Time dependence of composite shrinkage using halogen and LED light curing

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Polymerization shrinkage is a significant drawback in light-cured dental composites, potentially compromising restoration integrity.
• Light-emitting diode (LED) technology offers a newer alternative to conventional halogen light curing units (LCUs).

Purpose of the Study:

• To compare the linear and volumetric composite shrinkage strain using LED LCUs versus traditional halogen LCUs.
• To evaluate the impact of different light curing technologies on dental composite polymerization shrinkage.

Main Methods:

• Volumetric shrinkage strain was measured using the Archimedes buoyancy principle.
• Linear shrinkage strain was assessed with a dynamic mechanical analyzer for four composite types (Z100, Spectrum, Solitaire2, Definite).
• Light curing units (halogen: Trilight; LED: Freelight I, LED63) and their spectral output/irradiance were analyzed.

Main Results:

• No significant shrinkage difference was observed for Z100, Spectrum, or Solitaire2 composites between LED63 and Trilight LCUs.
• A statistically significant difference in shrinkage strain was found for the Definite composite when polymerized with LED63 compared to Trilight.
• The Trilight's spectrum changed significantly, while LED63 maintained consistent light output; Freelight I experienced irradiance drop and was withdrawn.

Conclusions:

• Dental composites with camphorquinone as the sole photoinitiator demonstrated comparable shrinkage strain with both LED and halogen LCUs.
• The irradiance of some LED LCUs can decline over time, necessitating regular monitoring.