Τίτλος:
Light intensity effects on resin-composite degree of conversion and
shrinkage strain
Γλώσσες Τεκμηρίου:
Αγγλικά
Περίληψη:
Objective: The aim of this study was to investigate the relationship
between the degree of conversion (DC) and shrinkage strain values of two
representative resin-composites when irradiated by two light intensity
levels, for different time periods.
Methods: The DC of Z100 and Tetric Ceram was measured by FTIR
spectroscopy immediately post-cure and shrinkage strain values were
obtained continuously for 30 min from photoinitiation with the
bonded-disk technique. All samples were photopolymerized at an initial
temperature of 23 degrees C with the Elipar Highlight unit under the
following modes of variable light intensity (I) 40 s at 750 mW/cm(2);
(II) a two-step ‘soft-start’ irradiation mode of 10 s at 200 mW/cm(2)
plus 30 s at 750 mW/cm(2); (III) 40 s at 200 mW/cm(2); and (IV) 10 s at
200 mW/cm(2). Temperature effects of the light and curing exotherm were
not eliminated.
Results: Mode II of irradiation did not reduce the DC for each material,
relative to the values obtained with mode I (p > 0.05). The
corresponding shrinkage strain values after 30 min were also not
significantly different (p > 0.05). However, the effects of reduced
light intensity levels for 10 s and 30 a (modes III and IV), were in
agreement with previous findings implying reduced shrinkage strain
levels. For both resin composites, data from all curing times and
light-intensities gave a linear regression relationship (with r(2) >
0.99) between the bonded-disk shrinkage strain versus DC values.
Significance: For the materials and light-intensities studied, the
correlation between DC and shrinkage strain values means that some
reductions in the problems of shrinkage may be achieved by an acceptable
reduction in DC. However, this must also be consistent with generating
adequate curing performance in the resin-network. Nevertheless, DC is
not the exclusive parameter describing network character and a fuller
understanding of the latter is an important research goal. (C) 2000
Academy of Dental Materials. Published by Elsevier Science Ltd. All
rights reserved.
Συγγραφείς:
Silikas, N
Eliades, G
Watts, DC
Περιοδικό:
DENTAL MATERIALS
Εκδότης:
Elsevier Sci Ltd, Exeter, United Kingdom
Λέξεις-κλειδιά:
dental materials; composites; FTIR; polymerization; shrinkage;
conversion; light intensity
DOI:
10.1016/S0109-5641(00)00020-8
