Implant Design

• Types & Direction

  • Force along axis of implant=compressive loading of the supporting bone

    • Perpendicular, Vertical force is favorable,

  • Force non-axial & transverse to axis =tensile and shear force applied

  • Cantilever= tensile forces transmited to bone adjacent to implant

  • Compression>Tensile force>Shear force

• Magnitude:

  • Molar: 135-200psi up to 1000psi for some (women vs men vary)

  • Larger # of implants - distributes this force

  • Titanium provides best strength for these forces

• Occlusal table: narrow

• Larger the implant surface = lower stress experienced by implant

• Force distrubuted differently in crestal vs trabecular

• Crestal bone:

  • High stress with bone thickness less than 2mm

• Below Cortical region of implant = shape effects surface area & load distribution

  • Trabeculae bone dissipates remaining occlusal forces

  • Vital in poor-quality bone areas

  • Bone dentistry decreases=more implant surface area is required to dissipate occlusal forces

• TAPERED IMPLANTS

  • • Less marginal bone loss

    • Greater stability at insertion

• Diameter= 4mm+

  • Higher diameter implant=more surface area for force transmission

  • Diameter has a more significant effect than Length when relieving Crestal stress

  • Decrease stress at Bone-implant interface

  • Wider diameter=3.8% lower loss than normal

    • Every 1mm increase, 96.9% decrease in fracture chance

  • ALSO wider=more resistant against fracture

    • • Implant fastened to restoration via abutment screw, which extends internally into implant & engages internal threads

      • Screw receives bore inside implant & removes material & this decreases x-sect area distributing forces

      • Thus, increases stress

      • Wider implant has more x-section/wall thickness to accommodate for this

• Length=10+mm

  • Shorter implants (3-9mm)=9.9% increased incidence rate of loss

  • Implant legnth alone may be insufficient to compensate for diameter

• Avoid short AND wide implants, esp in posterior

• Purpose: transition b/w restoration and implant body

  • Helps seal implant site against fibrous tissue & bacteria

• Supragingival connection:

  • extended region above implant thread protruding above gingiva

  • Surface: smooth

  • Diameter: larger than body of implant below

  • No need for healing abutments & tissue forming components

• Subgingival bone-level connection:

  • Crestal bone interface can vary due to osseous curve

    • Some portion of collar can be supracrestal, contacting gingiva

    • Upper region of collar may be transosteal after placement=leads to roughened surfaces and higher chance of peri-implantitis

• MACHINED Collar=better because less rough

• Increased diameter in collar=reduced crestal stress

• Taper in collar: increased stress (reduces SA)

• PLATFORM SWITCHING:

  • Use of ABUTMENTS with diameter less than that of the IMPLANT COLLAR=less cortical bone stress

  • Preserves marginal bone levels

  • Shifts stress concentration away from the cervical bone-implant interface

  • Microbiota of platform switch vs non=not statistically different

  • Biomechanical process NOT fully understood!

• MICROTHREADS IN COLLARS:

  • Maintains marginal bone levels

  • Higher degree of bone-implant contact

  • Very small threads =better at stress distribution in cortical region

  • Shape of thread profile has profound effect on magnitude of stress

  • Stress at bone-implant interface ALWAYS perpendicular to lower flank of each microthread regardless of Oblique force

    • Thus, lower shear stress

• Purpose: junction b/w implant & restoration

  • transmits insertion forces to place implant into osteotomy

  • Fastened via abutment screw

• External Prosthetic Connections:

  • 1st made. Mostly hexagonal

  • Place connection external to implant body

  • Used in early implants because ext hex connected to fixture AND transmucosal element for edentulous arch

  • NOT ideal for single crown/partially edentulous restorations because abutment screw subject to LATERAL loading than in splinted

• Internal Prosthetic Connections:

  • Developed when single implants became more popular

  • Connection inside of implant body

  • Less tipping forces, reduces screw loosening

  • Designs:

    • 45-degree lead-in bevel: first one, still popular

    • Conical implant connection: deeper within the implant body

    • Angle is smaller

    • Improves abutment stability, fit, seal

    • Lower peri-implant bone loss, less stress on alveolar bone , higher resistance on axial loads

• Pitch:

  • Thread pitch less than 1.7mm is optimal, but varies

  • One start thread more SA than four-start

• Shapes:

  • Buttress or Square: optimized SA for compressive loads

  • V thread: Nobel Biocare, Zimmer Dental, Biomet 3i

  • Square: Biohorizons

  • Buttress: Glidewell, Straumann

  • Reverse Buttress: Nobel Biocare

  • Immediate loading: faired better with V-threads and reverse buttress threads

• Depth:

  • Depths: 0.44mm+, Widths: .19-.23mm+ are best for low stress

  • Depth has greater effect than width

• Purpose: facilitates insertion into osteotomy & initiate engagement of implant threads w/i bone

• Flat to rounded in shape to minimize perforation

• Can include hole/slot for bone to grow into and increase anchorage

• Can have flat regions/grooves circumferentially to stabilize against rotation and help insertion

• As threads advance, create bone chips that build up in these features instead of at the bottom of implant

• Qualities

  • Biocompatible

  • Tensile/Compressive strength for resist forces

  • Fracture toughness/fatigue resistance

  • Resist corrosion/wear

  • Modulus of elasticity similar to surrounding bone

    • • If not=stress transfer compromised

      • Dense cortical =16GPa

      • Titanium=105-114GpA - grade dependent

      • Ceramic = 200GPa (stiff)

  • Fatigue limit

• Titanium - BEST

  • Alloyed with Aluminum, Vanadium, Niobium, Zirconium

  • Grade 5 titanium is most common

  • Grade 4 is twice as strong as grade 1, ect.

  • Corrosion Resistance - spontaneously forms titanium oxide passive film

• Zirconia

  • Not used as often

  • Microstructural properties and osseoconductive

  • LARGER compressive strength

  • POOR tensile strength

  • Vulnerable to bending loads

  • Sufficient ultimate strength to resist clinically relevant laods

  • Corrosion - inert in oral, but suspectible to low-temp degradation

    • Y-TZP (yttrium oxide stabilized tetragonal zirconium dioxide) can contact water and go from Tetragonal to weaker Monoclinic phase

      • Reduced strength in that area

  • Elastic Module:

    • Higher potential for relative motion or diuse atrophy due to Stress Shielding at bone-implant interface

    • LOAD only AFTER osseointegration complete

Shape: tapered

Diameter: wider is better

Length: longer is better

Collar: machined at upper region, slightly larger or same size as implant screw, platforming switching, and with microthreads for stress distribution

Smooth collar might transit shear forces

Connection: conical, internal connection type used

Thread pitch: 0.8-1.6mm is optimal

Thread shape: buttress and square transfer force nearly perpendicular to implant axis

Thread depth: greater than 0.4mm

Apical region: tapered, rounded/flat with region/grooves circumferentially on implant body for stabilization

Material: titanium is best