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Nanogel-modified composite materials: Route to low shrinkage and stress
d e n t a l m a t e r i a l s 2 6 S ( 2 0 1 0 ) e1–e84
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83
84
12-h Post-polymerization of a nanohybrid resin composite: Conversion degree’s evaluation
Rugosimetric analysis of a microhybrid composite polished with four protocols
N. Scotti 1 , A. Venturello 2 , F. Pera 1 , D. Pasqualini 1 , E. Berutti 1
D. Angerame, D. Sossi, M. Cattaruzza, F. Spizzo, M. De Biasi
1
University of Trieste, Trieste, Italy
2
University of Turin, Italy Polytechnical School of Turin, Italy
Objectives: The aim of this in vitro study was to evaluate the conversion degree progression, during the post-photopolymerization, of a nanohybrid resin composite irradiated with a LED lamp (Trouffier-Boutry et al., J Dent Res; 2006). Materials and methods: A commercially available nanohybrid resin composite (Venus Diamond, Heraeus Kultzer, Hanau, Germany) was selected for this study. The resin composite was bulk placed inside aluminum rings, 10 mm diameter, with different thickness (1 mm, 2 mm). A total of 32 samples were prepared and divided in 2 groups of sixteen samples each. The curing device employed in this study was a LED light (Translux Power Blue, Haereus Kultzer, Hanau, Germany). Each group was divided in 2 subgroups on the basis of the irradiation time (10 s, 40 s). The degree of conversion at the bottom surface of each sample was accomplished by Attenuated Total Reflection Fourier Transform Infrared (ATR F-TIR) analysis (Eqinox 55, Bruker Optics S.p.A.) immediately after photopolymerization and every 10 min for 12 h. In this study the conversion degree obtained immediately (T = 0), after 30 min (T = 1) and after 12 h (T = 2) from the photo-polymerization was considered. Differences among groups were analyzed with the non-parametric Mann–Whitney U-test (p < 0.05). Results:
10 s 40 s 10 s 40 s
1 mm 1 mm 2 mm 2 mm
T=0
T=1
T=2
31.8% 24.1% 40.5% 38.6%
44.6% 35.9% 47.8% 45.3%
52.4% 43.1% 54.2% 52.3%
Conclusions: Within 1 mm specimens, 10 s curing time produced in T = 0 and T = 1 a conversion degree significantly lower than the conversion degree obtained with a curing time of 40 s (p < 0.05); however, during the post-polymerization process, the mean conversion degree values got closer being not statistically different after 12 h (p = 0.09). On the contrary, 2 mm samples did not achieve a satisfactory conversion degree after 10 s curing, which is significantly lower than 40 s curing time (p < 0.05). Even during post-polymerization the conversion degree did not significantly increase, concluding that 2 mm composite stratification needs 40 s curing time to achieve a sufficient conversion degree. doi:10.1016/j.dental.2010.08.091
Objectives: Composite restorations with complex anatomy are difficult to polish; rigidity of rubber points can alter surface texture. The purpose of this study was to investigate the surface roughness of a microhybrid composite polished with abrasive pastes or rubber points, with or without superficial light-cured resin. Materials and methods: Forty discs (diameter 7 mm × 1.5 mm) of composite (Filtek Z250, 3M ESPE) were light cured and randomly divided into four groups (n = 10): group 1 (G1), rubber points (70, 40, and 5 m, Identoflex AG); group 2 (G2), abrasive pastes (80, 35, and 4 m, FGM); group 3 (G3), rubber points (=G1) and Seal Coat Fast resin (DEI Italia); group 4 (G4), abrasive pastes (=G2) and Seal Coat Fast resin. The specimens were analyzed using a rugosimeter (Talysurf CLI 1000, Taylor Hobson) considering a linear parameter (Ra ); nine standardized 0.5 mm long measurements were made for each specimen. A 0.2 m roughness value was assumed as clinically acceptable threshold. Collected data were statistically analyzed with Kruskal–Wallis and Mann–Whitney tests (p < 0.05). Samples were then observed with SEM, running in low vacuum mode, without any sample preparation and by means of backscattered electron detector. Results: Roughness values were lower than 