Implant biomechanics / crown and bridge dentistry

11www.indiandentalacademy.comwww.indiandentalacademy.com

22
Clinical biomechanics inClinical biomechanics in
implant dentistryimplant dentistry
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
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ContentsContents

44
1.1. What is biomechanics ?What is biomechanics ?
2.2. Why study biomechanics ?Why study biomechanics ?
3.3. Forces acting on dental implantsForces acting on dental implants
4.4. Moment loads and moment armsMoment loads and moment arms
5.5. Biological response to mechanical loadsBiological response to mechanical loads
6.6. Biomechanical based bone remodeling theories.Biomechanical based bone remodeling theories.

55
8.8. The biomechanical responseThe biomechanical response
9.9. Scientific rationale for dental implant designScientific rationale for dental implant design
10.10. Implant macro geometryImplant macro geometry
11.11. Surface coatingsSurface coatings
12.12. ConclusionConclusion
13.13. ReferencesReferences

66
What is biomechanics ?What is biomechanics ?
 Biomedical engineering : It is the application ofBiomedical engineering : It is the application of
engineering principles to living systemsengineering principles to living systems
 One aspect of this field is biomechanicsOne aspect of this field is biomechanics
 Biomechanics is concerned with the response ofBiomechanics is concerned with the response of
biological tissues to applied loadsbiological tissues to applied loads

77
Why study biomechanics ?Why study biomechanics ?

88
Issues to be consideredIssues to be considered
Mechanical loading on the implants in vivoMechanical loading on the implants in vivo
Transmission of the loadings to the interfacialTransmission of the loadings to the interfacial
tissuestissues
Biological reaction of interfacial tissues to theseBiological reaction of interfacial tissues to these
loads transmittedloads transmitted

99
Loads applied to the dentalLoads applied to the dental
implantsimplants
Dental implants are subjected to occlusal loadsDental implants are subjected to occlusal loads
when placed in functionwhen placed in function
Such loads vary in magnitude , frequency &Such loads vary in magnitude , frequency &
duration depending on patients parafunctionalduration depending on patients parafunctional
habitshabits

1010
Forces acting on the dentalForces acting on the dental
implantsimplants
Forces may be described by magnitude,Forces may be described by magnitude,
duration, direction, type and magnificationduration, direction, type and magnification
factorsfactors
Forces acting on dental implants are vectorForces acting on dental implants are vector
quantities and poses both magnitude andquantities and poses both magnitude and
directiondirection
Three dominant loading axes existThree dominant loading axes exist

1212
Types of forcesTypes of forces
Forces may be compressive, tensile or shear inForces may be compressive, tensile or shear in
naturenature
Shear forces the most destructiveShear forces the most destructive
Compresses forces are best accommodated andCompresses forces are best accommodated and
should be dominant In implant prostheticshould be dominant In implant prosthetic
occlusionocclusion

1414
Stresses acting on implantsStresses acting on implants
Mechanical stress can be defined as the mannerMechanical stress can be defined as the manner
in which the force is distributed over a surfacein which the force is distributed over a surface
Internal stresses that develop in an implant andInternal stresses that develop in an implant and
surrounding tissue have an effect on the long termsurrounding tissue have an effect on the long term
successsuccess
Magnitude of stress depends on force magnitudeMagnitude of stress depends on force magnitude
and cross sectional area of the Implantand cross sectional area of the Implant

1515
Force magnitude is not completely controlled by theForce magnitude is not completely controlled by the
operatoroperator
The operator however has control over the functionalThe operator however has control over the functional
surface area over which force is distributedsurface area over which force is distributed
Functional surface areaFunctional surface area can be defined as that surfacedcan be defined as that surfaced
that participates significantly in load bearing and stressthat participates significantly in load bearing and stress
dissipationdissipation
FSA can be optimized by increasing the number ofFSA can be optimized by increasing the number of
implants and selecting well designed Implant geometryimplants and selecting well designed Implant geometry

1616
Deformation and strainDeformation and strain
Load application may induce deformation of bothLoad application may induce deformation of both
implant and surrounding tissuesimplant and surrounding tissues
Biological tissue interprets deformation and it’sBiological tissue interprets deformation and it’s
manifestations and responds with remodelingmanifestations and responds with remodeling

