Two-step curing: influence on conversion and softening of a dental polymer.
OBJECTIVE
The study investigates the influence of two-step curing of a BisGMA/TEGDMA based polymer on degree of conversion (DC) and on hardness before and after 1 day ethanol storage.


METHODS
The specimens were pre-cured at 25, 50, 100, 200, or 400 mW/cm(2) for 10, 20, or 40 s. The final cure as well as the cure of the control group was carried out at 750 mW/cm(2) for 20 s. DC was determined on thin films by FTIR. Hardness was determined on disks by the method of Wallace.


RESULTS
At intermediary energy densities of the pre-cure, the DC was reduced as compared to that of the control group. The hardness before ethanol storage was not influenced by the curing mode. Except for the lowest and the two highest energy densities of the pre-cure, the two-step curing mode resulted in polymers that after ethanol storage were softer than the control polymer.


CONCLUSIONS
Two-step curing of resin composites may result in polymers with increased susceptibility to the action of softening substances in food and beverage.
Asmussen
Erik
E
Department of Dental Materials, School of Dentistry, University of Copenhagen, 20 Nørre Alle, DK-2200 Copenhagen N, Denmark. ea@odont.ku.dk
Peutzfeldt
Anne
A
D017438:Bisphenol A-Glycidyl Methacrylate / Q000528:radiation effects; D003188:Composite Resins / Q000528:radiation effects*; D006244:Hardness / Q000528:radiation effects; D008027:Light; D016014:Linear Models; D008422:Materials Testing; D015394:Molecular Structure; D011092:Polyethylene Glycols / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000528:radiation effects; D018709:Statistics, Nonparametric; D013674:Technology, Dental / Q000379:methods
D003188:Composite Resins; D011108:Polymers; D011109:Polymethacrylic Acids; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate