Scientific rationale and biomechanics in implants

RationaleAnd biomechanics

GOOD MORNING

RationaleAnd biomechanics

SCIENTIFIC RATIONALE ANDBIOMECHANICS IN IMPLANTS

Dr Deepa P M

CONTENTS

Introduction Definition Types of biomechanics Role of biomechanics Elements of biomechanical properties Loads applied to dental implants Forces acting on dental implants Stresses acting on dental implants force delivery and failure

mechanisms Force delivery and failure mechanism Clinical moment arms and crestal bone loss Conclusion References

Introduction Definition Types of biomechanics Role of biomechanics Elements of biomechanical properties Loads applied to dental implants Forces acting on dental implants Stresses acting on dental implants force delivery and failure

mechanisms Force delivery and failure mechanism Clinical moment arms and crestal bone loss Conclusion References

INTRODUCTION

Primary functional design objective is todissipate and distribute biomechanicalloads…

A scientific rationale of dental implant designmay evaluate these designs…

This seminar will build on and apply basicbiomechanics…

Primary functional design objective is todissipate and distribute biomechanicalloads…

A scientific rationale of dental implant designmay evaluate these designs…

This seminar will build on and apply basicbiomechanics…

BIOMECHANICS

It is the relationship between the biologicbehavior of oral structures and the physicalinfluence of a dental restoration.(GPT-8))

Biomechanics is the scientific study of theload-force relationships of a biomaterial inthe oral cavity. (Ralph Mc Kinney).

It is the relationship between the biologicbehavior of oral structures and the physicalinfluence of a dental restoration.(GPT-8))

Biomechanics is the scientific study of theload-force relationships of a biomaterial inthe oral cavity. (Ralph Mc Kinney).

TYPES OF BIOMECHANICS

Reactive Biomechanics:

is the interaction of isolated biomechanical factorswhich when combined, produce a cumulative effect.

TYPES OF BIOMECHANICS

Therapeutic Biomechanics

is the clinical process of altering each biomechanicalfactor to reduce the cumulative response causing implantoverload.

Therapeutic Biomechanics

is the clinical process of altering each biomechanicalfactor to reduce the cumulative response causing implantoverload.

TERMINOLOGIES

MASS: is the degree of gravitationalattraction the body of matter experiences.

FORCE ( F) = ma; m = mass anda= acceleration.

WEIGHT: is the gravitational force acting onan object at a specified location.

MASS: is the degree of gravitationalattraction the body of matter experiences.

FORCE ( F) = ma; m = mass anda= acceleration.

WEIGHT: is the gravitational force acting onan object at a specified location.

TERMINOLOGIES

STRESS: = F/A, F= force and A = Area.

STRAIN: is defined as the change in lengthdivided by the original length.

MODULUS OF ELASTICITY : stress/ strain

STRESS: = F/A, F= force and A = Area.

STRAIN: is defined as the change in lengthdivided by the original length.

MODULUS OF ELASTICITY : stress/ strain

TERMINOLOGIES

ELASTIC LIMIT : the maximum stress a materialcan withstand before it becomes plasticallydeformed.

YIELD STRENGTH: the stress required toproduce a given amount of plastic deformation

ULTIMATE TENSILE STRENGTH: is the measureof stress required to fracture a material.

ELASTIC LIMIT : the maximum stress a materialcan withstand before it becomes plasticallydeformed.

YIELD STRENGTH: the stress required toproduce a given amount of plastic deformation

ULTIMATE TENSILE STRENGTH: is the measureof stress required to fracture a material.

LOADS APPLIED TO DENTAL IMPLANTS

Occlusal loads

Passive mechanical loads

Perioral forces

Non passive prostheses

Occlusal loads

Passive mechanical loads

Perioral forces

Non passive prostheses

CLINICAL LOADING AXES

A force applied to adental implant rarelyis directed absolutelylongitudinally along asingle axis.

Three clinical loadingaxes exist:

1. Mesiodistal2. Faciolingual3. Occlusal.

A force applied to adental implant rarelyis directed absolutelylongitudinally along asingle axis.

Three clinical loadingaxes exist:

1. Mesiodistal2. Faciolingual3. Occlusal.

COMPONENTS OF FORCES

A single occlusal contact most commonlyresult in a three-dimensional occlusal force.The process by which three-dimensionalforces are broken down into their componentparts is referred to as vector resolution.

A single occlusal contact most commonlyresult in a three-dimensional occlusal force.The process by which three-dimensionalforces are broken down into their componentparts is referred to as vector resolution.

COMPONENTS OF FORCES contd..

•Compressive forcesattempt to push massestoward each other.Compressive forces tend tomaintain the integrity of abone-to-implant interface

•Tensile forces pull objectsapart.

•Shear forces on implantscause sliding forces.

•Compressive forcesattempt to push massestoward each other.Compressive forces tend tomaintain the integrity of abone-to-implant interface

•Tensile forces pull objectsapart.

•Shear forces on implantscause sliding forces.

FORCEForces acting on dental implants are referred to as vector

quantities.

