HAL Id: jpa-00230039
https://hal.archives-ouvertes.fr/jpa-00230039
Submitted on 1 Jan 1990
HAL
is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire
HAL, estdestinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
OBSERVATION OF A LOW ANGLE GRAIN BOUNDARY IN TOOTH ENAMEL CRYSTALS
USING HREM
E. Brès, J. Hutchison, J.-C. Voegel, R. Frank
To cite this version:
E. Brès, J. Hutchison, J.-C. Voegel, R. Frank. OBSERVATION OF A LOW ANGLE GRAIN
BOUNDARY IN TOOTH ENAMEL CRYSTALS USING HREM. Journal de Physique Colloques,
1990, 51 (C1), pp.C1-97-C1-102. �10.1051/jphyscol:1990113�. �jpa-00230039�
OBSERVATION OF A LOW ANGLE GRAIN BOUNDARY IN TOOTH ENAMEL CRYSTALS USING HREM
E.F. BRES, J.L. HUTCHISON', J.-C. VOEGEL and R.M. FRANK
INSERM U 157, CNRS TJRA 588, Faculte de Chirurgie Dentaire, Universite Louis Pasteur, 1, Place de l'lbpital, F-67000 Strasbourg, France ' ~ e p a r t m e n t of Metallurgy and Science of Materials, University of Oxford, Parks Road, OX1 3PH GB-Oxford, Great-Britain
Resume - Plusieurs types de joints de grains a faible desorientation lies a l'anisotropie de la dissolution carieuse des cristaux d'email dentaire humains ont et6 observes par microscopie Blec- tronique a haute r6solution (HREM).
Abstract
-
Several types of low angle grain boun- daries linked to the anisotropy of the carious dissolution of human dental enamel crystals have been observed by HREM.1- INTRODUCTION:
Human dental enamel is composed of 96% by weight of an inorganic phase which is mainly composed of poorly crystalline carbonated hy- droxyapatite crystals (chemical formula: Calo(P04)e(OH)z, space group:
P6=/m) /l/. These crystals show strong differences with hydroxyapatite crystals synthetized in the laboratory:
1 ) Tooth enamel crystals possess a flat hexagonal prismatic mor- phology which differs from the dipyramidal hexagonal morphology of mineral hydroxyapatite crystals /2/. The average dimensions of enamel crystals are: width (W) S 89 nm, thickness S 50 nm and length S 150 nm. The difference in morphology between biological and mineral apatite crystals is indicative of different growth processes between the two minerals / 3 / .
2) A relatively large concentration of (Coal2- ions are in- corporated into the enamel crystals. Two types of substitutions can be observed: a) these ions can either substitute two (OH)- ions, or b) the substitution of one (PO4I3- ion is accompanied by the simultaneous loss of one CaZ+ and one (OH)- ions. The largest proportion of car- bonate is incorporated inside the bulk of the crystals and not on their. surface. Substitution of hydroxyl ions by carbonate ions cannot be obtained in the laboratory at experimental conditions compatible with life.
3) During the carious dissolution process, all enamel crystals are first attacked on their basal planes.-Qn each of these faces a central hexagonal lesion elongated along 121101 is observed (Fig. 1).
This lesion is limited by the { 1 0 1 0 } planes while it develops ani- sotropically parallel to the 100011 direction / 4 / . This observation can be correlated to the work of Love11 /5/, Pate1 et al. /6/ as well as Phakey and Leonard /7/ who have shown using acid etching, X ray topography and multiple beam interferometry that screw dislocations of burgers vectors b = c [ 0 0 0 1 ] are often present in hydroxyapatite crystals
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990113
Cl-98 COLLOQUE DE PHYSIQUE
We have already identified three distinct types of crystal di- sorder which may act as dissolution sites /8/: a) regions of lattice buckling with departure from hexagonal symmetry, b) dislocations, and
C) grain and twin boundaries. From the observations of these defects, we have been able to suggest two distinct growth mechanisms for enamel crystals: a) the low angle grain boundary is the nucleating site of the crystal, After nucleation, the crystal grows parallel to the [00011, [21101 and [lT00] directions until it gains its final shape, dislocations being formed during nucleation, 2) two crystals are nu- cleated nearly adjacent and slightly tilted with respect to each other, the crystals fuse during growth forming a low angle grain boun- dary. Once the interface is formed the whole crystal grows outwards and so achieves its final shape.
Figure 1: Schematic diagram of a tooth enamel crystal.
2- EXPERIMENTAL:
Carious human enamel was obtained from proximal white spot lesions of a molar tooth. The incipient carious lesion was dissected into small blocks and fixed for 3 hr in a 2% glutaraldehyde paraformaldehyde solution in a 0.1 M cacodylate buffer at pH 7.4.