0.2 m in all groups. Mean Ra values ± SD (m) were: G1 = 0.07 ± 0.02, G2 = 0.06 ± 0.01; G3 = 0.06 ± 0.04; G4 = 0.03 ± 0.01. Significant differences among groups were found: G1 vs. G2 (p < 0.05); G1, G2 and G3 vs. G4 (p < 0.01). Grooves and loss of superficial filler were found in G1 and G2; grooves in G1 were parallel. Specimens treated with surface resin coat presented smoother aspect than untreated specimens. Conclusions: All tested techniques offered roughness values under clinically acceptable threshold on flat surfaces. Abrasive pastes seem to be a valid alternative to rubber points when used on restoration with complex anatomy. Best results were obtained in G4; resin coating improves surface smoothness obtained with pastes. doi:10.1016/j.dental.2010.08.092 85 Nanogel-modified composite materials: Route to low shrinkage and stress J.W. Stansbury, R.R. Moraes, J.W. Garcia, M.D. Barros, S.H. Lewis, C.S. Pfeifer University of Colorado, Aurora, USA Objectives: The use of reactive pre-polymerized, nanosized particles to reduce reactive group concentration (and, as a consequence, shrinkage and stress) is proposed here. As opposed to ground, micro-sized, cured composite particles previously used as additives, nanogels allow for a higher amount of prepolymer to be added, without interfering with inorganic filler
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d e n t a l m a t e r i a l s 2 6 S ( 2 0 1 0 ) e1–e84
loading. In addition, because they bear methacrylate reactive groups in their backbones, these particles are covalently bound to the resulting network, with potential mechanical reinforcement. Materials and methods: Nanogels were synthesized by photoactivating a 30:70 mol% mixture of urethane dimethacrylate and isobornyl methacrylate, respectively, in solution with toluene (1:4 vol%). Mercaptoethanol was added to control molecular weight and provide reaction sites for isocyanoethyl methacrylate, rendering the material polymerizable. After purification, the resulting powder was added to triethyleneglycol dimethacrylate at 0 (control), 5, 10, 20, 30 and 40 wt%. Materials were tested as neat resins or composites (70 wt% silanated barium glass; 0.4 m average diameter). Real-time monitoring of polymerization kinetics was carried out using near-infrared (NIR) spectroscopy. Volumetric shrinkage was evaluated in a linometer. Polymerization stress was obtained with a NIR-coupled tensometer. Flexural modulus was obtained by three-point bending. In all cases, samples were irradiated for 5 min at 50 mW/cm2 (Acticure 4000, EFOS). Results: The onset of autodecceleration in the nanogelmodified materials (resins and composites) occurred at lower conversion compared with the control, but no differences in final conversion were observed (approximately 70% for all materials). The maximum rate of polymerization decreased, as expected, since the presence of nanogel limits the potential exotherm. Because of the polymerizable methacrylate groups at readily accessible chain ends, the prepolymer behaves as a macromolecular monomer (macromer) and even at the highest nanogel loading mechanical strength properties remain unaffected, which was true both for resins and composites, indicating that effective covalent attachment is maintained between the filler and the nanogel-modified polymeric matrix. As expected, volumetric shrinkage and polymerization stress decreased monotonically with nanogel content. Stress reductions reached 50% with 40 wt% nanogel loading. Conclusions: Nano-scaled, highly crosslinked, reactive polymeric particles have efficiently reduced shrinkage and stress with no compromise to final degree of conversion or mechanical properties of neat resins or composites. The relatively simple synthesis procedure and the swellability in common dimethacrylates allows for commercial dental materials to be envisioned in the near future, especially because the incorporation of nanogels would not require any modifications in the photopolymerization procedure used currently in the clinic. Support: NIH/NIDCR 1R21-DE18354 and RC1-DE020480.
