Correction of positional change of frontal cephalometric landmarks caused by vertical head rotation / 대한치과교정학회지

OBJECTIVE: Superimposition of frontal cephalograms cannot be performed when the cephalograms are taken with different vertical head rotations. The purpose of the present study was to evaluate the validity of correcting the positional change of frontal cephalometric landmarks caused by vertical head rotation. METHODS: In 30 adult individuals, frontal and lateral cephalograms were taken at a 90degrees angle. Geometric principles of radiography were used to calculate the possible vertical and horizontal landmark changes if the head should be rotated down 5degrees about an ear rod axis. The calculated changes were then compared with cephalometric changes measured on frontal cephalogram actually taken with the head rotated down 5degrees. RESULTS: When the frontal cephalograms were taken with the head rotated down 5degrees about an ear rod axis, significant changes in the vertical position of the landmarks occurred, particularly in the landmarks located farther anteriorly from the ear rod axis. The comparison of calculated changes and real cephalometric changes showed that the differences were less than 0.4 mm in the vertical direction and less than 0.2 mm in the horizontal direction. The differences between calculated and real changes were smaller in the landmarks less affected by vertical head rotation. CONCLUSIONS: Even when frontal cephalograms are taken at different vertical head rotations, the concomitant changes in the position of the landmarks can be corrected through calculation using the geometric principle of radiography as long as frontal and lateral cephalograms are taken perpendicular to each other.

Use of Head Posture Aligner to improve accuracy of frontal cephalograms generated from cone-beam CT scans / 대한치과교정학회지

OBJECTIVE: The purpose of the present study was to evaluate the effectiveness of the use of Head Posture Aligner (HPA) during cone-beam computed tomography (CBCT) scan in generation of frontal cephalograms using 3D CBCT images. METHODS: CBCT scans and frontal cephalograms were made in 30 adult individuals. While a couple of CBCT scan was made for one subject, one was made with conventional method, without use of HPA, the other was acquired with the use of HPA. After creation of virtual frontal cephalogram from each 3D CBCT image, it was traced and compared with the tracing of real frontal cephalogram. RESULTS: In the comparison of the measurements, the virtual cephalograms with the use of HPA did not show statistically significant differences with the real cephalograms whereas the virtual cephalograms without the use of HPA presented significant differences with real cephalograms in many measurements. In the correlation analysis with the measurements of the real cephalograms, the virtual cephalograms with the use of HPA showed higher correlations in all measurements than the virtual cephalograms without the use of HPA. CONCLUSIONS: Measurements from CBCT-generated cephalograms become similar to those from real cephalograms with the use of HPA during CBCT scan. Thus, the use of HPA is suggested during the CBCT scan in order to construct accurate virtual frontal cephalograms using 3D CBCT images.

Prediction of frontal soft tissue changes after mandibular surgery in facial asymmetry individuals / 대한치과교정학회지

OBJECTIVE: To aid the development of a frontal image simulating program, we evaluated the soft tissue frontal changes in relationship to movement of hard tissue with orthognathic surgery of facial asymmetry patients. METHODS: Preoperative and postoperative frontal cephalograms and frontal view photographs of 45 mandibular surgery patients with facial asymmetry were obtained in a standardized manner. Vertical and horizontal changes of hard tissue and soft tissue were measured from cephalograms and photographs, respectively. Soft tissue change in result to hard tissue change was then analyzed. RESULTS: Both vertical and horizontal correlation analysis showed a weak relationship between the changes. Hard tissue points that were picked for 1:1 mean ratio with soft tissue points did not show any significant relevance. For each soft tissue change, regressive equation was formulated by stepwise multiple regression analysis, and the equation for soft tissue Menton was most reliable in predicting changes. Both vertical and horizontal hard tissue changes were used together in prediction of vertical or horizontal soft tissue change. CONCLUSIONS: The results suggest that computerized image simulation using regression analysis may be of help for prediction of soft tissue change, while 1:1 mean ratio method is not useful.

Correction of mandibular ramus height with frontal and lateral ramal inclinations in cephalograms and its effects on diagnostic accuracy of asymmetry / 대한치과교정학회지

OBJECTIVE: Defining right and left side differences in mandibular ramus height is one of the key elements in the diagnosis of facial asymmetry. The purpose of the present study was to evaluate the effect of correction of ramus height with frontal and lateral ramal inclinations (FRI and LRI) in 2-dimensional cephalograms and observe how this affects the diagnostic accuracy of asymmetry. METHODS: Frontal and lateral cephalograms were obtained in 40 individuals with chin deviation. FRI and LRI were measured on each side and ramus height measurement was corrected with these inclinations using Pythagorean's theorem. The results of diagnosis before and after correction on cephalograms were compared with the results in 3D CT images. RESULTS: Both FRI and LRI showed greater values in the contralateral side than in the chin-deviated side and these contributed to an increase in the right and left side ramus height differences. After comparison of diagnostic results before and after correction on cephalograms with the results on 3D CT images, the sensitivity increased significantly (from 74 to 94 %) whereas the specificity decreased (from 44 to 22 %). Overall accuracy increased from 68 to 78 % with the correction using FRI and LRI. CONCLUSIONS: The results of the present study indicate that correction of ramus height with FRI and LRI is useful for an accurate diagnosis of facial asymmetry on frontal cephalograms.

