Three-dimensional finite element analysis of the deformation of the human mandible: a preliminary study from the perspective of orthodontic mini-implant stability / 대한치과교정학회지

OBJECTIVE: The aims of this study were to investigate mandibular deformation under clenching and to estimate its effect on the stability of orthodontic mini-implants (OMI). METHODS: Three finite element models were constructed using computed tomography (CT) images of 3 adults with different mandibular plane angles (A, low; B, average; and C, high). An OMI was placed between #45 and #46 in each model. Mandibular deformation under premolar and molar clenching was simulated. Comparisons were made between peri-orthodontic mini-implant compressive strain (POMI-CSTN) under clenching and orthodontic traction forces (150 g and 200 g). RESULTS: Three models with different mandibular plane angles demonstrated different functional deformation characteristics. The compressive strains around the OMI were distributed mesiodistally rather than occlusogingivally. In model A, the maximum POMI-CSTN under clenching was observed at the mesial aspect of #46 (1,401.75 microstrain [microE]), and similar maximum POMI-CSTN was observed under a traction force of 150 g (1,415 microE). CONCLUSIONS: The maximum POMI-CSTN developed by clenching failed to exceed the normally allowed compressive cortical bone strains; however, additional orthodontic traction force to the OMI may increase POMI-CSTN to compromise OMI stability.

Morphological characteristics of the upper airway and pressure drop analysis using 3D CFD in OSA patients / 대한치과교정학회지

OBJECTIVE: Obstructive sleep apnea (OSA) is a common disorder which is characterized by a recurrence of entire or partial collapse of the pharyngeal airway during sleep. A given tidal volume must traverse the soft tissue tube structure of the upper airway, so the tendency for airway obstruction is influenced by the geometries of the duct and characteristics of the airflow in respect to fluid dynamics. METHODS: Individualized 3D FEA models were reconstructed from pretreatment computerized tomogram images of three patients with obstructive sleep apnea. 3D computational fluid dynamics analysis was used to observe the effect of airway geometry on the flow velocity, negative pressure and pressure drop in the upper airway at an inspiration flow rate of 170, 200, and 230 ml/s per nostril. RESULTS: In all 3 models, large airflow velocity and negative pressure were observed around the section of minimum area (SMA), the region which narrows around the velopharynx and oropharynx. The bigger the Out-A (outlet area)/ SMA-A (SMA area) ratio, the greater was the change in airflow velocity and negative pressure. CONCLUSIONS: Pressure drop meaning the difference between highest pressure at nostril and lowest pressure at SMA, is a good indicator for upper airway resistance which increased more as the airflow volume was increased.

Factors influencing the axes of anterior teeth during SWA en masse sliding retraction with orthodontic mini-implant anchorage: a finite element study / 대한치과교정학회지

OBJECTIVE: With development of the skeletal anchorage system, orthodontic mini-implant (OMI) assisted en masse sliding retraction has become part of general orthodontic treatment. But compared to the emphasis on successful anchorage preparation, the control of anterior teeth axis has not been emphasized enough. METHODS: A 3-D finite element Base model of maxillary dental arch and a Lingual tipping model with lingually inclined anterior teeth were constructed. To evaluate factors influencing the axis of anterior teeth when OMI was used as anchorage, models were simulated with 2 mm or 5 mm retraction hooks and/or by the addition of 4 mm of compensating curve (CC) on the main archwire. The stress distribution on the roots and a 25000 times enlarged axis graph were evaluated. RESULTS: Intrusive component of retraction force directed postero-superiorly from the 2 mm height hook did not reduce the lingual tipping of anterior teeth. When hook height was increased to 5 mm, lateral incisor showed crown-labial and root-lingual torque and uncontrolled tipping of the canine was increased. 4 mm of CC added to the main archwire also induced crown-labial and root-lingual torque of the lateral incisor but uncontrolled tipping of the canine was decreased. Lingual tipping model showed very similar results compared with the Base model. CONCLUSION: The results of this study showed that height of the hook and compensating curve on the main archwire can influence the axis of anterior teeth. These data can be used as guidelines for clinical application.

