Is the soft-start polymerisation concept still relevant for modern curing units?
Shrinkage stress, degree of cure and mechanical properties are contradicting properties, forcing to a compromise between an adequate curing and low stress at the interface tooth-restoration. The purpose of this study was to quantify this relations for a micro-hybrid composite, by analysing in real time the development of degree of cure at depths of 2 and 6 mm, shrinkage stress and curing time until gelation, as well as the variation of micro-mechanical properties with depth, after curing with 13 regimes of one halogen and two light-emitting diode (LED) curing units. A nano-dynamic mechanical test was additionally performed on selected regimes (Ramp, Pulse and Fast Cure) of the same curing unit. The present study showed that the soft-start polymerization concept is still valid for less deep cavities (2 mm), even by curing with high-power LED curing units, since a soft-cure polymerization resulted in a delayed gel point and a lower shrinkage stress, keeping simultaneously the degree of cure and mechanical properties constant. At 6 mm depth, curing with soft-start regimes resulted in a significant decrease in degree of cure, although this decrease was less than 10%, while the mechanical properties were maintained.
Ilie
Nicoleta
N
Department of Restorative Dentistry, Dental School of the Ludwig-Maximilians-University, Goethestr. 70, 80336 Munich, Germany. nicoleta.ilie@dent.med.uni-muenchen.de
Jelen
Esther
E
Hickel
Reinhard
R
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects; D055117:Curing Lights, Dental; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006219:Halogens; D006244:Hardness; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D053761:Nanocomposites / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization; D012666:Semiconductors; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical
D003188:Composite Resins; C466112:Esthet-X; D006219:Halogens