induced stress in teeth restored with resin composites, due to the differences between the coefficients of thermal expansion (CTE) of tooth tissues and the restorative materials, seem to be related to induction of microleakage and mechanical degradation. The purpose of this study was to measure the CTE values of 4 types of composite resins and the effect of light intensity of the LED curing device on the values of CTE. Materials and methods: A nanohybrid resin composite, a giomer, an experimental ormocer and silorane (color A2) were tested. Eight 4 mm thick specimen were made from each material and divided into two groups and polymerized with a high and a low energy LED curing device. Dilatometer Netzsch DIL 402c was used to determine the values of CTE of composite resin materials at a 20–85 ◦ C temperature range, with a heating rate of 2 ◦ C/min. Results:
doi:10.1016/j.dental.2010.08.093
Manipulation of a dental composite resin using bovine enamel as reinforcing filler
86 Coefficient of thermal expansion of different types of composite resins K. Tolidis 1 , T. Vaimakis 2 , P. Gerasimou 1 , C. Boutsiouki 1 1 2
Aristotle University of Thessaloniki, Greece University of Ioannina, Greece
Objectives: Temperature changes induced mainly by hot and cold drinks are frequent in the oral cavity. Thermally
Group
Ormocer low Ormocer high Giomer low Giomer high Nanohybrid low Nanohybrid high Silorane low Silorane high
Results (10−6 /◦ ) at 36.6 ◦ C
Results (10−6 /◦ ) at 55.0 ◦ C
Mean
Standard deviation
Mean
Standard deviation
14.89 8.760 15.49 38.67 5.434 12.04 16.47 5.753
3.58 5.075 9.453 23.44 3.962 15.49 12.44 2.640
35.82 23.77 47.06 48.87 22.20 30.69 47.54 41.74
3.217 5.564 6.159 14.13 9.937 13.12 9.128 28.76
Despite the differences in CTE diagrams, statistical analysis showed no significant differences.
Conclusions: All the tested materials demonstrated a reduction in CTE values at the beginning of the temperature rise. During the entire measurement period, CTE values of the resin composites were still higher than those of enamel (11.4) and dentine, as expected. CTE values of the samples cured with high energy LEDs exhibited fluctuation for all materials, especially for silorane. Ormocer seemed to have the less fluctuations of CTE, even less when polymerized with low power LED. Silorane and ormocer polymerized with high power LED demonstrated the lower values of CTE. doi:10.1016/j.dental.2010.08.094 87
J.T. Tribioli, D.P. Jacomassi, V.S. Bagnato, C. Kurachi Physics Institute of São Carlos-University of São Paulo, Brazil Objectives: We propose a new dental composite resin based on the replacement of the conventional fillers by bovine enamel particles. Materials and methods: Charged particles were obtained from grinded bovine enamel, sinalized and incorporated in a resin matrix of Bis-GMA, TEGDMA, UDMA. Camphorquinone
e39
83
84
12-h Post-polymerization of a nanohybrid resin composite: Conversion degree’s evaluation
Rugosimetric analysis of a microhybrid composite polished with four protocols
N. Scotti 1 , A. Venturello 2 , F. Pera 1 , D. Pasqualini 1 , E. Berutti 1
D. Angerame, D. Sossi, M. Cattaruzza, F. Spizzo, M. De Biasi
1
University of Trieste, Trieste, Italy
2
University of Turin, Italy Polytechnical School of Turin, Italy
Objectives: The aim of this in vitro study was to evaluate the conversion degree progression, during the post-photopolymerization, of a nanohybrid resin composite irradiated with a LED lamp (Trouffier-Boutry et al., J Dent Res; 2006). Materials and methods: A commercially available nanohybrid resin composite (Venus Diamond, Heraeus Kultzer, Hanau, Germany) was selected for this study. The resin composite was bulk placed inside aluminum rings, 10 mm diameter, with different thickness (1 mm, 2 mm). A total of 32 samples were prepared and divided in 2 groups of sixteen samples each. The curing device employed in this study was a LED light (Translux Power Blue, Haereus Kultzer, Hanau, Germany). Each group was divided in 2 subgroups on the basis of the irradiation time (10 s, 40 s). The degree of conversion at the bottom surface of each sample was accomplished by Attenuated Total Reflection Fourier Transform Infrared (ATR F-TIR) analysis (Eqinox 55, Bruker Optics S.p.A.) immediately after photopolymerization and every 10 min for 12 h. In this study the conversion degree obtained immediately (T = 0), after 30 min (T = 1) and after 12 h (T = 2) from the photo-polymerization was considered. Differences among groups were analyzed with the non-parametric Mann–Whitney U-test (p < 0.05). Results:
