Implants bio mechanics /certified fixed orthodontic courses by Indian dental academy

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Definition
Process of analysis and determination of loading and
deformation of bone in a biological system.
Role
Natural tooth and implants anchored differently in bone

The loading of teeth, implant and peri implant bone of prosthetic
superstructure
Optimize the clinical implant therapy

Types


Reactive



Therapeutic

Reactive Biomechanics
Any prosthesis that increases implant loading.


Therapeutic Biomechanics
Process of remediating each biomechanical factor in order to
deiminish implant overlaoding


Interrelated Factors
Analyzed during diagnosis and treatment planning and
maintained in a state of equilibrium.


Biomechanics



Occlusion



Esthetics


Methods of Analysis
 Finite element analysis – Siegele 1989, Chelland 1991
Determined the distribution and concentration of strain and
deformation within implant and stated that force distribution to
surrounding bone occurs at crestal bone and level of third screw
thread.


 Birefringence Analysis
Done on plastic model utilizing polarized monochromatic light.
 Load Measurement : Lundreg 1989, Montag 1991
Precise data about forces exerted on Implant to supporting
bone.

Complicated - invivo

Invitro- valuable

 Bond strength between implant and bone : Schmitz 1991
Done it by test of shearing, expulsion and torsion.


FORCE
Definition
Any application of energy, either internal or external to a
structure, that which initiates, changes or arrests motion.
Related Factors


Magnitude



Duration



Type



Direction



Magnification

Magnitude
Anatomic region and state of dentition.
Craig, 1980
Molar

-

390 – 880N

Canine

-

453N

Incisor

-

222N

Parafunction -

1000Psi

Colaizzi, 1984
Complete denture

-

77 – 196N

Carlsson & Haraldson, 1985
Denture with implant -

48 – 412N


Duration
Mastication

-

9mt/day with 20 to 30 psi

Swallowing

-

20mt/day with 3 to 5 psi

Type
Compressive, Tensile and Shear
Cowin 1989
Bone -

Strongest -

Compression

-

30% weaker - tension

-

65% weakest – shear

Compressive force

-

Maintain integrity

Tensile and shear

-

Disrupts integrity

Direction

On centric vertical contact

Angle load

Axial load

Greater tensile & shear stress

Greater compressive
stress

Misch 1994
30% offset load – Decreases compressive strength – 11%
- Decreases tensile strength – 25%


Magnifying Factors
Applied Load  Torque
Includes,
 Extreme angulation
 Cantilevers
 Crown height
 Parafunction
 Bone density
Crown height - Increase in 1mm – 20% increase in torque.
With same load,
D1 Bone
Accommodate
D4 Bone
Cannot accommodate

Torque / Moment Load / Bending Load
Product of inclined resultant line of force and distance from
center of rotation.
Torque
Natural tooth -

=

Force x Distance

Apical 1/3rd

Chelland, 1991
Implant - First third screw level.
Force


Vertical - towards supporting bone



Lateral - away supporting bone – Creates lever arm torque

FORCE DISTRIBUTION
Chelland 1991,
&
Reiger 1990

Weinberg, 1994

Natural teeth

Rigidly fixed

Periodontal ligament

Stiff

Flexion

Concentrates at crestal bone

Even force distribution

& 1st 3 thread level

Implant

Increase
Root length – increase in surface area - better force distribution.
Implant length – Initial mobilization

FORCE DISTRIBUTION PRINCIPLES
System Components


Vertical element – tooth or implant



Connecting element



Supporting medium – periodontal ligament or bone


Flexible Medium


Stiff Medium


Flexible and Stiff Medium


DIFFERENTIAL MOBILITY
Qualitative difference between the flexion of periodontal
ligament and stiffness of osseointegration.
Micro movement
Natural teeth with good bone
Will move laterally approximately 0.5mm
Measured occlusally.
Micron Movement – Weinberg, Rangert, 1994
Implant can move laterally 0.1mm or less measured
occlusally.

Natural Teeth

Implant

Periodontal ligament - flexion

Rigidly fixed – stiff

Even force distribution

Concentration at crestal bone

0.5µm movement

0.1µm movement

Shock absorber

Rigid

Reduces the magnitude of

Increases the magnitude

stress
Occlusal trauma –

No such warning signs only

Signs of cold sensitivity,

bone microfracture

Wear facets, Pits, Drift away
& mobility

 Elastic modiolus similar to bone

5-10times different
Therefore, with same load
Increase stress,
concentrates at crestal
bone

Surrounding bone formed childhood

Forms rapid and intense

Lateral force – exert

Lateral force exert

Movement

No movement

Dissipates to apex

Concentrates at crestal
bone

Forces acting on Implants


Occlusal loads during function



Para functional habits

Passive Loads



Mandibular flexure
Contact with first stage cover screw and second stage

permucosal extension.


