Assessment of lipopolysaccharide microleakage at conical implant-abutment connections

The aim of this in vitro study was to assess lipopolysaccharide microleakage at conical implant-abutment connections of two-piece dental implants in terms of the expression levels of genes involved in lipopolysaccharide-mediated proinflammatory cytokine production. Two implant systems with conical implant-abutment connections were inoculated with lipopolysaccharide and submerged in human whole blood. Positive-control blood samples (without implants) were stimulated with 4 mu g/ml, 2 mu g/ml, 200 ng/ml, and 20 ng/ml lipopolysaccharide. Sampling was performed after 1, 8, and 24 h of incubation. Changes of gene expression levels of Toll-like receptor 9, tumor necrosis factor-alpha, nuclear factor kappa light chain enhancer of activated B cells, interleukin-1 beta, and interferon-gamma were assessed by real-time quantitative PCR. In addition, protein expression levels of interleukin-6, tumor necrosis factor-alpha, interleukin-1 beta, and interferon-gamma were determined by immunoassay. Changes in cytokine expression at the genomic and proteomic levels indicated lipopolysaccharide leakage at the interfaces of both tested implant systems, although some implants showed no sign of microleakage. Any tested concentration of lipopolysaccharide stimulated similar gene expression. Conical implant-abutment connections of two-piece dental implants do not prevent microleakage on a molecular level. Changes in lipopolysaccharide-induced proinflammatory cytokine gene expression facilitate the detection of lipopolysaccharide microleakage at implant-abutment interfaces. Small amounts of lipopolysaccharide released from intra-implant cavities can stimulate a detectable immunological response in human whole blood and may induce alveolar bone resorption via the osteoclast-activating pathway.