1717
Stress - strain relationshipStress - strain relationship
The closer the modulus of elasticity of theThe closer the modulus of elasticity of the
implant to the bone, less the likelihood of relativeimplant to the bone, less the likelihood of relative
motion at the tissue to implant interfacemotion at the tissue to implant interface
It is more important to decrease stress in softerIt is more important to decrease stress in softer
bone because of greater elastic difference andbone because of greater elastic difference and
lower ultimate strengthlower ultimate strength

1818
Impact loadsImpact loads
When two bodies collide in a very small intervalWhen two bodies collide in a very small interval
of time, relatively large reaction forces developof time, relatively large reaction forces develop
Such collisions are called impactsSuch collisions are called impacts
Example : occlusal loadsExample : occlusal loads
Cause deformation of implants and surroundingCause deformation of implants and surrounding
tissuetissue

1919
Impact loads can be decreased byImpact loads can be decreased by
- Using acrylic teeth – ShalakUsing acrylic teeth – Shalak
- Weiss advocated fibrous tissue to implant interfaceWeiss advocated fibrous tissue to implant interface
for shock absorptionfor shock absorption
- Use of intramobile element to lower the stiffnessUse of intramobile element to lower the stiffness
than rest of the implantthan rest of the implant
- Misch advocates and acrylic provisional withMisch advocates and acrylic provisional with
progressive occlusal loading to improve B-I interfaceprogressive occlusal loading to improve B-I interface
before final restorationbefore final restoration

2020
Moment loadsMoment loads
Moment of force about a point tends to produceMoment of force about a point tends to produce
rotation or bending about that pointrotation or bending about that point
M = F x perpendicular distance (moment arm)M = F x perpendicular distance (moment arm)
from the point of interestfrom the point of interest
Also called torque or torsional loadAlso called torque or torsional load

2222
Clinical moment arms and crestalClinical moment arms and crestal
bone lossbone loss
Six moments may develop about the 3 clinicalSix moments may develop about the 3 clinical
coordinate axes .coordinate axes .
Such loads induce microrotation and stressSuch loads induce microrotation and stress
concentration at the crest of alveolar ridge – implantconcentration at the crest of alveolar ridge – implant
– bone interface and leads to crestal bone loss– bone interface and leads to crestal bone loss
Three clinical moment arms exist in implantThree clinical moment arms exist in implant
dentistry, minimization of each is necessary todentistry, minimization of each is necessary to
prevent failureprevent failure

2424
Occlusal height moment armOcclusal height moment arm
Acts as aActs as a
moment armmoment arm
for a forcefor a force
componentscomponents
directed alongdirected along
faciolingual andfaciolingual and
mesiodistalmesiodistal
axisaxis

2525
Cantilever length moment armCantilever length moment arm
Large moments from vertical axis forceLarge moments from vertical axis force
component is seen in prosthetic environmentscomponent is seen in prosthetic environments
designed with cantilevered extensions or offsetdesigned with cantilevered extensions or offset
loads from rigid implantsloads from rigid implants
Discal cantilever should not extend 2.5 x the A-PDiscal cantilever should not extend 2.5 x the A-P
distance under ideal conditionsdistance under ideal conditions

2626
Occlusal width moment armOcclusal width moment arm
Wide occlusal tables increase moment arm forWide occlusal tables increase moment arm for
any offset occlusal loadsany offset occlusal loads
Faciolingual rotation can be reduced by narrowFaciolingual rotation can be reduced by narrow
occlusal tables and adjusting occlusion toocclusal tables and adjusting occlusion to
provide more centric contactprovide more centric contact

2727
Bone response to mechanical loadsBone response to mechanical loads

2828
The biological responseThe biological response
Interface is defined as a plane forming theInterface is defined as a plane forming the
common boundary between two parts of mattercommon boundary between two parts of matter
or spaceor space
It may be a discrete boundary or a region ofIt may be a discrete boundary or a region of
interaction between two materials (interface thatinteraction between two materials (interface that
exists between implant and bone)exists between implant and bone)

