In this cross-sectional retrospective pilot study, medical patient records from the department of oral surgery and the department of orthodontics at the University Hospital Düsseldorf were screened from January 2019 until December 2021. Patients, aged 6-18 years, who had at least 1 CBCT scan taken with either the Planmeca Proface Romexis (version 4.6.1.R; Planmeca Oy, Helsinki, Finland) or the Pax Duo 3D (Orange Dental GmbH & Co KG, Biberbach a. d. Riß, Germany), were included, except for patients with bone malignancies or craniofacial malformations, as well as orthodontic treatment affecting the shape of the anterior palate (eg, maxillary protraction and expansion). The CBCT scans had been previously taken for oral health-related reasons, including analyses of bone support for OMIs, displaced teeth in the mandible, planned placement of miniplates, suspected tooth ankylosis or tooth retention, cysts, trauma, or other justifications. However, none of the justifications of the CBCTs affected the present analyses. It has to be noted that, owing to the retrospective pilot study design, no additional CBCTs were taken specifically for this study.

For both CBCT machines, the tube voltage was set at 90 kV. The tube current was 5.6 mA for the Planmeca Romexis (version 4.6.1.R; Planmeca) and 3-5.5 mA for the Vatech Pax Duo 3D (Pax Duo) device. The voxel size was 0.15 mm for the Planmeca device and 0.2 mm for the Pax Duo device. The exposure time varied depending on the device and settings, ranging 5.057-24 seconds. Because all measurements adhered to the as low as reasonably achievable principle, exposure time and field of view varied, sometimes capturing additional structures outside the maxilla (eg, the mandible).

The study protocol was initially approved on March 31, 2016, by the local ethics committee of the medical faculty at Heinrich Heine University Düsseldorf, Germany (Ref. 5418). The amended version was approved on March 9, 2020.

A measurement grid was constructed, consisting of 13 transversal and 8 sagittal planes, extending over the anterior palate and containing 104 measurement points ( Fig 1 ).

Measurement grid comprising 13 × 8 points. The points were located at a distance of approximately 1.2 mm in the sagittal and 1.0 mm in the transversal direction.

The grid boundary was formed by an anterior transversal reference plane passing through the tip of the canines. The most anterior transverse reference line was directed along the cusp tips of the canines and orthogonal to the occlusion plane. If only 1 canine had erupted or in case of asymmetry, this reference line was placed tangential to the cusp tip of the erupted canine (or the cusp tip of the canine that had not migrated to the mesial or distal site, respectively) and orthogonal to the palatal suture. If both permanent canines had not yet erupted, the maxillary primary canines were used for placement of the reference line as described above.

Patients with a minor diastema, or moderate tipping of the maxillary anterior teeth, were included in the pilot study. However, the pilot study excluded patients whenever there was a diagnosis of mesial or distal migration of the canines (eg, owing to anterior crowding, incisor protrusion or retrusion, or an anterior diastema). In addition, patients with craniofacial syndromes and clefts were also excluded.

Eight transversal planes were placed orthogonally to the suture at distances of approximately 1.2 mm. Sagittal reference points were placed at a distance of approximately 1.0 mm, whereby the most anterior transversal reference line was touching the cusp tips of the canines as described above.

The measuring points were named according to the palatal side, the transversal reference plane, and the distance to the suture. The letter L or R indicated whether the measuring point was located at the left or right half of the palate, respectively. The following digit described the sagittal plane, and the digit behind the dot represented the distance to the suture. Thus, point L4.1 would be located on the left paramedian aspect at the fourth sagittal point, 1 mm away from the suture.

Image processing was performed using Amira (version 2021.1; Thermo Fisher Scientific Inc, Waltham, Mass).

First, the CBCT was aligned with respect to the palatal suture and the occlusion plane. This was achieved by using a volume rendering that added transparency to the soft tissues, rotating the volume, and eventually applying the transformation.

Next, the first transversal slice was exported to intersect the cusp tips of the (deciduous or permanent) canines. Thereafter, transversal slices were exported such that they were parallel and taken at distances of 1.2 mm.

