title: The influence of adhesive thickness on the microtensile bond strength of three adhesive systems.
abstract: OBJECTIVE
  To evaluate the effects of multiple adhesive layers of three etch-and-rinse adhesives on both adhesive thickness and microtensile bond strength (microTBS).
  
  
  METHODS
  Midcoronal occlusal dentin of 36 extracted human molars was used. Teeth were randomly assigned to 3 groups (EB, XP, PQ) according to the adhesive system to be used: PQ1 (Ultradent) (PQ), EnaBond (Micerium) (EB), or XP Bond (Dentsply/DeTrey) (XP). Specimens from each group were further divided into three subgroups according to the number of adhesive coatings (1, 2, or 3). In all subgroups, each adhesive layer was light cured before application of each additional layer. After bonding procedures, composite crowns were incrementally built up. Specimens were sectioned perpendicular to the adhesive interface to produce multiple beams, approximately 1 mm2 in area. Beams were tested under tension at a crosshead speed of 0.5 mm/min until failure. Adhesive thicknesses and failure modes were evaluated with SEM. The microTBS data and mean adhesive thickness were analyzed by two-way ANOVA and multiple-comparison Tukey's test (alpha = 0.05).
  
  
  RESULTS
  The mean bond strength (in MPa (SD)) of group EB gradually increased from 1 to 3 consecutive coatings (27.02 (9.38) to 44.32 (4.93), respectively) (p < 0.05). The highest mean bond strengths for the PQ (46.66 (12.95)) and XP groups (40.55 (5.69)) were obtained applying two adhesive coatings. The mean thickness of the adhesive layer (in microm (SD)) significantly increased with the number of coatings (p < 0.05), ranging from 29.45 (1.42) to 77.64 (1.10) for PQ, from 5.12 (0.68) to 37.75 (0.92) for EB, and from 12.64 (0.68) to 37.92 (0.71) for the XP group. Failure modes for EB specimens were mainly classified as adhesive failure between adhesive and dentin. The XP3 and PQ3 subgroups showed a greater number of total cohesive failure in adhesive.
  
  
  CONCLUSIONS
  Multiple adhesive coats significantly affected bond strength to dentin. An excess of adhesive layer thickness can negatively influence the strength and the quality of adhesion.
authors.affiliation: Department of Operative Dentistry, Dental School, University of Chieti, Italy. cdarcang@unich.it
authors.forename: Camillo
authors.initials: C
authors.lastname: D'Arcangelo
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Vanini
authors.forename: Gianni Domenico
authors.initials: GD
authors.lastname: Prosperi
authors.forename: Giulia
authors.initials: G
authors.lastname: Di Bussolo
authors.forename: Francesco
authors.initials: F
authors.lastname: De Angelis
authors.forename: Maurizio
authors.initials: M
authors.lastname: D'Amario
authors.forename: Sergio
authors.initials: S
authors.lastname: Caputi
mesh_terms: D000269:Adhesives / Q000737:chemistry; D003188:Composite Resins; D003442:Crowns; D045662:Dental Etching; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents / Q000737:chemistry; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D013718:Tensile Strength
chemical_list: D000269:Adhesives; D003188:Composite Resins; D017220:Dentin-Bonding Agents; C542520:EnaBond; C119199:PermaQuik; D019279:Resin Cements; C532387:XP-Bond