Cytotoxicity of post and core composites as a function of environmental conditions

Objectives: In the revised version of ISO 7405 there are so far no detailed recommendations concerning temperature and humidity during specimen production for light curing and chemically setting dental materials. The main objective of the present study was to observe if different environmental conditions during specimen production influence cytotoxicity and degree of conversion of four post and core composite materials and to investigate if cytotoxicity of post and core materials is influenced by their corresponding bonding substances.

Methods: Specimens of four different post and core composite materials (LuxaCore - Dual, Core X-Flow, Flow White and MultiCore Flow) were produced in a climate test chamber at 23°C/50% relative humidity or 37°C/95% relative humidity and were dual-cured or self-cured, with or without their corresponding bonding substances. Specimens were added to cell cultures immediately after production or after preincubation for 7 days. Specimens were incubated with L-929 fibroblasts for 72h and cell numbers determined by a flow cytometer. FTIR spectroscopic measurements of post and core materials were performed at the same temperature conditions as for the cytotoxicity assay (23°C or 37°C).

Results: Dual-cured specimens of all post and core composites exhibited less cytotoxicity under both environmental conditions than self-cured specimens. All self-cured specimens manufactured at 37°C/95% showed less cytotoxicity than specimens produced at 23°C/50%. All dual-cured specimens showed similar cytotoxicity at both environmental conditions. After 7 days of preincubation most dual-cured specimens produced at 23°C/50% showed less cytotoxicity than self-cured specimens (with the exception of Flow White). Compared to fresh specimens, 7-day aged specimens of most materials showed reduced cytotoxicity. Materials already showing low cytotoxicity as fresh specimens did not further reduce their cytotoxicity after 7 days of preincubation. For dual-cured materials the degree of conversion was higher compared to self-cured materials.

Significance: Different temperatures during specimen production have an impact on cytotoxicity and degree of conversion of dual-curing composite materials. Detailed recommendations for standardization concerning environmental conditions during specimen production are required.