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Implant quality scale : Osseointegration, success criteria and basic guides
Definitions
Mechanism of osseointegration
Factors effecting osseointegration
Methods of evaluation of
osseointegration
Osseointegration
Bone implant interface
Fibro – osseous integration
Success criteriaSuccess Survival,
And failureEvaluation of
dental Implants
HISTORICAL REVIEW•The concept of osseointegration was developed
and the term was coined by Dr. Per-Ingvar Branemark, Professor at the institute for Applied Biotechnology, University of Goteborg, Sweden
.
Definitions
“The apparent direct attachment or connection of osseous tissue to an inert, alloplastic material without intervening connective tissue”. - GPT 8
Structurally oriented definition
“Direct structural and functional connection between the ordered, living bone and the surface of load carrying implants”.
- Branemark and associates (1977)
Histologically Direct anchorage of an implant by the formation of bone directly on the surface of an implant withoutany intervening layer of fibrous tissue.
- Albrektson and Johnson (2001)
Clinically
Ankylosis of the implant bone interface.“Functional ankylosis” -Schroeder and colleagues 1976
“It is a process where by clinically asymptomatic rigid fixation of alloplastic material is achieved and maintained in bone during functional loading”
- Zarb and T Albrektson 1991
Biomechanically oriented definition
“Attachment resistant to shear as well as tensile forces”
- Steinmann et al (1986).
Bone physiology
Bone can be classified as • Compact bone • Spongy bone
Depending on age, developmental age, localization and function, bone consists of three tissue types that differ in collagen fibril arrangement and mineral content.
Woven bone Lamellar bone Bundle bone
Woven bone• Formed by the osteoprogenitor cells in the vicinity
of blood vessels during prenatal
development ,growth and healing .
• Forms 30-50 µm /day
• High cellular osseous tissue
• Low mineral content
• More pliable than mature lamellar bone
• Capable of stabilizing an unloaded implant,woven
bone lacks the strength to resist functional loads .
Woven bone
Lamellar bone • Principle load-bearing tissue
• Predominant component of mature cortical and
trabecular bone
• Forms relatively slow (< 1.0µm/day)
• Have highly organized matrix, and are densely
mineralized
• Orientation of the collagen fibrils differs from one
layer to another .
Lamellar bone
Bundle bone
• Found in the area of ligament and tendon attachment
along the bone-forming surfaces.
• Striation are extension of sharpey’s fibers composed of
collagen bundles from adjacent connective tissue that
insert directly into the bone
• It is formed adjacent to the periodontal ligament of
physiologically drifting teeth.
Bundle bone
Modelling
• A surface specific activity that produces a net change in
the size and/or shape of bone .
• An uncoupled process, meaning that cell activation(A)
proceeds independently to formation(F) or resorption(R)
• Generalized change in overall dimension of a bone’s
cortex or spongiosa
• Modelling is a fundamental mechanism of growth ,
atrophy and reorientation.
Bone Remodeling
• It is the turnover or internal restructuring of previously existing bone .
• Coupled tissue level phenomenon
Bone to implant interface There are two basic theories
Osseointegration(Branemark 1985)
Fibro-osseous integrationLinkow 1976James 1975Weiss 1986
FIBROINTEGRATION OSSEOINTEGRATION
In 1986, the American Academy of Implant Dentistry (AAID)
“Tissue-to-implant contact with healthy dense collagenous tissue between the implant and bone”
Fibro-osseous integration
Presence of connective tissue between the implant and
bone
Collagen fibers functions similarly to Sharpey’s fibers
found in natural dentition.
The fibers are arranged irregularly, parallel to the implant
body, when forces are applied they are not transmitted
through the fibers
Weiss concept Collagen fibers at the interface - peri-implant membrane
with an osteogenic effect. Collagen fibers invest the implant, originating at the
trabeculae of cancellous bone on one side, weaving around the implant, and reinserting into a trabeculae on the other side.
It was felt that, this membrane gave a cushion effect and acted as similar as periodontal membrane in natural dentition.
Failure of fibro-osseous theory
No real evidence Forces are not transmitted through the fibers -
remodeling was not expected Forces applied resulted in widening fibrous
encapsulation, inflammatory reactions, and gradual bone resorption there by leading to failure.
