Dental Base resin ( LEC. 5 ) Uses

Dental resin materials or acrylic resin material has multiple uses not just for making denture they can be used to :-

make special tray or custom tray

to make a base plate on which we attach the wax and set the teeth

and they also can be used for repair for relying denture

Process of making denture involve tacking impression ,pouring the impression to make a module doing a wax up then de- waxing “removing the wax” then replacing it with acrylic risen material and do the procedure of processing or flasking to cure the material and allow it to set and then u finish be polishing your prosthetics and give it to you patient

Why acrylic risen material

now the material of choice for this sort of restoration “ which is complete or partial denture” acrylic risen material . among good properties that it’s cheep , it’s easy to use and process it’s provide reasonable aesthetic but it’s disadvantages it is not strong enough especially the impact strength “ that mean if it drops on the floor it can be easily fractured “ …. it used to be translucent so if your patient swallow part of it , it won’t be visible in the x-rays but newer material have component that are radio oblique so u can actually see it on radiograph

if part of the denture break off and the patient swallow it , it’s important for us to see it on a radiograph we want to see if it in the stomach or in the lung

if in the stomach -------- good news :P if in lung -------- bad news

another disadvantage it is susceptible to distortion it might distort . and if it distort it wont fit probably

it got low thermal conductivity why is this bad if a patient drinks hot drink “too hot” . and the material slowly transfer s the heat he might actually burn a tissue without actually feeling quickly enough that he drinking something is very hot so he dose not relaise that he’s drinking very hot liquid and it’s already in his mouth and there is a chance to burning his tissue underneath the denture .

patient commonly burn there tissue because the material does not quickly give the sensation of heat because it hve low thermal conductivity .

as I said it can be use to make denture , acrlic teeth , denture teeth also can be made from acrylic material base plate or special trays some if can be use for relying denture to make the fit properly ,, some time if the denture making trauma to the tissue we can use what we call a tissue conditioners again making of acrylic material powder liquid mixed together it’s placed on a inner surface of the denture and it will act like a cushion it’s soft so the patient could continue wearing the denture and it will not heart because something is cushioning his tissue and it’s more comfortable .

this is an example of heat cure material “powder and liquid component “ it also can be called cure which mean I can set be time no need for heating

some of the material as was mentioned in the LAB light cured materials some of them are pour and cure risen “which mean that they are highly flowable you mix them and u actually pour them to the mould or the flask .

In genral the reaction is polymerization reaction , so we got monomer cross linked to polemer

so the monmer is called methyl acrylate and the polymer is polymethyel acrylate , this a commonly used material . There is for example poly ethyl acrylate which is slightly different .

as a definition a polymer is made of large long chain molecules formed by chemically joining smaller molecule together .

what decide weather the end product is flexible or rigid it depend on the bond “ the cross linking “

it they were strong and highly charged then the end result is a rigid material if the bond between the component slightly weaker than this the the end result material will be slightly flexible

Briefly, what do we mean by addition polymrayzation reaction it got four stages

the first one call the activation …. Followed by intiation …. Two occure togother

two ways to activating these materials either by heat hence we have heat cure material or by certain chemical materials in the chemical cure material

when does the reaction starts ? - once you mix the powder with the liquid now the activator is present in the liquid so the initiator will be present in the powder

the chemical activator mostly is called tertiary amine

the most commonly used initiator is benzoate peroxide {you have to memorize them }

this is in chemical cure material

In heat cure material the intial is benzyl peroxide but the activation occure by heat “ when we place the material on hot water ‘

What will happen when these come on contact benzyl peroxide start to break up and release very active component we call them free radical

Free radical are very active the start breaking bond and making a new bond and cross linking between different monomers

Once all monomers are tighte up or no more free radicals reaction stops terminates