Perioral forces



Non –passive prosthesis.

TRAUMATIC FORCES OR IMPLANT OVER LOADING


Non passive prosthesis



Parafunction



Initial contact during maximum intercuspation



Labial stresses generated during eccentric movements.

Therefore,


Eliminate posterior contact during protrusion and lateral

excursion.


Prosthesis come in contact only during intercuspation.

FORCE DISTRIBUTION IN MULTIPLE IMPLANT PROSTHESIS
Splinting
 Natural tooth – Periodontal ligament – forced distribution
 Implant – stiff – no force distribution and only concentration at
crestal bone


FORCE DISTRIBUTION IN COMBINED PROSTHESIS


Supported by both natural teeth and implants



Mode of attachment


Flexible



Stiff



Flexible – internal attachment



Stiff – when terminal abutments are implants


FLEXIBLE ATTACHMENT


Tooth supported prosthesis – Female attachment



Implant supported prosthesis – Screw retained
Flexion Occurs
Not Deleterious


STIFF ATTACHMENT


Natural tooth – permanently cemented substructure

telescopic crown


Implant supported prosthesis – over crown, coping with

temporary cement
Tend to Loosen
To eliminate, permanent cementation rather than fixed retrievability


DIAGNOSTIC FACTORS IN COMBINED PROSTHESIS
Standard Prosthesis design
Internal attachment placed in distal of natural tooth
Differential mobility
Natural tooth cannot support implant
Increase in lever arm
Increase Torque

Recommended Prosthesis Design
One cantilever pontic from each segment
Flexible internal attachment
Drifting apart of segment
Decreased Torque


FOUR CLINICAL VARIANT WITH IMPLANT LOADING
Includes


Cuspal inclination



Implant inclination



Horizontal Implant Offset



Apical Implant Offset


Cuspal Inclination
Increase in 10°  increased 30% torque
Implant Inclination
Increase in 10°  Increased 5% torque


Horizontal Implant Offset
Increase in 1mm  increased 15% torque

Apical Implant Offset
Increase in 1mm  Increased 5% torque


Staggered Implant Offset – Rangert 1993
Staggered buccal and lingual offset
Tripod Effect
Compensates torque
Implant placed 1.5mm bucal and lingual from centre line to
achieve Tripodism.


Weinberg 1996
In maxilla, lingual offset - increased 24% torque
Buccal offset - Decrease 24% torque
Maxilla

-

Tripod –increase in 24% torque

Mandibular

-

Tripodism

Maxilla

-

As far as bucally


Weinberg, 1996
In posterior working side, occlusion.

Produces buccally

inclined resultant line of force on maxilla and lingually inclined
resultant line of force on mandible.
Reduces 73% of torque in mandible


THERAPEUTIC BIOMECHANICS


Decrease cuspal inclination
It reduces the distance between implant and resultant line of

force.




Cross occlusion
Buccolingual relation  cross occlusion
Reduces horizontal implant offset
Reduces torque




Implant Position
Implant head as close to center line of restoration –

Reduces horizontal offset.


PHYSIOLOGIC VARIATION – CENTRIC RELATION
Kantor, Calagna, Calenza, 1973.
Centric relation record show physiologic variation of ±
0.4mm

Weinberg 1998
Occlusal anatomy modified to 1.5mm horizontal fossa
Produce vertical resultant line of force within expected range of
physiologic variation.



Anterior Vertical Overlap
Steep vertical overlap

Extreme Torque


Less steep

Less Torque

BIOMECHANICS AND RESORPTION PATTERN
Posterior Mandible
Bone resorbs along root inclination
Therefore, posterior mandible – bone resorb lingually
Reactively Biomechancis
Lingual position of restoration +
Buccal implant placement - increased torque




Therapeutically
Can be done by



Reduced cusp inclination



Implant head close to centre line of restoration



Angulated abutment - parallelism




Posterior Maxilla

Reactively


Restricted maxilla



Location of sinus



Buccal cortical plate fracture



Unfavourable biomechanics


Therapeutically


Cuspal inclination – reduce



Head of implant close to center of restoration



Angled / custom – reangulated abutment



Cross occlusion



1.5mm horizontal fossa.


Anterior Maxilla
Reactively
Esthetically

-

Labially Proclined

-

Steep vertical overlap


Therapeutically


Lingual horizontal stop – redirect the force as vertically as

possible.