In detail, each transversal slice was saved as a TIFF file and further processed using the image processing software FIJI. Each measurement point was marked as specified in the measurement grid, and bone thickness was measured orthogonally to the occlusion plane.

The measurements were performed by 1 author (A.M.). The entire workflow, including image processing and measurements, was repeated by the same observer after 6 months for 6 randomly selected patients to assess intraobserver reliability.

A total of 20 patients were included (8 females and 12 males). Female patients were, by trend, older than males, but no significant difference was observed ( Table I , Mann-Whitney-U-Test, P = 0.43).

The statistical analysis revealed an ICC of 0.994 for the repeated measurements, whereas for the whole workflow, the ICC amounted to 0.863. This confirmed the high reliability of the methodology and measurement accuracy.

Overall, bone thickness measurements showed a large variance in thickness, and ranged 1.7-23.7 mm (median: 10.0 mm; mean: 10.0 mm; standard deviation [SD]: 3.8). The mean bone thickness values and the SDs for the age groups 6-12 years and 13-18 years split per sex are given in Supplementary Table I .

The pooled bone thickness in the sagittal direction can be found in Figure 2 . A decrease in bone thickness was noted from anterior to posterior measurement positions, and significant differences were observed among all the sagittal measurement positions, except for positions 1 and 2. The P values are given in Table II .

The figures represent the bone height measurements for male and female patients in the sagittal direction. Jitter points represent the individual measurements: the color of the jitter points indicate the age group, the color of the boxes represents the sex.

When considering the sagittal measurements only, significant differences were only detected between the more distant positions ( Supplementary Table II ).

In Figure 2 , individual data points are represented as jitter points, with the size of each point indicating the patient’s age. Age groups are further differentiated using a color-coded scheme, enabling a clear visualization of variations across sagittal positions, sexes, and age groups. This figure highlights the trends in bone thickness associated with posterior positions, age, and sex, providing a comprehensive overview of the observed patterns.

Age did not reveal a significant impact ( P = 0.08), but tended to be higher in older patients (13-18 years) compared with younger patients (6-12 years) at the more posterior positions (grid positions 6 to 8) ( P = 0.33) ( Fig 2 ). When comparing the pooled data for the anterior and more posterior positions, a significant difference was observed for the posterior region ( P <0.001), but failed to reveal significance anteriorly ( P = 0.66).

The overall bone thickness values tended to be higher in male patients compared with female patients ( P = 0.068). The pooled bone thickness measurements were higher in male patients (min: 6.40 mm; max: 13.37 mm; mean: 10.02 mm; median: 10.52 mm; SD = 2.10 mm) compared with female patients (min: 5.06 mm; max: 14.3 mm; mean: 9.86 mm; median: 10.13 mm; SD = 3.14 mm) ( Fig 2 ). When grouping the data for the anterior and posterior palate and comparing the pooled values between male and female patients using the Mann-Whitney U test, a significant difference was observed for the posterior ( P <0.001), as well as for the anterior positions ( P <0.001), with higher values for the male patients.

In the transversal direction, a significant increase in bone thickness was noted from the median to the paramedian regions ( P <0.001). The post-hoc pairwise test revealed significant differences among most transversal measurement positions, whereby no differences were noted in the median areas ( Fig 3 ). The P values are listed in Table III .

Paramedian and median bone height distribution by sex, age group, and sagittal position. Paramedian and median bone height values for female and male patients are given in the upper and lower rows. The x-axis denotes the sagittal position of the measurements. The individual bone height is represented by jitter points, and the respective age group is color-coded.

No significant differences were noted between the left and corresponding right aspects ( P = 0.99). Even though the interaction between sex and transversal position was significant ( P <0.001), significant differences were only found within a single sex among different measurement positions, but not between sexes ( P >0.05). The same was true when testing for the interaction between transversal measurement position and age groups ( P <0.001), as the significant differences only occurred among measurement positions.

