The influence of plasma arc vs. halogen standard or soft-start irradiation on polymerization shrinkage kinetics of polymer matrix composites.
OBJECTIVE
To determine polymerization shrinkage kinetics and hardness of photo-activated polymer matrix composites (PMC) after plasma arc vs. halogen standard or soft-start irradiation.


METHODS
Polymerization shrinkage was measured using the 'deflecting disk technique', and Knoop hardness was measured at the bottom of 1.5 mm thick specimens stored for 24 h at 37 degrees C. The materials comprised one micro-filled (Silux Plus) and four fine hybrid PMC (Definite, Herculite XRV, Solitaire 2 and Z250). The irradiation protocols included halogen standard irradiation at three intensities (TriLight, ESPE), ramp curing (dito), step curing (HiLight, ESPE), pulse polymerization (VIP Light, BISCO) and plasma curing (Apollo 95E, DMDS; PAC Light, ADT).


RESULTS
Standard halogen irradiation at reduced intensity delayed the start and slowed down the progression of shrinkage strain, but (except for Z250) as well produced lower hardness. Soft-start halogen curing produced similar kinetics but maintained hardness. Plasma arc irradiation resulted in an immediate start and a rapid progression of polymerization contraction, but produced low hardness values in Definite (cured by the ADT unit) and in Solitaire 2 (both units). Z250 featured the highest, Silux Plus the lowest maximum rate of contraction. Despite soft-start irradiation, contraction of Z250 progressed faster than that of Silux Plus with halogen standard irradiation at high intensity.


CONCLUSIONS
Soft-start halogen irradiation protocols provide better chances for compensation of shrinkage stress by flow within PMC without compromising hardness and may contribute to a better marginal integrity of the restorations. Irradiation protocols should be individually adjusted to compensate for the different curing characteristics of PMC.
Hofmann
Norbert
N
Department of Operative Dentistry and Periodontology, Bavarian Julius-Maximilian-University of Würzburg, Pleicherwall 2, D-97070, Würzburg, Germany. norbert.hofmann@mail.uni-wuerzburg.de
Denner
Walter
W
Hugo
Burkard
B
Klaiber
Bernd
B
D000704:Analysis of Variance; D003188:Composite Resins / Q000528:radiation effects*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D006219:Halogens; D006244:Hardness; D007700:Kinetics; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000528:radiation effects; D012833:Siloxanes / Q000528:radiation effects; D013674:Technology, Dental; D013729:Terpenes / Q000528:radiation effects; D014978:Xenon
D003188:Composite Resins; C421785:Definite composite resin; C444701:Filtek Z250; D006219:Halogens; D011108:Polymers; D019279:Resin Cements; D012833:Siloxanes; C469658:Solitaire 2 composite resin; D013729:Terpenes; C065770:Herculite XR; C074741:Silux Plus; D014978:Xenon