Treatment outcome in endodontics: the Toronto Study. Phase 1: initial treatment.

This study assessed the 4- to 6-yr outcome of initial endodontic treatment during Phase 1 of the "Toronto Study" project. A total of 450 teeth were treated, alternating the "Schilder" technique and step-back with lateral condensation, and examined clinically and radiographically by an independent examiner. Apical periodontitis was recorded as absent (periapical index < 3) or present (periapical index > or = 3) and outcome dichotomized as "healed" (no apical periodontitis, no signs or symptoms) or "disease." Univariate, bivariate, and multivariate analyses were performed (p = 0.05) on 120 examined teeth. The "healed" rate (81% overall) was significantly higher for teeth treated without apical periodontitis (92%) than with apical periodontitis (74%). Several other factors were associated with healing rate differential of 10% or higher, but no statistical significance. This study confirmed apical periodontitis as the main prognostic factor in initial endodontic treatment. Continuation of the project will allow assessment of other prognostic factors with better power.