Application of finite element analysis in root canal therapy

Finite element analysis (FEA) is an engineering method for the numerical analysis of complex structures based on their material properties. It is used to determine the distribution of stress when a structure is subjected to force. Recently, FEA has been employed in endodontic. Endodontic diseases, such as pulpits or periradicular periodontitis, often require root canal therapy. During or after treatment, the pulpless teeth are more prone to fracture as an increasing amount of tooth structure is lost from disease or operative procedures. An important cause of endodontic failure is vertical root fracture (VRF), defined as a longitudinal fracture confined to the root that usually begins on the internal wall and extends outward to the root surface (Walton 2002). VRF is an increasingly common cause of failure of tooth restoration. Beside the difficult diagnosis, the management often requires rather aggressive approaches, i.e., extraction or root amputation. Although a conservative approach has been suggested, the long-term outcomes are still questionable (Kawai & Masaka 2002, Trope & Rosenberg 1992). It has been reported that approximately 0.2% of root filled teeth each year are lost directly because of VRF (Dammaschke et al. 2003, Fuss et al. 1999). Due to the high prevalence, poor diagnosis and prognosis of VRF, prevention is therefore of great importance. To avoid the problems caused by VRF, a full understanding of the etiological factors of root fractures is pivotal before preventive measures can be developed. Finite element analysis was first used more than 10 years ago to determine the factors that influencing fracture susceptibility. This chapter will focus on the contribution of finite element analysis to root canal therapy. Root canal therapy and the use of intraradicular dowels are the two main iatrogenic factors associated with VRF. In root canal instrumentation, enlargement of the coronal third of the root canal space is considered important to support root canal length measurement, debris removal, and canal obturation. However, extensive use of rotary instruments, to be cut dentin to straight lines at curvatures during preparation of the canal space, weakens the root structure. With infected root canals especially, a balance should therefore be sought between the need to remove infected dentin and to maintain sufficient root thickness to withstand the forces of mastication. Special attention to securing sufficient remaining dentin should be given to the teeth and roots most susceptible to fracture, i.e., the maxillary and mandibular premolars and the mesial roots of the mandibular molars. 4