So again we have initiation, activation ,propagation that’s mean that the reaction is continuing by macking new bond breaking old bonds … and once there’s no monomers or no more free radicals the reactions stop and the setting is final which is termination

this what we meant be addition polymrayzation reaction and usually it is not accompanied by byproduct formation ,,,,,remember addition selicon so this basically what happens in addition selicons materials same steps . same principle

now in condensation polymerization usually there is more than one type of monomers and usually assiociated with byproducts whether it hydrogen , alcohol or water . so it’s different

so addition polymrezation are more stable dimenshinaly because theres no byproduct formation “general speaking”

Heat cured resin

composition of the material

as we mention before powder “polymethyel acrylate” and liquid “methyl methacrylate monomers “

the powder is made off small particles or granules , these granules are actullay polymerized methacrylate “ so it is a monomer that had been polymerized and then dryed up and then ground up into a small particle , it has intiator it has pigment for different shade and different color it has material to make it radio obaque we calle it opacifiers , it got plactifiers tomake it easy to manibulate and synthetic fiber these synthetic fibers look like small just to make it look more natural so these are the major component of the powder

liquid as mentioned is methyel methacrylate material and it has a cross linking agent to add strength and stability to the materials and usually ethylene glycol dimethacrylate is the most common used cross linking agent in this material

so we said there is heat cure , cold cure , light cure ..ect ,,

some time we don’t need to place the material in hot water we can use another source of heat .. the microweave but u need to be carful or in these cases the don’t use metal flask because if you place metal in the micro weave what will happen? it will exploed , so they use plastic flask , so this is a different source of heating

pic on slide # 14 represent the flasking steps

once you mix the powder and liquid you will get different stages through out the setting process we have the

intial stage “ sandy stage” material has sandy texture very flowable it will not be easly mainbulated i

second stage the sticky stage u can’t actullay mold it as u like

and then we have the dough stage it’s cohesive not sticky u can manipulated ,shape it as u like

rubbery stage the doctor didn’t say any thing about this stage

then we place it in the flask then we close it up

the Dr’ pointed that when we close the 2 part of the flask we must have excess coming out indicating that there’s an enough material so your denture will not be deficient in certain area

so we close up the 2 part of the flask then remove excess open it again any ensure that the excess are removed the closed up placed in hot water

why we have the acrylic reisn this way composed of powder and liquid with polymerized methacrylategranules ? ,it has a purpose

now in general when we have material that contain a monomer and is going to polymerized when the reaction goes on some shrinkage might occur we call this polymerization shrinkage

we don’t want a lot of shrinkage . if it happened “ lot of shrinkage” your denture will be deficient “small”

if part of your mix is already polymerized the the polymerization shrink will be less that’s why the powder contain pre polymerized poly methyl methacrylate the particle is already polymerized and done and you mix that with the liquied so because we are decressing the amount of monomer you are decressin shrinkage because part of the material is already polymerized

so this composition will decrease polymerization shrinkage and also will decrease the exothermic reaction the heat that come out from the reaction .

the steps of processing it’s called

flasking when you place your model which has wax and the teeth in the flask

when u get red of the wax it called de waxing then u need to place you acrylic material then u pack it close it up remove excess we call it packing and the the processing is when you heat curing

it’s very important when we clos up the flask to do this under pressure because if there isn’t enough pressure to close up the flask completely metal to metal contact the material maught separate the 2 part of the falsk from each other during processing and your denture is going to be to high in the patient mouth .

the process of flasking is need to be very accurate

the length of time you need you need to place your flask for curing there are different ways curing the material one of them is facing it to 74 degrees for 8 hours or longer so some time we palace it in hot water path “of 74 degrees” and leave it overnight next day it will be done

there is another way of doing it place it on 74 degrees for 2 hour then boiling it for 1 hour this is a short cycle

after the curing are doin there is the coloing process

cooling need to be slowly you don’t place it in the fridge for it to cool quickly because if u do that u will distort it “ distortion” of the shape of the denture

after it cool “slowly “ we can take it from the flask polish it and give it to the patient

