## 4 Discussion
\begin{table}
\begin{tabular}{c c} \hline \hline \multirow{2}{*}{**Parameter**} & **Modified Palatal Height Index** \\ \cline{2-3}  & **Spearman’s Correlation Coefficient** \\ \hline M1 (mm) & r = \(-\)0.113, \(p\) = 0.264 \\ M2 (mm) & r = \(-\)0.206, \(p\) = 0.04 \({}^{\star}\) \\ M3 (mm) & r = \(-\)0.151, \(p\) = 0.134 \\ D1 (mm) & r = \(-\)0.208, \(p\) = 0.038 \({}^{\star}\) \\ D2 (mm) & r = \(-\)0.249, \(p\) = 0.012 \({}^{\star}\) \\ D3 (mm) & r = \(-\)0.184, \(p\) = 0.066 \\ I1 (mm) & r = 0.091, \(p\) = 0.369 \\ I2 (mm) & r = 0.175, \(p\) = 0.081 \\ I3 (mm) & r = 0.147, \(p\) = 0.146 \\ \hline \hline \end{tabular} \({}^{\star}\) statistically significant (\(p<0.05\)).  
\end{table} 
Table 11: Correlation between the bone thickness and palatal height index. with the abovementioned theory, the decrease in bone depth with growing vertical distance from the occlusal plane is not so notable. The mean difference in bone depth between the insertion point at the height of 12 mm and 16 mm is 0.8 mm in the case of the area of the mesial root of the first molar, 1.12 mm at the area of the distal root of the first molar, and 2.57 mm in the interdental space. Results of our study indicate the presence of a significant and negative correlation between the age of the patients and bone thickness buccally to the first molar. Similar correspondence can be also observed in the case of interdental point of insertion, but the results are not statistically significant. Only a few studies assessed age dependency. [PERSON] et al. [18] did not notice age dependency in the case of insertion site between the first and the second molar among patients aged 18 to 42 years. Considering differences in bone thickness among sexes, bigger values were observed in the case of male patients, but the only significant differences were found in the I2 and I3 measurements. Similarly, [PERSON] et al. [19] and [PERSON] et al. [18] did not find any differences in the bone thickness buccally to the distal and mesial root of the maxillary first molar respectively, comparing sexes. Since there are studies where some correlation between facial pattern and bone availability at the IZC area has been found [20], the aim of our study was also to observe dependency between the shape of the maxilla, expressed as a modified palatal index, and the structure of the IZC region. Although it needs to be emphasized that significant results were obtained only in the case of M2, D1, and D2 points, the bone thickness bucucally to the first molar tends to decrease with the increase of modified palatal height index. Interestingly, the bone depth In the interdental space tends to grow slightly with the increase of the modified palatal height index. To conclude, a narrow or high maxilla might be associated with a thin buccal bone plate in the area of the first molar and superior implantation conditions between the first and second molar. A study by [PERSON] et al. partially supports our results [17]. They found that bone thickness between the first and the second molar was greater in dolichofacial patients when compared to meso- and brachyfacial individuals. On the other hand, [PERSON] et al., in a similar study, did not observe significant differences in the IZC thickness among groups [16]. Inconsistencies in the above-mentioned investigations may result from the different methods of classification of patients to brachy-meso- and dolichofacial groups (based on the angle between SN and Go-Gn line or VERT index). It should be also accentuated that the above-mentioned measurements might be strongly affected by the morphology of the mandible. Consequently, the palatal index used in our study may provide more uninfluenced information regarding spatial conditions for the implantation of mini-screws. Considering the practical implications of the abovementioned research, it can be stated that in Polish patients, the mean bone depth at the area of infrazygomatic ridge rarely reaches a minimum recommended value of 6 mm.