Smear layer production by 3 rotary reamers with different cutting blade designs in straight root canals: a scanning electron microscopic study.
OBJECTIVE
The design of the cutting blade of rotary instruments may affect the outcome of root canal instrumentation in terms of cleanliness. The aim of this scanning electron microscopic study was to compare the quality and amount of smear layer generated in the apical third of straight root canals by 2 rotary nickel-titanium reamers and 1 rotary steel reamer with different cutting blade designs.


METHODS
Seventy intact, single-rooted human mandibular premolars with straight, fully developed roots were selected for this study. Before instrumentation, the cervical portion of all teeth was removed by using a microtome (Isomet), leaving 13-mm-long roots. Automated preparation was performed with ProFile (n = 20) and Hero 642 (n = 20) reamers by using the crown-down technique and with a stainless steel engine reamer (Mani; n = 20) by using a reaming motion. All root canals were instrumented to No. 40. A control group (pulp extirpation with barbed broaches; n = 10) was also included. Irrigation with 3 mL of a 1% sodium hypochlorite (NaOCl) solution was performed after each instrumentation. After the instrumentation, each root was split longitudinally, and a scanning electron microscope was used to examine the selected areas of the canal walls at the apical third from 2 different perspectives. A 4-category scoring system for smear layer was used, and the resulting scores were statistically analyzed.


RESULTS
The least smear layer remained in the Hero 642 group at the selected apical third of straight root canals (P < .05). However, all instruments left a smear layer. The surface texture of the smear layer, in addition to the depth and the frequency of packed materials into the dentinal tubules, varied with instrument type.


CONCLUSIONS
These data revealed that the design of the cutting blade of rotary instruments can affect root canal cleanliness in straight root canals. This information may be useful in the selection of nickel-titanium rotary reamers.
Yonsei University, Department of Endodontics, College of Dentistry, Oral Science Research Center, Seoul, South Korea.
In-Soo
IS
Jeon
Larz S W
LS
Spångberg
Tai-Cheol
TC
Yoon
Reza B
RB
Kazemi
Kee-Yeon
KY
Kum
D003722:Dental Alloys; D003786:Dental Pulp Cavity / Q000648:ultrastructure*; D003804:Dentin / Q000648:ultrastructure; D004867:Equipment Design; D006801:Humans; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D011670:Pulpectomy / Q000295:instrumentation; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation*; D016369:Smear Layer; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013193:Stainless Steel; D013499:Surface Properties; D014025:Titanium; D019227:Tooth Apex
D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite