http://www.endoexperience.com/filecabinet/Endo%20Related%20Restorative%20Dentistry/Post%20and%20Cores/scwartz%20post%20review%20article.pdf

Post placement and restoration of endodontically treated teeth: a literature review.

OBJECTIVE: The restoration of endodontically treated teeth has long been guided by empirical rather than biomechanical concepts. Part I of this literature review presented up-to-date knowledge about changes in tissue structure and properties following endodontic therapy, as well as the behavior of restored teeth in monotonic mechanical tests or finite element analysis. The aim of the second part is to review current knowledge about the various interfaces of restored, nonvital teeth and their behavior in fatigue and clinical studies. REVIEW METHOD: The basic search process included a systematic review of articles contained in the PubMed/Medline database, dating between 1990 and 2005, using single or combined key words to obtain the most comprehensive list of references; a perusal of the references of the references completed the review. RELEVANT INFORMATION AND CONCLUSIONS: Nonvital teeth restored with composite resin or composite resin combined with fiber posts resisted fatigue tests and currently represent the best treatment option. In comparison to rigid metal and/or ceramic posts, when composite resin or composite resin/fiber posts fail, the occurrence of interfacial defects or severe tooth breakdown is less likely. Adhesion into the root, however, remains a challenge because of the unfavorable ovoid canal configuration, as well as critical dentin microstructure in the deepest parts of the canal. Thus, specific combinations of adhesives and cements are recommended. The clinical performance of post-and-core restorations proved satisfactory overall, in particular with a contemporary restorative approach using composite resin and fiber posts. However, the clinical literature does not clearly isolate or identify exact parameters critical to success. This, in turn, emphasizes the importance and relevance of in vitro studies to further improve the quality and long-term stability of prosthetic foundations.

Biomechanical considerations for the restoration of endodontically treated teeth: a systematic review of the literature, Part II (Evaluation of fatigue behavior, interfaces, and in vivo studies).

Statement of problem Endodontically-treated, dowel-restored teeth may experience fracture, but investigations of variables related to fracture are often inconclusive and occasionally contradictory. Purpose The finite element method was used to analyze the stresses in dowel-restored teeth. The variables studied were material, shape, bonding, modulus of elasticity, diameter, and length of the dowel. Material and methods The model of the dowel-restored tooth involved dentin, ligament, cortical and trabecular bone, gingiva, and gutta-percha. The dowels were made of glass fiber, titanium, or zirconia and modeled as an approximation of the brands ParaPost Fiber White, ParaPost XH, and Cerapost, respectively. The dowel was cemented with zinc-phosphate cement or with bonded or nonbonded resin luting agents, and an approximation of the material properties of these 2 materials were used in the modeling. The restoration included a composite resin core and a gold crown. Other variables included taper versus parallel-sided posts, modulus of elasticity, diameter, and length of post. The model was axisymmetrical in 3 dimensions. A load of 100 N was applied to the crown at an angle of 45 degrees, and tensile, shear, and von Mises stresses were calculated. Results The generated stresses decreased with respect to the dowel material in the following order: glass fiber, titanium, and zirconia. Stresses were in general higher with tapered than with parallel-sided dowels. Stresses were reduced by bonding and with an increasing modulus of elasticity, increasing diameter, and increasing length of the dowel. Conclusions Within the limitations of this study, it was found that all investigated dowel-related factors influenced the stress field generated in dowel-restored teeth.

Finite element analysis of stresses in endodontically treated, dowel-restored teeth

The prognosis of root-filled teeth depends not only on the success of the endodontic treatment but also on the amount ofremaining dentine tissue, and the nature offinal restoration. Fractures ofrestored endodontically treated teeth are a common occurrence in clinical practice. This article outlines the mechanisms and risk factors for fracture predilection in endodontically treated teeth. Different mechanisms of fracture resistance in dentine and the biomechanical causes of fracture predilection in restored endodontically treated teeth are described. Furthermore, dentinal, restorative, chemical, microbial, and age-induced factors that predispose restored endodontically treated teeth to fracture are also reviewed.

