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Scientific rationale for dental implant design

Scientific rationale for dental implant design

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Scientific rationale for dental implant design

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  1. Scientific rationale fordental implant design Presented by:Dr.PirozGivehchian Supervised by: Dr. MansourRismanchian And Dr.saiedNosouhian Dental of implantology Dental implants research center Isfahan university of mediacal science

  2. Treatment planning sequence for implant dentistry • design of final restoration ( position and number of teeth replaced and type of prosthesis ) • patient force factor • bone density • key implant positions and additional implant number • implant size • available bone in the edentulous sites • When it is not present, modification of treatment is necessary: • Bone augmentation • consideration of optional implant locations usually with additional implants, increase in implant size • optimization of implant design

  3. implant designed to answer cause of implant failure : • implant surgery • bacterial plaque complication • loading condition

  4. Body design for surgical ease of placement • tend to have tapered , short implant body • press_fit insertion • Cylinder or press-fit implant were popular in 1980s: • has a friction-fit insertion and have less risk of pressure necrosis • has no need to bone tap (even in dense bone) • but after 5 years of loading , they include more of loss of crestal bone and implant failure : • fatigue overload condition • harmful shear loads on bone causing large bone turnover rates • less bone_implant contact (BIC) percent • higher risk of overload failure surgical success rate is usually higher than 98% regardless of implant size or design , so designing an implant for surgical easedose not appear to be the most important aspect to reduce the incidence of complications

  5. Design to reduce the plaque-related complication • smooth crest module: • easier to clean • collects less plaque • problem with this philosophy: • smooth crest module is initially placed below the crest of the bone • encourage marginal bone loss from the extension of biological width after uncovery and from shear forces after occlusal loading • so this plaque-reducing design feature increases the peri-implant sulcus depth • Therefore

  6. Implant body designed for: ease of surgery reduce plaque-related and peri-implantitis Dose not the most common complications observed in implant prostheses

  7. Most implant body complications in literature: • early implant failure after loading • marginal bone loss before loading but after exposure of the implant • marginal bone loss after the loading of the implant-bone interface Goodacare 1981-2003 (soft bone) Misch 1981-2004 (<10mm) Implant body designs should attempt to primarily address the primary causes of complication Factors that address the loading condition of the implant after implant are placed in function

  8. Implant design related to occlusal forces • primary functional design objective is to manage (dissipate and distribute) biomechanical loads to optimize the implant-supported prosthesis function • load management is dependent: • Character of applied force • functional surface area which the load is dissipated

  9. Force type and influence on implant design • 3 type of forces be imposed on implants: • Compression • tension • shear • bone is strongest when loaded in compression, • 30% tensile • 65% shear • implant has macroscopic body design and a microscopic component. • Microscopic features : important during initial healing and initial loading period • Macroscopic design : important during early loading and mature loading periods

  10. Smooth-sided, cylindrical implants: • Ease in surgical placement • larger shear condition in bone-implant interface • smooth-sided, tapered implants: • Greater the taper, greater the component of compressive load delivered • taper cannot be greater than 30 degrees: • body length to be reduced • immediate fixation and initial healing to be reduced • less overall surface area and less initial stability • tapered threaded implants: • provide some surgical advantage during insertion • lesser surface area of tapered implant increase the amount of stress at crestal portion • thread at apical half are often less deep because of the outer diameter continues decrease and limit the initial fixation

  11. smooth cylinder implant results in shear load at interface, so must rely on a microscopic retention system for initial loading period: • Roughening or coating, acid etch, mechanical etch, coat with plasma spray or HA • the quality of coating as absolutely paramount in such application • surface condition of an implant may enhance BIC and adhesion qualities at initial healing • surface coating don’t permit compressive loads to be effectively transmitted to bone cells because the micro features of the coating are too small for cells to be loaded in compression so: surface area_bone contact percentage is greater during initial healing but the functional surface area is most dependent on macroscopic design of implant body

  12. Watzek et al

  13. Bolind et al

  14. Bolind et al Implant body design was more important than the surface condition of the implant for crestal bone loss and overall BIC after loading

  15. Force direction and influence on implant body design • bone is weaker when loaded under an angled force • greater the angle of load, the greater the stresses • … • implant body long axis should be perpendicular to the curve of wilson and curve of spee • axial alignment places less shear stress on the overall implant system and decrease the risk of complications as screw loosening and fatigue fractures So: Virtually all implant are designed for placement perpendicular to occlusal plan

  16. implant body design with threaded features have ability to convert occlusal loads into more favorable compressive loads at bone interface • under axial load to an implant-bone interface: • buttress or squre-shaped thread would transmit compressive forces to bone ( BioHorizons, BioLok , Ankylosis ) • V-tread face angle(Zimmer , LifeCore, 3i and some Noble Biocare) is comparable to the reverse buttress thread (Noble Biocare) because of the similarity in the inferior portion of thread face angle the thread shape (macroscopic design) is independent from the surface coating (microscopic design)

