[Effect of hydrofluoric acid etching time and resin bonding on the flexural strength of lithium disilicate glass ceramic].
OBJECTIVE
To analyze the effect of hydrofluoric acid(HFA) etching time and resin bonding on the flexural strength of IPS e.max® Press glass ceramic, and evaluate the efficacy of resin cements to seal the cracks of the etched ceramic.


METHODS
Two hundred and twenty-five bars (25.0 mm×3.0 mm×2.0 mm) were made from IPS e.max® Press ingots using lost-wax, hot-pressed ceramic fabrication technology and randomly divided into five groups, forty-five each.In each group, the surfaces of ceramic bars were etched by 9.5% HFA gel for 0, 20, 40, 60 and 120 s respectively. Three specimens from each group were selected to observe the microstructure by the field emission scanning electron microscope (FE-SEM). Then each group were randomly subdivided into two subgroups (n = 20).One subgroup were coverd with a thin (approximately 0.1 mm) layer of resin cement (Variolink N), whereas the other subgroup remained unaltered.Half of the specimens were stored in 37°C water bath for 24 h and the other half went through thermocycle 10 000 times before 3-point bending test to determine their flexural strength.Interfaces between resin cement and etched ceramic were examined with FE-SEM.


RESULTS
FE-SEM results showed that etching with HFA resulted in preferential dissolution of glass ceramic, and partially supported crystals within the glass matrix were lost with the increasing of etching time.FE-SEM indicated that resin cement sealed the cracks and defects and bonded tightly to etched ceramic surface. The mean flexural strength values of group 0, 20, 40, 60 and 120 s were (384 ± 33), (347 ± 43), (330 ± 53), (327 ± 67) , and (317 ± 41) MPa respectively. The mean flexural strength of each group except group 0 s increased significantly to (420 ± 31), (435 ± 50), (400 ± 39), and (412 ± 58) MPa respectively after the application of resin cement.


CONCLUSIONS
Overtime HFA etching could have a wakening effect on IPS e.max® Press glass-ceramic. The application of dual-curing resin cement can compensate the strength loss of the etched glass ceramic.
Department of Prosthodontics, School of Stomatology, Nanjing University & Nanjing Stomatological Hospital, Nanjing 210008, China.
Dong-feng
DF
Ren
Xiao-ping
XP
Luo
D000134:Acid Etching, Dental / Q000379:methods; D002516:Ceramics / Q000737:chemistry*; D001840:Dental Bonding; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006858:Hydrofluoric Acid / Q000737:chemistry*; D011897:Random Allocation; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties
C508050:IPS e.max Press; D019279:Resin Cements; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics; D006858:Hydrofluoric Acid