Three-dimensional CT image study on the correction of gonial angle width enlarged on frontal cephalogram / 대한치과교정학회지

Enlargement is an inherent property of X-rays which occurs when straight lines diverge from small a focal spot. The purpose of the present study was to evaluate the validity of the correction of gonial angle width enlarged on frontal cephalogram, using frontal and lateral cephalograms taken orthogonally from each other. In 40 adult individuals, frontal and lateral cephalograms were taken at a 90 degrees angle using the Head Posture Aligner. The angle width was measured on the frontal cephalogram and subsequently, the corrected angle width was calculated using the magnification rate of two cephalograms. Measured and corrected angle widths were compared with the measurement from the 3D CT image. The measurement on the frontal cephalogram showed a 9.10 mm of enlargement on average, ranging from 7.92 to 11.31 mm. Corrected angle width measurement showed a 0.14 mm difference with the 3D CT image measurement, which was not statistically significant. The results of the study indicate that actual angle width can be approached through calculation using frontal and lateral cephalograms taken orthogonally with the help of the Head Posture Aligner. The study also showed that the magnitude of correction error did not show a significant correlation with the amount of menton deviation, and it suggests that the present correction method is valid even in individuals with severe facial asymmetry.

Stability and Relapse of Facial Asymmetry following Orthognathic Surgery in Patients with Asymmetric Prognathism

The purpose of this study is to evaluate the amount of correction and relapse after orthognathic surgery in patients with facial asymmetry and prognathism by means of the frontal cephalogram. Out of twenty prognathism patients who had been diagnosed as having skeletal facial asymmetry in need of orthognathic operation at our institute during last 6 years, only thirteen patients with pre-existing pre-operative(T0), immediate postoperative (T1) and long term follow up(T2) frontal cephalograms were included in the study. The population was divided according to the kind of surgical operation and severity of asymmetry. The midline sagittal reference line (MSR) was drawn and four basic landmarks were marked on the frontal T0, T1 and T2 cephalograms. Radiographic facial asymmetry was found most obviously in the lower jaw(Deviation from MSR: 2.21mm at ANS, 8.34mm at menton). Facial asymmetry was corrected to minimal degree(1.34 at menton) with orthognathic procedures. On long-term follow up, the correction of deviation was maintained as 1.98mm. The relapse rate was 24.1% at menton. The contributing factor was searched and the amount of asymmetry correction and the amount of prognathism correction proved to have statistical significance (p<0.05). In conclusion, asymmetry could be corrected with orthognathic procedures, which could be maintained with minimal degree of relapse. However, in preoperative planning, the degree of relapse should be considered to maximize the aesthetic outcome.

Frontal cephalogram study on the natural head position of facial asymmetry patients / 대한치과교정학회지

The purpose of this study was to find the characteristics of the frontal natural head position(NHP) of patients with facial asymmetry, and to contribute to the diagnosis of facial asymmetry in the clinical examination of orthodontic patients. Twenty adult patients who had apparent facial asymmetry and no severe sagittal skeletal discrepancy were selected as the asymmetry group, and 21 young adults who had symmetric faces were selected as the symmetry group. Frontal cephalograms were obtained in the state of NHP using a pivot-mounted fluid level device. The degree of the menton deviation was defined as the angle between the line drawn through crista galli and anterior nasal spine and the line drawn through crista galli and menton. The following angles were measured and each of them was compared with the degree of the menton deviation: one is the angle between the true vertical line and the supra-orbital line which is a tangent line to the extreme cranial point on the supra-orbital margin, and the other is the angle between the true vertical line and the cervical line drawn through the midpoint of atlas and the 4th cervical vertebra. Through the statistical analysis, following results were obtained. 1. The angle between the supra-orbital line and the true vertical line was much more deviated from the right angle in the asymmetry group than in the symmetry group. 2. The angle between the cervical line and the true vertical line in the asymmetry group showed greater tendency than in the symmetry group, but the difference was not statistically significant. 3. In the asymmetry group, the degree of the menton deviation was positively correlated with the angle between the supra-orbital line and the true vertical line. The above results suggest that facial asymmetry patients show the tendency to have the tilted NHP to compensate the deviation of menton position.