Insufficient cure under the condition of high irradiance and short irradiation time

Abstract 

Objectives

To investigate if and why a plasma arc curing (PAC) light tends to undercure methacrylate-based resins or resin composites.

Methods

Model dimethacrylate resins, commercial dental adhesives, and commercial resin composites were cured using a PAC light and a halogen light with the similar radiant exposures but different combinations of irradiance and irradiation time. The degree of double bond conversion (DC) was measured with FTIR spectroscopy and analyzed as a function of radiant exposure.

Results

The PAC light produced a lower DC than the halogen light for the model resin with the lowest viscosity and for three of the four adhesives. With a high irradiance, the PAC light could cure three of the four composites as thoroughly as its halogen counterpart. When the irradiance was reduced, however, three composites yielded a lower DC.

Conclusions

Insufficient cure by PAC lights or any curing lights with very high irradiance is likely to happen when too short an irradiation time is used. It is because under higher irradiance, the lifetime of free radicals is shorter.

Keywords: Photopolymerization, Composite, Adhesive, Degree of conversion, Irradiance, Irradiation, PAC light, Curing light, FTIR