Observation of trabecular changes of the mandible after orthognathic surgery using fractal analysis

OBJECTIVES: This study sought to evaluate trabecular changes in the mandible using fractal analysis and to explain the transient osteopenia related to rapid orthodontic tooth movement after orthognathic surgery. MATERIALS AND METHODS: Panoramic radiographs were taken of 26 patients who underwent bilateral sagittal split ramus osteotomy. Radiographs taken before the surgery and 1 month after surgery were overlapped, and 40x40 pixel square regions of interest were selected near the mandibular canines and 1st molars. After the image processing procedure, the fractal dimension was calculated using the box-counting method. RESULTS: Fractal dimension after orthognathic surgery decreased in a statistically significant manner (P<0.05). The change in fractal dimension on the canine side had greater statistical significance as compared to that seen on the 1st molar side. CONCLUSION: This study found that bone density decreases after orthognathic surgery due to transient osteopenia related to the regional acceleratory phenomenon. This result can provide a guide to evaluating orthodontic tooth movement after orthognathic surgery.

Correlation between menton deviation and dental compensation in facial asymmetry using cone-beam CT / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to evaluate the correlation between menton deviation and dental compensation in facial asymmetry. METHODS: Tooth axis and distance of first molar and canine to the reference plane were investigated by cone-beam computerized tomography. The subjects consisted of 50 patients with asymmetric mandibles (male 21, female 29, mean age 24.3 years). Control groups were also assessed (male 11, female 9, mean age 25.6 years). Nine measurements (5 linear measurements and 4 angular measurements) were measured in order to evaluate the correlation between menton deviation and the linear and angular difference of first molar and canine in the deviated and none-deviated sides using the defined MPR images. The differences between deviated and non-deviated side, according to menton deviation, were statistically analyzed using stepwise multiple regression analysis. RESULTS: From the result, Menton deviation was negatively correlated with mandibular first molar's angular measurement (Delta Angle LM6-Mn plane (dev.-ndev.)) and positively with maxillary fist molar's angular measurement (Delta Angle UM6-FH plane (dev.-ndev.)) (p<0.01). Two angular measurements (Delta Angle LM6-Mn plane (dev.-ndev.), Delta Angle UM6-FH plane (dev.-ndev.)) explained the variability in menton deviation with a significant r2 value of 0.589. CONCLUSIONS: This study suggests that the tooth axis of upper and lower first molars leans towards the deviated side of Menton when there is mandibular asymmetry with Menton deviation.

Factors that influence treatment duration for patients with palatally impacted maxillary canines / 대한치과교정학회지

OBJECTIVE: The aim of this study was to determine the relationship between the status of a unilateral palatally impacted maxillary canine (as seen on the panoramic radiograph) and the orthodontic treatment duration. METHODS: A total of 36 subjects were chosen (8 males and 28 females, 13.7 +/- 2.5 years). All patients had undergone orthodontic traction of the impacted canine after a closed flap surgery. The position of impacted canine on the panoramic radiograph was traced and calculated with regard to the treatment duration. RESULTS: The canine overlap over the lateral incisor (COGr) had significant statistical difference between the short-term and the long-term treatment duration groups (divided by average treatment time of 21 months) (p < 0.05). Multiple regression indicated that the variables of significance (with treatment duration as the dependent variable) were the canine vertical height from the occlusal plane (HCV, r(2) = 0.115; p < 0.05) and the mandibular anterior width (MnDW, r(2) = 0.142; p < 0.05). The treatment duration, the canine angle to the incisor midline (CA), and HCV decreased from primary dentition (under 12 yrs) to permanent dentition (15 yrs). Howerer, these increased again at the adolescent ages (over 16 yrs). CONCLUSION: These findings suggested that orthodontic treatment of a palatally impacted canine would show good prognosis at an age of early permanent dentition with the canine showing smaller CA and HCV.