Influence of curing protocol on selected properties of light-curing polymers: degree of conversion, volume contraction, elastic modulus, and glass transition temperature.
OBJECTIVE
The purpose of this study was to investigate the effect of light-curing protocol on degree of conversion (DC), volume contraction (C), elastic modulus (E), and glass transition temperature (T(g)) as measured on a model polymer. It was a further aim to correlate the measured values with each other.


METHODS
Different light-curing protocols were used in order to investigate the influence of energy density (ED), power density (PD), and mode of cure on the properties. The modes of cure were continuous, pulse-delay, and stepped irradiation. DC was measured by Raman micro-spectroscopy. C was determined by pycnometry and a density column. E was measured by a dynamic mechanical analyzer (DMA), and T(g) was measured by differential scanning calorimetry (DSC). Data were submitted to two- and three-way ANOVA, and linear regression analyses.


RESULTS
ED, PD, and mode of cure influenced DC, C, E, and T(g) of the polymer. A significant positive correlation was found between ED and DC (r=0.58), ED and E (r=0.51), and ED and T(g) (r=0.44). Taken together, ED and PD were significantly related to DC and E. The regression coefficient was positive for ED and negative for PD. Significant positive correlations were detected between DC and C (r=0.54), DC and E (r=0.61), and DC and T(g) (r=0.53). Comparisons between continuous and pulse-delay modes of cure showed significant influence of mode of cure: pulse-delay curing resulted in decreased DC, decreased C, and decreased T(g). Influence of mode of cure, when comparing continuous and step modes of cure, was more ambiguous.


CONCLUSIONS
A complex relationship exists between curing protocol, microstructure of the resin and the investigated properties. The overall performance of a composite is thus indirectly affected by the curing protocol adopted, and the desired reduction of C may be in fact a consequence of the decrease in DC.
Dewaele
Magali
M
Laboratory of Chemistry and Physics of High Polymers, Université catholique de Louvain, Louvain-la-Neuve, Belgium. Magali.Dewaele@uclouvain.be
Asmussen
Erik
E
Peutzfeldt
Anne
A
Munksgaard
E Christian
EC
Benetti
Ana R
AR
Finné
Gauthier
G
Leloup
Gaëtane
G
Devaux
Jacques
J
D010129:4-Aminobenzoic Acid / Q000737:chemistry / Q000528:radiation effects; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D002152:Calorimetry, Differential Scanning; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D055119:Elastic Modulus; D005898:Glass / Q000737:chemistry; D006801:Humans; D008027:Light; D008422:Materials Testing; D055595:Mechanical Phenomena; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D013499:Surface Properties; D013729:Terpenes / Q000737:chemistry / Q000528:radiation effects; D044366:Transition Temperature; D062366:para-Aminobenzoates
D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; D011109:Polymethacrylic Acids; D013729:Terpenes; D062366:para-Aminobenzoates; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; C030747:ethyl 4-dimethylaminobenzoate; D010129:4-Aminobenzoic Acid