title: Influence of differently oriented dentin surfaces and the regional variation of specimens on adhesive layer thickness and bond strength.
abstract: BACKGROUND
  Adhesive systems can spread differently onto a substrate and, consequently, influence bonding.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effect of differently oriented dentin surfaces and the regional variation of specimens on adhesive layer thickness and microtensile bond strength (MTBS).
  
  
  METHODS
  Twenty-four molars were sectioned mesiodistally to expose flat buccal and lingual halves. Standardized drop volumes of adhesive systems (Single Bond [SB] and Prime & Bond 2.1 [PB2.1]) were applied to dentin according to the manufacturer's instructions. Teeth halves were randomly divided into groups: 1A-SB/parallel to gravity; 1B-SB/perpendicular to gravity; 2A-PB2.1/parallel to gravity; and 2B-PB2.1/perpendicular to gravity. The bonded assemblies were stored in 37 degrees C distilled water for 24 hours and then sectioned to obtain dentin sticks (0.8 mm2). The adhesive layer thickness was determined in a light microscope (x200), and after 48 hours the specimens were subjected to MTBS test. Data were analyzed by one-way and two-way analysis of variance and Student-Newman-Keuls tests.
  
  
  RESULTS
  Mean values (MPa +/- SD) of MTBS were: 39.1 +/- 12.9 (1A); 32.9 +/- 12.4 (1B); 52.9 +/- 15.2 (2A); and 52.3 +/- 16.5 (2B). The adhesive systems' thicknesses (microm +/- SD) were: 11.2 +/- 2.9 (1A); 18.1 +/- 7.3 (1B); 4.2 +/- 1.8 (2A); and 3.9 +/- 1.3 (2B). No correlation between bond strength and adhesive layer thickness for both SB and PB2.1 (r = -0.224, p = 0.112 and r = 0.099, p = 0.491, respectively) was observed.
  
  
  CONCLUSIONS
  The differently oriented dentin surfaces and the regional variation of specimens on the adhesive layer thickness are material-dependent. These variables do not influence the adhesive systems' bond strength to dentin. CLINICAL SIGNIFICANCE Adhesive systems have different viscosities and spread differently onto a substrate, influencing the bond strength and also the adhesive layer thickness. Adhesive thickness does not influence dentin bond strength, but it may impair adequate solvent evaporation, polymer conversion, and may also determine water sorption and adhesive degradation over time. In the literature, many studies have shown that the adhesive layer is a permeable membrane and can fail over time because of its continuous plasticizing and degradation when in contact with water. Therefore, avoiding thick adhesive layers may minimize these problems and provide long-term success for adhesive restorations.
authors.affiliation: Department of Prosthetic Dentistry, University of Espírito Santo, Vitória, Espírito Santo, Brazil. flaviabpazinatto@yahoo.com.br
authors.forename: Flávia Bittencourt
authors.initials: FB
authors.lastname: Pazinatto
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Atta
mesh_terms: D000096:Acetone / Q000737:chemistry; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D011109:Polymethacrylic Acids / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D011109:Polymethacrylic Acids; C444444:prime and bond 2.1; C115612:single bond; D014867:Water; D000096:Acetone; D017438:Bisphenol A-Glycidyl Methacrylate