Materials and methods

A retrospective analysis of the CBCT scans of 100 patients who had been referred to a university dental clinic for routine dental evaluation was performed. Patients were selected from the centre database according to the following inclusion criteria: CBCT imaging of the entire maxillary bone, complete physical growth (age ≥20 years), and dentate (from tooth 14 to 24). Patients with developmental malformations of the maxilla, tumours or cysts of the hard palate, severe periodontitis involving the region from tooth 14 to 24, and impacted teeth in the area of study were excluded from further evaluation.

The study was conducted in accordance with the principles outlined in the Declaration of Helsinki (first adopted at the 18th World Medical Association General Assembly, Helsinki, Finland, June 1964). Ethical approval was obtained from the local ethics committee of clinical research. Written informed consent for CBCT analysis was obtained for each case. Patient confidentiality was safeguarded in compliance with the 15/1999 Organic Law. There was no direct or indirect contact with any of the study subjects, and their personal information was appropriately separated from the study database and filed for any possible audits, inspections, or confirmation of information veracity. Accordingly, each patient was assigned a number (consecutive from 1 to 100).

CBCT scans were obtained with an i-CAT device version 17–19 (Imaging Sciences International, Hatfield, PA, USA). The radiological parameters used were 120 kV and 5 mA; the axial slice default distance was 0.300 mm and the voxel size was 0.3 mm ³ . The facial mode with 23-cm field of view (FOV) was used. Primary images were stored as DICOM (Digital Imaging and Communication in Medicine) files.

The metric analysis was performed as described in a previous publication. This methodology was applied to each of the three anatomical regions studied: PPM, ANS, and SN. The patient’s dataset was opened in SIMPLANT Pro 16.0 software (Materialise, Leuven, Belgium). The region of interest was defined in a sagittal slice view, eliminating all unnecessary areas. By default, the slice thickness was 0.3 mm. In order to obtain a thickness per slice of 0.9 mm, two segments from each slice were omitted. In ‘segmentation mode’, a mask was created marking the starting point of the bone. All areas irrelevant to the study were again eliminated. Then, maximum quality was set for the three-dimensional (3D) analysis. Once in ‘planning preparation mode’, a panoramic curve was created to facilitate the readings on the different spatial planes. A ±0.1 mm error deviation was established for all calculations. All measurements were taken from the axial plane in a caudal–cranial direction. Three references were set for each slice (anterior, posterior, and lateral margins). Once this protocol was implemented, a surface was created for each slice.

For the purpose of quantitative volumetric analysis, a 3D image of the delimited zone was constructed. Each of the three volumes of interest was defined as outlined below.

For the PPM, the starting slice was the base of the hard palate. The ending slice was the nasal floor. The anterior margin was the palatine area from tooth 14 to 24. This limit was defined by marking a point in the medial/palatine area of each tooth ( Fig. 1 ). The same procedure was followed for the mesial and distal views wherever an adjacent tooth was not observed (usually in the longest canine roots) ( Fig. 2 ). A 2-mm safety margin was established around the incisive canal. In this case, three peripheral points were marked (one on either side of the paramedials and one middle posterior). Similarly, a 2-mm safety margin was also set wherever the maxillary sinus appeared in the most cranial slices ( Fig. 3 ). Wherever any of these teeth were no longer observed (usually in the most cranial slices), the anterior margin was delimited by the facial buccal plate. The posterior margin was the palatal vault (never beyond 14 and 24) and the lateral margins were projected lines in the distal area of 14 and 24.

Palatine process of the maxilla: axial caudal slice.

Palatine process of the maxilla: axial middle slice.

Palatine process of the maxilla: axial cranial slice.

For ANS, the starting slice was 2 mm above the apices of the upper central incisors (UCI). The ending slice was the nasal floor. The anterior margin was the facial buccal plate, the posterior margin was 2 mm anterior to the incisive canal, and the lateral margins were projected lines 2 mm from both distal apices of the UCI ( Fig. 4 ).

Anterior nasal spine: axial middle slice.

The SN area was assessed bilaterally (SN _R , SN _L ). The starting slice was 2 mm above the apices of the upper lateral incisors (ULI). The ending slice was the nasal floor. The anterior margin was the facial buccal plate, the posterior margin was the posterior bony margin of the palatal vault (never beyond 14 and 24), and the lateral margins were projected imaginary lines from the distal apices of the ULC to the mesial apices of the upper canines (UC). A 2-mm safety margin was also set between these teeth ( Figs 5 and 6 ).

Subnasal bone: axial middle slice.

Total volume reconstruction in 3D: oblique view.

After volume calculation, the mean density of each volume of interest was calculated automatically by the software.

Linear measurements were also performed in order to facilitate better understanding of the areas. These were outlined as follows: (1) For PPM, the height was the distance from the most caudal to the most cranial slice. (2) For ANS, the height was the distance from 2 mm above the apices of the UCI to the nasal floor. The width was the distance from 2 mm distal to the apex of the right UCI to 2 mm distal to the apex of the left UCI; the starting point was 2 mm above the apices of the UCI. The depth was the minimum distance from the incisive canal to the facial buccal plate; the starting point was 2 mm above the apices of the UCI. (3) For SN, the height was the distance from 2 mm above the apices of the ULI to the nasal floor. The width was the distance from 2 mm distal to the UCI to 2 mm mesial to the UC; the starting point was 2 mm above the apices of the ULI. The depth was the distance from the facial buccal plate to the posterior bony margin of the palatal vault (never beyond 14–24); the starting point was 2 mm above the apices of the ULI.

All measurements were submitted to statistical analysis using SPSS version 15.01 software (SPSS Inc., Chicago, IL, USA). A paired t -test was used to assess the degree of similarity between SN _R and SN _L . Pearson’s linear correlation was used to study potential correlations among the different variables and all the areas studied. A multiple linear regression test was conducted to explain relationships between individual demographic characteristics and the volumes and densities of the three areas studied.

Results

The study sample comprised 52 women and 48 men with a mean age of 49.6 ± 14.5 years. Application of a Kolmogorov–Smirnov test confirmed the normality of the sample distribution ( P > 0.200). Figures 7–9 display the mean volume, linear, and bone density measurements obtained for the PPM, ANS, SN _R , and SN _L . Table 1 shows the results of paired t -tests for the comparison of SN _R and SN _L , which revealed a very high degree of symmetry.

Bone volumes (means and standard deviations) for the palatine process of the maxilla (PPM), anterior nasal spine (ANS), and subnasal bone (right, SNr; left, SNl).

Linear measurements (means and standard deviations) for the palatine process of the maxilla (PPM), anterior nasal spine (ANS), and subnasal bone (right, SNr; left, SNl) (Ht, height; Dp, depth; Wt, width).

Bone densities (means and standard deviations) for the palatine process of the maxilla (PPM), anterior nasal spine (ANS), and subnasal bone (right, SNr; left, SNl).

Stay updated, free dental videos. Join our Telegram channel

Join