In vitro comparison of different composite resins for aligner attachment production : Amount of adhesive flash, flash removal time, and shear bond strength.

Introduction: The aim of this in vitro study was to determine the difference between aligner attachments constructed from four different composite resins in terms of adhesive flash amount, removal time, and shear bond strength.

Materials and methods: In all, 80 extracted human premolars were divided into four groups (N = 20) based on the type of composites used for the fabrication of aligner attachments (Group 1: GC Aligner Connect and Group 2: GC Ortho Connect [both from GC Dental Products, Tokyo, Japan]; Group 3: Z350 XT flowable and Group 4: Filtek Z350 XT Universal [both from 3M Unitek, Monrovia, CA, USA]). After bonding, the attachments were scanned with the iTero Element® (Align® Technology, San Jose, CA, USA). The amount of adhesive flash in the overflowing areas was analyzed by comparing the bonded attachments before and after removing the adhesive flash via the software 3D Geomagic Control (3DS Systems, Rock Hill, SC, USA). A color map was used to reveal the percentage of overflowing resin. Flash adhesive removal time per tooth and shear bond strength of the attachments were also analyzed. The significance level was set at p < 0.05.

Results: The median values for the overflowing flash adhesive (surface deviation values) were 0.26, 0.29, 0.35, and 0.26 mm for Groups 1, 2, 3, and 4, respectively, with a significant difference between the groups (3 > 1, 2, 4; p < 0.001, effect size (η²) = 0.215). The percentage of red color deviation in overflowing areas was mostly observed in Group 3 (58.8%), while the green color was mostly noted in Group 4 (25%; p < 0.05). The time for removal of the adhesive flash was significantly higher in Group 1 than in Groups 2, 3, and 4 (p < 0.001, η² = 0.340). The mean bond strength of Group 4 (19.27 ± 6.37 MPa) was higher than those of Groups 1 (11.42 ± 2.54 MPa) and 2 (14.43 ± 4.61 MPa; p < 0.001 and p = 0.015, η² = 0.261).

Conclusion: Z350 XT flowable composite showed a higher overflow value and percentage of color deviation than the attachments made from the other resins. The universal restorative resin Filtek Z350 XT Universal was found to be advantageous in terms of both causing less flash adhesive and demonstrating higher bond strength to the tooth.