[The investigation of the testing method on fracture toughness of dental adhesive resins].
OBJECTIVE
The testing method for mode I fracture toughness (GIC) of dental adhesive resins was investigated.


METHODS
The dental adhesive resins were placed between two Co-Cr alloy plates to make up test specimen, so test specimen had a metal/adhesive resin/metal construction. The category of adhesive resins, the dimensions of test specimen and testing speed were used as the variants. The testing method for mode I fracture toughness (GIC) was investigated by using double cantilever beam (DCB) testing. The correlation between the GIC and each factor was analysed by regression analysis.


RESULTS
In all test specimens, it was found that the values of fracture toughness (GIC, GIR) at the process of crack propagation were nearly constant. Therefore, it was found that fracture toughness (GIC) at maximal load might only be measured to evaluate an adhesive resin. On the values of GIC, there was no effect from the dimensions of the test specimens, width (b = 3.5 mm), thickness (2 hm = 2.4 mm), initial crack length (ao = 10-19 mm) and testing speed(Vc = 0.1 mm/min, 0.2 mm/min). But, it was found that the fracture toughness was influenced by thickness of adhesive layer (hr). In case of SB, the value of GIC had a tendency to increase as the adhesive layer became thicker, and then the crack propagating area observed as cohesive failure became remarkably rougher. In case of PV, the values for hr = 100 and 200 microns were similar, however, that for hr = 20 microns somewhat decreased resulting in an interfacial failure. By the way, cohesive failures of hr = 100 and 200 microns were observed as similar flat surfaces.


CONCLUSIONS
Fracture toughness was not influenced very much by the dimensions of test specimen, but was influenced by thickness of adhesive layer. Thus, it was recognized that this testing method was more effective for evaluating the adhesive resin.
Ai
H
H
College of Stomatology, China Medical University.
Zhao
Y
Y
Nagai
M
M
Miyairi
H
H
Yasuda
N
N
D008422:Materials Testing / Q000379:methods*; D019279:Resin Cements; D013718:Tensile Strength
D019279:Resin Cements; C095998:Adhesive cement