bio mech of dent implants

8/9/2019 Bio Mech of Dent Implants

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BIOMECHANICS OF DENTAL

IMPLANTS


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CONTENTS

Introduction

Loads applied to dental implants

Mass, orce and !ei"#t

Forces and components o orces

T#ree t$pes o orces

Stress

Stress%strain relations#ip

Bitin" orces

Predictin" orces on oral implants

Stiness o teet# and implant

Models or predictin" orces on prost#esis supported &$teet# and implants


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Force deli'er$ and ailure mec#anism

Moment loads

Clinical moment arms

Fati"ue ailure

T#e &iomec#anical response to loadin"

A scientiic rationale or dental implant desi"n

C#aracter o t#e applied orces

Functional surace area

Biomec#anics o rame!or(s and misit

Treatment plannin" &ased on &iomec#anical ris( actors

Conclusion

List o reerence


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LOADS APPLIED TO DENTAL IMPLANTS

In function occlusal loads

Absence of function Perioral forces

Horizontal loads

Mechanics help to understand such physiologic and non

physiologic loads and can determine which t/t renders more risk.

MASS, FO)CE AND *EI+HT

Mass A property of matter is the degree of gra!itational attraction

the body of matter e"periences.

#nit kgs $ %lbm&


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FO)CE -SI) ISAAC NE*TON ./012

'ewton(s II law of motion

) * ma

+here a * ,.- m/s

Mass etermines magnitude of static load

)orce 0ilograms of force

*EI+HT

Is simply a term for the gra!itational force acting on an

ob1ect at a specified location.


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FO)CES AND FO)CE COMPONENTS

Magnitude duration direction type and magnification

23ector 4uantities(

irection dramatic influence

5reak down of 6 forces into their component parts 7

2!ector resolution(

Point of action of a !ector3ECTO)

F/ ) Magnitude )


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) * 88.9 ' at pt 5

Analysis 7 !ector resolution

:o7ordinate system

Angles that the ) !ector makes with co7ordinate a"es

resolution of ) into its 6 components is possible

i.e. )" )y ; )z

) * )

" < )

y < )

z

:os" < :osy < :osz * =

>ateral as well as !ertical components are acting at the same

time

'ot ?? to direction of long a"is of implant


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3ector addition4 More than one force F)5 F.6 F76 F8

MOMENT 9 TO):;E

@end to rotate a body #nits '.m '.cm lb.ft oz.in

E" 4

In addition to a"ial force there is a moment on the implant which is

e4ual to magnitude of force times %multiplied by& the perpendicular

distance %d& between the line of action of the ) and center of theim lant


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TH)EE T


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@ensile Bhear

Pull ob1ect apart Bliding

istract / disrupt bone implant interface

Bhear most destructi!e cortical bone is weakest

:ylinder implants highest risk for shear forces

re4uire coating

@hreaded / finned implants

Impart all 6 force types

Ceometry of implant


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ST)ESS

@he manner in which a force is distributed o!er a surface is

referred as mechanical stress

5 F9A

D!en distribution of mechanical stress in the implant system and

contiguous bone

Force ma"nitude

Eeducing magnifiers of force

=. :antile!er length

. :rown height

6. 'ight guards

8. Fcclusal material

9. F!erdentures

Functional cross sectional area

=. 'umber of implants

. Implant geometry


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DEFO)MATION = ST)AIN

Applied load deformation

eformation and stiffness of implant material

Interface

Dase of implant manufacture

:linical longe!ity

:oncept of strain key mediator of bone acti!ity

Implant

@issue

Btrain * deformation per unit length


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ST)ESS ST)AIN )ELATIONSHIP

>oad !ersus deformation cur!e stress 7 strain cur!e

Prediction of amount of strain e"perienced by the material underan applied load.

In stress

In stiffness difference Eelati!e motion

Interface is more affected

3iscoelastic bone can stay in contactwith more rigid titanium more

predictably when the stress is low

Modulus of elasticity

tnalpmI >biologic tissue

>esser the relati!e motion


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ST)AIN

:ontrolling applied stress :hanging density of bone

Btrength Btiffness

Creater the strength stiffer the bone

>esser the stiffness greater the fle"ibility %soft bone&

ifference in stiffness is less for :p@i ; =bone but more for 8bone

Btress reduction in such softer bone

@o reduce resultant tissue strain

#ltimate strength

Hook(s law

Btress * Modulus of elasticity " strain*


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BITIN+ FO)CES

A"ial component of biting forces $ %=GG 9GG '& / % 99G lbs&

It tends to increase as one mo!es distally

>ateral component 7 G ' %appro".&

'et chewing time per meal * 89G sec

:hewing forces will act on teeth for * , min/day

If includes swallowing * =.9 min/day

)urther be increased by parafunction

Pro!ides minimum time /day that teeth %implants& are bearing load

due to mastication and related e!ents


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P)EDICTIN+ FO)CES ON O)AL IMPLANTS

Pro&lems 4

@o compute the loading on the indi!idual supporting abutment

More than two implant supporting prosthesis

COMPLICATIN+ FACTO)S

Nature o mastication

:hewing fre4uency

se4uence

5iting strength

fa!oured side

Mandibular mo!ements

Nature o Prost#esis

)ull / partial

@issue supported

3s

Implant supported

'o. ; location

Angulation

Properties

Dlastic moduli

Btiffness

:onnection

eformability


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T!o implants supportin" a cantile'er portion o a prost#esis

P * )orce

a * :antile!er length

b * ist. 5etween two implants

If beam is in static e4uilibrium sum of forces and sum ofmoments are zero.

