Depth Dependent Curing Behaviour of Dental Composites using DEA

Objectives:

Photo-curing dental filling composites should cure completely and very quickly for the patients convenience and the required mechanical performance. However, the curing rate depends significantly on the light intensity generating the required initiator radicals which is affected by the kind of lamp and the absorption behaviour of the composites. This work investigates the question: How are curing process and ion-viscosity linked to each other, and does the curing behaviour and curing kinetics depend on the depth within the sample?

Methods:

Two photo-curing composites Arabesk Top OA2 and Grandio OA2 (VOCO, Germany) were investigated using the dielectric cure analyser NETZSCH DEA 231 with the frequency of 1 kHz. The surface of Mini-IDEX-sensors was covered with layers having thicknesses of 0.5 up to 6 mm. The curing process was initiated with the LED curing device Celalux (VOCO) for 80 seconds. The temperature dependency was investigated for 1 mm thick samples at temperatures between 25 and 50°C.

Results:

With increasing depth i) the initial slope of the ion-viscosity decreases significantly indicating a lower curing rate, Fig. 1. Furthermore, it seems that curing mechanisms change for thicknesses exceeding 2 mm; ii) the ion-viscosity drops due to inhibition processes directly after starting the illumination. This drop is more prounounced for Arabesk Top OA2, iii) the final ion-viscosity is slightly higher for slow curing rates. The temperature affects mainly the ion-viscosity of the uncured state and the initial slope, not the final ion-viscosity.

Conclusions:

The DEA allows to measure the curing behaviour depth sensitively as the penetration depth of the electric field corresponds to the electrode distance. Furthermore, it indicates that slower curing rates lead to higher final conversion degrees.

Acknowledgements:

Financial support by the BMBF-FHProfUnt grant no. 17081X10

.