Sliding behaviour and surface quality after static air polishing of conventional and modern bracket materials

Abstract

Objectives As part of orthodontic treatment, air polishing is routinely used for professional tooth cleaning. Thus, we investigated the effects of static powder polishing on sliding behaviour and surface quality of three different bracket materials (polymer, ceramic, metal), including a 3D-printed bracket. Methods Two bracket types of each material group were polished with an air-polishing device using sodium bicarbonate. Exposure times were set at 10, 20, and 60 s; the application distance was 5 mm. The force loss due to sliding resistance was tested with an orthodontic measurement and simulation system (OMSS) using a 0.016 inch × 0.022 inch stainless steel archwire. Untreated brackets served as control. Polishing effects and slot precision were evaluated using an optical digital and scanning electron microscope. Results Sliding behaviour and slot precision differed significantly between and within the groups. Prior to polishing, polymer brackets showed the least force loss, ceramic brackets the highest. With progressive polishing time, the resistance increased significantly with titanium brackets (26 to 37%) and decreased significantly with steel brackets (36 to 25%). Polymer brackets showed the smallest changes in force loss with respect to polishing duration. Slot precision showed the largest differences between material groups and was primarily manufacturer-dependent with hardly any changes due to the polishing time. Conclusion Powder polishing can positively or negatively affect the sliding properties of the bracket–archwire complex but is more dependent on the bracket–archwire material combination (i.e., manufacture-dependent slot precision). For titanium brackets, resistance only increased after 60 s of polishing. For ceramic brackets, effective reduction was observed after 10 s of polishing. Polymer brackets, including the 3D-printed brackets, showed better sliding properties than ceramic or metal brackets even after polishing for 60 s. Removal of plaque and dental calculus should lead to a noticeable improvement of the sliding properties and outweighs structural defects that may develop.

Precision of slot widths and torque transmission of in-office 3D printed brackets

“…Special attention was paid to the implementation of the digital bracket design especially regarding rounded edges, excess resin residues, and polishing defects. Of course, this methodology only has limited validity regarding biomechanical properties; thus, further tests were carried out [17].…”

“…However, in the present study the slot size measurements were only relevant for the subsequent interpretation of the torque values; thus, the comparability of slot sizes between the material groups suffices. Further studies will be necessary to verify the exact morphological characteristics of the PCR slots, e.g., by using established methods such as visual measurement in a digital optical microscope, machine measurement using specially manufactured inspection systems, or with the aid of a micro-CT (computed tomography) [14,17,[37][38][39].…”

“…To ensure correct orientation, all 90 brackets (30 PCR, 30 ceramic, 30 metal) were bonded to metal plates (5 mm × 5 mm) with a positioning aid (DeguDent GmbH, Hanau-Wolfgang, Germany) [17]. Visual inspection of the brackets was performed using a Keyence ® VHX500 digital microscope (Keyence Corporation, Osaka, Japan; Fig.…”

“…Polycarbonates are thermoplastics, which allow easy matching to the tooth color thanks to their transparent properties [14]. In addition, they have been shown to exhibit low sliding resistance [15][16][17]. However, given their poor stability and stiffness, resulting in permanent plastic deformation even at low force, polymer brackets are only rarely used in practice [18].…”

Force-Controlled Biomechanical Simulation of Orthodontic Tooth Movement with Torque Archwires Using HOSEA (Hexapod for Orthodontic Simulation, Evaluation and Analysis)

“…Simulating an extraction therapy case, the first premolars were removed and replaced by canines. The model was divided into two segments, an anterior (teeth 12,11,21,22) and one posterior segment (teeth [13][14][15][16][17][23][24][25][26][27]. The anterior segment was attached to the sensor and the posterior segment to the Stewart platform by a SAM articulator plate and base (SAM Praezisionstechnik GmbH, Munich, Germany) (Figure 1).…”