MMA monomer “methyel methacrylate material of the liquied “

it is volatile so it should be kept in a sealed container it is flammable so shod kept in a safe place a way of fire and heat

and it should be kept a dark container because some light may be actually activate it and produce free radical and it will sart 2 polymerize

they shouldn’t be any contact between the material and the powder until we want to mix it and work on your denture

it’s an irritant material so we have to wear gloves when we work on it

COLD CURE MATERIAL

It’s similar but it has an activator which is tertiary amine

It also has what we call an inhibitor hydroquinone now this inhibitor the reason of that is to make the material last longer on your shelf when you store it

What does the inhibitor do ?

It capture the free radical so the reaction does not start by it’s on that’s one thing the other thing that when you actually mix the powder and liquid your working time will be longer so u have enough time to manipulate the material and place it in the flask

So it’s prolonged the shelf life and it’s prolonged the working time because it capture the free radical prevent reaction from occurring very quickly .

So cold cure material is mixed in the same way powder and liquid then you mould it in the dough stage and make special trays or baseplate from it..it’s got different properties compared to heat cure material,,the granules or particles are smaller so that you can mix them easily with liquid.. and it terms of properties, compared to heat cure material if you make a denture from cold cure resin it’s going to have lower strength, lower stability,there is a chance of unset or unpolymerized monomer which can irritate the patient,, and the shape may change a little bit. It is susceptible to creep.. those are the disadvantages of cold cure acrylic compared to heat cure acrylic..lower color stability, more susceptible to distortion,more residual monomer, loer strength.

Some say that because you are not directing it to heat,there’s less stress within the material so it’s more stable dimensionally.

Pour and cure material

It’s very flowable, it’s mixed and poured into the mould,because it’s flowable , it gives us very accurate details which is very good,,but because it’s highly flowable it’s not very strong and that’s one of it’s problems it’s very weak.

Light cure material

It’s composition is slightly different, because it’s light cure, and subjective to light,it has to have components that are sensitive to light to initiate setting. This photoinitiater is called camphor quinone. Which is a commonly used photoinitiater in acrylic resin, in tooth color filling composite. Once the material is subjected to light it’s going to cause the release of free radicals and reaction will go on.

A type of monomer or polymer which also may be different in it, is urethane dimethacrylate. It also has fillers and silica to control the flow. So components are slightly different. It can be used to make special trays it can also be used to make a

whole complete dentue. You can see that it is adapted on the mould and then teeth are set, carved ( to make it more esthetic) and then it is light cured.

Light curing can be done either in a chamber of light or by using a light cure device by subjecting it directly towards the material.

A very important rule is to always use the manufacturer’s recommendations in terms of liquid powder ratio and manipulation( working time, setting time,..) . for example if you add too much powder , or too little monomer ,your mix will be very dry, grainy and this can lead to porosity in your denture at the end, there’s no chance of voids or bubbles. If your mix has too much of the monomer and too little powder, there will be more exothermic reaction (more heat) and this residual monomer will cause more irritation and more polymerization shrinkage.

Another important thing to know about is the pores that can occur within the material or within the denture. One of the mistakes that can happen are pores which can be generated within the denture , it can be caused by many things, one of them: if you are placing your flask during setting in extremely hot water for a very long period of time, the monomer is going to evaporate more than it should, leading to voids in the denture, this is called gaseous porosity, or volatilation porosity. Due to evaporation of the monomer,, so this happens if the temperature is beyond the boiling temperature of the monomer.

Another type of porosity is contraction porosity or polymerization shrinkage. Which mainly occurs if you don’t put enough material, part of the denture will be deficient or has pores in it because there is no enough acrylic resin to fill that needed area. You need to put excess, you need the material to be in the dough stage, so that when you place it under pressure it will flow and cover all the necessary areas and if polymerization shrinkage occurs there will be no shortage you will have enough material, and if you don’t have enough or if you don’t patch the material when it’s in the dough stage this can lead to contraction porosity.

