According to current knowledge, carious lesions should be filled with fluoride-releasing adhesive materials. Compomers were developed in the 1990s as a result of combining composite materials and glass ionomer cements (1, 2). These materials contain a modified monomer and fluoride-releasing silicate glass. For this reason, inter alia, they arouse great interest among dental practitioners, particularly pediatric dentists (2, 3). An important advantage of the aforementioned materials, compared to glass ionomer cements, is their unlimited working time, as their binding occurs under the influence of light emitted by equipment for curing dental fillings. Halogen lamps commonly used for polymerisation are more and more often replaced by diode (LED) lamps due to the rapid wear and insufficient energy efficiency of the former (4). The first diode lamps were not received positively since they did not always enable the full required range of polymerisation, thus offering inadequate quality of polymerised materials, which was particularly expressed as high cytotoxicity. This was due to insufficient power of the light emitted by these lamps. The beginning of the 21^st century marked the introduction of the second generation of diode lamps characterised by higher efficiency of light-emitting diodes. In the available literature, doubts are expressed in connection with biocompatibility of compomers cured with halogen and diode light (5).

The aim of this study was to evaluate cytotoxicity of selected compomers, using halogen and diode lamps for their polymerisation.

The study was conducted with the use of two compomers, Dyract Extra (Dentsply) and Compoglass F (Ivoclar Vivadent). A₂-coloured materials were applied to plastic rings with dimensions of 5 mm (inner diameter) x 5 mm (height). Twelve samples of each material were prepared. Half of the samples (6 pieces) were polymerised for 20 seconds in two layers with a halogen lamp (Polylux II, Kavo) and the other half – with a diode lamp (B-Max, Tecno-Gaz, 1600 mW/cm²). The rings with the materials were placed in inserts (from Nunc) with an area of 0.47 cm² and 0.4 μm diameter of pores located in 24-well culture plates (Nunc) containing human gingival fibroblasts. In each of the 24-well plates, 6 wells with inserts without materials served as the control.

Human gingival fibroblasts with adherent permanent cell lines (ATCC^® CRL-2014HGF-1, LGC Promochem) were grown in Falcon containers (growth area: 75 cm²) in DMEM (Dulbecco’s Modified Eagle Medium) supplemented with 10% foetal bovine serum (FBS), at 37°C, with 5% CO₂ and 95% humidity. After reaching confluent growth, cells were detached with 0.25% trypsin solution with added 0.53 mM EDTA. The enzyme activity was inhibited by adding medium with 10% FBS. The cell suspension was diluted in fresh medium, seeded in 24-well plates, and incubated for 24 hours.

The toxicity of the tested materials against human gingival fibroblasts was assessed with the use of the MTT assay. This method enables the determination of cell viability and proliferation based on mitochondrial succinate dehydrogenase activity. In living cells, this enzyme causes the reduction of the yellow tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to purple formazan. The dye content is determined in an absorption spectrophotometer. The amount of formazan is directly proportional to the number of viable cells in the culture. At low cell survival rate, low enzyme activity and thus low purple formazan content and reduced absorbance values are observed.

Culture plates with cells and the applied materials were incubated at 37°C, with 5% CO₂ and 95% humidity for 24 hours. After that time, the inserts with materials were removed, then 1 ml of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide at a concentration of 0.5 mg/ml of medium was added to each well and incubated for 2 hours in the above-mentioned conditions, without access to light. Next, the culture fluid was aspirated and 1 ml of isopropanol acidified with hydrochloric acid (0.04 mol/L^-1) was added. The obtained solution was stirred briefly to dissolve the formazan crystals. Absorbance was measured using a Lambda EZ 201 (Perkin Elmer) double beam absorption spectrophotometer at 560 nm wavelength.