Scientific rationale for dental implant i mplant design.
Single tooth implant and biomechanics.
Cantilever prosthesis and biomechanics.
iomechanics of frame wor!s and misfit.
Treatment planning based on biomechanical ris! factors.
Conclusion.
"eferences.
Page #
Biomechanics of implants
INTRODUCTION:
iomechanics comprises of all !inds of interactions between tissues and organs of the body and forces acting on them. It$s the response of the biologic tissues to the the applied loads. %ental implants function to transfer load to surrounding biological tiss tissue ues. s. Thus Thus the the prim primar ary y func functi tion onal al desi design gn ob&e ob&ect ctiv ivee is to mana manage ge 'dissipate and distribute( biomechanical loads to optimi)e the implant supported prosthesis function. Definition
*rocess of analysis and determination of loading and deformation of bone in a biological biological system. +atural tooth s ImplantImplant-
+atural tooth #. +atural tooth is anchored in to
Implant #. Impl Implan antt is rigi rigidl dly y fie fied d by
the bone by fleible periodontal
functional an!ylosis.
ligament. /.
The
around
perio riodont dontaal the
natural
lig ligamen amentt tooth
significantly reduces the amount of stress transmitted to the bone
/. The concentration of stresses mainl inly occu occurs rs at the the cres cresttal region.
Page /
Biomechanics of implants
and
facilitates
even
force
distribution. 0. The The pdl pdl acts acts as visc viscoe oela last stic ic shoc!
absorber
serving
to
0. The implant is fied and rigid.
decrease the magnitude of stress to the bone. 1. The precursor signs of a premature contact or occlusal traum raumaa
on
natural ral
teeth
are
usua usuall lly y reve reversi rsibl blee and and incl includ udee
1. These initial reversible signs and symptoms of trauma donot occur with implants.
sign signss of cold cold sens sensit itiv ivit ity, y, wear wear facets, pits, drift away and tooth mobility. 2. This condition often helps in
2. The magnitude of stress may
the patien patientt see!in see!ing g profes professio sional nal
cause bone microfractu microfracture, re, bone
treatment by occlusal ad&ustment
loss loss
and
mech mechan anic ical al fail failur uree of impl implan antt
a
reduction
in
force
magn magnit itud udee in force force magn magnit itud udee
which which ultim ultimate ately ly leads leads to to
components.
which further reduces the stress magnitude. 3. The elastic modulus of a tooth is closer to the bone than any of
3. The implant materials differs by
the the
24#5 24#5 time timess from from the the surr surrou ound ndin ing g
curr curren entl tly y
avai availa labl blee
dent dental al
implant implant biomaterial biomaterial.. The greater greater
bone structure. Page 0
Biomechanics of implants
the fleibility difference between the two materials, the greater the potential
relative
generated
between
motion the
two
surfaces at the endosteal region. 6. Implants deliver a slow dull 6. The proprioceptive information
pain that triggers a delayed
relayed by teeth and implants also
reaction if any.
differs differs in 7ualit 7uality. y. +atura +aturall teeth teeth deliver
a
pressure
rapid,
sharp, rp,
that
high
triggers
proprioceptive mechanism. mechanism. 8.
The
surrou rounding
bone
8. ;he ;here as the bon bone load loadiing around an implant is performed by
of
natural teeth is developed slowly
the dentist in a much more rapid and intense fashion.
and and grad radual ually in resp respo onse nse to biomechanical loads. loads. 9. Late Latera rall forc forces es in impl implan ants ts 9. : lateral force on natural tooth is dissip dissipate ated d rapidl rapidly y away away from
concentrat rates
at
the
crestal
region.
the crest of bone toward toward the ape of the tooth.
