Imaging Sci Dent.  2016 Sep;46(3):159-165. 10.5624/isd.2016.46.3.159.

Panoramic radiographs underestimate extensions of the anterior loop and mandibular incisive canal

Affiliations
  • 1Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, University of Campinas, São Paulo, Brazil. acarolinerb@hotmail.com
  • 2Department of Stomatology, Public Oral Health and Forensic Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, São Paulo, Brazil.

Abstract

PURPOSE
The purpose of this study was to detect the anterior loop of the mental nerve and the mandibular incisive canal in panoramic radiographs (PAN) and cone-beam computed tomography (CBCT) images, as well as to determine the anterior/mesial extension of these structures in panoramic and cross-sectional reconstructions using PAN and CBCT images.
MATERIALS AND METHODS
Images (both PAN and CBCT) from 90 patients were evaluated by 2 independent observers. Detection of the anterior loop and the incisive canal were compared between PAN and CBCT. The anterior/mesial extension of these structures was compared between PAN and both cross-sectional and panoramic CBCT reconstructions.
RESULTS
In CBCT, the anterior loop and the incisive canal were observed in 7.7% and 24.4% of the hemimandibles, respectively. In PAN, the anterior loop and the incisive canal were detected in 15% and 5.5% of cases, respectively. PAN presented more difficulties in the visualization of structures. The anterior/mesial extensions ranged from 0.0 mm to 19.0 mm on CBCT. PAN underestimated the measurements by approximately 2.0 mm.
CONCLUSION
CBCT appears to be a more reliable imaging modality than PAN for preoperative workups of the anterior mandible. Individual variations in the anterior/mesial extensions of the anterior loop of the mental nerve and the mandibular incisive canal mean that is not prudent to rely on a general safe zone for implant placement or bone surgery in the interforaminal region.

Keyword

Radiography, Panoramic; Cone-Beam Computed Tomography; Mandible; Anatomic Variation

MeSH Terms

Anatomic Variation
Cone-Beam Computed Tomography
Humans
Mandible
Radiography, Panoramic

Figure

  • Fig. 1 A panoramic radiograph shows the anterior loop and incisive canal (right side) and the anterior loop (left side). 1. The lower mandibular cortex as the plane of reference. 2. The line perpendicular to the line passing through the mesial border of the mental foramen. 3. The line perpendicular to the line passing through the most mesial point of the anterior loop of the mental nerve with the mandibular incisive canal. 4. The distance between lines 2 and 3, corresponding to the mesial length of the extent of the anterior loop or incisive canal.

  • Fig. 2 Visualization of the anterior loop and incisive canal (red dotted line) on the panoramic reconstructions. a: The lower mandibular cortex as the plane of reference. b: The line perpendicular to the line passing through the mesial border of the mental foramen. c: The line perpendicular to the line passing through the most mesial point of the anterior loop of the mental nerve and the mandibular incisive canal. d: The distance between lines b and c, corresponding to the mesial length of the extent of the anterior loop or incisive canal.

  • Fig. 3 Cross-sectional images (perpendicular to the occlusal plane) demonstrate the presence of the anterior loop (red arrows) and the incisive canal (green arrows).


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