<title>Abstract</title> <bold>Background: </bold>To assess the neuropeptide Y (NPY) expression in healthy human dental pulp following tooth bleaching with three in-office hydrogen peroxide-based systems: Opalescence Boost^© (Ultradent Products, South Jordan, UT), Pola Office^© (SDI, Victoria, Australia), and Zoom^© (Zoom! Bleaching System; Discuss Dental, Culver City, CA). <bold>Methods: </bold>This observational study was designed following the STROBE guidelines.<bold> </bold>Forty dental pulps were collected from healthy premolars scheduled for extraction for orthodontic reasons. Teeth were divided into four groups containing ten healthy premolars each: Control group (n= 10): the teeth were not exposed to dental bleaching agents (healthy pulps assessed for normal/basal NPY values). Pola Office system group (n= 10): application of Pola office (35% H2O2) for 8 minutes. Opalescent Boost system group (n= 10): application of Opalescent Boost (40% H2O2) for 20 minutes. Zoom system group (n= 10): application of Zoom! (25% H2O2 + cold blue light) for 15 minutes. We rigorously followed the manufacturer's instructions for all bleaching systems. Following the extractions, the pulpal tissue was collected, placed in a 4% formaldehyde solution in Eppendorf tubes, and processed. NPY levels were measured using enzyme-linked immunosorbent assay (ELISA). <bold>Results: </bold>The expression levels of NPY in the dental pulp of human premolars showed the lowest value in the control group (0.0263 pmol/mg of pulp tissue), followed by the Zoom group (0.0314 pmol/mg of pulp tissue). An increase in expression was observed in the Pola Office group (0.0399 pmol/mg of tissue), with the highest NPY expression found in the Opalescence Boost group (0.0441 pmol/mg of pulp tissue), which demonstrated a significant difference compared to the control group (P = 0.03). <bold>Conclusion: </bold>NPY - whose expression is closely correlated with the bleaching agent's concentration and the intensity of the inflammatory response - mediates the pulp's responses to tooth bleaching agent-induced neurogenic pulp inflammation. NPY is expressed in the dental pulp in both pathological and physiological conditions. The highest NPY expression values were found in OPALESCENCE BOOST^® followed by POLA OFFICE^®, and ZOOM^®. <bold>Trial registration: </bold>Clinical Trials.gov ID NCT06606236.