bone density ppt

PRESENTED BY:APURVA THAMPI

BONE DENSITY

Contents •Introduction•Bone morphology•Bone physiology•Influence of bone density on implant success rates•Aetiology of various bone density•Bone classification schemes•Bone density classification - Misch

•Bone density location•Radiographic assessment of bone density•Tactile sense - bone density•Scientific rationale•Effect of bone density on surgical approach and healing•Case studies•Conclusion•References

Basic bone biology in implantology

05/01/2023

Textbookof human histology , Inderbir Singh ; 5th ed

4

Bone

33% organic67% inorganic hydroxyapetite

28% collagen

5% non collagenous protiens

There are 4 types of cells in bone tissue….

Oste

opro

geni

tor

cells• Unspecialise

d cells• Develop into

osteoblasts• Found in

periosteum, endosteum and in canals of vital teeth

Oste

obla

sts • Formation of

bone• Role in

calcification• Synthesis of

protien

Oste

ocla

sts • Responsible

for bone resorption

Oste

ocyt

es • Maintenance

of bone• Exchange of

calcium between bone and ECF

TEXTBOOKOF HUMAN HISTOLOGY , INDERBIR SINGH ; 5TH ED

Can be broadly classified into :

Compact bone

Trabecular bone


What is lamellar bone?Structure of adult bone

Made up of layers – lamellae – thin plate of bone consisting of collagen fibres and mineral salts

Lacunae – between each lamellae

Each lacuna consists of one osteocyte

Canaliculi spread out from each lacuna

A

B

C

Unit of bone - lamellus

Bone acquires thickness by stacking of lamellus

Between adjoining lamellae – spaces called lacunae - Occupied by osteocytes


What is woven bone?Osteocyte in lacuna canaliculi

Collagen fibres present in bundles – at random

Interlaced – woven bone

All newly formed bone

Abnormal persistence of woven bone – Paget’s disease

Compact bone VS Trabecular bone

Osteon of compact bone

Trabeculae of spongy bone

Haversian canals

Volkmann’s canal

periosteum

osteon

canaliculi

lamellae

Lacunae containing ostecytes

Compact boneLamellae

arranged in concentric circles –

surround - Haversian

canals

Occupied by blood vessels and nerves

Haversian canal +

lamellae = osteon or haversian

system

Between adjoining osteons – interstitial lamellae

At the surface – lamellae are

parallel – circumferential lamellae


Trabecular boneBony plates or rods –

meshwork – trabeculae

Made of number of lamellae

Enclose wide spaces filled with bone

marrow – receive nutrition

Bone physiology

Calcium metabolism

Contemporary implant dentistry, Carl E Misch, 3rd edition

Rapid influx of calcium from bone fluidShort term response of osteoclasts

and osteoblastsLong term control of bone turnover

Normal serum

calcium levels –

10mg/dL

Low calcium level tetany

and death

High serum calcium levels – kidney stones,

dystrophic calcification of

soft tissues

Dec in calcium levels – transport of ions to

osteocytes

Calciferol enhances pumping of calcium ions from cells into

ECF

Net flux of Ca ions

PTH + calciferol + calcitonin

Transiently suppresses bone

resorption

Profound effect on skeleton

PTH is the primary regulator – mean bone age

Important determinant of

fragility

Instantaneous regulation (within

seconds)Short term regulation

Long term regulation

CONTEMPORARY IMPLANT DENTISTRY, CARL E MISCH, 3RD EDITION

Calcium conservation

Kidney excretes phophates by minimising loss of calcium Renal dysfunction – high risk for osseous manipulative procedures – renal osteodystrophy

Body spends 300mg calcium per day – recovered by absorption from gut – depends of Vit D

Kidney is the primary calcium

conservation organ of the

body


Cortical bone growth and maturation

Osseous landmarks

for superimpo

sition

Anterior curvature

of the sella

turcica

Cribriform plate

Internal curvature of frontal

bone

Most reliable means of determining post

adolescence growth essential for treatment

planning

MELSEN, BIRTE. THE CRANIAL BASE: THE POSTNATAL DEVELOPMENT OF THE CRANIAL BASE STUDIED HISTOLOGICALLY ON HUMAN AUTOPSY MATERIAL. VOL. 32. ACTA ODONTOLOGICA SCANDINAVICA, 1974.

