Microtensile Specimen Attachment and Shape—Finite Element Analysis

Abstract

Microtensile bond strength values are influenced by specimen shape and attachment method to the gripping device during testing. We hypothesized that stress distribution inside the testing specimen is affected by microtensile specimen shape and attachment method. Rectangular, hourglass-, and dumbbell-shaped specimens, all with a 1 mm(2) cross-sectional testing region, were modeled as indirect ceramic restorations luted to dentin. Three specimen attachments were investigated: (1) posterior surface; (2) posterior, superior, and lateral surfaces; and (3) all surfaces. Qualitative and quantitative analyses were carried out according to von Mises' criteria. Stress analysis showed a direct correlation between attachment modes and stress distribution, with shear stresses observed in models with less surface attachment. Increasing the number of faces for specimen attachment to the metallic gripping device resulted in a more homogeneous and regular distribution of stress, with tensile stress concentrated at the adhesive interface. Dumbbell-shaped specimens showed improved stress distribution compared with rectangular and hourglass-shaped specimens.

Influence of the bracket on bonding and physical behavior of orthodontic resin cements

“…We applied a µTBS model in hourglass shape. FEA studies on stress distribution in µTBS specimens showed the hourglass shape has lower failure stress for the adhesive mode of failure than other specimen geometries, as bar or dumbbell shapes, because stress concentrates at the neck of the specimen 23,24) . Hourglass shape has also been described as less sensitive to uneven adhesive layers 23) .…”

Parameters that influence microtensile bond testing of adhesive systems

“…The remaining 25 studies, which we included, evaluated the following parameters: 1) in relation to specimens: geometric aspects [5][6]9,[11][12][13][14][15][16][17][18][19][20][21] cutting speed [22][23] , cutting method 24 , wear-and-tear and integrity method after cutting 23 , storage time 22 , inclusion of specimens with premature failure 24 , imperfection during manufacture 16 , bonding surface area 5,[19][20]25 , wear-and-tear method for the dentin 26 , form of filling and fixing 6,15,19;27 ; 2) storage time of teeth used in the assay 28 ; 3) angle of the bond interface 29 ; 4) incline of the dentin walls 30 ; 5) variation in adhesive resistance between the teeth or within the same tooth 31 ; 6) adhesive thickness 30 ; 7) use of the cohesive resistance of dentin near the bonding interface as a standard of reference 18 ; 8) loading speed during the test 19,32 ; 9) thickness of remaining dentin 19 ; 10) imperfections in the adhesive layer 16 . The characteristics of the included studies are summarized in Chart 1.…”

The effect of disk type and cutting speed on the micro-tensile bond strength of ceramic specimens to resin cement

“…The effect of a failure induced on the edges of specimens is "fatal," whereas a fissure or fracture in the middle of a specimen could be better tolerated. Furthermore, the greater the length of the defect, the greater the fracture tension, particularly when the direction of the defect is perpendicular to the direction of the tensile stresses 18,24,29) . The influence of the cutting process on compositeto-enamel bond strength has been reported in the literature.…”