2929
The biomechanical environment plays anThe biomechanical environment plays an
immediate role in the quality and compositionalimmediate role in the quality and compositional
outcome of the new interfaceoutcome of the new interface
Relative movement (micro motion) betweenRelative movement (micro motion) between
implant and bone at the time of placement leadsimplant and bone at the time of placement leads
to the development of fibro osseous interfaceto the development of fibro osseous interface

3030
Bone responds to hormonal and biomechanicalBone responds to hormonal and biomechanical
regulation [functional loading]regulation [functional loading]
These two are often in opposition with eachThese two are often in opposition with each
otherother
The objective of good implant design would beThe objective of good implant design would be
to establish and maintain a strain environmentto establish and maintain a strain environment
within the host bone tissue and interface thatwithin the host bone tissue and interface that
favors osseointegration of the implantfavors osseointegration of the implant

3131
Biomechanical based boneBiomechanical based bone
remodeling theoriesremodeling theories

3232
1887 Meier1887 Meier
1892 Wolff1892 Wolff
1895 Roux1895 Roux
H M Frost proposed theory of mechanostat andH M Frost proposed theory of mechanostat and
`Flexure drift hypothesis``Flexure drift hypothesis`
Cowin proposed potential mechanism by whichCowin proposed potential mechanism by which
bone cells sense mechanical loadbone cells sense mechanical load

3434
The biomechanical responseThe biomechanical response

3535
Strain has been generically defined in relation toStrain has been generically defined in relation to
deformation and applied stressdeformation and applied stress
The mechanical properties of trabecular andThe mechanical properties of trabecular and
cortical bone found within the oral environmentcortical bone found within the oral environment
exhibit a high degree of variation as a function ofexhibit a high degree of variation as a function of
load direction, rate and durationload direction, rate and duration
The mechanical strain exhibited in bone IsThe mechanical strain exhibited in bone Is
ultimately a function of bone densityultimately a function of bone density

3636
Dependence on direction of loadingDependence on direction of loading
The degree to which the mechanical propertiesThe degree to which the mechanical properties
of cortical bone are dependent on its structure isof cortical bone are dependent on its structure is
referred to as anisotropyreferred to as anisotropy
A material is said to be orthotropic if it exhibitsA material is said to be orthotropic if it exhibits
different properties in all three directionsdifferent properties in all three directions
Isotropic if its properties are same in all threeIsotropic if its properties are same in all three
directiondirection

3737
Transversely isotropic describes the material inTransversely isotropic describes the material in
which two of the three directions exhibited thewhich two of the three directions exhibited the
same mechanical propertiessame mechanical properties
Example cortical bone of human mandibleExample cortical bone of human mandible
Ashman & Van Bushirk suggest that corticalAshman & Van Bushirk suggest that cortical
bone of mandible functions as the long bone thatbone of mandible functions as the long bone that
has been molded into a curved beam geometryhas been molded into a curved beam geometry

3838
Dependence on the rate of loadingDependence on the rate of loading
A material is said to be viscoelastic if itsA material is said to be viscoelastic if its
mechanical behavior is dependent on the rate ofmechanical behavior is dependent on the rate of
load applicationload application
Bone fails at a higher load but with lessBone fails at a higher load but with less
allowable elongation (deformation) at higher asallowable elongation (deformation) at higher as
compared with lower strain stresscompared with lower strain stress
Thus bone behaves in a more brittle fashion atThus bone behaves in a more brittle fashion at
higher strain ratehigher strain rate

3939
Dependence on duration of loadingDependence on duration of loading
Carter and Caylor have described bone damageCarter and Caylor have described bone damage
or fracture caused by mechanical stress as theor fracture caused by mechanical stress as the
sum of both the damage caused by creep orsum of both the damage caused by creep or
time dependent loading and cyclic of fatiguetime dependent loading and cyclic of fatigue
loading and the relative interaction of these twoloading and the relative interaction of these two
types of damagetypes of damage
CreepCreep
Fatigue strengthFatigue strength

4040
Dependence on species anatomic locationDependence on species anatomic location
Dependence on side constraintDependence on side constraint
Dependence on structural densityDependence on structural density

4141
Scientific rationale for dentalScientific rationale for dental
implant designimplant design
Implants function to transfer to load theImplants function to transfer to load the
surrounding biological issuesurrounding biological issue
Biomechanical load management Is dependentBiomechanical load management Is dependent
on two factors:on two factors:
- Character of the applied forceCharacter of the applied force
- Functional surface area which the load isFunctional surface area which the load is
dissipateddissipated