Angled abutment



Implant head close to center of restoration


COMPLETE EDENTULISM AND BIOMECHANICS


Screw loosening not common these patients
Implant placed across and around arch
Cross splinting
Lateral forces –Vertical force
Tripodism
Excellent resistance to bending

WIDER IMPLANTS
Developed by Dr.Burton Langer
Advantages


Increase in surface area



Limited bone height



Upon removal of failed standard size implant



Wider implant

-

Abutment screw 2.5m m Larger size – tighter joint –
overall strength increases


BONE DENSITY AND BIOMECHANICS
Density

∞

Strength

∞

Amount of contact with implant

∞

Distribution and dissipation of force

Misch 1995

FEM study – stress contour is different for each bone
density.
With same load
D1

-

Crestal stress and lesser magnitude

D2

-

Greater crestal stress and along implant body

D4

-

Greatest stress and farther apically

BONE DENSITY AND TREATMENT PLAN MODIFIER


Prosthetic factors



Implant number



Implant – Macrogeometry



Implant – Design



Coating



Progressive loading

PROSTHETIC FACTOR
As density decreases, biomechanical load should also
decreased


Shortened cantilever length



Narrow oclusal table



Offset load minimized



RP4 > FP1, FP2, FP3, removal at night



RP5 – force shared by soft tissue



Force directed along long axis of implant

Implant Number
Increase in number  Increase in functional loading area
Implant Macrogeometry
Length


D1

-

10mm



D2

-

12mm



D3

-

14mm with V-shaped thread screw

Density decreased  Length increased


Width


Increase in width – increase in surface area



1mm increases  30% increase in surface area



D3 & D4  wider implants

Implant Design

Smooth cylindrical implant – shear force at Interface –
Coating with HA / Titanium

Titanium alloy (Ti-6Al-4V) exhibit best biomechanical,
biocompatible, corrosion resistance.
Coating


Increased bone contact area



Increased surface area

Progressive Loading
Misch 1990
Gradual increase in occlusal load separated by a time
interval to allow bone to accommodate.
Softer the bone  increase in progressive loading period.
Protocol
Includes,


Time



Diet



Occlusal Contacts



Prosthesis Design

Time
Two

surgical

appointments

between

initial

placement and stage II uncovery may vary on density.


D1

-

5 Months



D2

-

4 Months



D3

-

6 Months



D4

-

8 Months

Diet


Limited to soft diet – 10 pounds



Initial delivery of final prosthesis-21 pounds

implant

Occlusal Material
Initial step – no occlusal material placed over implant
Provisional – Acrylic – lower impact force
Final - Metal / Porcelain
Occlusion


Initial

-

No oclusal contact



Provisional

-

Out of occlusion



Final

-

At occlusion

Prosthesis Design
First transititional –

No occlusal contact
No cantilever

Second transititional - Occlusal contact
with no cantilever
Final restoration

- Fine occlusal table and cantilever


SINGLE TOOTH IMPLANT AND BIOMECHANICS


Requires good bone support



Control of occlusal lever parallel to long axis



Access for oral hygiene


When space exceeds 12mm

When space less than 12mm


When space exceeds 8mm with limited width

Should not be placed off center


Posterior Triangular Zone


Active zone



Occlusal loading parallel to long axis


Cantilever Prosthesis and Biomechanics


It result in greater torque with distal abutment as fulcrum.



May be compared with Class I lever arm.



May extend anterior than posterior to reduce the amount of

force
It depends on stress factors


Parafunction



Crown height



Impact width



Implant Number

Arch form
English 1993 – AP Spread


Cantilever length = AP spread x 2.5



Tapering

-

canine and posterior implants with
anterior cantilever



Square

-

Anterior implant with posterior
cantilever


Tapering  Ovoid  Square

Less dense bone  Anterior cantilever with prosthesis  Distal
implants, placed to increase AP-spread.
Maxilla - more implants required than mandible


CANTILEVER FIXED PARTIAL DENTURE



Sufficient bone height exist to place long implant,

Avoid contact on central incisors during protrusion, labial
excursion and maximum intercuspation





Group function - lateral movement



Avoid loading on canine



Lateral guidance provided by central and lateral incisor


Two implant supporting a first molar and 2nd premolar with 1st
premolar cantilever  Active cusp eliminated  canine palatal
structures.


Three implants placed with

Two implants  risky

2nd premolar as cantilever

and /or contraindicated


MANDIBULAR FLEXURE
Picton 1962
Stated that mandibular move towards midline on opening 
Because of external pterygoid muscle on ramus of mandible


Medial movement occur distal to mental foramen and
increases as it approaches ramus.


