Novel photoinitiator system (RAP) enhances dental composite properties

Rapid amplified photopolymerization (RAP) initiator technology has been presented to enhance light-curing efficiency of dental composites by increasing the free radicals produced from each activated camphoroquinone (CQ) molecule (AADR #1392-1393, 2006).  But equivalent composites with and without the technology have not been compared.  Objectives: The purpose of this study was to compare the flexure strength and modulus of two light-cured dental composites with RAP and without (CQ only). The hypothesis to be tested was that the mechanical properties of the composites are enhanced when RAP is added, and that shorter curing times (lower radiant exposure) can be used for composites with RAP.

Methods: The flexure strength-FS and modulus-E of two experimental composites (Tokuyama Dental) were evaluated: ESQ-201 (82 wt% supra-nanofillers; 200 nm) and EPQ-101 (83 wt% hybrid containing supra-nanofillers).  Each composite was formulated with the RAP initiator system (RAP+CQ) and without (CQ only).  Specimens (25x2x2mm) were light-cured in glass tubes for either 20 or 40 seconds/side (Triad II, Dentsply) and stored 24 hours in deionized water at 37°C before testing at 0.25 mm/min in 3-point bending (n=10).  Results for each composite were compared with 2-way ANOVA/Tukey's (p≤0.05; interactions were not significant).

Results: 

	Flexure Strength (MPa)		Flexure Modulus (GPa)
	20s	40s	20s	40s
ESQ-201 RAP	86.20±9.39	98.27±7.98	6.39±0.60	7.42±0.62
ESQ-201 CQ	73.00±9.25	89.04±10.8	4.69±0.61	6.28±0.70
EPQ-101 RAP	124.62±22.66	126.12±29.00	11.04±1.94	15.53±0.96
EPQ-101 CQ	94.55±28.13	104.57±34.60	8.91±1.54	11.81±1.34

For FS and E, the following relationships were significant for both composites:  RAP>CQ; 40s>20s (except 40s=20s for EPQ-101 FS), and RAP-20s=CQ-40s (except RAP 20s³CQ 40s for EPQ-101 FS).

Conclusions:  This study verified that the inclusion of the RAP initiator technology improved the flexure strength and flexure modulus vs. CQ only for two experimental composites, and enabled the use of one half the curing time to produce equivalent properties.  Supported by Tokuyama Dental Corporation.