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Anchorage Control Using the Pre-Adjusted Appliance INDIAN DENTAL ACADEMY

Leader in continuing dental education

Anchorage Control Using the PreAdjusted Appliance BENNETT AND MCLAUGHLIN: Anchorage control: ‘The maneuvers used to restrict undesirable changes during the opening phase of treatment, so that leveling and aligning is achieved without key features of the malocclusion becoming worse.’

Horizontal Anchorage Control:  

Control of Anterior Segments: Tendency for the incisors and the cuspids to tip forward when archwires are first placed To prevent anterior teeth from tipping forward, elastic force applied Opened the bite in the premolar area and deepened the bite anteriorly- Roller Coaster Effect

Horizontal Anchorage Control: 

To minimize this effect: A new system of force developed by Bennett and McLaughlin: Use of lacebacks: Initial tipping followed by a period of rebound due to levelling effect of the arch wire Bending the arch wire behind the most distally banded posterior tooth

ď Ž

Lacebacks and Bendbacks:

Horizontal Anchorage Control:  

Use of lacebacks: Study conducted by Robinson in 1989 Little additional loss of anchorage in posterior segments while a substantial gain in anchorage in anterior segments

Horizontal Anchorage Control: Control of Posterior Segments: Posterior anchorage requirements are greater in upper arch:  Upper anterior segment has larger teeth  Upper anterior brackets have greater amount of tip built into them  Upper incisors require greater torque control and bodily movement 

Horizontal Anchorage Control: Upper molars move mesially more readily  More Class II type of malocclusions encountered .˙. Extra-oral force to provide anchorage control in upper arch - High angle cases: occipital headgear - Low angle cases: cervical headgear - Supplemented with TPA 

Horizontal Anchorage Control:  

Control of Posterior Segments: Lower Arch Lingual arch and lacebacks adequate for anchorage support Class III elastics once the 0.016 round wire has been reached

Vertical Anchorage Control: ď Ž ď ś

Incisor Vertical Control: Distally tipped canines cause extrusion of the incisors- avoided by not bracketing the incisors or not tying the arch wire into incisor brackets

Vertical Anchorage Control: ď ś

Avoid early engagement of high labially placed canines

Vertical Anchorage Control:  

 

Molar Vertical Control: Upper second molars generally not initially banded; step placed behind the first molar Attempt to achieve bodily movement during expansion Palatal bars In high angle cases, highpull or combination pull headgear Upper or lower posterior bite plate

Lateral Anchorage Control: ď Ž

Intercanine Width: Should be maintained

ď Ž

Molar Crossbites: Avoid correction by tipping movements

Anchorage Control Using the PreAdjusted Appliance ď Ž

ď Ž

During space closure, heavy forces avoided by the use of active tiebacks Once completed, passive tiebacks used to maintain the correction

Inverse Anchorage Technique:  

José Carrière: Mandible is a preferred point of reference for diagnosis and treatment planning, while maxilla is better suited to accepting orthodontic correction Mandible is subjected to considerable movement and hence a variable reference point. Actively influenced by muscles surrounding it

Inverse Anchorage Technique: 

Maxilla bears a fixed anatomical relationship to the skull. Less influenced by vectors and forces generated by the surrounding muscles Histological difference between maxilla and mandible ; maxilla has more plasticity of response Treatment starts from the distal segments and moves sectionally towards the mesial part (distomesial sequence)

Inverse Anchorage Technique: Inverse Anchorage Equation: C - Dc/2 – R1 = 0 where, C= horizontal distance b/w the cusp tip of the upper canine and the end of the distal ridge of the lower canine Dc= arch length discrepancy of the mandibular arch, measured from distal of both lower canines R1= amount in mm which the anterior limit of the lower incisors should be moved in the cephalogram for the correction of a case ď Ž

Inverse Anchorage Technique:

Inverse Anchorage Technique: 

 

On knowing both the variables, it is possible to deduce the distance to which the upper canines have to be distalised C= Dc/2 + R1 If C > Dc/2 + R1; amount of anchorage prepared is greater than needed If C < Dc/2 + R1; a loss of anchorage has occured

Inverse Anchorage Technique: ď Ž

1. 2. 3.

