Structure of Matter / orthodontic courses by Indian dental academy

8/12/2019 Structure of Matter / orthodontic courses by Indian dental academy

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Contents:

1. Introduction.

2. Matter

3. Interatomic bonding

a). Primary bonding

Ionic

Covalent

Metallic

b). Secondary bonding

Hydrogen bonds

Vanderwaals orces

!. Interatomic bond distance " #ond energy.

$. Crystalline structure % &attice ty'es.

(. iusion.

*. +d,esion " bonding.

-. actors inluencing ad,esion.

a). /etting.

b). Surace energy.

c). Contact angle.

0. Solubility and sor'tion.

1. +d,esion to toot, structure.

11. eerences.

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INTRODUCTION:

+n obect can occu'y one o t,e t,ree dierent states o matter4 suc,

as solid4 li5uid4 gas.

In dentistry we ma6e use o all o t,em alt,oug, dental materials

e7ist 'rimarily as solids or li5uids.

8,e state o a material is a unction o tem'erature. 8,e more energy

t,at is 'ut into a material by increasing its tem'erature4 t,e more diicult it

is to 6ee' t,e atoms 9or) molecules in close 'ro7imity to one anot,er. 8,us4

t,e atoms 9or) molecules tend to move a'art and e7'and as ,eat is a''lied.

8,ereore increasing t,e energy wit,in a given material t,roug, t,e

a''lication o ,eat can ,ave a destabili:ing eect on bot, its structure and

dimensions. 8,e structure o a material can be described on bot, a

microsco'ic and macrosco'ic level.

;n t,e microsco'ic level4 we e7'erience t,e material t,roug, t,e

arrangement o its atoms and t,eir bonding sc,emes. ;n t,e macrosco'ic

level we see a material as a solid li5uid or gas.

8,e 'rinci'le goal o dentistry is to maintain or im'rove t,e oral

,ealt, o t,e 'atient. + wide variety o dental materials are involved in t,e

clinical a''lication. Material s,ould be careully selected. 8,roug,

understanding and e7'erimentation it is 'ossible to ma7imi:e any one

'ro'erty4 but in no a''lication is it 'ossible to select a material or one

'ro'erty above. It is 'recisely in t,e balance o one actor against anot,er

t,at t,e materials are used successully. Hence it is essential to 6now4 t,e

'ro'erties o t,e dental materials4 to be able to understand t,e 'ro'erties and

reactions o t,e material and 'redict t,e outcome.

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MATTER:

It is t,e substance rom w,ic, all ',ysical t,ings are made. Matter

is any t,ing t,at occu'ies s'ace and ,as weig,t. greater t,e mass o an

obect4 greater is its inertia.

3) ensity= +ll matter ,as density.

8,is is t,e mass 'er unit volume o a substance.

!) Matter can conduct ,eat and electricity.

$) 8,ere are t,ree states o matter.

Solid4 li5uid and gas.

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Molecule:

It is t,e smallest 'article o a substance4 w,ic, can e7ist on its own4

and retains t,e 'ro'erties o t,at substance.

Molecular weight: is t,e weig,t o a molecule relative to t,at o an atom o

carbon 12 ta6en as 12. 8,is is e7'ressed in gram molecule.

Atom: Is t,e smallest 'article o any element t,at s,ows t,e c,emical

be,aviour o t,at element. +tom cannot be divided as it is t,e smallest.

8,ere are many 6inds o atoms as t,ere are elements. +n element is made

u' o only one 6ind o atoms.

Element: Is a basic substance t,at cannot be se'arated into dierent

substances.

+tom is t,e basic unit rom w,ic, molecules and aggregates o

molecules4 w,ic, re'resent 'articular matter are built. +tom is made u' o a

3 ty'es o undamental 'articles li6e 'rotons4 neutrons and electrons.

?umber o 'rotons and number o neutrons4 gives t,e mass to t,e nucleusand also t,e atomic weig,t.

