Stress analysis of multiloop edgewise arch wire with various degree of tip back bend : a study using the finite element method / 대한치과교정학회지

This study have been carried out to find out the mechnical effect of Multiloop Edgewise Arch Wire(MEAW) making use of the finite element method. The tip back bend of MEAW taken in this analysis is 5degrees,12degrees and 15degrees. In addition, Class II or up & down elastic is applied to find out stress distribution and their values in PDL. A adult male of normal was selected to create the models of teeth and PDL. And the model of MEAW was also created using commercial finite element code (ANSYS version 5.2). The MEAW is forcibly engaged with a class II or up & down elastic, to determine the initial stress generated in PDL. Comparing the compressive and tensile stress at each reference-planes, following results are obtained. 1. When a MEAW of 5degrees, 10degrees, 15degrees tip back bend was engaged with Class II or up & down elastic, the distribution of compressive, tensile stress in entire PDL is similar in each case. 2. The values of compressive and tensile stress in PDL is higher in 15degrees tip back bend case than in 10degrees or 5degrees tip back bend case. 3. In the distal PDL of 1st and 2nd molar, compressive stress appears. The compressive area is more wide and its values is higher in PDL 2nd molar than those in 1st molar. The compressive area and its values become more wide and higher according to the increase of the tip back bend. 4. The value of compressive stress are comparatively smaller in PDL of molars than those in premolars. 5. Comparing class II and up & down elastic case, tensile stress values in anterior teeth PDL are smaller and their distribution is more wide in up & down elastic case than class II elastic case. On another hand, there is no difference in distribution and stress values in PDL of posterior teeth between two cases. 6 Comparing the tensile area in PDL of anterior teeth, tensile stress values are maximum in PDL of canine.

Three dimensional finite element analysis of the phenomenon during distal en masse movement of the maxillary dentition / 대한치과교정학회지

This study was designed to analysis the displacement and stress distribution of individual tooth by orthodontic force during distal en masse movement of the maxillary dentition. In this study, three dimensional finite element analysis was used. Author made the finite element model of maxillary teeth, periodontal ligament, alveolar bone and bracket with anatomic and physiologic characteristics on computer. Author analysed and evaluated the displacement and stress distribution of individual tooth when extraoral force, Class II intermaxillary elastics, ideal arch wire, MEAW and tip back bend were used for distal en masse movement of the maxillary dentition. These analyses were also applied in the case of the maxillary second molar were not extracted. Author compared the results of the cases which maxillary second molar were extracted or not. The results were expressed quantitatively and visually. Author obtained following results, 1. When anterior headgear was applied, the posterior translation, posterior tipping, and vertical displacement of teeth were produced more in the anterior segment of the dentition. 2. When Class II intermaxillary elastics were applied in the ideal arch wire, the teeth disp acement were usually produced in the anterior segment. But when tip back bend were added in the ideal arch, the orthodontic force produced by elastics were transmitted to the posterior segment. As increasing the tip back bend, posterior translation and lingual tipping of anterior teeth were decreased, posterior translation and tipping displacement of posterior teeth were increased, and extrusion of anterior teeth by Class II elastics were decreased. 3. When MEAW and Class II elastics were applied, the teeth movement were similar with the case of ideal arch wire and Class II elastics, but more small and uniform teeth displacement were produced. Compared with the ideal arch wire, posterior tipping of the posterior segment were more produced than lingual tipping displacement of the anterior segment. 4. When the maxillary second molar without orthodontic appliance existed, the displacement of maxillary first molar were decreased.

