Evaluation of cell responses toward adhesives with different photoinitiating systems

• Published in: Dental materials Vol. 31; no. 8; pp. 916 - 927
• Main Authors: Van Landuyt, Kirsten L., Krifka, Stephanie, Hiller, Karl-Anton, Bolay, Carola, Waha, Claudia, Van Meerbeek, Bart, Schmalz, Gottfried, Schweikl, Helmut
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2015
• Subjects: Adhesives; Advanced Basic Science; Antioxidants - metabolism; Apoptosis; Barriers; Biocompatibility; Camphor - analogs & derivatives; Camphor - toxicity; Cytotoxicity; Dental adhesive; Dental Pulp - cytology; Dentin; Dentistry; Glutathione; Humans; Light-Curing of Dental Adhesives - instrumentation; Materials Testing; Olefinic thermoplastic elastomers; Oxidative Stress; Phosphines - toxicity; Photoinitiator; Photoinitiators, Dental - toxicity; Reactive oxygen species; Reactive Oxygen Species - metabolism; Resin Cements - toxicity; Toxic; Toxicology; TPO; TPO; Reactive oxygen species; Dental adhesive; Cytotoxicity; Biocompatibility; CQ; Photoinitiator; Apoptosis
• ISSN: 0109-5641; 1879-0097; 1879-0097
• DOI: 10.1016/j.dental.2015.04.016

The photoinitiator diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) is more reactive than a camphorquinone/amine (CQ) system, and TPO-based adhesives obtained a higher degree of conversion (DC) with fewer leached monomers. The hypothesis tested here is that a TPO-based adhesive is less toxic than a CQ-based adhesive. A CQ-based adhesive (SBU-CQ) (Scotchbond Universal, 3M ESPE) and its experimental counterpart with TPO (SBU-TPO) were tested for cytotoxicity in human pulp-derived cells (tHPC). Oxidative stress was analyzed by the generation of reactive oxygen species (ROS) and by the expression of antioxidant enzymes. A dentin barrier test (DBT) was used to evaluate cell viability in simulated clinical circumstances. Unpolymerized SBU-TPO was significantly more toxic than SBU-CQ after a 24h exposure, and TPO alone (EC50=0.06mM) was more cytotoxic than CQ (EC50=0.88mM), EDMAB (EC50=0.68mM) or CQ/EDMAB (EC50=0.50mM). Cultures preincubated with BSO (l-buthionine sulfoximine), an inhibitor of glutathione synthesis, indicated a minor role of glutathione in cytotoxic responses toward the adhesives. Although the generation of ROS was not detected, a differential expression of enzymatic antioxidants revealed that cells exposed to unpolymerized SBU-TPO or SBU-CQ are subject to oxidative stress. Polymerized SBU-TPO was more cytotoxic than SBU-CQ under specific experimental conditions only, but no cytotoxicity was detected in a DBT with a 200μm dentin barrier. Not only DC and monomer-release determine the biocompatibility of adhesives, but also the cytotoxicity of the (photo-)initiator should be taken into account. Addition of TPO rendered a universal adhesive more toxic compared to CQ; however, this effect could be annulled by a thin dentin barrier.