Figure 3 illustrates the paramedian and median bone thickness values for female and male patients. The upper row represents data for females, whereas the lower row corresponds to males. The x-axis indicates the sagittal positions at which the measurements were taken. Individual bone thickness values are visualized as jitter points to enhance clarity and distinguish overlapping data points. In addition, the data is stratified by age group, with each group represented by a specific color. This visualization highlights variations in bone thickness across sagittal positions, sex, and age groups.

Table IV presents the frequency of potential root contact for a 13 mm long OMI, along with the corresponding odds ratios. The pooled odds ratios from Table V in the transverse plane reveal a progressive increase in the risk of root contact toward the paramedian region. In contrast, an analysis of the pooled odds ratios in the sagittal plane indicates a distinct decrease in the odds ratio from anterior to posterior positions. These results suggest that, according to the data obtained in this pilot study, the risk of root perforation is heightened in the paramedian area and diminishes progressively in the distal direction.

A 3D representation of the bone thickness measurements is given in Figure 4 . The y-axis denotes the respective local averaged bone thickness, and the x- and z-axes represent the median and paramedian measurement locations, respectively. The color coding also represents the mean bone thickness values (likewise to the y-axis).

Three-dimensional representation of mean bone heights.

In the z-axis direction, bone thickness decreased from anterior to posterior, whereas values increased toward the paramedian sites. The course slightly lowered from anterior to posterior. An interactive graph visualizing the bone thickness, likewise for younger (6-12 years) and older (13-18 years) patients, can be found in the Supplementary Figure .

A graphical summary of the findings is given in Figure 5 . The color coding corresponds to the mean bone thickness values.

Color-coded land map with recommendations derived from the risk of root damage and available bone height.

The recommendation for the suitability of insertion points for mini-implants was made based on the risk of root injury, as well as the bone thickness in the respective region. Three symbols were used to indicate the recommendation of the potential insertion points: (1) minus (–): a minus sign indicates that localization is not recommended for mini-implant insertion owing to an elevated risk of root injury; (2) circle (○): a circle indicates a moderate recommendation for mini-implant insertion. This was given to measurement grid points in direct proximity to “-” localizations or bone thickness below 7 mm; and (3) plus (+): a plus sign indicates localization recommendations for mini-implant insertion, and includes all points not allocated to the “-” or “○”.

The present pilot study aimed to quantify and analyze the anterior palatal bone thickness in growing patients and derive an updated map for this young group of patients. Therefore, bone thickness was measured within a standardized grid along the occlusion plane projected to the anterior palate. The insertion of OMIs was simulated in an orthogonal direction to the occlusion plane as suggested earlier.

In contrast to previous studies, ^,, and as indicated earlier, a V-shaped pattern of palatal bone thickness was identified in the anterior aspects, yielding the greatest bone supply in the paramedian aspects. Interestingly, overall bone thickness was higher in males, whereas this V-shape pattern tended to be more pronounced in females than in male patients, as well as in younger patients. Paramedian bone thickness of more than 8 mm was identified in more than 75% of included patients, regardless of age and sex, up to sagittal position 4 of the grid (located at the orthogonal projection of the connection line between the mesial aspects of the maxillary first premolars). Thus, this region was classified as a safe area. Zuh et al had also reported a V-pattern in the transverse plane and identified slightly higher bone thickness on the right side, which was suggested to result from higher masticatory forces at this side.

The values reported for the available median and paramedian bone thickness are in line with previous reports. Chhatwani et al identified a maximum mean bone thickness of 9.7 ± 2.8 mm, whereas Song Hee Oh et al determined bone thickness ranging 2.5-10 mm and a mean paramedian anterior bone thickness of 7.7 ± 2.31 mm in males and 6.45 ± 2.09 mm in females. It has to be noted that the 2 authors considered different ethnicities in their studies. Similar to previous reports, mean bone thickness was higher in male patients compared with female patients posteriorly, but failed to reach statistical significance in the anterior measuring positions. Bone thickness also tended to be higher with increasing age, as described earlier.

It is worth noting that bone thickness measurements depend on the accuracy of grid positioning in the maxilla, and values might slightly vary in case of readjustment of the grid. Nonetheless, previous studies indicated that the greatest bone thickness can be found in the anterior palate region, gradually decreasing distally. ^, These observations align with the results of our pilot study.