Page 1
Biomechanics of implants CHARACTER OF FORCES APPLIED TO DENTAL IMPLANTS -
<cess loads on an osseointegrated implant may result in mobility of supporting device and ecessive loads also may fracture an implant compon component ent or body. body. The intern internal al stress stresses es that that develo develop p in an implan implantt system and surrounding biological tissues under imposed load may have a significant influence on the long term longevity of the implants in vivo. : goal of treatment planning should be to minimi)e and evenly distribute mechanical stress in implant system and contiguous bone. LOADS APPLIED TO DENTAL IMPLANTS: o
In function = occlusal loads
o
:bsence of function = *erioral forces
>ori)ontal loads
o
Mechanics help to understand such physiologic and non physiologic loads and can determine which t?t renders more ris!. MASS, FORCE AND WEIGHT: Mass – : property of matter, is the degree of gravitational attraction the
body of matter eperiences. eperiences. @nit = !gs - 'lbm( FORCE (SIR ISAAC NEWTON !"#$:
+ewton$s II law of motion
Page 2
Biomechanics of implants F A ma ;here a A 9.8 m?s/
Mass = %etermines magnitude of static load
Force = Bilograms of force
WEIGHT:
Is simply a term for the gravitational force acting on an ob&ect at a specified location. FORCES AND FORCE COMPONENTS:
Magnitude, duration, direction, type and magnification
ector 7uantities$
%irection = dramatic influence MOMENT % TOR&UE:
The force which which tends to rotate a body. @nits = +.mD +.cm, +.cm, lb.ft D o).in In addition addition to aial force, force, there there is a moment moment on the implant implant which which is e7ual e7ual to magnit magnitude ude of force force times times 'multi 'multipli plied ed by( the perpen perpendic dicula ularr distance 'd( between the line of action of the F and center of the implant.
Page 3
Biomechanics of implants
FORCES ACTING ON THE IMPLANTS: T'ee t)*es of fo+es a+tin on t'e -enta. i/*.ants
Co/*essi0e
Tensi.e
s'ea
Compressivei(
Tend to push masses towards each other.
ii(
Maintains in integrit rity of of bo bone = implant in interfa rface.
iii(
:ccommodated best.
iv(
Cortical bone is stron rongest in compressi ssion.
v(
Cemen ementts, ret retent ention ion sc screw rews, implan plantt com comp ponen onents ts and and bo bone = im impla plant interfaces can accommodate greater compressive forces than tensile or shear forces. Page 6
Biomechanics of implants vi(
>ence compressive forces should be %ominant in implant
prosthetic occlusion. occlusion.
TENSILE FORCES
SHEAR FORCES
↓
↓
*ull ob&ects apart
Sliding
%istract ? disrupt bone implant interface.
Shear She
forc forces es are most ost dest destru ruct ctiv ivee, cort cortic ical al bone bone is wea! ea!est est to
highest highest ris! for for shear forces forces at
the implant tissue interface unless an occlusal load directed along the long ais of the implant body. They re7uire a coating to manage the shear forces to manage the shear
forces through a more uniform bone attachment. Threaded ? finned implants impart a combination of all three types of
forces forces at the interfac interfacee under under the the action action of single single occlus occlusal al load. load. This This Page 8
Biomechanics of implants conversion of a single force in to three types of forces is controlled by the implant geometry. STRESS:
The manner in which a force is distributed over a surface is referred as mechanical stress. 1 F%A
The magnitude of stress depends on two variables4
force magnitude.
4
cros crosss sec secti tion onal al area area over over whic which h the the forc forcee is is dis dissi sipa pate ted. d. Fo+e /anit2-e may be decreased by reducing magnifiers of force that
are#.
Cantilever le length
/.
Crown height
0.
+ight guards
1.
Ecclusal material
2.
Ever dentures F2n+tiona. F2n+tiona. +oss se+tiona. aea may be optimi)ed by-
#. increased by +umber of implants /. Selecting Selecting an Implant Implant geometry geometry that has has been designed designed carefull carefully y to maimi)e the functional cross sectional area.
Page 9
Biomechanics of implants DEFORMATION 3 STRAIN: : load applied to a dental implant may induce deformation of the implant
and surrounding tissues %eformation and stiffness of implant material may influence
A.
Implant tissue Interface Interface
B.
Ease of implant manufacture manufacture
C.
Clinical longevity
STRESS – STRAIN RELATIONSHIP:
: relationship is needed between the applied stress that is imposed on the implant and surrounding tissues and the subse7uent deformation.
The load values by the surface area over which they act and the strain eperienced by the ob&ect produces a stress strain curve. Page #5
Biomechanics of implants
The slope of the linear portion of the curve is referred to as the modulus of elasticity and its value indicates the stiffness of the material.
