Effects of the orthodontic miniscrew geometric design on the bone microdamage and primary stability

Abstract

This study investigated the effects of the pitch (P) and thread shape on orthodontic miniscrew cortical bone microdamage. The relationship between microdamage and primary stability was examined. Ti6Al4V orthodontic miniscrews had custom-made thread heights (H) and pitch sizes and were classified into the following groups: HCPC (control); HCPN (with a narrower pitch); and HTPC (with a taller thread height) (HC = 0.12 mm; HT = 0.36 mm; PC = 0.60 mm; PN = 0.30 mm). The orthodontic miniscrews were inserted in the pilot hole of prepared 1.0-mm-thick tibia cortical bone, and the maximum insertion torque (MIT) and Periotest value (PTV) were measured. After basic fuchsin staining, histological thin sections were examined using microdamage parameters, including the total crack length (TCL) and total damage area (TDA), and insertion state parameters, including the miniscrew surface length (SL) and bone compression area (BCA). The orthodontic miniscrews with taller thread height showed lower primary stability, minimal bone compression, and microdamage, while narrower thread pitch resulted in maximum bone compression and extensive bone microdamage. A wider thread pitch reduced microdamage, while decreased thread height increased bone compression, ultimately improving primary stability.