title: Comparison between regional micropush-out and microtensile bond strength of resin composite to dentin.
abstract: OBJECTIVE
  In this study we compared the micropush-out (micro-PO) and microtensile (micro-TBS) test methods for resin composites on different levels and surfaces of dentin.
  
  
  METHODS
  Thirty-four sound human molars were divided into two groups in accordance with the dentin surface used (occlusal (O) or mesio-distal (M)), then subdivided into a further two groups in accordance with the test method (micro-PO (P) or micro-TBS (T)). In groups OP and OT, teeth were ground occlusally perpendicular to their axis, and in groups MP and MT, mesio-distally parallel to their axis to expose dentin. Dentin disks were prepared from different regions of the teeth either in an occluso-cervical (group OP) (n=5) or mesio-distal direction (group MP) (n=5) (S, superficial; M, middle; D, deep). One-hundred-and-twenty standardized occlusal cavities were prepared in these dentin disks using a conical-shaped diamond rotary cutting instrument. The adhesive (Adper Scotchbond Multi-Purpose Dental Adhesive) and a composite material (Filtek Z250 Universal Restorative) were applied and polymerized with a LED light curing unit (Elipar FreeLight 2). The disks (n=20/per group) were tested in a universal testing machine and pushed out with a cross-head speed of 1.0 mm/min. In groups OT (n=12) and MT (n=12), the teeth were ground to expose superficial, middle, and deep dentin. Build-ups of resin composite were constructed with the same materials. The specimens were serially sectioned and trimmed to hour-glass shapes, then tested with the micro-TBS tester at a rate of 1 mm/min. Failure modes were examined using a stereomicroscope and scanning electron microscope.
  
  
  RESULTS
  ANOVA revealed significant differences among the groups (p<0.001). With the push-out test, no premature failure occurred, the variability of the data distribution was acceptable, and regional differences in bond strength among dentin levels could be assessed.
  
  
  CONCLUSIONS
  The micro-PO test method could be an alternative to the micro-TBS technique.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey. isilcekic@gazi.edu.tr
authors.forename: Isil
authors.initials: I
authors.lastname: Cekic-Nagas
authors.forename: Gulfem
authors.initials: G
authors.lastname: Ergun
authors.forename: Emre
authors.initials: E
authors.lastname: Nagas
authors.forename: Arzu
authors.initials: A
authors.lastname: Tezvergil
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D003188:Composite Resins; D001840:Dental Bonding; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis / Q000379:methods; D003804:Dentin; D017220:Dentin-Bonding Agents; D006244:Hardness; D006801:Humans; D008422:Materials Testing / Q000379:methods; D008875:Middle Aged; D008963:Molar; D019279:Resin Cements; D013718:Tensile Strength
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose