Bacterial Retention in Canal Walls In Vitro: Effect of Smear Layer

By Drake D, Wiemann A, Rivera E, Walton R

Date: 01/1994
Journal: JOE


Purpose:  to develop a clinically relevant model where the effect of the presence or absence of smear layer on bacterial colonization of root canal can be determined

N=   26 extracted maxillary or mandibular canines with single straight canals.


  • The experimental group was subdivided into two groups based on the type of high volume final flush
  • G1 smear layer not removed – received a final flush of 20 ml of sterile water
  • G2 smear layer removed – received a final flush of 10 ml of 17% REDTA followed by 10 ml of 2.5% NaOCI
  • Streptococcus anginosus was the organism used in this investigation
  • SEM examination for presence/absence of smear layer in canal surfaces

Most highlighted Results: 

  • Teeth with smear layer showed lower bacterial counts than where smear layer was removed
  • Over 10—fold higher count of bacteria were recovered from teeth without a smear layer compared to teeth with a smear layer
  • Sonicating the teeth for 5 min effectively removed the smear layer

Clinical significance

Removal of smear layer increased bacterial count. a smear layer of debris could be created after final flush and drying of the canal.

Weakness:  investigating a single type of microorganisms