Mechanisms and risk factors for fracture predilection in endodontically treated teeth

The specific biomechanical alterations related to vitality loss or endodontic procedures are confusing issues for the practitioner and have been controversially approached from a clinical standpoint. The aim of part 1 of this literature review is to present an overview of the current knowledge about composition changes, structural alterations, and status following endodontic therapy and restorative procedures. The basic search process included a systematic review of the PubMed/Medline database between 1990 and 2005, using single or combined key words to obtain the most comprehensive list of references; a perusal of the references of the relevant sources completed the review. Only negligible alterations in tissue moisture and composition attributable to vitality loss or endodontic therapy were reported. Loss of vitality followed by proper endodontic therapy proved to affect tooth biomechanical behavior only to a limited extent. Conversely, tooth strength is reduced in proportion to coronal tissue loss, due to either caries lesion or restorative procedures. Therefore, the best current approach for restoring endodontically treated teeth seems 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, and (3) use post and core materials with physical properties close to those of natural dentin, because of the limitations of current adhesive procedures.

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Biomechanical considerations for the restoration of endodontically treated teeth: a systematic review of the literature--Part 1. Composition and micro- and macrostructure alterations.

Statement of Problem. Very little is known about the resistance to fracture of endodontically treated teeth restored with newly developed esthetic post systems. Purpose. This in vitro study compared the effect of 1 titanium and 3 esthetic post systems on the fracture resistance and fracture patterns of crowned, endodontically treated teeth. Material and Methods. A total of 40 recently extracted human maxillary canines with their crowns removed were endodontically treated. Four groups of 10 specimens were formed. Teeth were restored with titanium, quartz fiber, glass fiber, and zirconia posts and numbered as groups 1, 2, 3, and 4, respectively. All posts were cemented with Single Bond dental adhesive system and dual-polymerizing RelyX ARC adhesive resin cement. All teeth were restored with composite cores, and metal crowns were fabricated and cemented with glass ionomer cement. Each specimen was embedded in acrylic resin and then secured in a universal load-testing machine. A compressive load was applied at a 130-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1 mm/min. One-way analysis of variance and a Tukey test were used to determine the significance of the failure loads between groups ( P 2 test was conducted for evaluation of the mode of failure ( P Results. The mean failure loads (kg) were 66.95, 91.20, 75.90, and 78.91 for groups 1 to 4, respectively. Teeth restored with quartz fiber posts (group 2) exhibited significantly higher resistance to fracture ( P P >.05). Fractures that would allow repair of the tooth were observed in groups 2 and 3, whereas unrestorable, catastropic fractures were observed in groups 1 and 4 ( P Conclusion. Within the limitations of this study, significantly higher failure loads were recorded for root canal treated teeth restored with quartz fiber posts. Fractures that would allow repeated repair were observed in teeth restored with quartz fiber and glass fiber posts. J Prosthet Dent 2002; 87:431-7.

Resistance to fracture of endodontically treated teeth restored with different post systems.

In this study, fatigue properties of a novel continuous glass fiber reinforced composite with an acrylic-based thermoplastic matrix Elium®, have been investigated and S-N curves were obtained. The effect of various fiber orientations of the plies with glass fibers of 0°/90°/±45°, 0°/90°, and ±45° alignment has been evaluated. The highest fatigue strengths have been recorded for composites with 0°/90° glass fiber ply orientations. Composite with ±45° alignment has the lowest fatigue strengths in S-N curves. Stiffness degradation of the composites with 0°/90° and 0°/90°/±45° at medium fatigue stress levels was calculated and showed higher degradation for stacking having more off-axis plies, i.e. 0°/90°/±45° alignment. Temperature increase during fatigue testing was measured using an IR camera for a medium fatigue stress level for 0°/90°/±45° alignment. Temperature increases were calculated for all stress amplitudes for composites with 0°/90°/±45° and 0°/90° alignment cross-ply sequences. The temperatures obtained were all below the glass transition temperature of the material. The 0°/90°/±45° plies had a higher temperature effect than 0°/90° plies in both analytical calculations and observations. 

Turgut Gülmez

Papers

Resistance to fracture of endodontically treated teeth restored with different post systems.

Fatigue behavior and self-heating mechanism of novel glass fiber reinforced thermoplastic composite