## 4 Discussion
As the lower level that is utilized in the present study is about 1.5-2 mm above the alveolar crest level, this is in correspondence with the 2 mm level of [PERSON] and [PERSON] [25], while the upper level is in correspondence with the 6 mm level. Thus, the results of this study are in agreement with [PERSON] and [PERSON] [25]. In the study conducted by [PERSON] et al. [28], the CEJ was utilized as the reference, and measurements were made at 2, 4 and 6 mm cuts in the CBCT images. They reached the conclusion that the buccal cortical thickness in the posterior maxilla increased as the level cuts moved in an apical direction from the CEJ to the 4 mm level, and then they decreased again at the 6 mm level. They utilized the 6 mm level as the maximum level of measurement, as such a distance from the CEJ is probably inside the region of the attached gingiva. However, since the upper level of the attached gingiva that was utilized in the present study, as the maximum level of measurements, might be beyond the 6 mm distance from the CEJ, this may be the reason for the disagreement as to the buccal cortical bone thickness at the posterior maxilla region. The same software and methodology used in the present study were used in a study of cortical bone thickness measurements at the buccal and lingual sides of the upper and lower jaw by [PERSON] et al. [44]. The results for the region mesial to the upper molars were found to range from 1.35 mm to 1.76 mm, while moving gradually to 2, 4, 6, 8 mm distance from the CEJ for males, and from 1.36 mm to 1.64 mm for females. In the literature, there is controversy regarding the impact of gender on cortical bone thickness measurements. In the study of [PERSON] et al. [45], no statistically significant difference was found in cortical bone thickness measurements between groups of different facial type regarding gender, and this is in agreement with [PERSON] et al. [46] as, in their study, no significant differences were recorded in cortical bone thickness between genders. However, [PERSON] et al. [26] stated that in the upper jaw, on the attached gingiva mesial to the first molar, the cortical bone wins thinner in females than in males. In the present study, only female patients were included, assuming that gender might affect the results, and the cortical bone thickness was recorded from 0.44 mm to 0.61 mm for the right side, and 0.67 mm to 0.99 mm for the left side, while moving from the lower to the upper height level. The findings of this study are also in relevant agreement with [PERSON] et al. [47], who stated that the cortical bone thickness and density at the buccal side of the alveolar process demonstrate a significant linear increase from crest to base. In their study, the cortical bone thickness and density were measured at 2, 4, 6 and 8 mm distance apical to the alveolar crest in several interradicular sites, in groups that were organized on the basis of age, gender, side, and site. However, the results of the current study suggest that there is a weak association between the buccal cortical bone density and the height levels (lower, middle and upper) of the attached gingiva, and a medium association between the buccal cortical thickness and the same height levels of the attached gingiva in the upper jaw, in the interradicular area between the first molar and second premolar. According to [PERSON] categorization [36], in this study, the cortical bone density on the right-side upper height level of the attached gingiva (mean: 1395.10 HU), and on the same side middle height level (mean: 1250.40 HU), belongs to the D1 range (above 1250 HU). On the left-side upper height level (mean: 1224.30 HU) and middle height level (mean: 1171.20 HU), and on the right and left-side lower height level (mean: 1155.75 HU and 995.85 HU, respectively), the cortical density falls in the D2 range (between 850 and 1250 HU). The trabecular bone density is measured below 850 HU in all sites, and thus is categorized in the D3 range (350-850 HU). In a similar methodological study, [PERSON] et al.