Background
There is limited information available regarding the bone volume in the sagittal dimension of the infrazygomatic crest (IZC) that is safe for the insertion of a temporary skeletal anchorage device. The objective of this study was to assess the sagittal bone availability when the anterior and posterior walls of the IZC reach an inclination of 45°.
Methods
A cross-sectional investigation was undertaken on 100 cone-beam computed tomography scans of 40 males and 60 females. A total of 20 landmarks were digitized for each IZC outline, 1 mm from the vestibular alveolar bone, and their x, y, and z coordinates were extracted. Afterward, the sagittal measurement of the IZC at which the curvature reached 45° was recorded. Symmetry of measurements was assessed using paired-samples t tests. In addition, these measurements were compared as a function of sex and age group (≤21 vs >21 years) using an independent-samples t test and the Spearman rank correlation coefficient test ( P <0.05).
Results
There were no significant differences between paired sagittal measurements of the IZC (3.5 ± 1.5 mm on the right side and 3.6 ± 1.3 mm on the left side; P = 0.144), except for younger patients ( P = 0.030). In addition, no significant differences were found between corresponding male and female measurements ( P ≥0.149). A significant discrepancy was identified between the younger age group (3.2 ± 1.2 mm) and the older cohort (3.8 ± 1.6 mm) for the sagittal dimension of the right IZC ( P = 0.038), with an estimated mean difference of 0.03-1.16 mm (95% confidence interval). A significant positive weak correlation was found between the sagittal dimension of the right IZC and age (ρ = 0.201; P = 0.045).
Conclusions
Sufficient IZC bone volume is available at an angle of 45° for inserting a temporary skeletal anchorage device, with no sex or side variation, except for the significantly greater sagittal dimension of the right IZC in older patients.
Highlights
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3D insertion site for temporary skeletal anchorage device in the IZC sagittal plane was identified.
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The coordinates (x, y, z) of the IZC were measured up to 45° curvature on the sagittal plane.
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Paired IZC sagittal measurements showed comparable bone availability at 45° inclination.
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Adults have a significantly greater bone volume at the right IZC than adolescents in the same region.
Anchorage management is a critical aspect of orthodontic treatment planning, ,, designed to resist undesirable tooth movement. Traditionally, reinforcement of anchorage has been achieved using intermaxillary elastics, extraoral forces, as well as transpalatal and lingual arches. However, over the last 2 decades, the development of temporary skeletal anchorage devices (TSADs) has widened the prospects of orthodontic treatment, using effective and predetermined force application. This innovation also facilitated the development of the concept of skeletal anchorage, significantly enhancing orthodontic treatment outcomes. ,,
TSADs are small temporary devices used to enhance anchorage and reinforce stability. The surgical procedure for their placement is relatively simple and allows for immediate loading. TSADs can be positioned in various alveolar and maxillomandibular sites ,,, and can serve as an anchor for various types of orthodontic tooth movements, including extrusion and intrusion, verticalization, mesialization and distalization of molars, retraction of anterior teeth, traction of impacted teeth, and indirect anchorage for space closure. ,
Initially, TSADs were used only in the inter-radicular sites. ,,, However, the limited inter-radicular distance might increase the risk of potential damage to proximal dental roots during specific dental movements. ,, Extra-alveolar sites, such as the hard palate, mandibular buccal shelf, and the infrazygomatic crest (IZC), were proposed to minimize potential iatrogenic risks during TSADs placement and the planned dentition movement, in addition to enhancing anchorage efficiency. ,,,,,
The IZC position relative to maxillary posterior teeth varies with age. In younger patients, the IZC is usually located between the maxillary second premolar and the permanent first molar. The most frequent IZC location in adults is above the maxillary first molar, between the buccal roots and the buccal cortex of the maxilla. ,,,, Several investigators have reported that the IZC bone is thicker in young patients and mostly longer in adults. This understanding of the IZC morphologic differences across age groups is critical for optimizing TSAD placement and effectiveness.
