title: Evaluation of cell responses toward adhesives with different photoinitiating systems.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany; KU Leuven BIOMAT, Department of Oral Health Sciences, University of Leuven & Dentistry University Hospitals Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium. Electronic address: kirsten.vanlanduyt@med.kuleuven.be.
authors.forename: Kirsten L
authors.initials: KL
authors.lastname: Van Landuyt
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Krifka
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany.
authors.forename: Karl-Anton
authors.initials: KA
authors.lastname: Hiller
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany.
authors.forename: Carola
authors.initials: C
authors.lastname: Bolay
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Waha
authors.affiliation: KU Leuven BIOMAT, Department of Oral Health Sciences, University of Leuven & Dentistry University Hospitals Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Van Meerbeek
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany; School of Dental Medicine -ZMK Bern, University of Bern, Freiburgstrasse 7, 3010 Bern, Switzerland.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Schmalz
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital Regensburg, D-93042, 93042 Regensburg, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Schweikl
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D002164:Camphor / Q000031:analogs & derivatives* / Q000633:toxicity; D003782:Dental Pulp / Q000166:cytology*; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation*; D008422:Materials Testing; D018384:Oxidative Stress; D010720:Phosphines / Q000633:toxicity*; D058567:Photoinitiators, Dental / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000378:metabolism; D019279:Resin Cements / Q000633:toxicity*
chemical_list: C520678:(2,4,6-trimethylbenzoyl) diphenylphosphine oxide; D000975:Antioxidants; D010720:Phosphines; D058567:Photoinitiators, Dental; D017382:Reactive Oxygen Species; D019279:Resin Cements; D002164:Camphor; C041330:Scotchbond; C553149:camphorquinone
keywords: Apoptosis; Biocompatibility; CQ; Cytotoxicity; Dental adhesive; Photoinitiator; Reactive oxygen species; TPO