Shear bond strength of 3-dimensional-printed orthodontic brackets

Introduction

This in vitro study aimed to evaluate the shear bond strength (SBS) and adhesive remnant index (ARI) of 3-dimensional-printed orthodontic brackets with 3 different base designs and to examine the surface morphologic differences of remaining adhesives using scanning electron microscopy (SEM).

Methods

Sixty maxillary premolar teeth (n = 20 per group) were randomly allocated into 3 bracket base design groups: (1) custom, (2) macroretentive, and (3) standard. After digital scanning of the teeth, the brackets were printed using a MAX UV DLP 3D printer (Asiga, Sydney, Australia). Each bracket was bonded using Transbond XT composite and light-cured for 10 seconds with a light-emitting diode curing unit (Valo; Ultradent, South Jordan, Utah). Subsequently, SBS testing was performed using a universal testing machine at a 1 mm/min crosshead speed, and fracture loads were recorded in megapascals (MPa). After debonding, ARI scores were evaluated under a digital microscope by a blinded investigator and reevaluated after 2 weeks for reliability. In addition, bracket bases and tooth surfaces were examined under a high-resolution SEM (30 kV, 20 mm working distance).

Results

The highest SBS values were observed in the custom base design group (group A, 8.05 ± 4.69 MPa), followed by the macroretentive group (group B, 6.31 ± 3.80 MPa) and the standard group (group C, 5.91 ± 6.09 MPa). The differences between groups A and C were statistically significant (P = 0.017). ARI scores revealed that in groups A and B, most adhesive remained on the tooth (ARI score 2 predominated), whereas group C demonstrated a more variable ARI distribution. In addition, according to the SEM results, most adhesives have remained on the teeth in all groups.

Conclusions

Custom mesh designs in 3D-printed orthodontic brackets significantly enhance bond strength and adhesive retention, making them a promising option for clinical use. Future studies should investigate their performance under conditions that simulate the oral environment to validate their clinical applicability.