Performing of CBCT: patient placement
The ray technician places the patient sitting in the i-CAT unit with the head positioned between the beam and the receiver. Adjust the height of the patient until the chin lies on the chin rest, remaining in an upright posture, and also adjust the headband around the forehead. The correct position is marked by laser lines projected onto the patient's head: a horizontal line coinciding with the occlusal plane, a vertical line 3.5 cm in front of the condyle, and another vertical line cutting across the sagittal plane of the patient's head. Perform a preview and scan of the patient's head. In adult patients use a radiation dose of 120 Kv and 5 mA, a radiation time of 14.7 seconds, a focus-plate distance of 70 cm, a resolution of 0.25 or 0.3 voxels and a field of view from 70 to 110 cm. Once the scanner has been completed, reconstruct digitally.
Choice and evaluation of the image
Analyze images with the i-CATVision program in the MPR Screen format, and simultaneously perform an analysis of the axial, sagittal and coronal anatomical planes. Arrange all cursors with a cut-off amplitude of 0.25 mm.
Perform linear and angular measurements of NC, as well as buccal bone plate (BBP) and palatal bone plate (PBP) on the three anatomical planes. In addition, perform a morphological analysis on the three anatomical planes of NC.
Image evaluation: NC and bone plates measurements
Make NC, the BBP and PBP measurements at three locations along the NC that we define as: level 1, level 2 and level 3. Do this simultaneously for all three anatomical planes (axial, sagittal and coronal) as follows (Figure 1).
i. Level 1
To find level 1, go to axial slice and find the NC image. To standardize our analysis, we must locate the axial slice when the incisive foramen of NC is completely closed (Figure 2 and 3). For this, perform a dynamic vision in axial slice, i.e., go to the most coronal zone of NC, and visualize the sequence of radiographies from the oral cavity to the nasal cavity, to visualize the closed NC at incisive foramen or level 1. We recommend performing measurements when level 1 is located in the three anatomic planes to optimize working time, as you move the cursor in the axial plane, the cursors of the sagittal and coronal planes are taken automatically to their respective level 1's(Figure 3).
In axial slice, take the following measurements. The diameters of NC are: buccal-palatal diameter (bpD1) and transversal diameter (tD1) of NC. The bpD1 corresponds to maximum diameter between buccal and palatal bone cortical of NC; the tD1 is the maximum diameter perpendicular to bpD1 (Figure 4). The BBP widths are the distances from BBP buccal wall to NC at three points of NC: left (LW1), central (CW1) and right (RW1). LW1 corresponds to the width that is established between the vestibular cortical of NC left border and the BBP external plate that is anterior to NC. CW1 corresponds to the width that is established between the anterior nasal spine and the most anterior and central point of the NC. RW1 corresponds to the width that is established between vestibular cortical of NC right border and the BBP external plate that is anterior to NC (Figure 5).
In coronal slice, take the following measurement on the horizontal line: NC diameter at level 1 (CD1) (Figure 6).
In sagittal slice, take the following measurements on the horizontal line: BBP width at level 1 (BW1), NC sagittal diameter at level 1(SD1), and PBP width at level 1 (PW1). In addition, take the following measurements from the horizontal line to the inferior edges of BBP and PBP: BBP length at level 1(BL1), and PBP length at level 1 (PL1) (Figure 7).
Figure 8 shows the simultaneous measurements made for the three anatomical planes.
ii. Level 2
To locate the level 2, you must first measure the length of NC (NCL), which corresponds to the distance between the incisive foramen and foramina of Stenson in the sagittal slice (Figure 9).
To find level 2, place the red horizontal line at the middle point NCL in the sagittal plane. (Figure 9).
In axial slice, take the following measurements: buccal-palatal diameter (bpD2) and transversal diameter (tD2) of NC. The bpD2 corresponds to maximum diameter between buccal and palatal bone cortical of NC; the tD2 is the maximum diameter perpendicular to bpD2 (Figure 10). BBP widths are the distances from BBP buccal wall of NC at three points of NC: left (LW2), central (CW2) and right (RW2) (Figure 11).
LW2 corresponds to the width that is established between the vestibular cortical of NC left border and the BBP external plate that is anterior to NC. CW2 corresponds to the width that is established between the anterior nasal spine and the most anterior and central point of the NC. RW2 corresponds to the width that is established between vestibular cortical of NC right border and the BBP external plate that is anterior to NC (Figure 11).
In coronal slice, take the following measurement on the horizontal line: NC diameter at level 2 (CD2) (Figure 12).
In sagittal slice, take the following measurements on the horizontal line: BBP width at level 2 (BW2), NC sagittal diameter at level 2 (SD2), and PBP width at level 2 (PW2). In addition, take the following measurements from the horizontal line to the inferior edges of BBP and PBP: BBP length at level 2 (BL2), and PBP length at level 2 (PL2) (Figure 13).