)y * G 7)=< ) P * GmJ* G 7)=b < Pa * G

Here )= * %a/b&P ) * %= < a/b& P

In most clinical situations a/b * .

Bo )= * P and ) * 6P

'ewton(s 6rdlaw of motion

Implant compressi!e load Implant =tensile load


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FO;) IMPLANTS S;PPO)TIN+ A F)AME*O)?

-B)ANEMA)? S


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5ridge and bone are rigid

Implants and/or their connections to bridge and/or bone elastic

Purely !ertical force Purely horizontal force

:ounterbalanced by distribution of ' no. of implants so there

will be both !ertical and horizontal forces on each implant


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8 or K implant symmetrically distributed in the arc of ==.9G

with radius of mandible at .9 mm

Arc of ==.9G* interforaminal dist. %appro"&

Bingle !ertical force of 6G' acts at a position defined by * =GG

%Bo how to predict the !ertical forces on each implant&

F 8 N Ma"nitude o orce is >>>


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)orces on remaining 8 implants become much larger than in

original K implant case

:ondition can be worsened if 8 implants are placed in a line acrossthe anterior mandible.

As ratio a/b is !ery large as b %interimplant distance& is !ery

small.

Implant angulation.


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Implant = at 6GGangulation.

Fffa"is loading detrimental to the system.

:annot be sol!ed by Bkalak or Eangert model.

)inite element modelling or analysis.

Properties of the prosthesis

Positioning and angulation of implants

Properties of interfacial bone can be accounted to )D


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S(ala( modle

Prosthesis is infinitely rigid

Acrylic and metal alloy bridge fle"ible

:oncentrating forces on the implants nearest to loading point

#ne4ual stiffnesses

Btiffest implant will generally take up most of the load


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STIFFNESS OF TOOTH AND IMPLANT

Prosthesis supported by teeth and implants.

'either Eangert nor Bkalak model specifically deal with

differencing mobility

A way to approach this problem is

=. isplacement in any direction

#nidirectional force but displacement in many direction

Becondary effect

. Application of constant force

Increase in displacement slowly with time

:reep

'ot significant with implants

6. Intrusi!e tooth displacement is not always >inear usually bilinear

8. 'et stiffness L natural tooth


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P)OSTHESIS S;PPO)TED B< TEETH AND IMPLANTS

#se of )DA

:oncept of IMD

e"4) * =GG '

'atural tooth * 6G when paired with an implant without IMD

* 6- when IMD is incorporated

Eationale for use of IMD

Dffecti!eness in clinical situations ha!e to be checked

Eangert et al

D4ual sharing of forces by tooth and implant so need for IMD

in an osseointegrated implant is 4uestionable.


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FO)CE DELI3E)< AND FAIL;)E MECHANISM

Manner of application of force

Moment loads

Interface breakdown

5one resorption

Bcrew loosening

5ar / bridge fracture

Clinical moment arms


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72 Cantile'er len"t#

3ertical a"is force components

>ingual force component

)orce applied directly o!er the implant

8 or K implant case

D"act cantile!er length

76 premolars

K instead of 8 implants

A7P spread

A7P spread the resultant load


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MISCH

Amount of stress applied to system

Cenerally

istal cantile!er not be L .9 times of A7P spread

Patients with parafunction not to be restored by cantile!er

B4uare arch form 7 A7P spread 7 cantile!er

@apered arch form largest A7P spread largest cantile!er

design.


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FATI+;E FAIL;)E


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FATI+;E FAIL;)E

D$namic c$clic loadin" condition

.2 Biomaterials

A plot of applied stress !s no. of loading cycles

High stress few loading cycles

>ow stress infinite loading cycles

Dndurance limit

@i alloy L :p@i.

72 +eometr$

Eesists bending and tor4ue

>ateral loads fatigue fracture

8thpower of the thickness difference

Inner and outer diameter of screw and abutment screw space


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82 Force ma"nitude

Eeduction of applied load 7 %stress&

Higher loads on posteriors

Moment loads

Ceometry for functional area

'o. of implants

2 Loadin" c$cles

'o. of loading cycles

Dlimination of parafunction

Eeduce occlusal contacts


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BIOMECHANICAL )ESPONSE TO LOADIN+

High degree of !ariation as a function of load direction rate and

duration

irection of load

Ort#otropic Isotropic Trans'ersel$ isotropic

MandibleArch of it ha!ing stiffest direction orientation

>ong bone molded into a cur!e beam

Primary loads * occlusal N )le"ural

Inferior border more compact bone

Inter forminal part increase 4uality of trabecular bone

)ATE OF LOADIN+


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)ATE OF LOADIN+

McDlhaney strain rate dependence

Higher strain rate stiffer and stronger

5one fails at higher strain rate but with less allowable

elongation

5rittle

Duration o loadin"