Through this equation, we are able to: Prescribe the amount of anchorage required Control the condition of the anchorage Ideal results

Inverse Anchorage Technique:

Inverse Anchorage Technique: Stages: ď Ž Maxillary stage: Treatment started in the maxilla with posterior leveling, canine retraction, anterior leveling and anterior retraction ď Ž Mandibular stage: same sequence

IMPLANTS : Boucher: ‘Implants are alloplastic devices which are surgically inserted into or onto jaw bone.’ Why implants? Limitations of fixed orthodontic therapy:  Headgear compliance  Reactive forces from dental anchors 


Anchorage Source: Orthopedic anchorage: - maxillary expansion - headgear like effects Dental anchorage: - space closure - intrusion ( anterior and posterior) - distalization

IMPLANTS :      

Implant designs for orthodontic usage: Onplant Impacted titanium post Mini-implant Micro-implant Skeletal anchorage system

IMPLANTS : Implants for intrusion of teeth:  Creekmore ( 1983)  Vitallium bone screw

IMPLANTS : ď&#x201A;§ Implants for space closure: Eugene Roberts: use of retromolar implants for anchorage Size of implant: 3.8mm width and 6.9mm length


Onplant: Block and Hoffman (1995) Titanium disc- coated with hydroxyapatite on one side and threaded hole on the other Inserted subperiosteally

IMPLANTS : Impacted titanium posts: Bousquet and Mauran (1996) Post impacted between upper right first molar and second premolar extraction space on labial surface of alveolar process

ď Ž

IMPLANTS : Mini-implant: Ryuzo Kanomi ( 1997) Small titanium screws 1.2mm diameter and 6mm length Initially used for incisor intrusion

ď Ž

IMPLANTS : Skeletal anchorage system (SAS): Sugawara and Umemori (1999) Titanium miniplates Placement in key ridge for upper molar and ramus for lower molar intrusion Uses: - molar intrusion - Molar intrusion and distalisation - Incisor intrusion - Molar protraction ď Ž


Micro-implants: For retracting the maxillary anteriors & uprighting the mandibular molars No side effects on the anterior teeth

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage Brite Melson Jens Kolsen Peterson Antonio Costa JCO/ MARCH 1998 ď Ž

ď Ž

Indicated in patients without sufficient posterior anchorage in whom other forms of anchorage have been ruled out Best bone quality is found in the zygomatic arch and infrazygomatic crest in a partially edentulous patient

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage  

Surgical Technique: A horizontal bony canal drilled in the region of infrazygomatic crest A double twisted 0.012 wire is pulled through this canal Wire covered by a thin polyethylene catheter to protect the mucosa

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage  

Orthodontic Technique: A coil spring is extended from the zygoma ligature to the point of force application Center of resistance determines point of force application Prosthesis should be constructed immediately after removal of the appliance Zygomatic wires are removed by pulling at one end

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage

Zygoma Ligatures: An Alternative Form of Maxillary Anchorage

Rapid orthodontic tooth movement into newly distracted bone after mandibular distraction osteogenesis in a canine model Eric Jein-Wein Liou Alvaro A. Figueroa John W. Polly AJO, April 2000

‘Distraction osteogenesis is a process of growing new bone by mechanically stretching preexisting vascularised bone tissue.’

 Purpose of the Study: To determine the feasibility, timing and rate of orthodontic tooth movement into the fibrous bone recently formed through distraction osteogenesis in the canine mandible

  

Material and Methods: Four mature beagle dogs A custom-made intraoral distraction device using an orthodontic palatal expander

 Surgical Procedure:  

Mandibular body osteotomy Care taken to preserve 0.5 to 1.0mm thickness of alveolar bone Distraction device fixed with bone screws

  

Distraction Procedures: 7 day latency period Distraction device activated 1mm each day for 14 days

 Orthodontic Tooth Movement: 

Calibrated elastic threads with 50g of orthodontic force applied to mandibular fourth premolars for 5 weeks

On one side, premolar moved simultaneously with the distraction procedure and on the other after the completion of distraction Distraction device and orthodontic appliances left in place for another 4 months before the dogs were sacrificed

 Results: 

Tooth movement at the same time as distraction- 6mm in 7 weeks

Tooth movement immediately after cessation of distraction- 6mm in 5 weeks Fourth premolars moved with distraction- horizontal bone loss. No native alveolar bone identified Radiographically, extruded and tipped forward Fourth premolars moved after distraction- mild to no alveolar bone loss Native alveolar bone preserved

 1. 

Discussion: Osteogenesis in rapid tooth movement: Average rate of tooth movement: 0.3 mm per week In the study, rate of tooth movement: 1.2 mm per week The process of osteogenesis on the tension side; a form of distraction osteogenesis No infrabony defect on tension side

2. Less bone resistance, faster tooth movement: 

Typical rate of tooth movement with 100g of tipping force: 1.5 mm in 5 weeks In this study, with 50g of tipping force: 6mm in 5 weeks Teeth moved into fibrous immature bone tissues

3. Timing to initiate rapid orthodontic tooth movement: ď&#x192;&#x2DC; Theoretically, during the first few days after distraction ď&#x192;&#x2DC; Transient burst of localized osteoclastic activity results in resorption of alveolar ď&#x192;&#x2DC; Native alveolar bone adjacent to fourth premolar moved simultaneously with distraction disappeared completely


Fourth premolars moved after distraction: native crestal alveolar bone preserved and brought into the distraction space

