Predictive Equation for Construction of Anatomic Porion with Machine Porion as Reference Point.

AIM: The aim of the study was to find a relationship between anatomic porion (PoA) and machine porion (PoM) and to construct PoA with the help of machine porion. METHODOLOGY: About 200 pretreatment lateral roentgenic cephalograms were used for the study. Perpendicular distances of PoA and PoM were measured from Sella-Nasion (SN) plane and SN perpendicular plane. The results were tabulated. With the help of statistical analysis, predictive equation was derived to construct PoA and PoM. p-value was set at p < 0.05. RESULTS: Anatomic porion distance from SN was 24.35 ± 3.96 and from SN perpendicular was 12.89 ± 4.56. Distance of PoM from SN was 22.46 ± 4.20 and from SN perpendicular was 16.76 ± 4.89. Sexual dimorphism was also seen. CONCLUSION: There is a relationship between the PoM and PoA, thus, PoA, which is more reliable, can be constructed with the help of PoM, which is easy to reproduce. CLINICAL SIGNIFICANCE: To overcome the inherent limitations of PoA and PoM, the present study aimed to find a relationship between the two so as to easily construct PoA that is more reliable while taking advantage of the ease of reproducibility of PoM.

SIDS plane: A simple and innovative alternative to Frankfurt horizontal plane.

AIMS AND OBJECTIVES: To derive a new horizontal plane which can be a suitable alternative to Frankfurt horizontal plane (FH plane). MATERIALS AND METHODS: 200 pre-treatment lateral roentogenic cephalograms from patient records in the department of orthodontics and dentofacial orthopaedics were traced. The landmarks were identified and marked and the measurements were carried out. Patients with all skeletal relationships were included in the study. The angle formed between the lines connecting anatomic porion, orbitale and machine porion was measured and tabulated. Dimorphism between the genders if any was also evaluated. RESULTS: The mean angulation between the planes from the anatomic porion to orbitale to machine porion (PoA-Or-PoM) in our sample is 3.14 ± 2.17°. PoA to Or to PoM angulation for males is 2.57° and for females is 3.4°. CONCLUSIONS: SIDS plane also called as derived FH plane given here is a reliable and easily reproducible alternative to the FH plane.

Landmarks of the Frankfort horizontal plane : Reliability in a three-dimensional Cartesian coordinate system.

OBJECTIVES: The goal was to investigate whether the three-dimensional (3D) reliability of the landmarks defining the Frankfort horizontal plane (FH) can be enhanced by reducing variance with the help of nearby anatomical structures. METHODS: Twenty multislice computed tomography (MSCT) datasets of evidently symmetrical patients (11 female and 9 male patients, 6.1-16 years old) were selected from 695 datasets archived at our department. In the 3D reconstructions, we located the anthropometric landmarks orbitale and porion, then these were modified with the help of frontomalare temporale, radiculare and the most anterior border of the left and right external acoustic pore. The resultant orbitale* and porion* reference points for the Frankfort horizontal plane were then compared to the original landmarks. Statistical analysis was performed. RESULTS: The superior reliability in the sagittal y-axis and in the transversal x-axis of the new reference points was confirmed. Based on the covariance matrices, the mean maximum standard deviation (square root of the maximum eigenvalue) in the direction of maximum variance was reduced from 0.77/0.94 mm to 0.47/0.48 mm for left/right orbitale, and similar reductions from 0.85/0.92 mm to 0.29/0.30 mm were noted for left/right porion (p < 0.001 for all four points). Vertical reliability did not improve further. CONCLUSIONS: The modifications significantly reduced the variance of the orbitale and porion landmarks, thus, clearly increasing the three-dimensional reliability. Hence these optimized reference points are better suited to construct the FH, which arguably is an important spatial reference plane in orthodontics.

Positional symmetry of porion and external auditory meatus in facial asymmetry.

BACKGROUND: The porion (Po) is used to construct the Frankfort horizontal (FH) plane for cephalometrics, and the external auditory meatus (EAM) is to transfer and mount the dental model with facebow. The classical assumption is that EAM represents Po by the parallel positioning. However, we are sometimes questioning about the possible positional disparity between Po and EAM, when the occlusal cant or facial midline is different from our clinical understandings. The purpose of this study was to evaluate the positional parallelism of Po and EAM in facial asymmetries, and also to investigate their relationship with the maxillary occlusal cant. METHODS: The 67 subjects were classified into three groups. Group I had normal subjects with facial symmetry (1.05 ± 0.52 mm of average chin deviation) with minimal occlusal cant (<1.5 mm). Asymmetry group II-A had no maxillary occlusal cant (average 0.60 ± 0.36), while asymmetry group II-B had occlusal cant (average 3.72 ± 1.47). The distances of bilateral Po, EAM, and mesiobuccal cusp tips of the maxillary first molars (Mx) from the horizontal orbital plane (Orb) and the coronal plane were measured on the three-dimensional computed tomographic images. Their right and left side distance discrepancies were calculated and statistically compared. RESULTS: EAM was located 10.3 mm below and 2.3 mm anterior to Po in group I.  The vertical distances from Po to EAM of both sides were significantly different in group II-B (p = 0.001), while other groups were not. Interside discrepancy of the vertical distances from EAM to Mx in group II-B also showed the significant differences, as compared with those from Po to Mx and from Orb to Mx. CONCLUSIONS: The subjects with facial asymmetry and prominent maxillary occlusal cant tend to have the symmetric position of Po but asymmetric EAM. Some caution or other measures will be helpful for them to be used during the clinical procedures.

