This micro-CT study investigated the largest original diameters of Vertucci type IV mandibular molar mesial root canals at 1-, 2-, 3-, and 4-mm levels short of the apical foramen. The diameters were then matched to currently available instrument sizes recommended for apical preparation. The study found that the original canal diameters were usually larger than recommended instrument sizes, making it impossible to fully shape most canals without risk of deviation, perforation, or root weakening. Approaches are needed to better determine optimal apical preparation size and address the problem of unprepared canal walls.

1. “Matching the Dimensions of Currently Available
Instruments with the Apical Diameters of
Mandibular Molar Mesial Root Canals Obtained
by Micro–computed Tomography”
Bernardo M. Almeida; PhD, Jose Claudio Provenzano; PhD, Marı´lia F. Marceliano-
Alves; PhD, Isabela N. R^oc¸as; PhD, and Jose F. Siqueira; Jr PhD
JOE, JUNE’19

2. INTRODUCTION
 Chemomechanical preparation is conceivably the most
important phase of endodontic treatment; however, it still
poses a challenge for clinicians because no technique or
instrument has been shown to promote complete cleaning
and disinfection of the root canal system.
 Micro–computed tomographic (micro-CT) studies:
approximately 10%–50% of unprepared wall areas
- increase in oval/flattened canals
- may harbor bacteria and tissue remnants
- may jeopardize the outcome of endodontic treatment
in teeth with apical periodontitis
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3.  Apical enlargement significantly influences the cleaning and
disinfection of the canal
 Perez et al --- showed that every increase in the size of the
instrument used in apical preparation significantly increased
the amount of prepared wall surfaces
- Final instrument used in preparation is smaller than
the largest diameter of the original canal.
 Over-enlargement: excessive and unnecessary removal of
tooth structure --- fracture of tooth
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4.  Clinically: difficult to determine the optimal diameter of apical
preparation.
 Micro-CT imaging: 3-dimensional high-resolution evaluation
of the root canal anatomy and reliable specimen selection
- accurate determination of the canal diameters short
of the apical foramen, instead of the anatomic root apex
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 “3 sizes above the first file size to bind apically”
 Based on morphological studies

5.  Most manufacturers have provided a minimum set of
instrument sizes and tapers for root canal preparation
 the size and taper of the instrument used for apical
preparation be based on the anatomic measurements of the
canal
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“This micro-CT study investigated the largest original
anatomic diameters of Vertucci type IV mandibular molar
mesial canals at 1-, 2-, 3-, and 4- mm levels that are short of
the apical foramen and then matched them to the
dimensions of instruments currently available and
recommended for apical preparation”

6. SPECIMEN SELECTION:
108 mandibular molars were selected from a bank of 450 molars
extracted for reasons unrelated to this study.
Materials & Methods
INCLUSION CRITERIA:
 complete root formation
 absence of fracture lines or cracks over the long axis of the mesial root
 the absence of apical root resorption
 the presence of 2 independent mesial canals throughout their paths
(Vertucci type IV configuration) as determined by micro-CT evaluation
 Third molars were not included.
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7. MICRO-CT SCANNING AND ANALYSIS:
Teeth: scanned in a micro-CT device (SkyScan 1174 v2; Bruker microCT, Kontich, Belgium)
operating at 50 kV and 800 mA.
3- dimensional images: NRecon v.1.6.9 software (Bruker microCT)
2-dimensional object analysis: CTAn program v.1.14.4 (Bruker microCT)
- for analysis and determination of the largest diameter of the apical foramen and
root canal diameters at 1, 2, 3, and 4 mm short of the apical foramen.
Overall, 1080 measurements were obtained
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8. ● Data were represented as the percentage of cases that each instrument would exhibit a
diameter that is larger than the canal diameter at each 1-mm level individually or over
the entire 4-mm apical segment. In addition, based on the mean and median data of the
diameters and tapers of the mesiobuccal and mesiolingual canals, the ideal dimensions
of an instrument with continuous or variable taper to be used for apical preparation
were calculated.
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Data analysis

9. 9
Results

10. 10

11. 11

12. Discussion
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13. 13
➜ Tronstad L et al; 1977: 0.15 to 2.2 mmat 1mm short of
the anatomic apex
○ light microscopy to evaluate horizontal sections
of mesial canals with different configurations and
number of canals
➜ Measurements were obtained having the apical
foramen as the reference and not the root apex
because modern preparation techniques set the
working length based on the apical foramen as
detected by electronic apex locators.

14. 14
➜ Isthmuses between the 2 canals in the apical portion:
increase in anatomic measurements, which would
introduce biases in instrument size determination.
➜ Mesiobuccal canal: 0.37 mm (range, 0.10–0.75 mm)
➜ Mesiolingual canal: 0.38 mm (range, 0.21–0.77 mm)
○ WU MK et al; 2000:
■ Mesiobuccal canal: 0.4 mm (range, 0.2–0.52
mm)
■ Mesiolingual canal: 0.38 mm (range, 0.32–
0.67 mm)

15. 15
➜ 40/.06 and 45/.02: best results in all levels evaluated
➜ High occurrence of unprepared walls in micro-CT
studies: apical canal diameters range considerably
not generally compatible with the dimensions of
currently available instruments
➜ continuous or reciprocating rotation: carve round
preparations & leave untouched recesses in irregular
noncircular canals
○ lack of methods to accurately determine the
initial canal diameters in clinical practice

16. 16
limitation in shaping inevitably affects the removal of
bacteria and tissue debris
➜ Important to develop strategies:
○ Modified instrument designs
○ Alternative instrument motion
○ Relying on the chemical effects of irrigation and
intracanal medication.

17. 17
➜ 40/.08: hypothetically ideal for preparing the
mesiobuccal canals of mandibular molars
○ increase the number of prepared walls
○ improve disinfection and cleaning
○ greater risks of accidents such as ledges,
perforations, and transportation and an increase
in the likelihood of root fractures

18. ● Original anatomic diameters of the apical region of mandibular molar
mesial root canals are usually larger than the instruments commonly
recommended for preparation of these canals
● Impossible to completely instrument most of the mesial canals evaluated in
this study without deviating, perforating, or weakening the root.
● Approaches to determine the optimal apical size of preparation and
overcome the problem of unprepared walls should be encouraged
18
Conclusion

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22. Thank You!
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