Effect of passive self-ligating bracket placement on the posterior teeth on reduction of frictional force in sliding mechanics / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT). METHODS: The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a 0.019 × 0.025-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed. RESULTS: Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT. CONCLUSIONS: These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT.

Space closure using micro-implant and sliding mechanics：the three-dimensional finite element modeling and numerical analysis / 安徽医科大学学报

A volunteer was scanned by spiral CT,the Dicom format images were imported into Mimics software to reconstruct 3-D mandibular model,then optimized by Geomagic and meshed in Ansys software. A good geometric precise three-dimensional finite element model was constructed. The displacement of dentition was similar with clin-ical situation by computer.

Avaliação do atrito em braquetes autoligáveis submetidos à mecânica de deslizamento: um estudo in vitro / Evaluation of friction in self-ligating brackets subjected to sliding mechanics: an in vitro study

INTRODUÇÃO: o atrito gerado na interface braquete/fio durante a mecânica de deslizamento pode reduzir a eficiência da movimentação ortodôntica. O método de ligação do fio ao braquete exerce importante papel na determinação desse atrito. MÉTODOS: o presente estudo comparou a força de atrito gerada por quatro tipos de braquetes autoligáveis (Time®; Damon 2®; In-Ovation R® e Smart Clip®) com um grupo de braquetes ortodônticos convencionais (Dynalock®) associados a ligaduras elásticas tradicionais (Dispens-A-Stix®), que serviu como grupo controle. A força de atrito estático foi mensurada através da máquina universal de ensaios EMIC® DL 500 com dois fios de aço inoxidável com secção transversal 0,018" e 0,017" x 0,025". RESULTADOS: a análise de variância ANOVA e o teste de Tukey mostraram baixos níveis de atrito nos quatro braquetes autoligáveis associados ao fio 0,018" (P<0,05). Entretanto, os resultados observados quando os braquetes autoligáveis foram testados com fios 0,017" x 0,025" mostraram alta resistência ao deslizamento nos grupos de braquetes autoligáveis ativos.

INTRODUCTION: Friction generated at the bracket/archwire interface during sliding mechanics can reduce the efficiency of orthodontic movement. The ligation method employed to tie the archwire to the bracket plays an important role in determining this friction. METHODS: This study compared the frictional force generated by four different types of self-ligating brackets (Time™, Damon 2™, In-Ovation R™ and Smart Clip™) with a group of conventional orthodontic brackets (Dynalock™) that require the use of traditional elastomeric ligatures (ExDispens-A-Stix™), which served as the control group. Static friction force was measured using an EMIC DL™ 500 universal testing machine using stainless steel round 0.018-in and rectangular 0.017x0.025-in archwires. RESULTS: ANOVA and Tukey's test showed low levels of friction in the four self-ligating brackets in tests with the 0.018-in wire (P <0.05). However, the results noted when the self-ligating brackets were tested using 0.017x 0.025-in archwires showed high resistance to sliding in the self-ligating groups.

Finite element analysis of effectiveness of lever arm in lingual sliding mechanics / 대한치과교정학회지

OBJECTIVE: The aim of this study was to conduct three-dimensional finite element analysis of individual tooth displacement and stress distribution when a posterior retraction force of 200 g was applied at different positions of the retraction hook on the transpalatal arch (TPA) of a molar, and over different lengths of the lever arm on the maxillary anterior teeth in lingual orthodontics. METHODS: A three-dimensional finite element model, including the entire upper dentition, periodontal ligaments, and alveolar bones, was constructed on the basis of a sample (Nissan Dental Product, Kyoto, Japan) survey of Asian adults. Individual movement of the incisal edge and root apex was estimated along the x-, y-, and z-coordinates to analyze tooth displacement and von Mises stress distribution. RESULTS: When the length of the lever arm was 15 mm and 20 mm, the incisal edge and root apex of the anterior teeth was displaced lingually, with a maximum lingual displacement at the lever arm length of 20 mm. When the posterior retraction hook was on the root apex, the molars showed distal displacement. When the length of the lever arm was 20 mm, anterior extrusion was reduced and the crown of the canine displaced toward the buccal side, in which case, the retraction hook was on the edge, rather than at the center, of the TPA. CONCLUSIONS: The results of the analysis showed that when 6 anterior teeth were retracted posteriorly, lateral displacement of the canine and lingual displacement of the incisal edge and root apex of the anterior teeth occur without the extrusion of the anterior segment when the length of the lever arm is longer, and the posterior retraction hook is in the midpalatal area.

Three-dimensional Finite Element Analysis of the Mechanical Stress on Root from Orthodontic Tooth Movement by Sliding Mechanics / 华中科技大学学报（医学）（英德文版）

In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when or- thodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/ram2 for cer- vical margin of the canine, and 0.114 N/mm2 for apical region of the canine. The top of canine crown showed the largest amount of displacement (2.417 μm), while the lowest amount of displacement was located at the apical region of canine (0.043 μm). In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily or- thodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.