The closer the modulus of elasticity of the implant to the biological tissues, the less the relative motion at the implant tissue interface. Ence a particular implant system is selected the only way for an operator to control the strain eperienced by the tissues is to control the applied stress or change the density of bone around ar ound the implant.
reater the strength stiffer the bone
%ifference in stiffness is less for CpTi G %# bone but more for %1 bone
Stress reduction in such softer bone
To reduce resultant tissue strain
Lower @ltimate strength
>oo!$s law Stress A Modulus of elasticity strain A <.ε γ A 4ITING FORCES:
:ial component of biting force- '#55 = /255 +( ? '/6 = 225 lbs( It tends to increase as one moves distally Lateral component 4 /5 + 'appro.(
time per meal A 125 sec +et chewing time Page ##
Biomechanics of implants
•
Chewing forces will act on teeth for A 9 min?day
•
If includes swallowing A #6.2 min?day
•
Further be increased by parafunction FORCE DELI5ER6 AND FAILURE MECHANISM:
The manner in which forces are applied to the dental implant restorations
within the oral environment dictates the li!elihood of system failure. :n understanding of force delivery and failure mechanisms is critically
impo import rtan antt to the the impl implan antt pract ractit itio ione nerr to avoi avoid d cost costly ly and and pain painfu full complications.
The moment moment or tor7ue tor7ue is the the product product of the force force
magnitude magnitude multipl multiplied ied by the perpendicu perpendicular lar distance distance from the point point of interest to the line of the action of the force.
Moment loads are destructive in nature and may result in-
Interface brea!down one resorption Page #/
Biomechanics of implants Screw loosening ar ? bridge fracture : total of si moments may develop about the three clinical coordinate aes4 occlusoapical 4 faciolingual 4 mesiodistal These moment loads induce microrotations and stress concentrations at the crest of the alveolar alveolar ridge at the implant implant to tissue tissue interface interface , which lead lead inev inevit itab ably ly to cres cresta tall bone bone loss loss.. Thre Threee clin clinic ical al mome moment nt arms arms in implant dentistry 4 occlusal height 4 cantilever length 4 occlusal width
Page #0
Biomechanics of implants Minimi)ation of each of these moment arms is necessary to prevent unreta unretaine ined d restor restorati ations ons,, fractu fracture re of compon component ents, s, cresta crestall bone bone loss loss or complete implant system failure. $ O++.2sa. 'ei't:
4 Ecclusal height serves as the moment arm for force components directed along the faciolingual ais4 wor!in wor!ing g or balanc balancing ing occlusal occlusal contac contacts, ts, tongue tongue thrus thrusts ts or peri peri oral oral musculature, and the force components directed along the mesiodistal ais. 4 force components components along the vertical vertical ais is not affected affected by the occlusal occlusal height because there is no effective moment arm. 4 in division : bone initial moment load at the crest is less than in division C or % bone because the crown height is greater in Cand %. 7$ Canti.e0e .ent':
Large Large moment momentss may develo develop p from vertic vertical al ais ais force force compon component entss in prosthetic environments designed with cantilever etensions or offset loads from rigidly fied implants.
: Lingual force component may also induce a twisting moment about the implant nec! ais if applied through a cantilever length.
Force applied directly over the implant does not induce a moment load or tor7ue because no rotational forces are applied through an offset distance.
Page #1
Biomechanics of implants
:ntero posterior spread is the distance to the center of the most anterior implant and the most distal aspect of the posterior implants.
The greater the :4* spread the smaller the resultant loads on the implant system from cantilevered forced because of the stabili)ing effect of the antero4posterior distance. :ccording to MISCH
Cantilever length is determined by the amount of stress applied to system
enerally =%istal cantilever = not be H /.2 times of :4* spread
*atients with parafunction = not to be restored by cantilever.
S7uare arch form involves smaller :4* spreads between splited implants and should have smaller length cantilever.
Tapered arch form = largest :4* spread = larger cantilever design. 8$9 O++.2sa. i-t':
;ide ;ide occlus occlusal al tables tables increa increase se the moment moment arm for any offset offset occlusal loads. Faciolingual tipping 'rotation( can be reduced significantly by narrowing the occlusal tables or ad&usting the occlusion to provide more centric contacts. : vicious destructive cycle can develop with moment loads and result in crestal bone loss.