Anatomically, the IZC has 2 cortical plates—the buccal and the maxillary sinus margin. This structural geometry enables bicortical TSAD fixation, reinforcing primary stability. The maxillary sinus frequently constrains the placement of a TSAD at the IZC, leading to sinus perforation, which is considered one of the most clinically significant complications, accounting for nearly 50% of the patients evaluated. This is especially true for a more vertical insertion angle to the occlusal plane, particularly in older patients. Although the literature does not report any adverse clinical signs or symptoms related to TSAD sinus perforation, a comparison between CBCT scans taken before TSAD insertion and those taken after TSAD removal showed increased sinus membrane thickness and bone resorption around the TSAD. ,
A thorough understanding of the IZC anatomy and its surrounding structures is essential for avoiding iatrogenic complications and enhancing stability. ,
The position and morphology of the IZC can vary among patients and populations because of genetic, environmental, craniofacial morphology, and developmental factors. However, investigations assessing the IZC geometric variations among populations are scarce. Previous studies have evaluated the IZC parameter in the coronal and axial planes. ,,,,,,, To the best of our knowledge, this is the first investigation examining the available bone in the sagittal plane when the anterior and posterior walls of the IZC reach an inclination of 45°. Therefore, the following null hypotheses were tested: (1) there are no significant differences in the mean sagittal dimensions of the IZC available for TSAD insertion between males and females when the inclination of the IZC wall reaches 45°, (2) there are no significant differences in the mean sagittal dimensions of the IZC available for TSAD insertion among age groups when the inclination of the IZC wall reaches 45°, and (3) there are no significant differences between the sagittal dimensions of the right and left IZC available for TSAD insertion when the inclination of the IZC wall reaches 45°.
Material and methods
This retrospective observational study was approved by the Egas Moniz ethics committee (PT-270/23). The research protocol adhered to the European Good Practice Guidelines and the World Medical Association’s Declaration of Helsinki, and followed the Strengthening the Reporting of Observational Studies in Epidemiology guidelines for observational studies. Informed consent was obtained from patients before the administration of the cone-beam computed tomography (CBCT) scans.
A total of 1390 CBCT scans from male and female patients of different age groups who had visited the Egas Moniz School of Health and Science University Clinic between December 2022 and January 2024 were screened to determine the available data. Patients were excluded from the study based on the following criteria: cleft lip and palate, craniofacial deformities, systemic diseases or taking medications that might affect bone density, hypodontia or supernumerary teeth, and impacted teeth or cysts. Only high-quality CBCT scans of Portuguese patients with complete permanent dentition and without significant dentoalveolar bone loss were included in the study.
The sample size calculation was performed based on the Cohen d moderate effect size ( d = 0.6) when analyzing the impact of age on IZC thickness. Under these conditions, considering a power of 80% and a significance level of 5%, a minimum sample of 90 participants is required. All the CBCT scans were obtained for diagnostic purposes, confined to the protocol of as low as diagnostically acceptable being indication-oriented and patient-specific.
The CBCT scans were acquired in natural head position using the Planmeca Viso G7 (Planmeca, Helsinki, Finland), implementing the following settings: 120 kVp, 5 mA, large field of view (20 × 17 cm), exposure time of 30 seconds, and a segment thickness of 0.45 mm. The CBCT scans were saved in digital imaging and communications in medicine format and converted into volumetric images. These 3-dimensional (3D) images were constructed using the Planmeca Romexis Viewer (version 6.0; Helsinki, Finland).
Each participant’s personal information was assigned a coded number to blind the examiner from probable bias regarding age and sex. The investigator is an orthodontist who conducted training sessions on using Plamenca Roemexis Viewer V6 software. This software features a ruler tool that is calibrated across 3 spatial planes, enabling accurate measurement of designated points in 3D.
Each image was oriented to a standardized position to ensure accurate measurements across the 3 spatial planes: sagittal, axial, and coronal. In the sagittal view, a plane joining the anterior nasal spine and the posterior nasal spine was drawn perpendicular to the vertical window frame ( Fig 1 , A ). Similarly, these landmarks were used to orient the scan in the axial plane, traced parallel to the reference vertical plane ( Fig 1 , B ). For the coronal plane, the center of the palatal root of the maxillary left first molar was identified. From there, a point 5 mm lateral to the midpalatal suture was established, and the midline between the nasal and the palatal cortical bones was delineated. In addition, a line was traced between the nasal and maxillary cortical bones to mitigate potential errors arising from asymmetries in bilateral bony structures or variations in bone thicknesses. This line was aligned parallel to the lower window frame ( Fig 1 , C ).
Image orientation: A, Sagittal plane; B, Axial plane; C, Coronal plane.