Previous studies confirmed that palatal bone density and suture ossification increase with age, ^,, though patient variation persists into adulthood, compared the width of the palatal suture in different age groups, and identified age-dependent changes. Up to the age of 26 years, suture ossification was complete in only 3.11% of the patients, whereas ossification was not complete in most patients during adolescence. ^,, Nie et al demonstrated suture opening in patients aged 16-51 years through microimplant-assisted rapid palatal expansion.

Although the midpalatal suture has traditionally been considered a safe and accessible site for temporary skeletal anchorage device insertion, especially because of its cortical bone support and elevated bone thickness values, its role in craniofacial growth remains a topic of ongoing debate. Importantly, the midpalatal suture is not a true growth center, but rather an intramembranous growth site that responds to mechanical forces—particularly distraction from adjacent growing bones. Sutural bone formation is believed to occur primarily through tension-mediated apposition at the suture margins, rather than intrinsic growth from within. Consequently, the implications of local tissue damage within the suture—such as that caused by temporary skeletal anchorage device insertion—are unclear. It is possible that surrounding mechanical forces continue to drive growth despite minor localized disruption. However, as the biological response of sutural tissue to such interventions has not been fully elucidated, a cautious approach remains advisable. Future research should aim to better define how suture integrity influences skeletal development, particularly during key growth periods.

In the present pilot study, the bone availability was particularly high in the more anterior paramedian regions. In previous studies, a slightly anterior angular orientation of the mini-implants was therefore recommended for paramedian implant insertion at the height of the first premolars or slightly more distally. ^, The present findings confirm the applicability of this procedure.

Soft tissue anatomy may also affect OMI stability, as insufficient keratinization or increased mucosal thickness has been shown to promote inflammation or mechanical instability. Although not assessed in this study, future work should examine how soft tissue height and bone thickness jointly influence safe insertion zones.

Although the hard palate is covered by keratinized gingiva, some authors reported that thickness values vary among patients and the different palatal locations. Higher soft tissue values are clinically relevant as the most coronal bone to implant contact shifts apically, which increases the lever arm, which can therefore affect OMIs stability ^,

Injury to the incisor roots represents a realistic risk during insertion in the paramedian region. Root resorption can begin at a distance of 0.6 mm from the roots, even without direct contact between the OMIs and the root. In most patients, lighter lesions are likely to heal by cemental repair. However, there are also reports of more severe complications requiring endodontic treatment. Although the superimposition of a scan and lateral cephalogram appears to be suitable for most patients, a recent report indicated that root damage may not be properly assessed by this method, as an OMI was placed too close to the incisor roots. Also in the present pilot study, root proximity was identified for implant placement up to the connection line of the mesial contact point of the first premolars, simulating the usage of implants of 13 mm lengths. Regions in which at least 1 root damage was simulated were classified to be of elevated risk, whereas neighboring regions were assigned with moderate recommendation only. This stringent criterion was applied because of the relatively low number of participants in the pilot study, ensuring a more conservative and precise assessment of root injury risk. Future studies correlating safe insertion zones identified via lateral cephalograms with CBCT findings could enhance the clinical safety of implant placement without the use of CBCT.

The division of age groups into 6-12 years and 13-18 years in our study is supported by developmental changes in palatal bone morphology during growth. Previous CBCT-based analyses have shown that palatal bone thickness increases significantly from early to late mixed dentition stages (approximately aged 8-12 years), with no significant differences observed between the late mixed dentition group and adults thereafter. This indicates that by approximately the age of 12 years, the palatal bone structure approaches adult-like characteristics, both in terms of thickness and stability. Consequently, grouping patients into 6-12 years and 13-18 years reflects a biologically meaningful distinction: The younger group includes children undergoing active skeletal and dental maturation, whereas the older group consists of patients with more stable and mature palatal structures. This grouping allows for a more precise evaluation of mini-implant placement considerations across different growth phases. In the present analysis, no differences were observed in the anterior palate, whereas in the posterior palate, higher bone thickness values were observed for older patients.