Natural teeth ImplantOblique and horizontal group of fibers
Parallel, irregular, complete encapsulation
Uniform distribution of load (Shock absorber)
Difficult to transmit the load
Failure : Inability to carry adequate loads -
Infection
Osseointegration
American Academy of Implant Dentistry (AAID) defined it as
"contact established without interposition of non-bone tissue
between normal remodeled bone and an implant entailing a
sustained transfer and distribution of load from the implant
to and within the bone tissue"
Mechanism of Osseointegration
• Healing process may be primary bone healing or secondary bone healing.
• In primary bone healing, there is well organized bone formation with minimal granulation tissue formation - ideal
• Secondary bone healing may have granulation tissue formation and infection at the site, prolonging healing period. Fibrocartilage is sometimes formed instead of bone - undesirable
Blood between the fixture and bone
Blood clot
Procallus (contains fibroblast)
Callus (contains osteoblast)
Bone
Remodelling
Phagocytic cellsPMNL
Mechanism of osseointegration
Phase Timing Specific occurrence 1.Inflammatory
phase Day 1-10 Adsorption of plasma proteins
Platelet aggregation and activation
Clotting cascade activation Cytokine release
Specific cellular inflammatory response
Macrophage mediated inflammation.
Phase Timing Specific occurrence
2. Proliferative phase
Day 3 - 42 NeovascularizationDifferentiation,
Proliferation and activation of cells.
Production of immature connective tissue
matrix.
Phase Timing Specific occurrence
3.Maturation phase
After Day 28
Remodeling of the immature bone matrix with coupled resorption and deposition of bone.
Bone remodeling in response to implant loading
Bone tissue response
• Distance Osteogenesis
A gradual process of bone healing inward from the edge of the osteotomy toward the implant. Bone does not grow directly on the implant surface.
• Contact Osteogenesis
The direct migration of bone-building cells through the clot matrix to the implant surface. Bone is quickly formed directly on the implant surface.
Mechanism of integration: (Davies - 1998)
Contact osteogenesis :
Early phases of osteogenic cell migration (Osteoconduction)
De novo bone formation Bone remodeling at discrete sites.
Osteoconduction
“Osteoconduction” refers to the migration of differentiating osteogenic cells to the proposed site.
Migration of the connective tissue cells will occur through the fibrin that forms during clot resolution.
The migration of cells through a temporary matrix such as fibrin - retraction of the fibrin scaffold.
De novo bone formation
Differentiating osteogenic cells, which reach the implant surface initially, secrete a collagen-free organic matrix that provides nucleation sites for calcium phosphate mineralization
Noncollagenous bone proteins - Osteopontin and bone Sialoprotein
Bone bonding in de novo bone formation
Bonding of de novo bone will occur by the fusion, or
micromechanical interlocking of the biologic cement line
matrix with the surface reactive layer
Bone remodeling
During the long-term phase of peri-implant healing, it is only
through those remodeling osteons that actually impinge on
the implant surface that de novo bone formation will occur
at these specific sites on the implant
Stages of Osseointegration
According to Misch there are two stages in osseointegration, each stage been again divided into two substages. They are:
Surface modeling Stage 1: Woven callus (0-6 weeks)Stage 2: Lamellar compaction (6-18 weeks) Remodeling, Maturation Stage 3: Interface remodeling (6-18 weeks)Stage 4: Compact maturation (18-54 weeks)
Stage 1: Woven callus0-6 weeks of implantation.
Woven bone is formed at implant site.
Primitive type of bone tissue and characterized
Random, felt-like orientation of collagen
fibrils
Numerous irregularly shaped osteocytes
Relatively low mineral density
Stage 2: Lamellar compaction
6th week of implantation and continues till 18th week. The woven callus matures as it is replaced by lamellar
bone. This stage helps in achieving sufficient strength for
loading.
Stage 3: Interface remodeling
This stage begins at the same time when woven callus is
completing lamellar compaction. During this stage callus starts to resorb, and remodeling
of devitalized interface begins. The interface remodeling helps in establishing a viable
interface between the implant and original bone.
Stage 4: Compact bone maturation
This occurs form 18th week of implantation and continues till the 54th week.
During this stage compact bone matures by series of modeling and remodeling processes.
The callus volume is decreased and interface remodeling continues.
Six different factors known to be important for the establishment of a reliable, long-term osseous anchorage of an implanted device
Implant biocompatibility Design characteristics Surface characteristics State of the host bed Surgical technique and Loading conditions
Implant Biocompatibility
Chemical interaction determined – properties of surface oxide
Commercially pure (c.p.) Titanium and Titanium alloy (Ti -6AL-4V)
Documented long term function Covered with adherent, self- repairing oxide layer Excellent resistance to corrosion – high dielectric
constant Load bearing capacity
Other metals Niobium, tantalum Cobalt chrome molybdenum alloys Stainless steels Ceramics - calcium phosphate hydroxyapatite (HA) and
various types of aluminium oxidesBiocompatible - insufficient documentation and very less
clinical trials - less commonly used.
