Curing behaviour of high-viscosity bulk-fill composites.

JJOD 2301 1–9 journal of dentistry xxx (2014) xxx–xxx

Available online at www.sciencedirect.com

ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden 1 2 3

Curing behaviour of high-viscosity bulk-fill composites

4

5 6 7

Q1

Nicoleta Ilie *, Katharina Stark Department of Operative/Restorative Dentistry, Periodontology and Pedodontics, Ludwig-Maximilians-University of Munich, Goethestr. 70, 80336 Munich, Germany

article info

abstract

Article history:

Objectives: This study aimed to assess the effect of curing conditions – exposure time, mode,

Received 1 April 2014

energy density, and exposure distance – on the mechanical properties of high-viscosity

Received in revised form

bulk-fill resin-based composites (RBCs) measured at simulated clinical relevant filling

19 May 2014

depths.

Accepted 22 May 2014

Methods: Three high-viscosity bulk-fill RBCs were investigated by assessing the variation in

Available online xxx

micromechanical properties in 200 mm steps (Vickers hardness [HV] and indentation modulus [E]) within simulated 6-mm deep fillings (n = 5) polymerized under 16 different curing

Keywords:

conditions. The exposure duration was 5, 20, and 40 s in the standard power mode; 3, 4, and

Bulk-fill resin-based composites

8 s in the high power mode; and 3 and 6 s in the plasma mode; the exposure distance was 0

Irradiance

and 7 mm. Energy density ranged from 2.63 to 47.03 J/cm2. Measurements were performed

Energy density

after 24 h of storage in distilled water at 37 8C. The depth of cure (DOC) was calculated as the

Hardness

80% hardness drop-off.

Modulus of elasticity

Results: The results were compared using one- and multiple-way ANOVAs and Tukey’s HSD post hoc test (a = 0.05). The effect of the parameter material was significant and strong on all measured properties ( p < 0.05, partial eta-squared h2P ¼ 0:492 for E, 0.562 for HV, and 0.087 for DOC). Energy density exerted the strongest influence on the measured properties in all materials, whereas the influence of the exposure distance was strong on DOC, low on E and not significant on HV. The high-viscosity bulk-fill RBCs responds heterogeneously to variations in curing conditions. Conclusions: A lower energy density limit was identified, allowing for a 4 mm material bulk placement (5.88 J/cm2 for EvoCeram Bulk Fill, 7.0 J/cm2 for x-tra fil, and 23.51 J/cm2 for SonicFill). This limit increased to 47.03 J/cm2 for a 5 mm bulk placement, as claimed for SonicFill. To maintain mechanical properties in depth, however, an energy density of at least 23.51 J/cm2 is recommended for EvoCeram Bulk Fill and x-tra fil and 47.03 J/cm2 for SonicFill, respectively. This energy density should be achieved at moderate irradiance and increased curing time.

Q2

# 2014 Published by Elsevier Ltd.

10 89 11 12 13

13

* Corresponding author. Tel.: +49 89 5160 9412; fax: +49 89 5160 9302. E-mail address: [email protected] (N. Ilie). http://dx.doi.org/10.1016/j.jdent.2014.05.012 0300-5712/# 2014 Published by Elsevier Ltd.

Please cite this article in press as: Ilie N, Stark K, Curing behaviour of high-viscosity bulk-fill composites. Journal of Dentistry (2014), http:// dx.doi.org/10.1016/j.jdent.2014.05.012

JJOD 2301 1–9

2

13

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

journal of dentistry xxx (2014) xxx–xxx

1.

Introduction

The incremental layering technique is accepted as a golden standard for the placement of resin-based composite (RBC) restorations.1 However, the latest developments in composite technology are materials intended for posterior bulk-filling placement, the so-called bulk-fill RBC. The materials can be applied in increments up to 4 mm thickness,2–8 thus skipping the time-consuming layering process. Improved self-levelling ability,9 decreased polymerization shrinkage stress,10–12 reduced cusp deflection in standardized class II cavities,13 and good bond strengths regardless of the filling technique and the cavity configuration14 are reported. On the basis of differences in viscosity and application technique, the materials are classified in low- and highviscosity bulk-fill RBCs. The low mechanical properties of the former15 require to finish a restoration by adding a capping layer made of regular RBCs. Regarding regular RBCs, the changes made in bulk-fill RBCs to enlarge the DOC addressed primarily the fillers, which generally increased in size in all materials and decreased in load in low-viscosity bulk-fill composites.15 Large fillers (>20 mm), as observed in several materials (x-tra fil and x-tra base, VOCO, Cuxhaven, Germany; SureFil SDR flow, DENTSPLY Caulk, Milford, DE, USA; SonicFill, Kerr, Orange, CA, USA),15 involve a lower total filler–matrix interface compared with regular composites, reducing light scattering and increasing the transmittance for blue light in the depth. The implementation of higher-molecular weight monomers (SureFil SDR flow) or new initiator systems (Ivocerin in Tetric EvoCeram Bulk Fill; Ivoclar Vivadent Inc., Amherst, NY)16 are further attempts headed for the same purpose. There is no general consensus on the adequate radiant exposure a material needs for proper polymerization because the susceptibility to variation in irradiance under simulated clinical conditions was often proven to be material dependent in both regular17,18 and bulk-fill RBCs,3,4 and calculations based on total energy delivered to guide irradiation protocols were shown to be invalid and to not recognize product behaviour.17 Despite this evidence, the irradiance of modern curing units continues to increase, keeping stubbornly the assertion that an adequate polymerization might be reached at short exposure times (5 s or less) at high irradiances.