Page #2
Biomechanics of implants
Mo/ent .oa-s
Cesta. ;one .oss
In+eases o++.2sa. 'ei't Fai.2e if ;io/e+'ani+a. ;io/e+'ani+a. en0ion/ent is not +oe+teO++.2sa. 't9 /o/ent a/
Fatigue behaviour of biomaterials is characteri)ed to a plot of applied stress vs no. of loading cycles
>igh stress = few loading cycles
Low stress = infinite loading cycles
Page #3
Biomechanics of implants
Ti
alloys
ehibits
a
higher
enduran rance
limit
compared
with
commercially pure titanium 'Cp Ti( 7$ Ma+o eo/et):
The geometry of an implant influences the degree to which it can "esists bending and tor7ue
Lateral loads also causes fatigue fracture
The fatigue failure is related as 1th power of the thic!ness difference
:lso affected by the difference in Inner and outer diameter of screw and abutment screw space 8$ Fo+e /anit2-e:
The magnit magnitude ude of loads loads on dental dental implan implants ts reduce reduced d by carefu carefull consideration of arch position
>igher loads on posteriors
Limitation of Moment loads
eometry for functional area
Increasing the +o. of implants
=$ Loa-in +)+.es
"educing the +o. of loading cycles
<limination of parafunction
"educing the occlusal contacts SCIENTIFIC RATIONALE FOR DENTAL IMPLANT DESIGN Page #6
Biomechanics of implants %ental implan implants ts functi function on to transf transfer er of load load to surrou surroundi nding ng biolog biologic ic %ental tissues. Thus the primary functional design ob&ective is to manage 'dissipate and
dist distrib ribut ute( e( biom biomec echa hani nica call load loadss to opti optimi mi)e )e the the impl implan antt supp support orted ed prosthesis function. iomechanical load management depends on two factors that are
#( Character of applied load.
/( Functional surface area
Forces applied to dental implant characteri)ed in terms of Magnitude,
duration, type, direction and magnification. FORCE MAGNITUDE
The The magn magnit itud udee of biti biting ng forc forcee varie variess as a func functi tion on of anatomic anatomic region and state of dentition dentition.. The magnitude magnitude of force is greater greater in molar region and lesser in canine region.
>igher >igher magnit magnitude ude demand demandss increa increased sed bone bone densit density y and Influence the selection of biomaterials.
Materials such as silicon hydroyapatite and carbon are characteri)ed by lesser ultimate strengths even though they are highly compatible with the biological tissues.
In
cont contem emp porar orary y
appl appliicat cation ions,
the these
materi teriaals
are
considered for use as coatings applied to stronger substrate materials.
Titanium and its alloy = <cellent biocompatibility Page #8
Biomechanics of implants 4 Corrosion resistance 4 ood ultimate strength 4 Closest appro. to stiffness of bone FORCE DURATION:
The duration of bite forces on dentition has a wide range under ideal conditionsD the total time of those brief episodes is less than 05 minutes per day.
*atients who ehibit bruism, clenching or other parafunctional habits may have their teeth in contact several hours each day.
The enduranc endurancee limit limit or fatigu fatiguee streng strength th is the level of highes highestt stress stress through whish a material may be cycled repetitively without failure. The endurance limit of a material is often less than one half its ultimate tensile strength.
The ability of implants and abutment screws to resist fracture from bending loads is related directly to the moment of inertia of the component.
This parameter is a function of the cross sectional geometry of the component.
Implant bodies are particularly susceptible to fatigue fracture at the apical etension of the abutment screw within the implant body or at the crest module around abutment 'eg- with an internal heagon(
The formula for the bending fracture resistance in these conditions is related to the outer diameter radius to the fourth power minus the inner diameter radius to the fourth power.
Page #9
Biomechanics of implants
The wall thic!n thic!ness ess of the implant implant body body in this this region region controls controls the resistance to fatigue failure. <ven a small increase in wall thic!ness results in a significant increase in bending fracture resistance because the dimension is multiplied to a power of four.