Degree ofCompatibility
Characteristics of Reactions of Bony Tissue
Materials
Biotolerant Implants separated from adjacent bone by a soft tissue layer along most of the interface: distance osteogenesis
Stainless steels: CoCrMo and CoCrMoNi alloys
Bioinert Direct contact to bony tissue contact osteogenesis
Alumina ceramics, zirconia ceramics, titanium, tantalum, niobium, carbon.
Bioactive Bonding to bony tissue: bonding osteogenesis
Calcium phosphate-containing glasses, glass-ceramics, ceramics, titanium (?)
Grouping of hard tissue replacement materials according to their compatibility to bony tissue
Implant Design (Macrostructure)
Threaded or screw design implants Promote osseointegration More functional area for stress distribution
than the cylindrical implants. Minimal - <0.2 mm/year bone loss
Cylindrical implants Press fit root form implants depend on
coating or surface condition to provide microscopic retention and bonding to the bone
Bone saucerization
Non threaded
•Tendency for slippage•Bonding is required
•No slippage tendency•No bonding is required
Threaded
Functional surface area per unit length of implant may be modified by the three thread geometry parameters
• Thread shape• Thread pitch • Thread depth
Grooves on the threads of all implants and on the collars, wherever appropriate.
Increase surface area Increase area for bone-to-implant contact
Implant Surface (Microstructure,Surface Topography)
“The extent of bone implant interface is positively correlated with an increasing roughness of the implant surface”
Roughened surface
Greater bone to implant contact at histological level Micro irregularities - cellular adhesion. High surface energy - improved cellular attachment.
• Roughness parameter (Sa)0.04 –0.4 m - smooth 0.5 – 1.0 m – minimally rough 1.0 –2.0 m – moderately rough 2.0 m – rough
• Wennerberg (1996) – stated that moderately rough implants developed the best bone fixation.
Smooth surface < 0.2 m will – soft tissue no bone cell adhesion clinical failure.Moderately rough surface more bone in contact with implant better osseointegration.
Surface treatments
Turned surfaceSandblasted surfaceAcid etched surfaceTitanium plasma spraySandblasting and surface etchingHydroxyapatite coatingsAnodized surface
Bone – implant contact areaSurface treatment 1 month 3 months 6 months
Machined/ truned 42% 44%
Machined/ sandblasted 54%
Machined/ acid etched 42% 51% 49%
Sandblastedand acid etched
58%
72%
52%
68%Oxidized 35% 43%
Titanium plasma-sprayed 52% 78%
Hydroxyapaptite 79%Ion implantation 68% 61%
Laser treated 38%
State of the host bed Ideal host bed Healthy and with an adequate bone stock Bone height Bone width Bone length Bone density
Undesirable host bed states for implantation Previous irradiation Ridge height resorption Osteoporosis
Implant bed - Bone QualityAccording to Lekholm and Zarb,1985
• Quality I composed of homogenous compact bone found in the lower anterior
• Quality II Thick layer of cortical bone surrounding dense trabecular bone found in the lower posterior
Quality III Thin layer of cortical bone surrounding dense trabecular bone – upper anterior and upper
& lower posterior region
Quality IV Very thin layer of cortical bone surrounding a core of low-density trabecular bone - very soft bone found in the upper anterior and posterior
Branemark system (5 year documentation) Mandible – 95% success Maxilla – 85-90% success
According to Branemark and Misch D1 and D2 bone initial stability / better osseointegration
D3 and D4 poor prognosis
D1 bone – least risk
D4 bone - most at risk
Selection of implant D1 and D2 – conventional threaded implants
D3 and D4 – HA coated or Titanium plasma coated implants
Surgical Considerations
Promote regenerative type of the bone healing rather than reparative type of the bone healing.
The critical time/ temperature - bone tissue necrosis - 47° for one minute.