The aim of this study was therefore to evaluate the effect of 16 different radiant exposures, adjusted by varying the curing regime, the irradiance, the exposure time, and the exposure distance (i.e., distance between the unit and the specimen’s surface) on the variation of Vickers hardness (HV) and indentation modulus (E) within the simulated 6 mm deep cavities field in bulk with three high-viscosity bulk-fill RBCs. Moreover, the study aims to assess the DOC at all abovementioned radiant exposures and to determine the bandwidth for adequate curing in response to the application of light. The tested null hypotheses were as follows: (1) the effect of the curing conditions would be similar in all materials; (2) there would be no difference within one material among the assessed curing conditions; and (3) there would be no difference in the mechanical properties and the DOC among the analyzed materials.

55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

2.

71

Materials and methods

Three high-viscosity bulk-fill RBCs were investigated (Table 1) by assessing the variation in micromechanical properties (HV and E) as a function of depth, irradiation mode, and exposure distance (0 and 7 mm). A blue-violet LED curing unit (VALO, Ultradent Products Inc., South Jordan, UT, USA) was therefore used in different curing modes and exposure times: standard power mode (5, 20, and 40 s), high power mode (3, 4, and 8 s), and plasma mode (3 and 6 s) and two exposure distances (0 and 7 mm) (Table 2), thus resulting in 16 different curing conditions for each material.

72 73 74 75 76 77 78 79 80 81

2.1.

82

Irradiance measurements

The analysis of the variation in the irradiance of the curing unit VALO with the distance as well as at the bottom of the 6 mm specimens was performed on a laboratory-grade NISTreferenced USB4000 Spectrometer (Managing Accurate Resin Curing System; Bluelight Analytics Inc., Halifax, Canada). The miniature fibre optic USB4000 Spectrometer uses a 3648element Toshiba linear CCD array detector and high-speed electronics. The spectrometer has been spectroradiometrically calibrated using Ocean Optics’ NIST-traceable light source (300–1050 nm). The system uses a CC3-UV Cosine Corrector to collect radiations higher than the 1808 field of

Table 1 – Materials, manufacturer, chemical composition of matrix and filler as well as filler content by weight (wt.%) and volume (vol.%). Bulk Fill RBCs

Manufacturer, colour, batch

Tetric EvoCeram1 Bulk Fill Nano-hybrid RBC

Ivoclar Vivadent, IVA, P84129

Bis-GMA, UDMA

X-tra Fil Hybrid RBC SonicFillTM Nano-hybrid RBC

Voco, Universal, 1230323 Kerr, A3, 3851737

Bis-GMA, UDMA, TEGDMA Bis-GMA, TEGDMA, EBPDMA

Resin matrix

Filler Ba–Al–Si–glass, prepolymer filler (monomer, glass filler and ytterbium fluoride), spherical mixed oxide

Filler wt.%/vol.% 79–81 (including 17% prepolymers)/60–61

86/70.1 SiO2, glass, oxide

83.5/–

Abbreviations: Bis-GMA, bisphenol-A diglycidyl ether dimethacrylate; EBPDMA, ethoxylated bisphenol-A-dimethacrylate; TEGDMA, triethyleneglycol dimethacrylate; UDMA, urethane dimethacrylate. Data are provided by manufacturers.


83 84 85 86 87 88 89 90 91 92 93

JJOD 2301 1–9

3


Table 2 – Influence of the parameters energy density reaching specimen’s surface, exposure distance and curing mode on the mechanical properties – indentation modulus (E), Vickers hardness (HV) and depth of cure (DOC). Table contains the partial eta-square values. The higher the partial eta-square, the higher the influence of the selected factor on the measured property (n.s. = non-significant). Material

Parameter

HV (N/mm2)

DOC (mm)

X-tra Fil

Energy density Distance Curing mode

0.346 n.s. n.s.

n.s. n.s. n.s.

0.866 0.249 0.843

Tetric EvoCeram1 Bulk Fill


0.387 0.104 0.282

0.376 n.s. 0.289

0.962 0.701 0.957

SonicFillTM


0.453 n.s. 0.407

0.326 n.s. 0.286

0.964 0.568 0.963

94 95

view, thus mitigating the effects of optical interference associated with light collection sampling geometry.

96

2.2.

97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135

E (GPa)

Micromechanical characteristics

The variation in micromechanical properties (HV and E) was assessed on 6 mm bulk specimens (n = 5) according to DIN 50359-1:1997-10.19 To simulate clinical conditions, the mould used to prepare the specimens was made out of a human molar, with an inner cylindrical cavity (height, 6 mm; diameter, 5 mm). Specimens were stored in distilled water after curing for 24 h at 37 8C, ground and polished under water in longitudinal direction from 5 to 2.5 mm diameter with diamond abrasive paper (mean grain sizes: 20, 13, and 6 mm) in a grinding system (EXAKT 400CS; Exakt, Norderstedt, Germany). Measurements were made with an automatic microhardness indenter (Fischerscope H100 C; Fischer, Sindelfingen, Germany) starting from 0.1 mm under the surface, with 200 mm intervals between the measuring points. The test procedure was carried out force-controlled, where the test load increased and decreased with constant speed between 0.4 and 500 mN. The load and the penetration depth of the indenter (Vickers pyramid: diamond right pyramid with a square base and an angle of a = 1368 between the opposite faces at the vertex) were continuously measured during the load-unload hysteresis. Universal hardness is defined as the test force divided by the apparent area of indentation under the applied test force. From a multiplicity of measurements stored in a database supplied by the manufacturer, a conversion factor (0.0945) between universal hardness and HV was calculated by the manufacturer and entered into the software so that the measurement results were indicated in the more familiar HV units. E was calculated from the slope of the tangent adapted at the beginning (at maximum force) of the nonlinear indentation depth curve upon unloading. The DOC, usually acknowledged as the thickness of an RBC that is adequately cured or rather as the depth where HV equals the surface value multiplied by an arbitrary ratio, usually 0.8 (HV 80%), was calculated. Therefore, for each sample, HV in the depth was compared with the reference surface value measured on the sample’s top at best curing conditions (40 s, 0 mm exposure distance) and noted when it became less than 80% (HV 80%).