Figure 14 shows the simultaneous measurements made for the three anatomical planes.
iii. Level 3
To find level 3, move the red horizontal line to the foramina of Stenson on sagittal plane. Perform measurements for the coronal and sagittal planes, excluding the axial plane because of poor image quality at the level of foramina of Stenson.
In coronal slice, take the following measurement on the horizontal line: NC diameter at level 3 (CD3) (Figure 15).
In sagittal slice, take the following measurements on the horizontal line: PBP width at level 3 (PW3), this is the width from the most posterior point of the transverse palatine suture (Figure16) to the palatal wall of NC, NC sagittal diameter at level 3 (SD3), and PBP width at level 3 (PW3). In addition, take the following measurements from the horizontal line to the inferior edges of BBP and PBP: BBP length at level 3 (BL3). PBP length at level 3 (PL3), and, the total BBP length (tBL) is also calculated by joining midpoints of coronal and apical BBP width (Figure 17).
Figure 18 shows the simultaneous measurements made for the coronal and sagittal planes. We can observe the poor image quality of axial plane at foramina of Stenson level.
iv. Nasopalatine angle
To obtain the nasopalatine angle, draw the LNC and the tangential line to the nasal floor. After this, simply measure the angle formed between these lines (Figure 19).
v. Morfological classification of NC
Classify NC morphology in each anatomic plane, following the classification by Mardinger et al.3 and Song et al.18 for the sagittal plane, the classification by Bornstein et al.5 for the coronal plane and the classification established by our research team for the axial plane.7
In order to establish NC morphology, evaluate all the radiological slices pertaining to NC. To do so in the sagittal plane, evaluate all the sagittal NC images; in the coronal plane evalute images from anterior to posterior; and for the axial plane evaluate from the incisive foramen to the foramina of Stenson.
Classify NC morphology in sagittal slice according to the protocol established by Mardinger et al.,3 who typified the NC into the following four forms:
Funnel: NCs with a narrower apical anatomy that widens coronally (Figure 20a and 21a).
Cylindrical: NCs with a stable morphology, ie, the NC presents both parallel vestibular and palatal cortices from the incisor foramen to the foramina of Stenson (Figure 20b and 21b).
Hourglass: NCs with both a wide incisor foramen and a wide foramina of Stenson, and a narrow area in the medial zone (Figure 20c and 21c).
Half-moon (or banana): NCs with a wider area in the medial zone (Figure 20d and 21d).
To establish the direction and course of the NC in sagittal slice, follow the protocol by Song et al.18 The direction of the NC is considered vertical when the canal runs perpendicular from the nasal floor to the oral cavity; and it is considered oblique when the trajectory is not perpendicular. The NC course is considered straight for canals that communicate the foramina of Stenson and the incisive foramen without linear breaks; and, otherwise is considered to be curved. We distinguish four categories (Figure 22 and 23):
Vertical-straight (Ia).
Vertical-curved (Ib).
Oblique-straight (IIa).
Oblique-curved (IIb).
Evaluate the NC coronal morphology by checking all tomographic slices containing the NC from anterior to posterior. Then classify into three main categories according to the classification by Bornstein et al.5 (Figure 24 and 25):
Single. All slices show a single cylindrical canal (Figure 24a and 25a).
Separate parallels. All slices show two seperate parallel canals (Figure 24b and 25b).
Y-type (Ya, Yb, Yc). All slices show a Y-shaped canal, i.e., two branches that descend from the foramina of Stenson that anastomose into one incisive foramen. There are three subcategories:
i. Ya. Two definite branches descending from the foramina of Stenson (Figure 24c and 25c).
ii. Yb. One of the two branches descending from the foramina of Stenson is bifurcated (Figure 24d and 25d).
iii. Yc. The two branches descending from the Stenson's foramina are bifurcated (Figure 24e and 25e).
If you observe more than one NC, as in Figure 26, use our team's7 modification of the classification by Bornstein et al.5 Figure 27 presents sample combinations of NC coronal morphology.
In the axial plane, classify NC by number of incisive foramina in level 1, and number of foramina of Stenson in level 3, as established by our research team.4 Make a designation with two figures ("X-X"), where the first refers to the number of incisive foramina, and the second refers to the number of foramina of Stenson (Figure 28).
Periodontal condition of the remaining teeth
The periodontal condition of remaining teeth is important to keep in mind because this can modify the biological behavior of the alveolar bone.
To evaluate periodontal bone loss on sagittal plane, measure the distance from the cemento-enamel junction to BBP in buccal surface and from the cemento-enamel junction to PBP in palate surface of teeth 11 and 21 (Figure 10). Periodontal condition is defined as the mean value of these measurements for both teeth 11 and 21. Subjects are then classified into three groups. The first group is normal periodontal condition ≤3 mm, (based on Faria Vasconcelos et al.9). The other groups reflect different levels of periodontitis: moderate periodontitis (>3-≤6 mm) and severe periodontitis (>6 mm) (Table 1).