T6PE OF FORCE:
Three types types of forces may be imposed imposed on dental dental implants implants within within the oral environment
4Compression
4Tension 4Shear
one one is stronge strongest st when when loaded loaded in compre compressi ssion. on. 05 wea!er wea!er when when sub&ected to tensile forces and 32 wea!er when loaded in shear
: smooth sided implant may be called a cylinder design, and this cylinder implant body result in essentially a shear type of force at the imp implan lant to bone bone inte interf rfaace. ce. Thus Thus this his body ody geom eometry etry mus must use a microscopic retention system by coating the implant with titanium plasma spray or hydroyl apatite
If the hydroyapatite resorbs from infection or bone remodeling, the remaining remaining smooth sided cylinder cylinder is severely severely compromised compromised for healthy healthy load transfer to the surrounding tissues
: thread threaded ed implan implantt may use micros microscop copic ic and macros macroscop copic ic design design features to load the bone in compression and tensile loads
Threa Threade ded d impl implan ants ts have have the the abil abilit ity y to tran transf sfor orm m the the type type of forc forcee impo impose sed d at the the bone bone inte interfa rface ce thro throug ugh h care carefu full cont contro roll of the the thre thread ad Page /5
Biomechanics of implants geometry. Thread shape is particularly important in changing force type at the bone interface
Thread shapes in dental implant design include s7uare, v shape and buttress
@nde @nderr aia aiall load loadss to a dent dental al impl implan antt a v thre thread ad face face 'typ 'typic ical al of paragon, 0i and +obel iocana( is comparable to the buttress thread and has a #5 times greater shear component of force than a s7uare or a power thread
: reduction in shear load at the thread to bone interface reduces the ris! of overloadD which is particularly important in compromised %0 and %1 bone. : threaded implant also may have a surface condition such as hydroyapatite, T*S or other roughed surface.
FORCE DIRECTION:
The anatomy of the mandible and mailla places significant constraints on the ability to surgically place root form implant suitable for loading along their long ais.
ony ony unde undercu rcuts ts furt furthe herr cons constr trai ain n impl implan antt plac placem emen entt thus thus forc forcee direction. Most of all undercuts occur on the facial aspects of the bone, with the eception of the submandibular fossa in posteroior mandible. >ence implant bodies often are angled to the lingual to avoid penetrating the facial undercut during insertion.
:s the angle of the load increases, the stresses around the implant increases, particularly in the vulnerable crestal bone region. :s a result all implants are designed for placement perpendicular to the occlusal plane.
Page /#
Biomechanics of implants This placement allows a more aial load to the implant body and reduces the amount of crestal loss. FORCE MAGNIFICATION-
Ther Theree are are vari variou ouss fact factor orss whic which h can can magn magnif ifie iess the the force forcess on dent dental al implants
Surgical placement resulting in etreme angulation of the implant
*ara functional habits
Cantilever and crown height
Increase in functional area
Increased density of the bone
Increase in implant number decreases cantilever length and limits the force magnifier.
FUNCTIONAL SURFACE AREA:
Functional surface area is defined as the area that actively serves to dissipate compressive and tensile non shear bonds through the implant to bone interface and provides initial stability of the implant following surgical placement.
The The tota totall surf surfac acee area area may may incl includ udee a pass passiv ivee area area that that does does not not participate in load transfer.
Func Functi tion onal al surf surfac acee area area also also play playss a ma&o ma&orr role role in addr addres essi sing ng the the variable implant to bone contact )ones related to bone density.
Page //
Biomechanics of implants
%# bone, is the densest bone found in the &aws is also the strongest bone and provides an intimate contact with a threaded root form implant at initial implant loading.
%1 bone has the wea!est biomechanical strength and the lowest contact area to dissipate the load at the implant to bone interface.
Thus an improved functional surface area per unit length of the implant is needed to reduce the mechanical stress to this wea! bone.
Implant macrogeometry and implant width are two important design variables for optimi)ing surface area.
IMPLANT MACROGEOMETR6
The The macr macro o desi design gn or shap shapee of an impl implan antt has has an impo import rtan antt bearing on the bone bone response.
rowing bone concentrates preferentially on protruding elements of the implant surface, such as ridges, crests, teeth, ribs or the edge of threaded surface.
The shape of the implant determines the surface area available for stress transfer and governs the initial stability of the implant.
Smoo Smooth th side sided d cyli cylind ndri rica call impl implan ants ts prov provid idee ease ease in surg surgic ical al placement, however the bone to implant interface is sub&ected to significantly larger shear conditions.
: smooth sided tapered implant allows for a component load to be delivered to the bone implant interface, depending on the degree of taper, however the greater the taper of smooth sided implant the less the overall surface area of the implant body.
Page /0
Biomechanics of implants
Threaded implants with circular cross sections provide for ease of surg surgic ical al plac placem emen entt and and allo allow w for for great greater er func functi tion onal al surfa surface ce area area optimi)ation to transmit compressive loads to bone implant interface.
