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Dr Harshavardhan Patwal
Direct bone to implant contact
Process of Osseointegration Primary stability- mechanical
interlocking Contact osteogenesis- direct apposition Secondary stability- mineralized nodule
formation (Berglundh,2003)
Forces acting on bone Favorable forces Remodelling of bone Woven bone formation
Unfavorable forces• excess load
Microcracks- osteoclast activation (Hansson &Werke,
2003) Insufficient remodeling-defect forms, accumulate ,
coalesce, filled with fibrous tissue (Misch 2001) Severe bone loss- implant failure (Bruski, 1999)
Forces Acting on Bone/Implant Compressive forces Tensional forces Shear forces
Stress= force/ surface area Forces may not be controlled Surface area?
Compressive stress –beneficial Tensile stress - harmful Shear stress – most harmful
Primary Stability Implant
Implant lengthImplant diameterImplant designLoading protocol
Bone Quality, volumeDensity
Surgical technique
Implant Length Length directly
proportional to surface area
Greater bone to implant contact
Longer implant- greater surface area- greater stability
Favorable crown/implant ratio Longer implants >10 mm compatible
with CSR(Adell 1982, Lee 1995)
D1 bone- bicortical stabilization unnecessary as bone is homogeneous
D2 , D3 bone- bone over heating D4 bone- apical areas too soft for local
compression stabilization
Stress concentration -maximum ?
Lateral stress distribution poor in short implants
Review on short implants <7mm (Hagi D, Deporter DA) Threaded implants- shorter implants,
higher failure rates Sintered, porous implants- high success
rates >95%
Short implants- 7mm or 9 mm (Misch CE, 2005) Survival rate-99% Increase diameter, eliminate lateral
forces, splint implants.
Implant Diameter Related to surface area Anatomical limitations
Traditionally wide implants >5mm associated with greater failure
Wide Body Implants > 5mm in diameter
(Vanderweghe, Ackernman A, 2009)
95.7% survival rates Used as rescue implants
extraction sockets in poor primary stabilitypoor bone quality
NDI implants <3.75 mm in dia (Arisan V, Bolukbusu
2010) Overdenture in mandible
94-100% survival rates
Follow up- 1-9 years, CSR .95% (Cho CS, Froum S)
Impact of length and diameter (Renourd F, Nisand D,
2006)
Dense bone, textured implants, good operator skill – short, wide, implants had same survival rates as traditional implants
Influence of diameter and length on early implant loss
(Olate S, Lynn MC, 2010) Early implant loss associated with short
implantsNot associated with diameter
Ultra short implants 5mm long, 5mm in diameter in posterior areas
(Deporter D,2008) 1-8 year follow up results Maxillary, mandibular failure rates 14.3
and 0%
Implant Design Macro design
Body shapeThreadThread design
Micro designImplant materialsSurface morphologySurface coating
Implant Body Shape Cylindrical, tapered implants Other shapes not in use Tapered implant- 4 degree non parallel 30 degree maximum
Tapered implants- increased compressive forces
Cylindrical implants- increased shear forces
(Lemons, 1993)
Cylindrical implants- increased failure rates (Misch,
2008)
Implant Threads Screw threads
tapped self tapping
Solid body press fit Sintered bead technology
Thread Geometry Increase bone implant contact area
○ Total vs functional surface area
Stress distributionStability
Bone bridge from one thread to another Cusp like bone formation Heterogenous stress field
Thread shapes available include; V-shape, square shape, buttress and reverse buttress shape (Boggan et al. 1999).
Bone implant contact-increased in square threads
(Steinganga,2004) Density highest below threads Weakest- tip of threads (Bolind,2005)
• Square, Buttress threads◦ Axial load - dissipated
through compressive force.
(Bungardener, 2000)
V shaped and reverse buttress◦ Axial load – dissipated
through compressive, tensile and sheer force.
( Misch, 2005)
Cancellous boneV shaped, broad square threadsSignificantly less stress
Cortical boneNo difference (Geng 2004)Square thread least stress concentration
(Chun et al 2000)
The face angle is the angle between a face of a thread and a plane perpendicular to the long axis of the implant.
• Face Angle Shear stress increased as face angle
increases V shaped, 30° Reverse buttress 15°
V shaped, buttress Generates excess forcesDefect formation
(Hansson & Werke 2003)
• Thread pitch refers to the distance from the center of the thread to the center of the next thread, measured parallel to the axis of a screw (Jones 1964).
• It may be calculated by dividing unit length by the number of threads (Misch et al. 2008).
Thread pitch
Maximum effect on design variables Affects surface area Lower pitch- increased % BIC Less pitch- deceased stress (Motoyosti, 2005)
.8 mm pitch optimal for primary stability *V shaped threads Shorter or longer pitch * Unfavorable forces Affects cancellous more than cortical
bone
Thread depth is defined as the distance from the tip of the thread to the body of the implant.
Thread width is the distance in the same axial plane between the coronal most and the apical most part at the tip of a single thread.
Thread depth & widthAffects implant surface areaDeeper the thread- wider surface area of
implantShallower thread- ease of placement
Progressive thread design Greater depth apically, decrease
gradually in a coronal direction Increased load transfer to more flexible
cancellous bone Decreased cortical bone resorption
Optimal thread depth - .34-.5mm Thread width- .18- .3 mm Depth more sensitive to peak stresses (Abrahamsson, 2010)
Macrodesign: Summary
Crest module Traditionally smooth Soft tissue formation, less plaque
formation
Sterile environment changes to open oral cavity
Thicker cortical bone- primary stability Increased force concentration (Bozkoya, 2004)
Microthreads in crest module
Insufficient data Postulated to reduce
crestal bone loss
(Kim 2009)
Approaches to alter implant surfaces can be classified as
Physicochemical Morphologic or Biochemical. (Ito et al.)
