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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 3  »  An in vitro comparison of the bactericidal efficacy of lethal photosensitization or sodium hyphochlorite irrigation on Streptococcus intermedius biofilms in root canals
An in vitro comparison of the bactericidal efficacy of lethal photosensitization or sodium hyphochlorite irrigation on Streptococcus intermedius biofilms in root canals
Results - Discussion - References.

The teeth ( n = 17) with S. intermedius biofilms receiving no experimental treatment served as baseline controls, the mean number of viable bacteria recovered from them was 1.62 10 8 CFU/canal (Table 1).
The individual and combined effect of TBO and laser light on the viability of S. intermedius biofilms are also presented in Table 1. ‘TBO only’ treatment and ‘laser light only’ treatment, both had mild bactericidal effects. A maximum of 3 log 10 viable bacterial reduction was observed with TBO (100 gmL –1 ) or laser light (120 s [4.2 J] and 600 s [21 J] ).
The combined effect of TBO and laser was bactericidal but could not achieve 100% bacterial kill. A maximum reduction of 5 log 10 of viable bacteria was achieved with 100 g mL –1 TBO and 600 s (21 J) laser dose compared to baseline control.
In stark contrast, no viable bacteria could be recovered from any teeth with S. intermedius biofilms treated with 3% NaOCl for 10 min. Even the most effective combination of TBO and laser dose applied at the access cavity could not compete in effectiveness with 3% NaOCl.

