Remaining dentine thickness following post space preparation in maxillary and mandibular molars: a micro–computed tomography study

This study aimed 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). Sixty molars (30 maxillary, 30 mandibular) with straight or slightly curved roots were allocated into homogeneous groups using pre-existing micro-CT datasets. Post spaces were prepared in the maxillary palatal and mandibular distal roots using Inod drills of three diameters (1.14, 1.25, and 1.55 mm; n = 10 per group). By superimposing pre- and post-preparation scans, the remaining dentine thickness was measured at 1-mm intervals apically from the furcal level (FL) in multiple directions. Data were analysed using ANOVA and post-hoc tests (α = 0.05). Maxillary molars generally retained ≥ 1 mm of dentine thickness across most surfaces and drill sizes, with buccal walls remaining consistently thicker than palatal ones. Only a single perforation occurred (buccal aspect, 1.55 mm group). Conversely, mandibular molars exhibited significantly thinner mesial walls compared to distal walls (p < .05), frequently resulting in postoperative thicknesses of ≤ 1 mm on the mesial surfaces. Furthermore, three perforations occurred on the mesial aspect with the 1.55 mm drill, whereas the distal walls generally maintained ≥ 1 mm thickness without perforations. Drill diameter significantly influences remaining dentine thickness in molar roots. The anatomical dimensions of palatal roots in maxillary molars permit post space preparation with a low risk of perforation, even with larger drills. However, highly conservative preparation or evidence-based post-free alternatives, such as endocrowns, are strongly recommended for mandibular molars.