The development of fracture toughness and fracture strength in posterior restorative materials

Fracture toughness testing: A discriminatory mechanical testing performance indicator for glass-ionomer restoratives?

“…Therefore, investigators [23,50,55] are in general agreement that although pre-cracking seems theoretically correct, invariably it will introduce errors when investigating brittle dental restorative materials, thereby negating any benefit produced. In the current study, SEN bend test-pieces were prepared with a sharp notch (0.3 m crack tip radius [46]) moulded around a scalpel blade which has previously been shown to yield valid results that are indicative of the K IC of the material [14][15][16][17][18]20,37]. This adequate sharpness was evident on profilometrically scanning the side surfaces of the SEN bend specimens, which highlighted crack tip radii of 0.3 m.…”

“…Some investigators have reported the use of a traveling microscope [18,20] or an optical microscope [31] for accurate quantification of the measurement of the crack length although images of the crack length were never supplied. In the current study, the crack length was determined after fracture by scanning the fracture surface of each fracture fragment using a contact profilometer, whereby three longitudinal traces were extracted from each scan, one at mid-thickness and two at quarterthickness points [44].…”

“…Fracture toughness (K IC ) is an intrinsic material property, independent of specimen dimensions, that represents a material's resistance to crack propagation [13] and has been employed to test resin-bonded composites (RBCs) [14][15][16][17][18][19][20][21][22][23][24][25][26], GIs [18][19][20]24,25,[27][28][29][30][31][32], ceramics [33][34][35] and dental amalgams [20,24,25,36,37]. The aim of the current study was to investigate whether the single-edge notched (SEN) bend test-piece K IC testing protocol is a reproducible and discriminatory testing methodology to act as a performance indicator for encapsulated and hand-mixed GI restorative materials.…”

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“…A core with a single post may not offer adequate retention for the core and resistance to dislodgment of the core, whether by the direct or indirect method. Passive placement of a flowable core material, such as resin composite or glass ionomer, for extensive coronal replacement with or without a matrix, is less suitable than metal materials for long-term service due to physical properties that can lead to failure (Lloyd & Adamson, 1987;Oliva & Lowe, 1987;Huysmans & others, 1992;Kovarik, Breeding & Caughman, 1992;Yaman & Thorsteinsson, 1992;Gateau, Sabek & Dailey, 1999).…”

Fracture toughness of aged dental composites in combined mode I and mode II loading

“…Mode I fracture toughness for most dental composites ranges between 0.7-2.0 MPa ⅐ m 0.5 depending on filler type, fillermatrix ratio, and testing method. [4][5][6][7][8][9][10][11][12] The sensitivity to technical deviations of several classic fracture mechanics tests when applied to dental composites has been described. 11,13 None of these tests is suitable for the assessment of fracture toughness under mode II stress application.…”