"Tissue Management & Impression Techniques"

"For Fixed Prosthodontics"Before we start:

1- this is an easy lecture so don’t start hitting your head by the walls of your room saying: it`s a long lecture I will never finish it, or starting pouring streams of tears on the lecture spoiling it, no, just read it and you will find it very easy.

2- I included the things mentioned in the slides not by Dr with small font (font 12) as usual so you don’t need to go back to the slides.

Now let`s start:

Why the impression in fixed prosthodontics is different?

As you studied in this course(C&B), of coarse in tooth preparation the situation is different, there is tooth, finish line, gum, it`s not like complete denture or RPD just take an impression (actually it`s not just take an impression) but the requirements are different here in (C&B) we need some different details, also you took in tooth preparation that the finish line could be supragingival or subingingival.

Indications for subgingival finish line:

Esthetics, mechanical retention we need 3mm minimum in the anterior teeth and 4mm minimum height in posterior teeth plus tapering within 10-20 degrees, so if you achieve that, your preparation will be acceptable clinically and beyond that you need to think of other solutions, so saying this we can go down subgingivally to increase the height, now if you want to go subgingivally how would you take an impression is by retraction cord which is a tissue management and we will talk about it later in this lecture

Part l: Tissue management

This part the Dr said that he will pass it very fast because it`s not recommended from him to give to us, it`s supposed to be covered later and the Dr will just pass on most things that will make our understanding to the video that was viewed in the lecture better.

Tissue management Aims and principles: why would you retract off the gingiva, simply because you want

to create a vertical as well as horizontal space to push the gum away so there will be access to the finish line so that the material will be injected in.

Techniques

Could be Mechanical, Chemo mechanical, Surgical or Combination of them.

Haemostatic agents discussed below

New cordless techniques discussed below

The impression should provide a precise and clear model of the prepared tooth and the surrounding tissues for the technician to fabricate an accurate dies and to produce a biologically, functionally and esthetically satisfactory fit restoration: So we know that we need to take an impression (accurate impression), and technician to create a model, accurate die (which is the single prepared tooth), and why die? because its removable, you will see it when you start working that this tooth can be put in and out on the same cast.

so you need an accurate impression and accurate die and the technician will have the full information to make the wax up and the laboratory procedures, but if you can`t pick up finish line or accurate tooth this means that your work will not be accurate and if it`s not accurate what will happen is all of this:

Tissue displacement: the proper definition for it is that it’s the deflection of the marginal gingiva away from the tooth.

Tissue displacement purposes:

Is to create sufficient lateral and vertical space between the gingival finish line and the gingival tissue.

Provide absolute control of the gingival fluid seepage and hemorrhage : the most famous material that you use in fixed prosthodontics work is the silicon which is hydrophobic material (can`t work properly when there is blood or saliva) so

"Mun: don’t worry just only 17 pages and you will end this easy lecture"

this is a another objective of retracting the gingiva, also when you do the preparation the retraction cord will help you, when you go subgingivally how would you go there and there is gum on the tooth ?, you will definitely injure the gingival margin, but you want to make the finish line equegingival or subgingival (slightly subgingival) so you will retract the gum using the retraction cord (usually the cord will retract the gingiva about 0.5 mm) then you go down with your finish line at the retraction cord, now when you remove the retraction cord the gum will go back to its place, so at the end you entered subgingivally without harming the gingiva.

So in order to produce that we need the ideal retraction material characteristics:

1- Effective for its intended use

2- Should not cause significant and irreversible tissue damage, the local

damage happens, when you use the retraction cord there will be reversible gingivitis (the gingival index GI increase), and most of the studies that we will pass on said that within 8 days the GI remains high but after that we will go back to normal so the procedure after a while is harmless, but the retraction cord can cause

recession depending on the force as we will see later also the effect on the gum

affected by number of retraction cords that you used, nature of the gingival tissues for ex. If the gingiva was highly scalloped, thin, biotied (not sure) it will be vulnerable to recession so you need to consider these things when you want to choose the technique that you want to use.

