title: Influence of photoactivation protocol and light guide distance on conversion and microleakage of composite restorations.
abstract: OBJECTIVE
  To evaluate the effect of light guide distance and the different photoactivation methods on the degree of conversion (DC) and microleakage of a composite.
  
  
  METHODS
  Three photoactivation protocols (600 mW/cm2 x 40 seconds; 400 mW/cm2 x 60 seconds or 200 mW/cm2 x 20 seconds, followed by 500 mW/cm2 x 40 seconds) and three distances from the light source (0, 3 or 7 mm) were tested. Cylindrical specimens (5 mm diameter; 2 mm tall; n=3) were prepared for the DC test (FT-Raman). Class V cavities were made in 90 bovine incisors to conduct the microleakage test. The specimens were conditioned for 15 seconds with phosphoric acid (37%), followed by application of the adhesive system Prime & Bond NT (Dentsply/Caulk). The preparations were restored in bulk. The specimens were stored for 24 hours in distilled water (37 degrees C) before being submitted to the silver-nitrate microleakage protocol. The restorations were sectioned and analyzed under 25x magnification.
  
  
  RESULTS
  Statistical analyses (two-way ANOVAs and Tukey test, alpha=0.05) found significance only for the factor distance (p=0.015) at the top of the composite for the DC test. Conversion was statistically lower for the 7 mm groups compared to the 0 and 3 mm groups, which were equivalent to each other. At the bottom of the specimens, none of the factors or interactions was significant (p<0.05). The Kruskal-Wallis test showed that, in general, the soft-start method led to lower microleakage scores when compared to the continuous modes, mainly when associated with a distancing of 7 mm (p<0.01). With the exception of specimens irradiated with 400 mW/cm2 that did not demonstrate variations on scores for the distances tested, higher microleakage was observed for shorter distances from the light source.
  
  
  CONCLUSIONS
  Soft-start methods may reduce microleakage when the light guide distancing provides a low level of irradiance, which also causes a discrete reduction in the DC.
authors.affiliation: Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil. niveafroes@gmail.com
authors.forename: N R G
authors.initials: NR
authors.lastname: Fróes-Salgado
authors.forename: C S C
authors.initials: CS
authors.lastname: Pfeifer
authors.forename: C E
authors.initials: CE
authors.lastname: Francci
authors.forename: Y
authors.initials: Y
authors.lastname: Kawano
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry; D003763:Dental Leakage; D003793:Dental Restoration, Permanent; D066298:In Vitro Techniques; D007180:Incisor; D055115:Light-Curing of Dental Adhesives; D011140:Polyurethanes / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; C466112:Esthet-X; D011140:Polyurethanes