Effect of retainer design and material on the fracture resistance of three unit bridge on endodontically treated abutments

Abstract

The conventional restoration protocol for endodontically treated teeth with excessive coronal loss has been metal post and core followed by a complete crown. The use of glass fiber posts combined with the dentin bonding technique made the restoration of endodontically treated teeth more straightforward, biocompatible, and economical.(1) Initially, the post was thought to reinforce the remaining tooth structure.(2) However, several studies have shown variable results with high incidences of root fracture, indicating that excessive removal of tooth structure to place a post further weakens the root.(3) The advent of high-strength ceramic materials and the progress made in adhesive dentistry has resulted in restoring posterior teeth without the use of a post and core.(4) Teeth with excessive coronal loss can be restored with the use of the endocrown. The first endocrown report was made by Pissis(5) in 1995 and is known as “the monoblock porcelain technique.” In 1999, Bindl and Mörmann(6) used the term “endocrown” to describe a ceramic crown which extends into the pulp chamber or the root canal orifices of an endodontically treated tooth in order to gain retention. Endocrowns have been recommended for teeth with short clinical crowns and calcified, short, or curved root canals that make post and core restorations impossible, also can be used in patients with limited interocclusal space, which prevents adequate thickness for both the ceramic veneer and the metal or ceramic framework.(7) But if depth of pulp chamber is less than 3mm or cervical margin is less than 2 mm wide and if adhesion cannot assured, in such cases endocrowns are contraindicated.(8)

A high-performance polymer, polyetheretherketone (PEEK) has recently been introduced in dentistry. It has been used for the fabrication of implant fixtures, fixed and removable dental prosthesis frameworks, and for implant frameworks and restorative implant parts.(9) A modified PEEK material containing 20% ceramic fillers (BioHPP; Bredent GmbH) can be used for the fabrication of prostheses either by injection molding or CAD-CAM procedures. The advantages of using this material are the elimination of allergic reactions, good mechanical properties, good wear resistance, good polishing properties, and low plaque affinity.(10)