Effects of orientation and postprocessing on the bonding of 3-dimensional printed brackets to printable permanent crown resin

Abstract

Introduction

This study aimed to evaluate the effects of different printing orientations and postcuring processes on the bonding performance of 3-dimensional (3D)-printed brackets to permanent crown resin.

Methods

A total of 90 disk-shaped specimens (2 mm thickness and 10 mm diameter) were manufactured from printable resin material (Formlabs Permanent Crown, Formlabs Inc, Somerville, Mass). The 3D printed brackets were fabricated at 3 build angles (0°, 45°, and 90°) with a 50 μm layer thickness. Each group consisted of 30 brackets. After printing, the postprocessing was performed either with or without glycerin immersion. Each printed resin surface and bracket base were sandblasted with 50 μm aluminum oxide particles before the bonding procedure. The 3D printed brackets were bonded with a conventional orthodontic composite resin (Transbond XT Primer, 3M Unitek, Monrovia, Calif) to printable resin surfaces. After thermal cycling, the shear bond strength (SBS) test was applied, and bonding failure was examined under a stereomicroscope at 10× magnification. Two-way analysis of variance, post-hoc Tukey, and chi-square tests were used for data analysis.

Results

Both orientation and postprocessing had significant effects on SBS. The 3D-printed brackets with 90° and glycerin immersion postcuring demonstrated the highest (13.74 ± 4.52 MPa), whereas 45° orientation without glycerin showed the lowest (7.06 ± 4.32 MPa) SBS. All specimens had cohesive-type bonding failures mainly accompanied by bracket fractures and without surface damage. The least fracture was found in 3D-printed brackets with the highest SBS.

Conclusions

The 3D printed brackets with 90° orientation and glycerin immersion postprocessing demonstrated the best bonding performance when applied to the printable permanent crown resin material.