Surface materials Commercially pure titanium and Ti-6Al-
4V niobium Molybdenum & manganese Zirconia
Surface energyZeta potentialInterfacial tension
Surface charge Net positive or negative charge
Surface compositionOxide layer
Physicochemical properties
Zeta potential○ Difference in potential between tightly bound
layers and diffuse layers
Interfacial tensionWettability- property of interaction forces
between different materials and interaction between cohesion forces within materials (Mollers)
Low wettability- low osteoblast cell attachment and decreased collagen production (Reddy 2000)
Increased polar components – increased osteoblast function
Electrostatic interaction in biological events -conducive to tissue integration.
(Baier RE et al., 1998) No selective cell adhesion Does not increase implant tissue
interface strength (Puleo DA et al., 2006)
Surface Morphology Surface topography/morphological
characteristics. Chemical properties.
Surface Roughness Increased surface area of implant
adjacent to bone. Improved cell attachment to bone. Increased bone present at implant
interface. Increased biochemical interaction of
implant with bone.
• Smooth surfaces: Sa value < 0.5 μm (e.g. polished abutment surface)
• Minimally rough surfaces: Sa value 0.5 to < 1.0 μm (e.g. turned implants)
• Moderately rough surfaces: Sa value 1.0 to < 2.0 μm (e.g. most commonly used types)
• Rough surfaces: Sa value ≥ 2.0 μm (e.g. plasma sprayed surfaces).
(Wennerberg and Albrektsson, 2009)
• Moderate roughness and roughness is associated with implant geometry-allowed for bone ongrowth and provided mechanical interlocking (Berglungh et al. 2003, Franchi et al. 2005)
• Higher BIC and removal torque force suggested enhanced secondary stability compared to smooth and minimally rough implants (Buser et al. 1991, Wennerberg et al. 1996).
Morphology Based on texture
Concave texture (mainly by additive treatments like hydroxyapatite (HA) coating and titanium plasma spraying)
Convex texture (mainly by subtractive treatment like etching and blasting)
Based on the orientation of surface irregularities Isotropic surfaces: have the same topography independent of measuring direction. Anisotropic surfaces: have clear directionality and differ considerably in roughness.
Surface coatings Chemical agents Biological agents
Chemical Al2 O3 and TiO2, with particle size
ranging from small, medium to large (150-350 μm) grit.
HA coating
Obtain improved bone implant attachment.
Being osteoconductive in nature, more
bone deposition has been reported
Lower the corrosion rates of the same substrate alloys.
Delamination of coating leads to failure of implant
Dissolution/fracture of HA coating results in failure.
• Predisposes to plaque retention.• Inflammatory reaction.
(Gross M 1999, Jansen, 1997)
Biological Coatings Cell adhesion molecules Biomolecules with demonstrated
osteotropic effects
Adhesion Molecules RGD sequence BMPR 2 peptide
Bioactive Proteins BMP PDGF TGF
Loading Protocol Immediate loading First longitudinal trial (Shitman,1990) Immediate , early loading in mandible
Esposito, 2009
Immediate- within 1 weekEarly- 1 week to 2 monthsConventional- > 2months
Immediate and early can be done with good success
* case selection * operator skill Failure rates:
early> immediate > conventional Primary stability- very important
Esposito, 2007 Differences between immediate & early:
not clear More studies needed
Esposito, 2004 Successful in mandible, dense bone Few well controlled RCT’s.
Publication bias in immediately loaded implants
(Polson, 2000) Trial aborted in UK due to unacceptable
failure rate
Progressive loading (Cannizaro,2003) Immediate provisionalisation Insertion torque- 40Ncm
Large , multicentric trial (Donati, Zollner,
2008) Insufficient information Risk of bias
Platform Switching Wide diameter implants-intro in late
1980s Fitted with standard diameter
abutments- showed no changes in crestal bone levels around implants
ConceptSmall diameter
prosthetic component connected to larger diameter implant platform- creating a 90° step
(Lazzara RJ 2006)
Long term studies (Wagenberg B 2010)advantage of platform switching in
preserving crestal bone levels. Recommended in anatomic sites where
minimum distance between implant and adjacent units cannot be achieved.
Theories1. Biomechanical theory
◦ Bone resorption limited by shifting stress concentration zone away from crest and directing it along axis (Maeda 2007)
2. Placement of implant- abutment junction (IAJ) at or below crestal bone level may cause vertical bone resorption to reestablish biological width (Hermann 2001).
3. Presence of inflammatory cell infiltrate at the IAJ (Ericsson 1995) and Peri-implant microbiota.
Esposito- SR, 2007 No evidence to show any implant better
than another
Implant survival rates Popelet A,Valet F 63% DID NOT REPORT INDUSTRY
FUNDING 66%-RISK OF BIAS
Inclusion/ exclusion criteria Blinding Drop out rates not reported
Survival rate significantly lower in industry non funded studies
Highest when funding undisclosed
Esposito 2004 Bone quality, volume most important
TO BE CONTINUED……………………….