Apoptotic effect of different self-etch dental adhesives on odontoblasts in cell cultures

We aimed to evaluate the potential cytotoxicity (apoptosis-induction) of three types of self-etch dental adhesives: two-component one-step (Xeno III), two-component two-steps (Clearfil Protect Bond) and one-component one-step (Xeno V) on cultured odontoblasts.

Each adhesive was prepared to simulate its clinical manipulation. Cured sterile individual masses were immersed in DMEM and left at 37 °C for 24 h. Then a volume of 100 μL of the extract medium was added to the cultured odontoblasts and incubated for additional 24 h, 48 h and 72 h, respectively. Acridine orange-propidium iodide (AO-PI) labelling was employed to assess the proportion of dead to total number of cells. In addition, an in situ apoptosis detection kit was used to evaluate the DNA cleavage and chromatin condensation employing the immunohistochemical (IHC) technique. Statistical analysis of the data was performed using one-way ANOVA.

Both apoptosis evaluation methods revealed comparable results with the exception that IHC showed 5-7% less number of dead cells when compared to similar groups evaluated by AO-PI. The percentages of dead to total cells after treatment with Clearfil Protect Bond, Xeno III and Xeno V, were significantly different from the percentage of dead cells after treatment with DMEM alone (-ve control), P value <0.05 and Xeno V dental adhesive had the weakest cytotoxic effect on odontoblasts followed by Xeno III especially after 24 h of incubation. Clearfil Protect Bond had the strongest cytotoxic effect on odontoblasts that was almost closer to that of Staurosporine in DMEM (+ve control).

All tested dental adhesives had remarkable adverse effect on the odontoblasts in vitro; this might be of concern when applied clinically in deep cavities where such cytotoxic chemicals become in close contact to dental pulp. Therefore, further in vivo studies on animal models are recommended to support or refute these in vitro findings.