4242
Design process for implant begins with theDesign process for implant begins with the
identification of clinical problems to beidentification of clinical problems to be
addressedaddressed
Scientific principles related to the force andScientific principles related to the force and
surface area are combined with engineeringsurface area are combined with engineering
solutions to pursue the desire to clinical goalssolutions to pursue the desire to clinical goals

4343
Character of forces applied toCharacter of forces applied to
dental implantsdental implants
Forces applied to dental implants may beForces applied to dental implants may be
characterized in terms of five distinctcharacterized in terms of five distinct
although related factors, namely :although related factors, namely :
- MagnitudeMagnitude
- DurationDuration
- TypeType
- DirectionDirection
- MagnificationMagnification

4444
Force magnitudeForce magnitude

4545
Physiologic constraints on designPhysiologic constraints on design::
- Magnitude of byte for some eighties As a function ofMagnitude of byte for some eighties As a function of
anatomical region and state of dentitionanatomical region and state of dentition
- After sustained period of edentulism bone foundationAfter sustained period of edentulism bone foundation
becomes less dense and may not be able to supportbecomes less dense and may not be able to support
normal physiological bite forces on the implantsnormal physiological bite forces on the implants
- Careful treatment planning & appropriate implant designCareful treatment planning & appropriate implant design
selection is imperative to lower magnitude of loads I-Bselection is imperative to lower magnitude of loads I-B
interfaceinterface

4646
Influence on biomaterial selection:Influence on biomaterial selection:
- Many biocompatible materials unable to sustainMany biocompatible materials unable to sustain
the magnitude of parafunctional loads imposedthe magnitude of parafunctional loads imposed
- Si , hydroxyapatite , C have tensile strength toSi , hydroxyapatite , C have tensile strength to
low for primary implant material, hence uselow for primary implant material, hence use
escort things on a stronger substrate materialescort things on a stronger substrate material

4848
- Ti and Ti alloys have excellent biocompatibilityTi and Ti alloys have excellent biocompatibility
- Titanium has closest approximation to boneTitanium has closest approximation to bone
stiffness than any other metal ( 6x )stiffness than any other metal ( 6x )
- Low modulus of elasticity (stiffness) lead toLow modulus of elasticity (stiffness) lead to
failure of carbon implantsfailure of carbon implants
- Excessive stiffness ( 33x ) led to disuse atrophyExcessive stiffness ( 33x ) led to disuse atrophy
and failure of ceramic implantsand failure of ceramic implants

4949
Force durationForce duration

5050
Force typeForce type

5151
Physiological constraints on design :Physiological constraints on design :
- Bone is strongest in compressive > tensile >Bone is strongest in compressive > tensile >
shearshear
- Endosteal implants load bone - implant interfaceEndosteal implants load bone - implant interface
in pure shear, unless surface features arein pure shear, unless surface features are
incorporated in design to transform shear loadsincorporated in design to transform shear loads
to more resistant force typesto more resistant force types

5252
Influence on Implant body design :Influence on Implant body design :
- Smooth cylinder body results essentially in shearSmooth cylinder body results essentially in shear
type of force at the interfacetype of force at the interface
- Threaded implants can transform the type ofThreaded implants can transform the type of
force at bone implant interfaceforce at bone implant interface
- Three types of thread implants are square, VThree types of thread implants are square, V
shaped and buttressshaped and buttress
- V shaped and buttress exert ten times greaterV shaped and buttress exert ten times greater
force than square threadforce than square thread

5353
Force directionForce direction

5454
Physiological constraints :Physiological constraints :
- Normal anatomy and bone resorption of theNormal anatomy and bone resorption of the
edentulism poses angulation challengesedentulism poses angulation challenges
- Bonus most resistant to compressive forcesBonus most resistant to compressive forces
falling along the long axisfalling along the long axis
- A 30° offset load reduces the compressiveA 30° offset load reduces the compressive
strand of the borne by 11% and tensile strengthstrand of the borne by 11% and tensile strength
by 25%by 25%