INTERATOMIC ONDIN!:

+toms do not e7ist singly4 instead are oined wit, ot,er atoms o t,e

same 6ind4 to orm molecules. 8,e number o atoms oining toget,er may

be two or in t,ousands. /,en suc, a t,ing ,a''ens t,ere e7ists a real t,ing

or substance. 8,e mec,anism o atoms coming toget,er is t,roug, orces o

attraction and t,e atoms going away rom eac, ot,er is t,roug, orces o

re'ulsion.

orces o attraction t,at ma6e t,e atoms to come toget,er are called

interatomic bonds.

8,ese bonds are classiied as

1) Primary bonds % C,emical in nature4 'ermanent and strong

a) Ionic bond

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b) Covalent bond

c) Metallic bond

2) Secondary bonds % P,ysical in nature4 wea6 bonds also called Vander>walls orces.

PRIMAR" OND:

Ionic #on$: ?ormally atom is electrically neutral because o balance o

'ositively c,arged 'roton and negatively c,arged electron. +n atom can

become ion i it loses or gains one o its outermost circulating electron. 8,is

can be a 'ositive ion or negative ion. +tom can be a 'ositive ion or a

negative ion. Suc, dierently c,arged two atoms will be attracted to eac,

ot,er because o diering 'olarity4 and a bond ta6es 'lace between atoms.


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Similarly c,lorine atom will oin wit, anot,er c,lorine atom and

s,are t,e outer electrons by covalent bond to orm Cl2covalent bond is very

strong and stable.8,is 6ind o bond is seen wit, carbon>carbon bond t,at ta6es 'lace in

denture base resin 9acrylic) or dental com'osite resin. +lso seen in silicon>

o7ygen bond o dental ceramics.

Metallic #on$:

8,is is seen in metallic elements. 8,e atoms o t,e metal are arranged

in orderly rows. 8,e atoms lose t,eir outermost valence electrons to orm

metal ions wit, a net 'ositive c,arge called cations .

8,e reed valence electrons roam about toget,er li6e a gaseous cloud

in t,e interstices ormed by t,e arrangement o solid s',eres. 8,is electron

cloud acts li6e a glue t,at ,olds toget,er dierent atoms. 8,is is called

metallic bond4 w,ic, is res'onsible or t,e strengt,4 conductivity4 o ,eat

and electricity o metals. 8,is bond is strong and stable.

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INTER ATOMIC &ECONDAR" OND&

In contrast to 'rimary bonds secondary bonds do not s,are electrons.

Instead4 c,arge variations among molecules or atomic grou's include'olar orces t,at attract t,e molecules.

'($rogen #on$ing

8,is bond can be understood by studying a water molecule. +ttac,ed to

t,e o7ygen atom are two ,ydrogen atoms. 8,ese bonds are covalent

because t,e o7ygen and ,ydrogen atoms s,are electrons.

+s a result t,e 'rotons o t,e ,ydrogen atoms 'ointing away rom t,e

o7ygen atoms are not s,ielded eectively by t,e electrons. 8,us t,e

'roton side o t,e water molecule becomes 'ositively c,arged. ;n t,e

o''osite side o t,e water molecule4 t,e electrons t,at ill t,e outer orbit

o t,e o7ygen 'rovide a negative c,arge. 8,us a 'ermanent di'ole e7ists

t,at re'resents an asymmetric molecule. H2bond4 associated wit, t,e

'ositive c,arge o ,ydrogen caused by 'olari:ation is an im'ortant

e7am'le o t,is ty'e o secondary bonding.

/,en a H2; molecule intermingles wit, ot,er water molecules4 t,e

,ydrogen 9@ve) 'ortion o one molecule is attracted to t,e o7ygen

'ortion o its neig,boring molecule4 and t,e ,ydrogen bridge is are

ormed.

)AN DER *AA+& ,ORCE&

It is a more a ',ysical t,an c,emical bond. 8,ese orces orm t,e

bases o a di'ole attraction.


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Inter atomic #on$ $istance an$ #on$ing energ(:

egardless o t,e ty'e o matter4 t,ere is a limiting actor t,at

'revents t,e atoms or molecules rom a''roac,ing eac, ot,er too closely4

t,at is t,e distances between t,e center o an atom and t,at o its neig,bor is

limited to t,e diameter o t,e atoms involved.

