Youn-Sic Chun

Effective en-masse retraction design with orthodontic mini-implant anchorage: A finite element analysis

INTRODUCTION The strategic design of an appliance for correcting a bialveolar protrusion by using orthodontic mini-implant anchorage and sliding mechanics must take into account the position and height of the mini-implant, the height of the anterior retraction hook and compensating curve, and midline vertical traction. In this study, we used finite element analysis to examine effective en-masse retraction with orthodontic mini-implant anchorage and sought to identify a better combination of the above factors. METHODS Base models were constructed from a dental study model. Models with labially and lingually inclined incisors were also constructed. The center of resistance for the 6 anterior teeth in the base model was 9 mm superiorly and 13.5 mm posteriorly from the midpoint of the labial splinting wire. The working archwires were assumed to be 0.019 x 0.025-in or 0.016 x 0.022-in stainless steel. The amount of tooth displacement after finite element analysis was magnified 400 times and compared with central and lateral incisor and canine axis graphs. RESULTS AND CONCLUSIONS The tooth displacement tendencies were similar in all 3 models. The height of the anterior retraction hook and the placement of the compensating curve had limited effects on the labial crown torque of the central incisors for en-masse retraction. The 0.016 x 0.022-in stainless steel archwire showed more tipping of teeth compared with the 0.019 x 0.025-in archwire. For high mini-implant traction and 8-mm anterior retraction hook condition, the retraction force vector was applied above the center of resistance for the 6 anterior teeth, but no bodily retraction of the 6 anterior teeth occurred. For high mini-implant traction, 2-mm anterior retraction hook, and 100-g midline vertical traction condition, the 6 anterior teeth were intruded and tipped slightly labially.

Volumetric Changes in the Upper Airway After Bimaxillary Surgery for Skeletal Class III Malocclusions: A Case Series Study Using 3-Dimensional Cone-Beam Computed Tomography

PURPOSE Postsurgical changes of the airway have become a great point of interest and often have been reported to be a predisposing factor for obstructive sleep apnea after mandibular setback surgery. The purpose of this study was to evaluate the 3-dimensional volumetric changes in the upper airway space of patients who underwent bimaxillary surgery to correct Class III malocclusions. MATERIALS AND METHODS This study was performed retrospectively in a group of patients who underwent bimaxillary surgery for Class III malocclusion and had full cone-beam computed tomographic (CBCT) images taken before surgery and 1 day, 3 months, and 6 months after surgery. The upper and lower parts of the airway volume and the diameters of the airway were measured from 2 different levels. Presurgical measurements and the amount of surgical correction were evaluated for their effect on airway volume. Data analyses were performed by analysis of variance and multiple stepwise regression analysis. RESULTS The subjects included 21 patients (6 men and 15 women; mean age, 22.7 yrs). The surgeries were Le Fort I impaction (5.27 ± 2.58 mm impaction from the posterior nasal spine) and mandibular setback surgery (9.20 ± 4.60 mm set back from the pogonion). No statistically significant differences were found in the total airway volume for all time points. In contrast, the volume of the upper part showed an increase (12.35%) and the lower part showed a decrease (14.07%), with a statistically significant difference 6 months after surgery (P < .05). Predictor variables affecting the upper and lower parts of the airway volume were presurgical A point to Nasion-perpendicular (A to N-perp) and vertical surgical correction of the pogonion and the posterior nasal spine (P < .05). CONCLUSIONS Bimaxillary surgery for the correction of Class III malocclusion affected the morphology by increasing the upper part and decreasing the lower part of the airway, but not the total volume.

Comparison of tooth displacement between buccal mini-implants and palatal plate anchorage for molar distalization: a finite element study

The purposes of this study were to mechanically evaluate distalization modalities through the application of skeletal anchorage using finite element analysis. Base models were constructed from commercial teeth models. A finite element model was created and three treatment modalities were modified to make 10 models. Modalities 1 and 2 placed mini-implants in the buccal side, and modality 3 placed a plate on the palatal side. Distalization with the palatal plate in modality 3 showed bodily molar movement and insignificant displacement of the incisors. Placing mini-implants on the buccal side in modalities 1 and 2 caused the first molar to be distally tipped and extruded, while the incisors were labially flared and intruded. Distalization with the palatal plate rather than mini-implants on the buccal side provided bodily molar movement without tipping or extrusion. It is recommended to use our findings as a clinical guide for the application of skeletal anchorage devices for molar distalization.