4. Pulp Vitality: ď&#x192;&#x2DC; Maintained in all teeth Conclusion: The best time to initiate tooth movement was immediately after the end of distraction

Ongoing Innovations in Biomechanics and Materials for the New Millennium Robert P. Kusy Angle Orthodontist, 2000

    

Glossary of Terms: FR: classical friction µ: coefficient of friction N: normal or ligation force θ: second order angulation of an arch wire relative to a bracket θc: critical contact angle or second order angulation after which binding (BI) occurs θz: second order angulation after which binding(BI) ends and physical notching(NO) begins

 

Glossary of Terms: BI: elastic binding caused by exceeding θc but less than θz

NO: physical notching caused by exceeding θz

Bracket Index: Width/Slot Clearance Index: 1Engagement Index Engagement Index: Size/Slot

Introduction: Biomechanics and materials complement one another; yet are presented as though they are independent of each other Biomechanics as a Science: For each arch-wire bracket combination a critical contact angle (θc ) exists given by the relationship: θc = 57.3( Clearance Index) (Bracket Index)

θc = 57.3( 1- Engagement Index) (Bracket Index)  Once binding occurs, it can assume two forms:  Elastic Deformation  Plastic Deformation (physical notching)  Overall resistance to sliding: RS = FR+BI+NO  FR occurs because of the ligation or normal force (N)

 

Elastic binding (BI) occurs once the wire contacts the diagonal tiewings of a bracket Physical notching: plastic deformation occurs at the diagonal tie-wings or the opposing wire contacts For optimal sliding θ ≈ θc Sliding at θ < θc results in increased treatment time Sliding at θc < θ <θz : amount of binding and the treatment time increases

Using Biomechanics to Innovate New Materials To reduce FR, 2 options exist: Decrease µ or decrease N  Reducing FR by decreasing µ for θ < θc Improving surface chemistry  Reducing FR by decreasing N for θ < θc Two methods: 1. Use of self ligating brackets 2. Development of stress relaxed ligatures 

Using Biomechanics to Innovate New Materials 

 

Use of self ligating brackets: Minimize N When θ < θc FR is low

BI behaves similar to conventional brackets  Perhaps the overstatement of their capabilities promoted practitioners to slide teeth when θ > θc 

Using Biomechanics to Innovate New Materials ď Ž ď&#x192;&#x2DC;


Development of stress relaxed ligatures: Short term forces resisted by elastic, high strength material; long term forces accommodated by stress relaxation and an accompanying decrease in N Formed from acrylic monomer n-butyl methacrylate and drawn polyethylene fibers by use of the photo-pultrusion process

Using Biomechanics to Innovate New Materials   1. 2.  

Stabilizing θ at θ ≈ θc 2 means are available: Power arms Composite arch wires Power arms A force that passes through the center of resistance generates no moment Once a tooth moves, the point of force application shifts away from the center of resistance

Using Biomechanics to Innovate New Materials  

Use of composite arch wires: To slide teeth a clinician chooses from among several archwire- bracket combinations By integrating two classes of materials (a ceramic and a polymer), a composite archwire can be fabricated. Mechanical properties differ, overall crosssectional area remains constant

Use of composite arch wires: 

Manufactured by the photo-pultrusion process using ceramic glass fiber yarns and acrylic monomers For 3 levels of fiber loading (49, 59 and 70% v/v) the values of µ and θc remained constant This constancy should be advantageous

Using Biomechanics to Innovate New Materials 

Reducing BI for θc < θ <θz : If θ exceeds θc , some binding occurs In the past, practitioners chose archwire bracket combinations that represent a compromise between binding and control

Reducing BI for θc < θ <θz : 

With increasing stiffness, decreasing interbracket distance, or both, binding increases In recent work, binding has been reduced by materials having high resiliencies and high yield strength- resistance to deformation and physical notching Use of composite wires made from ceramic glass fibers and a BIS-GMA-TEGMA matrix

Photo-pultrusion: 

Fibers are drawn into a chamber: spread, tensioned and coated with monomer Reconstituted into a profile of specific dimensions via a die As photons of light polymerize the structure into a composite Any shrinkage voids are replenished by a gravity fed monomer

Photo-pultrusion: 

If further shaping is required, composite is only partially cured (α staged) Further processed using a second die and β staged into final form

Conclusions: 

Sliding mechanics should occur only at values of angulation (θ) that are in close proximity to the critical contact angle (θc)

Material innovations can reduce FR at θ < θc by reducing the coefficient of friction, the normal force of ligation or both, among which various surface treatments and stress relaxed ligatures are 2 means

Conclusions: 

Composite materials can stabilize θ at θ ≈ θc by maintaining the same archwire bracket clearance while permitting the force deflection characteristics to vary Decreasing wire stiffness or increasing interbracket distance can reduce RS at θc < θ <θz, independent of the material used

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