Kinetic Parameters and Monomeric Conversion of Different Dental Composites

Objectives: The purposes of this study were to evaluate the photopolymerization kinetics and degree of conversion of commercial dental composites photoactivated by two LED curing units (standard and soft-start).

Methods: Samples (n=3) of composites: RelyX, Z-350, Z-250 and Z-350 flow (3M/ESPE) were light exposed (40s) by a LED standard and soft-start (IFSC/USP- São Carlos/ Brazil) (600mW/cm²). Infrared spectras were obtained kinetically (Varian/ FTS 7000-ATR) at one scan/second at 1 cm^-1 resolution for a period of 5 minutes and were analyzed for: maximum conversion rate (%/sec)-Rpmáx, time into exposure when maximum rate occurred (sec)-tmáx and total degree of conversion (%)-DC at 300sec by comparison of aliphatic to aromatic absorption IR peak ratios, before and after polymerization.

Results:

Composites	Curing units	Rpmáx (%/sec)-(sd)	tmáx (sec)-(sd)	DC after 300sec(%)-(sd)
RelyX	Standard	5.3(±1.5)	6.0(±0.0)	64.6(±3.5)
	Soft-start	3.8(±0.7)	14.3(±1.5)	56.6(±1.5)
Z-350	Standard	3.5(±0.5)	5.6(±0.5)	43.6(±1.5)
	Soft-start	5.6(±2.0)	10.0(±2.0)	49.3(±1.5)
Z-250	Standard	6.5(±0.0)	5.6(±0.5)	46.3(±1.5)
	Soft-start	5.6(±2.0)	8.6(±2.0)	47.6(±1.5)
Z-350 flow	Standard	4.0(±1.0)	6.0(±1.0)	51.0(±3.6)
	Soft-start	5.3(±1.0)	8.6(±1.5)	50.3(±1.5)

The results were analyzed using two-way analysis of variance and Tukey test (p<0.05). RelyX presented better values and statistic differences than the other composites. And only RelyX showed significant differences when photoactived by LED standard and soft-start.

Conclusions: Kinetic parameters varied greatly among the composites as well as between then curing units, but these results did not interfere significantly in the final degree of conversion.