title: The effects of soft-start vs continuous-light polymerization on microleakage in Class II resin composite restorations.
abstract: OBJECTIVE
  Despite the different light sources and polymerization techniques developed to eliminate it, microleakage of resin composite still remains a problem. This in vitro study was designed to compare the effects of exponential mode soft-start polymerization with those of standard and high-intensity continuous light polymerization on microleakage in Class II resin composite restorations.
  
  
  METHODS
  Standardized Class II cavities (4 mm wide, 4 mm long, 5 to 6 mm high, 2 mm deep) were prepared in 50 extracted human molars. Specimens were divided into 5 groups (n = 10) and restored using the same hybrid resin composite (Z250), but separately polymerized by one of five different methods: group 1: continuous halogen light polymerization for 40 s; group 2: continuous high-intensity halogen light polymerization for 10 s; group 3: exponential mode soft-start halogen light polymerization for a total of 40 s; group 4: continuous LED light polymerization for 40 s; Group 5: exponential mode soft-start LED light polymerization for a total of 40 s. All specimens were thermocycled for 1000 cycles at 5 degrees C to 55 degrees C and then placed in 0.5% basic fuchsin dye for 24 h. Specimens were then rinsed, embedded in resin and sectioned longitudinally. Dye penetration at occlusal and cervical margins was rated using a scale of 0 to 4. Data was analyzed using Kruskal-Wallis and Mann-Whitney U-tests.
  
  
  RESULTS
  Significantly lower marginal leakage was recorded with exponential mode soft-start polymerization when compared to continuous light polymerization. No significant differences in microleakage were observed between LED and halogen light polymerization.
  
  
  CONCLUSIONS
  Within the limits of this in vitro study, the use of the soft-start exponential mode of LED and/or halogen light units in the polymerization of hybrid composite was found to produce significantly lower microleakage at both occlusal and cervical margins when compared to continuous light polymerization methods.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Ankara University, Ankara, Turkey. analcaci@dentistry.ankara.edu.tr
authors.forename: Adil
authors.initials: A
authors.lastname: Nalçaci
authors.forename: Meriç
authors.initials: M
authors.lastname: Salbaş
authors.forename: Nuran
authors.initials: N
authors.lastname: Ulusoy
mesh_terms: D000134:Acid Etching, Dental; D004396:Coloring Agents; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003737:Dental Cavity Preparation / Q000145:classification; D003763:Dental Leakage / Q000145:classification*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000145:classification* / Q000295:instrumentation; D004867:Equipment Design; D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D012394:Rosaniline Dyes; D013997:Time Factors
chemical_list: D004396:Coloring Agents; D003188:Composite Resins; C444701:Filtek Z250; D011108:Polymers; D012394:Rosaniline Dyes; C025485:basic fuchsin