on the microhardness and young’s modulus .on the microhardness and young’s modulus of human...

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  • ON THE MICROHARDNESS AND YOUNGS MODULUS OF HUMAN TEETH

    A.D.Zervaki1, G.N. Haidemenopoulos1 and A. Giannakopoulos2

    1. Department of Mechanical Engineering, University of Thessaly, Volos, Greece

    2. Department of Civil Engineering, University of Thessaly, Volos, Greece

  • AIM OF THE WORK

    Determination of material hardness (H), and elastic properties such as Youngs modulus (E).

    Acquire knowledge of the physical properties of teeth and tissues : Important aid for understanding their mechanical behavior under clinical loading conditions

    Knoop indentation test enables the E value of human teeth to be obtained in a simple fashion and has potential to be used as a quality control tool in the development of dental implants or prosthetic teeth.

    Biomimetic aspects in mechanical engineering: design better coatings

  • OUTLINE

    Introduction Teeth structure

    Theoretical Background Determination of E from H

    Experimental Procedure Sectioning teeth and measuring hardness

    Results & Discussion Correlation between hardness and modulus

    Conclusions

  • Enamel

    Dentine

    Human Tooth, Structure

    Enamel:

    The hardest and most highly mineralizedsubstance of the body. It consists of 96 % ofhydroxyapatite, with water and organicmaterial composing the rest.

    Dentine:

    Hydrated composite of mineralized collagenfibers and nanocrystalline hydroxyapatite,with ~ 45% hydroxyapatite, 35 % collagen,20% water (by volume). Dentine consists ofmicroscopic channels (dentinal tubules) whichradiate outward through the dentine andcontain fluid and cellular structures.

  • Material Properties including hardness (H), Youngs modulus (E)and fracture toughness can be calculated from measurements taken from Knoop & Vickers indentations.

    Recovery of Knoop indentation

    Elastic recovery of Knoop indentation (elastic-plastic indentation). Geometry of Knoop indenter is also given at the upper part of the figure.

  • Methods of obtaining E

    Marshalls methodbased on the measurement ofelastic recovery of the in-surfacedimensions of Knoop indentations

    EH

    ab

    ab 1=

    Conways methodrelates / to the residual length of a

    minor diagonal (b) of Knoop indentations

    ( )[ ]

    =

    EH

    bb tan121 2

    2

    ab ratio of the diagonal dimensions a and b in

    the fully loaded state = 0.140646

    ab ratio of the altered dimensions after

    unloading

    1a proportionality constant

    v Poissons ratio average half angle of a Knoop indenter 75o

    Marshall et al, Comm. American Cer. Soc. 65(10), (1982), p. 175-176 Conway, J. Mat. Sci., 21 (1986) p.2525-2527

  • Experimental Procedure

    Specimen PreparationDental extractionLongitudinal sectioning using a low speed diamond wheelMounting in an epoxy resinGrinding with SiC papers 120, 320, 500, 800 and 1000 gritPolishing with diamond paste of 3 and 1 m diameter

    Specimen Examination, Microhardnes MeasurementsOptical Metallography Microhardness testing (Vickers and Knoop indenters)Instrument reliability was verified by using calibrated test blocks

  • H: Knoop hardness numberF: Force in Nt (0.98): length of the longer diagonal in m.

    3

    2

    1450 10FHa

    =

    =

    bb

    HE 1

    Values of Knoop hardness for enamel and dentine were calculated as follows

    Values of Youngs modulus (E) for enamel and dentine at different indentation distances were calculated by rearranging Marshals equation in terms of E:

    where: ab ratio of the diagonal dimensions a and b in

    the fully loaded state = 0.140646

    ab ratio of the altered dimensions after

    unloading

    1a constant

    1.5 Marshalls theoretical calculation using elliptical indenter

    0.45 Marshalls experimentally derived value

    0.34 Merediths proposed value

    Hardness and Modulus

  • Results

    Macroscopic appearance of a human tooth subjected to the specimenpreparation described previously

    dentine

    enamel

  • 43 HV 0,1

    301 HV 0,1307 HV 0,1

    Tooth surface

    enamel

    dentine Amelodentinal junction

    Results

    Typical Vickers Microhardness measurements in enamel and dentine

  • Typical Knoop Indentations

    Load: 100gr

    enamel

    dentine

    Residual Surface impressions after Knoop microhardness measurements

    in enamel and dentine

  • Results & Discussion

    enamel

    dentine

    Microhardness profile. Measurements were taken at distances of 150 m.

  • 100

    150

    200

    250

    300

    0 200 400 600 800 1000 1200 1400

    Distance from enamel surface, m

    Kno

    op h

    ardn

    es, H

    K

    Microhardness - Enamel

    Knoop microhardness in enamel with distance from the tooth surface

    Enamel

  • 30

    35

    40

    45

    50

    55

    60

    65

    70

    0 300 600 900 1200 1500 1800 2100

    Distance from amelodentinal junction, m

    Kno

    op h

    ardn

    ess,

    HK

    Knoop microhardness in dentine with distance from the amelodentinal junction

    Dentine

    Microhardness - Dentine

  • Youngs modulus - Enamel

    Calculated Values for Youngs Modulus of Enamel with distance from tooth surface

    0 200 400 600 800 1000 1200

    20

    40

    60

    80

    100

    120

    140

    160Yo

    ung'

    s mod

    ulus

    , GNm

    -2

    Distance from tooth surface, m

    1=0.34 1=0.45 1=1.5

    Enamel

  • Calculated Values for Youngs Modulus of Dentine with distance from amelodentinal junction

    200 400 600 800 1000 1200 1400 1600 1800

    5

    10

    15

    20

    25

    30

    35Yo

    ung'

    s mod

    ulus

    , GNm

    -2

    Distance from amelodentinal junction, m

    1=0.34 1=0.45 1=1.5

    Youngs modulus - Dentine

    Dentine

  • 0 200 400 600 800 1000 1200 1400100

    120

    140

    160

    180

    200

    220

    240

    260

    280

    300

    50

    75

    100

    125

    150

    175

    200

    Youn

    g's m

    odul

    us, E

    (GNm

    -2)

    Kno

    op h

    ardn

    ess ,

    HK

    Distance from enamel surface, m

    H-E correlation in Enamel

    Enamel

  • H-E correlation Dentine

    0 200 400 600 800 1000 1200 1400 1600 180030

    35

    40

    45

    50

    55

    60

    65

    70

    10

    15

    20

    25

    30

    35

    40

    Youn

    g's m

    odul

    us, E

    (GNm

    -2)

    Kno

    op h

    ardn

    ess ,

    HK

    Distance from amelodentinal junction, m

    Dentine

  • Conclusions

    Knoop, as well as, Vickers microhardness were determined for enamel anddentine and are in good agreement with other results reported in the literature.

    Microhardness of both enamel and dentine varied with depth

    Youngs modulus was determined by utilizing the method described byMarsall et all. Our values are in good agreement with those of otherresearchers.

    The variation of E with distance from the tooth surface and from theamelodentinal junction correlates with the variation of microhardness.

    Slide Number 1Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10 Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19

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