Impact of post preparation on dentin thickness of maxillary molars

Objective: This study aim to evaluate the dentinal reduction at the root canal walls in PRMM after successive preparations for post placement. Methods: Thirty-three extracted maxillary molars were embedded in acrylic resin using a metallic muffle and, further horizontally sectioned at two levels: 1 mm below the furcal level (coronal) and 1 mm above the apical limit of post preparation depth (apical). Each section was photographed at 20x magnification. After reassembling in the muffle, palatal roots were sequentially prepared, including the endodontic preparation with K file, largo drill preparation and a final preparation with Parapost drills. After each stage the sections were again photographed. The residual dentine thickness at the buccal, palatal, mesio and distal walls of the roots was measured (ImageTool for Windows 3.0). Repeated-measures ANOVA was used to compare the residual dentine thickness at each level (SPSS, 16.0). Results: The percentage of dentinal reduction was calculated to determine the risk of perforation/weakening the root. After Parapost preparation, buccal wall at the coronal level presented the highest reduction (25%) in dentinal thickness (P<0.05). At the apical level the palatal wall presented the highest reduction (45%) in dental thickness (P<0.05) and 13% of the roots remained with a dentinal thickness of 0.1 mm to 0.5 mm (high risk for root perforation/weakening) at the buccal wall in the coronal level, whereas in the apical level 26% at the palatal wall presented the same risk and 7% presented root perforation. Conclusion: After the subsequent preparation for post placement in PRMM using Parapost an elevated risk of perforation in the buccal wall at the coronal level and in the palatal wall at the apical level was observed, indicating that the radiographic control of dentinal thickness in PRMM is insufficient to reduce the risk of perforation/weakening the root.