After 1 h post fixation using a 2% osmic acid solution in the above mentioned buffer, the fragments were embedded in Epon 812. Non decalcified 20-38 nm thick sections were obtained with a Sorvall- Porter microtome equipped with a diamond knife. The specimens were examined in a JEOL 4000EX (CS = 1.0 mm, delta = 8 nm) and a Philips EM430ST electron microscopes (CS = 1.1 mm, delta = 6 nm).
3- OBSERVATION OF A LOW ANGLE TWIST BOUNDARY IN A TOOTH ENAMEL - CRYSTAL :
In this present paper, we present a low angle twist bougdgry con- sisting of two crystals oriented respectively along the l24231 and [l2111 directions and joined by (1010) planes rotated with respect to each other by an angle of 6.4' (Fig. 2). Several observations can be made from these images: 1 ) No amorphous layer is observed at the boun- -dary. 2) Sites of optimum matching can be observed at a distance of approximately 30 nm along the boundary (see arrows) in the part of
ay? uoJj apeu aq ue3 suorlwuasqo TPJaAaS ) q m a q 1 ~ 3 t 7 d o UP uo ~ ~ P J J ~ T U T ay? u o ~ j KPMP s a 3 u e ~ s ~ p IeJaAas P 39 y d e ~ t i o ~ 3 ~ ~ 1 aqa J O a ~ ~ 7 e 6 a u aq? paqOJd aheq aM I e l s A m srq? U! pahJasqo KJepunoq
~ S F M ~ aqq Kq p a l e ~ a u a 6 pxarj L I ~ P J J S ay2 aqe15tqsa~ur 03 lap20 u1 ' / O X / [PU~XPUI sr uotsuedxa antlqPI aql pup s a 3 u ~ 7 s r p aBJe1 A[aArJela..x 03 pualxa ue3 U ~ P J ~ S ay? 'a3rqedPAxoapKy se y m s S I P ~ S A J ~ ~ T U O J J O
ase3 aq? u1 - a ~ n ? z ~ n ~ q s aql ut paJaJuno3ua Burpuoq 1 ~ 3 y m a q 3 JO aaA3 aq7 uo quapuadap S: UoFSUPdXa srqL -KJepunoq ay7 02 1prnJou 6Ur3PdS aUPId 30 uorsuedxa 1 ~ 3 0 1 a c ~ n p o ~ d aJaq u ~ o q s auo ay3 se q3ns sarlepunoq J s y x Jelnorqled us pue sarlepunoq U I P J ~ Aq p a l ~ ~ a u a 6 s p 1 a ~ j ~ u t e - z ~ ~ ' ( E '6td) sIe?snm aq4 J O saprs ay?
03 A1Inz puaqxa ~ o u saop s 1 e ~ s A m Tameua ur q3ajap ay2 qeqq aIqPqOJd SF 3 1 'Jaded sry3 us u ~ o y s sauo aq? se q m s , [ O L L Z I 0 7 raIIQ-ied Iro33aA s ~ a 6 ~ n q q q r ~ suorleDo1srp 03 6 u ~ p u o d s a ~ ~ o 3 salrs uorlnlossrp 30 a 3 u a s q ~ aqa JOJ punoj uaeq s ~ q uor3eueIdxa K J O J ~ P J S ~ ~ P S ou 'aut?
>UaSald aqq JP 'JaAaMoH 'uorsa[ 1 ~ u o 6 e x a y p a q ~ 6 u o ~ a ay2 30 uorleuloj ay? 02 JOFJCI auoz
[ o l ~ z ]
ay3 6 ~ 0 1 ~ S ~ ~ U Q ? S F P IBnba JP s ~ e l s ~ ~ s Iameua 30 s a u ~ l d ~ e s e q aqa uo p a u 6 r 1 ~ adeys IPuoBexaq Ie3rJlaununs e J O saqrs uor?nlossrp ~ ~ r ~ r u r AJeA aql jo a3ua?stxa aq3 uyP1dxa pTno3 q3ajap srqq ~q paTeJaua6[ r o o o ]
03 Ia1IBJed xoq3aA s ~ a m n q 30 suoS7P3olsrp MaJ3S ayL 'adKq Xs'tMT $ 0 aq OSIP pInO3 SIPJSKJ3 IaUIPUa U! JUaSaJd qaajap Ieuuorsuamrp OM? ay? 3 ~ q 7 paqsa66ns KpPaJIP aAeq aM'yq6ray daqs aq? pue salts UTBJTS m u ~ u ~ u aq2 ~ J P ~ T P U ~ SMOJJB aqL .Ic-repunoq >SrM? 31BUP MOI e 6UrMOrlS ~ ~ J S K J : , Iaureua q ~ o o l u ~ u m ~ T'rJ
'[oJ[z]
G'€ 0 7 6uypuodsaJJo3 'uu E: KlaqPurrxoJddP 30 snlnpour e s a ~ r 6 PInuJoj S , ~ L I P J J jo u o ~ q e 3 ~ 1 d d e 73aJrp y ' / 6 / saqrs U F P J ~ S urnu:utu aqx uaafilaq Let+ JIB^ paJenlrs aq lsnu [ r - ~ l l ~ j 0 3 IaIteled JolDaA sla6Jng J O suorJPDolsyp eqa 'paAJasqo ~ P ~ s A J ~ 3 q l jo a3eJJns ay? 6UOTy' [ o ~ L z ]
PUP [ ~ 0 0 0 ] 03 IallPJPd K 1 a h r ~ 3 a d s a ~ s J o p a A sJa6Jng JO suotqe3oIsrp
M ~ J ~ S a3npoJd.sarJepunoq 7 s r ~ q Aq paznpur Jau suor?B3olsrp ayk
-
UMOqS o s ~ e sr slla2 ?run 01.17 02 BurpuodsaJJoa dals( c
