Objective: Insufficient cure of dental bonding agents undermines many of their properties and therefore needs be prevented. The present work investigated the effect of residual solvent on the rate of photocure.
Methods: Four DBAs were tested, including One-Step (OS, Bisco), Xeno III (XN, Dentsply), OptiBond FL (OB, Kerr), and Clearfil Protect Bond (PB, Kuraray). OS and XN contained solvents, which were either mostly retained or evaporated before curing. All the DBAs were photocured with a halogen light of 50 mW/cm2 in nitrogen. The rate of curing was assessed with differential scanning calorimetry (DSC) by measuring the heat of polymerization. To compare among the DBAs, a scaled degree of conversion (SDC) was used, which was defined as the ratio of the exotherm at a given time vs. that at 300s cutoff time.
Results:
DBA | Solvent, % | Irradiation time, s | SDC, % | |||
20s | 40s | 60s | 120s | |||
OS | > 20 | 120 | 14 | 37 | 58 | 94 |
XN | > 20 | 120 | 4 | 15 | 27 | 60 |
| ||||||
OS | < 5 | 30 | 51 | 86 | 94 | 97 |
XN | < 5 | 30 | 34 | 79 | 91 | 95 |
OB | 0 | 30 | 66 | 94 | 98 | 99 |
PB | 0 | 30 | 52 | 91 | 97 | 99 |
The DBAs with solvent cured much more slowly than those without, even much longer irradiation did not significantly increase the rate.
Conclusion: The presence of residual solvent in a DBA could substantially reduce its rate of cure. It is essential to remove the solvent as much as possible to ensure an adequate conversion.