Effect of tetragonal zirconia nanoparticle content on enamel strength

The fracture failure of enamel is caused by hole-type flaws and cracks generally present in enamel. In this study, the effect of tetragonal zirconia nanoparticles (nano-t-ZrO₂) on enamel strength was investigated. The addition of nano-t-ZrO₂ improved the surface morphology and reduced the porosity of the enamel as determined by morphological and porosity distribution analyses. The strain on the enamel surface was recorded using a strain gauge attached to the enamel surface. The crack initiation force and strain were measured using the strain gauge, and the crack propagation diagrams at various stages of the tensile process were recorded. The relationship between the crack initiation energy and nano-t-ZrO₂ content was found to be non-linear. Nano-t-ZrO₂ affected the strength of the enamel. Moreover, the tensile force required for the appearance of cracks first increased and then decreased with an increase in the nano-t-ZrO₂ content. The addition of nano-t-ZrO₂ to the enamel matrix suppressed the formation of stress concentration regions and decreased the brittleness of the enamel. At a nano-t-ZrO₂ content of more than 5 wt%, the ZrO₂ particles agglomerated.