title: Effect of dentin age and acid etching time on dentin bonding.
abstract: OBJECTIVE
  To compare the bond strengths of young and old dentin using a single-bottle etch-and-rinse adhesive system with two acid-etching times (15 s and 30 s), and to examine the correlation between dentin hardness and bond strength.
  
  
  METHODS
  Twenty-four molars from 18- to 22- or 55- to 60-year-old patients were prepared to expose the occlusal dentin, cut into two equal parts, and assigned to four groups (G), varying the etching time (15 s and 30 s) and dentin age (young [Y]or old [O]): G15Y, G30Y, G15O and G30O. After etching, AdperSingleBond (3M ESPE) adhesive was applied and the tooth was built up with a composite (Filtek Z250). The specimens were prepared for the microtensile bond strength test (μTBS) at a crosshead speed of 0.5 mm/min and the interfaces were observed under SEM. Also, the Knoop hardness (KHN) of young vs old dentin was measured.
  
  
  RESULTS
  The mean (± SD) μTBS (MPa) were: G15Y = 45.9 (± 10.7)a, G15O = 34.1 (± 9.4)b, G30Y = 48.6 (± 14.3)a and G30O = 47.7 (± 11.0)a. Two-way ANOVA showed no difference in μTBS between young and old dentin. Old dentin acid etched for 15 s (G15O) had a lower μTBS than when acid etched for 30 s (G30O). Dentin hardness was higher for old dentin (67.0 ± 4.8KHN) than young dentin (63.7 ± 2.9KHN) (p < 0.004). No correlation between μTBS and dentin hardness was observed. Resin tags were larger and more numerous for young dentin. The hybrid layer formed in intertubular old dentin (G15O) was very thin.
  
  
  CONCLUSIONS
  Bonding to old dentin with 30 s of etching time resulted in higher bond strength and more homogeneous hybrid layer formation than dentin acid etched for 15 s.
authors: Universidade Federal de Santa Catarina, Operative Dentistry, Florianopolis, Brazil. guilhermelopes@ccs.ufsc.br
authors: Guilherme Carpena
authors: GC
authors: Lopes
authors: Luiz C
authors: LC
authors: Vieira
authors: Elito
authors: E
authors: Araújo
authors: Tatiana
authors: T
authors: Bruggmann
authors: Jhonate
authors: J
authors: Zucco
authors: Gustavo
authors: G
authors: Oliveira