هو الحکیم

Stress Treatment Theorem for Implant Dentistry

Presented by:Dr.Mehrak AmjadiSupervised by: Dr. Mansour Rismanchian

And Dr.saied Nosouhian Dental of implantology

Dental implants research centerIsfahan university of mediacal science

 

Common complications related to the natural dentition (Biological)

CariesPeriodontal disease Endodontic problems

common complicationsfor three-unit fixed prostheses(Biomechanical & Biological)

CariesEndodontic problems

unretained prosthesis

porcelain fracture

The most common implant-related complications are biomechanical problems that occur after the implant is loaded.

Biomechanical problems

Implant overdentures

attachment fracture removable prosthesis fracture

implant-supported fixed Prostheses

acrylic resin veneer fracture abutment or prosthetic screw loosening porcelain fracture prosthesis metal fracture

implant failure

primarily occur within 18 months of initial implant loading

most often in the softest bone types or the shortest implant lengths picture

implant complication

most common causes for implant-related complications are centered around stress

the overall treatment plan should :

(1) assess the greatest force factors in the system

(2) establish mechanisms to protect the overall implant-bone-prosthetic system.

SURGICAL FAILURE

reasons for the failure of an implantintegration with the bone :

- primary causes :excessive heat excessive pressure at the time of implant insertion(tapered screw-type)

- Micromovement of the implant while the developing interface is established (20 microns)

99% of the time may obtain rigid fixations after surgical placementThe surgical component ofimplant failure is often the least risk of implant treatment.

EARLY LOADING FAILURE

- Within 6 to 18 months

- cause : excessive stress for the bone-implant interface.

- related to the amount of force and the density of the bone (15% of implant restorations)

IMPACT OF OCCLUSAL OVERLOAD ONMECHANICAL COMPONENTS

Screw Loosening

Fatigue Fractures

Screw Loosening

6% of implant prostheses

Singletooth crowns highest rate (25%) in early screw designs

Cantilevers also increasethe risk of screw loosening

increase length of the cantilever

Increase the forces

Screw Loosening

The height or depth of an antirotational component of the implant body (higheror deeper the hex height, the less stress)

The platform dimension is more importantthan the hex height dimension

Larger-diameter implants, with larger platform dimensions, reduce the forces

Fatigue Fractures

if a lower force magnitude repeatedly hits an object, it will still fracture

Prosthesis screw fracture in bothfixed partial and complete fixed prostheses 4%

Abutment screws are usually larger indiameter fracture less often 2%

Metal framework fractures of fixed complete andoverdenture restorations 3%

Implant body fracture has the least incidence 1%

Uncemented restorations

when chronic loads are applied to the cement interface

when shear forces are present (as found with cantilevers)

Cement strengths are weakest in shear loads.

MARGINAL BONE LOSS

range from loss of marginal bone to complete failure of the implant

For the one-piece bladeimplants, was described as a"saucerization" and occurred after implant loading

Loss of crestal Bone

Greater magnitude of bone loss during the first year 3.3 mm from crestal bone

The initial transosteal bone loss V- or aU-shaped pattern(described as ditching or saucerization)

hypotheses of crestal bone loss

hypotheses of crestal bone loss

reflection of the periosteum

Osteotomy

micromovement of the abutment

bacterial invasion

biological width

factors of stress

Periosteal Reflection Hypothesis

transitional change in theblood supply to the crestal cortical bone

osteoblast death on thesurface from trauma and lack of nutrition.

loss of the entire residual ridge reflectedgeneralized bone loss rarely is observedat the second-stage uncovery surgery

does notappear as a primary causal agent of crestalbone loss

Implant Osteotomy Hypothesis

osteotomy causes trauma to the bone in immediatecontact with the implant

devitalized bone zone of about 1 mm

crestal regionis more susceptible to bone loss

limited blood supply

Greater heat generated in this denser bone

Implant Osteotomy Hypothesis

bone loss of 1.5 mm from the first thread is not observed at Stage 11 uncovery.

bone often has grownover the first-stage cover screw

osteotomy hypothesiscannot be primarilyresponsible for this phenomenon.

Autoimmune Response of Host Hypothesis

primary cause of bone loss around natural teeth bacteria

Occlusal trauma may accelerate the process

why does most bone loss occur thefirst year (1.5 mm) and less (0.1 mm) each successive year?

this hypothesis as the primarycausal agent for the early crestal bone loss cannot be substantiated.

Biological Width Hypothesis

For a natural tooth, an average biological width of 2.04 mm

biological width also occurs with implants and may contribute to Some of the marginal bone loss(0/5 mm)

The crevice between the cover screw and the implantis similar to the crevice ofthe abutment-implant connection

The amount of bone loss from the biological width occurs within 1 month, whether the implant is loaded or not, and is related to the crest module implant design

Biological Width Hypothesis

Occlusal Trauma

an injury to the attachment apparatus as a result of excessive occlusal force.

To establish further a correlation between marginalbone loss and occlusal overload

cellular biomechanics

engineering principles

mechanicalproperties of bone

physiology of bone

implantdesign biomechanics

clinical reports

Cellular Biomechanics

Bone remodeling at the cellular level is controlled by the mechanical environment of strain

The amount of strain in a material is directly related to the amount of stress applied

Mechanosensors in bonerespond to minimal amounts of strain, and microstrainlevels 100 times less than the ultimate strength of bonemay trigger bone remodeling

bone fractures at 10,000 to 20,000 microstrain units(1% to 2% deformation)

levels 20% to 40% of this value (4000 units), bone cells may trigger cytokines to begin a resorption response.