2.3.

Statistical analysis

136

Results were compared using one- and multiple-way ANOVAs and Tukey’s HSD post hoc test (a = 0.05). A multivariate analysis (general linear model) assessed the effect of the parameters material, energy density reaching the specimen’s surface (varying among 2.63 and 47.03 J/cm2; Table 2), exposure distance (0 and 7 mm), and curing mode (standard power mode with an exposure time of 5, 20, and 40 s; high power mode with an exposure time of 3, 4, and 8 s; and plasma mode with an exposure time of 3 and 6 s) on HV, E, and DOC. The partial eta-squared statistic reports the practical significance of each term, based on the ratio of the variation accounted for by the effect. Larger values of partial etasquared indicate a greater amount of variation accounted for by the model effect, to a maximum of 1 (Version 22.0; SPSS Inc., Chicago, IL, USA).

137 138 139 140 141 142 143 144 145 146 147 148 149 150 151

3.

152

Results

The greatest mean amount of irradiance was delivered with the light unit set in the plasma programme, whereas the high power and the standard power programmes were delivered along the measured distances 48–53% and 32–39% of this energy level. A similar pattern in the variation of irradiance with increasing distance between the unit and the specimen’s surface was observed in all three programmes, whereas the irradiance showed a maximum at 2 mm distance from the sensor’s surface, measured at 1272 mW/cm2 in the standard power mode, 1939 mW/cm2 in the high power mode, and 3797 mW/cm2 in the plasma mode. The irradiance reaching the specimen’s surface under the analyzed curing conditions decreased from 1176 mW/cm2 (0 mm) to 646 mW/cm2 (7 mm) in the standard power mode, from 1766 to 875 mW/cm2 in the high power mode, and from 3416 to 1750 mW/cm2 in the plasma mode (Fig. 1a). The spectral distribution in each mode reveals two peaks at 457 nm and 400 nm which decrease with increasing exposure distance (Fig. 1 b and c). The effect of the parameter material was proved to be significant on all measured properties ( p < 0.05; partial eta -squared h2P ¼ 0:492 for E, 0.562 for HV, and 0.087 for DOC). Within one material, the effect strength of the parameters energy


153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175

JJOD 2301 1–9

4


Fig. 1 – LED curing unit VALO: (a) variation in irradiance with the distance; (b) emission spectrum for the three curing modes; and (c) emission spectrum at 0 and 7 distance from specimen’s surface exemplified for the plasma curing mode.

176 177 178 179 180

density (ranging from 2.63 to 47.03 J/cm2; Table 2), exposure distance (0 and 7 mm), and curing mode (standard power mode with an exposure time of 5, 20, and 40 s; high power mode with an exposure time of 3, 4, and 8 s; and plasma with an exposure time of 3 and 6 s) was stronger on DOC

than that on HV and E ( p < 0.05, h2P values are listed in Table 2). The parameter energy density ( p < 0.05, h2P values in Table 2) exerted the strongest influence on the measured properties in all materials, whereas the influence of the exposure distance was strong on DOC ( p < 0.05, h2P values in


181 182 183 184 185

JJOD 2301 1–9

5


Table 3 – Micromechanical properties of the three bulk-fill RBCs-indentation modulus E (GPa) and Vickers hardness HV (N/ mm2) – measured at different depths (0.2, 2, 4 and 6 mm) as function of curing conditions. Depth of cure, DOC (mm) was calculated from the variation of the Vickers hardness with depth (80% HV) as function of the curing. The mean hardness measured at sample’s surface at best irradiance conditions (no distance between curing unit and sample, 40 s irradiance in standard mode) was taken as reference. Superscript letters indicate statistically homogeneous subgroups within a column (Tukey’s HSD test, a = 0.05). (a) X-tra fil Curing mode

Energy (J/cm2)

Distance (mm)

E0.2mm

E2mm

E4mm

E6mm

5 s standard 20 s standard 40 s standard 3 s high 4 s high 8 s high 3 s plasma 6 s plasma

5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0

21.0ab (1.37) 21.5ab (0.71) 20.8ab (0.97) 20.2ab (2.40) 20.4ab (1.08) 22.9b (2.35) 20.0ab (0.90) 18.9ab (1.65)

20.4ab (1.14) 23.8abc (1.03) 24.1bc (1.31) 22.3abc (1.38) 22.2abc (0.90) 26.0c (3.85) 23.1abc (1.68) 22.3abc (1.29)

20.2bcd (1.04) 23.3de (0.67) 22.1cde (1.76) 19.8bc (1.46) 21.4bcde (0.95) 23.9e (1.11) 21.5cde (0.83) 22.3cde (1.22)

16.3bcdef (1.20) 20.1f (2.28) 19.9ef (2.32) 11.6b (3.96) 12.1b (3.18) 18.4cdef (0.94) 14.5bcde (2.16) 19.1def (1.70)


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

7

21.0ab (1.81) 20.6ab (2.86) 21.0ab (1.63) 17.4a (1.40) 20.7ab (0.96) 19.5ab (2.24) 21.2ab (0.66) 20.5ab (3.54)

21.3ab (2.58) 23.1abc (1.44) 23.5abc (1.21) 19.8a (0.68) 21.4ab (1.81) 20.6ab (2.27) 22.8abc (2.08) 22.9abc (0.42)

18.1ab (2.37) 22.7cde (1.40) 23.6e (1.01) 16.1a (1.36) 20.7bcde (1.89) 18.2ab (2.30) 19.9bc (1.27) 21.6cde (0.62)

