Mechanical deterioration of passive self-ligating lingual brackets under simulated prolonged use: An in vitro study

Passive, self-ligating lingual brackets are favored in Orthodontics for their simplified mechanism, eliminating the need for elastomeric and metallic ligatures. However, limited data exists on the effects of repeated use on their mechanical durability. An understanding of these effects is essential to ensure their long-term clinical performance. This study evaluates the mechanical degradation of the sliding cap locking mechanism of passive self-ligating lingual brackets after repeated opening and closing cycles.

In this in vitro study, 60 ALIAS mandibular incisor brackets were subjected to repeated opening and closing cycles (5, 10, 20, and 40 cycles). Mechanical tests were performed using an Instron 3344 electronic universal testing machine to measure maximum force at failure (F_max), energy absorption at F_max (U_max), and initial stiffness of the bracket opening mechanism (K).

The sliding cap remained functional throughout the test period. However, a significant reduction in F_max, U_max, and K over multiple opening and closing cycles. F_max showed a significant reduction after 5 opening and closing cycles (P = 0.0069), U_max after 10 cycles (P = 0.0243), and K showed after 5 cycles (P = 0.0002). The F_max reached a plateau at about 8-10 Newtons after 10 cycles, U_max at about 2.0 mJ (millijoules), and K at 50 N/mm after 10 cycles.

The study highlights significant advantages of passive self-ligating lingual brackets, showcasing their excellent initial performance. While ALIAS brackets may experience minor mechanical deterioration of the properties, their overall performance remains strong enough for entire duration of orthodontic treatment (2-3 years).