5555
Influence on Implant body design :Influence on Implant body design :
- As angulation of load increases stress aroundAs angulation of load increases stress around
the implant Increases particularly in thethe implant Increases particularly in the
vulnerable crestal regionvulnerable crestal region
- As a result all implants are designed forAs a result all implants are designed for
placement perpendicular to the occlusal planeplacement perpendicular to the occlusal plane
- The face of thread or plateau can change theThe face of thread or plateau can change the
direction of load from prosthesis to abutmentdirection of load from prosthesis to abutment
connection, to a different force direction at theconnection, to a different force direction at the
bonebone

5656
Force magnificationForce magnification
Extreme angulation and parafunctional habitsExtreme angulation and parafunctional habits
exceed the capability of the dental implantexceed the capability of the dental implant
design to withstand physiological loaddesign to withstand physiological load
Cantilever send crown heights are levers andCantilever send crown heights are levers and
force magnifiersforce magnifiers
Careful treatment planning and multiple implantsCareful treatment planning and multiple implants
had indicated in case of force magnificationhad indicated in case of force magnification

5757
Surface areaSurface area

5858
Anatomical constraints on surfaceAnatomical constraints on surface
area optimizationarea optimization
Bone vol : external architecture of boneBone vol : external architecture of bone
- Width is greater in the posterior regionWidth is greater in the posterior region
- In general 6 to 8mm bone is available in theIn general 6 to 8mm bone is available in the
anterior region and 4mm implant is usedanterior region and 4mm implant is used
- 7mm width is available in the posterior region7mm width is available in the posterior region
and 5mm implant is usedand 5mm implant is used
- Therefore implant width may increase asTherefore implant width may increase as
amount of force magnification increases fromamount of force magnification increases from
anteriors to post. regionanteriors to post. region

5959
- On the contrary born height usually decreasesOn the contrary born height usually decreases
from anterior mandible, compared with thefrom anterior mandible, compared with the
anterior maxilla, the posterior mandible, to theanterior maxilla, the posterior mandible, to the
least in the edentulous posterior maxillaleast in the edentulous posterior maxilla
- Hence as occlusal force increases bone heightHence as occlusal force increases bone height
and vol decreasesand vol decreases

6060
Bone quality : internal architecture of boneBone quality : internal architecture of bone
- four distinctly different bone densityfour distinctly different bone density
classifications exist within the max and mandclassifications exist within the max and mand
- Greater failure rate has been documented inGreater failure rate has been documented in
porous bone compared with dense boneporous bone compared with dense bone
- Additional implants or implants with greaterAdditional implants or implants with greater
surface area have to be used in porous bonesurface area have to be used in porous bone

6161
Functional surface area forcesFunctional surface area forces vs.vs.
Total surface areaTotal surface area
For a given bone vol, implant surface area mustFor a given bone vol, implant surface area must
be optimized for functional loadsbe optimized for functional loads
FSA: defined as the area that actively serves toFSA: defined as the area that actively serves to
dissipate compressive and tensile non sheardissipate compressive and tensile non shear
loads through the I-B interface and providesloads through the I-B interface and provides
initial stability of the implant following its surgicalinitial stability of the implant following its surgical
placementplacement

6262
Functional thread surface area: portion of the thread thatFunctional thread surface area: portion of the thread that
participates in compressive load transmission under theparticipates in compressive load transmission under the
action of a axial or near axial occlusal loadaction of a axial or near axial occlusal load
Total surface area : may Include a passive area thatTotal surface area : may Include a passive area that
does not participate in load transferdoes not participate in load transfer
Example : plasma spray coatings have 600% more TSAExample : plasma spray coatings have 600% more TSA
but less than 30% is actually exposed to the bonebut less than 30% is actually exposed to the bone
Since most stress to the I-B interface Is in the crestal 1/2Since most stress to the I-B interface Is in the crestal 1/2
of the implant, the crestal zone is most important toof the implant, the crestal zone is most important to
distribute stresses appropriatelydistribute stresses appropriately