Force may be described by:1. Magnitude

2. Duration

3. Direction

4. Type

5. Magnification factors

6. Position in the arch

7. Nature of opposing teeth.

Forces acting on dental implants are referred to as vectorquantities.

Force may be described by:1. Magnitude

2. Duration

3. Direction

4. Type

5. Magnification factors

6. Position in the arch

7. Nature of opposing teeth.

MAGNITUDE

Greater the force applied greater will the stressesdeveloped around the implant.

Parafunctional habits - the magnitude of force greatlyincreases……

normal bite force 23-30 psi

Maximum bite force 50-500 psi

Parafunction - increases upto 4-7 times about 990 psi.

Greater the force applied greater will the stressesdeveloped around the implant.

Parafunctional habits - the magnitude of force greatlyincreases……

normal bite force 23-30 psi

Maximum bite force 50-500 psi

Parafunction - increases upto 4-7 times about 990 psi.

DIRECTION

Implant and the surrounding bone can best withstand forcesdirected along the long axis of the implant…..

Maxillary anterior implants are rarely placed along thedirection of occlusal forces.

Mandibular molars are placed with a lingual inclination of theimplant body…..

Implant and the surrounding bone can best withstand forcesdirected along the long axis of the implant…..

Maxillary anterior implants are rarely placed along thedirection of occlusal forces.

Mandibular molars are placed with a lingual inclination of theimplant body…..

DIRECTION contdOn centric vertical contact

Angle load Axial load

tensile & shear stress compressive stress

Misch 1994

30% offset load - Decreases compressive strength -11%

On centric vertical contact

Angle load Axial load

tensile & shear stress compressive stress

Misch 1994

30% offset load - Decreases compressive strength -11%

TYPE

Cowin 1989

Bone - Strongest - Compression

- 30% weaker - tension

- 65% weakest – shear

Compressive force - Maintain integrity

Tensile and shear - Disrupts integrity

DURATION

Mastication - 9mins/day with 20 to 30 psi

Swallowing - 20mins/day with 3 to 5 psi

The perioral muscles also apply a constant yetlight horizontal force on the teeth and implants.

Parafunctional habits significantly increase theduration of these loads.

Mastication - 9mins/day with 20 to 30 psi

Swallowing - 20mins/day with 3 to 5 psi

The perioral muscles also apply a constant yetlight horizontal force on the teeth and implants.

Parafunctional habits significantly increase theduration of these loads.

The failure of the prosthesis can result from aphenomenon called as creep.

Due to increase in the function of time for aconstant load fatigue fracture occurs in theimplant components.

DURATION contd…

The failure of the prosthesis can result from aphenomenon called as creep.

Due to increase in the function of time for aconstant load fatigue fracture occurs in theimplant components.

FORCE MAGNIFIERS

The magnitude of the force may be decreased byreducing the significant magnifiers of force:-

CANTILEVER LENGTH

OFFSET LOADS

CROWN HEIGHT

The magnitude of the force may be decreased byreducing the significant magnifiers of force:-

CANTILEVER LENGTH

OFFSET LOADS

CROWN HEIGHT

POSITION IN THE ARCH

Maximum biting force occurs in the molar region anddecreases anteriorly.

molar region 127-250 psi

canine region 47-100 psi

Biting force anterior region 30-50 psi

In natural dentition anterior teeth are shorter andposterior teeth are longer and broader in size…………..

Maximum biting force occurs in the molar region anddecreases anteriorly.

molar region 127-250 psi

canine region 47-100 psi

Biting force anterior region 30-50 psi

In natural dentition anterior teeth are shorter andposterior teeth are longer and broader in size…………..

NATURE OF OPPOSING TEETH

Natural teeth offer greater loads than dentures.

The force depends upon-location-condition of the muscles-joint

Natural teeth offer greater loads than dentures.

The force depends upon-location-condition of the muscles-joint

STRESS

The manner in which a force is distributed over a surfaceis referred to as mechanical stress.

Stress = F/A

The internal stresses that develop in an implant systemand surrounding biologic tissues have a significantinfluence on the long-term longevity of the implants invivo.

The manner in which a force is distributed over a surfaceis referred to as mechanical stress.

Stress = F/A

The internal stresses that develop in an implant systemand surrounding biologic tissues have a significantinfluence on the long-term longevity of the implants invivo.

The magnitude of stress is dependent on two variables:-1. force magnitude and2. cross-sectional area over which the force is dissipated.

Force magnitude• Rarely be completely controlled by a dental practitioner.• The magnitude of the force may be decreased by reducing the

significant "magnifiers of force“ :-1. cantilever length,2. offset loads, and3. crown height.

The magnitude of stress is dependent on two variables:-1. force magnitude and2. cross-sectional area over which the force is dissipated.

Force magnitude• Rarely be completely controlled by a dental practitioner.• The magnitude of the force may be decreased by reducing the

significant "magnifiers of force“ :-1. cantilever length,2. offset loads, and3. crown height.