:
smooth
surface
cylinder
depends
on
a
coating
or
microstructure for load transfer to bone. IMPLANT WIDTH:
:n increase in implant width ade7uately increases the area over which occlusal forces may be dissipated.
;ider root form designs ehibit a greater area of bone contact than narrow row implants
of
similar
design because
of
an
increase
in
circumferential bone contact.
The The larg larger er the widt idth of the the imp implan lant the more ore it rese resem mbles les the the emergence profile of the natural tooth.
The increased width of implants 34#/ mm also enhances the bending fracture resistance. ut the crestal bone anatomy most often constrains implant width to less than 2.2mm.
THREAD GEOMETR6
Threads are designed to maimi)e initial contact enhance surface area and facilitate dissipation of stresses at the bone4 implant interface. Functional surface area per unit length of the implant may be modified by varying three thread geometry parameters 4
thread pitch
4
thread shape Page /1
Biomechanics of implants 4
thread depth
THREAD PITCH:
Thread pitch is defined as the distance measured parallel with its ais between ad&acent thread forms or the number of threads per unit length in the same aial plane or on the same side of the ais.
The smaller the pitch 'finer( the more threads on the implant body for a given unit length, and thus the greater surface area per unit length of the implant body.
If force magnitude increase or bone density decreases one may decrease the thread pitch to increase the functional surface area.
Some of the current popular designs which have different pitches.
The distance between pitches-
Page /2
Biomechanics of implants ITI Implant = #.2mm Sterioss
4 5.8mm
+obel biocare,)immer, 0i G life core = 5.3mm iohori)ons 4 5.1mm 4the fewer the threads , the easier to bond or insert the implant. THREAD SHAPE-
Thread shapes in implant geometry 'dental implant designs include s7uare, shape and buttress.
The shape thread design is called a fiture and is primarily used for fiating metal parts together not load transfer.
The buttress thread shape was designed initially for and is optimi)ed for pullout loads.
The s7uare or power threaded provides an optimi)ed surface area for intrusive, compressive load transmission.
The shear force on a threaded face 'typical of Jimmer, 0i and +obel biocare( is about #5 time greater than the shear force on a s7uare thread. Page /3
Biomechanics of implants T>"<:% %<*T>
The threaded depth refers to the distance between the ma&or and minor diameter of the thread.
the greater the thread depth, the grater the surface area of the implant if all the other factors are e7ual.
IM*L:+T L<+T>
:s the length of an implant increases so does the overall total surface area.
%# bone is the strongest and densest bone of the oral environment. The stre streng ngth th of the the bone bone and and the the inti intima mate te cont contac actt betw betwee een n the the bone bone and and implant provide resistance to lateral loading. icortical stabili)ation is not needed in %# bone because it is already a homogenous cortical bone.
: long implant in %/ or %0 bone in the anterior mandible may cause increased surgical ris!, since attempting to engage the opposing cortical plate and preparing a longer osteotomy may result in overloading of the bone.
In poor poor 7ual 7ualit ity y %0 and and %1 bone bone func functi tion onal al surf surfac acee area area must must be maimi)ed to distribute occlusal loads optimally, the placement of longer implants implants in posterior posterior regions re7uire surgical surgical modificat modifications ions li!e nerve repositioning, placement of sinus grafts in maillary posterior regions.
The shorter and smaller diameter implants had lower survival rates than their longer or wider counter parts.
CREST MODULE CONSIDERATIONS CONSIDERATIONS-
Page /6
Biomechanics of implants Crest module of an implant body is the transosteal region from the
implan implantt body body and charac character teri)e i)ed d as a region region of highl highly y concen concentra trated ted mechanical stress.
Slightly larger than outer diameter, thus the crest module seats fully over the implant body osteotomy, providing a deterrent for the ingress of bacteria or fibrous tissue. tissue.
The seal created by the larger crest module also provides for greater initial stability of the implant following placement.
*olished collar '5.2 mm( = perigingival area, provides for a desirable smooth surface close to the perigingival area.
Longer polished collar = shear loading = crestal bone loss
one is often lost to first thread, because the first thread changes the shear force of the crest module to a component of compressive force in which bone is strongest.