I t,e atoms a''roac, too closely4 t,ey are re'elled rom eac, ot,er

by t,eir electron c,arges. ;n t,e ot,er ,and4 orces o attraction tend to

draw t,e atoms toget,er. 8,e 'osition at w,ic, t,ese orces o re'ulsion and

attraction become e5ual in magnitude is t,e normal or e5uilibrium 'osition

o t,e atoms.

Thermal energ(

8,ermal energy is accounted or by t,e 6inetic energy o t,e atoms or

molecules at a given tem'erature. 8,e atoms in a crystal at tem'eraturesabove absolute :ero tem'erature are in a constant state o vibration and t,e

average am'litude will be de'endent on t,e tem'erature4 t,e ,ig,er t,e

tem'erature t,e greater t,e am'litude4 and conse5uently4 t,e greater t,e

6inetic or internal energy. 8,e overall eect re'resents t,e ',enomenon

6nown as t,ermal e7'ansion.

I t,e tem'erature continues to increase t,e interatomic s'acing will

increase4 and eventually a c,ange o state will occur.

8,e t,ermal conductivity de'ends mainly on t,e number o ree

electrons in t,e material.

+s metallic structures contain many ree electrons and most metals

are good conductors o ,eat as well as electricity4 w,ereas non>metallic

materials do not include many ree electrons and conse5uently t,ey are

generally 'oor t,ermal and electrical conductors.

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CR"&TA++INE &TRUCTURE:

ental materials consist o many millions o atoms or molecules.8,ey are arranged in a 'articular coniguration.

In 1(($ obert Hoo6e simulated t,e c,aracteristic s,a'es o crystals

by stac6ing mus6et balls in 'iles.

8,e atoms are bonded by eit,er 'rimary or secondary orces. In solid

state t,ey combine in t,e manner t,at will ensure a minimal internal energy.

or eg. Sodium and c,lorine s,are one electron as described

'reviously. In t,e solid state4 ,owever t,ey do note sim'ly 'air toget,er but

rat,er all o t,e 'ositively c,arged sodium ions attract all o t,e negative

c,lorine ions4 wit, t,e result t,at t,ey orm a regularly s'aced coniguration

6nown as s'ace lattice or crystal4 ,ere every atom is s'aced e5ually rom

every ot,er atom.

8,ere are 1! 'ossible lattice ty'es4 but many o t,e metals used in

dentistry belong to t,e cubic system.

?on crystalline structure eg. Blass and wa7es structures ot,er t,an

t,e crystalline orm t,at occur in t,e solid state eg. Blass and wa7es.

/a7es % solidiy as amor',ous materials meaning t,at t,e molecules

are distributed at random. 8,oug, t,ere may be a tendency or t,e

arrangement to be regular.

Blass is considered to be a noncrystalline solid4 yet its atoms tend to

orma s,ort % range order lattice instead o t,e long>range order lattice

c,aracteristic o crystalline solids. In ot,er words4 t,e ordered arrangement

o t,e glass is more or less locali:ed wit, a considerable number o

disordered units between t,em.

Suc, an arrangement is also ty'ical o li5uids suc, solids are

sometimes called su'ercooled li5uids.

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?on crystalline solids do not ,ave a deinite melting tem'erature but

rat,er t,ey gradually soter as t,e tem'erature is raised and gradually

,ardens as t,ey cool. 8,e tem'erature at w,ic, t,ere is an abru't decreasein t,e t,ermal e7'ansion cu4 is called t,e glass transition tem'erature or

glass tem'erature.

#elow 8g a glass loses its luid c,aracteristics and ,as signiicant

resistance to deormation.


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&i5uid ,as a deinite volume4 but not a deinite s,a'e. &i5uid ta6es

t,e s,a'e o t,e container in w,ic, it is 6e't. 8,e molecules in a li5uid are

ree to move about. 8,e molecules are suiciently close to eac, ot,er to,ave mutual attraction on eac, ot,er and on t,is de'ends t,e li5uids luidity

or viscosity.

!as:

Bas ,as molecules w,ic, ,ave reedom o movement and are not

restricted to a given area. Bas ,as no deinite s,a'e and no deinite volume.

