title: Effect of Smear Layers Created by Different Burs on Durability of Self-Etching Adhesive Bond to Dentin of Primary Teeth.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effects of a smear layer generated by a high-speed diamond or carbide bur on the durability of microtensile bond strength (μTBS) of a self-etching adhesive to primary dentin.
  
  
  METHODS
  Flat occlusal dentin surfaces of 105 human primary molars were exposed using 600 grit silicon carbide paper before being divided into 2 groups for further grinding with either a highspeed diamond or carbide bur. Ten prepared dentin surfaces treated by each bur were evaluated for the characteristics of the smear layer using a scanning electron microscope (SEM). Seventy-five specimens from each bur-prepared group were applied with a 2-step self-etching adhesive (Clearfil SE Bond(®)) then built up with a resin composite. Each bonded specimen was sectioned into a 1-mm thick slab and trimmed to a dumbbell shape with a cross-sectional area of approximately 1 mm(2). All slabs were divided into 3 groups (n=25) according to 3 storage times of 24 hrs, 3 months, and 6 months, in distilled water at 37°C. After storage, the μTBS was determined using a universal testing machine. All fracture specimens were prepared for observation of failure modes. Ten bonded specimens of each bur group were prepared for observation of the resin-dentin interface using an SEM. Smear-layer thickness, μTBS, and failure mode distributions were statistically analyzed.
  
  
  RESULTS
  The high speed carbide bur created a significantly thinner smear layer than the diamond bur (p < 0.05). Dentin surfaces treated with a high-speed carbide bur generally obtained significantly higher μTBS than the diamond bur group (p < 0.05). The μTBS gradually decreased over time such that specimens stored for 6 months had significantly lower bond strength than those stored for 24 hrs (p < 0.05). Self-etching adhesive created a hybrid layer of the same thickness when prepared with either a carbide bur or diamond bur, but the carbide bur group had longer and more resin tags.
  
  
  CONCLUSIONS
  Highspeed carbide bur groups had a higher μTBS than diamond bur groups for all storage times, and bond strengths decreased over time in both substrate groups. The use of a carbide bur produced a thinner smear layer and therefore is recommended when using this 2-step self-etching adhesive to bond the resin composite to primary dentin.
authors.forename: P
authors.initials: P
authors.lastname: Rirattanapong
authors.forename: P
authors.initials: P
authors.lastname: Senawongse
authors.forename: C
authors.initials: C
authors.lastname: Harnirattisal
authors.forename: W
authors.initials: W
authors.lastname: Wunsiw
mesh_terms: D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003754:Dental High-Speed Equipment; D003764:Dental Materials / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D018130:Diamond / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008963:Molar / Q000648:ultrastructure; D019279:Resin Cements / Q000737:chemistry; D016369:Smear Layer / Q000648:ultrastructure*; D013314:Stress, Mechanical; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014094:Tooth, Deciduous / Q000648:ultrastructure*; D014867:Water / Q000737:chemistry
chemical_list: D017554:Carbon Compounds, Inorganic; C438313:Clearfil SE Bond; D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; D019279:Resin Cements; D014867:Water; D018130:Diamond
keywords: bond strength; burs; hybrid layer; primary dentin; self-etching adhesive; smear layers