fudamentals of biomechanics and biomechanics of levelling and aligning(includes biomechanics of...

1

Fundamentals of Biomechanics including Mechanics of Leveling

and Aligning

Dr. Meenakshi Vishwanath

2

Contents

Introduction

Terms and definitions

Principles of biomechanics

One couple system

Two couple system

Leveling and aligning

-Begg and PAE systems

3

Introduction

Mechanics-is the discipline that describes the effect of forces on bodies.

Biomechanics-study of mechanics as it affects the biologic systems.

Application of mechanics to the biology of tooth movement.

4

Introduction

History

Studies concerning the biology of tooth

movement -1930’s

The study of mechanics and effect on

periodontium-1950’s

Various methods to study mechanics –

Laser holography, Photo-elasticity,

Complementary Strain Energy, F E M . .

5

Introduction

Orthodontic tooth movement –Force on the teeth.

Knowledge of mechanical principles and governing forces- necessary for the control of orthodontic treatment.Basis of orthodontic treatment-clinical application of biomechanic concepts

Proper mechanical force system = medications Treatment success.

6


Centre of Mass- All objects (finite) behave as if the entire mass is concentrated onto a single point.

Applicable in force - free stateBehaviour- Predictable if forces acting in relation to this point is known.

7


Centre of Gravity- objects subject to gravitational force Cmass / Cg -“ Balance point”

8


Centre of Resistance- analogous to the Cmass for restrained bodies.

Function of a body in a system of constraints-supporting tissues.

9


10


Cres depends on-1. Root length & Morphology2. Number of roots3. Level of alveolar bone support

11


Various authors differ in the estimation of Cres.Methodology.For single rooted teeth-

At 50% of root length-Proffit,Nikolai

B/w 50%-33% of root length-Smith and

Burstone

At 33% of root length-Burstone

B/w 25%-33% of root length-Nanda

The Cres of facial bones, entire arches of teeth,

or segments can also be estimated

12


Multirooted teeth-

Maxillary anterior dentiton Cres - maxillary anterior teeth-distal to lateral incisor-NandaIncorporation of lateral incisors-small distal shift,canines-significant distal movement-Burstone & Sachdeva

Mutirooted-close to bifurcation of the roots –Nanda

Trifurcation-Upper I molar- Worms, Isaacson and Speidel

13


Cres of -maxilla-slightly inferior to orbitale-Nanda

Postero-superior ridge of the pterygomaxillary fissure registered on the median sagittal plane-Tanne et al

14


Determination of the centers of resistance of all the individual teeth and groups of teeth using FEA.

Conclusions-1. Longer the root, the more apically placed was

the Cres.

2. The Cres of all teeth were slightly apical to the centroid of the teeth.

3. The Cres of Mand. Premolars lie at the same level, Cres of I Max. Premolar is more apical to that of the II premolar.

15


4. The Cres of the maxillary and Mandibular molar lies at the tri/bifurcation respectively.

5. Intrusive forces on groups of teeth-Cres shifts posteriorly as more number of teeth were included in the segment.

6. For retractive forces on groups of teeth-Cres shifts coronally as more number of teeth were included in the segment.

16


Precise location-not known, conceptual awareness needed.

Relationship of force systems to Cres of tooth-type of tooth movement

17


Centre of Rotation- a point around which an object rotates.

-The geometric point about which no movement occurs

Point around which an object seems to have rotated as determined from its initial and final positions.

18


Method for determining centre of rotation –

19


Can be at any point ON or OFF the tooth

If there has been no rotation-infinity

If tooth has followed an irregular path-several centers of rotation

20


Scalars and vectors

Force- vector

-a load applied to a object that will tend to move it to a different position in space

F=mass x acceleration Newtons or gm.mm/sec2

Orthodontics- (mm/s2 )-irrelevant

21


1 Newton=101.937 grams (or) 1 gram=.oo981 N

1 Pound=16 Oz =.4536 Kg

1Oz =28.35 grams

22


Direction and magnitude of force -

Origin/point of application

Magnitude Sense/Direction

Line of action

23


Multiple vectors can be combined through vector additionSum of 2 or more vectors- Resultant

Resultant

Force 1

Force 2

24


Different points of application-

Forces can be combined using the law of transmissibility of force.

“When considering the external effects of a force on a rigid body the force may be considered to have a point of application anywhere along its line of action”

25


Resolving a force into vectors-

26


Moment –Rotational tendency of a force that is not passing through the centre of resistance.

The magnitude of the moment=Force x lar distance of line of action (force) to

the Cres

27


Unit - Gram millimeters (Newton millimeters)

28


M=F x D

29


30


Important to distinguish between force and moment.“Cue ball concept”

31


Couple –consists of two forces of equal magnitude, with parallel but non-collinear lines of action and opposite senses.

- Two equal and opposite parallel forces separated by a perpendicular distance.

-Applied moments

Pure rotation about the centre of resistance

32


Magnitude of a couple=Mag.of 1 force x perpendicular dist b/w them Unit-Gram.mm

Translational effects cancel out each other

33


Moment arm of a couple-

34


Couples result in pure rotational movement regardless of where the couple is applied on the object.

50 x 10=-500gm-mm50x30=1500gm-mm

500gm-mm is negative Thus 1000gm-mm just as in

the previous case

35


Clinically

Centre of rotation coincides with the centre of resistance.

36


Forces indicated by-

Moments indicated by-

Moment of force-rotational tendency of a single force that does not pass though the Cres-(linear movement occurs)

Moment of couple-two forces that produce pure rotation (no linear movement)

37


Application of force/couple usually is at the brackets

Predicting the type of tooth movement-determine the Equivalent force system at the of resistance.

Equivalent force system- Analysis that replaces the applied force at the bracket with its equivalent at the at the Cres

38


The 2 extreme situations-Force exactly at the centre of resistance-only linear movement (translation).Forces that produce pure rotation.

All situations in between the two produce some translatory and some rotatory movements.

So what are the forces at the Cres and what type of tooth movement results?