  17. Implant body: functional versus theoretical surface area • to reduce stress, the force must decrease or the surface area must increase • functional surface area: the area that serves to dissipate compressive load to implant-bone interface • functional thread surface area: portion of the thread that participates in compressive load transmission under occlusal load • total theoretical surface area: “passive” area on implant that dose not participate in load transfer or has a feature so small, bone cannot adapt to load transfer • plasma spry coating provide up to 600% more total surface area for BIC • size of each plasma particle is less than 8µm and the 120µm bone cell dose not receive a transfer of mechanical stress from this feature • amount of actual BIC that can be used for compressive loading may be less than 30% of total theoretical surface area

  18. functional surface area is beneficial to reduce the mechanical stress to bone • most stress to implant-bone interface in D1 to D3 bone is in crestal 5 to 9 mm of implant • design of body in coronal 9mm is most important to appropriately distribute occlusal stress • 20mm V-shaped or reverse buttress threaded implant may have more total surface area compared with 13mm square threadedbutfunctional area may be higher in the 13mm implant because of thread geometry • Functional surface area plays major role in addressing variable initial BIC zone related to bone density • D4 bone has weakest biomechanical strength and lowest BIC area to dissipate the load at implant-bone interface • the functional surface area requirements would increase from a minimum for implants in D1 bone to maximum for implants in D4 bone • Functional S.A may be increased by diameter of an implant • however the higher bite force and lower bone density of posterior regions may not always be able to be addressed adequately by only implant diameter • Ivanoff 1999

  19. as results: Implant geometric body design , length , bone density are related to the functional surface area • an ideal treatment plan: Implant length of 12mm or greater with 4mm diameter for most anterior and 5mm or greater in molar regions • when ideal implant size cannot be insert, the alternative may be to increase the surface area of implant by modifying implant body design

  20. Implant body geometry versus occlusal load • The design of implant not only governs the initial stability of the implant but as important determines the BIC percent and location of contact available for effective load transfer to the bone after occlusal loading

  21. when bone did not fully occupy the threads, greater bone volume was observed on the lower aspect compared with upper aspect of square threads • bone bridge was found from one square thread to another • after dynamic loading the bone implant density was grater on the bottom of the thread face angle less on top of thread Duyck et al

  22. Hollister and kohn • during a lateral load, the strain was more concentrated at tip of thread and was decreased from the exterior to interior region of thread • at tip of each of thread, bone was resorbed • at depth of tread, bone was maintained • bone contact was least at tip of each thread ( the highest strain occurs) • bone was greatest under the thread face angle ( bone is loaded more on compressive)

  23. Scientific rational for implant design

  24. histological description of bone: lamellar, woven , composite, and bundle bone • Lamellar bone: most organized , highly mineralized , strongest of bone type , called load-bearing bone • Woven bone: unorganized , less mineralized, less strength, called immature bone • microstrain levels 100 times less than ultimate strength of bone may be responsible for remodeling rate because the bone cell membranes are able to act as a mechanosensory system in bone • load applied on bone >>>microstrain in cells >>> energy to open ion membrane channels • Bone remodeling rate (BRR), : • is time needed for new bone to replace the existing bone and allows for adaptation of bone to its environment • percentage or volume of new bone within a specific time period • lamellar bone forms at rate of 1 to 5 µm each day • woven bone forms at rate of more than 60 µm each day Adapted widow

  25. interface remodeling allows a viable bone interface to form between the dental implant and original bone after the implant has been surgically inserted • higher BRR is directly related to an increase in the amount of woven bone formation • so BRR may be directly to strength of implant interface and degree of risk for implant-bone interface • higher risk is related to higher turnover rate , because the bone is less mineralized, less organized and less strange at the interface

  26. before implant insertion: • bone is usually mature, lamellar bone • surgical trauma: • cause the bone to repair, with primarily woven bone formation • by end of 4 months: • osteoblasts have deposited about 70% of mineral found in mature vital bone have reformed lamellar bone • remaining 30% of mineral deposition occurs during secondary mineralization over the next 8-month period • after bone has healed and the implant is then loaded: • interface again remodels as influenced by its local strain environment • if woven bone forms as a result of mechanical loading. Its called reactivewoven bone and very similar in structure and properties to the repair woven bone from surgical trauma • long term maintenance of implant depends on: • continues remodeling of interface • allows new bone to replace bone, that may have sustained microfractures or fatigue as a result of cyclical loading

  27. Microdamage act as key step in signaling increases in remodeling and replacing of skeletal tissue • microdamage in cortical bone surrounding screw-type implants has been reported during both insertion and pullout force • amount of microdamage was related to the thread design of implant • strong association between microdamage, osteocyte apoptosis and subsequent bone remodeling • threaded implants with axial tensile loading have higher remodeling rates and less mineralized bone than implants didn't receive a load after healing • non axial loaded implants have a greater BRR compare with axially loaded so: implant design, direction of load, surface condition may affect the bone at interface and bone turn over rate

  28. thread geometry • Designed to:maximize initial contact ,enhance surface area , facilitate dissipation of load at bone-implant interface • three geometric thread parameters: • thread pitch • thread shape • thread depth • crest modulation considerations • apical design consideration

