Influence of Individual Bracket Base Design on the Shear Bond Strength of In-Office 3D Printed Brackets—An In Vitro Study

Abstract

(1) Background: Novel high-performance polymers for medical 3D printing enable in-office manufacturing of fully customized brackets. Previous studies have investigated clinically relevant parameters such as manufacturing precision, torque transmission, and fracture stability. The aim of this study is to evaluate different design options of the bracket base concerning the adhesive bond between the bracket and tooth, measured as the shear bond strength (SBS) and maximum force (Fmax) according to DIN 13990. (2) Methods: Three different designs for printed bracket bases were compared with a conventional metal bracket (C). The following configurations were chosen for the base design: Matching of the base to the anatomy of the tooth surface, size of the cross-sectional area corresponding to the control group (C), and a micro- (A) and macro- (B) retentive design of the base surface. In addition, a group with a micro-retentive base (D) matched to the tooth surface and an increased size was studied. The groups were analyzed for SBS, Fmax, and adhesive remnant index (ARI). The Kruskal–Wallis test with a post hoc test (Dunn–Bonferroni) and Mann–Whitney U test were used for statistical analysis (significance level: p < 0.05). (3) Results: The values for SBS and Fmax were highest in C (SBS: 12.0 ± 3.8 MPa; Fmax: 115.7 ± 36.6 N). For the printed brackets, there were significant differences between A and B (A: SBS 8.8 ± 2.3 MPa, Fmax 84.7 ± 21.8 N; B: SBS 12.0 ± 2.1 MPa, Fmax 106.5 ± 20.7 N). Fmax was significantly different for A and D (D: Fmax 118.5 ± 22.8 N). The ARI score was highest for A and lowest for C. (4) Conclusions: This study shows that conventional brackets form a more stable bond with the tooth than the 3D-printed brackets. However, for successful clinical use, the shear bond strength of the printed brackets can be increased with a macro-retentive design and/or enlargement of the base.

Shear bond strength of three different metal bracket base designs on human premolars: An in vitro comparative study

“…This disparity could be attributed to the use of brackets with rail or Treadlock base, double-mesh base, and horizontal groove base, along with a different highly transparent adhesive (Heliosit, Ivoclar Vivadent srl, Italy). Therefore, it can be stated that there are several factors that influence the adhesive bonding values of metal brackets ( 3 , 10 , 11 ).…”

“…This is likely because of the factory micro-sandblasting, which may enhance tooth enamel retention, as well as the presence of micro-pins that increase bonding surface area and anchorage to the adhesive ( 25 ). Kilponen ( 2 ) and Hodecker ( 3 ) previously noted that sandblasting, silanization of the bracket base, and chemical conditioning improve the bond strength of metal brackets. Discovery® Smart, another type of bracket with high average shear strength, has a laser-structured base that undergoes treatment with a powerful Nd:YAG laser.…”

“…The specimens were immersed in distilled water at 37°C for 24 hours ( 3 , 10 , 19 ). A universal testing machine (CMT-5L, 7419, LG, Seoul, Korea) with a crosshead speed of 0.75 mm/min was used to perform the shear bond strength test.…”

“…Several factors can affect the adhesion of orthodontic brackets, such as enamel surface nature, conditioning procedure, adhesive type, polymerization type, and bracket base design ( 3 , 10 , 11 ).…”

“…Therefore, the macroscopic retentive design of the bracket base is of critical importance ( 2 ). A high rate of bracket loss is considered detrimental in clinical practice because it increases treatment time and the number of unscheduled appointments ( 2 , 3 , 12 ).…”