39


Determining the force system at the Cres

1. Place force vector at the Cres (maintain

magnitude and direction)

2. Calculate -moment of force

3. Place MF - centre of resistance

4. Applied moment placed at the Cres

5. The MF and applied moment added –net

moment

6. Resulting force - expected tooth movement

100gm

10mm

1000gmm1000gmm

40


41


42


43

Biomechanics

Bio-mechanics

Cmass /gravity/res

Centre of rotation

Forces and Moments

Couple

Moment of force/Moment of couple

Equivalent force system

44


Equivalent force system- It is the forces at the centre of resistance that determine how teeth move.

The force system placed at the bracket is equated at the Cres to determine the tooth movement.

Helps in-Prediction of the tooth movement

Equivalent force system- Analysis that replaces the applied force at the bracket with its equivalent at the the Cres

45


46


Types of tooth movement-infinite variety but can be categorized into basic types

uncontrolled Tipping

controlled

Translation

Root movement

Rotation

47


Each type of tooth movement is due to the variation in the amount of applied moment and force.

The ratio of the applied counter moment and the applied force experienced at the Cres is called the Moment- to- force ratio .

The M/F ratio of the applied force and moment determines the type of movement at the centre of rotation.Unit-millimeters

48


Tipping- Greater movement of the crown than the root.

Centre of rotation-Apical to the Cres

Uncontrolled tipping Controlled tipping

Between Cres and root apex At the root apex

49


Uncontrolled tipping- Simplest type of movement –often

undesirable.

Simple forces-chain elastics, intraoral-arch elastics, or coil springs used on a round wire.

50


Non uniform stress generated

Maximum-root apex and crown

M/F =0:1 - 5:1(av.root lengths and 100% alveolar bone height)

Desirable-Cl II div 2 and Cl III patients with excessively upright incisors that need flaring & excessively flared Cl II div 1.

51


Controlled tipping – Control or maintenance of the root apex

position.Desirable type of tooth movement.

52


Stress at root apex is

minimal

Concentration of forces

at the cervical area-

timely tooth movement

Protrusive incisors

(Root apex in a good

position)

M/F=7:1

53


Translation (bodily movement)- crown and root move the same distance in the same direction.

Centre of rotation-infinity

54


For this type of tooth movement-Force-centre of resistanceForce applied at the bracket….

counter moment applied in such away that-equivalent force system at the Cres –pure force.

55


M/F-10:1

56


Root movement- crown is stationary -force and moment cause only root movement

Centre of rotation-incisal or bracketRequires a large moment-M/F ratio at or above 12:1

57


Stress levels high at apex –significant amount of bone resorption required.Undermining resorption-slow momentAdvantageous-augments anchorage

58


Clinically--Upright the incisors, correct the canine roots

after space closure.-crowns should be ligated to stop them from

moving-Lingual root movement of incisors-large forces

may cause a “Row –boat” effect

59


Rotation –requires a

couple

No net force at the Cres

Clinically-rotated teeth.

60


61


True relevance of M/F ratio-Biologic variations in estimation of CresDifference in the M/F ratio of various tooth movements is small.Difference in opinion about precise M/F ratios

62


The M/F ratio need not be taken as absolute-General principles are important-

63


Static equilibrium-

Effort was put to achieve the equilibrium

64


In orthodontics-equilibrium establishes itself

We do not have to achieve static equilibrium but recognize the forces and moments that have come into existence to establish the static state.

65


Newton’s laws of motion-underlie the fundamental concept of mechanics.

1.Law of inertia

2.The law of acceleration

3.The law of action and reaction

66


Application of these laws-orthodontics

Wire engaged into poorly aligned teeth-1st & 3rd laws

A more important application of Law of action and reaction is static equilibrium.

67


Static equilibrium implies -At any point within a body, the sum of forces and moments acting on a body is zero.The analysis of equilibrium as applied to orthodontics can be stated as

68


Sum of all vertical forces =0

Anterior intrusion-have to deal with-the balancing force-molar extrusion.

69


Sum of all horizontal forces=0

Correction of unilateral crossbite-not possible with a single horizontal force

70


71


Moment acting around any point must = 0.

Forces produced to maintain static equilibrium

Magnitude of forces exactly –necessary to produce a counter rotation.

72


73

Equilibrium situations

Many appliances and bends placed in clinical

situations

Many situations –unequal forces and moments

develop.

“Additional forces”-develop to obtain

equilibrium

Determination of complete system in

equilibrium-side effects.

74


The forces and moments that determine a appliances equilibrium –must exist.

If not-Newton’s 2nd law-teeth will accelerate out of the mouth!

75

Determinate Vs Indeterminate force systems

Force systems can be-

Statically determinate (One couple system) The forces and moments can readily be discerned, measured and evaluated.

Statically indeterminate (Two couple system) System is too complex for precisely measuring all forces and moments involved in equilibrium.

76

Biomechanical classification of orthodontic appliances

Equal and opposite force system (No couple appliance system)

One couple appliance system

Two couple appliance system

77

Force systems

Equal and opposite force system-No couple

Elastic band stretched between 2 points

78

Statically determinate

One couple system- Simplest arrangement of an orthodontic force system.

Couple is created ay one end of the attachment –only force at the other.

One end –tube or bracket and point contact at the other.

79


The direction of moment clinically can be estimated –placing one end of the arch wire over but not inside the slot.The wire crosses the bracket at an angle.

80


82


Magnitude of forces-measurable

Force multiplied by the distance b/w bracket and point of attachment=moment-equal and opposite to Mc at bracket.

Magnitude of forces of couple at the bracket-divide the magnitude of Mc by the length of bracket.

83


84


High predictability of tooth movement.

Decreased need of appliance reactivation.

Side effects known

85


Applications of one couple systems-

Cantilever spring applications

Canine extrusion springs

Midline springs

Anterior intrusion arches

Anterior extrusion arches

86

Statically Indeterminate

Two couple system-When the free end of the arch wire-inserted into a second bracket.

For the purpose of establishing the direction of associated equilibrium forces-sum of 2 successive 1 bracket systems

Couples-each of 2 brackets

87


The entry of wire –not accurate estimate of direction of Mc

When wire placed over bracket-angle of entry determines-larger/smaller moment

The force systems-depend on wire geometry and bracket angulation relationships.