It e7'ands to ill its container.

Change of state: /,en a solid is ,eated4 t,e molecules ac5uire more

6inetic energy and vibrate more ra'idly. 8,ey ac5uire enoug, energy to

brea6out o t,eir 'ositions and move about among t,e ot,er molecules.

/,en t,is ,a''ens solid turns into li5uid and t,e 'rocess is called melting.

/,en a li5uid is ,eated4 t,e molecules gain more < and some gainenoug, energy to brea6 away rom t,e surace o t,e li5uid and become gas.

8,is is eva'oration w,en bubbles are ormed during t,is c,ange it is called

boiling.

C,ange o state is basically controlled by 'ro'er tem'erature and

'ressure on t,e mass.

Cr(stal . Crystal is any solid w,ose atoms are arranged in an orderly and

re'eated 'attern e7= Crystals o 5uart: metals.

Uses of cr(stals: In ewellary4 in watc,es4 ,earing aids4 micro',ones mica

crystals are used as insulators in electrical e5ui'ments.

PROPERTIE&:

Ph(sical Properties: most crystals ,ave s,ar' melting 'oint e7= Metal

many crystals cleave or s'lit along c,ange 'lanes4 w,ic, are 'lanes o wea6

bonding t,at run 'arallel to one anot,er t,roug, out t,e crystal. 8,is is due

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to t,e orderly and re'eatition o atomic structure. Crystals conduct ,eat and

electricity in one direction but act as insulator in ot,er direction.

Optical properties: lig,t is reracted in crystals.

D>ray diraction % brea6ing u' s'read

8,e structure o t,e crystals can be studied by D>ray diraction.

Classification of cr(stals: Crystals are classiied by t,e orm o t,e unit

cells.

8,e unit cell is t,e basic 3 dimensional re'eating structure o w,ic,

crystals are com'osed.

8,e unit cell may grow in * basic dierent s,a'es4 determined by t,e

relative lengt,s o t,eir a7is and t,e angle t,at t,ese a7es ma6e wit,

eac, ot,er.

8,e seven orms o unit cell deine t,e crystal systems and every

crystal is classiied by t,e 'osition o t,e atoms or ions in t,ese cells. In a sim'le cubic ty'e4 only t,e corners o t,e cells are occu'ied by

atoms.

In body centered cells4 t,e corners and t,e centers o t,e cell are

occu'ied by atoms.

In ace centered cells4 t,e corners and t,e centers o t,e aces are

occu'ied by atoms.

8,ere are 1! dierent combinations o cell structures and atomic

arrangement. 8,ese combinations are called s'ace lattices roc6s4

metals and ice are not single crystals4 but are com'osed o many

small crystalline material.

Substances com'osed o single crystal are called monocrystalline unit

crystal cell is t,e smallest re'eating unit o atoms.

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Diffusion of atoms in soli$s: iuse A S'read out

+toms ,ave energy 'articles % means t,ey ,ave internal energy4 some

atoms ,ave ,ig, energy level t,an ot,ers. Hig, energy atom can move orc,ange its 'lace and occu'y anot,er 'osition in t,e material.

ate o diusion de'ends on tem'erature4 ,ig,er t,e tem'erature

greater will be t,e diusion.

Conse-uences of $iffusion of atoms:

/0 &oli$ state reactions: ?umber o solid state reactions occur in a solid

substance and it is due to t,e diusion o atoms.

or e7= In gold>co''er alloys4 gold and co''er atoms may be distributed

randomly in t,e s'ace lattices leading to disordered lattice. ue to ,eat

treatment t,is 'attern may c,ange in w,ic, gold atoms occu'y t,e center o

t,e cubic ty'e o s'ace lattice and co''er atoms occu'y t,e corner 'ositions

in t,e s'ace lattice.

8,is will c,ange t,e ',ysical 'ro'erties o ,ardness4 brittleness

strengt, and conductivity o a material.

2) iusion can bring about c,ange in t,e s,a'e or contour o a material

6nown as war'age or distortion.

