title: Effect of the regional variability of dentinal substrate and modes of application of adhesive systems on the mechanical properties of the adhesive layer.
abstract: OBJECTIVE
  This study assessed the effect of the dentin depth and the application mode on the hardness and elastic modulus of the adhesive layer.
  
  
  METHODS
  Occlusal surfaces of 48 caries-free human third molars were removed, at two levels: Superficial and deep dentin. For each type of surface, the test specimens were randomly divided into groups which underwent the application: A conventional two-step adhesive system (Adper™ Single Bond [SB]) and self-etch adhesives system (Adper™ SE Plus [SE] and AdheSE(®) [AD]). The adhesives applied were active or passive. Composite build-ups were constructed incrementally. The teeth were sectioned, embedded, and polished. The nanoindentation test was performed in the adhesive layer. The results were analyzed by ANOVA and Tukey tests.
  
  
  RESULTS
  In the adhesive layer, the higher hardness (0.307 ± 0.006 GPa) and elastic modulus (4.796 ± 0.165 GPa) of SE were obtained in superficial dentin in passive application. The elastic modulus of SE (4.115 ± 0.098 GPa) was lowest in active application in superficial dentin. The active application significantly increased the hardness of the SB in the deep dentin (0.011 ± 0.314 GPa) compared the superficial dentin (0.280 ± 0.010 GPa). For the AD, only the mode of application was statistically significant (P=0.0041) for the hardness, active application (0.289 ± 0.015 GPa) being higher than passive application (0.261 ± 0.013 GPa) (P=0.0042) in deep dentin.
  
  
  CONCLUSIONS
  The experimental results reveal that the mechanical properties were influenced for the application mode of adhesive systems and dentin depth.
authors.affiliation: Department of Restorative Dentistry, State University of Ponta Grossa, Ponta Grossa, Paraná, Brazil.
authors.forename: Yasmine Mendes
authors.initials: YM
authors.lastname: Pupo
authors.forename: Milton Domingos
authors.initials: MD
authors.lastname: Michél
authors.forename: Osnara Maria Mongruel
authors.initials: OM
authors.lastname: Gomes
authors.forename: Carlos Maurício
authors.initials: CM
authors.lastname: Lepienski
authors.forename: João Carlos
authors.initials: JC
authors.lastname: Gomes