Nickel-titanium (NiTi) rotary instruments have transformed endodontics by enabling efficient, predictable root canal shaping. However, concerns persist about their impact on dentin integrity, particularly microcrack formation and long-term fracture risks. This narrative review evaluates evidence on contemporary NiTi systems—including thermally treated alloys and reciprocating files—and their effects on dentin structural integrity. While advanced designs reduce torsional stress, in vitro studies report conflicting outcomes on microcrack induction. Clinicians must balance shaping efficiency with preservation of dentin strength. Further in vivo studies are needed to correlate laboratory findings with clinical outcomes.