A photoelastic study on the initial stress distribution of the upper anterior teeth retraction using combination loop archwire and sliding mechanics / 대한치과교정학회지

An unfavorable tipping movement can occur during the retraction of anterior teeth because orthodontic force is loaded by brackets positioned far from the center of resistance. To avoid this unfavorable movement, a compensating curved wire or lingual root torque wire is used. The purpose of this study is to investigate, using photoelastic material, the distribution of initial stress associated with the retraction of the incisors according to the degree of the compensating curve, to model changes associated with tooth and alveolar bone structure. The following results were obtained by analysis of the polarizing plate of the effects of initial stress resulting from retraction of the anterior teeth: 1. When the incisors were retracted using combination archwire or sliding mechanics, the maximal polarizing pattern of the apical area decreased as the degree of the compensating curve increased from 0 to 15 to 30. 2. When the incisiors were retracted by the combination archwire or sliding mechanics, the maximal polarizing pattern of t he canine and premolar area increased as the degree of the compensating curve increased from 0to 15to 30. 3. A lower degree of polarizing patterns were associated with the combination archwire technique than the sliding mechanics technique at a given force. The above results indicate that there is no significant difference between the combination loop archwire technique and sliding mechanics, for the retraction of maxillary anterior teeth with decreased lingual tipping tendency by a compensating curve on the arch wire. However, the use of sliding mechanics is more effective for the prevention of lingual inclination of the anterior teeth, because the hook used in sliding mechanics is closer to the center of resistance of the maxillary anterior teeth.

A new protocol of the sliding mechanics with micro-implant anchorage(M.I.A.) / 대한치과교정학회지

Anchorage plays an important role in orthodontic treatment. Because of limited anchorage potential and acceptance problems of intra- or extraoral anchorage aids, endosseous implants have been suggested and used. However, clinicians have hesitated to use endosseous implants as orthodontic anchorage because of limited implantation space, high cost, and long waiting period for osseointegration. Titanium miniscrews and microscrews were introduced as orthodontic anchorage due to their many advantages such as ease of insertion and removal, low cost, immediate loading, and their ability to be placed in any area of the alveolar bone. In this study, a skeletal Class II patient was treated with sliding mechanics using M.I.A.(micro-implant anchorage). The maxillary micro-implants provide anchorage for retraction of the upper anterior teeth. The mandibular micro-implants induced uprighting and intrusion of the lower molars. The upward and forward movement of the chin followed. This resulted in an increase of the SNB angle, and a decrease of the ANB angle. The micro-implants remained firm and stable throughout treatment. This new approach to the treatment of skeletal class II malocclusion has the following characteristics: . Independent of patient cooperation. . Shorter treatment time due to the simultaneous retraction of the six anterior teeth . Early change of facial profile motivating greater cooperation from patients These results indicate that the M.I.A. can be used as anchorage for orthodontic treatment. The use of M.I.A. with sliding mechanics in the treatment of skeletal Class II malocclusion increases the treatment simplicity and efficiency.

A clinical study on anchorage control of molar anchoring spring(MAS) during retraction of the maxillary canine / 대한치과교정학회지

In maxillary canine retraction by means of sliding mechanics, we designed MAS(molar anchoring spring) to prevent anchorage loss and uncontrolled tipping of tooth movement and have applied it in clinical cases. The anchorage control of the maxillary first molar and type of tooth movement of the maxillary canine were studied in 31 subjects. The measurements were made on cephalograms, orthopantomograms and dental casts. The obtained results were as follows. 1. In case of the maxillary first molar, there was a little sagittal anchorage loss, but there was no vertical & transverse anchorage loss. 2. In case of the maxillary canine, there was distal tipping movement and also there was a little intrusion tendency.

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.

Clinical consideration on using the elastic "tie backs" during space closure / 대한치과교정학회지

Preadjusted appliance, following the original concept of the Andrews Straight-Wire appliance, became increasingly common in the 1980s. In six phases of treatment, anchorage control, leveling and aligning, overbite control, overjet reduction, space closure, and finishing are very effective with using the preadjusted appliances. Space closure is the phase of treatment in which the difference between standard edgewise and preadjusted mechanics is most noticeable. Orthodontists have been able to reduce the use of closing loops and, because of the level slot lineup, enjoy the advantages of sliding mechanics. In 1990, Dr. John C. Bennett and Richard P. McLaughlin introduced the new space closure system, namely, elastic "tiebacks". They found an .019"X.025" working archwire most effective in an .022"-slot system. Hooks of .024" stainless steel or .028" brass wire are soldered to the upper and lower archwires. The force required for space closure is delivered by elastic "tiebacks". An elastic module stretched by 2-3mm(to twice its normal length) usually delivers 0.5-1.5mm of space closure per month. Group movement and sliding mechanics are combined for gentle, controlled space closure, so that about 0.5mm of incisor retraction and 0.5mm of mesial molar movement can be seen each month. The tiebacks are replaced every four to six weeks. By using the elastic "tiebacks", the next two cases were treated during space closure. Even though we found some clinical problems of this mechanics, long treatment time, hard to control of vertical dimension and anchorage, the application method of this system is so simple that orthodontists can manage many patients during short chair time. But we must apply this mechanics after perfect understanding of the biomechanics in tooth movement.