In Vitro Comparison of Orthodontic Shear Bond Strength Between Human and Bovine Enamel

Background: This in vitro study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets bonded using different techniques and assess whether bovine enamel demonstrates comparable behavior to human enamel in SBS testing. Methods: A total of 80 human premolars and 80 bovine mandibular incisors were randomly assigned to four bonding protocol groups according to the adhesive procedure applied: (1) adhesive only; (2) etching + adhesive; (3) etching + primer + adhesive; and (4) etching + primer + bracket base primer + adhesive. Shear bond strength (SBS) testing was performed using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed using two-way ANOVA and Tukey’s post hoc tests (p < 0.05). Results: Both bonding protocol and enamel substrate significantly affected SBS values (p < 0.001), whereas the interaction between these factors was not statistically significant (p = 0.061). SBS values generally increased as the bonding protocol became more complex. The adhesive-only groups demonstrated significantly lower SBS values than the other bonding protocols in both human and bovine enamel. Human enamel demonstrated significantly higher SBS values than bovine enamel overall (p < 0.001). Conclusions: Within the limitations of this in vitro study, increasing bonding protocol complexity generally resulted in higher SBS values in both human and bovine enamel. Although bovine enamel demonstrated similar overall trends across bonding procedures, significant differences between human and bovine enamel were observed. Therefore, bovine enamel should not be considered directly interchangeable with human enamel for absolute SBS measurements. Further in vivo and clinical studies are required before simplified bonding protocols can be recommended for clinical application.