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……………………….