Inside Dentistry
April 2006
Volume 2, Issue 3

The impact of instrument fracture on outcome of endodontic treatment

Howard E. Strassler, DMD

Spili P, Parashos P, Messer HH. J Endod. 2005 Dec;31(12):845-850.


Adoption of rotary nickel-titanium instruments has renewed concerns regarding instrument fracture and its consequences. The frequency of instrument fracture and its impact on treatment outcome were determined from an analysis of specialist endodontic practice records involving 8,460 cases. A case-control study of treatment outcomes was conducted on a subset of 146 teeth with a retained instrument fragment (plus 146 matched controls), for which clinical and radiographic follow-up of at least 1 year was available. Masked radiographs were assessed by 2 calibrated examiners. Overall prevalence of retained fractured instruments was 3.3% of treated teeth. In the case-control study, overall healing rates were 91.8% for cases with a fractured instrument and 94.5% for matched controls (P > .05, Fisher’s exact test). Healing in both groups was lower in teeth with a preoperative periapical radiolucency (86.7% versus 92.9%, P > .05). In the hands of skilled endodontists, prognosis was not significantly affected by the presence of a retained fractured instrument.


When performing endodontic treatment, especially with rotary instrumentation, there is a fear in the back of almost every clinician’s mind that the instrument may break and not be retrievable. What then? How will future success be affected? Very few studies have reported on the outcomes of endodontic treatment as it relates to broken instruments that are retained in the root canal. Fractured root canal instruments can include endodontic files, lateral condensation finger spreaders, spiral fillers, and Gates Glidden burs. The metals that these instruments can be made from include stainless steel (SS), nickel titanium (NiTi), or carbon steel. Most instances of instrument fracture and separation are a result of incorrect use or overuse of the instrument with fracture occurring at the tip of the instrument and the instrument being retained in the apical third of the root canal.

This retrospective study examined a large number of cases (8,460) over 13.5 years from 2 endodontic practices with 7 endodontists. The study had 2 different parts. The first evaluated the prevalence of retained fractured instruments (rotary NiTi and SS hand files [used only as pathfinders]) after treatment. Each was analyzed separately. The second part of the study analyzed cases from part 1 that had at least 1 year of clinical and radiographic follow-up. The findings indicated that of the 8,460 cases, 277 teeth had 1 or more instrument fragments (301 total) resulting in 3.3% of the treated cases having a retained instrument fragment. Of these fragments, NiTi instruments accounted for 78.1% of the total, SS 15.9%, paste filler instruments 4%, and lateral spreaders 2%. One interesting finding was that there was no consistent pattern of declining fracture rate with increasing years of experience among 5 of the endodontists. Treatment outcome evaluation used 146 matched-pair cases that met the criteria of the study. Overall, teeth without a periapical lesion had a higher success rate than teeth with a lesion. In those cases without a periapical lesion, the presence of a fractured instrument had no effect on treatment outcome. When a peripical lesion was present, healing was lower when a fractured instrument was present (86.7% vs 92.9% [control]), but this difference was not statistically significant.

With the trend to rotary instrumentation for endodontic treatment, there has been the fear that use of a rotary instrument-driven handpiece would result in an increase in instrument fracture and, potentially, a decrease in endodontic treatment success. This clinical study has shown that rotary NiTi instruments have a significantly higher fracture rate when compared with SS (78.1% vs 15.9%), but this instrument breakage was similar to previously reported data for hand files. Also, in the hands of an experienced endodontist, instrument fracture (particularly rotary NiTi) had no adverse influence on the outcome of nonsurgical root canal treatment and re-treatment when the instrument was retained in the canal. It would appear that the presence of a periapical lesion is an important criterion in predicting success after instrument separation and retention within the root canal.

About the Author

Howard E. Strassler, DMD
Professor and Director of Operative Dentistry
Department of Endodontics, Prosthodontics and Operative Dentistry
University of Maryland Dental School, Baltimore, Maryland

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