3- Should not cause potentially harmful systemic effects

Techniques:

Mechanical methods using a retraction cords:

Simply you push the gum away physically by the body of the cord, and remember if you don’t want to use any chemical agent as the next method you should not use it dry but you

should immerse it in water because if you use it alone you will injure the tissues so never use it alone.

Chemomechanical methods:

Is when you immerse the retraction cord in a haemostatic agent to control bleeding,

so here we use chemistry and mechanical means to control the situation.

Surgical methods:

Electro surgery: fully filtered rectified current (those things supposed to be covered later as the Dr

understood from the coordinator).

Rotary gingival curettage: using bur we cut some of the inner side of the gum to create space but this will cause bleeding.

Combination of these.

But the standard technique in tissue displacement is the retraction cord as the Dr answered one of the students.

Retraction cords:

Most of the dentists use it as a tool to retract the gum so it`s traditionally the most popular method, and there is another methods called cordless techniques we will talk about them later in this lecture.

Safe but to a certain degree, as we said it may cause recession if you leave it long time (you should not leave it beyond 10 minutes, and if you do that the injury on the tissues will be beyond what we said (remember we said that the tissue will heal within 10 days or maximum 2 weeks))

Easy, actually it`s not very easy and its time consuming you need to put it around the tissue ..etc, that’s why they invented the cordless techniques.

Quick

Effective it`s very effective and long history behind it so we know what we are doing and we know the effects of it

Inexpensive this cord is very cheap.

-There are numbers in this slide (slide 11) but they are not clear for what they are so I didn’t copy them.

Gingival retraction cord may damage the periodontal tissues.

Tissue damage may occur, with friable thin gingival tissue particularly susceptible and subject to tearing, we talked about these two points previously.

Factors Affecting Damage:

Force used in packing the cord

Size or Number of retraction cords: the cord comes in sizes 00,0, 1, 2, 3… to give you options which to use

Length of time the cord is left in place within the sulcus

Chemical agent with which the cord has been impregnated.

And these are some studies which studied the effect of retraction cord on the gingiva:

If the gingiva is healthy initially, healing will occur rapidly (yap&ong 1994)

Took about 8 days to heal, but with average postoperative gingival recession of about 0.2 - 0.1 mm (ruel et al.1980)

Healing occurred histologically in 7 to 10 days (godacre 1990)

The damage healed clinically within two weeks as was indicated by the GI (feng et al.2006).

So after these results we can all agree that this technique cause reversible damage to the tissues, there will be some inflammation but by the time things go back to normal.

Haemostatic Agents: (Dr said they should be covered more than this)

epinephrine (0.1%- 0.8%):

creates local vasoconstriction so they can use it as a tool to control bleeding a 1 inch of cord dipped (مغطس) with 1.0mg of epi contains 2.5x ( ونص ضعفين ) the

max recommended dose for healthy patients and 12x( 12 ضعف ) the dose recommended for cardiac patients, so you should have another thought Before using it in cardiovascular patients.

contraindications for epi use in cord: hx of cardiovascular disease, hyperthyroidism, allergy to epi signs of epi syndrome: tachycardia, increase in respirations, nervousness, increase in B.P., post op.

depression---these symptoms will appear after the cord has been in place for a few minutes or shortly after it is removed

potassium aluminum sulfate (ALUM):

only slightly less effective than epi at shrinking tissues

aluminum chloride (Hemodent) 5-10%:

conc in excess of 10% will cause local tissue destruction there are no major contraindications and minimal systemic effects

less effective in stopping the bleeding than the astringent (below), but you

use it to clean the area from debris because if you used cotton you may cause injury again but if you used cotton wet with hemodent it will clean the tissues without bleeding.

ferric sulfate (13.3%):

astringent

very good for hemostasis so it`s my choice if there is problem from bleeding and I have to control the bleeding.

does not noticeably traumatize tissues and heal more rapidly than hemodent

temporarily discolors tissues for 1-2 days

provides tissue displacement for at least 30min

zinc chloride (Bitartrate)8% & 40%:

tissue displacement equal to epi

* tissue necrosis is high

NOT RECOMMENDED FOR USE because more than 10% of it cause high injury to the tissues.

tetrahydrozoline (visine, afrin, murine plus, neosynephrine):

a sympathomimetic amine that produces vasoconstriction with minimal side effects.

