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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 1  »  Effects of instrumentation, irrigation and dressing with calcium hydroxide on infection in pulpless teeth with periapical bone lesions
Effects of instrumentation, irrigation and dressing with calcium hydroxide on infection in pulpless teeth with periapical bone lesions
Discussion - References



Discussion.
The presence of bacteria in the root canal system is essential for the development of apical periodontitis and the aim of root canal treatment is their elimination.
The use of Reduced Transport Medium (RTF), the rapid processing of specimens (within 15 min after collection) and the anaerobic techniques used ensured that the microbiological results of the present study were reliable and sensitive. Our results therefore allow comparisons with previous reports where similar microbiological techniques for recovery of microorganisms from the root canal were used.
The present study demonstrated that instrumentation and irrigation with 2% sodium hypochlorite reduced the total number of microorganisms significantly to 0.18% of the original number. Seventy-six per cent (32 out of 42) of the canals had no detectable bacteria after cleaning, disinfecting and shaping in the first visit. Sjögren et al. (1991, 1997) found 50–60% negative samples after similar preparation of infected root canals. The difference with our findings could be a result of the different concentration of sodium hypochlorite (0.5% vs. 2%) and different delivery systems used for irrigation. In addition, the difference in sampling techniques and transport media used may have also created differences. The mean numbers of viable bacteria after instrumentation and disinfection (s2) were low in this study, as well as in the studies of Sjögren et al. (1991, 1997) (102) and similar to the results of Byström & Sundqvist (1981). The median total CFU count of s1 in our study (7.6 104) is similar to those of Byström et al. (1985) and Sjögren et al. (1991), who reported CFU counts of 6.5 103 and 9.8 104. Byström & Sundqvist (1981) and Ørstavik et al. (1991) found CFU counts of 1 105–4 105 before the start of treatment.
The mean number of species at the start of the first visit was 4.6 (range 2–8). It dropped to a mean of 2.8 (range 2–6) species at the end of the first visit (s2), and did not change after 4 weeks of calcium hydroxide dressing (range 2–6). Indeed, the number of different species per infected root canal was relatively small, and generally ranged between 2 and 8 (Sundqvist 1976, Sundqvist 1992, Brauner & Conrads 1995, Le Goff et al. 1997, Sjögren et al. 1997, Dahlén & Haapasalo 1998). The percentage of anaerobes (of the total CFU counts) in our study was 97% at the start of the first visit. After 4 weeks of calcium hydroxide dressing the percentage of anaerobes remained at 95%, even though the total number of CFU and the mean number of anaerobic species had dropped significantly. Percentages of 78–93% have been found by others (Bergenholtz 1974, Byström & Sundqvist 1981, Sundqvist et al. 1989, Brauner & Conrads 1995, Sjögren et al. 1997 and Le Goff et al. 1997). Various periods of application of calcium hydroxide dressing have been recommended. Cvek (1973) reported 90% negative cultures after 3 months. Byström et al. (1985) reported 100% negative cultures after 4 weeks; Reit & Dahlén (1988) found 74% negative after 2 weeks, Sjögren et al. (1991) reported 100% bacteria-free after only 1 week, whereas Ørstavik et al. (1991) found 65% of their samples negative after 7 days of calcium hydroxide dressing.
After the application of calcium hydroxide for 4 weeks, we expected the bacterial cell counts (s3) to be similar to or lower than those following preparation of the first visit (s2). However, we found that the median cell count had increased to 140 (range 0–1.2 102), although this represented only 0.18% of the original CFU counts at s1. Ørstavik et al. (1991) found that only one of eight positive samples (total of 23 samples) showed higher numbers (5 104); from the other seven samples growth was detected but reported as non-quantifiable, meaning very low numbers of bacteria. Although there is some variation, the bacterial cell counts of the ‘positive’ canals after calcium hydroxide are generally similar in all these studies (most often less than 102). One explanation for the differences that do occur could be that remnants of calcium hydroxide are transferred to the microbiological samples, influencing the results. After rinsing with RTF, we consistently visualized remnants of calcium hydroxide in the root canals when checking with the operating microscope (16using vertical illumination). Before sample s3 was taken, the use of the microscope was essential for complete removal of calcium hydroxide.