88


Applications of two couple systems-

Utility arches

Upside-down Utility arches

Torquing arches

Upside-down torquing arches

Transverse activations

Segmented springs

Transpalatal/lingual arches

89


Description of Force system in 3 bracket – wire situations-

1. Off-Centre “V” bend

2. Centre “V” bend

3. Step Bend

4. Straight wire passed through non - aligned

brackets

90


Location of the centre of resistance-

91


Off-centered “V” bends (asymmetric bend relationship)

Creates unequal and opposite couples.

The net equilibrium forces-intrude one

unit, extrude the other.

Total magnitude of system-not certain,

relative magnitude can be determined.

The larger moment-indicates the direction

of equilibrium forces.

92


93


Magnitude of b-does not mean stronger extrusion –as the anchorage value of the tooth is more.

94


95


1/3rd the way along the inter bracket span-no moment on the distant tooth.

Closure than 1/3rd moment generated in the same direction.

96


Centered “V” bend Creates equal and opposite couples at the brackets.

The associated equilibrium forces at each bracket-equal and opposite – cancel each other out.

97


•The location of Cres has no effects on the reactions produced

98


Need not be half-way b/w the 2 groups of teeth

If 1 tooth is larger-equal and opposite moments require-bend to be placed closer to the larger tooth

99

3_D wire will cause torsion and bending to occur.

FEM used-description of forces & couples along the global co-ordinates.

17 X 25 ss wire

MY1 ,MY2 & associated equilibriums-FZ1 & FZ2

101


2 opinions on location of Cres-

2 teeth as individual unitsA single unit -1 Cres

102


Step bends-

Creates 2 couples in the same direction-regardless of location between brackets.

Location of step bend-no effect on either magnitude of moments or equilibrium forces.

103


Forces generated are stronger than the off-centered “V” bend situation

If the Cres changes-similar effect of that seen in Off-centre “V” bend .

104


105


106


107


Straight wire placed in a non - aligned brackets-

Arch wire is placed in mouth-complicated set

of forces on each tooth

Simplest basic unit- two tooth segment of an

arch

Series of 2 tooth systems-forces can be found

along the arch.

Force systems in a ideal arch wire-Burstone &Koenig AJO-1974

108


The force system produced by a straight wire placed between two attachments-determined by defining the Wire-attachment geometry.

Interbracket axis-L-connects the 2 centers of attachmentθA & θB -angles of attachment –respect to interbracket axis

109


Six basic 2 tooth geometries –θA/ θB

110

Relative force systems-

111

Actual M/F ratios

112

Actual M/F ratios

113

Actual M/F ratios

114

Actual M/F ratios

115

Actual M/F ratios

116

Actual M/F ratios

117


Dogma of ideal arch-wire is bent into a shape one would like the brackets to be found at the end of treatment –teeth move into that positions on the ideal arch.

Validity???

Rigid wire-acts as a mould.

118


Each segment of the arch wire (2 tooth) has different forces and moments generated.

Not under the control of orthodontist.

Sheer chance that desired force system would be produced!

119


Common sense application of mechanical principles.

Dealing with the biologic environment-variation in response - challenges the orthodontist.

Understanding of the appliance of choice and the various force systems.

Treat in a practical & realistic manner.

120


Visual inspection-Frequently used to determine the forces an arch wire will produce

May seem obvious-Faulty conclusions.

Determine the forces and moments

121


What force will be produced?On the molar? Extrusive . Intrusive. None.On the Cuspid? Extrusive. Intrusive. None.

122


What force will be produced?On the Central Incisor?On the Lateral Incisor?Extrusive. Intrusive. None.

123

All figures described only 4 situations

Archwire bends-centre and off-centre

Can describe the force system by noting the location of the bend.

124


A Simple Rule.

Bend off center: short and long segment.

Short segment engaged –long segment point in direction of the force produced.

Short segment points in the opposite direction of the force.

125


Bend at center: no short or long segments- forces as cancel each other upon engagement leaving only pure moments.

126


and Aligning


127

Biomechanics of leveling and aligning-Introduction

Usually the first step –orthodontic treatment plan.

Division of treatment into stages-Begg, but

reasonably applicable to PAE.

3 major stages in comprehensive treatment plan-

1. Alignment and leveling

2. Correction of molar relation and space closure

3. Finishing

128

Introduction

Goals of I phase of treatment-

To create a harmonious dental arch without irregularities

& Correct vertical discrepancies by leveling

out arches.

129

Introduction

Leveling and aligning in PAE - synonymous with the stage I in Begg.

Proper alignment- one not only brings malposed teeth into the arch but- control antero-posterior positions, width of arches and form of dental arches.

Leveling-determine and control-extrusion of posterior teeth ,intrusion of anteriors or a specific combination of the 2.

130

Introduction

Types of tooth movement-infinite variety but can be categorized into basic types

uncontrolled Tipping

controlled

Translation

Root movement

Rotation

131

Introduction

Uncontrolled tipping-M/F =0:1 - 5:1

Controlled tipping –M/F=7:1

132

Introduction

Translation (bodily movement)-M/F-10:1

133

Introduction

Root movement-M/F ratio at or above 12:1

Rotation -

134

Alignment

Though generally agreed- ‘Bite before Jet’- BUT treating cases of maligned arches alignment becomes important.

Once the teeth are aligned-all teeth can be intruded.

Alignment-create space for correcting crowded teeth or to close excess space if present.

135

Alignment

Depending on individual treatment goals-all teeth aligned at the same time or some teeth excluded to avoid round - tripping.

Early alignment-corrections maintained for a

longer time biologic adaptation and enhanced

stability.

A combination of labiolingual and mesiodistal

tipping guided by an arch wire is needed.

136

Principles in choice of alignment arches

Initial arch wires should provide-light continuous

force -50grams

Most often achieved- placing wires with low load

deflection rates and shape memory-

NiTi ,multistranded and small cross-sec SS wires.

Arch wires should freely slide within the brackets-

at least a 2mil clearance B/w arch wire and bracket.

137


• Wires should be loosely ligated

• Loosely ligated, so that it can slide through the brackets, it has ¼th the stiffness of a wire that is tightly ligated.

