| Objective: To evaluate the biological safety of the nanometer SiO2/(P)MMA denture composite material before clinical application.Methods: According to the standard of ISO 7405-1997(E), cytotoxicity test, haemolysis test, acute systemic toxicity test (by oral),oral mucous membrane irritating test, sensitization test and micronucleus assay were investigated on the nanometer SiO2/(P)MMA denture composite material1. Cytotoxicity test : The proliferations of the Vero cells were investigated using a tetrazolium-based colorimetric assay(MTT assay). Eluates from two tested materials were added into 96-well culture plates. The samples were tested with ultraviolet spectrophotometer at 492nm wavelength for 2, 4, 7days after the adding of the extracts. Morphology of these cells was also observed with phase-contrast microscope.2. Haemolysis test: Added the dilute blood of rabbit 0.2 ml into the normal saline maceration extract of the sample-material, centrifugated for five minutes, took supernatant and moved it into color comparator, assayed every cylinder's optical density(O.D.).3. Acute systemic toxicity test by oral (limit experiment): Irrigated the KunMing mice's stomach with the normal saline maceration extract of the sample-material at the dose of 15000mg/kg, observed the little mice's general condition, venenous manifest and the number of the dead in a week after they were irrigated.4. Oral mucous membrane irritating test: Sutured the materials round pieces with ophthalmology bullet and line on bilateral buccal bursa of healthy Golden hamsters. In two weeks the general reaction, oral mucosa reaction in contacted site were observed .We killed the animals after two weeks and did pathological examination of local oral mucosa with hematoxylin and eosin (HE) stain andobserved changes in the tissue cells.5. Skin sensitization test : Selected white healthy male guinea pig , induced to contact them with the positive control of 10% dinitrocholorobenzne (DNCB), the negative control of normal saline maceration extract of the sample-material, Freund complete adjuvant(FCA) , the emulsion of the tested material and FCA, stimulated to contact and observed the result of stimulation in 24 and 48 hours.6. Micronucleus assay: Selected healthy KunMing white mice and divided into high, middle, low dose groups, irrigated stomachs with suspended liquid on dose of 15.0g/kg, 7.5g/kg, 3.75g0.05);The toxicity grades of the two kinds of material are 2. The cells growing in the extract showed normal morphology.2. Haemolysis test: The Haemolysis rate of the sample-material was lower than 5%, consulted ISO/TR 7405-1984(E) the result of haemolysis experiment was up to ISO standard.3. Acute systemic toxicity test by oral: In a week there were no toxicity symptoms on the animals and there was no death. LD50 was more than15000mg/kg. According to the standard of acute toxicity grade, the suspended liquid tested was no toxicity actually.4. Oral mucous membrane irritating test:Experiment observation: The animals' exercise and diet was normal with two week's observation. There was no abnormal reaction on local mucous membrane such as hyperemia, haemorrhage, erosion, ulcer and so on. There was no significant difference with the negative control.Slicings of tissue: The tissue slicings of the two kinds of materials showed: the epitheliums were complete, cells stratifications were clear, the permutations were well-distributed. Hypodermises were Rarefaction, the forms of glands were regular, there was no infiammatry cell infiltration in connective tissue. All these had no significant difference with tissue slicings of the negative control group.5. Skin sensitization test : There was no patho-change on the skin of tested sample-material and the negative contrast, but the skin of positive contrast showed obvious oedema and middle or serious erythema in 24 hours after stimulated, later showed erosion and scab.6. Micronucleus assay: The sternum marrow cells formation (PCE/NCE) of this experiment was normal and no obvious inhibition was found. There was no significant difference between female and male little mice's micronucleus(P>0.05) , so amalgamated and counted the date, founded that there was no significant difference between every dose group of tested sample-material and the negative contrast (P>0.05), there was significant difference between the positive control and the negative control (P<0.01) .Conclusions: The nanometer SiO2/(P)MMA denture composite material was proved to have good biological safety by preliminary selected tests.
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