Stress distribution in roots restored with different types of post systems with composite resin

Dental Materials Journal 2008; 27(4): 605－611 Original Paper

Stress Distribution in Roots Restored with Different Types of Post Systems with Composite Resin
Daizo OKADA, Hiroyuki MIURA, Chikako SUZUKI, Wataru KOMADA, Chiharu SHIN, Masahiro YAMAMOTO and David MASUOKA
Fixed Prosthodontics, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima,Bunkyo-ku, Tokyo 113-8549, Japan Corresponding author, Daizo OKADA; E-mail: d.okada.fpro@tmd.ac.jp

Although composite resin core is used with various types of prefabricated posts, it remains unclear which kind of material is most suitable for the post. The aim of this study was to evaluate the influence of prefabricated posts on the stress distribution within the root by finite element analysis.Posts and cores were built up with composite resin and four types of prefabricated posts: two types of glass fiber posts (GFP1, GFP2) with low and high Young’s moduli, a titanium post (TIP), and a stainless steel post (SSP). In all models, stress distribution during function was calculated. There were differences in stress concentration at the root around the end of posts. The magnitudes ofstress for GFP1, GFP2, TIP, and STP were 8.7, 9.3, 11.7, and 13.9 MPa respectively. Given the results obtained, GFP1 was the most suitable material for post fabrication since this model showed a lower stress value. It would therefore mean a lower possibility of root fracture. Key words: Nonlinear finite element analysis, Young’s modulus, Von Mises stress Received Feb 5, 2008: Accepted Mar 13, 2008INTRODUCTION Posts and cores are frequently used to restore endodontically treated teeth, prior to the final restoration. Traditionally, cast post and core systems are the preferred choice because of their superior mechanical strength1-3). However, owing to a large difference in Young’s modulus between metal and dentin, an excessive concentration of functional stresses may occur around the end ofthe post, resulting in catastrophic vertical root fracture2,5,6). When the latter occurs, re-restoration is difficult in most cases, leading to the extraction of teeth4). 　　Recently, composite resins have been used as core build-up materials after endodontic treatment instead of cast posts and cores. By virtue of a Young’s modulus that is similar to that of dentin5,6), use of composite resin coresaids to reduce stress concentration within the roots of endodontically treated teeth and hence prevent catastrophic vertical root fracture. It should also be mentioned that composite resins can be used as core build-up materials because of remarkable improvement in the mechanical properties of composite resins7). 　　On the other hand, it has been suggested in many researches that composite resincores with prefabricated posts have significantly lower fracture strength than cast posts and cores1,7-9). Nonetheless, composite resin cores weld several upper-hand advantages over cast post and core systems. For example, with composite resin cores, there is reduced risk of unrepairable root fracture (versus catastrophic

vertical root fracture caused by cast posts and cores) and reduced leachingof corroded metal ions (which may trigger an allergic reaction)10). On esthetic appeal, composite resin cores are able to reproduce the shade and translucency of natural teeth when all-ceramic crowns or polymer-based restorative material crowns are chosen as the final restoration11,12). Against this backdrop of laudable functional and esthetic advantages, use of composite resin cores combinedwith various kinds of prefabricated metal and non-metal posts is gaining in popularity and on the rise ― such as glass fiber post5,8,11), quartz fiber post5), stainless steel post5,13), titanium post13), and carbon fiber post14). 　　However, in this wide gamut of prefabricated post systems, there belies a large difference in Young’s modulus among the various kinds of post materials ― and this...