title: Effects of thermal fatigue on shear punch strength of tooth-colored restoratives.
abstract: OBJECTIVE
  This study investigated the effect of thermal fatigue on the shear strength of a range of tooth-colored restorative materials including giomers, zirconia-reinforced glass ionomer cement (GIC), nano-particle resin-modified GIC, highly viscous GICs, and composite resin.
  
  
  METHODS
  Twenty specimens of each material were fabricated in standardized washers (17 mm outer diameter, 9 mm internal diameter, 1 mm thick). The specimens were cured, stored in 100% humidity at 37.5°C for 24 h, and randomly divided into two groups of 10. Group A specimens were nonthermocycled (NT) and stored in distilled water at 37°C for 168 h. Group B specimens were thermocycled (TC) for 10,000 cycles (168 h) with baths X, Y, and Z adjusted to 35°C, 15°C, and 45°C, respectively. Each cycle had dwell times of 28 s in X, and 2s in Y/Z in the order XYXZ. Specimens then underwent shear punch testing at a crosshead speed of 0.5 mm/min with a 2 kN load cell. Statistical analysis of shear strength was done using t-test and two-way ANOVA/Scheffe's post hoc test at significance level P < 0.05.
  
  
  RESULTS
  The effect of thermal fatigue on shear strength was material dependent. Except for the "sculptable" giomer (Beautifil II) and a highly viscous GIC (Fuji IX GP Fast), no significant differences in shear strength were generally observed between the NT and TC groups. For both groups, the composite resin (Filtek Z250XT) had the highest shear strength while the zirconia-reinforced (zirconomer) and a highly viscous GIC (Ketac Molar Quick) had the lowest.
  
  
  CONCLUSIONS
  The effect of thermocycling on shear strength was material dependent. Thermal fatigue, however, did not significantly influence the shear strength of most materials assessed. The "sculptable" composite and giomer were significantly stronger than the other materials evaluated. Shear strength of the "flowable" injectable hybrid giomer was intermediate between the composite and GICs.
authors: Faculty of Dentistry, National University of Singapore, Singapore 119083, Republic of Singapore.
authors: Fam Mei Shi
authors: FM
authors: Melody
authors: Faculty of Dentistry, National University of Singapore, Singapore 119083, Republic of Singapore; Department of Dentistry, Ng Teng Fong General Hospital and Jurong Medical Centre, Jurong Health Services, Singapore 609606, Republic of Singapore.
authors: Yap Adrian
authors: YA
authors: U-Jin
authors: Faculty of Dentistry, National University of Singapore, Singapore 119083, Republic of Singapore; Department of Dentistry, Ng Teng Fong General Hospital and Jurong Medical Centre, Jurong Health Services, Singapore 609606, Republic of Singapore.
authors: Tan Wei Min
authors: TW
authors: Natalie
authors: Faculty of Dentistry, National University of Singapore, Singapore 119083, Republic of Singapore.
authors: Tay Wan Ling
authors: TW
authors: Elizabeth
authors: Faculty of Dentistry, National University of Singapore, Singapore 119083, Republic of Singapore.
authors: Jessica Yeo Siu
authors: JY
authors: Chien
keywords: Composite; giomer; glass ionomer; shear strength; thermal fatigue