The Effect of Crown Design on the Potential to Develop a Vertical Root Fracture Following Endodontic Treatment

Patients often ask if a proposed endodontic treatment is guaranteed.  What they are meaning is will they be able to keep their tooth for the rest of their life.  Endodontic success studies have repeatedly shown that overall success rates are approximately 85% with tooth survival in the 98% range.  Most endodontic failures are related to either inadequate removal of bacteria or post-endodontic recontamination.  More distressing for patient and dentist alike is the development of vertical root fractures (VRF) and subsequent loss of the tooth.

Many patients present with visible signs of bruxing and clenching including enamel craze lines, cuspal fractures, and cracks on marginal ridges which often extend apically.  There is very little sound research in the literature to help us determine when a tooth with a crack should be treated or extracted and, if the tooth is to be retained, what type of restoration to be place to protect the endodontically treated tooth from developing a vertical root fracture in the future.

Lin et al, JOE 39:3 March 2013, studied the effect of three restorations on the probability of developing a catastrophic VRF.  The authors looked at the loading effects of a milled all ceramic onlay (onlay), a milled all ceramic crown having 360 degree butt joints using the pulp chamber for retention (endocrown), and a conventional PFM with post/composite core (PFM) placed on endodontically treated teeth with a mesial wall crack which extended to 1mm above the crestal bone (AB) or 1mm below the crestal bone (BB).  Teeth were loaded to failure (0-2000N).  Normal biting forces average 322N with a range of 200-500N.

The authors found that the probability of developing a VRF was highest in the onlay group.  In teeth restored with a milled onlay the probability of VRF was 27% in teeth with an AB crack and 70% with a BB crack.  Stress analysis showed that stresses concentrated at the apical extent of the pre-existing crack leading to high probability of crack propagation.  There was little difference between the endocrown and PFM restorations.  The probability of VRF for the endocrown was 2% in teeth with an AB crack and 10% with a BB crack.  The probability of VRF for the PFM was 1% in teeth with an AB crack and 2% with a BB crack.  The occlusal load stresses were distributed equally around the root when full coverage restorations were used.

Not unexpectedly the authors found that under the high, extended loads of clenching conditions, probability of VRF went to 95% in the onlay group, the endocrown group soared up to 80%, while the PFM group developed VRF 5-8% of the time.

While this study is limited by the researcher’s ability to recreate the complex forces of human occlusal patterns there clearly are indications of how to restore endodontically treated teeth to reduce the probability of vertical root fracture.  First and foremost is that posterior teeth should be restored with full coverage crowns whether milled or conventional, closely following endodontic treatment.  Partial coverage should be avoided. We can also reassure our patients that when the pulp chamber crack is 1mm above the interproximal bone level the probability of crack propagation is minimal.  A more difficult diagnostic challenge is to determine how far the crack is below the bone level and at what point should endodontic treatment be aborted and the tooth is extracted.  The CBCT is helpful here.  3D imaging will often show bone loss around the crack and the apical extent of the crack

The take home message is that cracks above the pulpal floor are restorable with full coverage crowns and those that extend into the root more than 1mm, especially when confirmed by CBCT evidence of bone loss, should be extracted.

 

ABOUT DR. HOWARD BITTNER

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 a wide background in all facets of general dentistry, with advanced dental training in prosthetic dentistry from respected educational facilities such as Creating Restorative Excellence in Tacoma, Washington, and The Pankey Institute in Miami, Florida. He has been practicing the dental specialty of Endodontics since 1995.

He is a past president of the British Columbia Society of Endodontists, the Dental Specialists Society of British Columbia, and the Concentric Endodontic Study Club. Dr. Bittner is also a guest lecturer in the Faculty of Dentistry at the University of British Columbia.

On June 3, 2013, posted in: News for Doctors by