138


Rectangular wires –avoided -(root apices are

closure to the normal position).Better to tip the crowns into position during initial alignment.

Rectangular wire useful-torque expression right from start-root positions not favorable-

Instanding lateralsSoon after arch expansion

139

Properties of alignment arch wires

Combination of strength, springiness and long range of action.

The variables in selecting appropriate arch wires for alignment-

Arch wire materialCross-sectionDistance between attachments

140

Arch wire material

Titanium based wires – NiTi and TMA –offer better combination of springiness and strength.NiTi wires-better (springier and stronger) than TMA-preferred.Remarkably -Low-load deflection.

If steel is used in this stage-Multistranded wires or loops.

141

Size of wire

Strength changes as a cubic fn of the ratio of the 2 cross sections.Springiness-4th powerRange-direct proportion

As the wire size increases though strength increases rapidly, springiness decreases even more.

The smallest diameter wire (springy) of adequate strength can be used.

142

Size of wire

Multistanded wire- They are composed of specified numbers of thin wire sections coiled around each other to provide round or rectangular cross section

On bending - individual strands slip over each other , making bending easy.

Result - high elastic modulus wire behaving like a low stiffness wire

143

Distance B/w attachments

Increase the length of the wire-Loops

Proportionate decrease in strength, but the stiffness will decrease as a cubic function

The width of bracket determines the beam length if a continuous wire is used.

144

Arch wire -materials

145

Space creation

In case of crowding , space required for alignment can be obtained in the following ways-

Proclination Canine distalizationArch expansionInterproximal reduction

146

Aligning in Begg

Stage-I

SUB-STAGE I-A SUB-STAGE I-B

Objectives of substage I-A

1.Create space

2.Alingment of anterior teeth-Labio-lingual

displacements & rotations,anterior crossbites

3.Improve incisor inclination-+/- 10 ° of normal

147

Aligning in Begg

4.Rotations ,bucco-lingual positions of molars-crossbites

5.Premolar rotations

6.Upper arch form corrected-0.016

Completion of substage I-A-full engagement of plain arch wire-intrusive -forces applied to all teeth.

Inclinations are improved-true intrusion & controlled tipping is achieved.

148

Aligning in Begg

Alignment best carried out-flexible wires –low load deflection rate.

Easy engagementLight constant forces-long distancesPermit sliding

149

Aligning in Begg

Multilooped archwire-though made of stiff wire-loops incorporated-anterior area

Disadvantages-Inadequate bite openingLabial flaring of incisorsLoss of control over molar positions & anchorageDifficulty in construction and adjustmentDifficulty in maintaining the arch form

150

Aligning in Begg

Alignment without multilooped wires-0.016 –canine distalization-sliding along the arch wire.Flexible wires-steel base wire.

Thus –choice made between various sizes of steel, multistranded wires and NiTi-singly or combinations.

151

Aligning in Begg

Full length NiTi can be used- Highly placed canine-class II elastics (ultra light)-bite does not deepen as extrusive component of elastic is negated.Open bite situations

If bite already deep-and elastics given-combination of flexible and steel wire-(anchor bend is given )-can be used

152

Aligning in Begg

If canine has to be distalized for space creation-the SS wire 0.014 or 0.016 is to be used.Minimal crowding-cuspid circle positions can be altered ;offset bends can be given in the wire-partially active.

More crowding-canines slide along the wire-elastics.

153

Aligning in Begg

Rotational correction-bracket slot should be filled

Larger diameter NiTi are better

If small diameter steel used-Exaggerated horizontal offsets have to be given.

154

Aligning in Begg

Flexible sectionals are used-

Only after canine distalization and there is

sufficient space for decrowding.

NiTi,Co-ax or supreme wires used as-

sectionals with a base wire to prevent

adverse effects.

Base wires are given offsets to keep away

from brackets.

155

Aligning in Begg

Anchorage considerations in stage IVery efficient control- sagittal direction-stationary anchorageAnchorage loss-heavy elastic forceAnchorage conserved-

TPAAnchor bendsStiff wires-molar stopsLip bumpers

156

Aligning in PAE

Pre adjusted edgewise system-

The tooth movement needed to achieve passive

engagement of a steel rectangular wire

of .019/.025 dimension and of suitable arch

form, into a correctly placed preadjusted .022

bracket system.

157

Aligning in PAE

Anchorage control gains importance-

Successful alignment depends on recognizing unwanted tooth movements - occur early in the treatment –built in tip in the brackets.

Final treatment goal-kept in mind

Anchorage requirement changes-case to case-most cases do require some form

158

Aligning in PAE

Reduce anchorage needs-

Arch wire forces-very light

E-chains to be avoided

Lace backs to be given-restrict canine tipping-mainly used premolar extraction cases

159

Aligning in PAE

Bendbacks for antro-posterior control

160

Aligning in PAE

Wire sequencing

161

Aligning in PAE

Vertical control of incisors-built in tip-increases the overbite Canine distally tipped-extrusion of incisors

162

Biomechanics of aligning

Biomechanics-Continuous arch/Segmented arch

Special situations-Impacted canine Midline correctionDiastema closureMolar rotations

163


Biomechanics in a continuous arch-

164


165


To avoid undesirable force-Bracket fewer teeth-sectional arch system

Segmented arch technique-

Concept-the arch is divided into segments

Better control and favorable force levels

Well defined units of teeth-anchorage and

movement segments clearly defined

166


In segmented mechanics-TPA/lingual arches used; stabalizing wire segments

Stabilization requires-most rigid wire-.022 edwiese slot preferred

21 x25 –anchor segments

167


Segmented arch treatment-

Initial alignment within antero-posterior

segments

Once teeth within segments-aligned, each

treated as 1 large multi-rooted tooth

Creation of appropriate-anchorage and tooth

moving segment

Vertical correction and space closure with

differential movement of anterior& posterior

segments

Friction –almost avoided

168


Vary the cross section of wire-Segmentation allows-use of different cross-sec wires at different locations in same arch.

169


Special situations- AligningCanine extrusion spring- High facially placed

•Wire bent passive to

occlusal to canine

•Wire activated-2nd order

couple created

•Equilibrium forces

develop

170

If continuous wire were used-incisor intrusion-anterior open bite

171


Effects extrusive force-Third order moment createdCanine-crown lingual ;root-facialForce passes facial to Cres

Wire inserted into the bracket-lingual root torque applied-side effect labial root torque on molar.