FORCE MAGNITUDE

Night guards to decrease nocturnalparafunction, Occlusal materials that decrease impact force,

and Overdentures rather than fixed prosthesis so

they may be removed at night….. are further examples of force reduction

strategies.

Night guards to decrease nocturnalparafunction, Occlusal materials that decrease impact force,

and Overdentures rather than fixed prosthesis so

they may be removed at night….. are further examples of force reduction

strategies.

FUNCTIONAL CROSS-SECTIONAL AREA

It may be optimized by :-

(1) Increasing the number ofimplants for a givenedentulous site, and

(2) Selecting an implantgeometry that has beencarefully designed tomaximize functional cross-sectional area.

It may be optimized by :-

(1) Increasing the number ofimplants for a givenedentulous site, and

(2) Selecting an implantgeometry that has beencarefully designed tomaximize functional cross-sectional area.

DEFORMATION AND STRAIN

STRAIN

TENSION COMPRESSION

In shear, the shape change is expressed in termsof a change in angle of one part of the bodyrelative to the other.

LENGTHENING SHORTENING

STRESS-STRAIN CHARACTERISTICS

The deformation and strain characteristics ofthe materials used in implant dentistry mayinfluence interfacial tissues, and clinicallongevity.

Elongation (deformation) of biomaterialsused for dental implants range from 0% foraluminum oxide (Al2O3) to up to 55% forannealed 316-L stainless steel.

The deformation and strain characteristics ofthe materials used in implant dentistry mayinfluence interfacial tissues, and clinicallongevity.

Elongation (deformation) of biomaterialsused for dental implants range from 0% foraluminum oxide (Al2O3) to up to 55% forannealed 316-L stainless steel.

STRESS-STRAIN CHARACTERISTICS contd

A relationship is needed between the applied force(and stress) and the subsequent deformation (andstrain).

If any elastic body is experimentally subjected to anapplied load, a load-vs.-deformation curve may begenerated.

A relationship is needed between the applied force(and stress) and the subsequent deformation (andstrain).

If any elastic body is experimentally subjected to anapplied load, a load-vs.-deformation curve may begenerated.

STRESS-STRAIN CHARACTERISTICS contd

Such a curve provides for the prediction of how much strainwill be experienced in a given material under an applied load.

The slope of the linear (elastic) portion of this curve isreferred to as the modulus of elasticity (E), and its value isindicative of the stiffness of the material under study.

STRESS-STRAIN CHARACTERISTICS contd

The closer the modulus of elasticity of the implantresembles that of the biologic tissues, the less thelikelihood of relative motion at the tissue-to-implant interface.

Once a particular implant system (i.e., a specificbiomaterial) is selected, the only way to control thestrain is to control the applied stress or change thedensity of bone around the implant.

The closer the modulus of elasticity of the implantresembles that of the biologic tissues, the less thelikelihood of relative motion at the tissue-to-implant interface.

Once a particular implant system (i.e., a specificbiomaterial) is selected, the only way to control thestrain is to control the applied stress or change thedensity of bone around the implant.

IMPACT LOADS• When two bodies collide in a

very small interval of time(fractions of a second), relativelylarge forces develop. Such acollision is described as impact.

• In dental implant systemssubjected to occlusal impactloads, deformation may occur in

1. the prosthetic restoration,

2. in the implant itself, or

3. in the interfacial tissue.

• When two bodies collide in avery small interval of time(fractions of a second), relativelylarge forces develop. Such acollision is described as impact.

• In dental implant systemssubjected to occlusal impactloads, deformation may occur in

1. the prosthetic restoration,

2. in the implant itself, or

3. in the interfacial tissue.

IMPACT LOADS contd

• The higher the impact load, the greater the riskof implant and bridge failure and bone fracture.

• Rigidly fixed implants generates a higher impactforce than a natural tooth with its periodontalligament.

Various methods have been proposed toaddress the issue of reducing implant loads.

• The higher the impact load, the greater the riskof implant and bridge failure and bone fracture.

• Rigidly fixed implants generates a higher impactforce than a natural tooth with its periodontalligament.

Various methods have been proposed toaddress the issue of reducing implant loads.

IMPACT LOADS contd

Skalak suggested the use of acrylic teeth in conjunction withosteointegrated fixtures. (JPD ; June 1983, vol 49)

Weiss has proposed that a fibrous tissue-to-implant interfaceprovides for physiologic shock absorption in the same manner asby a functioning periodontal ligament.

Misch advocates an acrylic provisional restoration with aprogressive occlusal loading to improve the bone-to-implantinterface before the final restoration, occlusal design, andmasticatory loads are distributed to the system.

Skalak suggested the use of acrylic teeth in conjunction withosteointegrated fixtures. (JPD ; June 1983, vol 49)

Weiss has proposed that a fibrous tissue-to-implant interfaceprovides for physiologic shock absorption in the same manner asby a functioning periodontal ligament.

Misch advocates an acrylic provisional restoration with aprogressive occlusal loading to improve the bone-to-implantinterface before the final restoration, occlusal design, andmasticatory loads are distributed to the system.

