Purpose: To present an overview of the current knowledge about composition changes, structural alterations, and status following endodontic therapy and restorative procedures.
Materials and methods:
•The research included a review of the PubMed/Medline database for dental journals from 1990 to 2005.
•Studies were classified and analyzed according to specific parameters ( Dentin composition and physical characteristics, Fracture resistant, and Stress simulation ).
Most highlighted results:
•Biomechanical changes following loss of pulp vitality or endo therapy:
•Tissue composition: The loss of vitality is accompanied by a change in tooth moisture content, which has a slight influence on young modulus and proportional limit. However no decrease in compressive and tensile strength is associated with with this change in water content.
•Dentin physical characteristics: No or minor differences in micro-hardness values were found between vital and nonvital dentin of contralateral teeth after 0.2 to 10 years. Some products used for canal irrigation and disinfection interact with mineral and organic contents and then reduces dentin modulus of elasticity and flexural strength.
•Fracture resistance and tooth stiffness: The major changes in tooth biomechanics are attributable to the loss of tissue following caries lesion, fractures, or cavity preparation including access cavity. The largest reduction in tooth stiffness results from additional preparation, especially the loss of marginal ridges. The literature reports 14% to 44% and 20% to 63% reduction in tooth stiffness following occlusal and MOD cavity preparations respectively. Moreover, the ferrule effect and a large amount of residual tissue in general proved to increase tooth resistance to fracture. A minimum of 1-mm ferrule is considered necessary to stabilize the restored teeth.
•Restorative materials and techniques and their influence on tooth biomechanics:
•The rationale for using stiff or strong materials as posts has always been to strengthen the tooth, however this concept is questioned because of existing limitations of adhesive procedures within the root canal or between the post and luting cement.
•Comparison of the fracture resistance of the teeth restored with either zirconium ceramic or resin-fiber posts revealed a higher resistance of teeth with fiber posts.
•Cemented posts causes less stress than do threaded posts.
•The larger the post diameter, the more stress generated in the root.
The best approach for restoring endodontically treated teeth is to: 1.Minimize tissue sacrifice, especially in the cervical area so that a ferrule effect can be created,
2.Use adhesive procedures at both radicular and coronal levels to strengthen remaining tooth structure and optimize restoration stability and retention, 3.Use post and core materials with physical properties close to those of natural dentin.