It must be noted that several limitations were associated with the present pilot investigation. First, the study was restricted to nonadult patients and included only 20 patients. The small sample size limited statistical power, prevented stratification by age or sex, and likely underpowered comparisons between male and female patients or between younger and older groups. Consequently, type I and type II errors remain possible, and the findings cannot be generalized. Moreover, as the primary outcome of this pilot study was a descriptive mapping of anterior palatal bone thickness, no formal sample size calculation was feasible. Larger, multicenter studies are needed to confirm these preliminary findings.

Second, only 1 observer performed the measurements, so no interobserver calibration was possible. Third, the risk for root injury was simulated with a 13 mm implant, whereas in clinical practice, 7 mm and 9 mm implants are more common. One implant length was selected to reduce complexity, given the small sample size. Fourth, no soft tissue thickness measurements were performed, which may also affect clinical applicability.

Fifth, only radiologic examinations were included, and no patient-based stability measurements were carried out to validate the radiologic findings. In addition, cortical bone content was not separately assessed, even though it contributes substantially to primary stability; future studies should evaluate whether cortical bone quantity changes with age and growth.

Finally, owing to the pilot nature of the study, rare events or unforeseen interactions could not be captured.

Furthermore, one might argue that in clinical practice, orthodontic implants are frequently placed perpendicular to the bone surface. Owing to the variance in bone surface steepness, the respective findings might, however, be difficult to interpret for the clinician, and in the present pilot study, we therefore aimed to create a 3D visualization of a typical palate.

The present pilot study provides a map that highlights the recommended regions, as well as regions with increased risk for root injury or insufficient bone availability. Such a map is a practical aid for the clinician during insertion. Nonetheless, the lack of recommendation of an ideal insertion angle must be regarded as a methodological weakness. Because of the different 3D curvatures of the palate, only 1 insertion direction, perpendicular to the occlusal plane, appeared practicable within the scope of the pilot study. In practice, a slightly anterior angulation to the palatal surface is commonly preferred. On the other hand, the selected OMI length was above average to avoid false-negative results regarding root contact.

Furthermore, different bone thicknesses in relation to age seemed to have a minor impact on the posterior regions. Considering the rather small number of patients and the continuous age distribution, further studies are needed to investigate if increased safety is associated with more anterior placement of implants in younger patients.

In summary, the present investigation suggests that in growing patients, paramedian implant insertion might be advisable. In addition, insertion should be performed at the height of the first premolars, which represents the region of the third pair of palatal folds or slightly distally. In patients with orthoinclined or palatally tipped crowns of maxillary incisors, anterior inclination of the implants can be applied when bone availability is limited. Eventually, clinicians should carefully consider that individual bone thickness might vary. It has to be noted that the present pilot study did not investigate whether CBCT may be justified in specific patients, such as patients with palatally displaced teeth, clefts, low bone quantity, or increased soft tissue height, for which a strict indication of CBCT is recommended in current guidelines.

Owing to the small sample size of the present pilot study, future investigations are needed to further elucidate the age-dependent maturation of palatal bone thickness at the different median and paramedian locations in the sagittal and transversal directions.

With its limitations (small sample size of only 20 patients, lack of generalizability, and limited scope), the present pilot study revealed the following:

• 1.

  Younger patients tended to have a more pronounced anterior palatal V-shaped bone thickness pattern.

• 2.

  The V-shaped pattern was also more pronounced in female patients, whereas overall bone thickness was higher in male patients.

• 3.

  Paramedian placement slightly behind the connecting line between the mesial aspect of the first premolars yielded the highest bone thickness.

• 4.

  An elevated odds ratio for root damage was observed at more anterior positions.

Kathrin Becker contributed to conceptualization, methodology, writing– original draft preparation, visualization, and supervision; Anela Mekic contributed to writing– original draft preparation, investigation, conceptualization, and software; Manuel Nienkemper contributed to supervision, methodology, and writing– review and editing; Katharina Mücke contributed to validation and writing– review and editing; Lisa Josefine Langer contributed to validation and writing– review and editing.