10.8ab (0.71) 18.1cdef (3.50) 19.9ef (0.69) 5.8a (1.18) 13.1bc (0.67) 14.3bcd (4.63) 13.3bc (2.32) 17.7cdef (1.42)

Curing mode

Energy top (J/cm2)

Energy Distance bottom (J/cm2) (mm)

HV0.2mm

HV2mm

HV4mm

HV6mm

DOC


5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0.09 0.51 1.48 0.08 0.11 0.29 0.15 0.40

0

134.2a 129.8a 135.5a 141.1a 130.7a 147.0a 119.3a 125.0a

(7.78) (9.60) (15.18) (16.51) (7.07) (27.90) (4.95) (15.04)

110.8a 140.5a 136.0a 123.3a 116.3a 149.1a 132.9a 129.2a

(18.49) (17.91) (1.14) (11.08) (8.03) (35.19) (19.50) (9.55)

118.9abcde (16.55) 128.8bcde (6.93) 127.0bcde (10.24) 111.0abc (14.88) 119.8abcde (10.81) 137.6cde (13.87) 117.6abcde (8.08) 123.2abcde (3.48)

89.6bcde (9.21) 124.9ef (22.24) 133.7f (25.36) 65.5abc (36.15) 67.3abc (21.07) 112.7def (18.13) 92.6bcdef (21.81) 119.2ef (22.92)

4.5bcde (0.54) 6.0f (0.00) 6.0f (0.00) 3.7abc (0.58) 4.4bcd (0.45) 4.7cde (0.50) 4.9def (0.64) 5.8f (0.26)


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

0.05 0.26 0.61 0.04 0.06 0.13 0.08 0.21

7

135.1a 136.7a 136.3a 120.8a 121.9a 143.2a 135.4a 137.6a

(27.85) (6.07) (9.56) (7.34) (10.51) (16.48) (10.60) (21.80)

128.9a 134.9a 141.6a 110.8a 113.6a 139.2a 126.2a 131.6a

(30.57) (9.19) (21.69) (9.26) (16.74) (16.74) (23.27) (12.53)

95.7a (20.50) 145.1e (15.57) 142.5de (11.50) 103.0ab (14.21) 111.9abc (9.18) 121.4abcde (12.47) 115.0abcde (19.07) 114.7abcd (5.79)

61.6ab (6.75) 114.4def (10.81) 124.8ef (10.39) 28.1a (5.59) 76.0bcd (6.58) 122.0ef (11.91) 74.2bcd (9.84) 107.8cdef (9.84)

3.0a (0.65) 5.9f (0.12) 6.0f (0.00) 2.9a (0.90) 3.6ab (0.59) 5.6ef (0.49) 3.8abc (0.30) 5.5def (0.38)

(b) Tetric EvoCeram Bulk-Fill Curing mode

Energy (J/cm2 (

Distance (mm)

E0.2mm

E2mm

E4mm

E6mm


5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0

13.6ab (0.45) 13.7ab (0.78) 13.4ab (0.73) 13.2ab (0.26) 13.0ab (1.01) 13.4ab (0.71) 13.2ab (0.91) 13.9b (0.36)

13.9abcd (0.83) 14.8def (0.28) 15.2f (0.36) 14.0abcde (0.31) 13.9abcd (0.43) 14.9ef (0.36) 14.1abcde (0.54) 14.6cdef (0.28)

11.9bcd (0.27) 13.6f (0.47) 14.5f (0.26) 11.6bcd (0.43) 11.4bc (0.40) 13.5ef (0.48) 12.0bcd (0.40) 13.7f (0.55)

6.5de (0.52) 11.2gh (0.71) 12.6h (0.43) 5.2bcde (0.76) 2.6ab (0.48) 9.4fg (0.54) 5.8cde (0.76) 10.6gh (1.39)


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

7

12.7ab (0.36) 14.1b (0.45) 13.3ab (1.07) 12.0a (1.33) 12.1a (1.14) 13.1ab (1.00) 13.0ab (0.26) 13.3ab (0.41)

13.4a (0.35) 14.7def (0.48) 14.5bcdef (0.69) 13.4a (0.19) 13.6abc (0.21) 14.4abcdef (0.38) 13.6ab (0.26) 14.1abcde (0.51)

10.2a (0.44) 13.6f (0.26) 14.6f (0.38) 10.1a (0.56) 11.3bc (0.44) 12.5de (0.47) 11.0ab (0.48) 12.2cd (0.99)

2.0a (1.31) 11.1gh (0.50) 11.6gh (0.31) 4.3abcd (1.77) 5.1bcde (3.11) 5.6cde (0.63) 3.4abc (1.81) 7.6ef (1.75)


JJOD 2301 1–9

6


Table 3 (Continued) Energy top (J/cm2)

Energy bottom (J/cm2)

Distance (mm)

HV0.2mm

HV2mm

HV4mm


5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0.07 0.43 0.82 0.07 0.09 0.19 0.13 0.31

0

79.4ab (3.62) 83.2b (6.84) 80.9ab (1.18) 80.8ab (6.80) 77.4ab (5.79) 81.2ab (2.49) 76.8ab (6.46) 80.7ab (2.01)

68.7abc (8.14) 77.3de (1.46) 80.2e (2.01) 72.4abcd (2.25) 72.8bcd (2.27) 80.5e (1.73) 74.6cde (2.05) 80.0e (0.83)

57.5bc (2.41) 69.8de (4.17) 77.6f (1.63) 55.8b (4.11) 54.1ab (1.84) 69.6de (2.07) 64.4cd (4.47) 70.5def (1.05)

28.5cd (4.14) 63.5fg (3.28) 68.8g (2.71) 22.0abc (4.69) 11.5ab (2.09) 49.3ef (2.43) 28.4cd (4.36) 61.7fg (2.33)