6363
Design variables in SA optimizationDesign variables in SA optimization

6464
Implant macrogeometryImplant macrogeometry
Smooth sided cylindric implants provide surgicalSmooth sided cylindric implants provide surgical
ease however B-I interface is subjected toease however B-I interface is subjected to
significantly large shear conditionssignificantly large shear conditions
Smooth sided , tapered implants allows for aSmooth sided , tapered implants allows for a
component of compressive load to be deliveredcomponent of compressive load to be delivered
to bone B-I interface depending on the degree ofto bone B-I interface depending on the degree of
tapertaper

6565
Threaded implants with circular cross sectionThreaded implants with circular cross section
provide ease of surgical placement and allow forprovide ease of surgical placement and allow for
>FSA optimization to transfer compressive>FSA optimization to transfer compressive
forces to the B-I interfaceforces to the B-I interface
Also gives initial rigid fixation to limit microAlso gives initial rigid fixation to limit micro
movement during healingmovement during healing
Smooth sided cylinder depends on coating ourSmooth sided cylinder depends on coating our
micro structure for load transmission to bonemicro structure for load transmission to bone

6666
Implant widthImplant width
Over the years implants have graduallyOver the years implants have gradually
Increased in widthIncreased in width
Scientific principle being > the width greater theScientific principle being > the width greater the
surface areasurface area
4mm implants have 33% > SA than 3mm4mm implants have 33% > SA than 3mm
implantsimplants
Largest the width better the emergence profile ofLargest the width better the emergence profile of
the crownthe crown

6767
Crestal bone anatomy limits implants to <Crestal bone anatomy limits implants to <
5.5mm except in limited situations5.5mm except in limited situations
Thus implant design innovations in crestalThus implant design innovations in crestal
region are required to provide increase in FSAregion are required to provide increase in FSA
in this vulnerable regionin this vulnerable region

6868
Thread geometryThread geometry
FSA for unit length of the implant may beFSA for unit length of the implant may be
modified by varying three geometric parametersmodified by varying three geometric parameters
of implantof implant
- Thread pitchThread pitch
- Thread shapeThread shape
- Thread depthThread depth

6969
Thread pitch is defined as the distanceThread pitch is defined as the distance
measured parallel with its axis between adjacentmeasured parallel with its axis between adjacent
thread forms ( for V type threads ), for thethread forms ( for V type threads ), for the
number of threads per unit length in the samenumber of threads per unit length in the same
axial plane and on the same side of the axisaxial plane and on the same side of the axis
Smaller / finer pitch : more threads on theSmaller / finer pitch : more threads on the
Implant body for given unit length and thusImplant body for given unit length and thus
greater surface area per unit lengthgreater surface area per unit length

7171
Thread shape:Thread shape:
• V shapedV shaped
• SquareSquare
• ButtressButtress
- Dental implant applications dictates the needDental implant applications dictates the need
for a thread shape optimized for a long-termfor a thread shape optimized for a long-term
function ( load transmission ) under occlusalfunction ( load transmission ) under occlusal
intrusive ( opposite of pull out ) load directionsintrusive ( opposite of pull out ) load directions

7373
The square thread provides an optimum surfaceThe square thread provides an optimum surface
area for intrusive & compressive loadarea for intrusive & compressive load
transmissiontransmission
Shear loading most detrimental to boneShear loading most detrimental to bone
Shear force on V thread face its ten timesShear force on V thread face its ten times
greater than on square threadgreater than on square thread
Buttress has similar shear component as VButtress has similar shear component as V
under occlusal loadunder occlusal load

7575
Thread depth : refers to the distance betweenThread depth : refers to the distance between
the major and minor diameter of the threadthe major and minor diameter of the thread
It may be varied for the length of the implant toIt may be varied for the length of the implant to
increase FSA in the region of highest stress,increase FSA in the region of highest stress,
example : crestal regionexample : crestal region
Reverse taper leads to a dramatic increase inReverse taper leads to a dramatic increase in
functional surface area at the crest of the bonefunctional surface area at the crest of the bone
where stresses are highestwhere stresses are highest

7777
Implant lengthImplant length
As length of the implant increases so does theAs length of the implant increases so does the
overall total surface areaoverall total surface area
Once I-B interface is formed excessively longOnce I-B interface is formed excessively long
implants do not receive stress transmission toimplants do not receive stress transmission to
the apical region and are not neededthe apical region and are not needed
D3, D4 bone in the posterior region have lessD3, D4 bone in the posterior region have less
available bone heightavailable bone height

