Objectives: The purpose of this study was to evaluate the bonding durability of soft denture liner to a denture base material after fatigue processes. Methods: Denture base resin (Pour Resin, Shofu) was auto-polymerized into a cylinder shape (8mm diameter, 4mm high). The bonding surface of denture base specimens was polished with a 600-grit silicon carbide paper, followed by application of resin primer (Sofreliner Primer, Tokuyama). Test specimens were fabricated by polymerizing a 2 mm thickness of polyvinylsiloxane denture liner (Sofreliner MS, Tokuyama) between a pair of primed cylinders. Fracture loads were evaluated before the fatigue process (control), and after subjecting to thermo-cycling (4-60˚C, maximum 30,000 cycles) or cyclic loading (75N, 1.2Hz, maximum 400,000 times), by tensile testing with a 25.4mm/min cross-head speed. All data were statistically analyzed by ANOVA (p<0.05). Results: For the thermo-cycled group, fracture loads were maintained up to 20,000 thermo-cycles (corresponding to 2years clinically). The fracture load after 20,000 cyclic loads (corresponding to 2 months clinically) was significantly decreased compared to the control (p<0.05). Conclusions: It was concluded that cyclic loading is one of the important factors that decrease the fracture loads of soft relining material, and thermo-cycling also causes a decrease in fracture load.

Table. Results of tensile tests:  mean (s.d.), Fracture load units: N, n= 5,

Control	Number of thermo-cycles (cycles)
108.2 (5.1)	10,000	20,000	30,000
	106.7 (6.6)	103.5 (6.3)	70.8 (14.4)
	Number of cyclic loading (times)
	20,000	100,000	400,000
	60.3 (4.6)	37.7 (2.9)	18.3 (5.4)