Laser-Induced Changes in Root Dentin Microhardness: Evidence From a Systematic Review

Dentin plays a critical role in tooth strength and function, yet conventional rotary instrumentation produces a smear layer that impedes bonding and cleaning. Laser technology has been introduced as an alternative for dentin conditioning, offering precise ablation and minimal thermal damage when properly applied. However, variations in laser type and parameters have led to inconsistent findings regarding their effects on dentin. This systematic review aimed to evaluate the effects of laser irradiation on dentin microhardness, smear layer removal, and surface morphology in in-vitro studies, focusing on Er:YAG, Er,Cr:YSGG, Nd:YAG and diode laser systems. A comprehensive search of PubMed, Scopus, Embase, Web of Science, and Google Scholar was conducted up to June 15, 2025. Eligible in vitro studies investigated dentin's structural, compositional, or mechanical changes following laser irradiation. Data were extracted on laser parameters, outcomes, and bias using the Joanna Briggs Institute checklist. Due to heterogeneity, findings were narratively synthesized. Thirteen studies published between 2012 and 2025 met the inclusion criteria. Diode and Er,Cr:YSGG lasers showed superior smear layer removal and enhanced surface cleanliness. Er:YAG lasers demonstrated effective cleaning with minimal damage. Nd:YAG and high-powered Er,Cr:YSGG reduced microhardness and caused morphological changes. Most studies had low to moderate risk of bias. Diode and erbium-based lasers effectively enhance smear layer removal and preserve dentin integrity when used under controlled parameters. Optimized laser protocols show strong potential as adjunctive tools for safer and more efficient dentin conditioning in restorative and endodontic practice.