3.7de (0.11) 5.6ij (0.46) 6.0j (0.00) 3.2bcd (0.20) 3.4cd (0.22) 4.9gh (0.27) 4.2ef (0.22) 5.7ij (0.27)


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

0 0.26 0.53 0.04 0.06 0.13 0.06 0.13

7

75.6ab (1.36) 81.7ab (0.74) 80.5ab (3.74) 73.9a (3.74) 73.7a (5.15) 82.2ab (3.70) 78.7ab (1.70) 80.7ab (1.01)

67.4ab (1.55) 75.9de (3.27) 80.2e (1.94) 65.7a (1.27) 69.1abc (2.36) 74.5cde (1.59) 70.5abcd (2.73) 74.5cde (4.34)

47.0a (3.06) 70.0de (3.87) 75.1ef (3.79) 48.1a (2.13) 54.4ab (3.35) 64.9cd (4.63) 54.4ab (2.51) 66.3d (5.29)

8.6a (8.51) 57.9fg (2.08) 65.9g (3.38) 21.6abc (11.13) 24.2bc (15.82) 26.2bcd (4.08) 15.6abc (9.10) 40.4de (7.88)

2.7ab (0.30) 5.3hi (0.23) 5.9j (0.27) 2.4a (0.26) 2.9abc (0.27) 4.2ef (0.28) 3.2bcd (0.17) 4.4fg (0.36)

Curing mode

HV6mm

DOC

(c) SonicFill Curing mode

Energy (J/cm2)

Distance (mm)

E0.2mm

E2mm

E4mm

E6mm


5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0

15.7abc (0.72) 16.8c (0.36) 15.9abc (0.83) 14.4ab (1.98) 16.2bc (1.24) 16.4c (0.66) 15.4abc (0.80) 16.3bc (0.72)

15.9cd (0.70) 18.2f (0.43) 18.2f (0.21) 14.3ab (0.50) 15.6c (0.32) 17.2ef (0.48) 16.0cd (1.01) 17.7ef (0.61)

10.5bcd (0.70) 15.2g (0.27) 16.6g (0.28) 7.9a (1.84) 9.9ab (2.38) 12.5def (0.19) 10.8bcde (0.84) 14.4fg (0.18)

4.7abcdef (1.55) 7.1defg (1.28) 10.0g (0.68) 2.6abc (1.49) 3.5abc (2.75) 2.1ab (0.75) 1.8ab (0.72) 5.3bcdef (0.91)


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

7

15.4abc (0.90) 15.5abc (0.82) 16.5c (0.44) 14.0a (1.22) 15.4abc (0.58) 16.6c (0.61) 15.8abc (0.96) 16.2bc (0.52)

14.0ab (0.25) 17.3ef (0.38) 17.4ef (0.56) 13.4a (0.33) 14.3ab (0.96) 15.9cd (0.36) 14.8bc (0.40) 16.8de (0.36)

10.1abc (1.46) 12.7def (0.47) 15.6g (0.29) 9.9ab (1.61) 9.9ab (0.77) 12.3cdef (0.12) 10.9bcde (0.69) 12.8ef (0.24)

3.6abcd (1.10) 3.8abcde (1.73) 7.7fg (1.12) 1.7a (1.03) 4.6abcdef (1.61) 3.8abcde (1.05) 6.2cdef (2.63) 7.2efg (2.29)

Curing mode

186 187 188 189 190

Energy top (J/cm2)

Energy bottom (J/cm2)

Distance (mm)


5.88 23.51 47.03 5.30 7.06 14.13 10.25 20.50

0 0 0 0 0 0 0 0

0

92.2a 93.6a 88.4a 85.4a 93.0a 96.0a 86.8a 92.4a


3.23 12.93 25.85 2.63 3.50 7.00 5.25 10.50

0 0 0 0 0 0 0 0

7

95.4a 93.5a 93.7a 83.1a 89.6a 94.0a 89.4a 90.1a

HV2mm

HV4mm

HV6mm

DOC

(4.38) (3.40) (3.03) (10.84) (8.37) (3.33) (11.55) (2.96)

81.1cde (3.55) 94.1g (3.70) 92.9g (1.68) 72.4ab (3.40) 79.2bc (2.99) 88.5efg (1.21) 80.4cd (6.57) 91.1fg (4.06)

51.1bc (2.62) 76.6fgh (1.60) 85.0h (1.65) 39.4a (8.80) 49.1ab (9.67) 65.0de (4.48) 54.3bcd (2.49) 70.3efg (1.98)

23.8abcde (10.66) 36.8cdef (6.41) 51.0f (3.17) 13.5ab (8.11) 17.2abc (15.45) 11.1a (4.52) 8.5a (6.03) 26.0abcde (5.96)

2.7cdef (0.30) 4.3i (0.23) 5.4k (0.38) 2.2abcd (0.17) 2.7def (0.18) 3.6gh (0.26) 3.0ef (0.09) 4.0hi (0.09)

(9.34) (2.00) (3.41) (4.36) (1.49) (3.25) (3.51) (0.65)

72.4ab (2.39) 87.7defg (3.77) 91.2fg (2.66) 65.9a (2.63) 71.8ab (4.08) 84.5cdef (4.49) 76.8bc (2.81) 87.4defg (3.03)

53.0bc (5.98) 67.7ef (4.92) 80.3gh (3.39) 49.6ab (8.74) 49.8ab (3.77) 61.6cde (1.80) 52.0bc (4.35) 65.2de (2.57)

18.1abcd (6.24) 20.5abcde (10.23) 40.2ef (6.01) 6.7a (5.84) 22.8abcde (10.28) 19.4abcd (5.61) 33.9bcdef (16.09) 38.0def (12.28)

2.2abc (0.14) 3.9hi (0.23) 4.8j (0.22) 1.8a (0.22) 2.2ab (0.26) 3.2fg (0.17) 2.5bcde (0.11) 3.8hi (0.20)

