هو الحکیم

Stress Treatment Theorem for Implant Dentistry Presented by:Dr.Mehrak Amjadi Supervised by: Dr. Mansour Rismanchian And Dr.saied Nosouhian Dental of implantology Dental implants research center Isfahan university of mediacal science  

Caries Periodontal disease Endodontic problems Common complications related to the natural dentition (Biological) Caries Endodontic problems common complications for three-unit fixed prostheses (Biomechanical & Biological) 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 : 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 implant integration with the bone : excessive heat excessive pressure at the time of implant insertion(tapered screw-type) - primary causes : - Micromovement of the implant while the developing interface is established (20 microns) 99% of the time may obtain rigid fixations after surgical placement The surgical component of implant 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 ON MECHANICAL COMPONENTS Screw Loosening Fatigue Fractures

Screw Loosening 6% of implant prostheses Singletooth crowns highest rate (25%) in early screw designs Cantilevers also increase the 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 (higher or deeper the hex height, the less stress) The platform dimension is more important than 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 both fixed partial and complete fixed prostheses 4% Abutment screws are usually larger in diameter fracture less often 2% Metal framework fractures of fixed complete and overdenture 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 For the one-piece blade range from loss of marginal bone to complete failure of the implant For the one-piece blade implants, 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 the blood supply to the crestal cortical bone osteoblast death on the surface from trauma and lack of nutrition. does not appear as a primary causal agent of crestal bone loss loss of the entire residual ridge reflected generalized bone loss rarely is observed at the second-stage uncovery surgery

Implant Osteotomy Hypothesis osteotomy causes trauma to the bone in immediate contact with the implant devitalized bone zone of about 1 mm crestal region is more susceptible to bone loss limited blood supply Greater heat generated in this denser bone

Implant Osteotomy Hypothesis bone often has grown over the first-stage cover screw bone loss of 1.5 mm from the first thread is not observed at Stage 11 uncovery. osteotomy hypothesis cannot be primarily responsible 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 the first year (1.5 mm) and less (0.1 mm) each successive year? this hypothesis as the primary causal 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 implant is similar to the crevice of the abutment-implant connection

Biological Width Hypothesis 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

Occlusal Trauma an injury to the attachment apparatus as a result of excessive occlusal force. cellular biomechanics To establish further a correlation between marginal bone loss and occlusal overload engineering principles mechanical properties of bone physiology of bone implant design 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 bone respond to minimal amounts of strain, and microstrain levels 100 times less than the ultimate strength of bone may trigger bone remodeling

Cellular Biomechanics 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.

Engineering Principles The relationship between stress and strain determines the modulus of elasticity (stiffness) when two materials of different elastic moduli are placed together , a stress contour increase will be observed where the two materials first come into contact. marginal bone loss observed around implants 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 implant insertion 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 implants with 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, the implants were removed and evaluated

180 Micron premature contacts

Clinical Reports

Clinical Reports an increase in marginal bone 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 be the 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, but may 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) design and surface condition more than the biological width, microgap position, and/or surgical causes are involved in bone loss

Discussion

Discussion Limited marginal bone loss during the first year of function after Stage Il surgery has been observed around the implant that occlusal overload may be an etiology for crestal bone loss does not mean other factors are not present. the microgap and the biological width often affect the marginal bone during the first month after the implant becomes perrnucosal

Discussion if 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 Physiology The bone is less dense and weaker at Stage 2 implant surgery than it is 1 year later after prosthetic loading The bone changed from a fine trabecular pattern after initial healing to a more dense and coarse trabecular pattern after loading

Implant Design Biomechanics Implant design may affect the magnitude or type of forces applied to the bone-implant interface A smooth collar at the crest module may transmit shear forces to the bone. The first thread or a roughened surface condition of the implant is where the type of force changes from primarily shear to compressive or tensile loads

EFFECT ON TREATMENT PLANNING Stress-related conditions that affect the treatment planning 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

EFFECT ON TREATMENT PLANNING Understanding the relationships of stress and related complications provides a basis for a consistent treatment system

Patient Force Factors force factors to consider : 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 Density is directly related to the strength of the bone Dense cortical bone is 10 times stronger 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 be placed in each prospective tooth position, without a cantilever In a three- to four-unit restoration, the most important abutments are the terminal abutments

Key Implant Positions & Implant/Abutment Number In a 5- to 14-unit prosthesis, intermediary abutments are also important to limit the edentulous spans to less than three pontics. It is suggested : multiple missing adjacent teeth be replaced 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 reduced By : 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 an increase in implant diameter extra length does little to decrease the stress at the crest of the ridge during occlusal loading The surface area of each implant is directly related to the width of the implant. an increase in implant diameter may be more effective than implant staggering to reduce stress.

Implant Design implant design may be the Implant macrodesign may affect surface area even more than an increase in width A cylinder implant provides 30% less surface area than a conventional threaded implant of the same size implant design may be the easiest method to increase surface area and decrease overall risk to the implant interface

SUMMARY

SUMMARY To decrease stress : Additional implants etiology of implant complications has led to the development of a stress-based treatment plan theorem To decrease stress : Additional implants increase in implant width or height use of more implants to decrease the number of pontics

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