Three dimensional finite element analysis for reaction to molar uprighting spring / 대한치과교정학회지

The purpose of this study was to investigate the stress distribution and tooth displacement at the initial phase produced by 5 types of molar uprighting springs using finite element method. The three dimensional finite element model of lower dentition, bone and springs was composed of 5803 elements and 2071 nodes. The results were as follows: 1. In case of helical spring and root spring, intrusion of lower canine and first premolar were observed and distal tipping, translation and extrusion of lower second molar were observed. 2. In case of T-loop, modified T-loop and box loop, intrusion and distal translation of lower second premolar were observed, and the largest crown distal tipping and translation of lower second molar were observed in T-loop and the smallest were observed in box loop. 3. In case of T-loop with cinch-back, crown distal tipping and translation of lower second molar were decreased, but extrusion was also decreased. 4. With increase of activation in T-loop, mesial translation and crown distal tipping of lower second molar were increased and edentulous space was closing, but distal translation of second premolar was also increased. 5. With increase of tip-back bend in T--loop, distal tipping and translation of lower second molar were increased, but extrusion was also increased more largely.

A photoelastic study on the initial stress distribution of the molar anchoring spring(MAS) during retraction of the maxillary canine / 대한치과교정학회지

The efficiency of maxillary canine retraction by means of sliding mechanics along an 0.016 continuous labial arch and an 0.009 inch in diameter with a lumen of 0.030 inch NiTi closed coil spring was compared with that using the same NiTi closed coil spring and Molar Anchoring Spring(MAS) which was designed by author. MAS was made of .017" X .025" TMA wire and was given 60 degree tip-back bend on the wire close to the molar tube. This study was designed to investigate molar and canine root control during retraction into an extraction site with continuous arch wire system. Two techniques were tested with a continuous arch model embedded in a photoelastic resin. A photoelastic model was employed to visualize the effects of forces applied to canine and molar by two retraction mechanics. With the aid of polarized light, stresses were viewed as colored fringes. The photoelastic overview of the upper right quadrant showed that stress concentrations were observed in its photoelastic model. The obtained results were as follows. 1. Higher concentration of compression can be seen clearly at the distal curvature of the canine and mesial curvature of the molar and premolar when NiTi closed coil spring was applied only, which means severe anchorage loss of the molar and uncontrolled tipping of the canine. 2. The least level compression was presented at the mesial root area of the molar and premolar, and mesial root area of the canine when NiTi closed coil spring and MAS were used simultaneously. Especially mesial alveolar crest region of the canine was shown moderate level of compression that means MAS can be used as a appliance for anchorage control and prevention of canine extrusion and uncontrolled tipping during canine retraction.

A photoelastic study on the initial stress distribution of 3 types TMA multi-vertical loop arch wire / 대한치과교정학회지

Multi -Vertical Loop Arch Wire(MVLAW) is a kind of appliance for uprighting the mesially inclined posterior teeth axes simultaneously. In this study MVLAW was classified as 3 types by modifing the vertical loop design and named type A, B and C. Each MVLAW was fabricated from .017" x .025" TMA wire and preactivated at the distal end of the open vertical loop with 10 degree tip-back bend(type B has an electric welding stop at the distal end of each loop and type C has no electric welding stop). Type A MVLAW was preactivated at the apex of each open vertical loop with 10 degree tip-back bend(the electric welding stop of type A is positioned at the mesial side of each loop). The aim of the present study was to identify when and which MVLAW is more effective to correct the buccal segment axes simultaneously. The photoelastic overview of the upper and lower right quadrant showed that stress concentrations were observed in its photoelastic model. The obtained results were as follows: 1. Higher level compression can be seen clearly at the distal curvature of the lower 1st and 2nd molar when A type MVLAW was applied without short class III elastic, but mild compression cannot be seen at the distal curvature of lower anterior teeth using the class III elastic. 2. Higher concentration was presented at the mesial curvature from the lower 1st premolar to the 2nd molar than the anterior teeth when B type MVLAW without short class III elastic was applied, but using the short class III elastic, higher concentration of compression was presented in the anterior teeth area. 3. Areas of higher compression and tension were not observed at the mesial and distal curvature of the entire lower teeth except lower central and lateral incisors in C type MVLAW without short class III elastic, but using the short class III elastic, higher concentration was seen at the mesial curvature of the lower 1st premolar and lower anterior teeth.