Lecture 5, Glass Inomer Cements (Script)

8/3/2019 Lecture 5, Glass Inomer Cements (Script)

1/13

1


2/13

Direct esthetic restorative material:

Glass Inomer Cements (GIC(

Our lecture today is a continuation on direct restorativematerials which are esthetic or white fillings ,, last coupleof lectures we talked about composites we will talk todayabout glass inomer cements , another white filling, it'sslightly different , actually it's very different , it's notavailable in several shapes like in composites so it's notreally your first choice when you want an esthetic materialthat looks like natural teeth.

usually it appears a little bit opaque rather than similar to

a normal tooth shape.

Now originally , glass inomer cements were self- cured,tooth colored material and they are able to release fluoridewhich enable them to prevent caries or inhibitdemineralization , they can bound chemically to toothstructure without needing a bonding agent; you don't needa bonding agent to bound them to enamel and dentine,they can chemically bound to enamel and dentine.

Now, they are newer classes of glass inomer cements thatcan be light cured as well, they are a little bit modified butbasic glass inomer cements are self- cured which meansthat you have a powder and a liquid to mix together tostart the sitting reaction and the material needs a fewminutes (5-6 minutes) or (4-5 minutes) to set, light- curedmaterials will be slightly modified so that they aresensitive to light so they set when they are subjected to

light.

now many types of glass inomers exist ,they can bedifferent in some properties like for example there abilityto flow or there viscosity ...so we have what we called

(luting agents) or cementing agents; ((these materials or cements are usually highly flowablebecause we use them to attach crowns on prepared teethso they should have the ability to flow very well to cover

the internal surface of the crown and spread all around the

2


3/13

tooth structure so we call them cements or (lutingagents.(

some glass inomer cements are filling materials

(restorative materials ) but since they are weak (brittlematerials) we can't use them in areas that are subjected tohigh stress or high stress bearing area so they are specificfor certain cases for example class (5) cavities : in thecervical marginal teeth whether labially or lingually, it'snot subjected to high stress so you can safely place themthere for example in primary teeth , force or stress is notvery high or as high as permanent teeth so you can usethem even in the occlusal surface for class (1) cavities for

example.

In some cases ,we use them as a temporary filling... forexample, when you need to place composite in class (3) ,you don't have enough time to place composite you wantto place temporary material or filling instead of using zincoxide Euginol because we said that we shouldn't use itunder composite , we can use GIC ,in some cases somepatients need root canal treatment... (3elaj 39b).... in

between visits or in vacations when you need to go for along time before you come back to the doctor to finish thetreatment you need a temporary filling that can last for along time and it's able to bound very well to toothstructure and prevent microleakage all around it ... glassinomer cement is an option

It Can be use as:*liners (1

2(bases underneath restorations. like amalgam orcomposite in deep cavities.

If the cavity is( 2-2.5 )mm deep that's ok! we don't reallyneed a liner or a base here , there is enough dentineremaining that can protect the pulp... isolate the pulpprevent any transfer of heat or any damage reaching thepulp but if your cavity is deeper and there is only a thinlayer of dentine remaining ,you need something to isolate

the pulp to protect it from the outer environment , if youhave a deep cavity with a large amalgam filling that is able

3


4/13

to transmit heat because it's a metalic filling we needsomething to protect your pulp so we need a liner or abase like glass inomer cements (GIC) can be use as a lineror a base to protect the pulp in deep cavities.

It can also be used as a core build up material, it's notthe first option ,if you have a bad destroyed tooth and youwant to build it up again and place crown on top ...it's notyour first option but some materials of GIC can be used to

build up tooth structure before placement of a crown.

The strongest material among the restorative material ,it's amalgam ,the second option is composite while GIC isanother option.

For example let's say you only have a remaining lingualand buccul walls , that are thin , you want to restore therest of the toothbefore you prepare for a crown so youneed some structure to prepare or to drill ... you can useamalgam , in some cases there is not enough tooth

structure to retain amalgam so composite can be used wecan bound it or GIC.