:*IC:L %<SI+ CE+SI%<":TIE+S"ound "ound cross sectional sectional implants implants do not resist torsional torsional shear forces when abutment screws are tightened hence anti rotational feature is incorporated usually in the apical region of the implant body, with a hole or vent. one can grow through the apical hole and resist torsional loads applied to the implant. The apical hole region may increase the surface area available to transmit compressive loads on the bone. The disadvantage of the apical hole occurs occurs when the implant is placed through the sinus floor or becomes eposed through a cortical plate. The apical hole may fill with mucous and become a source of Page /8
Biomechanics of implants retrograde contamination. :nother anti rotational feature of implant body may be flat sides or grooves along the body or apical region of the implant body. The apical end of each implant should be flat rather than pointed, this allows for the entire length of the implant to incorporate design features that maimi)e desired strain profiles. Poessi0e Loa-in Mis+' (>"?$ proposed that
radual increase in occlusal load separated by a time interval to allow bone to accommodate. accommodate. Softer the bone à increase in progressive loading period. Poto+o. In+.2-es,
Time
%iet
Ecclusal Contacts and occlusal material
*rosthesis %esign
Ti/e:
Page /9
Biomechanics of implants Two surgical appointments between initial implant placement and stage II uncovery may vary on density.
%#
4
0 Months
%/
4
1 Months
%0
4
2 Months
%1
4
3 Months
Diet:
Limited to soft diet = #5 pounds Initial delivery of final prosthesis4/# pounds O++.2sa. Mateia.:
Initial step = no occlusal material placed over implant *rovisional = :crylic = lower impact force Final 4 Metal ? *orcelain *orcelain O++.2sion:
Initial
4
*rovisional 4
Eut of occlusion
Final
:t occlusion
4
+o occlusal contact
Post'esis Desin:
First First tran transit sititi itiona onall = +o occl occlusa usall conta contact ct
Page 05
Biomechanics of implants +o cantilever Seco Second nd tran transi siti titi tion onal al 4
Eccl Ecclus usal al cont contac actt ;ith no cantilever
Final restoration
4 narrow occlusal table and cantilever with implant
protective occlusion occlusion guidelines.
SINGLE TOOTH IMPLANTS
Single Single tooth tooth impla implants nts re7uir re7uiree good good bone bone suppor supportt and contro controll of harmful effects of occlusal levers that are not parallel to the long ais of the implant.
The prosthesis must be designed to allow good oral hygiene, with easy access to inter proimal surfaces and the retaining screw.
: molar can be replaced with two standard diameter implants or one wide implant.
This type implant is contraindicated for larger spaces because the masticato masticatory ry and occlusal forces to the most distal distal or mesial mesial portions portions will be harmful.
To avoi avoid d ece ecess ssiv ivee load loads, s, the the impl implan antt must must be cent centere ered d in the the edentulous space during placement.
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Biomechanics of implants
ANTERIOR SINGLE TOOTH RESTORATIONS: RESTORATIONS:
The anterio anteriorr
single single tooth tooth restor restorati ation on is achiev achieved ed using a standa standard rd
diameter implant, which is preferred over a narrow implant because it provides a larger surface for osseo integration integration
enerally the use of wide implants in this area is not advocated because it may compromise good esthetic results.
To avoid levers that may be produced during parafunction in centric and eccent eccentric ric positi positions ons,, its recomm recommend ended ed that that the implan implantt suppor supported ted restoration be left out of occlusion. S>E"T S*:+ FIK<% *:"TI:L %<+T@"<The construction of a 0 unit particularly cantilever fied partial dentures re7uire a posterior triangular )one of occlusal surface between the supporting supporting implants. The chances of overloading the implants are far less and this this provid provides es a better better long long term
progno prognosis sis,, becaus becausee it offers offers a wider wider
active )one while also achieving good occlusal load in relationship to the aes of the implants. the use of wide implants to support cantilever fied partial dentures improves the prognosis further, especially in those cases where only two wide implants are needed compared compared to three of standard diameter. wide implants allow for an increased occlusal surfaces in these circumstances. Page 0/
Biomechanics of implants The proimity proimity of anatomica anatomicall features features such as the mandibular canal or the maillary sinus limit the use of long implants. In the presence of ade7uate bucco lingual bone width these limitations ca be managed with the use of wide implants. C:+TIL<<" FIK<% *:"TI:L %<+T@"<
It results in greater tor7ue with distal abutment as fulcrum.
May be compared with Class I lever arm.
May etend anterior than posterior to reduce the amount of force It depends on stress factors
*arafunction
Crown height
Impact width
Implant +umber The The desi design gn of cant cantil ilev ever er fie fied d part partia iall dent dentur ures es is depe depend nden entt on the the occlusal forces that can be elicited at the free end of the denture and the length and width of the implants selected.
