Influence of the geometry of ceramic specimens on biaxial flexural strength: experimental testing and finite element analysis

Abstract

This study evaluated the influence of the geometry of ceramic specimens (disc vs. square plate) on the biaxial flexural strength (BFS) using an experimental set and finite element analysis (FEA). Leucite glass-ceramic blocks were used in the preparation of disc (D; n=14) and square plate (S; n=13) specimens with the same lower (tensile) surface area. The specimens were subjected to a piston-on-three-ball flexural test (ISO 6872:2008). To calculate the BFS of the S group, the specimen radius, indicated by the ISO 6872:2008 formula for discs, was replaced by half of the side length. FEA compared the pattern of stress distribution and the first principal stress between D and S specimens having the same and different lower (tensile) surface area. Student's t-test showed no difference (p=0.85) in the BFS between D (95.0±9.6 MPa) and S (84.3±10.3 MPa). FEA indicated a similar pattern of stress distribution, with almost no difference in the first principal stress of discs and square plates with the same lower (tensile) surface area. In the experimental condition investigated, square plate ceramic specimens can be used in piston-on-three-ball tests. For the calculation of the BFS, the specimen radius may be replaced by half side length of the square specimen.

Mechanical properties, aging stability and translucency of speed-sintered zirconia for chairside restorations

“…Compared to the set-up described in ISO standard 6872, the set-up applied in this work was adjusted for testing square disk samples (length of 12-16 mm), without losing the accuracy of the tests [63]. Importantly, finite element analysis showed the same stress distribution when testing disk-and round-shaped samples using the applied test set-up, thus rendering comparable biaxial strength values by substituting the radius value of the disk-shaped specimen by half the length of the square-plate specimen [30]. As most commercial dental ceramic materials are supplied in the form of blocks, one of the main advantages of this set-up is that it allows the fabrication of samples for biaxial flexural strength testing without reshaping the sample.…”

“…Regarding the biaxial flexural strength, a piston-on-3-balls (P3B) test was performed. Although this set-up has already been used for some time, multiple studies have tried to validate and adjust the P3B test with respect to specimen size and geometry [30,[60][61][62]. Minimizing the applicable specimen size is considered to be crucial as most of the ceramic CAD/CAM materials are supplied in the form of small CAD/CAM blocks or disks intended for fabrication of small dental restorations, such as inlays, onlays or single crowns.…”

“…After fracture, all fragments were carefully collected and their amount was registered. The biaxial flexural strength of square samples was calculated as indicated in the ISO standard 6872 for disks, with the specimen radius replaced by half of the sample side length [30].…”

Evaluation of Biaxial Flexural Strength and Shear Bond Strength of a Novel Chair-Side Cad/Cam Pre-crystalized Zirconia Reinforced Lithium Silicate (In-Vitro Study)

“…In the provided equation: σ max represents the maximum tensile stress P is the calculated fracture load 'a' is the radius of the knife-edge support 'v' is the Poisson's ratio for the material (typically substituted with 0.25 for ceramics) 'h' represents the thickness of the disc and is measured using a digital caliper 'ln' stands for the natural logarithm.. 12…”

Fatigue behavior and colorimetric differences of a porcelain-veneered zirconia: effect of quantity and position of specimens during firing

“…After firing, the feldspathic ceramic surface was ground using a polishing machine (EcoMet/AutoMet 250) with #200, #400, #600 and #1200 grit silicon carbide papers under constant water cooling to standardize the specimens thickness (feldspathic layer of 0.7 mm, summing a final specimen thickness of 1.4 mm and diameter of 15 mm, in accordance to ISO 6872:2015 [11] specifications) and to acquire a polished surface. The porcelain around the zirconia was equally ground, using the same approach, to avoid excess of veneer material on the margins of the specimens, without any interference in the fatigue test results, since the margins were out of the stress concentration area, which is inside the three steel balls diameter [13]. Finally, the specimens were visually inspected under an optical microscope (Stereo Discovery V20; Carl Zeiss, Göttingen, Germany) to verify the presence of porosities or defects on their surface, if so the specimen was discarded and replaced by a new one.…”