title: Influence of light-curing distance on degree of conversion and cytotoxicity of etch-and-rinse and self-etch adhesives.
abstract: BACKGROUND
  The degree of conversion (DC) of resin based materials depends, beside other factors, on the light-intensity applied during light curing. A lower DC might be correlated with an increased cytotoxicity of the respective materials. Therefore, aim of the present study was to investigate the influence of the distance between light-curing tip and adhesives on their cytotoxicity and degree of conversion (DC).
  
  
  METHODS
  For the cytotoxicity assay, a total of 98 bovine dentine samples were prepared, distributed to seven groups (G1-G7; n = 14) and treated as follows: G1: untreated; G2-G4: OptiBond FL; G5-G7: OptiBond All-In-One. Adhesives were light-cured (1200 mW/cm(2)) at 1 mm (G2;G5), 4 mm (G3;G6) or 7 mm (G4;G7) distance. Samples were stored in culture media for 24 h and extracts were added to cell cultures (dental pulp cells and gingival fibroblasts) for a further 24 h. Finally, released lactate dehydrogenase activity (LDH) was photometrically determined, as measure for the cytotoxic effects of the extracts. The cytotoxicity assay was performed three times. Additionally, the DC of the adhesives was determined by FTIR spectroscopy. DC measurements were performed five times.
  
  
  RESULTS
  For both cell types, no significant difference of LDH release was observed between untreated control group (G1) and treated groups G2-G7 (p > 0.05, respectively), between the groups treated with same adhesive and light-cured at different distance (p > 0.05, respectively), as well as between groups treated with different adhesives and light-cured at the same distance (p > 0.05, respectively). Within the respective adhesive, no significant difference in the DC was observed when light-cured at different distance (p > 0.05, respectively), while OptiBond FL showed significantly higher DCs compared to OptiBond All-In-One when light-cured at same distances (p < 0.05, respectively).
  
  
  CONCLUSIONS
  The distance between light-curing tip and adhesive surface does not significantly influence either the cytotoxicity or the DC of the tested adhesives.
authors.affiliation: Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zurich, Plattenstrasse 11, 8032, Zürich, Switzerland. florian.wegehaupt@zzm.uzh.ch.
authors.forename: Florian J
authors.identifier: http://orcid.org/0000-0002-3972-0561
authors.initials: FJ
authors.lastname: Wegehaupt
authors.affiliation: Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zurich, Plattenstrasse 11, 8032, Zürich, Switzerland.
authors.forename: Nancy
authors.initials: N
authors.lastname: Lunghi
authors.affiliation: Section of Oral Microbiology and Immunology, Institute of Oral Biology, University of Zürich, Plattenstrasse 11, 8032, Zürich, Switzerland.
authors.forename: Georgios N
authors.initials: GN
authors.lastname: Belibasakis
authors.affiliation: Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zurich, Plattenstrasse 11, 8032, Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Attin
mesh_terms: D000818:Animals; D002417:Cattle; D003188:Composite Resins; D055117:Curing Lights, Dental; D003738:Dental Cements; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D019279:Resin Cements; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D019279:Resin Cements
keywords: Cytotoxicity; Degree of conversion; Dental adhesives; Light-curing