The Dr wants us to remember that tethydrozoline cause the same effect as epinephrine in cardiac patients.

New cordless techniques:

Expasyl:

Viscous paste acts as a chemo-mechanical haemostatic and retraction agent so it’s a clay which deflects the gingival, you syringe the finish line so instead of cord packing you just syringe it in and it will push the gum away.

Component

Organic, clay material (kaolin): easy and quick tissue displacement.

Aluminum chloride (15%): haemostatic agent the Dr said zinc chloride instead of aluminum chloride and continued explanation according to this (and I searched on the and I

found it aluminum chloride also), saying that it may cause injury to the tissues with this high concentration as a chemical effect in addition to the mechanical effect from the clay so the clay cause chemomechanical effect (look above zinc chloride is not recommended because more than 10% of it can injure the tissues, and again in the slides its aluminum chloride and he said zinc chloride)

Additional ingredients include colorants, water, and essential oil of lemon.

Cartridge Form Stainless Steel Dispenser

Disposable Tips

Technique Principle:

The strength of the epithelial attachment is 1 N/ mm2

Injured by the application of a pressure of 2.5 N/ mm2

Pressure of 0.1 N/mm2 enable sulcus opening of 1.5 mm & a delayed recovery up to 2 minutes per 0.5 mm opening

Too low to damage , Sufficient to obtain sulcus opening.

Magic Foam Cord:

There is no haemostatic agent, its silicon and silicon is expanding (بنفش) so you syringe it around the tooth using the gun and tip

The first expanding PVS material designed for easy and fast retraction of the sulcus

Cartridge similar to the regular impression materials

Disposable tips

Cotton cap (Comprecap) they are emptied from below

The patient bite on them to push the sillicon material in, and

After 5 minutes the silicon will enlarge

Used with the same gun of the regular addition silicone impression material

Principle of Work:

Silicone foam expands in the sulcus and its mass becomes larger precisely to achieve the retraction we require.

In cordless techniques (both expasyl and magic foam) you should remove and rinse them exactly before taking the impression, and the magic needs 5 minutes and expasyl needs 2 minutes only.

Before you start reading the next part (efficacy of cordless techniques on gingiva and in gingival retraction) Dr said it`s not required because its new things and it was not studied yet.

The efficacy of them on gingival health and in gingival retraction is not studied, but the Dr made a study on them(published in general clinical periodontology, only the effect on gingival health), he compared the cordless techniques with retraction cords, so after tooth preparation on several teeth and before taking the impression he used on one of them retraction cord and on another one expasyl and on other one magic foam, and he followed

the effect on the gum, and he found that expasyl has clinically significant gingival Index more than others, and the Dr explained that by saying that its expectable because it has 15% zinc chloride.

These are the results as in the slides:

Principal findings: all retraction techniques caused a temporary inflammation, measured through the gingival index.The recovery at 7 days was slower for Expasyl. Bleeding during or after retraction was only encountered with the use of conventional retraction cords.

Practical implications: This study showed that none of the techniques tested seems to harm the tissues in the long term; however, clinicians should be aware that Expasyl use is less friendly to the gingival tissues.

Cordless techniques do not require haemostatic agents to control bleeding.

So by now we ended the first part of the lecture (tissue management) with all its divisions aims and principles….. tell new cordless techniques which you can easily read and even if you don’t know the technique you can read it on the brochure behind it.

Part ll: impression techniques

By the beginning of this part the Dr started playing a video about preparation for a molar and the impression techniques and below are the comments by the Dr on these videos (I hoped that I can insert the videos in this lecture but unfortunately it`s not applicable, maybe in the future it will applicable to see videos on papers).

Here (in the video) we decided to make a crown on tooth, so we started preparation using a round end tapered diamond bur no shoulder no chamber just only use this bur and you can prepare everything even the proximal areas, the tip of this bur is 0.8 mm so if you want to prepare a finish line just enter half of it when you are doing preparation and it will make a finish line, and if your crown is metal ceramic which needs 1mm shoulder finish line all the tip should be in and by that you prepare what we call heavy chamfer which is the substitute to shoulder (Dr said that he don’t use the shoulder bur at all, but we as students should study all techniques then select what we like in the future).

