Effects of Access Cavity Design on the Shaping Ability and Dentine Thickness Following Canal Preparation Using <scp>XP</scp> ‐Endo Shaper or Reciproc

This study compared the shaping ability and remaining dentine thickness in mandibular molars prepared with traditional (TradAC) or ultraconservative (UltraAC) access cavities using Reciproc or XP-endo Shaper instruments. Thirty-two molars were scanned with micro-CT before and after preparation to assess canal surface, volume, untouched walls, and dentine thickness. Both access cavity designs showed a significant reduction in dentine thickness after preparation, but no differences were found between TradAC and UltraAC in either mesial or distal roots (p > 0.05). In the distal root, Reciproc produced a greater reduction in dentine thickness compared with XP-endo Shaper (p < 0.05), whereas shaping ability parameters did not differ significantly between instruments (p > 0.05). Some canals exhibited residual dentine thickness below 0.5 mm, particularly when preoperative thickness was already minimal. Within the limitations of this laboratory study, access cavity design had no influence on dentine preservation, while the choice of instrument affected dentine reduction only in the distal root.