HV0.2mm

Table 2) but low on E (Tetric EvoCeram Bulk Fill, p < 0.05, h2P ¼ 0:104; p > 0.05 in the other materials) and not significant on HV ( p > 0.05). At best curing conditions (highest energy density of 47.03 J/ cm2, corresponding to 40 s irradiation in the standard power

mode by applying the curing unit on specimen’s surface), the E measured at the specimen’s surface of the tested materials ranked in three statistically significant subgroups ( p < 0.05) in the following sequence: x-tra fil (20.82A 0.97 GPa), SonicFill (15.90B 0.83 GPa), and Tetric EvoCeram Bulk Fill


191 192 193 194 195


196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239

(13.42C 0.73 GPa). A similar ranking of the materials was also measured with regard to HV (135.50A 15.18 N/mm2, x-tra fil; 88.38B 3.03 N/mm2, SonicFill; 80.94B 1.18 N/mm2, Tetric EvoCeram Bulk Fill; the superscript letters indicate statistically homogeneous subgroups, one-way ANOVA with Tukey’s HSD test, a = 0.05). The HV and the E results for all materials at selected depths (0.2, 2, 4, and 6 mm) as well as the DOC values as a function of the 16 curing conditions are summarized in Table 3a–c and Fig. 2. Within one material, a low variance in HV and E was measured until 2 mm depth, whereas a different effect of the curing modes on the measured properties was distinguished in deeper layers. The susceptibility to variation in irradiance under simulated clinical conditions is dependent on the material. Only 3 of the 16 curing regimes (0 mm exposure distance, standard power mode, 20 or 40 s exposure; and 7 mm exposure distance, standard power mode, 40 s) induced DOC values of 4 mm or larger in SonicFill, the value considered as the thickness limit for allowing to place a material in bulk. This would correspond to a minimum energy density of 23.51 J/cm2 for bulk placement. This value decreases to 7.0 J/cm2 for x-tra fil and 5.88 J/cm2 for the Tetric EvoCeram Bulk Fill. At an approximately equivalent energy density of 7.0 J/cm2 (4 s exposure time in high power mode at 0 mm exposure distance and 8 s exposure time in high power mode at 7 mm exposure distance) or 10.25 J/cm2 (3 s plasma, 0 mm and 6 s plasma, 7 mm), a shorter exposure to a higher irradiance is reflected in significantly lower DOC compared with a longer exposure to lower irradiance (Table 3). Overall, 20 and 40 s exposure (standard power mode) at both exposure distances (0 and 7 mm) induced the significantly highest mechanical properties in all depths. Sporadically, the above-mentioned curing conditions were equivalent to 8 s (high power mode) and 6 s exposure (plasma). Short exposures (5 s standard power mode, 3–4 s high power mode, and 3 s plasma) induced lower mechanical properties, predominantly evident in lower DOC. With the exception of SonicFill specimens, transmitted light was detected at the bottom of the 6 mm specimens during curing. The energy density at the bottom of the specimens was generally larger in X-tra fil (ranging from 0.04 J/ cm2 to 1.48 J/cm2) compared with Tetric EvoCeram Bulk-Fill (0– 0.82 J/cm2) (Table 3a–c).

240

4.

241 242 243 244 245 246 247 248 249 250 251 252

The present study simulated 16 different clinically relevant curing conditions by varying and quantifying precisely the amount of light reaching specimens, simulating energy density ranging from 2.63 to 47.03 J/cm2. The strategies to ensure an enhanced polymerization in depth were grabbed differently in the three analyzed materials. Although a new initiator system was implemented in the Tetric EvoCeram Bulk Fill by keeping the filler system comparable with the regular nanohybrid RBC pendant Tetric EvoCeram, the materials x-tra fil and SonicFill revealed changes focused primarily on the filler system, particularly on filler size.15 The inorganic filler amount was directly

Discussion

7

Fig. 2 – Depth of cure (DOC) as a function of energy density.

reflected in the measured mechanical properties because the highest filled material x-tra fil also reached the highest mechanical properties, followed by SonicFill and Tetric EvoCeram Bulk Fill. Unexpectedly, the largest DOC was also observed in the highest filler loaded material, x-tra fil, at a given exposure condition. This is however in accordance with measurements of the transmitted light (360–540 nm wavelength) through the specimens of different thicknesses (2, 4, and 6 mm), emphasizing a higher translucency for x-tra fil compared with Tetric EvoCeram Bulk Fill. The amount of light transmitted through SonicFill specimens was the lowest among the bulk-fill RBCs and was rather comparable with regular nano- and microhybrid RBCs.20 These results are in accordance with the identified transmitted light through the 6 mm specimens as function of the different curing conditions (Table 3a–c). The energy density at the bottom of the specimens was very low, even not measurable for SonicFill, though, the measured micromechanical properties were not reduced to zero. The reason therefore is that the polymerization at a certain depth is not only depended on the amount of photons reaching that depth, but also from the polymerization process already initiated in other (upper) layers, which is propagating in depth. The explanation for the high translucency in x-tra fil despite a high filler amount must be searched in the increased filler size and a potentially improved matching between the refractive indices of filler particles and the resin matrix.21,22 The last essentially determines how light is scattering within a material.23 Similar refractive indices of the components of an RBC, as demonstrated for bisphenol-A-dimethacrylate and silica filler particles, were shown to improve translucency in experimental dental materials.24 To enable an enhanced polymerization in depth in Tetric EvoCeram Bulk Fill, although less change in translucency compared with regular RBCs was performed, an additional initiator system – Ivocerin – was introduced. Ivocerin is described as a germanium-based initiator system with a higher photocuring activity than CQ because of its higher absorption in the region between 400 and 450 nm. Moreover,


