Influence of the interaction of light- and self-polymerization on subsurface hardening of a dual-cured core build-up resin composite.
OBJECTIVE
To investigate the influence of time delay and duration of photo-activation on subsurface microhardness of a dual-cured resin composite.


METHODS
A commercially available dual-cured core build-up resin composite (Rebilda DC) was filled in cavities (diameter: 4.0 mm; height: 6.0 mm) of polystyrene molds and light-cured for 20 or 60 s either immediately after the filling procedure (time delay 0 s) or after a time delay of 30, 90, 180 or 300 s. Non-irradiated self-cured specimens served as a control group (n = 15). Specimens were stored in complete darkness and at 100% relative humidity at 37°C for 2 weeks and cross-sectioned. Knoop Hardness Numbers (KHNs) were measured six times per depth and averaged at distances of 0.25, 0.50, 1.00, 2.00, 3.50 and 5.50 mm from the light-exposed surface. Data were statistically analyzed using one- and two-way ANOVA followed by Scheffé's post-hoc test at a level of significance of 0.05.


RESULTS
Mean hardness values in all experimental groups ranged between 54.3 ± 2.1 and 58.1 ± 2.3 KHN. Light-curing did not significantly increase composite KHN at any depth measured. Delaying light exposure had no influence on KHN, irrespective of depth. A longer light-exposure time (60 versus 20 s) resulted in significantly higher KHN only at depths of 3.50 and 5.50 mm.


CONCLUSIONS
Photo-activation of the tested dual-cured resin composite provided no clinically relevant benefit compared to self-curing regarding the degree of hardening.
Tauböck
Tobias T
TT
Department of Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, University of Zürich, Switzerland. tobias.tauboeck@zzmk.uzh.ch
Buchalla
Wolfgang
W
Hiltebrand
Urs
U
Roos
Malgorzata
M
Krejci
Ivo
I
Attin
Thomas
T
D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D017220:Dentin-Bonding Agents / Q000737:chemistry / Q000528:radiation effects; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D058105:Polymerization; D055116:Self-Curing of Dental Resins; D013997:Time Factors
D003188:Composite Resins; D017220:Dentin-Bonding Agents; C529053:rebilda DC