Reprocessing Clinically Used Rotary NiTi files - Cleanliness Validation Assays

Rotary NiTi instruments are routinely used in non-surgical endodontic treatment. Previous studies observed debris from manufacturing process adherent to new instruments, as well as presence of dentinal debris following clinical application and reprocessing. Therefore, rotary NiTi instruments that undergo multiple cycles of clinical use may represent a reprocessing challenge. This was a pilot study designed to quantify presence of dentinal debris on clinically used and reprocessed rotary NiTi instruments, using recently developed protein and hydroxyl-apatite quantification assays by ADA. Clinically used and reprocessed VortexBlue rotary instruments sizes 25/.04, 30/.04, 35/.04 and 40/.04 were selected. A reprocessing procedure included of ultrasonication in enzymatic solution followed by steam sterilization in autoclave. Comparable new instruments were subject to same reprocessing protocol as controls. Residual debris was visualized by observing under microscope (20x magnification) and phloxine B staining. Dentin residue was extracted and assessed via ARS assay for hydroxyl-apatite, and via OPA assay for protein, using recently developed ADA protocol (Gopal 2020, IADR). Data statistically analyzed through t-test (p<0.05). Residual dentin was visualized on the cutting edges and evident accumulation towards the shank and rubber stopper. Protein residue on used and reprocessed files could not be quantified. Amounts of HA around 450 ug/ml were extracted from used and reprocessed files. In addition, considerable amounts of debris were observed on rubber stoppers (approximately 500 ug/ml). The Alizarin Red Stain assay provides quantification of hydroxyl-apatite residues on used and reprocessed rotary NiTi instruments. In absence of more sophisticated clinical reprocessing protocol, it is advisable to discard them after single use.