Force Angulation Research Articles

Biomechanical analysis for total distalization of the maxillary dentition: A finite element study

This study aimed to identify the tooth movement patterns relative to various force angulations (FAs) when distalizing the total maxillary dentition. Long-term orthodontic movement of the maxillary dentition was simulated by accumulating the initial displacement of teeth produced by elastic deflection of the periodontal ligament using a finite element analysis. Distalization forces of 3N were applied to the archwire between the maxillary canine and first premolar at 5 different FAs (-30°, -15°, 0°, 15°, and 30°) to the occlusal plane. Maxillary incisors and molars showed lingual and distal tipping at all FAs, respectively. At a force angulation of 30°, almost bodily distalization of the total maxillary dentition occurred, but incisors showed considerable lingual tipping because of the effect of clearance gap (0.003-in, 0.022×0.025-in bracket slot, 0.019×0.025-in archwire) and elastic deflection of the archwire. Medial displacement of the maxillary anterior teeth occurred because of lingual tipping during distalization. The occlusal plane rotated clockwise at all FAs because of extrusion of the maxillary incisors and intrusion of the maxillary secondmolars, and the amounts decreased as FA increased. Tooth movement patterns during distalization of the total maxillary dentition were recognized. With an understanding of the mechanics, a proper treatment plan can be established.

An extended algorithm for autonomous grasping of soft tissues during robotic surgery.

Autonomous grasping of soft tissues can facilitate the robotic surgery procedures. The previous attempts for implementing auto-grasping have been based on a simplistic representation of the actual surgery maneuvers. A generalized three-zone grasp model was introduced to consider the effect of the pull force angulation on the grasp mode, that is, damage, slip, or safe grasp. Also, an extended auto-grasping algorithm was proposed in which the trigger force is automatically controlled against the pull force magnitude and direction, to achieve a safe and secure grasp. The autonomous grasping experiments against a varying pull force in a phantom study indicated a good agreement between the desired and actual pinch and trigger forces (root mean square errors lower than 0.168 N and 0.280 N, respectively) and no sign of tissue tear or slippage. The proposed auto-grasping algorithm can help manipulating the soft tissues safely and effectively during robotic surgery procedures.

Biomechanical analysis for total mesialization of the mandibular dentition: A finite element study.

To clarify the mechanics of tooth movement in mesialization of the whole mandibular dentition when changing the force angulation. A finite element method was used to simulate long-term movements of the whole mandibular dentition. Tooth movement was simulated by accumulating the initial displacement, which was produced by elastic deformation of the periodontal ligament. Mesial forces of 3N were applied to the second molar bracket at -30°, -15°, 0°, 15° and 30° to the occlusal plane. The whole dentition and occlusal plane were rotated depending on the direction of the force with respect to the centre of resistance (CR). At a force angulation of -30°, the line of action of the force passed near the CR, and the whole dentition translated without rotation of the occlusal plane. The second molar tipped buccally due to a clearance gap between the archwire and bracket slot. When increasing a force angulation from -30°, the line of action of the force passed above the CR, and thereby, the occlusal plane rotated clockwise. This rotation of the whole dentition induced tipping of the individual teeth. Buccal tipping of the molar due to an elastic deformation of the archwire was prevented by using a lingually pre-bent archwire. Careful selection of force angulation and biomechanics is essential to obtain proper tooth movement in total mesialization of the mandibular dentition.

Biomechanical analysis for total distalization of the mandibular dentition: A finite element study.

The aim of this finite element study was to analyze and clarify the mechanics of tooth movement patterns for total distalization of the mandibular dentition based on force angulation. Long-term orthodontic movement of the mandibular dentition was simulated by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. Displacement of each tooth was caused by movement of the whole dentition, elastic deflection of the archwire, and clearance gap between the archwire and bracket slot. The whole dentition was rotated clockwise or counterclockwise when the line of action of the force passed below or above the center of resistance. Elastic deflection of the archwire induced a lingual tipping of the anterior teeth. It became larger when increasing the magnitude of angulation. The archwire could be rotated within the clearance gap between the archwire and the bracket slot, and thereby the teeth tipped. Mechanics of total mandibular distalization was clarified. Selective use of force angulation with a careful biomechanical understanding can achieve proper distalization of the whole mandibular dentition.

Comparative evaluation of insertion torque and mechanical stability for self-tapping and self-drilling orthodontic miniscrews \u2013 an in vitro study

BackgroundThe aim of the present study was to evaluate the relationship between insertion torque and stability of miniscrews in terms of resistance against dislocation, then comparing a self-tapping screw with a self-drilling one.MethodsInsertion torque was measured during placement of 30 self-drilling and 31 self-tapping stainless steel miniscrews (Leone SpA, Sesto Fiorentino, Italy) in synthetic bone blocks. Then, an increasing pulling force was applied at an angle of 90° and 45°, and the displacement of the miniscrews was recorded.ResultsThe statistical analysis showed a statistically significant difference between the mean Maximum Insertion Torque (MIT) observed in the two groups and showed that force angulation and MIT have a statistically significant effect on miniscrews stability. For both the miniscrews, an angle of 90° between miniscrew and loading force is preferable in terms of stability.ConclusionsThe tested self-drilling orthodontic miniscrews showed higher MIT and greater resistance against dislocation than the self-tapping ones.