•The manner in which forces are applied to implant restorationsdictates the likelihood of system failure.

•If a force is applied some distance away from a weak link in an

implant or prosthesis, bending or torsional failure may result

from moment loads.

FORCE DELIVERY AND FAILUREMECHANISMS

•The manner in which forces are applied to implant restorationsdictates the likelihood of system failure.

•If a force is applied some distance away from a weak link in an

implant or prosthesis, bending or torsional failure may result

from moment loads.

The moment of a force about a point tends to producerotation or bending about that point.

The moment is a vector quantity.

MomentMoment LoadsLoads == forceforce magnitudemagnitude XX momentmoment armarm

This imposed moment load is also referred to as a torque or

torsional load and may be quite destructive with respect to

implant systems.

Moment Loads

The moment of a force about a point tends to producerotation or bending about that point.

The moment is a vector quantity.

MomentMoment LoadsLoads == forceforce magnitudemagnitude XX momentmoment armarm

This imposed moment load is also referred to as a torque or

torsional load and may be quite destructive with respect to

implant systems.

100 N

Proper restorative design must necessarily include considerationof both forces and the moment loads caused by those forces.

CLINICAL MOMENT ARMS AND CRESTAL BONE LOSS

A total of six moments (rotations) may develop about the threeclinical coordinate axes.

Such moment loads induce microrotations and stressconcentrations at the crest of the alveolar ridge at the implant-to-tissue interface, which leads to crestal bone loss.

Three "clinical moment arms" exist in implant dentistry:-1. Occlusal height,2. Cantilever length, and3. Occlusal width.

Occlusal height serves as the moment arm for force componentsdirected along the faciolingual axis as well as along the mesiodistalaxis.

OCCLUSAL HEIGHT MOMENT ARM

Moment of a force along the vertical axis is not affected by theocclusal height because there is no effective moment arm. Offsetocclusal contacts or lateral loads, however, will introduce significantmoment arms.

Morecrownheight

Furtherincrease in

crownheight

OCCLUSAL HEIGHT MOMENT ARM

Morecrownheight

Verticalcantilever

Morestress at

the crestalareas

Boneresorption

Furtherincrease in

crownheight

• Large moments may develop from vertical axis forcecomponents in cantilever extensions or offset loads fromrigidly fixed implants.

• A lingual force component may also induce a twistingmoment about the implant neck axis if applied through acantilever length.

CANTILEVER LENGTH MOMENT ARM

• Large moments may develop from vertical axis forcecomponents in cantilever extensions or offset loads fromrigidly fixed implants.

• A lingual force component may also induce a twistingmoment about the implant neck axis if applied through acantilever length.

• A 100-N force applied directly over the implant does not induce amoment load or torque because no rotational forces are appliedthrough an offset distance.

• This same 100-N force applied 1 cm from the implant results in a100 N-cm moment load.

• Similarly, if the load is applied 2 cm from the implant, a 200 N-cmtorque is applied to the implant-bone region, and 3 cm results in a300 N-cm moment load.

(Implant abutments are typically tightened with less than 30 N-cmof torque).

• A 100-N force applied directly over the implant does not induce amoment load or torque because no rotational forces are appliedthrough an offset distance.

• This same 100-N force applied 1 cm from the implant results in a100 N-cm moment load.

• Similarly, if the load is applied 2 cm from the implant, a 200 N-cmtorque is applied to the implant-bone region, and 3 cm results in a300 N-cm moment load.

(Implant abutments are typically tightened with less than 30 N-cmof torque).

A - P DISTANCE

The distance from the center ofthe most anterior implant to thedistal of each posterior implant iscalled the anteroposterior (AP)distance.

The greater the A - P distance,the smaller the resultant load onthe implant system fromcantilevered forces, because ofthe stabilizing effect of theanteroposterior distance.

The distance from the center ofthe most anterior implant to thedistal of each posterior implant iscalled the anteroposterior (AP)distance.

The greater the A - P distance,the smaller the resultant load onthe implant system fromcantilevered forces, because ofthe stabilizing effect of theanteroposterior distance.

Maxillary anterior teeth in a taperedarch form requires more posteriorimplants than in a square arch form,

A - P DISTANCE

A tapered arch form permits greatercantilever length than a square archform in mandibular anterior region.

• The most ideal biomechanical arch form depends on the restorativesituation:-

• Tapering arch form is favorable for anterior implants with posteriorcantilevers.

• Square arch form is preferred when canine and posterior implants areused to support anterior cantilevers in either arch.

• Ovoid arch form has qualities of both tapered and square arches.

• Clinical experiences suggest that the distal cantilever should notextend 2.5 times the A-P distance under ideal conditions.

• Patients with severe bruxism should not be restored with anycantilevers.

A - P DISTANCE• The most ideal biomechanical arch form depends on the restorative

situation:-

• Tapering arch form is favorable for anterior implants with posteriorcantilevers.

• Square arch form is preferred when canine and posterior implants areused to support anterior cantilevers in either arch.