Protraction of mandibular second and third molars into missing first molar spaces for a patient with an anterior open bite and anterior spacing

In a young woman, aged 18 years 8 months, who had an anterior open bite and anterior spacing, the right and left mandibular first molar extraction spaces were closed by protraction of the second and third molars without reciprocal retraction of the incisors and the premolars. The amounts of protraction for the second molars were 12 mm on the right side and 11 mm on the left side. Two miniscrews were inserted into the mesiobuccal side of the edentulous spaces, and 2 more screws were inserted into the anterior sites after removing previous miniscrews. In addition, 4 miniscrews were inserted into the buccal and palatal sides between the first and second maxillary molars to intrude the maxillary posterior teeth, which had extruded into the missing mandibular spaces. Careful biomechanical consideration was used to prevent extrusion of the molars and worsening of the anterior open bite from protraction of the posterior teeth. Ultimately, the anterior open bite was corrected by both intrusion of the maxillary molars and extrusion of the maxillary anterior teeth. Excellent occlusion and correction of the anterior open bite were achieved without tipping, rotation of the posterior teeth, or other problems. The right mandibular third molar, which had been impacted at the beginning of treatment, erupted into the second molar space and functioned properly. At the 1-year follow-up examination, the patient had a slight anterior open bite, but closure of the first molar extraction spaces was well maintained.

Finite element modeling technique for predicting mechanical behaviors on mandible bone during mastication

PURPOSE The purpose of this study was to propose finite element (FE) modeling methods for predicting stress distributions on teeth and mandible under chewing action. MATERIALS AND METHODS For FE model generation, CT images of skull were translated into 3D FE models, and static analysis was performed considering linear material behaviors and nonlinear geometrical effect. To find out proper boundary and loading conditions, parametric studies were performed with various areas and directions of restraints and loading. The loading directions are prescribed to be same as direction of masseter muscle, which was referred from anatomy chart and CT image. From the analysis, strain and stress distributions of teeth and mandible were obtained and compared with experimental data for model validation. RESULTS As a result of FE analysis, the optimized boundary condition was chosen such that 8 teeth were fixed in all directions and condyloid process was fixed in all directions except for forward and backward directions. Also, fixing a part of mandible in a lateral direction, where medial pterygoid muscle was attached, gave the more proper analytical results. Loading was prescribed in a same direction as masseter muscle. The tendency of strain distributions between the teeth predicted from the proposed model were compared with experimental results and showed good agreements. CONCLUSION This study proposes cost efficient FE modeling method for predicting stress distributions on teeth and mandible under chewing action. The proposed modeling method is validated with experimental data and can further be used to evaluate structural safety of dental prosthesis.

Condylar Positional Changes Up to 12 Months After Bimaxillary Surgery for Skeletal Class III Malocclusions

PURPOSE Postsurgical changes in the condylar position are of great importance to surgical stability, especially in asymmetric double-jaw surgery. The aims of this study were to evaluate positional changes of the condyle up to 12 months after surgery in patients with Class III malocclusion and to identify the factors affecting postsurgical condylar position. MATERIALS AND METHODS The study included 33 adult patients diagnosed with skeletal Class III malocclusion who underwent bimaxillary surgery and had full cone-beam volumetric imaging (CBVI) records up to 1 year after surgery. The CBV images were obtained before surgery and 2 weeks, 3 months (T2), 6 months (T3), and 12 months after surgery. Condyles with deviated and nondeviated sides were examined separately regardless of the degree of asymmetry. Analyses of variance and multiple regression analysis were performed to identify factors that could affect the position of the mandibular condyles. RESULTS The condyles exhibited anterior displacement at T2, which returned to a more distal position afterward in the axial view, and an inward rotation in the coronal view up to T3. From the sagittal view, the deviated and nondeviated condylar sides rotated forward and remained stable after T2. The degree of menton deviation affected the angle of condylar rotation (horizontal angle). CONCLUSION The results of this study suggest that condyles tend to move in a certain direction, and this can influence postsurgical relapse up to 6 months after surgery. However, they remain relatively stable afterward.

Factors controlling anterior torque with C-implants depend on en-masse retraction without posterior appliances: biocreative therapy type II technique.

INTRODUCTION Our objective was to evaluate the factors that affect effective torque control during en-masse anterior retraction by using intrusion overlay archwire and partially osseointegrated C-implants as the exclusive sources of anchorage without posterior bonded or banded attachments. METHODS Base models were constructed from a dental study model. No brackets or bands were placed on the posterior maxillary dentition during retraction. Different heights of the anterior retraction hooks to the working segment archwire and different intrusion forces with an overlay archwire placed in the 0.8-mm diameter hole of the C-implant were applied to generate torque on the anterior segment of the teeth. The amount of tooth displacement after finite element analysis was exaggerated 70 times and compared with tooth axis graphs of the central and lateral incisors and the canine. RESULTS The height of the anterior retraction hook and the amount of intrusion force had a combined effect on the labial crown torque applied to the incisors during en-masse retraction. The difference of anterior retraction hook length highly affected the torque control and also induced a tendency for canine extrusion. CONCLUSIONS Three-dimensional en-masse retraction of the anterior teeth as an independent segment can be accomplished by using partially osseointegrated C-implants as the only source of anchorage, an intrusion overlay archwire, and a retraction hook (biocreative therapy type II technique).

