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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 4  »  Prevalence of yeasts in saliva and root canals of teeth associated with apical periodontitis
Prevalence of yeasts in saliva and root canals of teeth associated with apical periodontitis
Discussion.



The sample collection (imprint culture, mucosal swab, mouth rinse, saliva) (Arendorf & Walker 1980, Samaranayake et al. 1986) and cultivation techniques (Najzar-Fleger et al. 1992) appear to influence the recovery of yeasts. The saliva culture technique used in this study was one of the most sensitive methods for assessing Candidal carriage in healthy individuals (Oliver & Shillitoe 1984), except that it does not allow study of the intraoral distribution of yeasts as would be demonstrated by imprint culture (Arendorf & Walker 1980). Most of the studies using non-selective blood agar (Tronstad et al. 1987, Najzar-Fleger et al. 1992, Sundqvist et al. 1998, Molander et al. 1998) have reported a lower prevalence of yeasts in root canals compared to the present (10%) and other (7.6–55%) studies (Jackson & Halder 1963, Wilson & Hall 1968, Najzar-Fleger et al. 1992) using selective sabouraud dextrose agar for cultivation.
The prevalence of yeasts in untreated cases in this study was 5.7%, in contrast to the 1.9% (Wilson & Hall 1968) and 26% (Jackson & Halder 1963) reported in previous studies. The prevalence increased to 6.8% and 33.6%, respectively, after placement of an intracanal dressing in the above studies; this would appear to substantiate the hypothesis that inadequate treatment may allow yeasts to overgrow (Sirén et al. 1997, Sundqvist et al. 1998). It is possible the differences were due to coronal status of the tooth, details of which were not given. Investigation of treatment-resistant cases by Waltimo et al. (1997) found a prevalence of 4.9% in 967 retreatment cases compared to the 16% recovered in this study. In their study, the sampling was carried out by a number of general dental practitioners following written instructions on the sampling procedure, the samples being processed 1–3 days following acquisition. The low recovery of yeasts may also be attributed to the use of tryptic-soyagar medium for isolation and the method used for preliminary identification of yeasts. A range of identification protocols were used in the present study, ranging from the germ tube formation test to microscopic examination on corn meal agar to rapid identification kits (Rapid ID32C ® ). The correlation of the identifications was good for 30 out of 32 isolates, the tests validating each other, implying a robustness and consistency.
Of the Candida species isolated from saliva samples in this study, C. albicans was the most prevalent (17/23), corroborating the findings of others (Odds 1979). However, Rodotorula mucilaginosa, Candida dubliniensis, Cryptococcus humicolus and Trichosporan mucoides, which are usually associated with immuno-compromised patients (Campbell et al. 1996) and possess increased virulence in susceptible hosts (McCullough & Hume 1995), were recovered from healthy individuals in this study. C. dubliniensis was recently identified by Sullivan et al. (1995) and is believed to be strongly associated with human immunodeficiency virus infection (Coleman et al. 1997). More recently, it has also been recovered from HIVnegative individuals (Odds et al. 1998, Pinjon et al. 1998). In the present study, C. albicans was recovered from one patient (patient 1) at his initial visit, whilst C. dubliniensis was recovered from the saliva a month later. This may be explained by the fact that C. albicans and C. dubliniensis are closely related (Sullivan et al. 1995), with the colonies appearing identical on SAB plates; both strains may have been present on each occasion and not detected.
All five patients (six teeth) with yeasts present in the root canal sample were healthy and had no history of immunodeficiency, but had received a course of antibiotics within the previous 12 months. The root canal systems of five teeth had some communication with the oral cavity, via coronal restoration leakage, sinus tract or oro-antral communication (Table 4). The sixth case had a history of post crown decementation and incision/drainage of a swelling associated with the tooth in question some months earlier, although the corresponding saliva sample was negative for yeasts. The periodontal probing profile associated with these teeth was less than 4 mm for all the cases, except patient 2, who had a deep vertical bony defect that communicated with the periapical lesion.
Of the yeast species isolated from the root canals, R. mucilaginosa (4/8) and C. albicans (3/8) were almost equally prevalent, whilst C. sake (1/8) was recovered as a single strain from only one tooth (patient 3). The isolation of Rhodotorula species from three root canals and the saliva of two patients (patients 1 and 5) was unusual, because its presence in root canals has not been reported previously.
Yeasts were shown to be more prevalent in previously treated (16%) than untreated (5.7%) canals; in either case, they were strongly associated with their presence in saliva (odds ratio = 13.8, P = 0.021, 95% CI = 1.5–129.9). Although the number of yeast-positive samples is small, the small P-value indicates that the detected difference is likely to be real, whilst the wide confidence interval suggests that the true magnitude of this difference is difficult to estimate with precision. The yeasts may have invaded root canals during initial treatment via leaking restorations or by colonization of dentinal tubules. Once Candida species enter the root canal, they may further penetrate into root canal dentinal tubules by adoption of a range of growth patterns (blastospores and hyphae) and interact with other microorganisms to form a complex biofilm (Bagg & Silverwood 1986, Jenkinson et al. 1990, Qen et al. 1997, 1999). Fungi, unlike most bacteria, are highly resistant to routine root canal irrigants such as sodium hypochlorite (Qen et al. 1999, Waltimo et al. 1999) and medication (calcium hydroxide) (Waltimo et al. 1999). The antifungal effect of sodium hypochlorite may be further hindered by the presence of a smear layer (Qen et al. 1999). Mechanical instrumentation of canals may help to disrupt and expose biofilm organisms to irrigating solutions but at the same time may produce a smear layer that may enhance the growth of surviving yeast cells. On the basis of this, a case could be made for ethylenediaminetetraacetic acid (EDTA) irrigation to remove the smear layer and perhaps an antifungal medicament for recalcitrant cases. Furthermore, EDTA has been shown to have a potent antifungal effect (Qen et al. 2000), possibly due to its ability to chelate calcium ions which have a critical role in morphogenesis and pathogenicity of C. albicans.
The role of yeasts in root canal infection and periapical disease is still poorly understood and warrants further investigation.

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