Disinfection of intracanal dentin by ND:YAG, HO:YAG and ER:YAG laser irradiation: an in vitro model / "Desinfecção da Dentina Radicular pela Irradiação dos Lasers de Nd: YAG e Er: YAG: um Modelo "in vitro""

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

SUMMARY Disinfection of intracanal dentin by Nd:YAG, Ho:YAG and Er:YAG laser irradiation: an in vitro model A possible cause for root canal failure is the persistence of bacteria that have colonized dentinal tubules. To reduce this risk and, if possible, to also shorten the time-consuming endodontic therapy, new equipment and materials are constantly being introduced. The aim of the present investigation was to study the effect of disinfection of dentinal tubules by intracanal laser irradiation using an in vitro model. The groups irradiated by various lasers were compared with calcium hydroxide, a material frequently used as intracanal medication between appointments. Freshly extracted, intact bovine incisors were used. The root cementum was removed and the teeth cut to produce 180 standardized specimens. For bacterial colonization, specimens were incubated at 37 o C in test tubes with Tryptic Soy Broth and Enterococcus faecalis, which carried a plasmid that allowed the growth in a selective medium containing chloramphenicol. The specimens were divided in five treatment groups and three control groups. For irradiation, pulsed delivered Ho:YAG laser at 2.1 µm, Nd:YAG laser (1.06 µm), and Er:YAG and Er:YAG laser (2.94µm) with and without air/water coolant, were used. Lasers groups received three different laser settings for treatment: output energy below the physical modification threshold (½ of PMT) for 60 sec, at the PMT for 60 sec and above the PMT (120 sec). Group 5 received a seven-day treatment with calcium hydroxide. As controls, three specimens for each treatment group received sterile water instead of bacteria (negative control), three received iodine potassium-iodide after bacterial exposure (negative control), and three did not receive treatment after bacterial exposure (positive control). The number of bacteria was estimated by counting CFU. In order to evaluate whether the lasers used in the experiment could be absorbed by the bacteria E. faecalis, an UV, VIS and NIR spectra were obtained using a spectrophotometer. Statistical analysis showed the bacterial reduction as follow: Ho:YAG laser >hidróxido de cálcio>Nd:YAG laser >Er:YAG laser with air/water coolant >Er:YAG laser without air/water coolant. There was a significantly higher bacterial reduction in the group irradiated by the Ho:YAG at the PMT (50mJ, 10 Hz, 66 J/cm 2 for 120 sec), followed by Ho:YAG irradiated at 50mJ, 10 Hz, 33 J/cm 2 for 60 sec, and the group that received calcium hydroxide. The latter two groups were not significantly different. The UV and VIS absorbance spectrum presented two absorbance peaks at 361nm and 337nm (UV). The NIR spectrum revealed a very low absorbance by the E. faecalis.

ASSUNTO(S)

desinfecção laser dentina radicular dentinal tubules endodontia terapêutica odontológica dental therapy túbulos dentinários intracanal dentin disinfection endodontics

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