Farklı Kök Kanal Preparasyon Şekillerinin Düz ve Eğimli Köklere Sahip Mandibular Molar Dişlerin Stres Dağılımı Üzerindeki Etkisi: Sonlu Elemanlar Stres Analizi

Abstract

Vertical root fractures are one of the most significant factors that caused to the failure of endodontic treatments and subsequently to the extraction of endodontically treated teeth. The vertical root fractures are observed in mandibular molars frequently. One of the most important factors on the effect of stress distribution in tooth structure are root canal shaping and anatomical structure of the root. In particular, over-preparation of the cervical third of the root pose a risk for vertical root fracture. In the scope of this study, the rotary systems as ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) (F2 and F3), FlexMaster (VDW, Munich, Germany) (25.04 and 30.04) and Hero Shaper (Micro-Mega, Besançon, France) (25.04 and 30.04) with different taper degrees and cutting surface length and MM.Tooth (Micro-Mega, Besançon, France) models which are similar to mandibular molar tooth structure were used. Root canal preparation was performed by using different rotary systems in MM.Tooth models and three-dimensional images of the models were obtained by scanning micro computed tomography. In addition to the curved-roots models, curved degrees of mesial roots were modified and straight mesial root models were obtained. The stress distribution in the models were examined using static linear finite element stress analysis (FEA) by applying occlusal forces of 200 N to both vertical and oblique directions. Thereby, the effect of preparation of different rotary systems and root inclination on stress distribution of mandibular molar teeth was evaluated under functional occlusal forces. Maximum principal stress (Pmax) distributions were reviewed. Under oblique loading, the maximum principal stress was observed mostly on cervical and middle third of mesial lingual external roots surface in straight root models, on the other hand, it was observed mostly on cervical of mesial lingual external root surface in curved-root models. Under vertical loading, maximum principal stress was observed mostly on bifurcation areas in both root morphologies. The highest stress values were recorded at ProTaper Universal F3 models in all groups while the lowest stress values were recorded at intact original models. The lowest stress values following intact models were recorded at Hero Shaper (25; %4) models. The stress values of straight rooted teeth were lower than the ones of curved-rooted teeth but stress distribution area was wider in straight rooted teeth. As a conclusion, stress distribution of the straight rooted teeth was more well-balanced than curved-rooted mandibular molars. It was also concluded that the increasing of both coronal diameter and inclination of mesial root increased the risk of vertical root fracture on mandibular molar teeth.