• Ovoid arch form has qualities of both tapered and square arches.

• Clinical experiences suggest that the distal cantilever should notextend 2.5 times the A-P distance under ideal conditions.

• Patients with severe bruxism should not be restored with anycantilevers.

BIOMECAHNICAL CONSIDERATIONS INOSSEOINTEGRATED PROSTHESES-

Richard Skalak JPD 1983

Cantilevered ends of afixed partial dentureincreases the loadingon the first screwnearest thecantilevered end. Moderate overhangs

may be tolerated iffixtures aresufficiently strong.

Cantilevered ends of afixed partial dentureincreases the loadingon the first screwnearest thecantilevered end. Moderate overhangs

may be tolerated iffixtures aresufficiently strong.

OCCLUSAL WIDTH MOMENT ARM

Wide occlusal tables increase the moment arm for any

offset occlusal loads.

Faciolingual tipping (rotation) can be significantly reduced

by narrowing the occlusal tables and/or adjusting the

occlusion to provide more centric contacts.

Wide occlusal tables increase the moment arm for any

offset occlusal loads.

Faciolingual tipping (rotation) can be significantly reduced

by narrowing the occlusal tables and/or adjusting the

occlusion to provide more centric contacts.

BONE RESPONSE TO MECHANICAL LOAD

Bone responds to number of factors includingsystemic and mechanical forces.

Cortical and trabecular bone are modified bymodelling and remodelling…. Controlled bymechanical environment of strain.

Bone responds to number of factors includingsystemic and mechanical forces.

Cortical and trabecular bone are modified bymodelling and remodelling…. Controlled bymechanical environment of strain.

FROST ZONES OF MICRO STRAIN

Pathologic overload zone and acute diseasewindow are the two extremes of the strainconditions.

Each of these conditions result in less bone.

Higher BRR ……. Increased woven boneformation. Mild overload zone…. Higher BRR…..

Increases woven bone formation.

FROST ZONES OF MICRO STRAIN Pathologic overload zone and acute disease

window are the two extremes of the strainconditions.

Each of these conditions result in less bone.

Higher BRR ……. Increased woven boneformation. Mild overload zone…. Higher BRR…..

Increases woven bone formation.

The adapted window zone is most likely to beorganized, highly mineralized, lamellar bone.

It is the ideal strain condition next to a dentalimplant,

FROST ZONES OF MICRO STRAIN

The adapted window zone is most likely to beorganized, highly mineralized, lamellar bone.

It is the ideal strain condition next to a dentalimplant,

FATIGUE FAILURE

FATIGUE FRACTURE: Continuous forces on acertain material, results in internal deformationwhich after a certain amount results inpermanent deformation or fracture.

Biomaterial Force factor Number of cycles Geometry

FATIGUE FRACTURE: Continuous forces on acertain material, results in internal deformationwhich after a certain amount results inpermanent deformation or fracture.

Biomaterial Force factor Number of cycles Geometry

BiomaterialStress level below which an implant biomaterial can beloaded indefinitely is referred as endurance limit.Ti alloy exhibits high endurance limit compared withpure Ti.

Number of cyclesLoading cycles should be reduced.

Eliminate parafunctional habits.

Reduce occlusal contacts.

FATIGUE FRACTURE

BiomaterialStress level below which an implant biomaterial can beloaded indefinitely is referred as endurance limit.Ti alloy exhibits high endurance limit compared withpure Ti.

Number of cyclesLoading cycles should be reduced.

Eliminate parafunctional habits.

Reduce occlusal contacts.

Implant geometry

should resist bending & torsional load . Related to metal thickness. 2 times thicker in wall thickness – 16 timesstronger.

Force magnitude

Arch position( higher in posterior & anterior)Eliminate torqueIncrease in surface area

FATIGUE FRACTURE

Implant geometry

should resist bending & torsional load . Related to metal thickness. 2 times thicker in wall thickness – 16 timesstronger.

Force magnitude

Arch position( higher in posterior & anterior)Eliminate torqueIncrease in surface area

MOMENT OF INERTIA

MOMENT OF INERTIA (RADIUS)4

Important property of cylindrical implant designbecause of its importance in the analysis of bendingand torsion.

Bending stress and likelihood of bendingfracture decreases with increasing moment ofinertia.

MOMENT OF INERTIA (RADIUS)4

Important property of cylindrical implant designbecause of its importance in the analysis of bendingand torsion.

Bending stress and likelihood of bendingfracture decreases with increasing moment ofinertia.

GOOD MORNING

SCIENTIFIC RATIONALE

The biomechanical principles are related toimplant design in order to decrease the morecommon complications observed in implantdentistry.

A scientific rationale of dental implant designmay evaluate these designs as to the efficacyof their biomechanical load management

The biomechanical principles are related toimplant design in order to decrease the morecommon complications observed in implantdentistry.

