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Effect of PWM-controlled light on the polymerization kinetics of composite
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d e n t a l m a t e r i a l s 3 3 S ( 2 0 1 7 ) e1–e92
Materials and methods: Zirconia strips of ICE Zirkon Transluzent (Zirkonzahn), with a cross section of 3.0 mm × 0.5 mm, dry prepared from presintered blanks, were sprayed with a solution of tetraethyl orthosilicate (TEOS), ethanol and HCl, mixed with water at one surface in three different conditions, G1: in green state, G2: sintered and etched with KHF2 and G3: as-sintered. Thereafter they were sintered a second time at 1500 ◦ C. As-sintered samples without spray-treatment served as a control group, GC. Six specimens in all groups were veneered with Vita VM9, a feldspar porcelain, according to manufacturer’s instructions (Vita Zahnfabrik). Results: All silicatized groups were covered with a silicatelayer having an even thickness of 0.5–0.9 nm measured by XPS-analysis. Also the non-silicatized control group was covered with a layer, though thinner and containing silicate (0.1 nm), alumina, as well as carbon. All groups revealed equal bond strength (27–31 MPa). The modulus of elasticity for G1was reduced compared to the other groups. Conclusions: High temperature silicatization revealed an even zirconiumsilicate layer at the surface. However, the material seemed to be contaminated from constituents in the air, which may be the cause why bond values were not improved by any of the surface treatments which were investigated in this project. Surface contaminations may have been decisive for the bond strength since all groups revealed equal bond strength despite quite different surface treatments. http://dx.doi.org/10.1016/j.dental.2017.08.087 87 Effect of PWM-controlled light on the polymerization kinetics of composite I.B. Lee ∗ , C.H. Lee School of Dentistry, Seoul National University, Republic of Korea Purpose/aim: To investigate the effect of pulse width modulation (PWM)-controlled LED curing light on the polymerization shrinkage (stress) kinetics of composite. Materials and methods: A pulse width modulation (PWM) controlled LED curing light system was made, which consisted of a high power LED (2000 mW/cm2 ) and a transistor switched by a microcontroller and software. The duty ratio of the PWM light and total cure time were varied as follows: 10% (100 s), 50% (20 s), 100% (10 s), increasing ramp mode from 0% to 100% (20 s), and decreasing ramp mode from 100% to 0% (20 s). The switching frequency of the PWM light was set at 50 Hz and the total radiant energy was identical for all groups. A universal composite (Z250, 3M ESPE) was used, and the kinetics of polymerization shrinkage (stress) was measured using an LVDT probe and a stress analyzer with feedback mechanism. The polymerization shrinkage (stress), maximum shrinkage (stress) rate, and the time to reach peak shrinkage (stress) rate were determined. Results: The polymerization shrinkage stress, maximum shrinkage stress rate, and the time to reach peak shrinkage stress rate were shown in Table 1. The change in duty ratio could not influence the polymerization shrink-
Table 1 Pulse width modulation (duty ratio/time)
Stress (MPa)
Maximum stress rate (MPa/s)
Time to reach peak stress rate (s)
10%/100 s 50%/20 s 100%/10 s Increasing ramp mode (0%–100%)/20 s Decreasing ramp mode (100%–0%)/20 s
3.27 (0.26) 3.41 (0.20) 3.73 (0.21) 3.39 (0.31)
0.08 (0.01) 0.22 (0.02) 0.30 (0.02) 0.19 (0.02)
16.18 (1.74) 5.19 (0.77) 4.68 (0.96) 12.70 (1.60)
3.59 (0.21)
0.27 (0.03)
4.99 (0.37)
age of composite; however the maximum shrinkage rate increased with increasing the duty ratio while the time to peak shrinkage rate decreased with increasing the duty ratio. The increasing ramp mode showed much lower maximum shrinkage rate and delayed peak time compared to the decreasing ramp mode. The change in duty ratio influenced the polymerization shrinkage stress kinetics of composite; the polymerization shrinkage stress and maximum shrinkage stress rate increased with increasing the duty ratio while the time to peak shrinkage stress rate decreased with increasing the duty ratio. The increasing ramp mode showed lower shrinkage stress and maximum shrinkage rate, and delayed peak time compared to the decreasing ramp mode. Conclusions: The light irradiance controlled by PWM greatly influences the polymerization shrinkage (stress) kinetics of composite. With identical total radiant energy, the reduced light intensity or increasing ramp mode can reduce the polymerization shrinkage stress compared to the high light intensity or decreasing ramp mode. http://dx.doi.org/10.1016/j.dental.2017.08.088 88 Effect of chitosan solution as irrigant on dentin surface V.L.C. Araújo ∗ , R.G. Palma-Dibb, R.G. Silva University of São Paulo, Brazil Purpose/aim: To evaluate, in vitro, the effect of 0.2% chitosan (CH), 1% sodium hypochlorite (NaOCl) and 17% EDTA as irrigant, on dentin surface and the bonding interface of the filling material/dentin by means of confocal laser microscopy (CLM). Materials and methods: Twenty-four human maxillary canines, divided into 4 groups (n = 6) were submitted to a crown cut, and roots prepared with K3 rotary files up to #60.04. During the preparation, the roots were irrigated with 1% NaOCl and 0.2% CH, and the final irrigation was performed by 17% EDTA and 0.2% CH irrigation: G1 – NaOCl + EDTA + NaOCl, G2 – NaOCl + CH + NaOCl, G3 – CH + CH + CH, G4 – CH + EDTA + CH. The samples were cut longitudinally to analyze the number, perimeter of exposed tubules at different times, the surface roughness before and after each treatment set besides the endodontic sealer penetration and the evaluation of the filling
