Toronto Study. Revisitation.

  In 1993 Friedman and coworkers started the so called "Toronto Study project", a prospective-dynamic-modular cohort study aimed to assess the outcome of initial endodontic treatment and the influence of potential prognostic factors ( Friedman et al. 2003; Farzaneh et al. 2004;  Marquis et al. 2006; De Cherigny et al. 2008).

All patients had been treated at the Graduate Endodontic Clinic, Faculty of Dentistry, University of Toronto. The treatment providers were graduate students supervised by qualified endodontists. Both step-back technique with lateral compaction of guttapercha and Schilder techinque were used.



 treated teeth sample


 Teeth analyzed


 drop-out rate


 Toronto phase I  405  120  70
 Toronto phase II  442  122  72
 Toronto phase III  532  132  76
 Toronto phase IV  582  137  76



    From the above table, we can see a very low recall rate, lower than 30%. According to Sackett (Sackett D, Hayness RB, Guyatt GH, Tugwell P Clinical Epidemiology: a basic science of clinical medicine 2.nd edition: Little, Brown, 1991) the erosion of cohort at the follow-up higher than 20-30% has to be considered biased. Besides, the authors have excluded (unreasonably in my opinion) from the controlled sample the teeth wich had been extracted for different reasons (periodontal, restorative, unknow reasons). This adds to the studies another bias with dangerous distortion      .  



Teeth extracted and excluded from analyzed sample


Toronto phase I 21
Toronto phase II 31
Toronto phase III 10
Toronto phase IV 15


   Adding the teeth extracted at the sample analyzed, we shall obatain the following table about the clinical success rate at 4-6 years (clinical success was defined in the Toronto papers as a functional tooth with no symptoms and clinical signs):   



Clinical success rate at 4-6 year follow-up


Toronto phase I 83
Toronto phase II 80
Toronto phase III 88
Toronto phase IV 83


If we consider in the definition of success also the radiologic aspect, the Toronto success rate would lower than 70%.



Are we sure that success rate of endodontic therapy had been changing in the last 50 years and more? There a lot of metanalysis nurturing this suspicion (…suspicion wich borders with Truth). But it's enough to watch the numbers above! A university endodontic specialist deparment, with microscopy, apex locators, warm vertical guttapercha, virgin teeth has got an average clinical success of 85% ( below 70% for clinical and radiological success) at 4-6 years follow-up. Without forgetting that 70% of sample have not been controlled!