A scientific rationale of dental implant designmay evaluate these designs as to the efficacyof their biomechanical load management

IMPLANTDESIGN

Macroscopicbody design

Microscopicbody design

Macroscopicbody design

Early loadingand mature

loading periods

Microscopicbody design

Initial implanthealing and initial

loading period

Biomechanicalload

management

Character offorce applied

Functionalsurface area

FORCE TYPE AND INFLUENCE ONIMPLANT BODY DESIGN

• Bone is strongestCompressive

• 35% weakerTensile

• 65% weakerShear

IMPLANT MACRO GEOMETRY

Smooth sided cylindrical implants– subjected to shear forces

Smooth sided tapered implants –places compressive load at interfac

Tapered threaded implants-compressive load to bone

Greater the taper – greater thecompressive load delivery

Smooth sided cylindrical implants– subjected to shear forces

Smooth sided tapered implants –places compressive load at interfac

Tapered threaded implants-compressive load to bone

Greater the taper – greater thecompressive load delivery

Watzeck et al-histologic andhistomorphometric analysis after 18 months

of occlusal loading in baboons

Bone trabeculae pattern and the higher BICresulted in superior support system forthreaded implants than smooth cylinderimplants.

Bone trabeculae pattern and the higher BICresulted in superior support system forthreaded implants than smooth cylinderimplants.

Bolind et al- compared cylinder implantswith threaded implants from functioning

prosthesis

Greater BIC was found in threaded implant Greater marginal bone loss was observed

around cylinder implants. Cylinder implants had roughened surface

condition but still bone loss was observed. Hence implant body design is more important

than surface condition.

Greater BIC was found in threaded implant Greater marginal bone loss was observed

around cylinder implants. Cylinder implants had roughened surface

condition but still bone loss was observed. Hence implant body design is more important

than surface condition.

FORCE DIRECTION AND INFLUENCEON IMPLANT BODY DESIGN

Bone is weaker when loaded under an angledload. A 300 angled load increases overall stress by

50%. Implant body long axis should be

perpendicular curve of wilson and Spee toapply long axis load.

Bone is weaker when loaded under an angledload. A 300 angled load increases overall stress by

50%. Implant body long axis should be

perpendicular curve of wilson and Spee toapply long axis load.

FUNCTIONAL V/S THEORETICALSURFACE AREA

Plasma spray coating provide 600% more ofTSA. Bone cell does not receive a transfer of

mechanical stress from this feature. The amount of actual BIC that can be used for

compressive loading < 30% of TSA. length or diameter of implant FSA

Plasma spray coating provide 600% more ofTSA. Bone cell does not receive a transfer of

mechanical stress from this feature. The amount of actual BIC that can be used for

compressive loading < 30% of TSA. length or diameter of implant FSA

IMPLANT LENGTH

Increase in length –Bi cortical stabilization

Maximum stress generated by lateral loadcan be dissipated by implants in the range of10-15mm

Softer the bone –greater length or width

Sinus grafting & nerve re-positioning to placegreater implant length

Albrektsson et al (1983)

Increase in length –Bi cortical stabilization

Maximum stress generated by lateral loadcan be dissipated by implants in the range of10-15mm

Softer the bone –greater length or width

Sinus grafting & nerve re-positioning to placegreater implant length

Albrektsson et al (1983)

IMPLANT WIDTH

Increase in implant width –increases functional surface areaof implant

Increase in 1mm width – increasein 33% of functional surface area

Wider diameter implants reducethe likelihood of componentfracture in dental implants

(Steven Boggan et al; JPD 1999)

Increase in implant width –increases functional surface areaof implant

Increase in 1mm width – increasein 33% of functional surface area

Wider diameter implants reducethe likelihood of componentfracture in dental implants

(Steven Boggan et al; JPD 1999)

IMPACT OF IMPLANT SHAPE ONSTRESS DISTRIBUTION

Endosteal dental implant designs may be generallyconsidered as blade or root form.

When viewed from the broad end, blade implantsshow a relatively favorable stress pattern,

when viewed from the front….extremelyunfavorable stress pattern…..horizontal forces.

Endosteal dental implant designs may be generallyconsidered as blade or root form.

When viewed from the broad end, blade implantsshow a relatively favorable stress pattern,

when viewed from the front….extremelyunfavorable stress pattern…..horizontal forces.

IMPACT OF IMPLANT SHAPE ON STRESSDISTRIBUTION

Blade implants are designed to serve in those bony siteswhich are too narrow to accommodate root formimplants.

They have reduced cross-sectional area available to resistaxial loads as compared to root form implants.

Perforations or "vents" serve to increase the amount ofcross-sectional area available to resist axial loads.

Blade implants are designed to serve in those bony siteswhich are too narrow to accommodate root formimplants.

They have reduced cross-sectional area available to resistaxial loads as compared to root form implants.

Perforations or "vents" serve to increase the amount ofcross-sectional area available to resist axial loads.

THREAD GEOMETRY Maximize initial contact.

Enhance surface area

Facilitate dissipation of loads at the boneimplant interface.

FSA can be modified by varying three threadparameters: Thread pitch, thread shape andthread depth

Maximize initial contact.

Enhance surface area

Facilitate dissipation of loads at the boneimplant interface.

