ObservationOkajimas of maxillary Folia Anat. incisive Jpn., canal92(2): in 37–42, childhood Aug, 201537 (Original) Observation of maxillary incisive canal using dry skulls between Hellman’s dental age IA and IIIC By Munetaka NAITOH1, Tomoko ARIKAWA2, Wataru NISHIYAMA1, Kenichi GOTOH3, Hiroyuki NAWA2, Osamu FUKUTA2, Eiichiro ARIJI1 1Department of Oral and Maxillofacial Radiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan 2Department of Pediatric Dentistry, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan 3Division of Radiology, Dental Hospital, Aichi-Gakuin University, Nagoya, Japan –Received for Publication, June 29, 2015– Key Words: Maxillary incisive canal, Cone-beam computed tomography, Dental age, Hellman’s classification Summary: The maxillary incisive canals were observed in childhood from infancy to school-aged children to clarify their development. Cone-beam computed tomography was performed to investigate 44 dry child skulls. Two-dimensional images of various planes in the maxillary incisive canal were reconstructed on a computer using 3-dimensional visualization and measurement software. Then, antero-posterior angulation, and antero-posterior and lateral axes of the maxillary incisive canal were measured at the inferior and middle levels. The mean difference of angulation between the inferior and middle levels was 2.3 degrees in IIC, and 11.1 degrees in IIIC. The mean ratio of the lateral axis to antero-posterior axis at the middle level was 2.54 in IIC, and 1.93 in IIIC. In conclusion, it was antero-posteriorly straight from IA to IIC, and, after IIIA, it curved at the middle level. The cross-sectional shape in IIC was depressed with a larger lateral axis. Introduction Materials and Methods The location and configuration of the maxillary inci- Objectives sive canal are important in surgical procedures involving Forty-four dry child skulls were used in the investi- the anterior maxillary region, such as in dental implant gation. On classifying the dental age of each skull using treatment, extraction of a supernumerary mesiodens, and Hellman’s classification,10) one skull belonged to IA, 6 to cysteotomy of radicular and nasopalatine cysts.1–3) IC, 8 to IIA, 7 to IIC, 13 to IIIA, 3 to IIIB, and 6 to IIIC. The diameter and angulation to the palatal plane of the maxillary incisive canal in adults were reported in Cone-beam CT previous studies using spiral and cone-beam computed Cone-beam CT employing Alphard VEGA (Asahi tomography (CT).4–6) However, development of the Roentgen Ind., Kyoto, Japan) was performed to investi- maxillary incisive canal in childhood was not evaluated. gate 44 dry child skulls. The exposure volume was set at The spatial resolution of cone-beam CT is high in 102 mm in diameter and 60 mm in height, and the voxel comparison with multislice CT, and fine anatomical struc- size was 0.2 x 0.2 x 0.2 mm. The DICOM files of axial tures can be clearly observed using it.7–9) images were saved to a portable hard disk (HD). In the present investigation, maxillary incisive canals were observed using cone-beam CT and dry skulls in Assessment of maxillary incisive canal childhood from infancy to school-aged children to clarify Two-dimensional (2-D) cone-beam CT images of their development. various planes in the maxillary incisive canal were recon- structed on a computer (Mac Book Pro Retina, Apple Computer Inc., Cupertino, CA, USA) using 3-dimen- sional (3-D) visualization and measurement software Corresponding author: Munetaka Naitoh, Department of Oral and Maxillofacial Radiology, School of Dentistry, Aichi-Gakuin University, 2-11, Suemori-dori, Chikusa-ku, Nagoya 464-8651, Japan. E-mail: 38 M. Naitoh et al. Fig. 2. Measurements of angulation of the maxillary incisive canal. a: Angulation at the inferior level, b: Angulation at the middle level. Fig. 3. Measurements of anterior-posterior and lateral axes of the max- illary incisive canal. a: Antero-posterior axis, b: Lateral axis Fig. 1. 2-D cone-beam CT images. A. Sagittal image. B. Axial image paralleling the palatal plane at the inferior level. C. Axial image between the most inferior point of the posterior edge of paralleling the palatal plane at the middle level. the maxillary incisive canal and nasal floor. The differ- ence of angulation between the inferior and middle levels was calculated. (OsiriX, Imaging Software; The OsiriX Foundation, Axial images paralleling the palatal plane were recon- Geneva, Switzerland11)) (Fig. 1). structed and antero-posterior (a) and lateral (b) axes of Then, the antero-posterior angulation of the maxillary the maxillary incisive canal were measured supero-inferi- incisive canal to the palatal plane based on anterior and orly at the two levels (Fig. 