Statically indeterminate systemCare taken-no 2nd order activation at the canine

173


Canine extrusion spring- Palatally placed

•Similar activation as previous situation

•Third order couple created at molar-passive TPA

174


Palatal to facial canine movement

•1st order couple at molar tube

•Equilibrium forces-Facial canine movement

•TPA- molar

176


Midline springs

•Wire lateral to incisors in direction in which movement required

•Force system-similar to previous situation

178


Diastema closure

179


Molar rotations-Transverse correctionsCan be done on a 2 x 2/4

2x6 –anterior segment –visualized as one large tooth.

Predominantly molar movement

180


Symmetrical ‘V’ bends

Molar mesial- out rotations

Molar mesial- in rotations

181


Moments-Bilateral toe-in

Canine -distal outMolar –mesial out

Anterior segment-large tooth-cancel each other

Increases arch perimeter

Correction of class II malocclusion

182


Bilateral toe-outsMesial-in molar rotations

Correction of molar rotation

Decrease the arch perimeter

183


Asymmertrical ‘V’ bends

Larger angle of entry-determines direction and not magnitude of equilibrium forces

Premolar should not be engaged

184


185


Molar mesial-out rotations-

Molar M-out rotations and intermolar expansion

186


Molar mesial –in rotationsReversal of situations

Bilateral molar M-in rotations and constriction of inter molar width

187


Molar constrictionBend-closure to canineLittle or no molar rotation

Constriction of intermolar width with minimum molar rotations are desired

188


Molar expansion

Molar expansion-minimal rotations

189


Step bends

Magnitude of the 2 M of couple need not be equal-but associated equilibrium forces are always equal

190


Molar expansion-Toe-out

M-out rotations & enhanced expansive equilibrium forces.

191


Molar constriction-Toe-in

M-out rotations and greater constrictive forces

192


and Aligning


193

Biomechanics of leveling-Introduction

Goals of I phase of treatment-

To create a harmonious dental arch without irregularities

& Correct vertical discrepancies by

leveling out arches.

194

Introduction

Overbite- vertical overlap of the incisors.

Lower incisal edges contact the lingual surface of the upper incisors at or above the cingulum.

Normal overbite-2-3mm

Deep bite-increased to more than 3mm -1oo% biteOpen bite-no vertical overlap of the teeth.

195

Introduction

Etiologic classification of deep bite-Developmental

Skeletal deep biteDentoalveolar deep bite –supraeruption of incisors (interocclusal clearance-small)-pseudo-deep bite

196

Introduction

Acquired deep bite-Lateral tongue thrust-infraocclusion of posterior teeth-large freeway space-class II div 2.-true deep bitePremature loss of deciduous teeth or early loss of permanent molarsWearing away of occlusal surface

197

Introduction

Etiologic considerations of open bite-Epigenetic factors-

Posture, morphology and size of tongueSkeletal growth pattern of maxilla and mandibleVertical relation of jaws

198

Introduction

Environmental factors-Abnormal respiration

199

Introduction

The development of vertical problems-The anterior teeth continue to erupt until contact is made with opposing anterior teeth.

If increased jet-continue to erupt-touch palate

200

Introduction

Stop erupting if mechanical obstruction-thumb/tongue restricts

Unrestricted eruption of lower 2nd permanent molar-posterior part of curve of spee.

201

Tooth movements of bite opening

Bite opening can mainly be done by-

Absolute intrusion

Relative intrusion

Extrusion of posterior teeth/distal tipping

Proclination of incisors

Combination

202


Criteria for the mode of bite opening-

Age of patient- amount of growth left

Growth pattern-horizontal/vertical

Incisor exposure at rest-

upper incisor exposure more than 2 - 3mm

Upper exposure normal-deep curve of

spee-lower incisor intrusion.

203


Tooth movements of bite opening-1.Absolute intrusion of incisors-

Required when hyperdivergent growth pattern

204


Adult patients-molar extrusion is not compensated by vertical ramal growth.

205

Tooth movements of bite opening2.Relative intrusion of incisors- kept where

they are, mandible grows and posterior teeth erupt.

Eruption of posterior teeth is a normal molar vertical change in a growing individual-stable

206


Increase in vertical face height-accommodates if any orthodontic extrusion occurs –leveling the COS, intermaxillary elastics

207

Tooth movements of bite opening3-a Extrusion of posterior teeth-not

compensated in adults-Low mandibular plane angle-not stable-musculature resists extrusionHigh angle cases-weaker musculature-teeth may remain stable-opening of the mandibular plane-undesirable

208

Tooth movements of bite opening3-b Distal tipping of posterior teeth-similar to

the previous situation

209

Tooth movements of bite opening 4.Proclination of incisors- retroclined incisors-

deep bite.

210


Combination of the above-Ex-Bite plate effect-Proclination

Incisor intrusion

Posterior extrusion

211


The importance of 2nd molars-Early banding esp. in low angle and deep bite cases.Inclusion of 2nd molars-lever for extrusion of premolars and assists molar intrusion.

212

Principles for intrusion

Burstone’s important principles for intrusion-

Light constant force

Single point of force application

Sequential intrusion

Good anchorage control

Analysis of forces and moments in each biomechanical situation

213

Leveling by intrusion

Bypass mechanics -

Begg bends and modifications

Cetlin’s intrusion arch

2x 4 mechanics

Utility arch

214


Segmented mechanics-

Burstone’s intrusion arch

3-piece intrusion arch

Connecticut intrusion arch

215

Leveling by extrusion (relative intrusion)Continuous arch-

COS

Kameda’s modification

Anchor curve

K-SIR archwire

216

Bypass Arches

Begg mechanics-Conventional Begg-mainly resulted in molar extrusion.

Heavy elastics and not so rigid base wires.

More emphasis –true incisor intrusion

Various methods of incisor intrusion and

different arch wire modifications for

improving efficacy of incisor intrusion.