FSA can be modified by varying three threadparameters: Thread pitch, thread shape andthread depth

THREAD PITCH

•Chun et al, Evaluation of designparameters of osseointegrateddental implants using FEAJ Oral Rehab 2002; 29:565-574

•Maximum effective stressdecreased with decrease in screwpitch.••Changing screw pitch was an moreeffective way than changingimplant length in reducing thestresses.

•Chun et al, Evaluation of designparameters of osseointegrateddental implants using FEAJ Oral Rehab 2002; 29:565-574

•Maximum effective stressdecreased with decrease in screwpitch.••Changing screw pitch was an moreeffective way than changingimplant length in reducing thestresses.

LIANG KONG, ELECTION OF THE IMPLANT THREAD PITCH FOROPTIMAL BIOMECHANICAL PROPERTIES: A THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS,

Effects of the implant thread pitch on the maximumstresses were evaluated in jaw bones and implant–abutment complex by a finite element method.

The thread pitch ranged from 0.5 mm to 1.6 mm.

When thread pitch exceeded 0.8 mm, minimum stresseswere obtained.

Cancellous bone was more sensitive to thread pitch thancortical bone did.

Clin Oral Implants 2010 Feb;21(2):129-36

Effects of the implant thread pitch on the maximumstresses were evaluated in jaw bones and implant–abutment complex by a finite element method.

The thread pitch ranged from 0.5 mm to 1.6 mm.

When thread pitch exceeded 0.8 mm, minimum stresseswere obtained.

Cancellous bone was more sensitive to thread pitch thancortical bone did.

IMPLANT THREAD SHAPE

v shaped reverse buttress square threads

v shaped reverse buttress square threads

Kim et al. They evaluated an implant with the same number anddepth of threads with different thread shapes. The V-shape andreverse buttress had similar values.The square thread had less stress in compressive and moreimportantly shear forces.

IMPLANT THREAD SHAPE contd

V shaped threads convert the primarycompressive forces to the and result in 30 0

angled load Square shaped threads are more resistant to a

shear load.

THREAD DEPTH

Greater the thread depth , greater thesurface area of the implant.

Thread depth is most in v shaped threads

As the diameter thread depth also

Thread depth can be modified along withdiameter of implant to the TSA by 150%for every 1mm in diameter.

Greater the thread depth , greater thesurface area of the implant.

Thread depth is most in v shaped threads

As the diameter thread depth also

Thread depth can be modified along withdiameter of implant to the TSA by 150%for every 1mm in diameter.

Should be slightly larger than outer diameter of the implant

1. to completely seal the osteotomy site…

2. Seal provides for greater initial stability

3. Increase FSA thereby reducing stress at the crestal region.

Height should be sufficient to provide biologic width.

CREST MODULE DESIGN

Should be slightly larger than outer diameter of the implant

1. to completely seal the osteotomy site…

2. Seal provides for greater initial stability

3. Increase FSA thereby reducing stress at the crestal region.

Height should be sufficient to provide biologic width.

CREST MODULE DESIGN

Smooth parallel sided crest –shear stress… Angled crest module less than 20 degree-

-Increase in bone contact area-Beneficial compressive load

Larger diameter than outer thread diameter-Prevents bacterial ingress-Initial stability-Increase in surface area

Smooth parallel sided crest –shear stress… Angled crest module less than 20 degree-

-Increase in bone contact area-Beneficial compressive load

Larger diameter than outer thread diameter-Prevents bacterial ingress-Initial stability-Increase in surface area

APICAL DESIGN

Round cross-section donot resist torsional load

Incorporation of anti –rotational feature

- Vent\ hole- bone growsinto it

- Resist torsion

- Flat side\groove - bonegrow against it.

- places bone incompression

Round cross-section donot resist torsional load

Incorporation of anti –rotational feature

- Vent\ hole- bone growsinto it

- Resist torsion

- Flat side\groove - bonegrow against it.

- places bone incompression

IMPLANT BODY BIOMATERIALRELATED TO FRACTURE

• Modulus of elasticity optimal• Ultimate strength not adequate

VITREOUSCARBON

• Ultimate strength adequate• Modulus of elasticity 33 times stifferCERAMIC

• Closest approximation of modulus ofelasticity

• Ultimate strength adequateTITANIUM

IMPLANT BODY BIOMATERIALRELATED TO FRACTURE contd

Titanium

CPTitanium

Ti-6Al-4Valloy

CPTitanium

Ti-6Al-4Valloy

•Titanium alloy is 4 times stronger than CPtitanium•The fatigue strength is also 4 times stronger thanCP titanium

IMPLANT COMPONENTS AND THEIRREACTION TO FORCE

RETENTION SCREWS:The retention screw loosening may result from the

following factors

-occlusal interferences,-increased crown height,-its design-load on the abutment-material type.

RETENTION SCREWS:The retention screw loosening may result from the

following factors

-occlusal interferences,-increased crown height,-its design-load on the abutment-material type.

Screw loosening can be decreased by a preload with atorque wrench on the screw.

