Comparative evaluation of different debonding and reconditioning methods for orthodontic ceramic brackets regarding effectiveness for reuse : An in vitro study

Abstract

Purpose: To investigate the reusability of ceramic brackets in terms of shear bond strength, friction behavior, slot dimension, fracture strength, and color stability.

Methods: A total of 90 conventionally debonded and 30 by an Er:YAG laser debonded ceramic brackets were collected. All the used brackets were inspected under a stereomicroscope at 18 × magnification and sorted according to their adhesive remnant index (ARI). Five groups were formed (n = 10): (1) new brackets as a control group, (2) flamed and sandblasted, (3) flamed and acid bathed, (4) laser-reconditioned, and (5) laser-debonded brackets. The bracket groups were tested regarding different properties such as shear bond strength, friction behavior, slot size, fracture strength, and color stability. Analysis of variance (ANOVA) and nonparametric Kruskal-Wallis tests were used for statistical analysis (significance level: p < 0.05).

Results: Shear bond strength values of the acid reconditioned brackets were significantly lower (8.0 ± 3.1 MPa) compared to the control group (12.9 ± 2.9 MPa). Laser-reconditioned (32.8 ± 2.7%) and laser-debonded (30.9 ± 2.4%) brackets showed the lowest force loss due to friction (control group 38.3 ± 3.0%). No significant differences were observed between groups regarding slot size and fracture strength. All groups had color differences of ${∆E}_{ab}^{*}$ < 10. Scanning electron microscope images and ARI scores indicated that most of the residues on the bracket bases were removed.

Conclusion: All reconditioning methods yielded adequate results regarding bracket properties. Yet, focusing on the need to protect the enamel and the bracket base, laser debonding seems to be the most suitable method for reconditioning ceramic brackets.

Keywords: Er:YAG laser; Fixed orthodontic appliances; Material properties; Reusability; Shear bond strength.

Fig. 1

Detached adhesive from the bracket base due to fast cooling down after flaming. 18 × magnification Abgelöster Klebstoff von der Bracketbasis durch schnelles Abkühlen nach Abflämmen. Vergr. 18:1

Fig. 2

Mechanical test setup for measuring the force loss due to friction in the Orthodontic Measurement and Simulation System (OMSS). Test model with ligated arch wire and glued bracket to the force/torque sensor. Orthodontic force is transferred to the bracket by a NiTi tension spring Mechanischer Versuchsaufbau zur Messung des Kraftverlusts durch Reibung im orthodontischen Mess- und Simulationssystem (OMSS). Testmodell mit ligiertem Führungsbogen und am Kraft‑/Drehmomentsensor aufgeklebtem Bracket. Die Kraft wird durch eine NiTi-Zugfeder auf das Bracket übertragen

Fig. 3

Measurement of the slot size using a pin gauge Messung der Slotgröße mit einem Lehrdorn

Fig. 4

Experimental setup: a Bonded bracket on a specimen holder connected with a pulley on the force sensor mounted in the material testing machine. b The ligature wire was placed under the bracket wing. c Overall view of the experimental setup with specimens installed in the materials testing machine Versuchsaufbau: a geklebtes Bracket auf einem Probenhalter, der über eine Umlenkrolle mit dem Kraftsensor in der Materialprüfmaschine verbunden ist. b Der Ligaturendraht wurde unter dem Bracketflügel platziert. c Gesamtansicht des Versuchsaufbaus mit den in der Werkstoffprüfmaschine installierten Prüfkörpern

Fig. 5

Force loss due to friction expressed as a percentage of the applied force on the brackets. Asterisks show a significant difference between groups (p < 0.05). See Table 1 for abbreviations Kraftverlust aufgrund von Reibung, als Prozentsatz der aufgebrachten Kraft auf die Brackets. Sternchen zeigen einen signifikanten Unterschied zwischen den Gruppen (p < 0,05). Abkürzungen siehe Tab. 1

Fig. 6

Box and whisker plot illustrating the measured slot sizes in mm. See Table 1 for abbreviations Box-und-Whisker-Diagramm zur Darstellung der gemessenen Slotgröße in mm. Abkürzungen siehe Tab. 1

Fig. 7

Box and whisker plot illustrating the fracture strength in MPa. See Table 1 for abbreviations Box-und-Whisker-Diagramm zur Darstellung der gemessenen Bruchfestigkeit in MPa. Abkürzungen siehe Tab. 1

Fig. 8

Scanning electron microscope images showing the bracket bases at 300 × magnification. a DN b DS c DA d DL e DLD. See Table 1 for abbreviations Rasterelektronenmikroskopische Aufnahmen der Bracketbasis, Vergr. 300:1. a DN b DS c DA d DL e DLD. Abkürzungen siehe Tab. 1