The hard palate is an essential region of the skull; its gross anatomy and morphological variation have been of interest in several studies. Different clinical problems may require surgical approach to the bony palate such as dentofacial orthopedics, implant-assisted dental reconstruction of oncology patients, maxillary orthodontic protraction, and obvious oral pathology [1].
Greater palatine canal approach to maxillary nerve block demands a perfect three-dimensional orientation of position, direction, and extent of the canal. The preliminary step is identification of GPF. Utilizing multiple anatomical landmarks to identify the GPF increases the accuracy and minimizes the complications of injecting anesthetic drug [7]. In numerous previous studies using dry adult skulls, there is more emphasis on all the measurements of present study. However, our study, being radiological evaluation, the location of GPF is more accurate than the dry bone studies.
In all examined CT scans, the presence of GPF on both sides was a constant finding. This is consistent with the majority of the surveyed studies [4, 8, 9]. However, discrepancy in the number of GPF has previously been reported by Cagimni et al. [5]. They reported a single GPF in 81%, double GPF in 16%, and triple GPF in 2% of the examined skulls. Multiple GPF transmit greater palatine neurovascular bundle, similar to the single GPF. The presence of multiple GPF is anticipated when the pain is not effectively blocked during anesthesia [5].
In the present study, the GPF was most frequently located opposite M3 (41%). Other less frequent locations were behind M3 (25.8%), between M2 and M3 (23.2%), and opposite M2 (10%). The same most frequent location (opposite M3) was reported by Shalaby et al. [9] in their study on Egyptian skulls (84%). Our results also match with Varalakshmi et al. [6] and Beetge et al. [10] who stated that GPFs were close to the third maxillary molar in 69.8% and 66.65% of their cases, respectively. Also, this stands in agreement with Tomaszewska et al. [11] who found GPF most frequently located opposite M3 (74.7%), both in Europe and worldwide. On the other hand, Wang et al. [12] who conducted their study on Chinese recorded that the most frequent location of GPF was between M2 and M3, while Klosek and Rungruang [13], in Thais, considered the most frequent location to be opposite M2. Despite numerous studies, there is still no agreement to whether the position of GPF is prone to ethnic variability. The cause of GPF position diversity may be due to the difference in the quality of procedures performed, as well as the way the GPF was related to maxillary molars [10, 11].
Despite differences in the methods of assessment of GPF, the dimensions did not significantly differ among studies. In our study, the mean AP diameter of GPF was 3.94 ± 1.13 mm on the right side and 4.22 ± 1.21 mm on the left, while the mean LM diameter was 2.17 ± 0.59 mm on the right side and 2.28 ± 0.74 mm on the left. The GPF was described as AP elongated in 90.5% and circular in 9.5%. These results are almost close to most prior studies [4, 11]. In the study of Beetge et al. [10], the mean GPF dimensions were an A-P of 5.22 mm and an L-M of 2.81 mm. Shalaby et al. [9] measured the mean AP as 4.86 ± 0.9 mm on the right side and 4.78 ± 1.01 mm on the left. The mean LM diameter was 3.02 ± 0.7 mm on the right side and 3.01 ± 0.9 mm on the left side. This minimal discrepancy could be attributed to the fact that measurements in the present study were obtained radiologically unlike Shalaby et al. [9] who performed it manually on dry skulls.
The present study is similar to the majority of studies [11, 13, 14] in which the GPF was mostly described as anteroposteriorly elongated rather than oval in shape.
In this work, it was attempted to locate the GPF in relation to specific surrounding anatomical landmark such as posterior border of hard palate (PBHP), midline maxillary suture (MMS), posterior nasal spine (PNS), and incisive fossa (IF).
The distance between GPF-PBHP holds its importance in successful localization of GPF and prevention of accidental injury to nearby lesser palatine nerves and soft palate. Moreover, this dimension helps in localization of GPF in these cases where the third maxillary molar failed to erupt or is damaged due to any reason [15].
In the present study, the GPF-PBHP distance was 3.9 ± 1.21 mm on the right side and 3.93 ± 1.13 mm on the left. This is consistent with [16] where GPF-PBHP distance was recorded as 3.63 ± 1.91 mm on the right side and 3.94 ± 1.97 mm on the left. Shalaby et al. [9] in their Egyptian study on dry skulls measured the GPF-PBHP distance as 4.39 ± 1.73 mm on the right side and 4.53 ± 1.23 mm on the left. However, Shalaby et al. [9] took their measurement from the posterior edge of GPF to the point of maximum concavity on PBHP, while in the present study it was taken from the center of GPF to the shortest distance on the posterior border of hard palate.
Linear measurements in the present study showed the mean distance from the center of GPF to MMS as 14.95 ± 1.3 mm on the right side and 14.99 ± 1.24 on the left. These values were close to radiological results of [8] in which the GPF-MMS distance was estimated as ± 1.45 mm.
In the present study, the mean distance from the center of GPF to PNS was 16.55 ± 1.61 mm on the right side and 16.48 ± 1.6 mm on the left while the distance from the center of GPF to the center of IF was 38.06 ± 3.10 on the right side and 37.96 ± 3.17 on the left. These figures are disparate from the radiological results of Tomaszewska et al. [11], who estimated the GPF-MMS distance as 34 ± 3 mm on the right side and 34.3 ± 3.1 on the left, though the same methodology was applied in both studies.
Surveying different studies, it could be deduced that variation exits in linear measurements in different population; even interpopulation variation could exist. These differences might be related to ethnic factor [17] or quality of procedure performed [11]. Aterkar et al. [18] pointed out that linear measurements from GPF increase in edentulism; therefore, this distance may become variable according to palate width.
In the present study, a statistically significant side difference was found in the dimensions of GPF. Previous radiological studies provided no data regarding this point [8, 11, 19]. Although Shalaby et al. [9] did not recognize a statistically significant difference between the dimensions of GPF on both sides in their study on dry skulls, radiological data should be considered more accurate in this respect.
In the present study, a statistically highly significant difference in linear measurements from the center of GPF to surrounding anatomical landmarks as well as the dimensions of GPF existed between males and females. This is similar to results of [9, 11, 20]. Male skulls are generally larger than the female ones [20].
Although Moreira et al. [21] and Nascimento et al. [22] observed a statistically significant difference between males and females regarding the distance from GPF to IF, no statistically significant difference existed regarding the distance between right and left GPF.
According to Tomaszewska et al. [11], position of GPF in relation to surrounding anatomical landmarks could be used in forensic examination to identify a person’s sex. Nascimento et al. [22], though considering this method valid, simple, reproducible, and inexpensive, recommended using it only when more accurate techniques are not applicable. Although the present study adopts this point view as confirmed by the radiological results, but it would not have been accurate to rely on the general features to govern out gender of skulls without available records.
CT scans revealed one lesser palatine foramen on both sides in 75.5%, two foramina in 22%, three foramina in 2%, and none in 0.5% (two skulls on the left side only). The results presented in the present study are comparable with those by Sushobhana et al. [23].
In the present study, the palatine crest was a constant finding in all CT scans. However, the percent of the presence of palatine crest was highly variable among previous studies. Jaffar and Hamadah [24] reported a 67% on both sides, Piagkou et al. [25] a 57.8% on the right side and 56.3% on the left.
The limitations of our study included the relative small number of patients, and we have not commented on the length of the canal in the present study.