Effects of Three Novel Bracket Luting Agents Containing Zirconia Primer on Shear Bond Strength of Metal Orthodontic Brackets Attached to Monolithic Zirconia Crowns: A Preliminary In Vitro Study

Abstract

Background. The increased use of zirconia crowns in adult orthodontic patients warrants the establishment of methods and materials to adhere orthodontic brackets properly to zirconia crowns. However, studies in this regard are scarce, and many materials remain untested. This preliminary study aimed to examine three new adhesives containing zirconia primers for the first time. Methods. Sixty identical monolithic zirconia crowns were fabricated and randomly divided into 4 groups of 15 each (Panavia SA Cement Plus, G-CEM, TheraCem, and Transbond XT Composite (control)). After glaze removal with a diamond bur, a metal orthodontic bracket was attached to the surfaces of the crowns using the respective adhesive. Specimens were incubated at 37°C and then thermocycled for 2000 cycles. Shear bond strengths (SBS) of brackets in different groups were estimated using a universal testing machine. Mean SBS values were compared with the values 6, 8, and 10 (as acceptable SBS values) and 13 MPa (as the maximum SBS tolerable by zirconia) using the one-sample t-test. They were also compared with each other using the one-way ANOVA and Tamhane post hoc test (α = 0.05). Results. The ANOVA indicated a significant overall difference; the Tamhane test showed that the difference between the control group and all test groups was significant ( $P$  < 0.0005); however, the 3 test groups were not significantly different from each other ( $P$  > 0.30). The SBS of the control group was significantly lower than the minimum acceptable SBS (6 MPa, $P$  < 0.0005). The mean SBS of the TheraCem was not significantly different from 10 MPa ( $P$  = 0.902), while the mean SBS values of Panavia SA Cement Plus and G-CEM were significantly greater than 10 MPa ( $P$  < 0.05). None of the three zirconia adhesives had mean SBS values higher than 13 MPa. Conclusion. All novel zirconia adhesives (Panavia SA Cement Plus, G-CEM, and TheraCem) generated SBS values adequate to attach metal orthodontic brackets to zirconia prostheses (at or greater than 10 MPa) without damaging the zirconia during bracket removal (not above 13 MPa).