/0 AD'E&ION:

+d,esion is attraction between unli6e molecules. i.e.4 i two dierent

substances are made to come in contact wit, eac, ot,er at t,eir inter

suraces and i t,e two suraces are stuc6 toget,er it is said t,at ad,esion ,as

ta6en 'lace.

or e7am'le gum and 'a'er.

Bum and 'a'er are two dierent ty'es o materials ,aving dierent

ty'es o molecules. /,en gum is a''lied to t,e surace o t,e 'a'er4 t,e

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attraction between t,e molecules o gum and molecules o 'a'er ta6es 'lace

and it is ad,esion.

10 CO'E&ION:

Co,esion is attraction between li6e molecules. In t,is case only one

materials is involved. or e7am'le water.

It is mad u' o molecules o ,ydrogen and o7ygen. 8,e two toget,er

orm water molecule suc, as H2;. 8,ere are innumerable numbers o water

molecules in water. /ater remains as water as long as t,ere is attraction

between one water molecule and anot,er molecule. 8,is attraction between

similar ty'e o molecules is co,esion.

+d,esion and co,esion ,el' in t,e retention o com'lete dentures as

ollows.

/,en t,e denture is 'laced in t,e mout, in contact wit, mucous

membrane4 ad,esion and co,esion bot, 'lay a role.

In t,is t,ree materials 9or) t,ree ty'es o molecules are involved4 t,ey

are %

enture material

Saliva

Mucous membrane.

itting surace o denture ,as saliva layer4 and saliva is in contact

wit, mucous membrane. 8,us4 t,ere is ad,esion between denture surace

molecules and saliva molecules. 8,ere is co,esion between saliva molecules

and saliva molecules. 8,ere is ad,esion between saliva molecules and

mucous membrane surace.

In dentistry4 ad,esion is an im'ortant re5uirement o any restorative

materials so t,at t,ere is a bond between toot, enamel and artiicial

restorative materials4 w,ic, ,el's in retention o t,e restoration in t,e toot,.+d,esive % is a material 9or) ilm o material used to 'roduce ad,esion.

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+d,erand % is t,e materials or surace o a material to w,ic, ad,esive is

a''lied.

or e7= Bum is an ad,esive4 'a'er on w,ic, it is a''lied is ad,erand.+ttraction between molecules o gum and 'a'er is ad,esion.

,actors influencing a$hesion:

8,ese are

1) /etting

2) Surace energy

3) Contact angle.

/0 *ETTIN!:

It is t,e ability o a li5uid 9ad,esive) to low and ada't to t,e surace

o a solid.

It is mainly de'endent on surace tension. Surace tension is t,e

molecular attraction at t,e surace o li5uids and so t,e surace o a li5uid isactually in a state o tension as i it were being 'ulled tig,t. 8,is 'ro'erty

ma6es t,e surace o a li5uid to be,ave li6e t,inly stretc,ed rubber s,eets.

Suc, suraces tend to become as small as 'ossible.

or e7am'le= + dro' o water is round in s,a'e4 mercury also orms a

dro'let o round s,a'e. #ut water as suc, ,as low surace tension4 w,ere as

mercury ,as ,ig, surace tension.

8,ereore a dro' o water may be round in s,a'e but s'reads

immediately and lows on t,e surace. ;n t,e ot,er ,and dro' o mercury

remains same and does not s'read out4 but will wet t,e surace only i t,e

surace is clean.

It is diicult to orce two solid surace to ad,ere.

/,en 'laced in a''osition only ,ig, s'ots are in contract. #ecause

t,ese areas usually constitute only a small 'ercentage o t,e total surace4 no

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8,e increase in energy 'er unit area o surace is reerred to as t,e

surace energy. In li5uids t,e surace energy is 6nown as surace tension.

20 CONTACT AN!+E:

8,e contact angle is t,e angle ormed by t,e ad,esive wit, t,e

ad,erend at t,eir interace. 8,e e7tent to w,ic, an ad,esive will meet t,e

surace o an ad,erend may be determined by measuring t,e contact angle4

between t,e ad,esive and t,e ad,erend.

8,e greater t,e tendency to wet t,e surace4 t,e lower t,e contact

angle4 until com'lete wetting occurs at an angle e5ual to :ero.

