title: Effect of early water exposure on the strength of glass ionomer restoratives.
abstract: This study examined the effect of early water exposure on the shear strength of a spectrum of glass ionomer restoratives. The materials evaluated included conventional auto-cured (Fuji II [FT], GC), resin-modified light-cured (Fuji II LC [FL]) and, recently introduced, high strength auto-cured (Fuji IX GP Fast [FN], GC; Ketac Molar Quick [KQ], 3M-ESPE; Ketac Molar [KM], 3M-ESPE) cements. Sixteen specimens (8.7-mm in diameter and 1-mm thick) of each material were prepared in metal washers and randomly divided into 2 groups. The specimens were allowed to set for 6 minutes between polyester strips, to ensure completion of the initial set. The strips were subsequently removed, and the surfaces of Group 1 specimens were coated on both sides with resin (Fuji Coat LC, GC) and light cured for 10 seconds. Group 2 specimens were left uncoated. All specimens were then conditioned in distilled water at 37 degrees C for 4 weeks. After conditioning, the specimens were restrained with a torque of 2.5 Nm and subjected to shear punch testing using a 2-mm diameter punch at a crosshead speed of 0.5-mm/minute. The mean shear strengths of the materials were computed and subjected to Independent Samples t-test and ANOVA/Scheffe's tests at significance level 0.05. Mean strength ranged from 78.34 to 99.36 MPa and 79.88 to 95.78 MPa for Groups 1 and 2, respectively. No significant difference in shear strength was observed between the 2 groups. For both groups, KM and KQ were significantly stronger than FT. Contrary to current teaching, early exposure to water did not weaken glass ionomer restoratives. A marginal increase in strength was actually observed for some materials.
authors.affiliation: Department of Cariology, Endodontology and Operative Dentistry, Peking University School and Hospital of Somatology, PR China. wangxiaoyanpx@gmail.com
authors.forename: X Y
authors.initials: XY
authors.lastname: Wang
authors.forename: Adrian U J
authors.initials: AU
authors.lastname: Yap
authors.forename: H C
authors.initials: HC
authors.lastname: Ngo
mesh_terms: D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D019415:Torque; D014867:Water / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C079765:Fuji II LC cement; C439808:Fuji IX GP Fast; D005899:Glass Ionomer Cements; C454800:Ketac-Molar Quick; D019279:Resin Cements; D012117:Resins, Synthetic; C110712:ketac-molar; D014867:Water; C084541:Fuji glass-ionomer lining cement