Purpose: To focus on the biomechanical behavior of endodontically treated teeth following fatigue tests and subsequent influence of the numerous restoration interfaces involved.
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 mainly to clinical studies.
Most highlighted results:
•Fatigue testing of restored nonvital teeth:
•The more rigid ceramic and metal posts showed highest proportion of gaps at the dentin-post or dentin-core interface.
•The use of rigid post, such as zirconium oxide, will result in higher failure rates, mainly in the form of root fractures.
•Placement of a post in a nonvital incisor with two proximal restorations has no affect on fracture resistance.
•However, A 100% survival rate was found for teeth with access cavities closed with only composite resin.
• Fiber posts provided better bond strength values than ceramic posts. •Restoration adaptation and quality of interfaces:
•Total etch adhesives combined with a dual-curing cement appear to be the best choice.
•Hybrid layer thickness and tag density diminished from coronal to apical third of a root because of reduced numbers of tubules apically
•Coronal dentin has the best bond strength followed by pulpal floor dentin then root canal dentin, this is due to the differences in the collagen cross-linking structure at different dentin locations.
•Irrigants used in endodontics like chloroform, halothane, hydrogen peroxide and sodium hypochlorite reduce bond strength, while chlorhexidine did not affect adhesion.
•Fatigue studies have clearly demonstrated the importance of tissue conservation and presence of a ferrule effect to optimize tooth biomechanical behavior, 0.5- &1.0-mm ferrule heights led to earlier failure than 1.5- &2.0-mm.
•Comparing the 4-year clinical behavior of cast posts and cores to fiber-reinforced, composite resin posts and cores, a 95% clinical success was obtained with the adhesive approach against only 84% for the metal restoration; root fractures and crown dislodgments were observed only in the cast post-and-core group.
• Parallel serrated metal posts with composite resin cores showed a lower failure rate (8%) than tapered cast gold posts and cores (15%), decementation proved to be the most common reason for failure.
•Current recommendations for the treatment of nonvital teeth is shown in Fig5.
•Non vital teeth restored with composite resin and composite resin with fiber post are currently the best treatment option.
•The occurrence of interfacial or severe breakdown is less likely when using composite resin with composite resin or composite resin with fiber post compared with rigid metal and/or ceramic posts.