Influence of bone density on implant success rates

Anterior mandibl

eAnterior maxilla

Posterior

mandible

Posterior maxilla

Position / Arch location Quality of

bone dependent

on the position


•10% greater success rates in anterior mandible as compared to anterior maxilla (Adell et al)

•Lower success rates in posterior mandible as compared with the anterior mandible (Schnitman et al)

•Highest clinical failure rates – posterior maxilla – force is greater and poor bone density


Quality of bone


Aetiology of various bone density

Hormones

Vitamins

Mechanical influences

Duration of edentulous

ness

Changes in bone -

adaptability


“Every change in the form and function of bone or of its function alone is followed by certain definite changes in the internal architecture, and equally definite alteration in its external conformation in accordance with mathematical laws”

Wolff - 1892

Adaptive phenomena Alteration of mechanical forces and strain development within the bone density evolves as a result of mechanical deformation from microstrain

MODELLING Independent sites of formation and resorption

Results in change in shape and size of bone

REMODELLING Resorption and formation at the same site

Replaces previously existing bone


The maxilla is a force distribution unit and mandible is a force absorption

unitCONTEMPORARY IMPLANT DENTISTRY, CARL E MISCH, 3RD

EDITION

The trabecular bone in dentate mandible is more coarse compared to the maxilla


Anterior mandibl

e

Posterior maxilla

Density change after tooth loss.

• Initial density• Flexure and torsion• Parafunction before

extraction

NEUFELD JO: CHANGES IN THE TRABECULAR PATTERN OF THE MANDIBLE FOLLOWING THE LOSS OF TEETH, J PROSTHET DENT 685-697, 1958

ORBAN B: ORAL HISTOLOGY AND EMBRYOLOGY, ED 3, ST LOUIS, 1953, MOSBY

Based on Frosts’s mechanostat theory

50 1500 3000 10000+Acute Disusewindow

Adaptedwindow

MildOverloadwindow

PathologicOverloadwindow

Spontaneous fracture

Stress F/A

Strain O

Strain

Acute disuse window : lowest microstrain amount

Adapted window : ideal physiologic loading zone

Mild overload zone : cause microfracture; triggers an increase in bone remodelling – more woven bonePathologic overload : increased fatigue fractures, remodelling and bone resorption

FROST, H. M. "MECHANICAL ADAPTATION. FROST’S MECHANOSTAT THEORY." STRUCTURE, FUNCTION, AND ADAPTATION OF COMPACT BONE (1989): 179-81.

Acute disuse window•Loses mineral density•Disuse atrophy – modelling for new bone inhibited•Net loss of bone•Microstrain – 0 – 50•Cortical bone density decrease – 40% and trabecular bone density decrease – 12%


Adapted window phase•50 – 1500 microstrain•Equilibrium of modelling and remodelling•“homeostatic window of health”•18% trabecular bone and 2-5% cortical bone•Ideally desired around an endosteal implant

Mild overload zone•1500 – 3000 microstrain•Greater rate of fatigue microfracture•Bone strength and density decreases•State of bone when endosteal implant is overloaded•Repair – woven bone is weaker than lamellar – “safety range” for bone strength is reduced


Pathologic overload zone•Microstrains <3000 units•Physical fracture of cortical bone•Formation of fibrous tissue•Marginal bone loss in implant overloading – implant failure

Bone classification schemes in implant dentistry

Linkow in 1970 : Class I

• Ideal• Evenly

spaced trabeculae with small cancellated spaces

Class II• Less

uniformity• Larger

cancellated spaces

• Large marrow filled spaces exist


Lekholm and Zarb in 1985:Quality 1

• Homogenous compact bone

Quality 2• Thick layer of

compact bone around a core of dense trabecular bone

Quality 3• Thin layer of

cortical bone around dense trabecular bone

• Favorable strength

Quality 4• Thin layer of

cortical bone around a coreof low density trabecular bone


Misch in 1988Bone density Description Tactile analogue Typical anatomic

locationD1 Dense cortical Oak / maple wood Anterior mandibleD2 Porous cortical and

coarse trabecularWhite pine or spruce wood

Anterior mandiblePosterior mandibleAnterior maxilla

D3 Porous cortical (thin) and fine

Balsa wood Anterior maxillaPosterior maxillaPosterior mandible

D4 Fine trabecular Styrofoam Posterior maxilla

D5 type of bone exists – most

immature bone – found in a

developing sinus graft.


To be continued…

Bone density location

Location of bone density types (% occurance)Bone Anterior

maxillaPosterior maxilla

Anterior mandible

Posterior mandible

D1 0 0 6 3

D2 25 10 66 50

D3 65 50 25 46

D4 10 40 3 1


D1 Bone• Incresed torsion / flexure • Div A Kennedy’s class IV• Antr/postr mandible – lingual cortex

D2 Bone• Partially edentulous antr/postr mandible (premolar)

• Single tooth or 2 teeth missing

D3 Bone• Most common in maxilla• Also present in posterior mandible

D4 Bone• Softest bone• Posterior maxilla – after sinus augmentation or iliac crest bone graft


• First way to identify bone density in implant site

◦ Anterior maxilla – D3◦ Posterior maxilla - D4◦ Anterior mandible - D2◦ Posterior mandible – D3

D2

D3 D4


Radiographic bone density

IOPAR

OPGs

• Lateral cortical plates obscure the trabecular bone density

• More subtle changes cannot be qualified

Correlation between Misch bone density classification and Hounsfield units….

