Influence of Ferrule, Post System, and Length on Biomechanical Behavior of Endodontically Treated Anterior Teeth

Endodontically treated anterior teeth are always of concern to the restorative dentist and endodontist alike.  Anterior teeth are the most likely teeth to be affected by both accidental trauma and parafunctional occlusal forces.  Anterior teeth which are biomechanically compromised, whether through caries, trauma, or injudicious endodontic access are often restored, following endodontic treatment, with  post and core foundation restorations prior to placement of a crown.

Historically, cast post cores have been the restorative dentist’s primary choice for anterior teeth      foundations.  Over the last few years fiber posts bonded to the dentin of the root canal system with a bonded composite core have become more widely used.

Many studies show that anterior, root filled teeth are subject to higher risk of failure either through dislodgement of the post/core and crown or more drastically, vertical root fracture.  Several factors may be involved in the failure including root dentin thickness, type of post and crown, length of post, and amount of ferrule.

Endodontic and restorative failures are problematic for all parties involved.  Failure, especially of short to medium term, may result in animosity between the doctor and patient.  Doctors concerned about the financial, time, and esthetic impact on their patients, as well as their reputation in the community often redo or replace failing treatment at their own expense.  Subsequently it is imperative for both the restorative dentist and endodontist to understand the parameters for successful restoration of an endodontically treated anterior tooth.

Martins et al, JOE 40:1 January 2014, compared cast post cores (CPC) and bonded fiber post composite cores (BFP).  They looked at effect of ferrule and post length in this in vitro, fracture resistance study.  80 intact bovine teeth were cleaned, shaped, and packed with gutta percha.  Post space was placed to either 7mm or 12mm from the CEJ for each post type.  Both posts were cemented with  RelyX resin cement.   The teeth were prepared with 2mm of ferrule or no ferrule and fitted with cast metal crowns.  The teeth were then placed under a 135o oblique load till failure.

The investigators found that the CPC group concentrated stresses at the ferrule and dentin/post interface while the fiber post distributed stresses throughout the tooth in a fashion similar to an untreated tooth.  The CPC group failed most often with fracture in the middle or coronal third of the root with the shorter post increasing failure in the coronal third.  The BFP failed most often at the post-core interface without root fracture and with post length not affecting the outcome.  Teeth without ferrule had an increased degree of root fracture for both post types.

In an adjunctive study by Amato et al, JOE 39:12, December 2013, the authors found that use of a rubber dam for post placement significantly increased the endodontic success from 73% to 93%.

The take home message is that there is an increase in stresses with a cast post compared with a fiber post.  As found in other studies, a 2mm ferrule significantly reduces the possibility of root fracture.  In all cases, according to this study, especially when the ferrule is less than ideal, it is better to place a 7mm bonded fiber post under a rubber dam with aseptic conditions rather than a cast post core. 

 
ABOUT THE AUTHOR, DR. HOWARD BITTNER, DMD, CAGS

Dr. Bittner was born and raised in the Surrey/Langley area. Following his pre-dental training at Simon Fraser University, he received his Doctor of Dental Medicine from the University of British Columbia in 1982 and his Certificate in Advanced Graduate Studies in Endodontics from Boston University’s Goldman School of Dental Medicine in 1995.

Dr. Bittner was in private practice in general dentistry for 11 years in Langley prior to his Endodontic specialty training. He has been practicing the Dental Specialty of Endodontics since 1995.

In his free time, Dr. Bittner loves to participate in a variety of sports including most recent, golfing! He also enjoys being a new grandfather, which if you ask him is just the best!

On March 4, 2015, posted in: News for Doctors by