An In Vitro Study Of The Fracture Resistances Of Endodontically Treated Teeth Restored With Glass Fiber-zircon Reinforced Composite Post And Composite Core

Endodontically treated teeth are brittle and undergo much stress in function because of varies of reasons, thus are predisposed to root fracture. Conventionally cast metal posts and cores are used to rebuild enough tooth structure and to reinforce the tooth. Recently a kind of glass fiber-zircon reinforced composite post (FRC) system has been introduced into the market. It is said to be esthetic easily removable and corrosion resistant. And E-modulus of FRC post is close to that of dentin, so this kind of post can theoretically distribute the stress, impart minimal stress to the tooth, and is of relatively little risk to cause root fracture. However, the information about fracture resistance of FRC post/composite core and cast post and core is ambiguous, and conflicts exit because of difference in methodology.The aim of this research paper is: to compare the fracture resistances of endodontically treated teeth restored with a cast post and core or glass fiber-zircon reinforced composite post with a composite core when 2mm ferrule is prepared; to summarize and improve the methodology of model studies of post and core based on the former literature; and to observe the effect of 2mm ferrule.In this research ,a total of 16 matched pair teeth with their crowns removed at the level of 2mm above the cementoenamel juction were endodontically treated. The teeth were randomly divided into two groups, one was restored with FRC post and composite core, and the pair group with cast post and core. With a parallel muller, ferrule of 2mm length and core of similar size were prepared on all the teeth, and After metal complete crowns were cemented, the specimens were mounted on a universal testing machine and a compressive load was applied at an angle of 45°to the palatal surface of the crown at a speed of 0.5mm/min until failure occurred. Fracture loads and modes were recorded and paired samples test was used to compare the fracture resistance of the two posts (P=0.05) .The results of this paper are as follows: 1: Fracture thresholds of cast post and core group is significantly higher thanthat of FRC post group 2: Root fracture that can't allow repair of the teeth were observed in all thespecimens except one pair in which tooth displacement was observed.We can come to the following conclusions: 1: When 2mm ferrule length can be obtained, the fracture loads ofendodontically treated teeth restored with cast post and core were higherthan that of teeth restored with FRC post and composite resin core. 2: The fracture resistance of FRC post was lower than that of cast post,however it is much higher than physiologic occlusal loads, so the FRCpost is sufficient to be applied clinically. 3 The metal crown of the upper anterior tooth concentrates forces at itspalatal margins during occlusal loading, so clinical measures should beadopted to reinforce the tooth tissue in this area.4 When the loss of tooth tissue is too large for a ferrule of enough length to be prepared, the failure modes of FRC post and composite resin core are more favorable than that of cast post and core5 in the methodology of the model study:? The parallel muller provided a novel method for post and core model studyto control the size of ferrule and core, and this method was tested to beconvenient and precise. (D The crown should be cemented before the specimens were loaded, in orderto simulate the clinical condition and the crown didn't blur the differenceof fracture loads between the two posts.