C:S< #
: case with two implants placed for the lateral incisor and the canine with a free end central incisor.
Two implants of ade7uate length are re7uired.
The cantil cantileve everr tooth tooth should should avoid avoid contac contacts ts on the centra centrall inciso incisors rs during protrusion, lateral ecursions and maimum intercuspation. Page 00
Biomechanics of implants
C:S< II
;hen the implants serve as support for the central and lateral incisors with a free end canine, the occlusal configuration should provide group function during lateral movements and avoids loading of canine.
If it$s not possible lateral guidance may be provided by the central and lateral incisors avoiding any contact with the canine.
C:S< IIIplaced unilaterally unilaterally at the site of two maillary maillary ;hen two implants are placed premolars, the free end canine must must be left out of occlusion. occlusion.
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Biomechanics of implants C:S< I
Molar replacements achieve best results with a three Implant supported fied prosthesis providing premolar morphology to the restorations.
The length of the implants influences the outcome of treatment
%ue to the enormous occlusal loads in the second molar area the use of a free end fied prosthesis is contra indicated.
4IOMECHANICS OF FRAMEWOR@S AND MISFIT Fa/eo<s:
Metal framewor! for full arch prosthesis can fracture
More towards the cantilever section
Reasons: $ Everload of cantilever
@nli!ely to occur = typical prosthetic alloy. /( Metallurgic fatigue under cyclic loads *revention = substantial cross sectional area Page 02
Biomechanics of implants = 043 mm
TREATMENT PLANNING 4ASED ON 4IOMECHANICAL RIS@ FACTORS
%esign of final prosthetic reconstruction
:natomical limitation
Geo/eti+ is< fa+to
#( +o. of implants less than no. of root support
Ene implant replacing a molar = ris!.
# wide = plat form implant ? / regular implants Two implants supporting 0 roots or more = ris!
/ wide = platform implants
/( ;ide = platform implants
"is! = if used in very dense bone
0( Implant connected to natural teeth 1( Implants placed in a tripod configuration
%esired à counteract lateral loads
Page 03
Biomechanics of implants 2( *resence of prosthetic etension 3( Impl Implan ants ts plac placed ed offs offset et to the the cent center er of the the pros prosth thes esis is à in tripod tripod arrangement, offset is favorable. 6( <cessive height of the restoration
OCCLUSAL RIS@ FACTORS:
Force intensity and parafunctional habit
*resence of lateral occlusal contact
Centric contact in light occlusion
Lateral contact in heavy occlusion
Contact at central fossa
Low inclination of cusp
"educed si)e of occlusal table
4ONE IMPLANT RIS@ FACTORS
%ependence on newly formed bone
:bsence of good initial stability
Smaller implant diameter
*roper healing time before loading
1 mm diameter minimum = posteriors
Te+'no.oi+a. is< fa+tos
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Biomechanics of implants
Lac! of prosthetic fit and cemented prostheses
*roven and standardi)ed protocols
*remachined components
Instrument with stable and predefined tightening tor7ue
WARNING SIGNS:
=
"epeated loosening of prosthetic prosthetic ? abutment screw
=
"epeated fracture of veneering material material
=
Fracture of prosthetic ? abutment abutment screws
=
one resorption below the the first thread
CONCLUSION:
iomechan iomechanics ics is one of the most important important consideration affecting the design of the frame wor! for an implant bone prosthesis. It must be analy)ed during during diagnosis and treatment treatment planning as it may influence the decision ma!ing process which ultimately reflect on the implant supported prosthesis.
REFERENCES
#.
%ental implant prosthetics = Carl <. Misch
Page 08
Biomechanics of implants /.
*ri *rinci nciple ples an and pra pract ctic icee of of im implan lant den denttist istry = Cha Charl rlees ;ei ;eiss ss,, :d :dam ;eiss.
0.
Tiss Tissue ue = int integ egra rate ted d pro prost sthe hesi sis. s. Esse Esseoi oint nteg egra rati tion on in clin clinic ical al dent dentis istr try y = ranemar!, )arb, :lbre!tsson :lbre!tsson
1.
Eral ral reh rehaabil bilita itatio tion wit with h im impla plant sup support porteed pro prost sth hesis esis 4i 4in ncen cente