SEM Analysis of Smear Layer Removal after Manual and Automated Handpiece
Root Canal Preparation
Gilson Blitzkow SYDNEY1,2
Hildeberto Francisco PESCE4,5
Luciano Loureiro de MELO1,2
1Departamento de Endodontia, Faculdade de Odontologia,
Universidade Federal do Paraná, Curitiba, PA, Brasil 2Departamento
de Endodontia, Curso de Odontologia, Tuiutí, Curitiba, PA, Brasil
3Departamento de Endodontia, Faculdade de Odontologia,
Universidade Federal de Goiás, Goiânia, GO, Brasil
4Departamento de Endodontia, Faculdade de Odontologia,
Universidade de São Paulo, São Paulo, SP, Brasil
5Departamento de Endodontia, Faculadade de Odontologia,
Universidade São Francisco, São Paulo, SP, Brasil
Braz Dent J (1996) 7(1): 19-26 ISSN 0103-6440
| Introduction | Material
and Methods | Results | Discussion
| Conclusions | References
Scanning electron microscopy was used to analyze the smear layer removal
after root canal preparation by a manual technique and by an automated
handpiece, the Canal Finder System (CFS). When 1% sodium hypochlorite was
used as the irrigating solution, both manual and CFS techniques showed
root canal walls with a dense smear layer obscuring the dentinal tubules
entrance plus a large amount of debris. Root canal walls of the group of
teeth treated with a chelating agent (EDTA) for 5 min and a final flush,
after the preparation, with 1% sodium hypochlorite as an irrigating solution
showed the cervical, middle and apical thirds extremely smooth and clear.
Key Words: automated handpiece, smear layer, root canal preparation.
Root canal preparation has clear and well-defined goals: to eliminate all
pulp tissue, necrotic debris or microoganisms and to smooth, shape and
enlarge the canal space to conveniently accept a three-dimensional filling
(Schilder, 1974; Paiva and Antoniazzi, 1991). Since smear layer was recognized
some years ago, endodontists have been trying to understand the relationship
between the presence of this layer and the success of root canal treatment.
McComb and Smith (1975), Baker et al. (1975), Mizrachi et al. (1975) and
Moodnick et al. (1976) concluded that the presence of a smear layer was
related to the effectiveness of the endodontic instruments on the canal
walls, the amount of dentinal chips, necrotic tissue and debris. These
authors and others (Goldman et al., 1981; Baumgartner et al., 1984; Aun,
1990; Gavini, 1992) stated that the ability to remove debris depends on
the solution volume rather than the solution type and that different instruments
produce similar values of cleanliness. Goldman et al. (1981) showed that
the smear layer could be removed by a combination of irrigants (REDTA +
sodium hypochlorite in a final flush) according to its nature (either organic
or inorganic components). Czonstkowski et al. (1990) suggested that the
amount of smear layer produced by an automated handpiece preparation is
greater in volume than that produced by manual instrumentation. Mandel
et al. (1990), evaluating the cleansing efficiency of three root canal
preparation techniques, manual, ultrasonic and the Canal Finder System
using 2.5% sodium hypochlorite as irrigant, concluded that there was no
difference between these techniques. The aim of this study was to evaluate
the presence of the smear layer after manual root canal preparation and
by the use of an automated handpiece, the Canal Finder System, using 1%
sodium hypochlorite and EDTA.
Material and Methods
Thirty-five extracted human upper lateral incisors with one canal and a
moderate curvature were selected for this study. Prior to access cavity
preparation all teeth were immersed for at least 72 h in saline. After
access preparatioin, a size 10 K-file (Maillefer) was used to remove all
canal contents, and to determine the working length, estabilished 1-mm
short of the apex. The apexes were covered with nail polish (Risqué,
Niasi) and each root previously covered with vaseline was included in a
resin block. The teeth were then removed from the resin blocks and grooved
on the buccal and lingual surfaces by means of a diamond disk, without
penetration into the root canals. They were then split bucco-lingually
using a wire cutter and reinserted into its original block. The teeth were
then ramdomly divided into seven groups according to root canal preparation
technique and irrigating solution. Root canal surfaces in group 1 were
treated with a chelating agent (EDTA) for five min without instrumentation.
Root canals of the teeth in groups 2, 4 and 6 were instrumented by a manual
technique using the following irrigating solutions: saline (group 2), 1%
sodium hypochlorite (group 4) and 1% sodium hypochlorite plus EDTA for
five min with a final flush of sodium hypochlorite (group 6). The remaining
three groups (3, 5 and 7) were prepared using an automated handpiece, the
Canal Finder System (CFS), subjected to the same irrigating solutions.
In the CFS technique, proposed by Sydney and Melo (1996), root canal preparation
starts and ends manually and the automated handpiece is used as an auxilliary
aid. The root hemi-sections were then left 24 h in a drying chamber with
silica gel and finally mounted on aluminum studs, coated with palladium
gold and analyzed in a scanning electron microscope. Photomicrographs were
obtained from the cervical, middle and apical thirds of each hemi-section
of each root canal. Representative areas were photographed and blindly
evaluated by five investigators regarding the presence of smear layer,
debris and patency of dentinal tubules.