James 1980 & Burch 1982


Movement

-

0.8mm

-

1st molar

1.5mm

-

Ramus area


FLEXION
Implant

-

0.1mm

Natural teeth

-

0.5mm

mandible
10 to 20 times

Complete cross arch splinting of posterior molar  Mandible flexion
 Lateral force


Bone loss around implant



Loss of implant fixation



Material fracture



Unretained restoration



Discomfort on openings

FATIGUE FAILURE
 Characterised by dynamic cyclic loadind
 Depends on – biomaterial
geometry
force magnitude
number of cycles


Biomaterial
 Stress level below which an implant biomaterial can be
loaded indefinitely is referred as endurance limit.
Ti alloy exhibits high endurance limit
Number of cycles
Loading cycles should be reduced
To eliminate parafunctional habit
To reduce occlusal contacts

Implant geometry
 Resist bending & torsional load
 Related to metal thickness
 2 times thicker – 16 times stronger
Force magnitude
Arch position( higher in posterior & anterior)
Eliminate torque
Increase in surface area


IMPLANT DESIGN & BIOMECHANICS



Ti alloy offers best biomechanical strength & biocompatability
Bending fracture resistance factor
Wall thickness = (outer radius)4_ (inner radius)4



If outer diameter increases by 1mm & inner diameter unchanged

33% increase in bending fracture resistance


If inner diameter decreases by 1mm & outer diameter unchanged

20% increase in bending fracture resistance

Thread pitch

Thread depth


Depth –distance between major & minor diameter of thread


Implant macrogeometry
Smooth sided cylindrical implants – subjected to shear
forces
Smooth sided tapered implants – places compressive
load at interface
Greater the taper – greater the compressive load delivery
 Taper cannot be greater than 30 degree
Implant width
Increase in implant width – increases functional surface
area of implant
Increase in 1mm width – increase in 33% of functional
surface area

Implant length
Increase in length –Bicortical stabilisation
Maximum stress generated by lateral load can be dissipated by
Implants in the range of 10-15mm
Softer the bone –greater length or width
Sinus grafting & nerve re-posititioning to place greater implant length
Resistance to lateral loading


Crestal module design
Smooth parallel sided crest –shear stess
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

Larger diameter & angulated crestal module design


Surface Coating
-Titanium plasma spray
-Hydoxyapatite coating
Advantages
-Increase in surface area
-Roughness for initial stability
-Stronger bone – implant interface
Disadvantages
-Flaking and scaling upon insertion
-Plaque retention
-Nidus for infection
-Increased cost

IMPLANT PROTECTED OCCLUSION


Occlusal load transferred within physiologic limit



Misch,1993
width of occlusal table directly related to implant width



Narrow occlusal table with reduced buccal contour permits
sulcular oral hygiene



Restoring occlusal anatomy of natural tooth
-offset load
-complicated home care

Posterior crest of maxilla medial to
Mandibular crest

Narrow occlusal table + reduced
Buccal contour permits oral hygiene,
Axial loading & reduces fracture

Apical Design
Round cross-section do not resist torsional load
Incorporation of anti –rotational feature
-Vent hole- bone grow the hole
-resist torsion
-Flat sidegroove - bone grow against
-places bone in compression


Maxillary lingual cusp & contour reduced
Reduce offset load from opposing natural tooth

Mandibular buccal cusp -

in width & height


Occlusal material
Porcelain,resin,gold
Porcelain

-

esthetics, chewing efficiency

Gold

-

Impact force,chewing efficiency,fracture
resistance,wear,interarch space,accuracy

Acrylic

-

Esthetics , impact force,static load


IMPLANT ORAL REHABILITATION
Constitutes
 Muscle relaxation
Absence of articular inflammation
Stable condylar position
Creating organic occlusion
Absence of pain in stomatognathic system

Organic occlusion components
Correct vertical dimension
Maximum intercuspation in centric relation
Adequate incisal & condylar guidance
Stable bilateral posterior occlusal relation in equilibrium with
long axis of implant
Absence of prematurities
Absence of interferences in eccentric movements

Bruxism patients
Education & informed consent to gain co-operation in
eliminating parafunction
Use of night guard
- anterior guided disooclusion
- posterior cantilever out of occlusion
- soft night guard releived over
implant
Soft tissue supported prosthesis
- soft tissue tend to early load the
implant & hence relieved over it
Removable partial denture over healing abutment
- 6mm hole diameter through metal is
prepared

Final prosthesis
- narrow occlusal table
- centric occlusal contact aligned parallel to long axis
Important criteria
- additional implant
- greater diameter implant


CONCLUSION
Biomechanics is one of the most important consideration
affecting design of the framework for an implant bone
prosthesis.It must be analysised during diagnosis &
treatment planning as it may influence the decision
making process which ultimately reflect on the longevity of
implant supported prosthesis

Bibliography
Implant & restorative dentistry- Martin Dunitz
Atlas of tooth & implant supported prosthesis-Lawrence A.
Weinberg
Atlas of oral implantology- A.Norman Cranin
Contemprorary implant dentistry – Carl Misch
Branemark implant system- John Beumer
ITI dental implants- Thomas G.Wilson
Implant prosthodontics- Fredrickson
Dental implants- Winkelmann
Oral rehabilitation with implant supported prosthesis
- Vincente

Leader in continuing dental education


Implants bio mechanics /certified fixed orthodontic courses by Indian dental academy

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