An in‐vitro study of smear layer removal and microbial leakage along root‐canal fillings

Abstract

The objective of this study was to determine the effect of removal of the smear layer on canal obturation as measured by penetration of bacteria from a coronal direction. Fifty-four extracted human teeth were decoronated and instrumented in a uniform manner. Following instrumentation the root canals of 20 teeth were rinsed with 17% EDTA and 5.25% NaOCl to remove the smear layer before obturation. A second group of 20 teeth were flushed with NaOCl alone. The teeth of both groups were obturated with Thermafil plastic carriers and Roth's sealer. The root canals of another 10 teeth, five rinsed with EDTA and five without, were obturated with Thermafil without sealer. Two teeth serving as positive controls were instrumented but not obturated, while another set of two were sealed coronally and apically to serve as negative controls. The root surface of each tooth was sealed with nail varnish. A small chamber was thoroughly sealed around the coronal aspect of each tooth so that bacteria placed therein could move only through the obturated canal space. Each tooth was placed in a test tube containing sterile trypticase soy broth (TSB). An inoculum of Proteus vulgaris in TSB was placed in each coronal chamber at five day intervals and daily observations were made for bacterial growth in the apical reservoir for 21 days. Both positive control teeth showed bacterial penetration after 24 h. Neither of the two negative control teeth demonstrated penetration for the duration of the study. The frequency of bacterial penetration through teeth obturated with intact smear layer (70%) was-significantly greater than that of teeth from which the smear layer had been removed (30%) P < 0.05. All but one tooth obturated without sealer exhibited bacterial penetration, irrespective of the presence or absence of smear layer. Removal of the smear layer enhanced sealability as evidenced by increased resistance to bacterial penetration.

Microbial leakage of MTA, Portland cement, Sealapex and zinc oxide-eugenol as root-end filling materials

“…One possible mechanism is that smear layer may block bacterial entry into dentinal tubules. Behrend et al (30) found that smear layer removal during canal obturation enhanced sealability, as evidenced by increased resistance to bacterial penetration. In that study, root canals were completely filled and the experimental period lasted 21 days.…”

“…Thus, a perfect microbial control can be obtained without changing the dental structure or damaging the leakage apparatus. The other specimens (30) were not filled with EDTA.…”

In vitro Comparative Study of the Microbial Leakage of One-step, Thermafil and Lateral Condensation Techniques

“…The absence of smear layer could have improved the seal at the sealant-dentinal wall interface, as it has been proved that thermafil give a better seal when the smear layer is removed. 9 Desirable properties of AH26 sealer might have contributed to the low amount of leakage were observed in core-carrier techniques.…”

Influence of different auxiliary agents of biomechanical preparation in the filling of "artificially prepared" lateral canals

“…Many studies have been conducted in an attempt to relate the presence or absence of smear layer and the success of endodontic therapy, such as Economides, et al 9 Behrend, et al 3 Sen, Wesselink and Turkun, 16 Dautel-Morazin, et al 7 Czonstkowsky, et al 6 Aun, et al 1 These authors observed that the presence of smear layer allows a higher rate of infiltration on the obturation, does not constitute a barrier against the penetration of bacteria inside the dentinal tubuli, and its removal by means of chelants provides more opened dentinal tubuli, with a cleaner surface for the achievement of a hermetic root canal obturation.…”