Objectives: Exposure reciprocity law (ERL) promotes the common assumption that varying combinations of curing irradiance and exposure time provide similar material properties for the same radiant exposure. This study aims to investigate the applicability of ERL to commercial “flowable” resin composites and their higher viscosity counterparts.
Methods: A radiant exposure of 18J/cm2 using three different curing protocols (400mW/cm2 for 45s; 1500mW/cm2 for 12s; 3000mW/cm2 for 6s were used to polymerise various conventional restorative and low viscosity composite systems: Clearfil Majesty Posterior (CM-P) and Clearfil Majesty Flow (CM-F), Filtek Supreme Body (FS-P) and Filtek Supreme Flow (FS-F), Grandio (GR-P) and Grandio Flow (GR-F), Venus (VS-P) and Venus Flow (VS-F). Degree of conversion and polymerization kinetics were analysed using Fourier Transform near infrared spectroscopy in real-time for 70s.
Results:
Material | 400 mW/cm2 for 45s | 1500 mW/cm2 for 12s | 3000 mW/cm2 for 6s | ||||||
DC (%) | Rp max (s-1) | Time to Rp max (s) | DC (%) | Rp max (s-1) | Time to Rp max (s) | DC (%) | Rp max (s-1) | Time to Rp max (s) | |
CM-P | 44 a | 0.037 | 5.9 | 47 a | 0.091 | 3.0 | 46 a | 0.121 | 2.0 |
CM-F | 64 a | 0.037 | 5.9 | 65 a | 0.077 | 3.9 | 61 a | 0.075 | 2.9 |
FS-P | 42 a | 0.021 | 7.9 | 45 a | 0.057 | 3.0 | 42 a | 0.070 | 3.0 |
FS-F | 62 a | 0.029 | 10.6 | 62 a | 0.052 | 6.9 | 59 a | 0.075 | 4.9 |
GR-P | 50 a | 0.036 | 4.9 | 51 a | 0.070 | 3.0 | 49 a | 0.087 | 3.0 |
GR-F | 56 a | 0.022 | 11.8 | 49 b | 0.038 | 5.9 | 35 c | 0.043 | 4.9 |
VS-P | 45 a | 0.026 | 6.6 | 45 a | 0.054 | 2.8 | 44 a | 0.085 | 2.0 |
VS-F | 65 a | 0.023 | 14.8 | 60 b | 0.043 | 8.6 | 46 c | 0.055 | 5.8 |
Similar superscript letters across rows indicate no statistical significant difference (p>0.05)
Conclusions: Resin composites manufacturers accomplish lower material viscosity either by reducing the volume fraction of filler particles or by modification of the resin component. Flowable composite materials produced by decreasing resin matrix viscosity may not cure effectively using high irradiance and short exposure protocols.