AN IN-VITRO STUDY OF SMEAR LAYER REMOVAL AND MICROBIAL LEAKAGE ALONG ROOT-CANAL FILLINGS

The objective of this study was to determine the effect of removal of the smear layer on canal obturation as measured by penetration of bact eria hem a coronal direction, Fifty-four extracted human teeth were de coronated and instrumented in a uniform manner, following instrumentat ion the root canals of 20 teeth were rinsed with 17% EDTA and 5.25% Na OCl to remove the smear layer before obturation, A second group of 20 teeth were flushed with NaOCl alone, The teeth of both groups were obt urated with Thermafil(TM) plastic carriers and Roth's sealer, The root canals of another 10 teeth, five rinsed with EDTA and five without, w ere obturated with Thermafil(TM) without sealer, Two teeth serving as positive controls were instrumented but not obturated, while another s et of two were sealed coronally and apically to serve as negative cont rols, The root surface of each tooth was sealed with nail varnish, A s mall chamber was thoroughly sealed around the coronal aspect of each t ooth so that bacteria placed therein could move only through the obtur ated canal space, Each tooth was placed in a test tube containing ster ile trypticase soy broth (TSB), An inoculum of Proteus vulgaris in TSB was placed in each coronal chamber at five day intervals and daily ob servations were made for bacterial growth in the apical reservoir for 21 days, Both positive control teeth showed bacterial penetration afte r 24 h, Neither of the two negative control teeth demonstrated penetra tion for the duration of the study, The frequency of bacterial penetra tion through teeth obturated with intact smear layer (70%) was signifi cantly greater than that of teeth from which the smear layer had been removed (30%) P<0.05, All but one tooth obturated without sealer exhib ited bacterial penetration, irrespective of the presence or absence of smear layer. Removal of the smear layer enhanced sealability as evide nced by increased resistance to bacterial. penetration.