Capillar( rise : 8,e 'enetration o li5uids into narrow crevices is 6nown as

ca'illary action.

8,is e5uation relates t,e dierential ca'illary 'ressure develo'ed

w,en a small tube o radius r is inserted in a li5uid o surace tension

9usually e7'ressed in dynes E cm) and wit, a contact angle .

I t,e contact angle o t,e li5uid on t,e solid is less t,an 0P will

be negative and t,e li5uid will be de'ressed.

CONTACT AN!+E O, *ETTIN!

8,e e7tend to w,ic, an ad,esive wets t,e surace o an ad,erand

may be determined by measuring t,e contact angle between t,e ad,esive

and ad,erand.

8,e contact angle is t,e angle ormed by t,e ad,esive wit, t,e

ad,erend at t,eir interace. I t,e molecules o t,e ad,esive are attracted to

t,e molecules o t,e ad,erend as muc, as or more t,an t,ey are to

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P A 2cos


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t,emselves4 t,e li5uid ad,esive will s'read com'letely over t,e surace o

t,e solid4 and no angle 9A degrees) will be ormed. 8,us t,e orces o

ad,esion are stronger t,an t,e co,esive orces ,olding t,e molecules o t,e

ad,esive toget,er.

8endency o li5uid to s'read increases wit, decrease in contact angle.

8,ereore contact angle is t,e indication o s'readability or wettability.

8,us t,e smaller t,e contact angle between an ad,esive and an ad,erend4

t,e better t,e ability o t,e ad,esive to ill in irregularities on t,e surace o

t,e ad,erend. +lso t,e luidity o t,e ad,esive inluences t,e e7tent tow,ic, t,ese voids or irregularities are itted.

&O+UI+IT" AND &ORPTION:

;ne o t,e re5uired o a dental restorative material is t,at4 it s,ould be

stable in t,e oral environment.

It s,ould undergo a minimal amount o dimensional c,ange and

c,emical alteration.

+ll dental materials are soluble to some e7tent and dissolve in water.

8,e least soluble o dental materials are t,e 'orcelains and ceramics.

In 'olymers t,e unreacted molecules may be readily e7tracted or

dissolved into oral luids.

8,e loss o small organic molecules rom sot tissue conditioners and

denture liners is res'onsible or t,em ,ardening in t,e mout, and becoming

irritating.

Metallic ions are slowly released rom cast restorations and

amalgams.

Sor'tion is t,e u'ta6e o luids or substances by a material.

8,is 'rocess is usually conined to 'olymeric materials and can also

occur at t,e union between 2 materials4 suc, as 'orcelains and a metal

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interace as a PM restoration. Sor'tion may lead to subtle discoloration o

t,e 'orcelain. 8,e result o sor'tion in a 'olymeric material is oten a

swelling or increase in dimension.8,e u'ta6e o oreign materials can lead to c,emical disintegration

t,at occurring in dental cements at t,e margin between t,e cast restoration

and t,e toot,. 8,is results in loosening o restoration and decay o 'ossible

toot, structure.

AD'E&ION TO TOOT' &TRUCTURE:

+ssociated 'rinci'les o ad,esion can be readily related to dental

situations. or eg. w,en contact angle measurements are used to study t,e

wettability o enamel and dentin. It is ound t,at t,e wettability o t,ese

suraces is mar6edly reduced ater t,e to'ical a''reciation o an a5ueous

luoride solution.

8,us luoride treated enamel surace retains less 'la5ue over a given

'eriod4 'resumably because o a decrease in surace energy. 8,ereore

decreases in dental caries.

Hig,er surace energy o many restorative materials com'ound wit,

t,at o t,e toot,4 t,ere is great tendency or t,e surace and margins o t,e

restoration to accumulate debris. 8,ereore increases marginal caries.

Fnder certain instances4

1) ecurrent caries

2) Pul'al sensitivity

3) eterioration o t,e margins o restoration can be associated wit, a

lac6 o ad,esion between restoration.

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P,illi's Science o ental materialsJ 11t,edition 4 23

2. Combe S6inners Science o ental MaterialsJ0t,edition 4 1002

Structure of Matter / orthodontic courses by Indian dental academy

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