Thickness Dependent Dielectric Monitoring of Light-Curing Composite Samples 151439
J. Steinhaus1,4, B. Möginger1, M. Großgarten1, M. Meurer1, M. Frentzen2, M. Rosentritt3, B. Hausnerová4
Objectives: The curing behaviour of photo-curing composites is significantly affected by the locally available light intensity, which especially depends on the employed light-curing unit and the light absorption of composites [1, 2]. The aim of this study was to investigate the effects of light intensity on the curing behaviour of a dental composite in different specimen depths using three different curing units. 70000
Materials:
60000
Counts
Polofil Halogen
• ~23% photo-curing acrylic resin
40000
20000
light conductor of curing unit
10000 0 360
stacked cover slips for sample thickness control
Mini-IDEX Sensor fixed with doublefaced adhesive tape
sample
Methods:
Bluephase
20i
in turbo-modus
~U interdigitated electrodes
sensor surface
Fig.1: (left) Measuring principle of DEA 231 Epsilon Cure Analyzer [3] (NETZSCH); and Mini-IDEX sensor (right); electrode distance: 100µm
Acknowledgements: This study was supported by the German Ministry of Education and Research. Grant No.: 17081X10. The authors also thank Dr. Andree Barg, Voco GmbH, for supporting this work by supplying dental materials and photo-curing devices and Stephan Knappe, Netzsch Gerätebau GmbH, for his very helpful suggestions concerning our DEA measuring setup.
References: [1] [2] [3] [4] [5]
D. C. Watts: In: Material Science and Technology, Vol.14, Dent. Rest. Mat., Ed.: D. F. Williams, VCH (1992), 224-228 J. Li et al., Dental Materials, Vol.25 (2009), 829-836 K. Zahouily, et al., European Coatings J., Vol.11 (2003), 14-18 J. Steinhaus et al., Materials Engineering, Vol.18 (2011), 30-35 M. Rosentritt et al., J. Mater. Sci., Vol. 41 (2006), 2805-2810
440
460
480
500
520
540
Fig.4: Light spectra of the curing units and absorption spectrum of camphorquinone. 9 ,8 0
polyimide oven protection layer
heating device
9 ,6 0
C e la lu x L E D t0 ~ 8 8s
9 ,4 0 log (ion viscosity)
Fig.2: measuring setup for different sample thicknesses
The DEA-curves were evaluated with respect to reaction-time-constant τ and maximal slope (Fig.3) [4, 5].
0 .5 0 m m
9 ,2 0
0 .7 5 m m
9 ,0 0
1 .0 0 m m 8 ,8 0
1 .2 5 m m
8 ,6 0
1 .5 0 m m
8 ,4 0
1 .7 5 m m 2 .0 0 m m
8 ,2 0 80
log µ∞ max. slope
log µτ ≈ 63% ∆ log µ ?
start photocuring
log
t0
tmax
τ
time [s]
Fig.3: Characteristic development of DEA ion viscosity measurements during photo-curing of a composite
For all lamps the maximum slope of the ionviscosity depends significantly on the depth within the sample (Fig.5). All DEA-curves shown in Fig.5 are average curves out of 3 runs. When exceeding the reaction-timeconstant τ all curves decrease significantly in slopes. Plotting reaction-time-constant and d maximum of the slope dt (log-µ) of the ionviscosities µ versus sample thickness, a nicely exponential dependency acc. to the Lambert Law is found (Fig.6) [1, 4]: (1)
I(d) = I0 e
− γd
with: I0 original intensity d sample thickness y absorption coeff.
Regarding the τ-curves, high saturation levels are reached after much shorter times with the Bluephase turbo LED unit than with the other lamps. Nevertheless the weaker Celalux-LED Affiliations and Contact:
12 0
140
160
Fig.5: Average ion viscosity curves of all tested sample thicknesses; exemplarily shown for Celalux LED. 45
∆log µ
log µ0
100
tim e [s ]
µ
Results and discussion: composite sample
420
1 0 ,0 0
(IVOCLAR VIVADENT, ~2000mW/cm²)
Their light spectra in comparison to the absorption spectrum of camphorquinone can be seen in Fig.4.
400
0.4
dashed lines fitted acc. to lambert law
tau of halogen-curves
40
straight lines fitted acc. to lambert law
max. slope of LED-curves
0.35
max. slope of LED-Turbo-curves
tau of LED-curves
35
0.3
tau of turbo-LED-curves
max. slope of Halogen-curves
30 d log µ / dt
• LED Celalux (VOCO , ~880mW/cm²)
microscope slides
reaction-time-constant [s]
• Polofil Lux halogen (VOCO, ~780mW/cm²)
380
Wavelength, λ [nm]
oven body
log (ion viscosity, µ)
The exemplary dental composite was investigated using a dielectric cure analyser (NETZSCH, DEA231, Germany) with a frequency of 1kHz. The surface of Mini-IDEX-sensors was covered with composite layers of 0.5-2mm (Fig.1). Three different curing units were used for curing at 23°C and at 36°C with only 1mm on a heating device (Fig.2) with a polymerisation time of 80s respectively 40s with the Turbo-LED:
Absorption Spectrum Camphorquinone
30000
• ~76% micro-scale glass particles • ~1% additives (initiator, stabilizer, etc.)
Celalux LED
50000
Arabesk Top OA2 micro-hybrid dental composite (Voco)
• LED
Bluphase LED, Turbo
25
0.25 0.2
20 0.15
15 10
0.1
5
0.05
0.5
0.75
1
1.25
1.5
1.75
2
0.5
0.75
1
1.25
1.5
1.75
2
sample thickness [mm]
sample thickness [mm]
Fig.6: Reaction-time-constant τ (left) and maximal slope dtd (log µ) (right) versus sample thickness. -
showed significantly higher max. slopes for sample thicknesses below 1.25mm due to higher end-viscosities.
Conclusions: The DEA-provides precise, intensity dependent data of the curing behavior. A transition from the primary-curing to postcuring is found when exceeding the reaction-time-constant indicating a glass transition change of the polymer resin at the curing temperature. The reaction-times depend significantly on the radicalized initiator concentration. Thus, the curing rate slows down with increasing sample depth but the higher slopes of ion-viscosity for the Celalux-LED give rise to the assumption of higher degrees of conversion for slower curing processes up to ~1mm sample depth. e-mail:
[email protected] 1.
Department of Natural Sciences, Bonn-Rhine-Sieg University of Applied Sciences, Rheinbach, Germany,
2.
Department of Periodontology, Operative and Preventive Dentistry, University of Bonn, Bonn, Germany,
3.
Department of Prosthetic Dentistry, University Medical Center Regensburg, Regensburg, Germany,
4.
Faculty of Technology, Tomas Bata University in Zlín, Zlín, Czech Republic