217

Bypass Arches

Begg mechanics-

All 6 anteriors are intruded together -

Anchor bend

Anchor bend-

218

Bypass Arches

Round wire derives its bite opening force-anchor bend.Force passes labial to CresLabial flaring of incisors-undesirableClass II elastics

219

Bypass Arches

Class II elastics-horizontal and vertical component-

Vertical component-Dec the efficacy of intrusive force

Horizontal component-influences the net resulting force.

220

Bypass Arches

Interplay b/w intrusive force and retractive (elastic) force-Begg technique controls the vertical dimension- planned imbalance between archwire and elastic force.Optimal intrusive force-15-30 grams/upper incisor

221

Bypass Arches

Kesling –

Bite opening bends-1.5-1.2 oz –midlines

Class II extrusive force-I oz

Net intrusive force-0.5 oz

222

Bypass Arches

14 g for 3 teeth-below optimal force

Lower incisors-1.2 oz-30 grams

Upper incisors should receive -60-70 g net

force.

Class II elastic force-very light forces to be used (reqd for tipping)Yellow (5/16) or road runner (3/8)-5 g

223

Bypass Arches

Exact estimate of force value –not possible Higher intrusive archwire force and light extrusive forceArch wire size-table

224

Bypass Arches

Mollenhauer -0.18 ss (PP)-50°Severe tip of the anchor molars

Distal elastics –wire ends

Molar tubes on both 1st and 2nd molars-vertical anchorage -2 molars on either side

Bite opening curve

225

Bypass Arches

Direction of resultant force-Teeth move in direction of resultant-intrusive and elastic force.Resultant ideally - pass thro’ the Cres.

Resultant depends on -interplay B/w,

Magnitude of intrusive force (direction-constant)

226

Bypass Arches

Magnitude and direction of elastic force-

Different inclinations of anterior teeth-different combination of forces

227

Bypass Arches

Teeth - very proclined-low intrusive force & light class II-intrusion and retraction

As proclination decreases -increase amount of intrusive force-inc. bend /change wire

228

Bypass Arches

Change in vertical orientation becomes progressively smaller for same increments of inc. in intrusive force-Class II force-less magnitude

Class I-inclination improves (Reinforce anchorage)

229

Bypass Arches

Elastics from a higher point of attachment

Direct high pull headgear-inc in force level-damage the roots

230

Bypass Arches

Incisors-retroclined-no elastic force initially

231

Bypass Arches

Location of bite opening bends-different sites of bends-actions different

232

Bypass Arches

Conventional anchor bend-3mm mesial to molar tube-bowing of the archwire-more intrusion of upper canines

233

Bypass Arches

Gable bend-distal to canine-maintain intrusion-relative extrusion of canines

Hocevar’s modification-bend on either side of canine-only centrals intruded-canine and laterals extruded.

234

Bypass Arches

Modifications for uniform intrusion-6 anteriors-requiring significant amount of intrusion.

Gingival curve-Swain

235

Bypass Arches

Vertical step-up-augments intrusive action. Intrusive force applied higher –offsets extrusive action of gingival curve on canines-uniform intrusion 6 teeth

236

Bypass Arches

Cuspid circles –anterior incisal-prevents extrusion

237

Bypass Arches

Elastics from TPA (Palatal elastics) –Dr.JayadeDirection of elastic has to be changed.

Hooks soldered –line with lateral incisors.Oval shaped wire-soldered at the centre-lower from palate-neutralize extrusive component on molars.

238

Bypass Arches

Manipulating mechanics of palatal elastics-Neutralizes proclining effect of arch wireAugments intrusive force

239

Bypass Arches

Cephalogram used to find resultant-labially acting-intrusive force and palatal elastic (barium coated)

240

Bypass Arches

241

Bypass Arches

Power arms-Dr. Jyothindra kumar0.018 x 0.025 –hooks formed and soldered to the buccal aspect of upper molars

242

Bypass Arches

Cetlins‘s intrusion arches-Progressive /sequential intrusion-

243

Bypass Arches

Normally inclined incisors-Rectangular sectional on incisors

244

Bypass Arches

Intrusion arch tied to sectional wire-b/w central and lateralLight(2 oz) force-counter labial tipping

245

Bypass Arches

Labially inclined-PFA moved distallyRectangular-0.018x 0.025 inch/0.021 x 0.025Wire extended distally-2 helices bent-Rt. angles to intrusion arch

246

Bypass Arches

Helices=PFA-slightly in front of Cres.Light elastic force

247

Bypass Arches

Lingually inclined-PFA moved frontRigid rectangular -0.018 x 0.025/0.021 x 0.025-sectional on centrals

248

Bypass Arches

Wire bent forward and upward-hooks bentInserted into intrusion archLight elastic force

249

Bypass Arches

2 x 4 mechanics- 2 molars banded & 4 brackets on incisors.Analysis of the 2 x 4 appliance system-

Incisors considered as 1 unit -1 centre of resistance

Only molars and incisors bracketed-couples created and stored in the wires-larger with higher range than fully bracketed appliance system

250

Bypass Arches

The essence of activating a 2 x 4 –create and control moments and their equilibrium forces.2 x 4 –one couple

251

Bypass Arches

252

Bypass Arches

2 x 4 –two couple

253

Bypass Arches

254

Bypass ArchesMulligan’s 2 x 4 –can be used in the Begg set up-

Upper molars do not require tipping-helix bent into arch wire- 2-3mm mesialAnchor bend ,continuation of the helixNo cuspid circles required

‘Rowing effect’-moments at molars- retract incisors

255

Bypass Arches

256

Bypass Arches

Utility arches- one of the most versatile auxiliary arch wires-

Developed according to biomechanical principles described by Burstone and popularized by Ricketts.Originally developed-to level the curve of Spee.Through the incorporation of loops –performs more functions than intrusion.

Passive, intrusion, retraction, protraction utility

257

Bypass Arches

Basic components of utility arches-

Wire material- -blue elgiloy - in .018 slot .016 x .022- slot (maxilla) & .016 x .016-mandibular - in .022 slot-.019 x .019 Continuous rectangular steel wire-bypass mechanics

258

Bypass Arches

Intrusion utility-Stepped gingivally at the molars5mm space between anterior border of auxiliary tube and post. vertical segment.

