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This document discusses biomechanics as it relates to dental implants. It covers several key points in 3 sentences: Biomechanics aims to understand the physiological and non-physiological loads placed on implants and how implant design and surrounding tissues interact to distribute forces. Osseointegration provides a direct bone-implant interface to transmit stresses but cylindrical implants are at highest risk for shear forces. Several biomechanical factors like implant design, bone quality, occlusion, and parafunction can influence long term implant success and complications like screw loosening if forces exceed the implant's tolerance.

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I) Introduction to biomechanics 1) Biomechanics comprises of all kinds of interactions between tissues and forces acting on them. It’s the response of the biologic tissues to the applied loads. >>>Dental implants function to transfer load to surrounding biological tissues. 2) Thus the primary functional design objective >>> a- to dissipate and distribute the biting forces b- and deliver them safely to interfacial tissues over the long term. so , ...
- The internal stresses that develop in an implant system may have a significant influence on the long term longevity of the implants . o In function occlusal loads o Absence of function Perioral forces // Horizontal loads - Mechanics help to understand such physiologic and non physiologic loads . • is the measure of amount of matter in a body (kg). Mass • Mass AccelerationFORCE • Is simply a term for the gravitational force acting on an object at a specified location. WEIGHT FORCE COMPONENTS Magnitude magnification type duration Vector quantities direction MOMENT/ TORQUE: The force which tends to rotate a body.
Compressive • Tend to push masses towards each other. • Cortical bone is strongest in compression. TENSILE FORCES • Pull objects apart. SHEAR FORCES • Sliding forces • the most distructive Cylinder implants -in particular- are highest risk for shear forces at the implant tissue interface .
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 magnifiers of force are: Cantilever length Crown height para functional habits
1. The close apposition of bone to the titanium implant is the essential feature that allows a transmission of stress from the implant to the bone without any appreciable relative motion or abrasion. The absence of any intermediate fibrotic layer allows stress to be transmitted without any progressive change in the bond or contact between the bone and implant. II) Osseointegration in relation to biomechanics
2. A smooth, cylindrical implant may require an adhesive bond for satisfactory performance 3.The osseointegrated implant provides a direct contact with bone and therefore will transmit any stress waves or shocks applied to the fixtures
The operator should be aware of the biomechanical factors that affect the bone to implant contacts which have a direct effect on the success of the implant, a) type and density of bone B) Available remaining bone after extraction c) Parafunctional habits -Other factors a) Implant tilting.(HOw?) b) Prosthetic passive fit. a) Implant macro/micro design (implant body, length and diameter. Threads shape, pitch, lead, depth and width, and crest module). b) Implant surface treatment and coatings (surface topography). c) Cantilever, crown high and occlusal table. d) Loading time -Implant-related factors-Host related factors
• Bone is a tissue that changes its mass and its internal architecture adapting itself to the loading conditions.
• Bone remodeling oral implantology Success and longevity of dental implants? Relationship between *implant components *surroundin g oral tissues • peri-implant bone remodeling begins: 1-implant is exposed to oral cavity in second stage surgery 2-when the abutment is placed immediately after implant placement • Decrease in bone volume is inevitable
• Bone is a dynamic living tissue that remodels in response to: 1- mechanical 2- nutritional 3-hormonal • It responses favourably to functional stresses improving quality of : 1-bone structure itself 2-bone-implant interface
>> IV) biomechanical concept of A-P distance  The A-P distance or A-P spread is the distance from the center of the most anterior implant to a line joining the distal aspect of the two most distal implants.  -The distance provides an indication as to the amount of cantilever that can be reasonably planned.  -Patients with severe bruxism should not be restored with any cantilevers, regardless of other factors.
-The ovoid arch form has qualities of both tapered and square arches. • -The maxilla has less dense bone than the mandible. more distal implants may be required in the maxilla to increase the A-P spread for the anterior or posterior cantilever than in the mandible. • - the edentulous ovoid arch form is the most common, followed by the square, then the tapered form. - A square arch form involves smaller A-P spreads between splinted implants should have shorter length cantilevers. -A tapered arch form has the largest distance between anterior and posterior implants and may have the longest cantilever design.
• A solid screw design implant with a blunt apex with common diameter 3.75 mm anda available in various lengths from 7 to 20, but, implants with lengths from 10 to 16 mm are most widely used to provide adequate initial and long term fixation
**Asolidscrewpermitspreparationandplacementofthe implantindensecorticalboneaswellasfinetrabecularbone (thesurgerymaybeeasilymodifiedtoaccommodateboth extremes). **threadedscrewsmaybespraycoatedwithtitaniumor hydroxyapatitetoincreasesurfaceareamicrolockingofboneor biomechanicalpropertiesrelatedtosurfacecoating.
• Most press fit implants require a ‘’bioactive’’ or increased surface area coating for retention in the bone • **Ease of placement even in difficult access location: e.g. in the posterior of the maxilla in the very soft D-4 bone *
Since the 1980 It was hypothesized at the time that joining a rigid implant to a natural tooth would cause biomechanical complications on the implant, implant prosthesis, or both (why?) *** clinical case - A patient missing the first and the second posterior molars with the absence of third molar tooth which ttt plan is available if minimal number of implants is required ??