253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291

JJOD 2301 1–9

8

292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351


the initiator can be used without the addition of an amine as a co-initiator and forms at least two radicals able to initiate the radical polymerization, being thus more efficient than the CQ/ amine systems, resulting in only one radical able to initiate polymerization.16 The advantage of x-tra fil in terms of a better light transmittance in depth compared with Tetric EvoCeram Bulk Fill is thus repealed by the additional initiator because the data showed that the minimum exposure calculated in this study to allow placing a material in bulk was lower for Tetric EvoCeram Bulk Fill (5.88 J/cm2) than for x-tra fil (7.0 J/cm2). The low translucency of SonicFill is also clearly reflected in the higher amount of radiant exposure (23.51 J/cm2) necessary to induce a minimum DOC of 4 mm. It must, however, be considered that the material is advertised by the manufacturer as allowing placement of increments up to 5 mm thickness. Under the present curing conditions this was achieved in only one out of 16 curing conditions: highest energy density (47.03 J/cm2), 40 s exposure time and 0 mm exposure distance. The emission spectrum of the blue-violet LED unit used in the present study (Valo, Ultradent) matched the absorption spectrum of Ivocerin (400 and 450 nm) well. As for the blue LED curing units, there is only some overlap at the tail end of the absorption spectrum of Ivocerin. DOC data recorded with the same method for Tetric EvoCeram Bulk Fill polymerized with a blue LED curing units (Freelight 2, 3 m Espe, Seefeld, Germany; 1703 m/cm2 at 0 mm and 500 mW/cm2 at 7 mm exposure distance) reported, however, DOC values less than 6 mm only for short exposure times or large exposure distances (4.67 0.33 mm for 10 s exposure and 0 mm distance, 17 J/cm2; 4.13 0.32 mm for 10 s/7 mm, 5 J/cm2; and 4.40 0.14 mm for 20 s/7 mm, 10 J/ cm2).3 Although a direct comparison of the efficiency of both curing units is not possible because of the differences in irradiance and emitted heat, there is no clear advantage in evidence when blue-violet compared with blue LED curing units are used. Thus, the low overlap between the absorption spectrum of Ivocerin and the emitted spectrum of blue LED seems to allow initiating Ivocerin, and the statements presented in this study are not limited to blue-violet LED curing units. The measured data are confirming data valid in regular RBCs, in which calculations based on total energy delivered to guide irradiation protocols are invalid and do not recognize product behaviour17 because a shorter exposure to a higher irradiance is reflected in significantly lower DOC as a longer exposure to lower irradiance. Moreover, short exposures (5 s standard power mode, 3–4 s high power mode, and 3 s plasma) induced lower mechanical properties, predominantly evident in lower DOC (Table 3). Light transmission decreases with increasing specimen thickness but generally increases during the polymerization process of monomers to polymers. Thus, at prolonged exposure time, more light will consequently reach deeper layer as at the beginning of irradiation, explaining the deficits of short exposures. The present study demonstrated that the most sensitive parameter in describing the efficiency of curing was DOC (Table 2, larger partial eta-squared values). This parameter was strongly influenced by the energy density ( p < 0.05, h2P values in Table 2) in all analyzed materials. Nevertheless, it is questionable whether a 20% hardness drop-off compared with a

sample’s surface might be considered as a sufficient polymerization in deeper layers. Although a minimal acceptable energy density would allow fulfilling the requirements for a bulk placement, it must be considered that significant differences in HV and E were found when evaluating the variation of those parameters with depth (Table 2). A constant variation of the mechanical properties in depth was observed only when the specimens of Tetric EvoCeram Bulk Fill and x-tra fil were exposed to 20 s (23.51 J/cm2) or 40 s (47.03 J/cm2) irradiation, whereas an even longer time would be therefore necessarily for SonicFill. Therefore, all null hypotheses were rejected. To assess both, the elastic and the plastic part of deformation, a depth sensing hardness measurement device was used in this study, where a dynamic measuring principle was applied by simultaneously recording the load and the corresponding penetration depth of the indenter.19,25 Additionally, the modulus of elasticity was considered since it was identified previously to correlate with the modulus of elasticity measured in three point flexure tests.26 The present study also identified the modulus of elasticity as being more sensitive to variations in energy density compared with Vickers hardness.

352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373

5.

374

Conclusions

The analyzed high-viscosity bulk-fill RBCs react differently to the analyzed curing conditions, depending on their structure and composition. Generally, an increase in DOC with increased energy density was observed in all materials, whereas x-tra fill sowed at a given curing condition comparable or higher DOC values as EvoCeram Bulk Fill, and both had significantly higher DOC values than SonicFill. Although a lower energy density limit can be calculated from DOC measurements, allowing a 4 mm material bulk placement – which was 5.88 J/cm2 for EvoCeram Bulk Fill, 7.0 J/cm2 for x-tra fil, and 23.51 J/cm2 for SonicFill – to maintain mechanical properties in depth, an energy density of at least 23.51 J/cm2 is recommended for EvoCeram Bulk Fill and x-tra fil and 47.03 J/ cm2 for SonicFill, respectively.

375 376 377 378 379 380 381 382 383 384 385 386 387 388

references

389

1. Park J, Chang J, Ferracane J, Lee IB. How should composite be layered to reduce shrinkage stress: incremental or bulk filling? Dental Materials 2008;24:1501–5. 2. Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clinical Oral Investigations 2013;17:227–35. 3. Ilie N, Kessler A, Durner J. Influence of various irradiation processes on the mechanical properties and polymerisation kinetics of bulk-fill resin based composites. Journal of Dentistry 2013;41:695–702. 4. Finan L, Palin WM, Moskwa N, McGinley EL, Fleming GJ. The influence of irradiation potential on the degree of conversion and mechanical properties of two bulk-fill flowable RBC base materials. Dental Materials 2013;29:906–12. 5. Garoushi S, Sailynoja E, Vallittu PK, Lassila L. Physical properties and depth of cure of a new short fiber reinforced composite. Dental Materials 2013;29:835–41.