Comments have been made previously about the uncertainty of the bacteriological sampling procedure immediately after removal of a calcium hydroxide dressing (Reit & Dahlén 1988). It has been suggested (Reit et al. 1999) that microbiological samples should be taken after filling the canal with a sampling fluid (after removal of the calcium hydroxide) for 7 days. However, when the authors applied this procedure culture reversals were seen in both directions. Thus, Reit et al. (1999) reported seven canals that turned from a negative to a positive culture after 1 week but also seven canals that changed from a positive culture to a negative culture over the same period. It cannot be ruled out completely that some negative canals in the present study after calcium hydroxide removal (s3), may have become positive if evaluated 1 week later. This means that the results of this study are probably an overestimation of the bactericidal effect of calcium hydroxide. The studies of Reit & Dahlén (1988) and Reit et al. (1999) demonstrated the limitations of microbiologic root canal sampling and this should be taken into account when evaluating all root canal procedures and the effectiveness of root canal dressings. Since it was found that removal of calcium hydroxide from the root canal with the aid of the operating microscope was enhanced and because it has been shown previously that a second culture taken 7 days later did not result in more reliable data (Reit & Dahlén 1988, Reit et al. 1999, Molander et al. 1990), cultures were taken immediately after removal of the calcium hydroxide. This process was also less demanding for the patients as it reduced the number of appointments.
After irrigation with sodium hypochlorite and gentle filing with the master apical file, s4 showed a median CFU count of 0 (0–2 103) being significantly lower than s1 but not different from the counts recorded at s2. This indicates that there was no reduction in the number of microorganisms due to the activity of calcium hydroxide. This may be due to the lack of direct contact between the microorganisms and calcium hydroxide in the clinical situation. The pH of calcium hydroxide is approximately 12.5 and this is sufficient to kill rapidly most bacterial root canal species (Byström et al. 1985). However, there will always be areas in the canal space and in the root dentine that have low concentrations of hydroxyl ions in solution and where the local pH will be substantially lower (Siqueira & Lopes 1999). Bacteria vary in pH tolerance and most species grow well within a range of pH 6–9 (Padan et al. 1981). Prevotella intermedia, Fusobacterium nucleatum and Porphyromonas gingivalis can survive and grow at pH levels between 8.0 and 8.3 (Marsh et al. 1993).
Several different species of bacteria are located in the tubules of root dentine (Peters et al. 2001). It is difficult to predict the effectiveness of a calcium hydroxide dressing between visits and its ability to destroy the bacterial species located in this area. It is possible that bacteria present in the dentinal tubules escape the direct action of calcium hydroxide (Ørstavik & Haapasalo 1990, Siqueira & Lopes 1999) and are able to (re)infect the canal space. This may explain why root canals at the beginning of the second visit harboured more cultivable bacteria than at the end of the first visit. Another explanation could be that the effect of calcium hydroxide is reduced by dentine (Haapasalo et al. 2000).
The most dominant species in this study were P. intermedia, P. micros and A. odontolyticus. Bergenholtz (1974) commonly found species belonging to Bacteroides, Corynebacterium, Peptostreptococcus and Fusobacterium. Sundqvist (1992) frequently found F. nucleatum, P. intermedia, P. micros and P. anaerobius. Byström & Sundqvist (1981) found the same species to be dominant, whilst Brauner & Conrads (1995) found a high proportion of P. intermedia. Positive correlations between P. intermedia and P. micros and Eubacterium were previously reported by Lewis et al. (1988), Socransky et al. (1988) and Sundqvist (1992). These combinations may be of importance during root canal treatment, since their interrelationship possibly hinders total elimination of microorganisms or provides an environment in which bacteria multiply more rapidly. Of the seven species present at s4 four are frequently found in combination with each other (P. intermedia, Capnocytophaga spp., A. odontolyticus and P. micros).

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