Comparison Of Stress Distributions In Tooth After Root Canal Preparation With Three Different Instruments And Repair With Different Root Canal Post-core

Root canal preparation is the key procedure in root canal treatment, and its main purpose is to eliminate the infected material in the root canal so as to be good for root canal filling. Many clinical researches indicated that large-taper instruments were effective in root canal preparation and filling, however, over-preparation may cause root fracture of pulpless tooth. Also there are still arguments on what kind of root canal post-core is good for tooth repair. In order to investigate the change of tooth strength after the preparation and repair, three-dimensional finite element method was used to simulate root canal preparation with three different-tapered instruments and repair with different kinds of root canal post-core, and their effects on stress distributions in tooth were observed so as to provide theoretical data for dental clinical treatment.Objectives and methods:1. Three-dimensional finite element model of Human first mandibular molar was established. The scanned CT image was input into Phptoshop 7.0 and saved as BMP format. The primary three-dimensional image was obtained using Mimics software, Then the outline of different tissue was connected to form the surface using Geomagic Studio 7, Parten and UG. The final image was imported into three-dimensional finite element software MSC, MARC. Finally prepared root canals with three different instruments and retention forms with three different root canal posts were simulated.2. The same central vertical load was applied to different models and the stress distributions and concentration areas in different models were analyzed.Results:1. The three-dimensional finite element model including enamel, dentin, pulp, periodontal ligament membrane and alveolar bone was established.2. Stress distributions in dental roots after root canal preparation with K-type file, ProTaper or Profile were slightly different. ProTaper group showed a highest stress level, while K-type file exhibited lowest. 3. Fiber post was the best retention form in this study, and the stress distribution was almost the same with the situation not using the root canal post-core. The stress distribution in tooth, especially in root using silver amalgam post-core was better than that using stainless steel post-core.Conclusion:1. It is feasible to establish the three-dimensional element model of mandible teeth and mandible bone using scanned CT technique and finite element technique.2. Though the stress level in dental roots of ProTaper group was little higher than that of Profile or 35#K file group, the difference is quite small. This suggests that root canal preparation with the above tested 3 root canal instruments do not have obvious effects on the stress level and strength of the dental roots.3. Based on the results, we suggest use more fiber post and less stainless steel post in clinic, thus may reduce root fracture of pulpless tooth with large restoration.