390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407


408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440

6. Garcia D, Yaman P, Dennison J, Neiva G. Polymerization shrinkage and depth of cure of bulk fill flowable composite resins. Operative Dentistry 2013. [Epub ahead of print]. 7. Alrahlah A, Silikas N, Watts DC. Post-cure depth of cure of bulk fill dental resin-composites. Dental Materials 2014;30:149–54. 8. Goracci C, Cadenaro M, Fontanive L, Giangrosso G, Juloski J, Vichi A, et al. Polymerization efficiency and flexural strength of low-stress restorative composites. Dental Materials 2014;30:688–94. 9. Petrovic LM, Zorica DM, Stojanac I, Krstonosic VS, Hadnadjev MS, Atanackovic TM. A model of the viscoelastic behavior of flowable resin composites prior to setting. Dental Materials 2013;29:929–34. 10. El-Damanhoury H, Platt J. Polymerization shrinkage stress kinetics and related properties of bulk-fill resin composites. Operative Dentistry 2013. [Epub ahead of print]. 11. Jin X, Bertrand S, Hammesfahr P. New radically polymerizable resins with remarkably low curing stress. Journal of Dental Research 2009;88:1651. 12. Ilie N, Hickel R. Investigations on a methacrylate-based flowable composite based on the SDR technology. Dental Materials 2011;27:348–55. 13. Moorthy A, Hogg CH, Dowling AH, Grufferty BF, Benetti AR, Fleming GJ. Cuspal deflection and microleakage in premolar teeth restored with bulk-fill flowable resin-based composite base materials. Journal of Dentistry 2012;40:500–5. 14. Van Ende A, De Munck J, Van Landuyt KL, Poitevin A, Peumans M, Van Meerbeek B. Bulk-filling of high C-factor posterior cavities: effect on adhesion to cavity-bottom dentin. Dental Materials 2013;29:269–77. 15. Ilie N, Bucuta S, Draenert M. Bulk-fill resin-based composites: an in vitro assessment of their

16.

17.

18. 19. 20.

21.

22.

23. 24.

25. 26.

mechanical performance. Operative Dentistry 2013;38: 618–25. Moszner N, Fischer UK, Ganster B, Liska R, Rheinberger V. Benzoyl germanium derivatives as novel visible light photoinitiators for dental materials. Dental Materials 2008;24:901–7. Musanje L, Darvell BW. Polymerization of resin composite restorative materials: exposure reciprocity. Dental Materials 2003;19:531–41. Musanje L, Darvell BW. Curing-light attenuation in filledresin restorative materials. Dental Materials 2006;22:804–17. DIN-50359-1. Testing of metallic materials – Universal hardness test – Part 1: test method. 1997. Bucuta S, Ilie N. Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites. Clinical Oral Investigations 2014. Primus CM, Chu CC, Shelby JE, Buldrini E, Heckle CE. Opalescence of dental porcelain enamels. Quintessence International 2002;33:439–49. Shortall AC, Palin WM, Burtscher P. Refractive index mismatch and monomer reactivity influence composite curing depth. Journal of Dental Research 2008;87:84–8. Lee YK, Lu H, Powers JM. Measurement of opalescence of resin composites. Dental Materials 2005;21:1068–74. Azzopardi N, Moharamzadeh K, Wood DJ, Martin N, van Noort R. Effect of resin matrix composition on the translucency of experimental dental composite resins. Dental Materials 2009;25:1564–8. Fischer-Cripps AC. Nanoindentation: dynamic indentation testing. Berlin: Springer-Verlag; 2004. Ilie N, Hickel R. Macro-, micro- and nano-mechanical investigations on silorane and methacrylate-based composites. Dental Materials 2009;25:810–9.

9

Q3

441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474


Curing kinetics of visible light curing dental resin composites investigated by dielectric analysis (DEA).

Curing profile of bulk-fill resin-based composites.

Effect of light curing protocol on degree of conversion of composites.

Time reduction of light curing: Influence on conversion degree and microhardness of orthodontic composites.

Simultaneous measurement of polymerization stress and curing kinetics for photo-polymerized composites with high filler contents.

Depth of cure of bulk fill composites with monowave and polywave curing lights.

Effect of different curing protocols on the mechanical properties of low-viscosity bulk-fill composites.

Dielectric analysis of depth dependent curing behavior of dental resin composites.

Effect of resin thickness, and curing time on the micro-hardness of bulk-fill resin composites.

The use of visible light-curing composites in bonding ceramic brackets.

Light-Curing Volumetric Shrinkage in Dimethacrylate-Based Dental Composites by Nanoindentation and PAL Study.

Effect of Shade and Light Curing Mode on the Degree of Conversion of Silorane-Based and Methacrylate-Based Resin Composites.

Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography.

Graphite nanoplatelet enabled embeddable fiber sensor for in situ curing monitoring and structural health monitoring of polymeric composites.

Visible light curing of Epon SU-8 based superparamagnetic polymer composites with random and ordered particle configurations.

Bond strength of dental nanocomposites repaired with a bulkfill composite.

Effect of chemical treatments on flax fibre reinforced polypropylene composites on tensile and dome forming behaviour.

Cold-Curing Structural Epoxy Resins: Analysis of the Curing Reaction as a Function of Curing Time and Thickness.

Curing efficiency of dual-cure resin cement under zirconia with two different light curing units.

Curing arteriovenous malformations using embolization.

Effect on bonding of curing through dentin.

Light curing explored in Halifax.

Curing TB with open science.

Curing HIV: Moving Forward Faster.