Comparison of Endotoxin Adherence and Elution from Orthodontic Bracket Materials

Abstract

Endotoxin is the cell envelope lipopolysaccharide (LPS) produced by gramnegative bacteria. LPS can activate an immune response through a variety of pathways, reduce gingival fibroblast proliferation, and stimulate osteoclastic activity. Previous studies have documented LPS affinity for casting alloys, provisional resins, ceramics, and implant biomaterials. The purpose of this study was to determine Porphyromonas gingivalis and Escherichia coli LPS affinity for orthodontic bracket materials. The effects of bracket chemical composition and LPS type on LPS adherence to and elution from commercially available stainless steel, "gold", ceramic, and plastic orthodontic brackets were evaluated. Bracket surface areas were determined, and 16 brackets per experimental group were placed individually into water containing [3H]LPS (10 EU/mm2) and incubated for 24 hours at 3 7°C. Brackets were then transferred to fresh LPS-free water and incubated for 24 hours at 37°C to evaluate elution. This elution transfer was continued up to 96 hours total incubation. LPS adherence and elution levels were calculated after assaying the adherence and elution solutions for [3H]LPS using liquid scintillation spectrometry. Additional control brackets were placed in LPS-free water and evaluated throughout the study with an enzymatic assay to ensure extraneous LPS contamination did not occur. Mean initial LPS adherence ranged from 2.42± 0.26 EU/mm2 (E. coli, plastic) to 6. 75± 0.34 EU/mm2 (P. gingivalis, stainless steel). P. gingivalis LPS adherence was significantly greater than E. coli LPS adherence for all bracket types, and stainless steel brackets exhibited significantly greater LPS adherence with each LPS type (p:> 0.05). Regarding elution, only the P. gingivalis LPS exposed ceramic and plastic brackets at 24 hours and the stainless steel and ceramic brackets at 48 hours eluted measurable LPS. Results from this study confirm that P. gingivalis and£. coli LPS exhibit an affinity for orthodontic brackets. Jn vivo, this affinity could affect the concentration of LPS in the gingival sulcus, thereby influencing inflammation in tissues adjacent to the brackets. This study was supported by the Wilmer Eames Study Club and the MCG Biocombatibility Program.