If your mix has more powder than it should have or if the monomer evaporates ( if you don’t cover the container after mixing) it can cause another porosity called granular porosity.

All these porosities weaken your denture, make it look unesthetic .

Gaseous porosity, a note on it,, where does it usually occur??in Gaseous porosity we need very high temperatures beyond the boiling temperature of the monomer for it to evaporate and cause pores,, this happens in the thickest part of the denture, when you’ve got more material then you’ve got more monomer and more chance of excess monomer evaporating. In the upper denture the thickest part usually is the palatal surface of the teeth. So this is where temperature might rise too much and cause evaporation and gaseous porosity.

gaseous porosity :

to avoid gaseous porosity , by allowing a slow and controlled rise in temperature .So when we place the material in hot water , we need to raise the temperature slowly to avoid gaseous porosity , and of course not to reach the boiling point beyond the boiling point of the monomer.

another example are internal strains that can be created within the material , after processing I need to allow the flask to cool down slowly . if it doesn’t cool down slowly ,stress is going to be created within the material , any stress needs to be released . if this stress is released it’s going to change the shape of the denture . So I want to create as minimal stress as possible , one of the ways to avoid generating the stress is cooling down the flask after processing slowly . Another way of avoiding generating stress is using acrylic teeth rather than porcelain teeth .

Porcelain teeth are very esthetic, but they don’t bond chemically, we need to bind them mechanically . However, the acrylic material they bond chemically, they have ( acrylic ) similar coefficient thermal expansion to the denture base material . So there is no chance of deep bonding or stress being created, it’s the porcelain teeth attached to the denture they contract and expand in a different way because the coefficient thermal expansion is not similar, this generates stress that goes to the denture material itself and this stress can cause distortion or dimensional instability in the material . so using acrylic teeth which have similar properties to denture base material minimize stress, slowly cooling the material after it set also minimizes the creation of stress , which means you have less distortion and less stress .

Alright, properties of the resin:

Biocompatibility, cheap , easy to process , provides good esthetic . the biocompatibility: it’s got good biocompatibility but , some patients might be sensitive to the monomer if I caused irritation , they might cause allergic to it . There are alternative material such as poly carbonate material that can be used in a similar way to make the denture if your patient is allergic to PMMA .

Another problem with these material: they can fracture easily especially if they dropped down on the floor , so they have low impact length . sometime creep is the problem , so there shape might change by time ,this can be avoided within the material because of the cross linking agent . Another thing that can cause fracture If the denture is under stress over a long period of time which occurs if your denture does not fit properly in the patients mouth, if it’s not stable under continuous pressure and mastication this can create fatigue and can cause fracture of the denture . Sometimes if there are defect or porosity in the denture it can lead to also to fracture .

To improve the strength of the material , you have to give it a better impact strength to resist fracture if it’s dropped on the floor or in the sink . One of the modification is adding rubber, if ou add rubber to material you make it more flexible .

Adding rubber material can improve the impact strength and decrease cracking .

But , because the material is slightly flexible over a long period of time due to fatigue it can fracture . Another way of improving the strength of the material is reinforcing the material by adding fibers that can be made of glass or polyethylene fibers or carbon fibers .

Better choise is the glass fibes and Polyethylene

Polyehelyne they are good , biocompatible , no color , but they take time to process and incorporate to the material , so the glass fibers are usually the better choice .

So these are just two ways to make the material stronger.

We said that is got low thermal conductivity , it’s coefficient of thermal expansion (CTE) is High , so If you got porcelain teeth attached to the denture they might be deep bonding , because they don’t have same CTE . The material absorbs a bit of water after setting , it has low solubility , we always advise the patient after taking the denture to put it(denture) in a humid environment , because if not , it will dehydrate and it can

also distort . So it need to be cured in a humid environment either in a wet paper towel or in a glass of water.

Another use of this material is to replace missing facial part due to cancer or accident.

