Abstract
This in vitro study evaluated in fibroblast cultures the direct cytotoxicity of universal, self-etching and etch-and-rinse adhesive systems according to the polymerization time. Paper discs were impregnated with adhesives and light-cured (10, 20 or 40 s). The discs were then immersed in culture medium to obtain the eluates for the experimental groups (A1-Single Bond 2; A2-Scotchbond Multi-purpose; A3-Clearfil SE Bond; A4 Scotchbond Universal). As a negative control, paper discs were immersed in culture medium only. After 24 h or 7 days, the eluate obtained was applied on fibroblast culture. Cell viability, cell morphology, membrane damage and the presence of residual monomers were evaluated by MTT assay, SEM, flow cytometry and high-performance liquid chromatography (HPLC), respectively. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (=0.05). All adhesive systems significantly reduced 33-51% cell metabolism when compared to the negative control, regardless of polymerization time, storage period and adhesive system. Moreover, the adhesives caused intense morphological alterations and cell membrane damage. Toxicity was directly related to the presence of residual monomers in the eluates. Residual monomers and additional components are capable of reducing mitochondrial activity, causing morphological alterations and disruption of the cell membrane in fibroblasts, regardless of the polymerization time. This study highlights that despite the more complex composition of the universal adhesive system, its biological response was not more toxic when compared with other systems, even when the shortest polymerization time was tested in cell culture.
Highlights
Adhesive systems are constantly being developed with elaborate and complex chemistry
The L929 cell line has been usually employed to evaluate the direct toxicity of monomer-based materials as well as biomaterial behavior [10]
The L929 fibroblasts represent an established and immortalized cell line that allows the investigation of factors directly related to adhesive systems and polymerization time, excluding bias from the donor cell
Summary
Adhesive systems are constantly being developed with elaborate and complex chemistry. The chemical formulation of adhesive systems generally comprises hydrophilic and hydrophobic bifunctional monomers, acidic monomers containing radicals derived from carboxylic or phosphoric acid, or even derived from organic acids or minerals as additives [2] In addition to these monomeric components, solvents (water, alcohol or acetone), aromatic amines, photoinitiators and filler particles are present in the formulations. In these new universal systems, other components may be added to provide wider indications and applications, such as silane and chlorhexidine These additional components may alter the biological behavior of the pulp-dentin complex if they are not incorporated in the polymer network, and may be released after polymerization and diffused through dentinal tubules [3]. These authors observed that the time for Single Bond with little solvent to reach the conversion plateau was about 20 s, while the time for OneUp Bond F was about 25 s and for Adper Prompt as long as 40 s, and they indicated that the time required to reach the conversion plateau for adhesive polymerization is a valuable information for the dental clinic [6]
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