Recommendations Slow speed Graded series Adequate cooling Bone cutting speed of less than 2000 rpm Tapping at a speed of 15 rpm with irrigation Using sharp drills The optimal torque threshold – 35 N/cm. Implant should gently engage the bone in order to avoid
too much pressure at the bone interface which could jeopardize healing
Surgical skill / technical excellence
Progressive or two stage loading
Branemark et al to accomplish osseointegration
considered the following prerequisites
Countersinking the implant below the crestal bone
Obtaining and maintaining a soft tissue covering over
the implant for 3 to 6 months
Maintaining a non loaded implant environment for 3 to 6
months
Delayed loading: - Two-stage surgical protocol
- One-stage surgical protocol
Immediate loading:1. Immediate occlusal loading (placed within 48 hours)
2. Immediate non-occlusal loading (in single-tooth or short-span applications)
3. Early loading (within two months)
Frost’s mechanostat theory
Systemic factors
Active chemotherapy Type 2 (late-onset) diabetes: This is especially the
case where this is not well controlled
Treatment by an operator with limited surgical experience.
Patients who were smokers at the time of implant surgery had a significantly higher implant failure rate (23.08%) than non-smokers (13.33%)
Short implants and implant placement in the maxilla were additional independent risk factors for implant failure.
DeLuca S, Habsha E, Zarb GA. The effect of smoking on osseointegrated dental implants. Part I: implant survival. Int J Prosthodont 2006;19(5):491-8
Subjective criteriaAdequate functionAbsence of discomfortImproved aestheticsImproved emotional and psychological wellbeing
Harvard success criteriaThe dental implant must provide functional service for 5 years in 75% of cases
Objective criteria
Bone loss no greater than 33% of vertical length of implant
Gingival inflammation amenable to treatment
Mobility of less than 1mm in any direction
Absence of symptoms of infection
Absence of damage to surrounding structure
Healthy connective tissues
Possible criteria for success
MobilityPeri-implant radiolucencyMarginal bone lossSulcus depthGingival statusDamage to adjacent teethViolation of maxillary sinus , mandibular canal
or floor of nasal cavityAppearanceLength of service
Condition for application of criteria
Only osseointegrated implants should be evaluated with these criteria.
The criteria apply to individual endosseous implants.
At the time of testing, the implants must have been under a functional load.
Implants that are beneath the mucosa and in a state of health in relation to the surrounding bone should preferably not be included in the evaluations but reported as complications.
Complications of an iatrogenic nature that are not attributable to a problem with material or design should be considered separately when computing the percentage of success
Revised criteria - Albrektsson
Individual implant is immobile clinically
No evidence of peri-implant radiolucency is present as assessed on an undistorted radiograph.
Mean vertical bone loss is less than 0.2 mm annually after the first year of service.
No persistent pain, discomfort, or infection is attributable to the implant.
Implant design does not preclude placement of a crown or prosthesis with an appearance that is satisfactory to the patient and dentist.
By these criteria, a success rate of 85% at the end of a 5-year observation period and 80% at the end of a 10 year period are minimum levels for success.
Drago et al
anterior maxilla-89.1%
posterior maxilla-71.4%
anterior mandible-96.7%
posterior mandible-98.7%
Success rate
Moy et al –
maxilla-91.8% mandible-95.1%
Bass et al –
maxilla-93.4% mandible-97.2%
5-year survival
conventional tooth-supported FDPs of 93.8%
cantilever FDPs of 91.4%
solely implant supported FDPs of 95.2%
combined tooth-implant-supported FDPs of 95.5%
implant supported SCs of 94.5%
FDP vs Implants
After 10 years of function –
89.2% -conventional FDPs
80.3% -cantilever FDPs
86.7%- implant-supported FDPs
77.8% - combined tooth-implant-supported FDPs
89.4% - implant-supported SCs
Technical complications were (fractures of the veneer
material, abutment or screw loosening and loss of
retention)
Methods of evaluation of Osseointegration
Stability is a requisite characteristic of osseointegration.
Initial stability is a function of the Bone quality, Implant design and Surgical technique.
During the osseointegration healing and maturation process , the initial stability changes with increases in bone- to –implant contact and osseous remodeling.
Invasive Methods
Histological sections (10 microns sections)
Histomorphometric – To know the percentage of bone
contact
Transmission electron microscopy
By using Torque gauges
Non-Invasive Methods Percussion test Tapping with a metallic instruments
Ringing sound- osseointegrated. Dull sound - fibrous integration.