2:arter and :aler(

:reep %time7dependent loading& < cyclic / fatigue loading

Anatomic location and structural density also has got influence


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ANATOMIC LOCATION

Ddentulous mandible @rabecular bone continuous with cortical

shell

)DM cortical bone dissipation of occlusal loads

Attention to trabecular bone mechanical properties

Muscle loads on mandible orso!entral shear twisting

trans!erse

Anterior mandible large moment loads buccolingal fle"ure

Posterior mandible higher bite force

ensity and ultimate compressi!e strength %

&

>arge multirooted molars


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:u et al K9 higher stiffness for trabecular bone of mandible

when bounded by cortical plates

Structural densit$:u et al Mechanical properties of mandibular trabecular bone

I.e. Dlastic modulus and ultimate strength.

8 7 K- L in anterior compared to posterior

Premolars * molars.

Scientiic rationale or dental implant desi"n

@ransfer of load to surrounding biologic tissue. @wo factors are

=& :haracter of applied load & )unctional surface area

:haracter of forces applied to dental implant

Magnitude duration type direction and magnification


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FO)CE MA+NIT;DE

A2 P#$siolo"$ 's desi"n 4

>imits magnitude of force for a engineered design

)unction of anatomic region and state of dentition

Parafunction L Molar L :anine L Incisors

=GGG lb GG lb =GG lb 9769 lb

density forces

B2 Bi t i l l ti


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B2 Biomaterial selection 4

Bilicone HA carbon High biocompatibility

>ow ultimate strength

@itanium and its alloy D"cellent biocompatibility

:orrosion resistance

Cood ultimate strength

:losest appro". to stiffness of bone

K times more stiff

C2 Failures 4

3itreous carbon implant AlF6 ceramic implant

Modulus of elasticity #ltimate strength

#ltimate strength Modulus of elasticity


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FO)CE D;)ATION

A2 P#$siolo"$ 's desi"n

uration of bite force

Ideal condition O 6G min/day

Parafunction se!eral hours

B2 Implant &od$ desi"n

Dndurance limit = times O ultimate tensile strength

)atigue more critical especially in parafunction

Fff a"is cyclic loading

5ending loads in buccolingal plane

Eoot form implant not specifically designed to withstand

cyclic bending loads.


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:omponents moment of inertia

Apical e"tension of the abutment screw within the implant

body

:rest7module around an abutment screw

%FE&8 %IE&8

Bmall

in wall thickness is significant

F by G.= mm 66 in strength

I by G.= mm G in strength

Prosthesis / coping screw moment of inertia

Bcrew breakage long term ad!antage

)ailure Morgan et al


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FO)CE T


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TH)EADED IMPLANTS

5uttress comparable to 37shaped

37shaped =G times greater shear %s4uare / power&

:aution in 6and 8bone

Failure

Bmooth shear surface inade4uate load transfer

3%s#apedSGuareButtress


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FO)CE DI)ECTION

A2 P#$siolo"$

Positioning of root form implants suitable for a"ial loading

#ndercuts further limit

#sually occur on facial aspect e"cept

Bubmandibular fossa

Angled to the lingual

5one is strongest when loaded along its long a"is.

6GG offset load $ == compressi!e

9 tensile

B2 Implant &od$ desi"n

3ulnerable crestal bone region


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FO)CE MA+NIFICATION

D"treme angulation

Parafucntion

:antile!ers and crown heights le!ers

Indication for

functional surface area

ensity strength

8bone =G times weaker than =bone

@hus resultant force will be magnified when placed in softer

bone

D"ceeds the capability of anydental implant

S;)FACE A)EA


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S;)FACE A)EA

'ormal anatomy limits size and configuration

Bone 'olume -eternal arc#itecture2

Anatomic location and degree of bone resorption

*idt# 4 K7- mm in anterior8 mm implant

L mm in posteriors 9 mm implants

Implant widthanterior to posterior

Hei"#t 4

Anterior mandible L anterior ma"illa L post mandible L post ma"illa

Hence

occlusal forces

in bone heightBone Gualit$ -internal arc#itecture2

69 failure rate in 8 bone

Poor 4uality porous bone 7 ed clinical failure

'o. of implants design with greater surface area

S;)FACE A)EA OPTIMIATION


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S;)FACE A)EA OPTIMIATION

Implant macro"eometr$ 4

Bmooth sided cylindrical implants Dase in surgical placement

Creater shear at interface

Bmooth sided tapered implants

:omponent of compressi!e force@aper

@aper O 6GG

@hreaded implants

Dase of surgical placement

Creater functional surface area compressi!e loads

>imits micro7mo!ement during healing


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IMPLANT *IDTH

5ranemark 6.9 mm

Implant width 7 functional surface area

8 mm implant 66 greater surface area

iameter appropriate to ridge width

@eethK = mm

Bimilar implant width bending resistanceinade4uate

strain to boneresorption

:restal bone anatomyless than 9.9 mm


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TH)EAD +EOMET)

bio mech of dent implants

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