>>> BUT!!! Did you know ?? Cantilever prosthetics Implant-Tooth prosth. why? so
2)implant movement secondary mobility lateral mobility mesiodistal > labiolingual 1) natural tooth movement initial mobility secondary mobility horizontal>vertical movement uncomplete immediate rebound
conclusions: I) When a load acts on an implant-tooth prothesis 3- vertical movement of the prothesis II) horizontal movement difference between implant and tooth is more than vertical movement difference 3) prothesis movement vertical movement inherent flexibility compensatory effect
when no onther treatment options are available an implant tooth prothesis can be the treatment of choice guidelines affecting the decision making 1) no lateral forces on the prothesis 2) no clinical mobility of the abutment teeth 3) modification of occlusion minimum initial forces on the implant 4) avoid using anterior abutments why? 5) when there is clinical mobility of the abutments options??
6) rigid connectors + teeth with mobility prognosis?? 7) non-rigid connectors + teeth with NO CLINICAL MOBILITY prognosis?? 8) abutment teeth intrusion?? 9) under favorable condition, IMPLANT TEETH PROTHESIS > CANTILEVER PROTHESIS
10) PIER ABUTMENTS : -maybe either an implant or a tooth -implant pier abutment < tooth pier abutment (Why??) -addition of more implants is favorable -if additional implants are not possible i) in case of pier implant abutment using non-rigid connector (female part distal to the implant and the male part mesial the posterior pontic ) ii) in case of natural tooth pier abutment totally different situation (why?) totally ignored in the treatment plan (why ?) should we extract ?? (why ?)
12) Endodontic treated teeth prognosis?? 11) root delaceration / curvatures >> good or bad ??
I] Screw Loosening Loosening of abutment screw is one of the most common mechanical complications breaking the integrity between the implant and abutment.  Etiology   A) External Force Factors.  these forces may be called joint-separating forces when related to screw loosening.  When the external joint-separating forces are greater than the force holding the screws together (called clamping forces), the screw will become loose. kkkkmkjnk VII) Biomechanical Complications
 B) Cantilevers/Increased Crown Height Space. - One of the most common causative factors resulting in screw loosening. - Cantilevers increase the magnitude of lateral forces on the implant system. - increased Crown height space >>> greater force applied to the screw >>> increase vertical cantilever >>> screw loosening (or fracture)
 C) Parafunction. Bruxism >> lateral forces >> fatigue load failure >> screw loosening When the force exceeds the yield strength, plastic deformation occurs, and the screw begins to deform D) Splinted prosthesis > Nonsplinted prosthesis.
 E) Crown/Abutment Not Fully Seated. - unseated abutment, improper abutment placement, improper component fit and>> poor distribution of force >> screw loosening. -When the abutment is not fully seated and completely tightened, the prosthetic screw will be distorted >>> screw looşening or fracture .  G) Implant design. - increased implant platform diameter >> decreased force on the abutment screw
 F) Screw Diameter - Larger screw diameter within limits , greater clamping & tightening force , less screw loosening .
1-Cantilevers should be eliminąted or reduced., 2- Decreased cusp height. 3-Decreased occlusal table. The use of wider implant bodies results in decreased force on the screw.  Prevention 1-The ideal torque force on an abutment screw varies by manufacturer and may range from 10 to 35 N/cm. 2- After 5-10 mins the screw should be retourqued.
 cement-retained restorations are more passive and have less strain on the implant System than screw-retained restorations. ***We should avoid: >Undertorque will lead to insufficient clamping force. > Overtorque will lead to permanent deformation of the screw, which may lead to screw fracture.... >>> A more accurate torque values result under wet conditions versus in dry conditions.(why?)
II] Fractured Implant 3-The endurance limit or fatigue strength : it is the highest stress that a material can withstand due to repeated fatigue cycles . - A titanium alloy implant is preferably used. - Parafunctional habits treated with occlusal guards, narrow Occlusal tables, no lateral contacts. dramatically increases when force conditions are greater. 1-Static load (one load cycle) failures: cause the stress in the material to exceed its ultimate strength afterone load application. 2-Fatigue load failures: occur if the material is subjected to lower loads but repeated cycles of that load.
III] Early Loading Failure - Early implant failure from biomechanical overload as high as 40%, has been reported in the softest bone types. - The cause of early loading failure is usually excessive stress on the bone-implant interface. -In some cases , Crowns were attached to the healed implants with excessive premature occlusal contact offer greater risk factor for early implant failure than the distructive effects of bacterial plaque. >>> Early loading failure is directly related to the amount of force applied to the prosthesis.
Eg.21-27mm edentulous space may have 3 implant
NO TO CANTILEVER
2- implant dimensions 3-bone density Mesial cantilever is better than distal
Bridge from canine to 2nd molar
Greater the span greater the flexibility Flexure is more problematic in implant, As tooth has mobility and acts as stress absor ber
Ideally, pontic span should be between 13-16 mm or 2 premolars
Additional implant may be required depending upon other conditions
Canine and both premolars lateral incisor canine and 1st premolar central lateral incisor and canine
Because:
Missing lateral canine premolar If many teeth are missing along with canine , then Canine is key position
Single missing tooth
Esthetic region Non-Esthetic region
1-if we place 2 implants: 2-If we place single implant with cantilever Esthetics can be achieved prosthetically biomechanically not good 2 narrow D implant should be used Inter dental papilla wont grow good biomechanically
Maxilla resorb inward mandible resorb outward Lead to facial cantilever Maxillary bone is not good quality as in mandible
Mandibular flexure posterior mandible flexes due to iternal pterygoid BOne quality is generally good
Medical condition stress factor financial status bone anatomy Bone quality opposing teeth and occlusion
Presentation1