d e n t a l m a t e r i a l s 3 3 S ( 2 0 1 7 ) e1–e92
Materials and methods: Zirconia strips of ICE Zirkon Transluzent (Zirkonzahn), with a cross section of 3.0 mm × 0.5 mm, dry prepared from presintered blanks, were sprayed with a solution of tetraethyl orthosilicate (TEOS), ethanol and HCl, mixed with water at one surface in three different conditions, G1: in green state, G2: sintered and etched with KHF2 and G3: as-sintered. Thereafter they were sintered a second time at 1500 ◦ C. As-sintered samples without spray-treatment served as a control group, GC. Six specimens in all groups were veneered with Vita VM9, a feldspar porcelain, according to manufacturer’s instructions (Vita Zahnfabrik). Results: All silicatized groups were covered with a silicatelayer having an even thickness of 0.5–0.9 nm measured by XPS-analysis. Also the non-silicatized control group was covered with a layer, though thinner and containing silicate (0.1 nm), alumina, as well as carbon. All groups revealed equal bond strength (27–31 MPa). The modulus of elasticity for G1was reduced compared to the other groups. Conclusions: High temperature silicatization revealed an even zirconiumsilicate layer at the surface. However, the material seemed to be contaminated from constituents in the air, which may be the cause why bond values were not improved by any of the surface treatments which were investigated in this project. Surface contaminations may have been decisive for the bond strength since all groups revealed equal bond strength despite quite different surface treatments. http://dx.doi.org/10.1016/j.dental.2017.08.087 87 Effect of PWM-controlled light on the polymerization kinetics of composite I.B. Lee ∗ , C.H. Lee School of Dentistry, Seoul National University, Republic of Korea Purpose/aim: To investigate the effect of pulse width modulation (PWM)-controlled LED curing light on the polymerization shrinkage (stress) kinetics of composite. Materials and methods: A pulse width modulation (PWM) controlled LED curing light system was made, which consisted of a high power LED (2000 mW/cm2 ) and a transistor switched by a microcontroller and software. The duty ratio of the PWM light and total cure time were varied as follows: 10% (100 s), 50% (20 s), 100% (10 s), increasing ramp mode from 0% to 100% (20 s), and decreasing ramp mode from 100% to 0% (20 s). The switching frequency of the PWM light was set at 50 Hz and the total radiant energy was identical for all groups. A universal composite (Z250, 3M ESPE) was used, and the kinetics of polymerization shrinkage (stress) was measured using an LVDT probe and a stress analyzer with feedback mechanism. The polymerization shrinkage (stress), maximum shrinkage (stress) rate, and the time to reach peak shrinkage (stress) rate were determined. Results: The polymerization shrinkage stress, maximum shrinkage stress rate, and the time to reach peak shrinkage stress rate were shown in Table 1. The change in duty ratio could not influence the polymerization shrink-
Table 1 Pulse width modulation (duty ratio/time)
Stress (MPa)
Maximum stress rate (MPa/s)
Time to reach peak stress rate (s)
10%/100 s 50%/20 s 100%/10 s Increasing ramp mode (0%–100%)/20 s Decreasing ramp mode (100%–0%)/20 s
3.27 (0.26) 3.41 (0.20) 3.73 (0.21) 3.39 (0.31)
0.08 (0.01) 0.22 (0.02) 0.30 (0.02) 0.19 (0.02)
16.18 (1.74) 5.19 (0.77) 4.68 (0.96) 12.70 (1.60)
3.59 (0.21)
0.27 (0.03)
4.99 (0.37)
age of composite; however the maximum shrinkage rate increased with increasing the duty ratio while the time to peak shrinkage rate decreased with increasing the duty ratio. The increasing ramp mode showed much lower maximum shrinkage rate and delayed peak time compared to the decreasing ramp mode. The change in duty ratio influenced the polymerization shrinkage stress kinetics of composite; the polymerization shrinkage stress and maximum shrinkage stress rate increased with increasing the duty ratio while the time to peak shrinkage stress rate decreased with increasing the duty ratio. The increasing ramp mode showed lower shrinkage stress and maximum shrinkage rate, and delayed peak time compared to the decreasing ramp mode. Conclusions: The light irradiance controlled by PWM greatly influences the polymerization shrinkage (stress) kinetics of composite. With identical total radiant energy, the reduced light intensity or increasing ramp mode can reduce the polymerization shrinkage stress compared to the high light intensity or decreasing ramp mode. http://dx.doi.org/10.1016/j.dental.2017.08.088 88 Effect of chitosan solution as irrigant on dentin surface V.L.C. Araújo ∗ , R.G. Palma-Dibb, R.G. Silva University of São Paulo, Brazil Purpose/aim: To evaluate, in vitro, the effect of 0.2% chitosan (CH), 1% sodium hypochlorite (NaOCl) and 17% EDTA as irrigant, on dentin surface and the bonding interface of the filling material/dentin by means of confocal laser microscopy (CLM). Materials and methods: Twenty-four human maxillary canines, divided into 4 groups (n = 6) were submitted to a crown cut, and roots prepared with K3 rotary files up to #60.04. During the preparation, the roots were irrigated with 1% NaOCl and 0.2% CH, and the final irrigation was performed by 17% EDTA and 0.2% CH irrigation: G1 – NaOCl + EDTA + NaOCl, G2 – NaOCl + CH + NaOCl, G3 – CH + CH + CH, G4 – CH + EDTA + CH. The samples were cut longitudinally to analyze the number, perimeter of exposed tubules at different times, the surface roughness before and after each treatment set besides the endodontic sealer penetration and the evaluation of the filling