## 4 Discussion
Nonetheless, we observed a good to excellent ICC for the individual landmarks. Therefore, larger possibilities of intermediary reference planes can occur in cases of higher SOL, with constructed reference points at different levels. In addition, our study also presented and compared the SOL for the MSP formed in the individual groups. The assessment of facial symmetry while establishing a treatment plan is based on the MSP. Thus, a change in the MSP can either underestimate or overestimate the degree of asymmetry. [PERSON] et al. recommended the use of a plane that is perpendicular to the horizontal reference plane to define the MSP [25]. A recently published study by [PERSON] et al. compared the groups of MSPs constructed with and without the FH plane. It suggested using MSPs that are perpendicular to the FH plane in clinical practice [26]. The horizontal plane should be defined in reference to the MSP to reduce the dependence of the latter on the FH plane [23]. However, the deviation of the median landmarks used to define the MSP can show an inherent variation, particularly for skeletal asymmetry. Furthermore, the bilateral Po and Or are not always coplanar [27]. Hence, a horizontal reference plane based on a predefined MSP will result in a new plane, with or without the traditional landmarks (Or and Po). Me deviation serves as a reliable marker for the assessment and surgical correction of asymmetry. This can be attributed to the close relationship between the direction of canting and deviation of the Me point [28]. In addition, it also impacts the perception of symmetry for laypersons and professionals. This calls for the need for surgical correction to restore the transverse facial balance [29]. Therefore, we used similar guidelines to measure Me deviation by keeping a constant MSP definition while altering the FH plane group-wise. However, there were significant differences in the amount of Me deviation. FH1 and FH2 showed a significantly lower deviation, which was in corroboration with the preliminary findings, thus showing no gross asymmetry. In contrast, the Me to MSP distance presented an asymmetry \(>\)4 mm in more than 5% cases while referencing FH3 and FH4. This overestimation represented a perceptible gross asymmetry of the face [30]. The findings of FH3 and FH4 were also observed by [PERSON] et al. [9], who did not find any difference in the measurements from Me to MSP between the two reference planes. However, their study did not include FH1 and FH2. Subsequently, the researchers did not conduct an intergroup comparison, as in the present study. Both over- and underestimation of the changes in the transverse dimension can potentially affect the overall treatment plan in the case of orthognathic surgery for a functional and aesthetic correction. The similarity between the asymmetry findings for FH1-2 and FH3-4 could be argued by the way a plane is defined in 3D coordinate space, using three points and a normal vector. Thus, it can be implied that the commonality of landmarks between the planes gives similar outcomes. In addition, measurements in FH1 and FH2 revealed a statistically significant difference in the bilateral transverse dimension from Ag. Despite the statistical insignificance of the absolute differences, the selection of either FH1 or FH2 can lead to the overestimation of the mandibular transverse width. Our study comprised retrospective data where gross asymmetry was ruled out during the preliminary examination. However, we observed variations in the results with changes in the definition of the FH plane (FH1-4). Thus, such variations will likely also present in patients diagnosed with gross asymmetry, which in terms of clinical implication can be seen as magnified deviations from the norms. In a maxillofacial clinical practice, cephalometric measurement forms an integral tool to obtain accurate values for treatment planning.