Positional symmetry of porion and external auditory meatus in facial asymmetry / 대한악안면성형재건외과학회지

BACKGROUND: The porion (Po) is used to construct the Frankfort horizontal (FH) plane for cephalometrics, and the external auditory meatus (EAM) is to transfer and mount the dental model with facebow. The classical assumption is that EAM represents Po by the parallel positioning. However, we are sometimes questioning about the possible positional disparity between Po and EAM, when the occlusal cant or facial midline is different from our clinical understandings. The purpose of this study was to evaluate the positional parallelism of Po and EAM in facial asymmetries, and also to investigate their relationship with the maxillary occlusal cant. METHODS: The 67 subjects were classified into three groups. Group I had normal subjects with facial symmetry (1.05 +/- 0.52 mm of average chin deviation) with minimal occlusal cant (<1.5 mm). Asymmetry group II-A had no maxillary occlusal cant (average 0.60 +/- 0.36), while asymmetry group II-B had occlusal cant (average 3.72 +/- 1.47). The distances of bilateral Po, EAM, and mesiobuccal cusp tips of the maxillary first molars (Mx) from the horizontal orbital plane (Orb) and the coronal plane were measured on the three-dimensional computed tomographic images. Their right and left side distance discrepancies were calculated and statistically compared. RESULTS: EAM was located 10.3 mm below and 2.3 mm anterior to Po in group I. The vertical distances from Po to EAM of both sides were significantly different in group II-B (p = 0.001), while other groups were not. Interside discrepancy of the vertical distances from EAM to Mx in group II-B also showed the significant differences, as compared with those from Po to Mx and from Orb to Mx. CONCLUSIONS: The subjects with facial asymmetry and prominent maxillary occlusal cant tend to have the symmetric position of Po but asymmetric EAM. Some caution or other measures will be helpful for them to be used during the clinical procedures.

Three-dimensional symmetry and parallelism of the skeletal and soft-tissue poria in patients with facial asymmetry.

OBJECTIVE: The purpose of this study was to examine the symmetry and parallelism of the skeletal and soft-tissue poria by three-dimensional (3D) computed tomographic (CT) imaging. METHODS: The locations of the bilateral skeletal and soft-tissue poria in 29 patients with facial asymmetry (asymmetric group) and 29 patients without facial asymmetry (symmetric group) were measured in 3D reconstructed models of CT images by using a 3D coordinate system. The mean intergroup differences in the anteroposterior and vertical angular deviations of the poria and their anteroposterior and vertical parallelism were statistically analyzed. RESULTS: The symmetric and asymmetric groups showed significant anteroposterior angular differences in both the skeletal and the soft-tissue poria (p = 0.007 and 0.037, respectively; Mann-Whitney U-test). No significant differences in the anteroposterior and vertical parallelism of the poria were noted (p ≤ 0.05; Wilcoxon signed-rank test). CONCLUSIONS: In general, the skeletal poria are parallel to the soft-tissue poria. However, patients with facial asymmetry tend to have asymmetric poria.

Three-dimensional symmetry and parallelism of the skeletal and soft-tissue poria in patients with facial asymmetry / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to examine the symmetry and parallelism of the skeletal and soft-tissue poria by three-dimensional (3D) computed tomographic (CT) imaging. METHODS: The locations of the bilateral skeletal and soft-tissue poria in 29 patients with facial asymmetry (asymmetric group) and 29 patients without facial asymmetry (symmetric group) were measured in 3D reconstructed models of CT images by using a 3D coordinate system. The mean intergroup differences in the anteroposterior and vertical angular deviations of the poria and their anteroposterior and vertical parallelism were statistically analyzed. RESULTS: The symmetric and asymmetric groups showed significant anteroposterior angular differences in both the skeletal and the soft-tissue poria (p = 0.007 and 0.037, respectively; Mann-Whitney U-test). No significant differences in the anteroposterior and vertical parallelism of the poria were noted (p < or = 0.05; Wilcoxon signed-rank test). CONCLUSIONS: In general, the skeletal poria are parallel to the soft-tissue poria. However, patients with facial asymmetry tend to have asymmetric poria.

The veraciry of orientation on upright lateral cephalometric radiographs / 医学研究生学报

Objective:To investigation the veracity of orientation on modified upright lateral cephalometric radiographs. Methods:Fifty upright lateral cephalometric radiographs were analysed randomly.Twenty-three subjects,who had standard radiographs, were taken with modified technique. The chracterics both of radiographs were compared. Results:The orientations of porion?FH plane and the superimpositions of left and right gonion point on modified standard radiographs were more veracity. Conclusion:The veracity of orientation on upright lateral cephalometric radiographs can be improved.