Interlaboratory Testing of a New Cytotoxic Control Dental Material Formulation

Objectives: Recently, a new cytotoxic control material  (CM) for cytotoxicity testing of dental filling materials was evaluated in an interlaboratory test, where all components of this materials had been sent from the executive laboratory to the participating laboratories  (J Dent Res 90(Spec Iss A):273,2011). In this new test series the participating laboratories purchased components of this material themselves and tested cytotoxicity of the material according to the previous protocol.  

Methods: The CM is a powder/liquid system. The powder contains silanized glass powder (30µmħ10µm particle size; 66.3% w/w), polyacrylic acid (11.7%) and diphenyliodonium chloride (2%). The liquid contains HEMA (15%), camphorquinone (0.05%), ethyl-4-dimethylaminobenzoate (0.05%), and deionized water (4.9%). The powder (1g) was mixed with liquid (250µl), filled in teflon rings (5mm diameter, 2mm high), and specimens were light cured (40sec, > 500 mW/cm2). Cytotoxicity of the CM in L-929 fibroblasts was tested using the agar diffusion test (ADT) and a direct contact test (DCT) following ISO7405 and ISO10993-5 using 24 h culture medium eluates at 91.63 mm2/ml. A well characterized composite resin (Tetric EvoCeram;Vivadent, Liechtenstein) and a RMGIC (Vitrebond;3MESPE, Germany) served as controls. An interlaboratory test was performed according to ISO5725-2 and ISO TR22971 with 8 (ADT)/10 (DCT) laboratories from Europe, Asia and USA participating.

Results: ADT: RM was moderately, but significantly (Mann-Whitney test, α=0.05) more cytotoxic than the composite resin and the RMGIC (zone evaluation). The Spearman rank correlation coefficient between all laboratories was r2=0.79 to 0.84. DCT: CM was at all eluate dilutions significantly (Mann-Whitney test, α=0.05) more cytotoxic than the composite. In 9 out of 10 laboratories the 1:32 dilutions of the eluate reduced viability to 50% and less.

Conclusions:

Reproducible cytotoxicity caused by CM was observed in both test systems in all laboratories and thus the new material is recommended as standard cytotoxic control material.