-KJepunoq aqq JO 31r7 1Ieurs e 07 anp A ~ q ~ q o ~ d sr STY? 'paquarlosrur Ktqq6rIs sr IP?SAJ~ylnq aql aql ~ e q ? alou 07 Bu!Tsa~alur sg 'aJouJaqlJnj . ~ e w ~ u r u r sr a 3 ~ 3 ~ a ~ u r ay? JP p a l e ~ a u a 6 ssa,qs aql aJaqM salrs 02 pUOdSaJJO3' asnu I P ~ S K J ~ aqq'jo suoy6eJ a s a w - [ E Z ~ + Z I BUOIP paluarlo T e q s A m
Cl-100 COLLOQUE DE PHYSIQUE
2 1 1 2 and ?l02 as well as 2Ti2 and 1iOZ can be observed from Fig. 4d and e, b) optical diffractograms corresponding to both directions are observed in Fig. 4c and 4b. This second observation is rather surprising since the part of crystal probed by the laser beam in the diffractogram in Fig. 4c and 4d does not seem to suffer any distortions. The crystal observed must also contain a wedge of crystal oriented along the L24231 penetrating inside the crystal oriented along [ 1 2 1 1 ] , in this region the part of crystal oriented along [ 2 4 2 3 ] must be sufficiently thin for its contribution not to be observed in the image but thick enough for these contributions to be detected by the averaging procedure carried out by the optical diffraction process.
Fig. 3: Possible model for the two d,imenslonal defect in human enamel crystals.
CONCLUSION:
In the present paper, we have been able for the first time to show a low angle twist boundary inside an human tooth enamel crystal.
The observation of such a defect has allowed us to propose a model explaining the very initial dissolution mechanisms of these crystals during the carious process. The presence of a grain boundary inside human tooth enamel crystals is of a prime importance for the chemical properties of these crystals, since the very principle of the twinning and grain boundary operations is the creation at or near the boundary of atomic polyhedra different from the ones of the bulk structure /11/. Hence. it is quite probable that the the interface itself not only favours the dissolution of enamel crystals but also the segregation of foreign atoms on its surface. Furthermore, it is quite likely that such the tensile strain field that we have shown facilitates the substitution of interstitial atoms inside enamel crystals /12/, which phenomenon is of a considerable interest for the physiological properties of this tissue.
ACKNOWLEDGEMENTS: The authors are thankful to Mr. Steuer for the preparation of the specimens. They would also like to thank the French Ministery of Research for the grant N'86-5322 awarded in the framework of the "Interface Physique vers la Biologie".
the same size of the inserts themselves.
COLLOQUE DE PHYSIQUE
REFERENCES:
/l/ VOEGEL, J.-C. Le Cristal dlApatite des Tissus Osseux et Dentaires et sa Destruction Pathologique. Th&se d'Etat, Universit6 de Strasbourg, France. (1978).
/2/ BUERGER, M. Elementary Crystallography: An Introduction to the Fundamental Features of Crystals. MIT Press, Cambridge, Mass. (1978).
/3/ LOWENSTAM, H. A. Science 211. (1981) 1126.
/4/ VOEGEL, J.-C. and FRANK, R. M. Calcified Tissue International 24 (1977) 19.
/5/ LOVELL, L. C. Acta Metall. 6 (1958) 775.
/6/ PATEL, A. R., DESAI. C. C. and AGARWAL, M. K. Acta Cryst. 20 (1966) 796.
/7/ PHAKEY, P. P. and LEONARD, J. R. J. Appl. Cryst.
3
(1970) 38./8/ BRES, E. F., BARRY, J. C. and HUTCHISON J. L. Ultramicroscopy 12 (1984) 367.
/9/ BOLLMANN, W. Crystal Defects and Crystalline Interfaces. Springer, Berlin. (1970).
/10/MILKOWE, K. R., LAMARRE, P., SCHMUCKLE, F., VAUDIN, M. D. and SASS, S. L. J. Phys. Paris C4-46 (1985) 71.
/ll/ANDERSON, S. and HYDE, B. G. J. Solid State Chem.
2
(1974) 92./12/ SHALLITT, H. J. Photogr. Science