Radiographs
Reliable method to determine implant stability
Emg driven and electronically controlled
tapping head that hammers an object at a
rate of 4 times/sec
Periotest
Response to striking is measured by a small
accelerometer present in head
Signals converted to periotest value
Depends on damping characteristic of tissues
surrounding teeth or implant
Developed by Aoki and Hirakawa
Mech is similar to periotest
Microphone used as receiver and signals
transferred is processed by FFT for analysis
Dental mobility checker
Non invasive can be performed at any stage of
healing
Bite wing-measure crestal bone level
1.5 mm of CBL can be expected in the Ist year of
loading with 0.1 mm of subsequent annual bone
loss
Radiographic evaluation
Problems
Difficult for clinician to detect changes at 0.1mm
resolution
Can be measured when central ray of x-ray is
perfectly ll with the structure of interest
Excellent method to assess health of natural teeth
In implants little diagnostic value unless accompanied by signs & symptoms
Stable implants pocket depth- 2-6mm
Indicate bone loss but not necessarily disease
Sulcus depth greater than 5-6 mm-risk of anaerobic bacterial infection
Probing depth
Suggested by James, modified by Misch
Group I Group II Group III Group IV
Misch CE, Perel ML, Wang HL, et al. Implant success, survival, and failure: The International Congress of Oral Implantologists (ICOI) Pisa Consens Conference. Implant Dent 2008;17:5-15.
Implant quality of health scale
No pain or tenderness upon function
0 Mobility
Less than 2.0 mm crestal bone loss from initial surgery
No history of exudate
Group I (Success)
No pain on function
0 mobility
Crestal bone loss – 2 to 4 mm
No history of transient exudate
Prognosis good to very good
Group II (survival-satisfactory health)
Slight to moderate peri-implantitis
Sensitivity on function
Radiographic bone loss > 4 mm (<1/2 of implant
body)
No mobility (IM-O)
Probing depth >7 mm
May have exudates history
Group III (Survival-compromised health)
Implant removed Pain mobilityUncontrolled progressive bone loss;Uncontrolled exudate50% bone losssurgically removed/ exfoliated
Group IV(clinical or absolute failure)
Rigid fixation
Scale
Description
0 Absence of clinical mobility with 500g in any direction
1 Slight detectable horizontal movement
2 Moderate visible horizontal mobility up to 0.5 mm
3 Sever horizontal movement greater than 0.5 mm
4 Visible moderate to sever horizontal and any visible vertical movement
Cutting Torque resistance analysis (CRA)
Reverse Torque test (RTV)
Resonance Frequency analysis (RFA)
Other methods
Johansson and strid and improved by Friberg et al
Energy required for a current fed electric motor in cutting off a unit volume of bone during surgery is measured.
Energy is correlated with bone density which influences the implant stability
Cutting Torque resistance analysis (CRA)
Torque guage-in drilling unit measures the insertion torque in Ncm, gives idea about the bone quality
Gives more objective assessment than clinician dependent evaluation
Advantages
a. Detect bone density
b. Identify bone density during surgery
c. Can be used in daily practice
Disadvantages
d. can only be used during surgery
e. longitudinal data cannot be collected to assess
bone quality changes after implant placement
Measures the ‘critical’ torque threshold where
bone-implant contact (BIC) was destroyed
Removal Torque value (RTV)-indirect
measurement of BIC/clinical osseointegration
Reverse Torque test (RTV)
Ranges from 45-48 Ncm
RTV >20 Ncm accepted as criteria for
successful osseointegration
Varies depending on bone quality & quantity
Disadvantages
a. RTV only provide information as to “all or
none” outcome
b. Mainly used in experiments
Non invasive method that measures implant stability & bone density at various time points
RFA utilizes a small L-shaped transducer that is tightened to implant or abutment
Resonance Frequency analysis (RFA)
Transducer comprises of 2 piezoceramic elements
One for vibration, and other serves as a receptor
for the signal
Resonance peaks from the received signal
indicates the first RF of the measured object
Earlier hertz was used as measurement unit
now implant stability quotient (ISQ)
RF values ranging from 3500-8500 Hz
translated into ISQ of 0-100
Higher value-greater stability
Low value-instability
Successful implant-ISQ >65
ISQ <50 indicates potential failure/increased risk
of failure
RFA can only give information regarding success
cannot provide information with respect to survival
or failure.
ISQ is fairly reliable when implant has achieved
osseointegration & the B-I interface is rigid.
ISQ tends to fluctuate when the interface is not rigid
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Pjetursson BE et al, Comparison of survival and
complication rates of tooth-supported fixed dental
prostheses (FDPs) and implant-supported FDPs and
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http://www.ecf.utoronto.ca/~bonehead/