10 s 40 s 10 s 40 s
1 mm 1 mm 2 mm 2 mm
T=0
T=1
T=2
31.8% 24.1% 40.5% 38.6%
44.6% 35.9% 47.8% 45.3%
52.4% 43.1% 54.2% 52.3%
Conclusions: Within 1 mm specimens, 10 s curing time produced in T = 0 and T = 1 a conversion degree significantly lower than the conversion degree obtained with a curing time of 40 s (p < 0.05); however, during the post-polymerization process, the mean conversion degree values got closer being not statistically different after 12 h (p = 0.09). On the contrary, 2 mm samples did not achieve a satisfactory conversion degree after 10 s curing, which is significantly lower than 40 s curing time (p < 0.05). Even during post-polymerization the conversion degree did not significantly increase, concluding that 2 mm composite stratification needs 40 s curing time to achieve a sufficient conversion degree. doi:10.1016/j.dental.2010.08.091
Objectives: Composite restorations with complex anatomy are difficult to polish; rigidity of rubber points can alter surface texture. The purpose of this study was to investigate the surface roughness of a microhybrid composite polished with abrasive pastes or rubber points, with or without superficial light-cured resin. Materials and methods: Forty discs (diameter 7 mm × 1.5 mm) of composite (Filtek Z250, 3M ESPE) were light cured and randomly divided into four groups (n = 10): group 1 (G1), rubber points (70, 40, and 5 m, Identoflex AG); group 2 (G2), abrasive pastes (80, 35, and 4 m, FGM); group 3 (G3), rubber points (=G1) and Seal Coat Fast resin (DEI Italia); group 4 (G4), abrasive pastes (=G2) and Seal Coat Fast resin. The specimens were analyzed using a rugosimeter (Talysurf CLI 1000, Taylor Hobson) considering a linear parameter (Ra ); nine standardized 0.5 mm long measurements were made for each specimen. A 0.2 m roughness value was assumed as clinically acceptable threshold. Collected data were statistically analyzed with Kruskal–Wallis and Mann–Whitney tests (p < 0.05). Samples were then observed with SEM, running in low vacuum mode, without any sample preparation and by means of backscattered electron detector. Results: Roughness values were lower than 0.2 m in all groups. Mean Ra values ± SD (m) were: G1 = 0.07 ± 0.02, G2 = 0.06 ± 0.01; G3 = 0.06 ± 0.04; G4 = 0.03 ± 0.01. Significant differences among groups were found: G1 vs. G2 (p < 0.05); G1, G2 and G3 vs. G4 (p < 0.01). Grooves and loss of superficial filler were found in G1 and G2; grooves in G1 were parallel. Specimens treated with surface resin coat presented smoother aspect than untreated specimens. Conclusions: All tested techniques offered roughness values under clinically acceptable threshold on flat surfaces. Abrasive pastes seem to be a valid alternative to rubber points when used on restoration with complex anatomy. Best results were obtained in G4; resin coating improves surface smoothness obtained with pastes. doi:10.1016/j.dental.2010.08.092 85 Nanogel-modified composite materials: Route to low shrinkage and stress J.W. Stansbury, R.R. Moraes, J.W. Garcia, M.D. Barros, S.H. Lewis, C.S. Pfeifer University of Colorado, Aurora, USA Objectives: The use of reactive pre-polymerized, nanosized particles to reduce reactive group concentration (and, as a consequence, shrinkage and stress) is proposed here. As opposed to ground, micro-sized, cured composite particles previously used as additives, nanogels allow for a higher amount of prepolymer to be added, without interfering with inorganic filler
e40
d e n t a l m a t e r i a l s 2 6 S ( 2 0 1 0 ) e1–e84
loading. In addition, because they bear methacrylate reactive groups in their backbones, these particles are covalently bound to the resulting network, with potential mechanical reinforcement. Materials and methods: Nanogels were synthesized by photoactivating a 30:70 mol% mixture of urethane dimethacrylate and isobornyl methacrylate, respectively, in solution with toluene (1:4 vol%). Mercaptoethanol was added to control molecular weight and provide reaction sites for isocyanoethyl methacrylate, rendering the material polymerizable. After purification, the resulting powder was added to triethyleneglycol dimethacrylate at 0 (control), 5, 10, 20, 30 and 40 wt%. Materials were tested as neat resins or composites (70 wt% silanated barium glass; 0.4 m average diameter). Real-time monitoring of polymerization kinetics was carried out using near-infrared (NIR) spectroscopy. Volumetric shrinkage was evaluated in a linometer. Polymerization stress was obtained with a