Three-dimensional analysis of tooth movement after intrusion of a supraerupted molar using a mini-implant with partial-fixed orthodontic appliances

OBJECTIVE To evaluate three-dimensional (3D) positional changes of an intruded tooth, a neighboring tooth, and a tooth connected to a mini-implant following intrusion of a single supraerupted molar, using a mini-implant with partial-fixed orthodontic appliances. MATERIALS AND METHODS The study consisted of 14 adult patients (two males and 12 females, mean age 41.9 years) with a supraerupted molar due to loss of an antagonist. Intrusion was performed using a mini-implant with a partial strap-up. The mean treatment time was 11.9 months, and the mean retention time was 23.3 months. To quantify the positional changes of the teeth, 3D models using a laser-based, dental scanning system and 3D software at pretreatment, posttreatment, and retention were oriented in a coordinate system and superimposed using nonmoved teeth as references. The changes on the x-, y-, and z-axes were measured at the tip of each cusp in the involved teeth. RESULTS A supraerupted molar was intruded by a mean amount of 1.35 ± 0.48 mm and was well maintained during the retention period. The overall change in the neighboring tooth was insignificant, although it showed opposite movement compared to the intruded tooth during the intrusion. The tooth connected to a mini-implant exhibited a secure anchorage. CONCLUSION 3D analysis showed the detailed positional changes of each tooth, and the involved molars were well maintained after intrusion.

Factors controlling anterior torque during C-implant-dependent en-masse retraction without posterior appliances

INTRODUCTION Our objective was to evaluate the factors that affect effective torque control during en-masse incisor and canine retraction when using partially osseointegrated C-implants (Cimplant, Seoul, Korea) as the exclusive source of anchorage without posterior bonded or banded appliances. METHODS Base models were constructed from a dental study model. No brackets or bands were placed on the maxillary posterior dentition during retraction. The working archwire was modeled by using a 3-dimensional beam element (ANSYS beam 4, Swanson Analysis System, Canonsburg, Pa) with a cross section of 0.016 × 0.022-in stainless steel. Different heights of anterior retraction hooks and different degrees of gable bends were applied to the working utility archwire that was placed into the 0.8-mm diameter hole of the C-implant to generate anterior torque on the anterior segment of the teeth. The amount of tooth displacement after finite element analysis was exaggerated 70 times and compared with tooth-axis graphs of the central and lateral incisors and the canine. RESULTS The height of the anterior retraction hook and the degree of the gable bend had a combined effect on the labial crown torque applied to the incisors during en-masse retraction. By using 30° gable bends and the longest hook, lingual root movement of the 6 anterior teeth occurred. By using 20° gable bends, the 6 anterior teeth showed a translation tendency during retraction. CONCLUSIONS Three-dimensional en-masse retraction of the 6 anterior teeth can be accomplished by using partially osseointegrated C-implants as the only source of anchorage, gable bends, and a long retraction hook (biocreative therapy type I technique).

Differences in molar relationships and occlusal contact areas evaluated from the buccal and lingual aspects using 3-dimensional digital models

Objective The aims of this study were to use a 3-dimensional (3D) system to compare molar relationship assessments performed from the buccal and lingual aspects, and to measure differences in occlusal contact areas between Class II and Class I molar relationships. Methods Study casts (232 pairs from 232 subjects, yielding a total of 380 sides) were evaluated from both the buccal and lingual aspects, so that molar relationships could be classified according to the scheme devised by Liu and Melsen. Occlusal contact areas were quantified using 3D digital models, which were generated through surface scanning of the study casts. Results A cusp-to-central fossa relationship was observed from the lingual aspect in the majority of cases classified from the buccal aspect as Class I (89.6%) or mild Class II (86.7%). However, severe Class II cases had lingual cusp-to-mesial triangular fossa or marginal ridge relationships. Mean occlusal contact areas were similar in the Class I and mild Class II groups, while the severe Class II group had significantly lower values than either of the other 2 groups (p < 0.05). Conclusions Buccal and lingual assessments of molar relationships were not always consistent. Occlusal contact areas were lowest for the Class II-severe group, which seems to have the worst molar relationships - especially as seen from the lingual aspect.