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Long-term studies examining the treatment outcomes of “cracked teeth” that received orthograde root canal treatment in the United States do not exist. The purpose of the present study was to examine the distribution and 1-year treatment outcomes of cracked teeth receiving orthograde root canal treatment in 1 private endodontic practice over a 25-year period.A total of 3038 cracked teeth were initially examined, and data from 2086 unique patients were analyzed. Pulpal and periapical diagnoses, year of treatment, tooth type, restorative material, and number of restored surfaces at the time of examination were recorded for all patients. Periodontal probing depths were also recorded. The patients' age and sex were added retrospectively for all patients whose data were available. Univariate frequency distributions for all collected variables were evaluated. Bivariate associations were analyzed between explanatory variables and the success of the root canal therapy.Of the 2086 cracked teeth observed among unique patients, the most common were mandibular second molars (36%) followed by mandibular first molars (27%) and maxillary first molars (18%). Among the 363 teeth eligible for multivariable regression analysis, 296 (82%) were deemed successes after 1 year. There were no statistically significant differences in success based on pulpal diagnosis (irreversible pulpitis, 85%; necrosis, 80%; previously treated, 74%), patients' age, sex, year of treatment, tooth type, restorative material, or number of restored surfaces at the time of examination. The 3 factors most significant in bivariate analyses were pocket depth, distal marginal ridge crack, and periapical diagnosis, which were used to generate a prognostic index for success of orthograde root canal therapy in cracked teeth called the Iowa Staging Index.The results of this study suggest that cracked teeth that received root canal treatment can have prognoses at higher success rates than previously reported. The Iowa Staging Index may prove to be useful in clinical treatment decision making.