3). The ratio of the lateral axis posterior nasal spines was measured supero-inferiorly to antero-posterior axis (ratio = lateral axis/ antero-poste- at two levels: inferior and middle levels, using sagittal rior axis) was calculated. The maxillary incisive canal of images (Fig. 2). The inferior level was set at the most one dry skull in IIIA could not be detected at the middle inferior point of the posterior edge of the maxillary inci- level. sive canal. The middle level was set at the middle point One of the authors (M.N.) with experience of 32 Observation of maxillary incisive canal in childhood 39 Fig. 4. The angulation of the maxillary incisive canal years in oral and maxillofacial radiology performed each Table 1. The differences of angulation between the inferior and middle measurement five times and then repeated them in the levels. same way after approximately one month. The measure- Hellman’s dental age Range Mean SD Median ments were averaged. IA 0.7 0.7 IC 0.2 – 18.4 7.2 7.4 5.3 Statistical analysis IIA –5.0 – 12.3 4.1 6.6 2.1 The differences among stages of Hellman’s dental IIC –4.6 – 5.7 2.3 3.6 3.6 age with different angulations between the inferior and IIIA 0.0 – 19.2 9.5 5.5 9.8 middle levels, and the ratio of the lateral axis to ante- IIIB 7.1 – 10.8 9.0 1.9 9.2 IIIC 6.1 – 21.4 11.1 6.1 8.7 ro-posterior axis of the maxillary incisive canal were evaluated using the Mann-Whitney U test. Differences Unit: Degrees were considered significant with P-values of less than Significant difference: Between IIC and IIIA, between IIC and IIIB, between IIC and IIIC 0.05. Results IIC and IIIC. Antero-posterior angulation of the maxillary incisive The antero-posterior and lateral axes, and ratio of axes canal of the maxillary incisive canal The mean and SD of angulation based on Hellman’s The mean and SD of axes based on Hellman’s dental dental age are shown in Fig. 4. The mean at the inferior age are shown in Figs. 5 and 6. level was 83.0 degrees in IC, and 75.3 degrees in IIIC. The mean antero-posterior axis at the inferior level The values decreased with progression of the stage of was 1.8 mm in IC, and 2.2 mm in IIIC. The values Hellman’s dental age. The mean at the middle level was slightly increased with progression of the stage of Hell- 75.8 degrees in IC, and 64.2 degrees in IIIC. The values man’s dental age. The mean lateral axis at the infe- decreased with stage progression of Hellman’s dental age. rior level was 2.6 mm in IIC. The value was higher in The differences of angulation between the inferior and comparison with that of IIIC. The ratio of the lateral axis middle levels are shown in Table 1. The mean difference to antero-posterior axis at the inferior level is shown in was 2.3 degrees in IIC, and 11.1 degrees in IIIC. Signifi- Table 2. The range of ratio of the lateral axis to ante- cant differences with different of angulations were noted ro-posterior was from 0.82 to 2.38 in IIC, and the mean between IIC and IIIA, between IIC and IIIB, and between was 1.48. The value was higher in comparison with those 40 M. Naitoh et al. Fig. 5. The antero-posterior and lateral axes of the maxillary incisive canal at the inferior level Fig. 6. The antero-posterior and lateral axes of the maxillary incisive canal at the middle level of the other stages. The differences regarding the ratio of dental age. The mean lateral axis at the middle level was the lateral axis to antero-posterior axis were not signifi- 2.5 mm in IIC. The value was higher in comparison with cant among Hellman’s dental age. that of IIIC. The ratio of the lateral axis to antero-pos- The mean antero-posterior axis at the middle level terior axis at the middle level is shown in Table 3. The was 1.2 mm in IIA, and 1.3 mm in IIIC. The values were range of the ratio was from 1.00 to 5.86 in IIC, and the similar among IIA, IIC, IIIA, and IIIC of Hellman’s mean was 2.54. The value was higher in comparison Observation of maxillary incisive canal in childhood 41 Table 2. The ratio of the lateral axis to antero-posterior axis at the in- Table 3. The ratio of the lateral axis to antero-posterior axis at the mid- ferior level. dle level. Hellman’s dental age Range Mean SD Median Hellman’s dental age Range Mean SD Median IA 0.78 0.78 IA 1.88 1.88 IC 0.75 – 1.33 1.14 0.48 0.96 IC 0.65 – 5.00 1.83 1.62 1.51 IIA 0.63 – 2.15 1.22 0.63 0.94 IIA 0.61 – 3.80 1.80 1.18 1.28 IIC 0.82 – 2.38 1.48 0.59 1.35 IIC 1.00 – 5.86 2.54 1.83 1.71 IIIA 0.36 – 2.71 1.17 0.61 1.11 IIIA 0.67 – 2.60 1.48 0.66 1.52 IIIB 0.82 – 1.09 1.00 0.15 1.08 IIIB 1.00 – 1.86 1.54 0.47 1.77 IIIC 0.59 – 1.81 1.18 0.46 1.14 IIIC 0.92 – 5.20 1.93 1.66 1.38 Significant difference: None Significant difference: None with those of the other stages (Fig.