Characteristics of posteroanterior cephalometric analysis in children with skeletal Class I malocclusion / 대한치과교정학회지

Three dimensional analysis of malocclusion and craniofacial deformation is essential for the successful orthodontic treatment. But the orthodontists are not familiar with diagnosis and treatment plane based on lateral cephalometric analysis. Since orthodontists do not posses a sufficient knowledge in standard value of posteroanterior cephalometric anaysis and of clinical importance for transverse jaw growth. In this study male(n=130) and female(n=171) aged from 6 to 16 and diagnosed as Class I malocclusion were selected to analysis width of cranium, maxilla and mandible on the posteroanterior cephalogram. The changes as a function of chronologic age and cervical vertebrae maturity index(CVMI) were examined. The proper regression model was selected by sex with polynominal regression models and method of variable selection. Mean of each measurements and 70% confidence interval of individual measurement according to age was assesed and a graphs were made. Results are as follows : 1. All the measurements for the width are gradually incresed as increase in chronologic age and CVMI. From the total amount of change between age 6 and 16, there is a tendency that mandibular width is broader than maxillary width and the width of male is broader than female. 2. There is no statistically significant sexual difference in Mx-Mn difference, Mx-Mn width differential, Mx/Mn ratio according to age and CVMI. 3. Mean of each measurement and 70% confidence interval of individual measurement according to age and sex were assessed and graphs were made for maxillary width, mandibular width, Mx-Mn difference, Mx/Mn ratio. 4. The width of maxilla and mandible in Korean children are broader than Western children during growth period.

Mandibular differential premolar extraction in growing patients / 대한치과교정학회지

The extraction for orthodontic treatment can be adopted for aligning crowded dentition, improving facial esthetics and solving a skeletal discrepancy as alternative for a surgical option. Mandibular second premolar extraction was often selected as treatment plan when there are very little or no space shortage in lower arch or limited retraction of the lower incisors was required. The primary object of this study was evaluate a pretreatment condition and examine the amount of tooth movement for a mandibular second premolar extraction in growing patients. Pretreatment and posttreatment lateral cephalograms of 14 cases that had their four first premolar extracted (4/4 group), 15 cases with upper first and lower second premolar extraction (4/5 group) were selected. Structural method superimposition was conducted to evaluate a difference of dental change between 4/4 and 4/5 group. The results were as follows, 1. Pretreatment factor for 4/4 extraction or 4/5 extraction choice included maxillary incisor axis to occlusal plane, Class II molar relationship, IMPA and interincisal angle. 2. The amount of molar anterior movement in 4/5 group was greater than that of 4/4 group(p<0.05). 3. There was no significant difference between 4/4 group and 4/5 group in aspects of maxillary tooth movement(p<0.05).

Changes in soft tissue profile after surgical correction of prognathic mandible / 대한치과교정학회지

The treatment plan for orthognathic surgery must be based on accurate predictions, and this can be produced the most esthetic results. Treatment of prognathic mandible in adult is usually orthognathic surgery using mandible set back, but mandible with retruded chin point os needed additional chin augmentation. In this case, the directions between mandible and chin point are different therefore, the prediction of soft tissue reactions must be modified. In this study, we materialize the patients who was taken orthognathic surgery due to prognathic mandible, 11each(Group A) was taken only Bilateral Sagittal Sprit Ramus Osteotomy (BSSRO), 9each(Group B) was taken additional advancement genioplasty. The lateral cephalometric radiography taken 8 months later after orthognathic surgery by this patients were used. The results of this study were as follows 1. The profile of lips was favorable after surgery due to upper lip to E-line became prominent and lower lip to E-line was retruded. 2. In both group, upper lip moved posteriorly and national angle was increased. 3. The ratio of the soft tissue profile change in POGs point to skeletal B point movement was 84% in group A and 66% in group B, and there was statistical significance between group A and group B. 4. Vertical movement of hard tissue points is decreased in group A.