NIR-coupled tensometer. Flexural modulus was obtained by three-point bending. In all cases, samples were irradiated for 5 min at 50 mW/cm2 (Acticure 4000, EFOS). Results: The onset of autodecceleration in the nanogelmodified materials (resins and composites) occurred at lower conversion compared with the control, but no differences in final conversion were observed (approximately 70% for all materials). The maximum rate of polymerization decreased, as expected, since the presence of nanogel limits the potential exotherm. Because of the polymerizable methacrylate groups at readily accessible chain ends, the prepolymer behaves as a macromolecular monomer (macromer) and even at the highest nanogel loading mechanical strength properties remain unaffected, which was true both for resins and composites, indicating that effective covalent attachment is maintained between the filler and the nanogel-modified polymeric matrix. As expected, volumetric shrinkage and polymerization stress decreased monotonically with nanogel content. Stress reductions reached 50% with 40 wt% nanogel loading. Conclusions: Nano-scaled, highly crosslinked, reactive polymeric particles have efficiently reduced shrinkage and stress with no compromise to final degree of conversion or mechanical properties of neat resins or composites. The relatively simple synthesis procedure and the swellability in common dimethacrylates allows for commercial dental materials to be envisioned in the near future, especially because the incorporation of nanogels would not require any modifications in the photopolymerization procedure used currently in the clinic. Support: NIH/NIDCR 1R21-DE18354 and RC1-DE020480.
induced stress in teeth restored with resin composites, due to the differences between the coefficients of thermal expansion (CTE) of tooth tissues and the restorative materials, seem to be related to induction of microleakage and mechanical degradation. The purpose of this study was to measure the CTE values of 4 types of composite resins and the effect of light intensity of the LED curing device on the values of CTE. Materials and methods: A nanohybrid resin composite, a giomer, an experimental ormocer and silorane (color A2) were tested. Eight 4 mm thick specimen were made from each material and divided into two groups and polymerized with a high and a low energy LED curing device. Dilatometer Netzsch DIL 402c was used to determine the values of CTE of composite resin materials at a 20–85 ◦ C temperature range, with a heating rate of 2 ◦ C/min. Results:
doi:10.1016/j.dental.2010.08.093
Manipulation of a dental composite resin using bovine enamel as reinforcing filler
86 Coefficient of thermal expansion of different types of composite resins K. Tolidis 1 , T. Vaimakis 2 , P. Gerasimou 1 , C. Boutsiouki 1 1 2
Aristotle University of Thessaloniki, Greece University of Ioannina, Greece
Objectives: Temperature changes induced mainly by hot and cold drinks are frequent in the oral cavity. Thermally
Group
Ormocer low Ormocer high Giomer low Giomer high Nanohybrid low Nanohybrid high Silorane low Silorane high
Results (10−6 /◦ ) at 36.6 ◦ C
Results (10−6 /◦ ) at 55.0 ◦ C
Mean
Standard deviation
Mean
Standard deviation
14.89 8.760 15.49 38.67 5.434 12.04 16.47 5.753
3.58 5.075 9.453 23.44 3.962 15.49 12.44 2.640
35.82 23.77 47.06 48.87 22.20 30.69 47.54 41.74
3.217 5.564 6.159 14.13 9.937 13.12 9.128 28.76
Despite the differences in CTE diagrams, statistical analysis showed no significant differences.
Conclusions: All the tested materials demonstrated a reduction in CTE values at the beginning of the temperature rise. During the entire measurement period, CTE values of the resin composites were still higher than those of enamel (11.4) and dentine, as expected. CTE values of the samples cured with high energy LEDs exhibited fluctuation for all materials, especially for silorane. Ormocer seemed to have the less fluctuations of CTE, even less when polymerized with low power LED. Silorane and ormocer polymerized with high power LED demonstrated the lower values of CTE. doi:10.1016/j.dental.2010.08.094 87
J.T. Tribioli, D.P. Jacomassi, V.S. Bagnato, C. Kurachi Physics Institute of São Carlos-University of São Paulo, Brazil Objectives: We propose a new dental composite resin based on the replacement of the conventional fillers by bovine enamel particles. Materials and methods: Charged particles were obtained from grinded bovine enamel, sinalized and incorporated in a resin matrix of Bis-GMA, TEGDMA, UDMA. Camphorquinone