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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 www.indiandentalacademy.com
Types ďƒ˜
Reactive
ďƒ˜
Therapeutic
Reactive Biomechanics Any prosthesis that increases implant loading.
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Therapeutic Biomechanics Process of remediating each biomechanical factor in order to deiminish implant overlaoding
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Interrelated Factors Analyzed during diagnosis and treatment planning and maintained in a state of equilibrium.
Biomechanics
Occlusion
Esthetics
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Methods of Analysis ďƒ˜ 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.
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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.
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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 www.indiandentalacademy.com
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
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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 www.indiandentalacademy.com
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%
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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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
FORCE DISTRIBUTION PRINCIPLES System Components
Vertical element – tooth or implant
Connecting element
Supporting medium – periodontal ligament or bone
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Flexible Medium
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Stiff Medium
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Flexible and Stiff Medium
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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. www.indiandentalacademy.com
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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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. www.indiandentalacademy.com
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. www.indiandentalacademy.com
FORCE DISTRIBUTION IN MULTIPLE IMPLANT PROSTHESIS Splinting Natural tooth – Periodontal ligament – forced distribution Implant – stiff – no force distribution and only concentration at crestal bone
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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
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FLEXIBLE ATTACHMENT
Tooth supported prosthesis – Female attachment
Implant supported prosthesis – Screw retained Flexion Occurs Not Deleterious
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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
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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 www.indiandentalacademy.com
Recommended Prosthesis Design One cantilever pontic from each segment Flexible internal attachment Drifting apart of segment Decreased Torque
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FOUR CLINICAL VARIANT WITH IMPLANT LOADING Includes
Cuspal inclination
Implant inclination
Horizontal Implant Offset
Apical Implant Offset
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Cuspal Inclination Increase in 10° increased 30% torque Implant Inclination Increase in 10° Increased 5% torque
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Horizontal Implant Offset Increase in 1mm increased 15% torque
Apical Implant Offset Increase in 1mm Increased 5% torque
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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.
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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
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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
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THERAPEUTIC BIOMECHANICS ďƒ˜
Decrease cuspal inclination It reduces the distance between implant and resultant line of
force.
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Cross occlusion Buccolingual relation cross occlusion Reduces horizontal implant offset Reduces torque
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ďƒ˜
Implant Position Implant head as close to center line of restoration –
Reduces horizontal offset.
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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. www.indiandentalacademy.com
ďƒ˜
Anterior Vertical Overlap Steep vertical overlap
Extreme Torque
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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
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Therapeutically Can be done by
Reduced cusp inclination
Implant head close to centre line of restoration
Angulated abutment - parallelism
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Posterior Maxilla
Reactively
Restricted maxilla
Location of sinus
Buccal cortical plate fracture
Unfavourable biomechanics
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Therapeutically
Cuspal inclination – reduce
Head of implant close to center of restoration
Angled / custom – reangulated abutment
Cross occlusion
1.5mm horizontal fossa.
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Anterior Maxilla Reactively Esthetically
-
Labially Proclined
-
Steep vertical overlap
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Therapeutically
Lingual horizontal stop – redirect the force as vertically as
possible.
Angled abutment
Implant head close to center of restoration
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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 www.indiandentalacademy.com
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
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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 www.indiandentalacademy.com
BONE DENSITY AND TREATMENT PLAN MODIFIER
Prosthetic factors
Implant number
Implant – Macrogeometry
Implant – Design
Coating
Progressive loading www.indiandentalacademy.com
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 www.indiandentalacademy.com
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
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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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
Prosthesis Design First transititional –
No occlusal contact No cantilever
Second transititional - Occlusal contact with no cantilever Final restoration
- Fine occlusal table and cantilever
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SINGLE TOOTH IMPLANT AND BIOMECHANICS
Requires good bone support
Control of occlusal lever parallel to long axis
Access for oral hygiene
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When space exceeds 12mm
When space less than 12mm
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When space exceeds 8mm with limited width
Should not be placed off center
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Posterior Triangular Zone ďƒ˜
Active zone
ďƒ˜
Occlusal loading parallel to long axis
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Cantilever Prosthesis and Biomechanics
It result in greater torque with distal abutment as fulcrum.
May be compared with Class I lever arm.
force
May extend anterior than posterior to reduce the amount of
It depends on stress factors
Parafunction
Crown height
Impact width
Implant Number www.indiandentalacademy.com
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
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Tapering Ovoid Square
Less dense bone Anterior cantilever with prosthesis Distal implants, placed to increase AP-spread. Maxilla - more implants required than mandible
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CANTILEVER FIXED PARTIAL DENTURE
Sufficient bone height exist to place long implant,
Avoid contact on central incisors during protrusion, labial excursion and maximum intercuspation
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Group function - lateral movement
Avoid loading on canine
Lateral guidance provided by central and lateral incisor
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Two implant supporting a first molar and 2nd premolar with 1st premolar cantilever ďƒ Active cusp eliminated ďƒ canine palatal structures.
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Three implants placed with
Two implants ďƒ risky
2nd premolar as cantilever
and /or contraindicated
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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
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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 www.indiandentalacademy.com
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FATIGUE FAILURE Characterised by dynamic cyclic loadind Depends on – biomaterial geometry force magnitude number of cycles
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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 www.indiandentalacademy.com
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
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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 www.indiandentalacademy.com
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Thread pitch
Thread depth
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ďƒ˜Depth –distance between major & minor diameter of thread
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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 www.indiandentalacademy.com
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
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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 www.indiandentalacademy.com
-Increase in surface area
Larger diameter & angulated crestal module design
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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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
Posterior crest of maxilla medial to Mandibular crest
Narrow occlusal table + reduced Buccal contour permits oral hygiene, Axial loading & reduces fracture www.indiandentalacademy.com
Apical Design Round cross-section do not resist torsional load Incorporation of anti –rotational feature -Vent\ hole- bone grow the hole -resist torsion -Flat side\groove - bone grow against -places bone in compression
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Maxillary lingual cusp & contour reduced Reduce offset load from opposing natural tooth
Mandibular buccal cusp -
in width & height
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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
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IMPLANT ORAL REHABILITATION Constitutes Muscle relaxation Absence of articular inflammation Stable condylar position Creating organic occlusion Absence of pain in stomatognathic system www.indiandentalacademy.com
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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
ďƒ˜Final prosthesis - narrow occlusal table - centric occlusal contact aligned parallel to long axis ďƒ˜Important criteria - additional implant - greater diameter implant
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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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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