The dentine powder model appears to be an efficient tool for the study of interactions between local endodontic medicaments, dentine, and microbes.

The relationship between bacteriological findings and clinical treatment procedures was investigated in root canal treatment cases that were selected for bacteriological investigation by general dental practitioners in Finland. The cultures were sent to the Oral Microbiological Service Laboratory at the Institute of Dentistry in Helsinki. Two groups of teeth were selected based on the type of infection present in the root canal system. The 'enteric bacteria' group consisted of 40 sequential cases where Enterococcus faecalis and/or other facultative enteric bacteria or Pseudomonas sp. were found in the samples in pure culture (35%) or together with other types of bacteria. The group 'non-enteric bacteria' consisted of 40 sequential cases where only non-enteric bacteria were found. The dentists who had sent the bacteriological samples received a questionnaire where they were asked about the treatment protocol and procedures. A total of 70 out of 80 questionnaires were returned. If the root canals had been unsealed at some point during the treatment, enteric bacteria were found more frequently than in canals with an adequate seal between the appointments. Of cases with enteric bacteria 55% had been open during the treatment, while in the group where only non-enteric bacteria were found 30% had been open. Enteric bacteria were also more frequently isolated in cases with a high number of appointments before sampling. In the enteric bacteria group 35% of the samples were taken at the 10th visit or later, while the corresponding percentage in the non-enteric group was 3%. In addition, the number of retreatment cases was significantly higher, 12 out of 34, in the enteric bacteria group than in non-enteric bacteria group, which was five out of 36. Other clinical parameters showed no differences between the two groups. The results emphasize the importance of controlled asepsis throughout the root canal treatment.

This study indicates that sodium hypochlorite, iodine potassium iodide and chlorhexidine acetate are more effective than calcium hydroxide against C. albicans in vitro. However, combining calcium hydroxide with sodium hypochlorite or chlorhexidine may provide a wide-spectrum antimicrobial preparation with a long-lasting effect.

The occurrence of yeasts in 967 microbiological endodontic samples taken from root canals in persistent endodontic infections was studied. The sampling was done by general practitioners in various parts of Finland from root canal infections which did not respond favourably to standard conservative therapy. The samples were cultivated aerobically on a non-selective enriched horse blood agar medium, on TSBV agar medium in 5% CO 2 and anaerobically on horse blood agar medium. Micro-organisms were found in 692 of the samples while 275 showed no growth. Forty-eight fungi were isolated from 47 samples which is 7% of the culturepositive samples. Twenty yeast strains were identified further by their colony morphology, growth and cellular characteristics and patterns of carbohydrate assimilation. All isolates except one belonged to the genus Candida. Candida albicans was the most common species. C. glabrata was found together with C. albicans in one sample. C. guilliermondii, C. inconspicua and Geotrichum candidum were each isolated once. Yeasts were found in pure culture in six samples and together with bacteria in 41 samples. In all the samples except two, the accompanying facultative bacteria were Gram positive. The most frequent of them were ␣and nonhaemolytic Streptococcus species which were found in 31 samples. Anaerobic bacteria were isolated together with yeasts from 12 root canals. They included both Gram positive species such as Peptostreptococcus micros and Gram negative species such as Fusobacterium nucleatum. The regular isolation of yeasts, also in pure culture, indicates that yeasts may have an important role in cases of apical periodontitis persisting after conventional treatment.

Several studies have shown a higher success rate of root canal therapy when the canal is free from bacteria at the time of obturation. Treatment strategies that are designed to eliminate this microflora should include agents that can effectively disinfect the root canal. Enterococcus faecalis is often associated with persistent endodontic infections. While in vivo studies have indicated calcium hydroxide to be the most effective all-purpose intracanal medicament, iodine potassium iodide (IKI) and chlorhexidine (CHX) may be able to kill calcium hydroxide-resistant bacteria. Supplementing the antibacterial activity of calcium hydroxide with IPI or CHX preparations was studied in bovine dentine blocks. While calcium hydroxide was unable to kill E. faecalis in the dentine, calcium hydroxide combined with IKI or CHX effectively disinfected the dentine. The addition of CHX or IKI did not affect the alkalinity of the calcium hydroxide suspensions. It may be assumed that combinations also have the potential to be used as long-term medication. Cytotoxicity tests using the neutral red method indicated that the combinations were no more toxic than their pure components.