Three-dimensional modeling and finite element analysis in treatment planning for orthodontic tooth movement

The objective of this study was to demonstrate the potential of 3-dimensional modeling and finite element analysis as clinical tools in treatment planning for orthodontic tooth movement. High stresses in bone and miniscrew implants under load can cause fractures and trauma for orthodontic patients, and treatments are typically planned by using clinical experience or simple 2-dimensional radiographs. Anatomically accurate 3-dimensional models reconstructed from cone-beam computed tomography scans were used to simulate the retraction of a single-rooted mandibular canine with a miniscrew placed as skeletal anchorage. Detailed stress distributions in the implant and peri-implant bone were found, in addition to the effect of the orthodontic bracket hook length and the angulation of retraction force on stress response in the periodontal ligament (PDL). The numeric results showed that the equivalent von Mises stress on the miniscrew under a 200-cN tangential load reached 42 MPa at the first thread recession, whereas von Mises stress in the peri-implant bone only reached 11 MPa below the neck. High tightening loads of 200 N·mm of torsion and 460 cN of axial compression resulted in much greater bone and implant von Mises stresses than tangential loading, exceeding the yield strengths of the titanium alloy and the cortical bone. Increasing the hook length on the orthodontic bracket effectively reduced the canine PDL stress from 80 kPa with no hook to 22 kPa with a hook 7 mm long. Angulating the force apically downward from 0° to 30° had a less significant effect on the PDL stress profile and initial canine deflection. The results suggest that stresses on miniscrew implants under load are sensitive to changes in diameter. Overtightening a miniscrew after placement might be a more likely cause of fracture failure and bone trauma than application of tangential orthodontic force. The reduction of stress along the PDL as a result of increasing the bracket hook length might account for steadier tooth translation by force application closer to the center of resistance of a single-rooted canine. The relatively minor effect of force angulation on the PDL response suggests that the vertical placement of miniscrews in keratinized or nonkeratinized tissue might not significantly affect orthodontic tooth movement. This model can be adapted as a patient-specific clinical orthodontic tool for planning movement of 1 tooth or several teeth.

顎顔面形態がこう合力およびそしゃく筋筋放電活動に及ぼす影響について ＩＸ‐１． 総義歯装着者の正貌顎顔面形態と偏側そしゃく指数およびこう合力の方向との関連性

This study was conducted to evaluate the influence of the frontal dentoskeletal form in complete denture wearers on the lateralized masticatory index and the direction of the bite force.The frontal dentoskeletal forms of eleven complete denture wearers in the normal face group were analyzed by posteroanterior cephalograms. The subjects were divided into left and right deviation groups, and the mechanisms of their jaw functions were analyzed in terms of the lateralized masticatory index and bite force angulation in the horizontal plane during vertical clenching. The magnitude of bite force was divided into two levels.As a result, it was found that the lateralized masticatory index was strongly influenced by the frontal dentoskeletal form and chewing habits during masticatory movement with relatively lower bite force.This suggested that the mandible function, including the direction of bite force and the frequency of the lateralized masticatory index, should be examined in detail to improve the right and left balance in the dentoskeletal form and denture retention and stability.

顎顔面形態がこう合力およびそしゃく筋筋放電活動に及ぼす影響について ＶＩＩ−２． 正貌顎顔面形態と偏側そしゃく指数およびこう合力の大きさ・方向との関連性

This study was carried out to evaluate the relationship between frontal dentoskeletal form and lateralized masticatory index or bite force magnitude and direction.Eighteen subjects, belonging to the normal face group were studied, and the frontal dentoskeletal form was analyzed with posteroanterior cephalograms. The subjects were divided into left deviation and right deviation groups, and mechanisms of jaw functions were analyzed in terms of lateralized masticatory index and bite force angulation in the horizontal plane during vertical clenching. The magnitude of bite force was divided into 4 steps, and the results were as follows:1. Lateralized masticatory index showed the chewing side to be the same as the deviation side of the frontal dentoskeletal form.A significant correlation was found between two groups for angle analysis item ∠Um-Um′ of frontal dentoskeletal form and right deviation group for distance analysis item Me-ML.2. Bite force angulation in the horizontal plane showed the same phenomenon with frontal dentoskeletal form and lateralized masticatory index.In the correlation of frontal dentoskeletal form and lateralized masticatory index and direction of bite force, significant correlation was noted in two groups of frontal dentoskeletal form of UUm-Um′, UCG-Me and Me-ML at 25% MC with lateralized masticatory index ∠(Zyg-AG)-(Zyg′-AG′) at 25% MC and 50% MC, as well as the left diviation group of ∠(Zyg-AG)-(Zyg′-AG′) at 75% MC with lateralized masticatory index and the right deviation group of ∠CG-Me at 50% MC.

The effects of load location and misalignment on shear/peel testing of direct bonded orthodontic brackets—A finite element model

A finite element model (FEM) of an orthodontic bracket bonded with glass ionomer cement was developed. The loading on the model simulated shear loading conditions associated with the testing of bonding system strength. The primary purpose of this project was to ascertain the effects of shear load placement and misalignment on the calculated stresses within the cement layer. Over the range of values considered, peak stress values depend profoundly on the location of force application. Peak stresses are less affected by shear force angulation. (A M J O RTHOD D ENTOFAC O RTHOP 1994;106:395-402.)