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Do orthodontic adhesives have a genotoxic effect on human lymphocytes?

AIM: To assess predictors of micronuclei and nuclear bud formation in the micronucleus assay performed on human lymphocytes treated with orthodontic adhesive system components. MATERIAL AND METHODS: Four primers, seven adhesives and seven primer-adhesive combinations were tested: Transbond XT primer with Transbond XT adhesive and Transbond Plus adhesive (3M Unitek, USA), Light Bond Sealant primer with Light Bond Paste adhesive, Light Bond Sealant With Fluoride primer with Light Bond Paste With Fluoride adhesive (Reliance Orthodontic Products Inc., USA), Tenure primer with Geristore adhesive (DenMat, USA) and two experimental adhesives, the first containing 40% wt. of amorphous calcium phosphate (ACP40), the second containing 70% wt. of strontium glass filler with fluoride (Sr70), both in combination with Transbond XT Primer. Specimens of each primer, adhesive and primer-adhesive system were cured for 10 or 20 s in a simulation of the clinical procedure. Ten specimens were used for the assessment of the degree of conversion (DC) using Fourier- transform infrared spectroscopy. Genotoxicity was assessed with the micronucleus assay. Lymphocyte cultures were treated for 24 h with one sample per tested material, in duplicate. Cell culture medium was used as negative and ethyl methanesulfonate in concentration 10 µg/mL of culture as positive control. Micronuclei (MN) and nuclear buds (NB) were counted in 2000 binuclear cells per material. Linear and logistic regression were performed for the assessment of predictors of MN and NB formation. RESULTS: Linear regression showed no significant predictors of MN and NB formation. Controlling for illumination time, DC, content of amorphous calcium phosphate, presence of fluorides and adhesive system component (primer, adhesive or primer-adhesive combination), the only significant predictor of NB formation in logistic regression was the experimental adhesive ACP40, with an odds ratio of 1.4x (CI 1.1-1.8 ; p=0.004), while there were no significant predictors of MN. CONCLUSION: While an increase in NB formation may indicate activation of DNA repair mechanisms, lack of MN induction indicates that the tested orthodontic adhesives do not have biologically relevant genotoxic potential. Further research is needed to determine the particular component of ACP40 inducing NB formation.

micronucleus assay ; lymphocytes ; orthodontic adhesives

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