title: Hardness comparison of bulk-filled/transtooth and incremental-filled/occlusally irradiated composite resins.
abstract: BACKGROUND
  Use of a bulk-fill/transtooth composite resin insertion/irradiation technique may not provide as well polymerized a restoration as when using a conventional incremental placement/irradiation technique. Little information exists as to how the hardness of restorations produced by the 2 techniques compare.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of composite resin placement and an irradiation technique on the axial hardness at various depths in a Class I composite resin to include the influence of composite resin filler classification and shade.
  
  
  METHODS
  Cylindrical Class I preparations were made in 70 recently extracted human molars and restored with either a light (A1) or dark shade (A4) of a microfill, microhybrid, or nanohybrid composite resin, or with a single shade of a translucent material. Half were placed using a conventional 2-mm-thick incremental-fill/occlusal irradiation technique, and half using a bulk-fill/transtooth irradiation method (n=5). Specimens were sectioned occluso-apically and axial Knoop hardness values were obtained at depths of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm. Hardness at 0.5 mm was used as a control to compare to deeper readings. Statistical analyses consisted of multiple ANOVAs and Dunnett's post-hoc tests performed at appropriately determined significance levels.
  
  
  RESULTS
  For 3 multishaded materials tested, axial hardness values were relatively unaffected by composite resin shade or filler classification for the incremental technique, but were significantly affected by these factors when using the bulk-fill/transtooth irradiation method. A single shade translucent material was not affected in either the bulk or incremental condition.
  
  
  CONCLUSIONS
  Use of a bulk-fill/transtooth irradiation technique for composite resin placement does not result in axial hardness values equivalent to that of an incremental-fill/occlusal irradiation technique.
authors: Department of General Dentistry, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1260, USA. dlazarchik@mcg.edu
authors: David A
authors: DA
authors: Lazarchik
authors: Barry D
authors: BD
authors: Hammond
authors: Christy L
authors: CL
authors: Sikes
authors: Stephen W
authors: SW
authors: Looney
authors: Frederick A
authors: FA
authors: Rueggeberg
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects; D000704:Analysis of Variance; D003116:Color; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D001840:Dental Bonding / Q000379:methods; D003793:Dental Restoration, Permanent / Q000379:methods*; D017220:Dentin-Bonding Agents / Q000627:therapeutic use; D006244:Hardness / Q000528:radiation effects; D006245:Hardness Tests; D006801:Humans; D036103:Nanotechnology; D011140:Polyurethanes / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D011140:Polyurethanes