7878
Nerve repositioning is cited as an acceptableNerve repositioning is cited as an acceptable
clinical treatment to facilitate longer implants inclinical treatment to facilitate longer implants in
the posterior mandiblethe posterior mandible
Maxillary sinus grafts done for posterior maxillaMaxillary sinus grafts done for posterior maxilla
Longer implants have been suggested toLonger implants have been suggested to
provide greater stability under lateral loadingprovide greater stability under lateral loading
Studies show that majority of stress generatedStudies show that majority of stress generated
by lateral load can be dissipated by implant inby lateral load can be dissipated by implant in
the range of 10 -15 mm length compared withthe range of 10 -15 mm length compared with
implant of 20 – 30 mm lengthimplant of 20 – 30 mm length

7979
Crest module configurationCrest module configuration
Crest module of implant body is the transostealCrest module of implant body is the transosteal
region from implant body and is characterized asregion from implant body and is characterized as
a region of high concentration of mechanicala region of high concentration of mechanical
stressstress
Many crest modules have been designed toMany crest modules have been designed to
reduce plaque accumulation once bone loss hasreduce plaque accumulation once bone loss has
occurredoccurred
However design of crest module contributes toHowever design of crest module contributes to
crestal bone losscrestal bone loss

8080
Angulated crest module > 20° with surfaceAngulated crest module > 20° with surface
texture that increases bone contact causestexture that increases bone contact causes
slightly beneficial cumbersome stress toslightly beneficial cumbersome stress to
adjacent bone and decreased bone lossadjacent bone and decreased bone loss
Crest module should be slightly larger than outerCrest module should be slightly larger than outer
thread diameterthread diameter
Crest module height is often 2 mmCrest module height is often 2 mm
A polished collar of minimum height should beA polished collar of minimum height should be
designed on the superior portion just below thedesigned on the superior portion just below the
prosthesis platform (0.5 mm)prosthesis platform (0.5 mm)

8282
Apical design considerationsApical design considerations
Most root form implants are circular in crossMost root form implants are circular in cross
sectionsection
Around cross section does not resist shearAround cross section does not resist shear
forcesforces
As a result anti - rotational feature isAs a result anti - rotational feature is
incorporated in apical region of implant bodyincorporated in apical region of implant body

8383
Another anti - rotational feature flat sides orAnother anti - rotational feature flat sides or
gross along the body or apical the region of thegross along the body or apical the region of the
implant bodyimplant body
When bone grows against flat end it is keptWhen bone grows against flat end it is kept
under compression with rotational loads , thusunder compression with rotational loads , thus
apical end must be flat than pointedapical end must be flat than pointed

8484
Abutment designAbutment design
Abutments for flat surfaced implants: implantsAbutments for flat surfaced implants: implants
that do not have any anti rotational elementsthat do not have any anti rotational elements
are flat surfaced and usually demandare flat surfaced and usually demand
attachment of one piece abutmentsattachment of one piece abutments
These implants are used only when multipleThese implants are used only when multiple
units are to be cemented by connecting themunits are to be cemented by connecting them
with overlay bars or crownswith overlay bars or crowns
Should not be used for replacing single to theShould not be used for replacing single to the
restorationsrestorations

8585
Abutments for implants with anti-rotationalAbutments for implants with anti-rotational
features: anti - rotational features arefeatures: anti - rotational features are
- The External hexThe External hex
- The Internal hexThe Internal hex
- The Spline attachment and variations , splinesThe Spline attachment and variations , splines
are fin to groove configurations with long andare fin to groove configurations with long and
successful history in engineeringsuccessful history in engineering
- The Park starThe Park star
- The Morse taper ( cold weld ) attachmentThe Morse taper ( cold weld ) attachment

8686
Abutments are commonly available into pieces ,Abutments are commonly available into pieces ,
which demands that the abutment be seated onwhich demands that the abutment be seated on
the implant their by engaging the anti-rotationalthe implant their by engaging the anti-rotational
component , a retaining screw is used to tightencomponent , a retaining screw is used to tighten
the abutment to the implantthe abutment to the implant
A critical factor that requires consideration whenA critical factor that requires consideration when
a retaining screw is fastened is thea retaining screw is fastened is the
`phenomenon of thread stretch`.`phenomenon of thread stretch`.