Pit and fissure sealants-:

to prevent caries , some preparation of ( GIC ) are used aspit and fissure sealants.

main components of glass inomer cements are-:

glass particles like quartz or silica.(12(a polyacid which is present in the liquid.(polyacrylic acid

(3(water : water is the reaction medium.. the reaction

happens within water , so when the reaction happens if thewater dehydrated, the reaction will not proceed normally

4

what's is our first option?we said it's core build up material.

((if you don't have enough tooth structure to retainamalgam ,don't use amalgam , you can use composite

or GIC)) .


5/13

and the material will be weak.4(tartaric acid is part of the liquid ( it will help to control

(regulate )working time and sitting time. (5(soduim ,fluoride.

They all are combined either withinthe powder or within the liquid.so in the glass or the glass particles have also several

things within it:)components of the glass particles(

Silica (1Alumina(2

3(Calcium fluoridesodium and aluminium fluorides(4

5(calcium or aluminum phosphates.

All these components are fused together and then groundto form small particles , so these small particles contain allof these components together and they are called glassparticles , so glass particles are made up of many things :silica, alumina, calcium fluoride, aluminium phosphate ,calcium phosphate all of them (small components )arefused together at high tempretures to form one large blockthen this block is ground in a machine to form the smallfine particles and these are supplied as a powder in abottle by the manufacturer , you are going to mix thepowder in a liqiud , now the liqiud component is a mixtureusually of several types of acids like (acrylic acid +itaconic acid or maleic acid) different types of acids ,now if it was only composed of acrylic acid on it's own itwill be highly viscous so they add different types of acidsto reduce the viscosity of the liquid , if it's reduced a littlebit it will be easy to mix and manipulate so it's not only

composed of acrylic acid ( several types of acids arecombined together to form the liquid which you mix with

the powder to control the viscosity. (

Tartaric acid is another component that will help inregulate working time and setting time by making theworking time not too short.

-it will allow you enough time to mix the material andmanipulate it.

-it will prevent the sitting time from being too long.

5


6/13

if the setting time is too long it's not practical , it's notclinically practical ; you can't keep the fillings inside thepatients mouth and ask him to keep his mouth open until

the material set for 10 minutes so this acids will influencethe working time and the setting time and we will see howin a couples of slides . so this is just a chemicalrepresentation of different acids that combined together toform the liquid component that form the glass inomercements.

so (GIC or self-cured GIC has powder made of glass whichcontain silica,aluminia,calcium fluoride and many thingsalso the liquid; the liquid is an acid that's why the setting

reaction they call it ( acid -base reaction) ; because youmixed an acid which is the liquid (polyacrylic acid ) andyou mix the base particles which is the glass , mix themtogether the setting will occur and the material willbecome hard bit by bit with time.

*Dispensing:2-bottle system hand mix**:

so it's available as a two bottle system hand mixed , onecontains the powder , one contains the liquid and you needto follow the instructions with regard to the ratio howmany spoons , how many drops of the liquid , you need tofollow manufacturer instructions.

**anhydrous cement:

supplements have both the acids and the glass particles

combined together within the powder the liquid is freezedride so powder and the acid are combined together in thepowder and we just mix it with distilled water so they call

it (anhydrous cement(

**capsules:GIC can also be available in capsules , this capsules is justlike amalgam; one end will have the powder and the other

will contain the liquid it's mixed by shaking it in themachine and you will have the paste coming out (GIC... (

6


7/13

setting reaction : (acid- base reaction(

we mix an acid liquid with a base powder which containsglass, there are stages for the setting reactions:

1(dissolution-:which means that when you mix the acid with the powderthe acid will attack the particles and starts dissolving themwhich will leads to the release of ions (Ca, Al , Na) so this iscalled dissolution(once you mix the liquid with the powder), so the polyacid (contain hydrogen ions ) will attack theglass particle this will lead to the release of many ions (AL,Ca , Fluoride) for example.