259

Bypass Arches

Activation-2 waysBench (1988) –tip back bend in molar

Posterior tipping of molars seen

260

Bypass Arches

Gable bend-unwanted posterior tipping avoided

261

Bypass Arches

Similar to intrusion arch-biomechanics differ

Line of force in utility arch dictated by the location of the bracket-always be facialIn one couple-point contact-line of force varied.

Third order couple created-equilibrium forces modified

262

Bypass Arches

263

Bypass Arches

If torque introduced-

264

Bypass Arches

• Cinching back the wire-new horizontal system

•Molar root-mesially- Cres of moves mesially

•Lingual force at incisor brackets-restricts flaring •Lingual root movement

265


and Aligning


266


Bite opening can mainly be done by-

Absolute intrusion

Relative intrusion

Extrusion of posterior teeth/distal tipping

Proclination of incisors

Combination

267


Bypass mechanics -

Begg bends and modifications

Cetlin’s intrusion arch

2x 4 mechanics

Utility arch

268


Segmented mechanics-

Burstone’s intrusion arch

3-piece intrusion arch

Connecticut intrusion arch

269

Leveling by extrusion (relative intrusion)Continuous arch-

COS

Kameda’s modification

Anchor curve

Leveling by Extrusive mechanics

270

Segmented mechanics

Initial alignment within antero-posterior

segments

Once teeth within segments-aligned, each

treated as 1 large multi-rooted tooth

Creation of appropriate-anchorage and tooth

moving segment

Segmented arch technique not only has

advantages when aligning or space closure is

required; but produces genuine intrusion of

anterior teeth

271

Segmented mechanics

Burstone’s intrusion arch-

The basic mechanism for intrusion in segmented arch consists of 3 parts-

1. Posterior anchorage unit2. An anterior segment3. Intrusive arch spring

272

Segmented mechanics

Posterior teeth aligned and joined together-

buccal stabilizing unit –at least -0.018 x 0.018

(0.022).

Right and left segments joined together-TPA /

low lingual arch

273

Segmented mechanics

No need of continuous adjustments-single

multirooted tooth

To increase stability-0.018 x 0.025 or 0.021 x

0.025 can also be placed in the posterior

segment

Intrusive springs-auxiliary tube -.018 x .025

Standardized regardless of slot dimension of strap up

274

Segmented mechanics

The tooth to tooth adjustments are not made-only adjustments required - b/w auxiliary tube on molar and anterior segment.

275

Segmented mechanics

The intrusion arch-.018 x .025 –edgewise wire3mm helix wound - 2 ½ times placed mesial to auxiliary tube.

276

Segmented mechanics

Curvature –placed so that incisal portion lies gingival to incisors.Arch - tied to level of the incisorsIn order that arch length does not increase during activation-gentle curvature given

277

Segmented mechanics

Curvature –increases as one approaches the helixActivated wire-appears straightAs arch length decreases during intrusion-no labial flaring produced

278

Segmented mechanics

Intrusive spring is not directly engaged into the incisor bracketAn anterior alignment arch 0r anterior segment wire-in incisor bracketsIntrusive wire is placed either labially, incisally,or gingivally to the wire.

279

Segmented mechanics

280

Segmented mechanics

Canine intrusion spring-Canine is bypassed during intrusion-

100 grams / side required-intrusion of incisors and canines

If perpendicular distance-30mm-3000 gm.mm of moment on the posterior segment

Headgear required

281

Segmented mechanics

2 situations requiring separate canine intrusion-

Canine lies (bilaterally) occlusal to premolar Canines have not erupted symmetrically

Canine intrusion spring- .018 x.025-auxiliary tube

Labial flaring prevented-constructive force in the spring

282

Segmented mechanics

If molar auxiliary tube not available-most anterior premolar tube used

Canine root spring-simultaneously retract the root and intrude the canine

283

Segmented mechanics

Three piece intrusion (base) arch-

Simultaneous correction of deep bite correction and space closure in patients with flared incisors.

Intrusive force and its direction-effectively controlled.

Simultaneous control in vertical & anteroposterior planes

Low load deflection rate- constant force

Statically determinate force system

284

Segmented mechanics

Intrusion arch developed-True intrusion of either upper or lower anteriorsIn a case with flared incisors-continuous arch wire-worsens the axial inclinations of anterior teeth.

285

Segmented mechanics

1 solution-distal extensions

286

Segmented mechanics

Using segmented arch technique-precise and predictable force system

Pure intrusion and axial inclination control –anteriors

Well controlled moment-posteriors

Constant levels of force maintained

287

Segmented mechanics

Right and left buccal segments-aligned-.017 x .025 SS

TPA-.032 x.032 SS

Canines may be retracted separately –included in the buccal segments or left in initial positions

Anterior segment-aligned-low stiffness wire

288

Segmented mechanics

Assessment of location of Cres

Lateral cephalogram

4 incisors –usually estimated-half way b/w crest of alveolar bone and root apex of lateral incisor-sagittal plane

289

Segmented mechanics

The intrusion arch-.018 x .025 or .021 x .25 SS wire with distal extensions below Cres –placed passively-anterior bracketsDistal extensions-end 2-3 mm distal to Cres Anterior segment-stepped around the canines

290

Segmented mechanics

Bilateral tipback spring -.017 x.025 TMA

291

Segmented mechanics

Biomechanics Intrusive force – perpendicular to distal extension -through Cres intrude incisor segmentChange in the net intrusive force-small distal forceForce-lingual to CresLine of force-parallel to long axis

292

The force-lingual to Cres-combination of intrusion and tipback of anterior teethLine of action-made parallel-appropriate distal forceLine of action-through Cres-point of force application –anterior-close to distal end of lateral bracket.

293

Segmented mechanics

Intrusive force-placed distally-moment generated –tip back of anterior teethDistal force-low-redirect the intrusive force

294

Segmented mechanics

Clinical applications-

Simultaneous intrusion and tip back-space closed b/w canines and incisors.

Distal movement of canines-as anteriors retract

If canines-distalized first-included in buccal segment

295

Tip back moment –molar-900 gm.mm

296

Segmented mechanics

Redirection of force-reduces the moment on the molar

Headgear not required

297

Segmented mechanics

Resulting force system-modified by changing –magnitudes, point of application of intrusive and distal forces with respect to Cres.