Procedure is similar: you take an impression, you make a model , you design the shape for a nose or an ear or eye .. but the important is that what is the material you’ll be using ? this material is going to be attached to the remaining part of the face , you got muscles , skin and flexible tissues , you need the material has high tensile strength , you need it to be not rigid .

so , PMMA is hard and stiff . Polyurethane may be used.

Now me move to another part of the lecture :

Artificial teeth :

Requirements :

1- good appearance

2- be able for bounding with anddenture base

3- resist abrasion or wear

4- has strength and toughness

5- Allow adjustment when checking occlusion

Two parts of teeth are available : acrylic and porcelain .

each one of them has advantages and disadvantages :

Acrylic teeth are usually made by using molds (reusable molds ) these teeth usually they divided them into 2 or 3 parts : one of them in the base which is going to be attached on the denture material

The maining part : the incisal or the the middle part of the tooth

these have many different properties :

The part that is going to be attached on the denture is a little more soft , because you want it to be able to integrate itself and to attach itself to the denture base material , so you want it to be slightly softer .

the other part ( Incisal half ) , made of highly crosslinked or strong polymer , the base is slightly soft ,so that it can attach itself in a better way to the denture base , bond with it chemically . the insical half is regulalr crosslinked , strong and rigid .

Porcelain teeth : when they make them they use a mold that is slightly larger than the actual size of the tooth because after it is set , porcelain usually shrinks a little bit .

because it’s not of the same chemical composition as the denture they need to attach the denture mechanicly , these provide mechanical retention of porcelain teeth on the denture base .

acrylic teeth ( chemically bond ) they do not harm natural teeth or cause any abrasion , you can easily do occlusal adjustment , you can polish them easily . The problem with them is that they wear quickly and they stain over time (because they are weaker than porcelain teeth)

porcelain : they have better esthetics , biocompatible , fail resistant . But, because they are tough you cannot make any adjustment of the shape or length of the tooth , they can wear opposing natural tooth , heavy ,produce a clicking sound , they are more expensive

Denture lining material

3 types :

1- Hard relining material2- Soft liners 3- Tissue conditioner ( when the patient has injury or trauma due to a sharp area in the

denture for example , he uses a tissue conditioner because it’s very soft , so the patient can wear the tissue conditioner and the tissues will heal . the problem with tissue conditioner Is that it will be hard with time , so you need to replace them every 2 or 3 days . so it need frequent replacement .

Now ,it’s ( tissue conditioner )made of polyehtylmethacrelate ,but it has no monomer , so it does not cause irritation

Hard relinig material :

when we use it ?

1- poor retention and stability

2- loss of vertical dimension

3- Part of the denture was destroyed or broken off .

4- Some patients specially old patients who cannot get used to a new denture easily they want their old denture so you can reline it for them to make it thick properly .

5- If the denture does not extend where it should be to give better tissue support .

Material used :

Heat cure or cold cure powder : PMMA liquid : MMA

There is another type of monomer called PEMA but it’s less irritant . Now cold cure material , easy to mix immediately , place it in the denture , place it in the patient mouth , But , it has disadvantages , you cannot actually control the amount of material you are using , it has poor color stability , exothermic reaction can actually cause burning sensation , poor taste .

Heat cure material : processed in the lab , it’s added on the fitting surface of the denture , placed in the flask , and then processed in the denture in hot water .

Now, there are soft lining materials that are semi –permanent. so it’s only a temporary solution , they can last up to 6 month , usually we use it if we make a denture to a patient , it’s a good denture , you will not see anything wrong with it , but still the patient complain with pains and he says that it’s not comfortable we use this ( semi –permanent solution ).

We can use it up to 6 months.

so this is usually accompanied with mandibular denture . The problem with mandibular area that there may be some resorption so it won’t be comfortable ,sharp and less stability . However, the upper ridge has a good adhesion and good retention, so it provides good support.

So any material to be used as a soft lining material needs to be resilient, flexible.