Group 1. Non-instrumented teeth.
Figure 1 shows the appearance of the canal wall treated with a chelating
agent (EDTA) for 5 min without root canal preparation. Dentinal tubules
are clearly seen with oval or circular openings and intracanal dentin.
- Canal wall of a tooth treated with a chelating agent (EDTA) for five
min without root canal preparation (Group 1). 1000X.
Groups 2 and 3. Instrumented teeth; irrigating solution, saline solution.
Figure 2 shows the typical appearance of the specimens of both groups.
A continuous smear layer completely obscures the dentinal tubules and a
large amount of debris is present.
- Groups 2 and 3. Instrumented teeth irrigated with saline. A, Manual technique.
B, CFS. c: cervical third; m: middle third; a: apical third. 1000X.
Groups 4 and 5. Instrumented teeth; irrigating solution, 1% sodium
Cervical, middle and apical thirds of the specimens in both groups (manual
and CFS technique) show the same characteristics. Dentinal tubules are
not visible and the smear layer is present in all lengths. The continuous
smear layer seems to be more dense in group 5 where the automated handpiece
was used (Figure 3).
- Groups 4 and 5. Instrumented teeth irrigated with 1% sodium hypochlorite.
A, Manual technique. B, CFS. c: cervical third; m: middle third; a: apical
Groups 6 and 7. Instrumented teeth; irrigating solution, 1% sodium
hypochlorite and EDTA (5 min).
Figure 4 represents the specimens treated by manual (A) and CFS technique
(B). All the thirds are extremely smooth and clean. The smear layer is
noticeably absent. Little superficial debris is seen in the manual preparation
group. In the CFS technique (group 7) the grooves produced by the use of
the Set-files are free of smear layer and debris. It is important to notice
that smear layer is not present in the dentinal tubules, common when the
manual technique is used.
- Groups 6 and 7. Instrumented teeth irrigated with 1% sodium hypochlorite
and EDTA for 5 min. A, Manual technique. B, CFS. c: cervical third; m:
middle third; a: apical third. 1000X.
Root canal preparation should remove all tissue, necrotic debris, infected
predentin and dentin and finally shape the canal to receive a three-dimensional
root filling (Schilder, 1974; Paiva and Antonizzi, 1991). When dentin is
cut by hand or by an automated handpiece the mineralized matrix is destroyed,
providing considerable debris. This results in a smear layer composed of
both organic and inorganic components (McComb and Smith, 1975; Mizrachi
et al., 1975; Moodnik et al., 1976; Goldman et al., 1981). Our study demonstrated
that both manual and CFS techniques did not influence the results regardless
of the irrigating solution used. These findings are in agreement with other
authors (Goldberg and Spielberg, 1982; Goldberg et al., 1984; Baumgartner
and Mader, 1987; Mandel et al., 1990; Batista et al., 1996). The advantages
of using the CFS are linked to the similarity of the movements provided
by this handpiece as compared to the manual technique added to the high
flexibility and cutting efficiency of the Set-file. However, endodontists
should understand that the CFS does not substitute hand instruments. It
must be used as an auxilliary aid in root canal preparation (Sydney and
Melo, 1996). Our results indicated that, using hand or automated handpiece
instrumentation, the presence of a smear layer is almost the same. The
continuous smear layer seemed to be more dense in Group 5 where root canal
preparation was performed with the CFS than in Group 4 (manual technique),
but not significantly. This was a common observation to all investigators,
probably because of the appearance of two or more different layers superimposed,
defined by Prati et al. (1994) as a tree-bark configuration. The use of
EDTA associated with 1% sodium hypochlorite resulted in cleaner canals,
with complete removal of smear layer. This fact is probaly due to the demineralization
action of EDTA on the inorganic components of this layer (Goldman et al.,
1981; Goldberg and Spielberg, 1982; Goldberg et al., 1984; Baumgartner
and Mader, 1987). It is important to note the findings in group 7 (CFS,
1% sodium hypochlorite and EDTA for 5 min) where the grooves produced by
the Set-files were free of smear layer and debris, including the dentinal
1. Smear layer is present when root canal preparation is performed by manual
and by an automated handpiece (CFS).
2. The continuous smear layer seems to be more dense in the group where
root canal preparation was performed by the automated handpiece (CFS).
3. The use of EDTA for 5 min after complete root canal preparation
and a final flush of 1% sodium hypochlorite showed the absence of the smear
layer in all groups.
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Correspondence: Gilson B. Sydney, Departamento de Endodontia,
Faculdade de Odontologia, Universidade Federal do Paraná, 80060-020
Curitiba, PA, Brasil.
Accepted March 4, 1996
Electronic publication: September, 1996
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