Roughness and microstructural changes in Y-TZP laser treated before sintering

Abstract

Purpose: The purpose of this work was to qualitatively assess the actual failure origin (bonded dentin interface or loaded resin cylinder surface) during shear bond testing, by scaling and fracture surface analysis. Failure behavior was assessedbyexamining scaling effects on failure loadsbybonding surface area (by r2) and bonded resin cylinder surface area (by r) with increasing r. Methods and materials: Non-carious human molar teeth were stored in 0.3% sodium azide solution. Nine 2-mm thick dental disks from the occlusal dentin were prepared using a low-speed sectioning saw and stabilized in a 1′′-dia. cold-cure acrylic resin. The tooth disks were prepared as instructed for the resin composite system (Filtek TM Supreme Ultra) and one of four resin composite cylinders (1.59mm, 3.18mm, 4.76mm, 6.35mm dia., all 5-mm in length) were bonded on the prepared tooth surface. Specimens were stored in saline for 1-day prior to testing. The samples were then shear tested at room temperature using an Ultratester testing machine (Ultradent Products) at a 1.0mm/min crosshead speed (5mm long square piston). Following shear testing, each dentin disk was finished with silicone carbide paper (240–600 grit) to remove any residual resin composite debris and tested again with the same resin composite of a different diameter cylinder, until each disk was tested with all four different diameter cylinders (all diameters used in each cycle). If failure involved the bonded surface area or the surface area of the loaded cylinder (contact stress between flat and cylinder), one of the following relationships would be constant with increasing radii (r): For bonded area?r/L?2 = 1/ps= constant; For cylinder surface r/L=2/psbl = constant where b=KvL and K= [2/pl ((1−v 12)/E 1+ (1−v 22)/E 2)/((1/d 1) + (1/d 2))](1/2) With: L= load l = cylinder length v1 and v2=Poisson’s ratios E1 and E2=elastic moduli d1 and d2=diameter of cylinder and flat (=8) [so K∼ 1/[pl(1/2r)]. Results: The relationship for the cylinder surface area was constant while the relationship for the bonded surface area was not. In addition, failure loads scaled linearly with r (r2 = 0.99, p=0.004) and not with r2. Fractographic analysis (SEM) is consistent with failures occurring from the loaded cylinder, not the bonded interface. Conclusion: “Shear bond” testing does not appear to test the bonded interface. http://dx.doi.org/10.1016/j.dental.2014.08.024