Cellular Biomechanics

Engineering Principles

The relationship between stress and strain determines the modulus of elasticity (stiffness)

when two materials of different elastic moduliare placed together , a stress contour increase will be observed where the two materials first come into contact.

marginal bone loss observed aroundimplants follows a similar pattern as the stress pattern

Bone Mechanical Properties

In denser bone, there is less strain under a given load compared with softer bone

less bone remodeling

The initial peri-implant bone loss from implantinsertion to uncovery was similar for all bone qualities

6 months after prosthesis delivery

the more dense bone, the less peri-implant bone loss

Animal Studies

Miyata placed crowns on integrated dental implantswith no occlusal contacts (control group)

Premature interceptive occlusal contacts of 100 , 180, and 250 11m in a monkey animal model

After 4 weeks of premature occlusal loads, theimplants were removed and evaluated

180 Micron premature contacts 250 Micron premature contacts

Clinical Reports

Clinical Reports

an increase in marginalbone loss around implants closest to a cantilever used to restore the lost dentition

Cantilever length and an increase in occlusal stress to the nearest abutment are directly related

Clinical Reports

overload from parafunctional habits may bethe most probable cause of implant loss and marginal bone loss after loading

occlusal loads on an implant may act as a bending moment, which increases stress at the marginal bone level and can cause implant body fracture

Bone loss from occlusal overload is not only possible, butmay even be reversible when found early in the process

Implant Design Biomechanics

The design and surface condition of the implant body may affect the amount of strain distributed to a implant-bone interface.

bone loss around loaded screw-type implants with machined surfaced V-threads or a sandblasted/acid-etched square-thread design

the average bone loss was 2.4 mm (v-thread) versus 1.6 mm (square thread)

more than the biologicalwidth, microgap position, and/or surgical causes areinvolved in bone loss

design and surface condition

Discussion

Discussion

Limited marginal bone loss during the first year offunction after Stage Il surgery has been observedaround the implant

that occlusal overload may be an etiologyfor crestal bone loss does not mean other factors are not present.

the microgap and the biologicalwidth often affect the marginal bone during the firstmonth after the implant becomes perrnucosal

Discussion

Implant crown height

puzzling element

is a vertical cantilever, which may magnify the stresses

if Occlusal loading forces can cause crestal bone loss, the resulting increased moment forces should further promote the loss of bone until the implant fails

bone physiology implant design mechanics

Bone PhysiologyThe bone is less dense and weaker at Stage 2 implantsurgery than it is 1 year later after prosthetic loading

The bone changed from a fine trabecularpattern after initial healing to a more dense and coarse trabecular pattern after loading

Implant Design Biomechanics

Implant design may affect the magnitude or type offorces applied to the bone-implant interface

A smooth collar at the crest module may transmit shear forces to the bone.

The first threador a roughened surface condition of the implant iswhere the type of force changes from primarily shearto compressive or tensile loads

EFFECT ON TREATMENT PLANNING

Stress-related conditions that affect the treatmentplanning in implant dentistry include :

bone volume lost after tooth loss

bone quaIity decrease after tooth loss

complications of surgery

implant positioning

initial loading of an implant

implant design

Understanding the relationships of stress andrelated complications provides a basis for a consistenttreatment system

EFFECT ON TREATMENT PLANNING

Patient Force Factors

stress : force divided by the area to which the forces are applied

force factors to consider :

(1) bruxism (2) clenching (3) tongue thrust(4) crown height (5) masticatory dynamics (6) the opposing arch

Bone Densityis directly related to the strength of the bone

Dense cortical bone is 10 timesstronger than the soft, fine trabecular bone

Progressive bone loading :

changes the amount and density of the implant-bone contact.

increases the quantity of bone

Key Implant Positions &Implant/Abutment Number

more important from a stress management perspective

In one- or two-unit prostheses, an implant should beplaced in each prospective tooth position, without acantilever

In a three- to four-unitrestoration, the most important abutments are theterminal abutments

Key Implant Positions &Implant/Abutment Number

In a 5- to 14-unit prosthesis, intermediary abutmentsare also important to limit the edentulous spans to less than three pontics.

It is suggested :

multiple missing adjacent teeth bereplaced in a staggered position (tripod effect)

a larger intermediary implant be inserted

Key Implant Positions &Implant/Abutment Number

An edentulous mandible : Anterior and the bilateral posterior regions

A key implant position is one implant in each region

An edentulous maxilla :

anterior region (laterals and centrals), bilateral canines,and the bilateral posterior

one implant in each region, or at least five key implants

Key Implant Positions &Implant/Abutment Number

The overall stress to the implant system may be reducedBy :

increasing the area over which the force is applied

The most effective method :

increasing the number of implants used to support a prosthesis

Implant Size

extra length does little to decrease the stress at the crest of the ridge during occlusal loading

The surface area of each implant is directlyrelated to the width of the implant.

an increase in implant diametermay be more effective than implant staggering to reduce stress.

Implant Design

Implant macrodesign may affect surface area even morethan an increase in width

A cylinderimplant provides 30% less surface area than a conventionalthreaded implant of the same size

implant design may be theeasiest method to increase surface area and decrease overall risk to the implant interface

SUMMARY

etiology of implant complications has led to the developmentof a stress-based treatment plan theorem

Additional implants

increase in implant width or height

use of more implants to decrease the number of pontics

SUMMARY

To decrease stress :

Thanks for your attention !