2(gelation :-(initial setting(if you remember when we talked about gypsums we saidthe loss of gloss represent initial setting so the material isnot hard but it will start to become hard from that stage

onwardso let's say that it will be in a form of gel (not completelysolid , not liquid or paste ) but it will start to become solidso it called the stage gelation ( what will happen in thestage that calcium willstart to make bridges between the acid chains , thesecross linking between the acid chains will lead the materialto gradually become hard or like the gel.

so calcium ions will go through acid liquid or polyacidchains and will crosslink them together , just like the

polymerization reaction ( free radicals will causecrosslinking between monomer chains and make them intopolymers or larger molecules that are harder, crosslinking

between anticomponents make them harder (when we link

7

so three forms are available:

1(2-bottle system.2(anhydrous cemenet: which is actually a powder and a

liquid but the liquid here is water and the powder here

contains the glass and the acid part.3(capsules : which can provide us by good mixing and it

will minimize the error in mixing because it's mechanical.


8/13

two things together we make it harder.(

the material in the end of this stage is not completely set ,it's not hard enough , it's not strong enough , it's still in gel

form.

-calcium is more reactive than aluminium ions itreacts quicker than the aluminium that's why thesecrosslinking is occurred due to calcium ions , now this is acritical things you need to be sure there is a good isolationaround the filling , no contamination and no dehydration.

you should not stop going air in the filling while it's stillgelling or initially setting , if you dehydrated any loss of

water or if there is contamination with saliva which leadsto removal of aliminuim ions for example this willcompromise the other stages of setting so you needto isolate the material very well (not dehydrated and

not allowed to saliva to be in contact or blood.(

3(hardening:when the material actually becomes hard ,still it's notcompletely set , it's just like amalgam ; it becomes hardafter few minutes but you can't finish it or polish itimmediately we need to wait 24 hours because the settingreaction is not finish yet.

usually this material needs 24 hours or a little bit more)it's hard ? yes but the setting reaction is not

complete.(

in this stage aluminium comes into contact with the acidsand replaces calcium so instead of calcium bridges

between the acid chains we will have aluminium this willleads to a harder material and this will lead to the hard setmaterial so aluminium comes in removes calcium andreplaces it.so initial setting involves calcium with the polyacidand the final setting involves aluminium with thepolyacid.

if you dehydrated any loss of water or if there is

contamination with saliva which leads to removal ofaliminuim ion for example this will comprimize the other

8


9/13

stages of setting so you need toisolate the material very well (not dehydrated and not

allowed to saliva to be in contact or blood.(

so there are stages the final cross-linked cementcontains aluminium cross-linked within the polyacid chains, we've got some glass particles that have not reacted aswell (not every single particle will react ) so the finalcement will be a mixture

doesn't happen with 10 miutes or two hours (this is agradual process(it takes at least 24 hours((

so again any finishing or polishing should be delayed for24 hours

water here is the reaction medium , if we remove it thereaction will not proceed properly

)3ashan haika we don't dehydrated , we don't try to dry upthe material while it's still setting , we need to maintain

water inside so the reaction can proceed normally()wojod el may eshi daroory jedan 7ata el tfa3ol ymshi

la2no el may howeh el wa9at yali b9eer feyo el tfa3ol ,,eza el nayeh enshalat w e7na bna-shef bel material , hadbe5ali el tfa3ol ma ymshi bshkl 9a7 w bel tali el materialma b9erelha set 9a7 w bel tali bt9eer da3efeh w shkelha

7ata mo mzbot(

Sodium fluoride didn't take part of the reaction , theyare just ions present within the matrix or within the

material ; that's why fluoride is not captured by anything ,it's free to be released , this is what special about (GIC) ,it's ability to release this fluoride

another thing if for example if you went to a dentist and heplaced a fluoride gel on your teeth , glass inomer is able tocapture this fluoride and then later on after few daysit's able to release it again this is called (recharging= itcaptures fluoride and can release it ) so it has the specialability to release fluoride (be recharged with fluoride and

release it.