Tighten the screw untighten it after few minutesretighten it to the required force again.

This causes a deformation at the thread interface whichforms a more secure reunion.

IMPLANT COMPONENTS AND THEIRREACTION TO FORCE

Screw loosening can be decreased by a preload with atorque wrench on the screw.

Tighten the screw untighten it after few minutesretighten it to the required force again.

This causes a deformation at the thread interface whichforms a more secure reunion.

CEMENT: loads over a cement retained prosthesis may causedisruption of the cement seal causing movement of theprosthesis.

These movements can further cause increase in thedirection of offset loads and may be detrimental to theprosthesis as well as the implant.

BONE -IMPLANT INTERFACE: When the implant receives anocclusal load there is increase in micro strain next to implant–bone interface resulting in increase in bone density.

Therefore increasing the bone implant interface densityreduces the crestal bone loss.

IMPLANT COMPONENTS AND THEIRREACTION TO FORCE

CEMENT: loads over a cement retained prosthesis may causedisruption of the cement seal causing movement of theprosthesis.

These movements can further cause increase in thedirection of offset loads and may be detrimental to theprosthesis as well as the implant.

BONE -IMPLANT INTERFACE: When the implant receives anocclusal load there is increase in micro strain next to implant–bone interface resulting in increase in bone density.

Therefore increasing the bone implant interface densityreduces the crestal bone loss.

OCCLUSION

Progressively loaded implants remain stable within thebone….

Lamellar bone is highly organized but takes about 1 yr tomineralize completely after the trauma induced by implantplacement.

PIERAZZINI: demonstrated the development of densertrabaculae around progressively loaded implants in animals.

IMPLANT COMPONENTS AND THEIRREACTION TO FORCE

OCCLUSION

Progressively loaded implants remain stable within thebone….

Lamellar bone is highly organized but takes about 1 yr tomineralize completely after the trauma induced by implantplacement.

PIERAZZINI: demonstrated the development of densertrabaculae around progressively loaded implants in animals.

CONCLUSION

The most common complications in implant-relatedreconstruction are related to biomechanical conditions.

The manifestation of biomechanical loads on dentalimplants (moments, stress, and strain) controls the long-term health of the bone-to-implant interface

It can be summarized that a destructive cycle candevelop with moment loads and result in crestal boneloss.

Unless the bone increases in density and strength , thecycle continues towards implant failure if thebiomechanical environment is not corrected.

The most common complications in implant-relatedreconstruction are related to biomechanical conditions.

The manifestation of biomechanical loads on dentalimplants (moments, stress, and strain) controls the long-term health of the bone-to-implant interface

It can be summarized that a destructive cycle candevelop with moment loads and result in crestal boneloss.

Unless the bone increases in density and strength , thecycle continues towards implant failure if thebiomechanical environment is not corrected.

REFERENCES

Contemporary implant dentistry - Carl ECarl E MischMisch EdEd3rd3rd

Endosteal Dental Implants -Ralf V McKinneyRalf V McKinney Dental implant prosthetics - Carl ECarl E MischMisch Atlas of tooth & implant supported prosthesis-

Lawrence A. Weinberg. Phillips Science of Dental Materials 10 th edition. Osseointegration and occlusal rehabilitation,

Sumiya Hobo. Basic bio-mechanics of dental implants in prosthetic

dentistry J Prosthet Dent 1989; 61:602-609

Contemporary implant dentistry - Carl ECarl E MischMisch EdEd3rd3rd

Endosteal Dental Implants -Ralf V McKinneyRalf V McKinney Dental implant prosthetics - Carl ECarl E MischMisch Atlas of tooth & implant supported prosthesis-

Lawrence A. Weinberg. Phillips Science of Dental Materials 10 th edition. Osseointegration and occlusal rehabilitation,

Sumiya Hobo. Basic bio-mechanics of dental implants in prosthetic

dentistry J Prosthet Dent 1989; 61:602-609

Biomechanical considerations in osseointegrated prostheses,J Prosthet Dent 1983,49:843-848.

Influence of hex geometry and prosthetic table width on staticand fatigue strength of dental implants, J Prosthet Dent1999,82:436-440.

Chun et al, Evaluation of design parameters ofosseointegrated dental implants using FEA, J Oral Rehab2002; 29:565-574

Liang kong, election of the implant thread pitch for optimalbiomechanical properties: a three-dimensional finite elementanalysis, Clin Oral Implants 2010 Feb;21(2):129-36

REFERENCES

Biomechanical considerations in osseointegrated prostheses,J Prosthet Dent 1983,49:843-848.

Influence of hex geometry and prosthetic table width on staticand fatigue strength of dental implants, J Prosthet Dent1999,82:436-440.

Chun et al, Evaluation of design parameters ofosseointegrated dental implants using FEA, J Oral Rehab2002; 29:565-574

Liang kong, election of the implant thread pitch for optimalbiomechanical properties: a three-dimensional finite elementanalysis, Clin Oral Implants 2010 Feb;21(2):129-36

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