During the follow-up period of 4.5 years, none of the patients had any discomfort and all teeth were functional. All patients returned for follow-up. One series of radiographs was excluded because of imperfections of radiographic technique.
There were no significant differences between patient groups related to gender, age and (the clinical parameters) tooth type, size of radiolucency, preparation length, master apical file size and the apical extent of the root-canal filling (P > 0.05).
Kappa scores between observers were 0.7-0.9. The agreement between treatment outcome scores of the individual observers and consensus score was at least 94% with kappa scores of 0.8-0.9.
The consensus on periapical scores and treatment outcome are presented in Tables 2 and 3.Before the treatment, all teeth had a periapical score 4 or 5. At the end of the follow-up period18% stillhada radiolucency (periapical score 4 and 5), in 82% a clear radiolucency was not present (periapical score 1 and 2). The periapical scores after the follow-up period were significantly lower (P < 0.05) than the scores before the start of treatment, indicating that the lesions had reduced significantly over the time.

Table 2. Consensus periapical score.


Score1-5, see Table 1. The values in parentheses are in per cent.

Table 3. Consensus treatment outcome.


Score A, B, C see Table 1. The values in parentheses are in per cent.

Consensus treatment outcome A or B was assigned in 97% of the cases. One case was judged as a failure (Table 3). Upon extraction a vertical root fracture was diagnosed in this case.
Of the 21 teeth treated in one visit (group1), 17 showed complete radiographic healing (score A, 81%), and 4 teeth a reduction in lesion size (score B, 19%). In group 2, 12 teeth showed complete radiographic healing (score A, 71%), and 4 had a reduction in the lesion size (score B, 23%) whilst one tooth had failed (score C, 6%) (Table 4).
The time necessary to complete the periapical healing used as basis for calculation ranged from 7 to 55 months. The individual observation times varied between 12 and 35 months for those teeth associated with incomplete healing or failure. The probability that complete healing occurred within a certain time span increased continuously with the length of the observation period (Table 5, Fig.1) The log-rank test did not reveal any significant difference between the one and two visit treatment groups (P > 0.05). Power statistics showed that the presented differences (91% vs. 94%) between one and two-visit root-canal treatment could be significant if one experimental group would comprise of1275 participants (power set at 80%).
Prior to the final obturation, there were eight teeth (seven in group 1, one in group 2) with a positive rootcanal culture (Table 6). Six positive root canals contained <102 CFU mL, one canal contained 2 x103 and one canal harboured 8 _104 CFU mL. The latter case scored a treatment outcome B. Of the 30 cases that were filled with a negative culture prior to obturation, 22 (74%) healed (11 from group 1 and 11 from group 2) whereas this was the case for seven out of eight cases (six from group 1 and one from group 2) with a positive root-canal culture prior to obturation (87.5%). The chi squared analysis showed no significant difference in healing whether cultivable bacteria were present or not prior to filling. Power statistics showed that the presented differences (74% vs. 87%) between negative and positive cultures at the time of obturation can be significant if one experimental group would comprise 160 patients (power set at 80%, P < 0.05).

Table 4. Treatment outcome scores related to one-and two-visit endodontic treatment.


Score A, B, C see Table 1. The values in parentheses are in per cent.

Table 5. Probability of success (95% confidence interval).



Figure 1. Estimation of the fraction of teeth [p(t)] that are successful following one-o r two-visit root-canal treatment with in 4 years.



Table 6. Positive and negative root-canal cultures related to treatment outcome.