In order to compare the data obtained in this study and the existing literature (Tables 3 and 4), a recent systematic review and meta-analysis article was selected for analysis: Kim et al. (2023) (15), which compiles data from 75 similar studies. Of these studies, 29 were based on imaging examinations and 46 on cadavers. From these, the overall values of the variables under study were taken and considered as reference values. It is important to note that, with regard to the position of the GPF in relation to the maxillary molars, the article in discussion presents a sample size of 36,994 individuals.

The sample size of Kim et al. (2023) [12] allows for the identification of subgroups for certain variables, which are associated with the continent of origin of the studies included. In particular, the results from Europe (where available) were consulted for discussion purposes.

The GPF-PNS, GPF-MMS distances and the anteroposterior diameter of the GPF obtained in this study show no statistically significant differences from the reference values (95% CI). The first two, with mean values that do not intersect the 95% CI of the RVs, suggest the potential for differences, although not proven by the present study.

The GPF-PBHP and GPF-ANS distances are higher than the RVs (95% CI); the GPF-IF distance and the lateromedial diameter of the GPF are lower than the RVs (95% CI).

The GPF-PBHP distance (4.83, 95% CI = 4.60–5.05) is in close proximity to the European value (4.18, 95% CI = 1.83–6.54). Additionally, the GPF-IF distance (35.18, 95% CI = 34.64–35.72) is also in close proximity to the same value (36.79, 95% CI 31.69–41.89).

Conversely, the lateromedial diameter of the GPF (2.24, 95% CI = 2.15–2.34) diverges from the European value in comparison to the overall RV (RV 2.77, 95% CI = 2.58–2.96; European value 3.04, 95% CI = 2.74–3.35).

The position of the GPF in relation to the upper molars is in accordance with the RVs, with no statistically significant differences. Therefore, in the majority of individuals, the GPF is located in opposition to the third molar (77.0%, 95% CI = 68.1–84.4). This result is also consistent with the findings of Bahşi et al. (2019) [2], who reported a prevalence of 66% for the left GPF and 67.33% for the right GPF, and with those of Tomaszewska et al. (2014) [23]. The latter paper also states that European studies do not show heterogeneity in the positioning of the GPF in relation to the upper molars, suggesting that the different results in the literature are explained by the quality of the analysis and the varying methodologies. For this reason, they introduced a classification system, used in this study, with the aim of establishing a generalised method of analysis.

In patients with no remaining teeth, the location of the GPF can be determined by measuring distances to easily identifiable landmarks. Kim et al. (2023) [12] propose that the most reliable landmarks are the MMS, the PBHP and the IF.

The most prevalent form of GPF is the ‘oval/ovoid’, which concurs with the findings of Ortug & Uzel (2019) [17]. No statistically significant differences were observed between the various GPF shapes, with the exception of the “other” category. Although this is a subjective (observational) analysis, the oval shape is the most frequently described in the literature and is consistent with the results obtained in our study.

Although the difference was not statistically significant, the results for the ‘slit’ shape (26%) were higher than the RV (8.4%). This result may be associated with the shorter lateromedial diameter in comparison to the RV (95% CI). Therefore, the findings indicate that the GPFs analysed exhibited a tendency towards greater elongation in the anteroposterior direction in proportion to the lateromedial diameter, in comparison to the RV. Consequently, the prevalence of the round shape (1%) is also lower than that of the RV (9.4%), although this is not statistically significant when the disproportion of the anteroposterior and lateromedial diameters is considered.

The results for the opening direction of the GPF for the oral cavity are not in accordance with the RV, with no vertical or anterior classification recorded. The most prevalent opening direction, despite being the same in relation to the RVs, is significantly higher (95% CI).

It should be noted that the sums of the RVs for the categorical variables (position, shape and opening direction) do not total 100 per cent, as they were estimated individually, considering the studies available for each classification. This is because a statistical analysis of a single global sample was not carried out.

The metric variables representing the measurements of the male subjects exhibited significantly higher values than those of the female (p < 0.05) (Table 5). This finding is consistent with the sexual dimorphism of the skull, which is typically more pronounced in males than in females. These results are consistent with those reported by Gibelli et al. (2017) [8] and Tomaszewska et al. (2014) [23], although these two studies refer to other authors who do not support the findings presented here. Tomaszewska et al. (2014) [23] also suggest that the position of the GPF in relation to reference points (metric variables) could be used to determine gender in the forensic field.

No statistically significant differences were observed in the categorical variables (position, shape and direction of opening) (Table 6). It is thus proposed that the protocol for approaching the GPF in females and males could be the same in terms of position in relation to the upper molars. However, it is recommended that the distances to reference points be taken into account.

There were no statistically significant differences in the variables studied between the right and left sides - Tables 7 and 8. Tomaszewska et al. (2014) [23] recorded differences in the GPF-MMS and GPF-IF variables, and Gibelli et al. (2017) [8] recorded differences in GPF-PNS and GPF-MMS. Therefore, it can be inferred that, clinically, an equivalent protocol can be used when approaching the right and left GPF.

With regard to local anaesthesia, the technique for blocking the greater palatine nerve described by Malamed et al. (2017) [15] appears to be suitable for the results obtained. This is based on the following description: ‘The entrance to the greater palatine foramen should be palpated as a depression or soft zone in the posterior area of the hard palate.’ It is frequently situated at the midpoint between the gingival margin and the median palatine suture, approximately opposite the distal aspect of the maxillary second molar [15]. Palpation may help locating this anatomical structure especially in cases with atypical shapes and positions of the GPF.

Furthermore, an understanding of the morphometry of the GPF will be beneficial in surgical procedures, with the objective of preventing iatrogenic damage to GPA and GPN [4, 10, 12, 18].

This type of study, to our knowledge, is the first to be carried out in a Portuguese population and makes it possible to adapt medical-dental clinical practice to the target population, based on data with good statistical significance (95% CI).

The inclusion and exclusion criteria present a challenge in selecting the records, as it is necessary to analyse the CBCTs individually. Only a small percentage of the subjects met the requisite criteria, namely having all their upper teeth fully erupted, and including the entire maxilla. In order to select the 50 records included in the sample, 1,256 CBCTs were consulted.

The lack of consistency in the methodologies employed for the morphometric analysis of the GPF precludes any meaningful comparisons of the resulting data. For this reason, this study places particular emphasis on the data and methodologies presented in the systematic reviews conducted by Tomaszewska et al. (2014) [23] and Kim et al. (2023) [12].

The CBCT images were obtained using a sensor with 0,4 mm voxel dimension. Although different voxel sizes may affect detail and diagnostic accuracy, different studies performed on different anatomical structures demonstrate that linear measurements are not necessarily affected [5, 7].

This study did not take into account ethnic differences, as this information was not available in the medical records consulted. There is no consensus in the existing literature on whether ethnicity influences the location of the GPF [17]. It is known that there are anatomical differences described between different ethnicities, both in the shape and dimensions of the GPF [13]. Therefore, the applicability of our findings outside the Portuguese population might be limited. However, while Portuguese findings may not fully represent global craniofacial diversity, they can still contribute to a broader understanding of the GPF anatomy.

It is recommended that future studies analysing GPF establish a universal method to ensure the data obtained is truly comparable.