Ultrasonic root-end preparation part 1: SEM analysis in humans

By Gutmann JL, Saunders WP, Nguyen L, Guo IY, Saunders EM.

Date: 10/1994
Journal: JOE

Purpose: to determine the degree of superficial debris and smear layer present on the dentinal walls of root-end cavity preparations, using 3 techniques: cavity preparation 1- with a bur only, 2-with a bur followed by a 10:3 citric acid: Fe3Cl3 rinse, and 3- with an ultrasonic retrotip

N= 60 single rooted teeth


• The teeth were divided into 3 groups of 20 teeth each that were prepared as follows;

Group I size 010 round bur was used to prepare an apical cavity 2-3 mm down the long axis of the root

Group II same as group 1 followed by a 60-s rinse with a solution of 10:3 (10% citric acid, 3% Fe2a3)

Group III an ultrasonic retrotip was used to prepare a 2-3 mm deep apical cavity under water spray

•Roots were grooved longitudinally, split and prepared for SEM analysis and examined by 2 calibrated examiners.

•Statistical analysis was done to determine whether there were any significant differences in the degree of superficial debris or smear layer with each technique at different cavity levels.

Most highlighted Results: 

•Greater amounts of superficial debris were present with both bur preparation techniques compared with ultrasonic preparation. However, there were no differences between groups I and II

Regarding amount of smear layer: significant differences were found among all 3 groups, with group II showing the least amount of smear layer and the greatest amount of clean dentine and patent tubules followed by group III

•No technique effectively removed the smear layer in the coronal one-third of the preparation

💡Clinical significance: The least amount of superficial debris was observed in the ultrasonic group; the least amount of smear layer was observed in the bur preparation rinsed with a solution of 10% citric acid and 3% ferric chloride. These findings may help to achieve thorough debridement of the root canal system which is  believed to be the key to long-term successful endodontic treatment.