9


10/13

back again over a long period of time (it can continuereleasing fluoride for years but of coarse the intensity ofrelease decreases gradually; it releases fluoride in highamount and quickly at the begining within the first few

hours after setting and then gradually decreased if you eator drink anything acidic (this will stimulate the release ofeven more fluoride because acid slightly attack the glassinomer surface filling this will lead to release of morefluoride

so this material interacts with the oral environment by thisway by releasing fluoride , capturing fluoride and releasing

it again.(

the gelation phase usually ends with (2-3 minutes)after you mix the material ; you can't manipulate thematerial (you can't keep adapting it to the cavity but it stillnot hard enough now within the next minute will start tobecome hard and this maturationor setting ,you can also call it maturation will go on manyhours =24 hoursif you try to finish and polish the material before the 24hours it will be very weak it will start to chip and breakdown and part of this cavity will be deficient (no filling) so

don't do that!!!!as i said usually setting finishes within 24 hour but it cango on for 48 hours for several days.

so the glass particles that haven't reacted are surroundedby silica in a matrix (polyacid cross-linked by aluminium. (

properties-:

when they invented the materials in early seventies (itwasn't like the current materials that we used ; the oldmaterial had to have a short working time or a long settingtime(

so they start to change percentage of certain componentsto make it better and this goes on for all dental materials.

Improvements in dental materials are alwayscontinuous(

10


11/13

The problem with GIC is that they aren't having aestheticslike composite due to their components. Pigments can beadded to make different shades but still it's not our first

choice.we use this material to restore anterior teeth but itdoesn't have the same shade like enamel (it will give nicetranslucency of natural teeth ) that's why it's inferior tocomposite, appear opaque(dull). Not like composite which

appears more natural (it's related to the glass component.(

This material is sensitive to moisture so during setting(atthe first five minute) we need to protect it from moisture

contamination and from dehydration that's why when youfinish placing the material after it set we need to place abarrier like bonding agent for example or a varnish (whichis made of resin and alcohol) when you place it with abrush alcohol will evaporate and a layer will be on the topof GIC, this layer will prevent the material fromdehydration or contamination and help the material setwithout any problem. If any contamination happens thematerial can be easily broken down because it's still weak

and doesn't set properly and it's still immature so it can beeasily broken by abrasion or corrosion.

So after it fully sets there's a less chance to break down orlose of the material (it will be stronger(

Fluoride release*:it helps in:

-fighting bacteria (antibacterial agent(-inhabiting demineralization

11


12/13

-Their action leads to re-mineralization by foldingflouroapatite

Biocompatiblity* :

This material is biocompatible, it's well tolerated bysurrounding structure like gingiva, buccal mucosa and thetongue when it comes in contact with them there's nodamage but the problem is because it contains acid beforeit starts to completely set it's acidic and it will take sometime to become neutral, so if your cavity is very deep itmight be a good idea to place a liner to protect the pulpfrom this acid.

It might cause sensitivity because of it's initial acidity andtake some time(few hours) to rise the PH.

Thermal expansion:

It has a moderate strength, low tensile strength so its abrittle material in terms of thermal expansion it's similar toenamel and dentine so there's no danger of microleakagearound it or percolation and it will expand and contract

similarly not like composite or amalgam.

Now in terms of powder : liquid ratio:If you decrease the P:L ratio the cement will be lessviscous and more flowable which will increase it'ssolubility,so you should not do that with your own. So ifyou want the material to be more viscous you can controlthis P:L ratio but there are available materials in themarket that are available as cementing agent " the P:L

ration is already set",materials that are restorative whichare more viscous and there is also a restorative materialwhich is highly viscous.

So you can play with the P:L ratio a little bit(to somedegree) but if it's increase or decrease this will lead to a

weaker material

12


13/13

Done by : Raya Hijazi

Forgive me for any mistake...Good luck all

Thank you my twini Lamees Nimri for helping me inthis script ma knt b3raf sho ra7 a3mal mn donek

Really thanx

Documents

Lecture 5, Glass Inomer Cements (Script)