The S. intermedius strain used in the study was isolated from an infected root canal in our laboratory. S. intermedius is a Gram positive, facultative anaerobe and has previously been identified in coronal and apical parts of infected root canals (Baumgartner & Falkler 1991, Sundqvist 1992), deep layers of root dentine (Ando & Hoshino 1990), acute apical abscesses (Lewis et al . 1986), and root-filled canals with persistent infections (Sundqvist et al . 1998). In addition, the choice was also influenced by the ease of growth and laboratory manipulation of this strain.
Previous studies on effectiveness of lethal photosensitization have focused mainly on bacterial suspensions (Wilson et al . 1992, 1993). Their effect on bacterial biofilms has rarely been investigated and most of these have been performed on single-species biofilms grown on nitrocellulose discs (Dobson & Wilson 1992, Poh et al . 2000). The laboratory extracted tooth model, with a S. intermedius biofilm coating the root canal used in this study, simulated the in vivo situation a little more closely. However, the single-species biofilm used is not representative of the polymicrobial infection encountered in the root canal (Nair 1987, Molven et al . 1991). Unpublished work in our laboratory attempting to create a simple polymicrobial biofilm has proved unpredictable and certainly not reproducible thus far. It was therefore decided to select one of the commonly isolated species likely to adhere to dentine and representative of those species more resistant to treatment. A series of pilot studies were carried out to establish the protocol for this model, including confirmation of the biofilm by SEM. The canals of all teeth were prepared to an apical size 25 with a 10% taper in order to allow accurate sampling and quantification of bactericidal effects, as well as to achieve a degree of standardization. The introduction of fibre optics into the canal was considered but not adopted in the first instance, as application at the access cavity is clinically straightforward, and experimentally avoids displacement of TBO and mechanical interference (not the subject of test) of the biofilm. Having shown the effectiveness of lethal photosensitization of a nitrocellulose disc biofilm model (Poh et al. 2000), the aim of the present study was to test the hypothesis that the structure of teeth would aid light transmission (Odor et al. 1996) and allow the reproduction of previous success in nitrocellulose-borne biofilms, in the current tooth model.
In this study, irradiation with He–Ne laser alone had no consistent bactericidal effect on S. intermedius biofilm. These data were in agreement with others (Wilson et al. 1992, 1993, Dobson & Wilson 1992, Sarkar & Wilson 1993, Burns et al. 1993) who investigated the effects of He–Ne laser on bacterial suspensions. TBO with an absorption maxima (632.2 nm) closest to the wavelength of the radiation emitted by the He–Ne laser (632.8 nm) has been shown to be an effective photosensitizer for He–Ne laser mediated killing (Wilson et al. 1992, Dobson & Wilson 1992). It was noted that TBO gave a bluish tinge to teeth after treatment but the discolouration could be easily removed with EDTA irrigation. The results of the present study have shown that the combined effect of TBO and He–Ne laser was bactericidal to the S. intermedius biofilm but not effective enough to achieve sterility even with a combination of high TBO concentration (100 gml–1) and laser dose (600 s, 428.6 J cm–2). Dobson & Wilson (1992) reported successful kills of periodonto-pathogenic species biofilms (Streptococcus sanguis, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum and Porphyromonas gingivalis) using low concentrations of TBO (50 gmL–1) and low doses of He–Ne laser light (30 s, 16.5 J cm–2). The difference in results could be explained by variations in the sensitivities of different bacterial species or indeed different properties of biofilms grown on agar plates compared to those on root canal walls. Low concentrations of TBO (<50 gmL–1) had no bactericidal effect on S. intermedius biofilms, but when they were incubated with 100 gmL–1 TBO for 30 s, a 3 log10 reduction in viable bacteria was observed. Previous reports have shown that some planktonically grown periodontal pathogen suspensions were sensitive to 25 and 50 gmL–1 of TBO (Wilson et al. 1993, Sarkar & Wilson 1993, Burns et al. 1993) but Actinomyces viscosus and Streptococcus mutans were significantly more resistant (Burns et al. 1993). Lethal photosensitization using a low power laser in an infected tooth model in the present study produced similar results to that of irradiation with higher power lasers (Nd:YAG, Nd:YAP, diode, CO2, Er:YAG) which have also achieved various degrees of bacterial killing but not to the extent of achieving sterility (Hardee et al. 1994, Fegan & Steiman 1995, Goodis et al. 1995, Gutknecht et al. 1996, Blum et al. 1997, Moritz et al. 1997, Ramsköld et al. 1997, Le Goff et al. 1999, Mehl et al. 1999). The inconsistent trends evident in bacterial killing with increasing TBO concentration and laser light dose could be attributed to the variation in root canal morphology. The anatomy could impact on this mode of treatment at two levels. First, the manner of interaction of the bacteria with individual root canal systems could result in variable biofilm properties. Secondly, the anticipated circumvention of anatomical complexities by light transmission appears to be confounded; whether this is a function of actual hindrance of light transmission, lack of penetration of TBO or lack of generation and dispersal of free radicals is unclear. Lethal photosensitization could not compete with NaOCl (3% v/v) in achieving consistent 100% bacterial kills in this study. This is however, different from treatment of polymicrobial infections, where NaOCl may not be so effective (Byström & Sundqvist 1981, 1983). The results of this study reinforce the use of NaOCl irrigation in root canal treatment because of its bactericidal effect, as well as its ability to denature bacterial toxins (Safavi & Nichols 1994) and dissolve organic tissues (Baumgartner & Cuenin 1992).
A major advantage of lethal photosensitization in treating root canal infections is the absence of thermal side-effects in the tissues surrounding the roots, as associated with the use of high power lasers. The anticipated benefits of ‘access’ of laser light and photosensitizer were more limited than hypothesized. Further studies are necessary to determine the penetration of photosensitizers into the complex root canal anatomy and the range of activity of ‘free radicals’. Moreover, refinement of the laser delivery system by introduction of the laser beam into the root canal and/or increased energy delivery may be needed to achieve a better antimicrobial effect. Overall the lethal photosensitization of single-species biofilms grown in a tooth model was interestingly effective considering delivery of the light dose at the access cavity, but ultimately not comparable to the conventional use of 3% NaOCl. The method may have potential, either as a modification of the current application or used as an adjunct to conventional approaches.


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