Fiber-reinforced Composite Core Filling in the Restoration of Endodontically Treated Molars - a Clinical Study

INTRODUCTION

Composite resins are routinely used for restoring vital and non-vital posterior teeth by most practitioners in Finland. Various clinical studies have found that the three main reasons for failure of direct composite fillings are secondary caries, wear and fracture of composite resin especially at molar region (1, 2, 3). Non-vital (endodontically treated) teeth are structurally compromised and their restoration is associated with technical failures such as debonding and vertical root fractures (4). Techniques, like root canal post insertion, that are used to overcome these problems, are time consuming and may even further increase the risk for root fractures.

This study is a continuum on material development conducted at the the Department of Prosthetic Dentistry, Biomaterials Science and Turku Clinical Biomaterials Centre - TCBC, University of Turku, in collaboration with TEKES (Technology Development Center of Finland) and StickTech (Turku, Finland). The data obtained has shown that, the use of a bilayered structure consisting of a fiber-reinforced composite substructure (core FRC) combined with an upper layer of conventional restorative composite, increases the fracture load of a restoration significantly (5,6 and 7). This newly developed material has increased mechanical properties when compared to conventional materials, while maintaining its clinical applicability. Moreover, volumetric polymerization shrinkage of the core FRC is found to be lower than commercially available composites (<1.8% for the new FRC-material; 2.0% for a commercial composite Z250) (8). This may be expected to result in less marginal leakage and secondary caries in long term. With this backround a multidirectional short-fiber composite (everX, StickTech) has been introduced as a base material (FRC substructure) for large cavities in vital or non-vital teeth.

The investigators in vitro experiments have shown that the FRC substructure retains and significantly reinforces composite crowns in endodontically treated molars. Moreover, in case of failure, the presence of the FRC substructure seems to orient the fracture propagation and result in more easily restorable fractures. Application on the core FRC material is simplified when compared to post and core techniques commonly used to restore endodontically treated teeth. Clinically, the use of core FRC offers a cost-effective way to restore endodontically treated molars without root canal involvement. In a recently published clinical pilot study the investigators have reported successful 1 year results of this technique (9).

Ceramic onlay-restorations, so called "endo-crowns", are currently used to restore endodontically treated molars with similar indications (without root canal involvement). Case studies have reported good clinical results with this type of method (10). The use of an indirect technique (multiple patient visits), material and technical fabrication costs make this treatment modality, however, more costly and not in the reach of every patient.