They also have plasticizer : to lubricate and to make the material more flexible.

Material are used as soft lining material, they can be based on rubber, or acrylic

Rubber: because they are made of a material different from acrylic you need something to bound them , so they need a bounding agent . usually they use a coupling agent , so they brush the coupling agent or liquid on the denture and then they place the soft lining material . The only disadvantage of this material is that weak bond and it encourages Candida Albicans.

Acrylic soft liners : ( based on acrylic )

1- leachable plasticizer systems composed of a mix of PMMA and PEMA

2- polymerisable plasticizier system . now , this sytem(polymerisable ) is unique, because it ‘s at room temperature they are hard but once you place them inside the patient mouth at this temperature 37 C .

Both materials are based on acrylic, PEMA or PMMA, they have also plasticizer to make them flexible. The 1st type of plasticizer leach out so it becomes stick, the other type give a unique property to the material where it becomes soft and flexible when it’s in the patients mouth. So they can be supplied in cartridges so you can actually inject on the fitting surface of the denture.

this table compares between the silicon rubber and the acrylic denture :

Silicon rubber material AcrylicHighly resilent Less resilient

Retains softness Goes hard with timeRequires bonding agent Self-adhesive

Susceptible to C.Albicans More resistant to bacteria

Weak bond Permanent bondPoor tear strength Acceptable tear strength

No permanent deformation Susceptible to creep

The doctor is going to answer midterm exam questions

She says : 30% of the final exam will be from the Midterm material .

QUESTIONS : Q1 : which of the following statements is true of gypsum material form1 ans : non of the above form2 ans : non of the above

Q2 : the following is true of dental stone except form 1 : stronger than die stone

Form2 : ideal formating wax pattern for crown

Q3 which of the following is false of mixing gypsum

ans : increasing the rate of spatualtion prolong the setting time

Q4 which of the following is true of mixing gypsum

Water temperature higher than 100 F can retard the setting time

Q5 : which of the following is not true of high strength stoneans : may be used in making study models for crowns and bridges

Q6 : which of the following is true of gypsum material

Ans : exothermic reaction

Q7 : which of the following describe gypsum that is found in nature

Calcium sulfate dehydrate

Q8 : which of the following describe gypsum that is processed by manufacturer

Ans : Calcium sulfate hemihydrates

Q9 :art portion of the diagnostic cast :

Ans :Base

Q10 : anatomical portion of diagnostic : ans : soft tissue & teeth

Q11 : which of the following is false of gypsum storage condition :ans : all are correct , non is false

Q12 : which of the following is false of agar material : ans : they are classified as non-aqueous material

Q13 : which of the following are false concerning agar :

May not be used in areas of under cut

Q14 : zinc oxide euginol impression material are characterized by : ans : all are correct

Q15 : impression plaster is susceptible to distortion mainly due to ans : the fact that is scored in the mouth and removed in pieces and reassembles extra orally

Q16 : disinfecting impression may distort the impression:: ans : if the disinfectant is not compatible of the impression materialQ17 : which of the following is true of alginate : ans : two are correct !Q18 : polysulfide material : ans : two are correct !Q19 : which of the following statements applied to condensation silicon :ans : two are correct !Q 20 : which of the following describe chroma :ans : color intensity Q21 : toughness refers to: ans : the ability of the material to resist permanent deformation Q22 : which of the following is true of high strength stone : ans : has high abrasion resistance

Q23 : which of the following components in agar insures the set of gypsumans : potassium sulfate :Q24 : which of the following are false concerning agar : ans : may not be used in areas of undercut

Q25 : disinfecting impression is done using :ans : a spray Q26 : which of the following is false of addition silicon :ans : palladium powder in incorporated to absorb release nitrogen .

Sorry for being late , Sorry for any mistake

Done by : Mohammed Al Wir

Nagham Rabi

Abdullah Waddah

Majd Hidmi .

Congratulations it’s the last lecture in this year .. enjoy studying !