Effects of fluoride on osteoclastic bone resorption during experimentally moved rat molars / 대한치과교정학회지

Orthodontic tooth movement requires remodelling of periodontal tissues, especially alveolar bone. Fluoride is known to be a potent inhibitor of osteoclastic bone resorption. The purpose of this study was to examine the effects of a consumption of fluoride on osteoclast numbers appearing on the pressure side of alveolar bones at experimental tooth movement. 40 male rats were exposed to 0, 10, 25 mg/kg/day of sodium fluoride(NaF) in their drinking water for up to 60 days. Orthodontic appliance were activated to mesially tip maxillary first molar with 50-70g. The rats were sacrificed at 1, 2, 4 days after initial activation. The number of osteoclast was counted in a 450 x 700 micrometer2 area interradicular septum on the pressure side of the maxillary first molar. The results were as follows, 1. There was significantly different osteoclast number between control group and 25 mg/kg/day group at all measured time. (p<0.05) 2. There was significantly different active bone-resorption area between control group and 25 mg/kg/day group except at 96 hours post activation. (p<0.05) 3. There was slight reduction of active bone-resorption area in control group from 48 hours to 96 hours but in both 10 mg/kg/day group and 25 mg/kg/day group a slight increase was observed from 48 hours to 96 hours.

A study on soft tissue facial profile changes in orthodontic treatment with four premolar extractions / 대한치과교정학회지

The purpose of this study was to evaluate the differences of soft tissue profile changes between the growing patients and the adult who had passed the growth peak, in orthodontic treatment with four premolar extraction. The results which was taken by correlating the soft tissue changes with hard tissue changes, lip thickness, molar relationship and arch length discrepancy in both groups was like the followings. 1. Significant hard tissue changes were decrease of VIs, Vii, U1PP, LIMP, HE and increase of HPog' in adults and decrease of Vls, Vii and increase of VA, VPog' and all the vertical measurements in adolescents. 2. Significant soft tissue changes were decrease of VLs, VIJ, and VILS in adults and increase of VSn, VSLS, VLs, VPog' and almost all vertical measurements in adolescents, and delta LsE, delta LiE in adults and delta LsE, delta LiE, delta LiSP and delta Mlang was also significant. 3. Correlation coefficient between delta VIs and delta VLs was the greatest in adults and the next was delta Ii/delta Li, delta Ii/delta ILS, delta ID/delta Li and delta ID/delta ILS. In contrast, al the vertical and horizontal measurements of hard and soft tissue in adolescents showed statistically significant corerlation. 4. There were differences in correlation between soft tissue changes and incisor inclination and retraction at both groups, but the lower lip, nasolabial angle and mentolabial angle were commonly less influenced by the hard tissue changes in both groups. 5. The thinner the upper lip was, the more the delta LsSP was in both groups, and the thinner the lower lip was, the more the delta LiE and delta LiSP was in adolescents. 6. Molar relationship didn't influence the soft tissue profile changes. 7. Arch length discrepancy didn't influence the soft tissue profile changes.

A study on the effect of treatment in the skeletal Class III malocclusion patient with anterior crossbite / 대한치과교정학회지

The purpose of this study was to investigate the treatment effects on anterior crossbite patients using chin cap and labiolingual arch appliance. In the present study, I statistically evaluated measurement values on a cephalogram before and after treatment form twenty anterior crossbite cases. The results were as follows: 1. In the craniofacial patterns, cranial base increased after treatment. 2. In the maxillo-mandibular relationship, ANB and Facial convexity significantly increased. 3. In the denture patterns, occlusal plane, U1 to FH and Overjet significantly increased. On the contrary overbite decreased significantly. Lower incisors inclined lingually. 4. In the soft tissue profile changes, lower lip protrusion was significantly improved.