298

Segmented mechanics

Connecticut intrusion arch- Ravindra Nanda et al

CTA-fabricated -NiTi alloyPreformed –appropriate bends2 wire sizes-.016 x .o22 & .017 x .025

299

Segmented mechanics

300

Segmented mechanics

Various applications-

Incisor intrusion

Class II molar correction

Incisor flaring

Correction of minor open bite

Correction of anterior occlusal cant

301

Segmented mechanics

Incisor intrusion-

50 grams

Slight differences in placement-alter force

system during activation

Spring gauges used

1mm-every 6 weeks

Headgear required

302

Segmented mechanics

Point contact-tying the intrusion arch

Excess flaring-tied at lateral incisors

Labial flaring prevented-tight cinch.

303

Segmented mechanics

Steps –how CTA is used for incisor intrusion-

1. Insert section of wire-incisor brackets

2. Choose appropriate CTA (long for non - extraction

or short for extraction/mixed dentition)

3. Cut-leaving 3mm/side –cinch back

4. Insert posterior legs into auxiliary tubes

5. Tie CTA to anterior segment at lateral incisors &

b/w centrals.

304

Segmented mechanics

305

Segmented mechanics

306

Segmented mechanics

Simultaneous class II molar correction-‘v’ bend –distal crownHigh-pull headgear –outer bow above Cres to upright the roots

307

Segmented mechanics

308

Segmented mechanics

Incisor flaring-Either full engagement into bracketNo cinch back

309

Segmented mechanics

Correction of open bite-CTA inserted upside downAnterior portion of wire-occlusal to incisorsExtrusion of incisorsMesial tipping moment-intrusive force –molarHigh pull headgear /inclusion of premolars-counter mesial tipping

310

Segmented mechanics

Correction of anterior occlusal cant-

Identify the offending teethTie only those teeth to be intruded/extrudedCant-tie only that side that needs to be corrected

311

Leveling by relative intrusion-Continuous arches

Bite opening curves-MBT-prefer not place in round or rectangular heat activated wiresPlaced only IF necessary after the SS rectangular wires have been in place for 6 weeks

312


In upper-bite opening curve increases palatal root torque-beneficial

Sometimes additional torque-required

313


Lower-bite opening curve-proclination of lower incisors10-15° of labial root torque to be addedNet effect-intrusive and retroclining force

314


Anchor curve –Mollenhauer & Kameda’s design-

Canines and premolars-extruded

Laterals and centrals-progressive intrusion

315


Extrusion-expresses fasterLeveling –more on account of extrusion

316


Rocking chair NiTi

317

Leveling-posterior extrusion

In cases where deep bite leveled extrusive mechanics-extrusion arches are used. Two types

Type-I-lower arch –to level the curve of SpeeCotinuous/3 –piece extrusion arch is used

318

Leveling-posterior extrusion

Type-IIParallel extrusion of posteriors

Extrusion arch with cervical headgear

Anterior bite plate

319

Knowledge is the antidote to fear.

- Ralph Waldo Emerson

320

References

1. Refined Begg for modern times-V.P.Jayade2. Contemporary orthodontics - William.R.Proffit(3rd

ed.) 3. Dentofacial orthopaedics with functional

appliances-Thomas M.Graber, Thomas Rakosi, Alexandrer G.Petrovic.

4. Orthodontics – current principles and techniques- T.Graber, R.L.Vanarsdall -3rd ed

5.Systemized orthodontic treatment mechanics- McLaughlin, Bennett ,Trevisi

321

References

6. Orthodontic and orthopedic treatment in the mixed dentition-J.A. McNamara

7. Biomechanics in clinical orthodontics-Ravindra nanda

8. Biomechanics and esthetic strategies in orthodontics

9. Biomechanics in orthodontics- Michael R.Marcotte

10. Modern edgewise mechanics and the segmented arch technique- Charles J. Burstone

322

References

11.Force systems from an ideal arch. Burstone and Koenig – AJO march 1974;65:3; 270-289

12.Deep overbite correction by intrusion. Burstone- AJO 1977;73;1.1-22

13.Common sense mechanics. Thomas F Mulligan .JCO 1979,80. Article numbers- 1,2, 3,8,13

14.Mechanics of tooth movement- Richard Smith and Charles Burstone- AJO April 1984 85:4-294-306

323

References

15.Utility arches. James A Mc Namara 1986 JCO. 2o;7;455- 456

16.Equilibrium situations in bend force systems: Christian Demange - AJO 1990;98:333-9

17.The ground rules for arch wire design Robert Isaacson- Seminars in orthodontics,

vol 1,No1(March),1995

324

References

18.One couple orthodontic appliance systems Steven j. Lindauer- Seminars in orthodontics, vol

1,No1(March),1995

19.Two couple orthodontic appliance system A Two couple Intrusion Arch Moshe Davidovitch- Seminars in orthodontics, vol 1,No1(March),1995

2o. Two couple orthodontic appliance systems: Activations in the Transverse Dimension

Joe Rebellato- Seminars in orthodontics, vol 1,No1(March),1995

325

References

21.Activating a 2x4 appliance. Isaacson and Rubenstein – AO 1993;63;1. 17-24

22.Segmented approach to simultaneous intrusion and space closure: Biomachenics of the 3 piece base arch appliance. Bhavna Shroff, Lindauer, Burstone, Leiss. AJO 1995; 107;2;136-143

23.Simultaneous intrusion and retraction using e 3 piece base arch. Bhavna Shroff et al. AO 1997; 67;6; 455-4622

24.The Connecticut intrusion arch. Ravindra Nanda et al. JCO 1998. 32;12;708-715.

326

References

25.M.D.S dissertation- Determination of the centers of resistance of all the individual teeth and groups of teeth using FEA. -Dr. Sujana chava

fudamentals of biomechanics and biomechanics of levelling and aligning(includes biomechanics of...

Documents

groups of teeth

number of teeth

individual teeth

estimation of cres

definitionsthe cres

cres of mand

entire arches of teeth

single rooted teeth