  29. Thread pitch • Distance measured parallel between adjacent thread • 1.5mm in ITI • 0.6mm in Zimmer, Biomet 3I • Smaller pitch, the more threads on body for given unit length and thus greater surface area per unit length • higher BIC was observed with the implant with greater thread number. • pitch has most significant effect on changing the surface area • when an ideal implant length cannot be planned without bone augmentation • pitch may be used to help resist the forces to bone with poorer quality • if force magnitude is increased , implant length is decreased , bone density decreased, the thread pitch be decreased to increase thread number and increase functional surface area • surgical ease of implant placement is related to thread number • fewer thread , easier to insert ( in denser bone)

  30. thread number may be affected by implant crest module design • extended smooth crest module , reduced thread number to support occlusal load

  31. implant bodies with double or triple thread leads • this term related to manufacturing process and don’t increase functional area • uses one or tow or three cutting blades to manufacture thread • at 1 rpm inserting implant, one thread lead implant insert a distance of one thread and double-thread insert two thread into bone • if revolution per minute is double(30rpm versus 15rpm), both implant thread into bone at same rate

  32. Thread shape • square, v-shape , buttress , and reverse buttress • Thread shape has application for loading conditions • In reverse buttress the force transfer for occlusal loads to bone is similar to v-shaped • square or power thread provides an optimizedsurface area for intrusive,compressive load transmission • buttress thread may also load with primarily a compressive load transfer • thread shape may contribute to initial healing phase of osteointegration • V-shaped and reverse buttress thread shapes had similar BIC percent and similar torque values to remove the implant after initial healing • square thread had higher BIC percent and greater reverse torque • face angle of the thread or plateau in an implant body modify direction of occlusal load • face angle of v-shaped is 30 degree off the long axis and square thread beperpendicular to long axis • occlusal loads in axial direction be compressive at bone interface in square or plateau design but can be converted to higher shear load in v-shaped design

  33. Thread depth • the distance between the major and minor diameter of thread • In conventional implants uniform thread depth throughout the length • tapered implant has a similar minor diameter , but outer diameter decreased in relationship to taper , so depth decreased toward the apical • tapered implant: • Decreased thread depth in apical • less overall surface area • less ability to fixate the bone in apical at initial insertion • has less functional surface area may result in higher stresses especially in shorter implant

  34. the greater thread depth, the greater surface area of implant • thread depth may be modified relative to diameter and overall surface area • as implant becomes wider the depth of thread may be deeper without decreasing the body wall thickness between the inner diameter and abutment screw space • more shallow thread depth, the easier it is to thread the implant in dense bone and less likely bone tapping is required

  35. Bioengineering of an implant design • when implant act as functionary unit for a prosthesis. An elevated BRR is an ongoing response adjacent to implants • BRR higher than 500% per year in bone immediately adjacent (5mm) to V-shape threaded implant • BRR 50% in the regions distant from interface • Bone atinterface of implants in this report is likely in the mild overload zone

  36. if implant design is bioengineering, so that loading will produce a microstrain in adapted window zone • it should maintain lamellar bone at interface • similar BRR adjacent to and distal to implant interface • a square-thread design be used on body of implant, showed 40_50% BRR and was same as observed in the bone away from the implant interface

  37. Crest module considerations • crest module: transosteal region, which extends from the implant body and often incorporates the antirotation components of abutment implant connection • it has: • Surgical influence • Biological width influence • loading profile consideration • prosthetic influence

  38. During surgical phase the crest module design benefits the crest implant interface • It should be slightly larger than outer thread diameter of body • Seals completely the osteotemy • Provide barrier and deterrent for ingress of bacteria or fibrous tissue during initial healing • greater initial stability of implant following placement, because it compresses the crest bone region • increases surface area ,can further decreases stress at crest region • increases platform of abutment connection with stress reduction to abutment screw during lateral loading • platform dimension is more critical to reduce the stress applied to abutment screw than height or depth of antirotational hex

  39. Crest module with a smooth collar : • the concept of this designing is for a reduction of plaque accumulation and improved hygiene • when bone loss occurs on the implant crest module, the gingival sulcus depth can not be accessed by hygiene procedures after crestal bone loss • “formation of biological width” and “ occlusal overload” have increased bone loss risk when smooth metal is placed below the bone

  40. Herman et al

  41. a biological width of at least 0.5 has been reported apical to abutment-implant connection regardless of implant crest module design : • a 0.5 mm collar length may provide for desirable smooth surface close to perigingival area • microgap between implant crest module and abutment may reduce when polished surface are approximate

  42. Crest module design and its relation to occlusal loading • most of occlusal stress occurs at the crestal region of an implant design • Smooth, parallel-sided crest module • will increase the risk of bone loss after loading • smooth metal promotes shear stresses in bone interface • smooth metal doesn't encourage bone cell contact before loading • amount of bone loss in machined (smooth) coronal region, is directly related to length of smooth crest module