8787
This is caused by relaxation of the screw metalThis is caused by relaxation of the screw metal
after it has been tightened . To ensureafter it has been tightened . To ensure
continuing screw tightness, retorque the screwcontinuing screw tightness, retorque the screw
subsequently with the proper force for upto foursubsequently with the proper force for upto four
additional procedures over a one week period.additional procedures over a one week period.
Two piece designs permit angulated abutmentsTwo piece designs permit angulated abutments
(10 to 30° )(10 to 30° )
Three piece designs are available , consist of anThree piece designs are available , consist of an
angled abutment , an interposed collar ( eachangled abutment , an interposed collar ( each
with Its own anti-rotational component ) and awith Its own anti-rotational component ) and a
fixation screw .fixation screw .
Custom cast abutments are made when preciseCustom cast abutments are made when precise
angulations are required for proper prostheticangulations are required for proper prosthetic
positionposition

8888
Surface coatingsSurface coatings
Titanium plasma spray ( TPS )Titanium plasma spray ( TPS )
- Implant body may be covered with a porousImplant body may be covered with a porous
coating , two materials commonly used for thiscoating , two materials commonly used for this
purpose titanium and hydroxyapatitepurpose titanium and hydroxyapatite
- Both are plasma sprayed on to implant bodyBoth are plasma sprayed on to implant body
- TPS increases B-I surface area and acts similarTPS increases B-I surface area and acts similar
to three dimensional surface rates may stimulateto three dimensional surface rates may stimulate
adhesion osteogenesisadhesion osteogenesis

8989
- There is 600% increase in total surface areaThere is 600% increase in total surface area
- FSA increases by 25 to 30% which is significantFSA increases by 25 to 30% which is significant
- Improved initial fixation of implant is seen specially inImproved initial fixation of implant is seen specially in
softer bonesofter bone
Hydroxyapatite coatings :Hydroxyapatite coatings :
- Similar roughness as TPS and increase FSASimilar roughness as TPS and increase FSA
- Direct bonding to bone which is of greater strengthDirect bonding to bone which is of greater strength
- Enhanced gap healing in hydroxyapatite coating is seenEnhanced gap healing in hydroxyapatite coating is seen

9090
Advantages of surface coatings:Advantages of surface coatings:
- Increased surface areaIncreased surface area
- Increased roughness for initial stabilizationIncreased roughness for initial stabilization
- Stronger B-I interfaceStronger B-I interface
Additional advantages of HA over TPSAdditional advantages of HA over TPS
- Faster healing of B-I interfaceFaster healing of B-I interface
- Increased gap healing between B & HAIncreased gap healing between B & HA
- Stronger interface than in TPSStronger interface than in TPS
- Less corrosion of metalLess corrosion of metal

9191
Disadvantages of surface coatings :Disadvantages of surface coatings :
- Coatings may be damaged when beingCoatings may be damaged when being
inserted in dense boneinserted in dense bone
- Increased surface roughness with the riskIncreased surface roughness with the risk
of bacterial contamination when presentof bacterial contamination when present
above boneabove bone
- HA : increased plaque retention whenHA : increased plaque retention when
exposedexposed
- Increased costsIncreased costs

9292
ConclusionConclusion

9393
ReferencesReferences
Contemporary implant dentistry – Carl E. Misch , 2Contemporary implant dentistry – Carl E. Misch , 2ndnd
editionedition
Dental materials – Philips 11Dental materials – Philips 11thth
editionedition
Fundamentals of implant dentistry, Weiss and WeissFundamentals of implant dentistry, Weiss and Weiss
Implants in restorative dentistry, ScortsessiImplants in restorative dentistry, Scortsessi
Journal of dental education vol 52 no 12 pg 755, 1988Journal of dental education vol 52 no 12 pg 755, 1988
Jpd 1985 : 54; 410-14Jpd 1985 : 54; 410-14
Jpd 1983 : 49; 843-49Jpd 1983 : 49; 843-49

9494
Thank you
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www.indiandentalacademy.com

Implant biomechanics / crown and bridge dentistry

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