title: Effect of etching time and resin bond on the flexural strength of IPS e.max Press glass ceramic.
abstract: OBJECTIVE
  To evaluate the effect of hydrofluoric acid (HFA) etching time and resin cement bond on the flexural strength of IPS e.max(®) Press glass ceramic.
  
  
  METHODS
  Two hundred and ten bars, 25mm×3mm×2mm, were made from IPS e.max(®) Press ingots through lost-wax, hot-pressed ceramic fabrication technology and randomly divided into five groups with forty-two per group after polishing. The ceramic surfaces of different groups were etched by 9.5% hydrofluoric acid gel for 0, 20, 40, 60 and 120s respectively. Two specimens of each group were selected randomly to examine the surface roughness and 3-dimensional topography with atomic force microscope (AFM), and microstructure was analyzed by the field emission scanning electron microscope (FE-SEM). Then each group were subdivided into two subgroups (n=20). One subgroup of this material was selected to receive a thin (approximately 0.1mm) layer of resin luting agent (Variolink N) whereas the other subgroup remained unaltered. Half of subgroup's specimens were thermocycled 10,000 times before a 3-point bending test in order to determine the flexural strength. Interface between resin cement and ceramic was examined with field emission scanning electronic microscope.
  
  
  RESULTS
  Roughness values increased with increasing etching time. The mean flexural strength values of group 0s, 20s, 40s, 60s and 120s were 384±33, 347±43, 330±53, 327±67 and 317±41MPa respectively. Increasing HF etching times reduced the mean flexural strength (p<0.05). However, the mean flexural strength of each group, except group 0s, increased significantly to 420±31, 435±50, 400±39 and 412±58MPa after the application of dual-curing resin cement. In the present investigation, no significant differences after thermocycling on the flexural strengths were evident.
  
  
  CONCLUSIONS
  Overtime HF etching could have a wakening effect on IPS e.max(®) Press glass ceramic, but resin cement bonding to appropriately etched surface would strengthen the dental ceramic.
authors.affiliation: Department of Prosthodontics, Nanjing Stomatological Hospital, Nanjing University, Nanjing, Jiangsu Province, China. Electronic address: L_xiaoping@yahoo.com.
authors.forename: Luo
authors.initials: L
authors.lastname: Xiaoping
authors.affiliation: Department of Prosthodontics, Nanjing Stomatological Hospital, Nanjing University, Nanjing, Jiangsu Province, China.
authors.forename: Ren
authors.initials: R
authors.lastname: Dongfeng
authors.affiliation: Manchester University Dental School, United Kingdom.
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods*; D000179:Acrylates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D001840:Dental Bonding / Q000379:methods*; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006858:Hydrofluoric Acid / Q000737:chemistry; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D018625:Microscopy, Atomic Force / Q000379:methods; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D058105:Polymerization; D011897:Random Allocation; D019279:Resin Cements / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D000179:Acrylates; C508050:IPS e.max Press; D019279:Resin Cements; D012821:Silanes; C493120:lithia disilicate; D014867:Water; D003776:Dental Porcelain; C103502:Variolink; C023506:Glass ceramics; C040415:heliobond; D006858:Hydrofluoric Acid
keywords: Flexural strength; Glass ceramic; Hydrofluoric acid; Resin cement; SEM