Objective: The main goal of this study was to compare the polymerization
degree of bulk-fill giomer resin cured with three different light-curing units
(LCUs): a polywave third-generation (Valo); a monowave (DemiUltra: DU);
and a second-generation LED (Optima 10: Opt) LCUs by using structural
and mechanical properties. Material and methods: Giomer samples of 2
and 4 mm cured with three LCUs were employed in vitro analysis. The
degree of curing (DC%) was determined with Fourier-Transform Infrared
Spectroscopy (FTIR). Microstructural features were observed with scanning
electron microscopy (SEM). Flexural strength (FS), compression strength
(CS), elastic modulus and fracturing strain were determined for mechanical
properties. Surface microhardness (SMH) values were also measured. Oneway
ANOVA, two-way analysis of variance and Tukey multiple comparison
tests were used for statistically analyzing the FS and SMH. Results: DC%
values were 58.2, 47.6, and 39.7 for the 2 mm samples cured with DU, Opt.,
and Valo LCUs, respectively. DC% values of the 4 mm samples were 50.4,
44.6, and 38.2 for DU, Opt, and Valo, respectively. SMH values were Valo,
Opt<DU at top of the samples; Valo<DU, Opt at 2 mm, and DU, Valo<Opt
at 4 mm depth. Giomer samples cured with Opt and DU exhibited higher
FS values than Valo. CS values were similar but compressive modulus and
fracturing strain (%) varied depending on the curing protocol. Conclusions:
Based on the results, it can be concluded that curing device and protocol
strongly affect crosslinking reactions and thus DC%, SMH, compressive
modulus and strain at break values. Consequently, it can be deduced that
curing protocol is possibly the most important parameter for microstructure
formation of highly-filled composite restoratives because it may bring some
structural defects and physical frailties on restorations due to lower degree
of polymerization.