The effect of post space preparation on root dentine thickness in maxillary and mandibular molars

Aim to evaluate the effect of different post space drill diameters on remaining dentine thickness in maxillary and mandibular molars using high-resolution micro–computed tomography (micro-CT). Methodology Thirty maxillary and thirty mandibular molars with straight or slightly curved roots were selected from pre-existing micro-CT datasets to form homogeneous groups. Palatal roots of maxillary molars and distal roots of mandibular molars were prepared with Peeso reamers in three diameters (1.14, 1.25, and 1.55 mm; n = 10 per group). Pre- and post-preparation scans were superimposed to measure remaining dentine thickness at 1 mm intervals from the furcal level (FL) to apical in multiple directions. Data were analysed using ANOVA and post-hoc tests (α = 0.05). Results Maxillary molars retained ≥ 1 mm remaining dentine thickness across most surfaces and drill sizes, with only one perforation (buccal aspect, 1.55 mm group). Buccal walls were consistently thicker than palatal. Mandibular molars showed significantly thinner mesial walls than distal walls (p <.05), with frequent postoperative thickness ≤ 1 mm in mesial surfaces, particularly in the 1.14 mm and 1.25 mm groups. Three perforations occurred in mesial surface with the 1.55 mm drill. Distal dentine walls generally maintained ≥ 1 mm remaining thickness with no perforations. Conclusion Drill diameter significantly influences remaining dentine thickness in molar roots. Palatal roots of maxillary molars can safely accommodate post space preparation with minimal perforation risk, even with larger drills. In mandibular molars, distal roots are at high risk of dentine thinning and perforation; conservative preparation or post-free restorations are recommended.