A bilateral IZC assessment was performed on each oriented scan. The sagittal plane was aligned tangentially to the vestibular cortical bone, and afterward, moved 1 mm toward the vestibular direction at the level of the IZC contour. At the level of the IZC contour, the IZC outline was traced using 20 landmarks on each IZC. The coordinates of the 3 planes of space were determined for each point (x, y, and z) ( Fig 2 ). The linear distance between the point in which the curvature reached 45° on the anterior and posterior walls of the IZC ( Fig 3 , A and B ) was determined using the formula d = ( x 1 − x 2 ) 2 + ( y 1 − y 2 ) 2 + ( z 1 − z 2 ) 2 .
Marking the IZC points and their coordinates ( top right ).
Sagittal view from IZC: A, CBCT image; B, Illustration.
Once the coordinate data had been extracted, the values obtained were then multiplied by the size of the corresponding voxel of each CBCT to obtain the linear computed distance in millimeters.
Statistical analysis
All measurements were saved in an MS Excel (Microsoft, Redmond, Wash) spreadsheet. SPSS (version 28.0; IBM, Armonk, NY) was used for statistical analyses. The evaluated variables were age, sex, and the coordinates of each landmark (x, y, and z).
Descriptive statistics included the mean, standard deviation, and minimum and maximum values. The differences in measurements between age and sex groups were performed using a paired-samples t test. Data adequacy to the normal distribution was evaluated using the Shapiro-Wilk test, and data homoscedasticity was assessed using the Levene test. Parametric analyses were, therefore, carried out. Paired-samples and independent-samples t tests were performed. The Spearman rank correlation coefficient (ρ) was used to evaluate the correlation between the sagittal measurements of the IZC and age.
One investigator (S.F.) conducted a reproducibility analysis of 10 CBCT scans selected at random, which had previously undergone measurements of the same 150 points of interest at 2-week intervals. The intraclass correlation (ICC) for agreement was employed to determine the degree of similarity between the 2 trials. The results suggest a high reproducibility between the paired measurements as follows: ICC for the right IZC = 0.99 (95% confidence interval: 0.98-0.99) and ICC for the left IZC = 0.98 (95% confidence interval: 0.93-0.99).
Results
The total sample analyzed comprised 100 participants, consisting of 60 females (60%) and 40 males, aged 12-49 years. The cohort was further divided into 2 age groups: adolescents (≤21 years, comprising 21 males and 27 females) and adults (>21 years, comprising 19 males and 33 females) ( Table I ) .
Table I
Demographic data of the participants included in the study
| Sex, n (%) | ≤21 y | >21 y | Participants |
|---|---|---|---|
| Males | 21 (52.5) | 19 (47.5) | 40 |
| Females | 27 (45.0) | 33 (55.0) | 60 |
A paired-samples t test demonstrated comparable paired sagittal dimensions of the IZC (right side at 3.5 ± 1.5 mm and the left side at 3.6 ± 1.3 mm) at P = 0.144 ( Table II ). The independent-samples t test detected no significant discrepancy between the sagittal measurements of the IZC in males (right side at 3.2 ± 1.4 mm and left side at 3.4 ± 1.3 mm) and the corresponding dimensions in females (right side at 3.7 ± 1.5 mm and left side at 3.8 ± 1.4 mm) at P ≥0.149 ( Table III ).
Table II
Distribution of the paired sagittal measurements of the IZC
| Right | Left | P value | ||
|---|---|---|---|---|
| Mean (SD) | Min-Max | Mean (SD) | Min-Max | |
| 3.5 (1.5) | 0.8-8.5 | 3.6 (1.3) | 1.1-8.1 | 0.144 |
Note. All values are in millimeters. Comparison is at a 5% significance level, using paired-samples t test (n = 100).
SD, standard deviation; Min, minimum; Max, maximum.
Table III
Distribution of the paired sagittal measurements of the IZC as a function of sex
| Sex | Participants | Right | Left | P value | ||
|---|---|---|---|---|---|---|
| Mean (SD) | Min-Max | Mean (SD) | Min-Max | |||
| Males | 40 | 3.2 (1.4) | 0.8-6.2 | 3.4 (1.3) | 1.1-6.4 | 0.358 |
| Females | 60 | 3.7 (1.5) | 1.1-8.5 | 3.8 (1.4) | 1.7-8.1 | 0.259 |
| P value | 0.152 | 0.149 | ||||
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