Aims of the Study: The current study aims to evaluate the influence of adding zirconium oxide and Titanium dioxide nanoparticles alone or in combination at three different concentrations (0.02%, 0.04% and 0.06%) on shear and tensile bond strengths of Transbondâ„¢ XT orthodontic adhesive (3M), and to detect the site of bond failure after debonding.

Materials and Methods: One hundred freshly extracted human upper premolar teeth were used. The teeth were divided equally into two main groups, one group for the shear bond strength test and the other for the tensile bond strength test. Each group was further divided into four

Groups: The Control group, zirconium oxide nanoparticles group, Titanium dioxide nanoparticles group, and zirconium oxide nanoparticles mixed with Titanium dioxide nanoparticles group. These groups were further subdivided into three sub-groups according to the concentration of the additives. The labial surface of each tooth was cleaned with fluoride-free pumice and water, etched with 37% phosphoric acid, rinsed and dried. The Transbond™ XT orthodontic adhesive and/or the modified adhesive was placed on the bracket’s mesh and bonded to the etched enamel. Universal testing

Machine (Tinius Olsen Ltd, England) was used to debond the brackets with a knife edge blade at cross head speed of 0.5 mm/min. for the shear bond strength, and 0.010 stainless steel ligature wire was used for debonding in tensile bond strength test. The bond strengths were in measured in Mega pascal, and the adhesive remnant was examined with a stereomicroscope using 10 X. Statistical analysis was done using SPSS Statistics, V21.

Results: The Shear bond strength of zirconium oxide nanoparticles mixed with Titanium dioxide nanoparticles group (0.06%) was statistically higher than the other groups. While in tensile bond strength of zirconium oxide nanoparticles mixed with Titanium dioxide nanoparticles group (0.06%) was significantly the highest.

Conclusion: Generally, the addition of ZrO₂NPs and TiO₂NPs together at the studied concentrations improved the physical properties of orthodontic adhesive related to shear and tensile bond strength and reduced the bond failure rate.