuates even more when the the influence of the exposure distance was lower
clinically relevant exposure distance of 7 mm is at the surface than at the bottom, and larger in the
additionally considered. The silorane-based material higher filled RBC Filtek ™ Supreme XTE, which is also
still performed well at both top and bottom sides, related to the attenuation of light [8].
the flowable methacrylate-based RBC reached A further aspect analyzed in the present study is the
comparable values with a 20-s polymerization in effect of the chemical composition of the organic
the standard mode, but the values measured at the matrix at a given filler amount or the viscosity of
bottom of the regular methacrylate-based material the material at a given chemical composition of the
are very low, indicating insufficient polymerization. organic matrix, on the material’s susceptibility to
Under these conditions, a fast, 6-s polymerization different curing conditions. To analyze this aspect,
at the highest analyzed radiant emittance can be all RBCs were chosen in the same shade, A3. This
unrestrictedly recommended only for the silorane- supposes that differences in the material reaction
108 Stoma Edu J. 2019;6(2): 100-110 http://www.stomaeduj.com
SUSCEPTIBILITY OF RBC TO VARIOUS CLINICAL RELEVANT CURING CONDITIONS: EFFECT OF FILLER AMOUNT AND
CHEMICAL COMPOSITION OF THE ORGANIC MATRIX
Original Articles
to different curing conditions are related to the type, to the high crosslinking density of the final
chemical composition of the individual ingredients, silorane-polymer, as the silorane monomer, which
the filler size and the proportional relation between was obtained from the reaction of oxirane and
filler and organic matrix. A further component siloxane molecules, is a four branched monomer
that may have an influence on the amount of light [19].
transmitted in the depth of the specimen is the The data presented allow rejecting all specified null
initiator. While there is less information about the hypothesis.
amount and exact composition of the initiator
system, it is likely that both methacrylate-based RBCs 5. Conclusions
are based on the same initiator, a camphorquinone/ The analyzed RBCs react differently to the analyzed
amine system. As for the silorane material, the curing conditions depending on their structure and
initiator is camphorquinone as well, but it contains composition. It can therefore be concluded that:
in addition an iodonium salt and aromatic amines The susceptibility to various curing conditions is
[19] that may have an effect on light transmission as materialdependent, while less filled methacrylate-
well. The lower filler amount in the flowable RBC lead based as well as the silorane micro-hybrid seems to
to the significant highest light transmission at the be more robust to this variations.
bottom of the specimens [8] when compared to the The indentation modulus, E, reacts more sensitively
higher filled methacrylate-based RBC. This is clearly to variations in curing conditions then the
reflected in the present study in a lower susceptibility hardness, HV, thus being a better indicator in the
of the flowable material to variations in light characterization of changes in polymerization.
exposure. A difference of 8.3 vol. % in filler amount Within the bounds of this study, exposure time has a
resulted in significantly lower light transmittance significantly stronger effect on the micro-mechanical
and a ca. 50% higher absorbance in the higher filled properties as the irradiance. The influence of radiant
methacrylate-based RBC [8]. This is directly related exposure, which is the product of exposure time
to the identified insufficient polymerization at the and irradiance, was lower compared to the effect
bottom of the 2-mm thick specimens of the last of exposure time. By comparison, the effect of the
mentioned material, also at high exposure times. exposure distance was in much lower.
At a given filler amount, 55 vol-%, the silorane- Fast polymerization (3s) with high irradiance is
based RBCs was less translucent as the flowable not recommended for the analyzed materials.
methacrylate-based RBCs, but the difference in the The doubled exposure time (6s) at high irradiance
light transmittance and absorbance characteristics proved to be insufficient for the methacrylate based
of both materials were lower compared to the RBCs, while acceptable for the silorane material.
differences related to the higher filled methacrylate- On the basis of these findings, under comparable
based RBC [8]. The reasons for the different light clinical conditions, a curing time of at least 20s at
transmittance at a similar filler volume amount is moderate irradiance is probably to be recommended
related, besides the above-mentioned differences for the majority of the tested materials, providing
in the type of initiator, to the monomer reactivity clinical conditions are comparable to those in the
and differences in refractive index between fillers described study.
and organic matrix as well as to the filler size and
chemical composition [20,21]. It must also be Author Contributions
emphasized that the micro-mechanical properties NI: designed the study, provided the infrastructure
measured in the silorane material were superior to (devices, materials), developed the measurement
the values measured in the flowable methacrylate- methods, supervised the experiment, performed
based flowable material at a similar filler volume statistics, and wrote the manuscript. EP: performed
content. This may also be related, besides the filler the experiments and recorded the data.
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Nicoleta ILIE
Dipl. Eng, PhD, Professor
Department of Operative/Restorative Dentistry, Periodontology and Pedodontics
Faculty of Medicine
Ludwig-Maximilians University of Munich, Munich, Germany
CV
Dipl. Eng. Nicoleta Ilie attended the Department of Technology of silicates and high-temperature oxides at the Traian
Vuia University, Timişoara, Romania (1989-1993). She studied material sciences with a focus on glass and ceramics at
the Friedrich Alexander University, Erlangen-Nuremberg, Germany (1994-1999). She got her doctoral degree in material
sciences from the Ludwig-Maximilians University, Dental School, Munich, Germany (1999-2004), followed by her
postdoctoral lecture qualification (habilitation) at the same university (2004-2009). Since 1999, she has been assistant
professor, associated professor (2009) and tenured professor (2014) of biomaterials at the Dental School of the Ludwig-
Maximilians University in Munich.
Questions
1. The highest influence on the micro-mechanical properties of a light cured resin-based
composite (RBC) is exerted by:
qa. Exposure time;
qb. Exposure distance;
qc. Incident irradiance;
qd. LCU’s irradiance.
2. When curing a RBC, following in valid:
qa. Fast polymerization (3s) with high irradiance is recommended, to speed up the restoration procedure;
qb. A curing time of at least 20 s at moderate irradiance;
qc. A lower increment can only be pre-cured for few seconds, since it will receive sufficient light while curing
the upper increments;
qd. All RBCs react similar to variations in radiant exposure.
3. What are “Silorane”?
qa. Resin-based composites with particular glass ionomer filler;
qb. Resin-based composites designed to release ions like F;
qc. Four branched monomer obtained from the reaction of oxirane and siloxane molecules;
qd. A sort of ceramic.
4. At a given composition of the filler and matrix in a RBC, an enhanced filler amount will
result in:
qa. Higher mechanical properties;
qb. Higher light transmittance;
qc. Lower susceptibility to variation in irradiation;
qd. Better polymerization at the bottom of the 2 mm increments.
110 Stoma Edu J. 2019;6(2): 100-110 http://www.stomaeduj.com