Type of bone

Hounsfield units

D1 >1250 HUD2 850 – 1250 HUD3 350 - 850 HUD4 150 – 350 HUD5 <150 HU

SOGO, MOTOFUMI, ET AL. "ASSESSMENT OF BONE DENSITY IN THE POSTERIOR MAXILLA BASED ON HOUNSFIELD UNITS TO ENHANCE THE INITIAL STABILITY OF IMPLANTS." CLINICAL IMPLANT DENTISTRY AND RELATED RESEARCH 14.S1 (2012): E183-E187.

Correlation between Lekholm and Zarb’s bone density classification and bone density…

NORTON, MICHAEL R., AND CAROLE GAMBLE. "BONE CLASSIFICATION: AN OBJECTIVE SCALE OF BONE DENSITY USING THE COMPUTERIZED TOMOGRAPHY SCAN." CLINICAL ORAL IMPLANTS RESEARCH 12.1 (2001): 79-84.

Failure in mandible –

higher Hounsfield

units

• Lack of vascularisation

• Overheating

ROTHMAN, STEPHEN LG, MELVYN S. SCHWARZ, AND NEIL I. CHAFETZ. "HIGH-RESOLUTION COMPUTERIZED TOMOGRAPHY AND NUCLEAR BONE SCANNING IN THE DIAGNOSIS OF POSTOPERATIVE STRESS FRACTURES OF THE MANDIBLE: A CLINICAL REPORT." INTERNATIONAL JOURNAL OF ORAL &

MAXILLOFACIAL IMPLANTS 10.6 (1995).

Bone density – tactile sense

Bone density Description Tactile analogue Typical anatomic location

D1 Dense cortical Oak / maple wood Anterior mandibleD2 Porous cortical and

coarse trabecularWhite pine or spruce wood

Anterior mandiblePosterior mandibleAnterior maxilla

D3 Porous cortical (thin) and fine

Balsa wood Anterior maxillaPosterior maxillaPosterior mandible

D4 Fine trabecular Styrofoam Posterior maxilla

Scientific rationale for a bone density - based treatment plan

Bone strength and

density

Bone elastic modulus and

density

Bone density and implant bone contact

interface

Bone density and stress transfer

Bone density and strength

Bone density is directly

related to the strength of bone before

microfracture


1 2 43 5 6 7 8 9 10

D1D2D3D4

MISCH, C. E., AND M. W. BIDEZ. "IMPLANT-PROTECTED OCCLUSION: A BIOMECHANICAL RATIONALE." COMPENDIUM (NEWTOWN, PA.) 15.11 (1994): 1330-1332.

Elastic modulus and density Directly related to the density of bone Relates to the stiffness of the material

Amount of strain as a result of a particular amount of

stress

EM of bone more

flexible than Ti

Pathologic

overload

Stresses minimize

d – adapted window

zone

Lamellar bone at

the interface


Ti - D1 bone interface – very little

microstrain

Ti – D4 bone interface – pathologic overload


Bone density and bone-implant contact percentage Area less area = greater stress

D1 bone has greatest BIC

D2 has 65 – 75% BIC

D3 bone has 40 – 50% BIC

D5 bone has 30% BIC


Bone density and stress transfer

Different stress contours for different types of

bone

Bone implant contact

Bone density

Elastic modulu

s

Crestal bone loss and early implant

failure due to

increased stress

D1 bone

Stress is of lesser

magnitude Highest

strains near the crest

D2 bone

Sustains greater strain intensity of

stress extends farther apically

D4 bone

Greatest crestal strain magnitude of

strain is further apical

Adapted window Mild overload Implant failure


A nutshell….Each bone density has different strengths

Bone density affects elastic modulus

Density differences result in difference in BIC

Different stress-strain distribution at a B-I interface


Effect of bone density on treatment planning

Modifications in treatment plan

Prosthetic factors

Implant surface

conditionImplant number

Need of progressive loading

Implant design

Implant size


Aim : decrease strain in the bone thereby decrease microfracture increase SA

Dense cortical D1 BoneAnalogous to oak or

maple wood

Almost all dense cortical bone

Mostly seen in anterior mandible and

sometimes in posterior mandible

Advantages/disadvantages of D1 bone

Highly mineralizedExcellent bone strengthBest implant bone contactLess force transmission to apical thirds

