During root canal preparation procedures, the potential for instrument separation is always present. Files, a lentulo, a Gates-Glidden (GG) bur or any manufactured obstruction can be left behind in the canal. Nickel-titanium (NiTi) rotary files are in common usage in these days. Despite their undeniable advantages, there is a potential risk of separation within the canals. It is very rapid, unpredictable, and creates a great deal of stress for the practitioner.

When an endodontic instrument separates, the best option is to remove it. Ultrasonic instruments and microscopes have improved the success rate for removing separated instruments. But it is difficult and not always possible. Therefore prevention is the key.

In this case report, several management methods of separated file in the canal are presented.

Hemolytic property is a specific feature of bacteria to obtain iron which is essential for its survival in host tissues. Therefore, it is thought to be one of several factors of virulence. The purpose of this study was to investigate the hemolytic properties of Prevotella nigrescens isolated from the teeth diagnosed as pulp necrosis and apical periodontitis under the presence of hemolysin inhibitors such as NaN₃ and dithiothreitol, heat, various pH and cultural conditions.

The results were as follows;

1. Clinically isolated P. nigrescens strains and standard P. nigrscens ATCC 33563 showed hemolytic activity.

2. P. nigrescens showed higher hemolytic activity against human erythrocytes than sheep or horse erythrocytes.

3. NaN₃ and dithiothreitol (DTT) reduced the hemolytic activity of P. nigrescens in a dose dependent manner (p < 0.05).

4. Optimal pH for the maximum hemolytic activity of P. nigrescens was 4.0 and the hemolysin was stable under the 50℃, but the hemolytic activity was significantly decreased at 95℃.

5. P. nigrescens cultured in 10% CO₂ condition showed higher hemolytic activity than the bacteria cultured in the anaerobic condition.