Implant crown ratio>1Less blood supply – not regenerativeEasily overheatedImplant height limited to less than 12mm

Prior to osteotomy…Amount of heat generated by each drill is directly related to the bone removal by each drill

First drill – 2mm diameter

Rotational speed – 2000rpm

Intermittent pressure “bone dances”

Osteotomy preparation in D1 bone

• Ext/Int irrigation• Intermittent pressure• Pause 3-5mins• New drills• Incremental drill sequence

Overheating

• Primarily from periosteum

• Minimal reflection• Precise approximation

Blood supply• Greater width• Greater height• Slower speed used

Final osteotomy

drill

• Short of full osteotomy depth

• Allows passive implant fit

• Removed drill remnants

Bone tap

• Unthread ½ turn to relieve internal stresses

Final implant

placement • Slower healing rate• 5 months to achieve

mature interface

healing

• 3-4 months• May use immediate

loading

Stage II recovery

D2 bone Dense-to-thick porpus cortical and carse trabeculae

Hounsfield values – 750-1250 units

Analogous to spruce or white pine wood

Occurs mostly in anterior mandible and posterior

mandible

Ideal implant dimension – 4mm diameter ; 12 mm height

Advantages/disadvantages

Excellent implant surface healingSecure initial rigid interfaceIntrabony blood supply

Osteotomy preparation in D2 bone

Rotation of drill – 2500 rpm Ext/int irrigation used Pause every 5-10 seconds – pumping motion Drill sequence similar to D1 bone Crestal bone drills should be used – reduce mechanical trauma Bone tap – engages lateral or apical cortical bone

Healing

Excellent blood supply

Initial rigid fixation

Lamellar bone

interface < 60% - 4 months healing interval

Abutment placement

may commence

D3 boneThinner porous cortical boneHounsfield values – 375 – 750 HUAnalogous to balsa woodFound in anterior maxilla and anterior mandible/maxillaIdeal implant dimension – 4X12Roughened implant body – acid etched or resorbable blast media

Advantages/ disadvantages

Time and difficulty for preparation is minimalBlood supply is excellentHighest survival rate

Disadvantages of D3 boneBone anatomy• Anterior maxilla is narrow

Osteotomy• Lateral perforation• Oversize by mistake• Apical perforation

BIC• 50%

Implant placement• One time• In level with crestal bone

Implant design• TPS or Hydroxyapatite coated• Costly• Threaded• Greater SA• Press fit

Healing• 6 months• Progressive loading more important than D1 or D2

D4 boneLeast density – no

cortical crestal bone

Found in posterior molar region

Analogous to stiff Styrofoam

Ideal Implant height – 14 mm (min 12

mm)

DisadvantagesDifficult to obtain rigid fixationRotating drills not to be used apart from pilot drillOsteotomes may be used to compress osteotomy siteCortical bone in the opposite landmark to be engaged (if any)Increase number of implants to improve load distributionNo cantilever advocated

Summary Densities vary depending of the location of edentulous ridge and the period of edentulousness

D1 is the strongest bone - 10 times greater than D4 Minimum of 12mm height of implant required for initial stability Additional bone healing and incremental loading will improve bone density

Conclusion Bone remodels in relationto the forces excerted upon it – density varies

References Textbookof human histology , Inderbir Singh ; 5th ed Contemporary implant dentistry, Carl E Misch, 3rd edition Orban B: Oral histology and embryology, ed 3, St Louis, 1953, Mosby Melsen, Birte. The cranial base: the postnatal development of the cranial base studied histologically on human autopsy material. Vol. 32. Acta Odontologica Scandinavica, 1974.

Neufeld JO: changes in the trabecular pattern of the mandible following the loss of teeth, J Prosthet Dent 685-697, 1958

Frost, H. M. "Mechanical adaptation. Frost’s mechanostat theory." Structure, function, and adaptation of compact bone (1989): 179-81

Sogo, Motofumi, et al. "Assessment of bone density in the posterior maxilla based on Hounsfield units to enhance the initial stability of implants." Clinical implant dentistry and related research 14.s1 (2012): e183-e187.

Norton, Michael R., and Carole Gamble. "Bone classification: an objective scale of bone density using the computerized tomography scan." Clinical oral implants research 12.1 (2001): 79-84.

Misch, C. E., and M. W. Bidez. "Implant-protected occlusion: a biomechanical rationale." Compendium (Newtown, Pa.) 15.11 (1994): 1330-1332.

bone density ppt

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