As we saw on the video the operator started preparing axially, the Dr said regarding the

order that you may start occlusaly as he do, so as we saw along the same path of insertion that you selected you keep the bur all the way in, then he continued to go proximally (here the Dr mentioned a mistake that the students always make which is

when they go up proximally they tilt the bur proximally) so don’t tilt the bur proximally and be on the same path of insertion.

and as we saw the skillful operator when he went proximally he kept the tilt the same and he entered the proximal area without changing the bur, unlike us (students) we are not skillful and we might change the bur and go to a small thin diamond bur to open proximal

contact so on…, but here he just kept going on because he is very skillful until he opened the contact.

The tooth that the operator was preparing has amulgum restoration which extending to the gingival margin and its one of the indications to go with the finish line subgingival beneath the restoration to house the restoration and as

you know your finish line should be on tooth structure.

One of the students asked about the operator who opened the proximal contact without changing the bur, and the Dr answered that we as students are not skillful as him and we should adhere to the same principles that we read in the books and the things we don’t read we should not memorize it from the clip (so there are different schools).

The Dr emphasized on an important point that the operator made an alignment between the mesial path of insertion and the distal path of insertion to make the same taper (remember we took in the principles of tooth preparation that we need to

keep the taper as minimum as possible).

previously they said that you should make the taper 6 degrees (this came from a study done in the fifties by preparing teeth and calculating the force required to pull the crowns against the path of insertion) and it remains the ideal degree, but recently they revised this

degree and found that we actually don’t achieve the six degrees at all even the specialists can`t achieve it, so the average is 18, 16 if it’s a good preparation, so they revised the study and said that the study examined the resistant to pull upward but

this is not what happen clinically because clinically the tooth is subjected to horizontal forces that’s why the resistance form is more important than the retention form (remember both of them are important), because there is nothing can pull the tooth upward or downward (according to Dr), so here after they considered the previous

things they found that the height with the taper with the other features is the important things in the preparation, so the recommendations mentioned that 10-20 degrees tapered is acceptable if you have 3mm minimum height anteriorly or 4mm minimum height posteriorely because the diameter of the crown is wide posteriorely, otherwise you should think of other solutions like guiding grooves boxes crown lengthening posts building up the tooth core so there are different ways to improve the resistance form.

The operator put guiding grooves then he started to prepare the occlusal surface, and he

followed the anatomy of the tooth so you should be as him, and he used the tip of the bur (0.8mm) as a tool to measure the amount of occlusal reduction also you could use indexes to control that, then the second plane of reduction buccally and palatally, then he came back to remove the sharp edges.

Now in order to assess the occlusal reduction you could use wax by making the patient bite on it then you measure the wax by wax gauge to know the amount that you removed or by the indexes that we talked about previously.

In the video the tooth was 90% ready and the finish line was still on the amulgum, so he needed to take it downward to house the amulgum within the crown.

Always students think that if you do not take much tooth structure then you are good but

this is not true, taking minimal tooth structure is as bad as taking excessive, because if you prepare minimal preparation your technician will either make your crown very big(to get the color as Dr said) to have the enough thickness of metal or ceramic so the

emergence profile will be distorted and it will be aesthetically ugly also it will

cause harmful effects on the gingival margin, or he will make it as its normal size so the thickness of the crown will not be enough (especially occlusally he can`t make the crown big because the crown will be high) and the ceramic will not cover it or there will be perforation so it will be a failed crown, also if you did over preparation you will get as bad results, so you should do what is needed. (here the Dr mentioned example with numbers (I (mun) think they are not accurate and they are different from book numbers so I think it's better not to memorize them and just get the idea)

about the effect of minimal preparation for metal ceramic crown on technician work, for you to cast a metal you need minimally 0.3-0.5mm thickness to cast a metal and at least 1mm for ceramic if it was supported by metal so you need 1.3-1.5mm (in lec 5 its 1.5-2mm occlusal

reduction)preparation and if you prepare below this, you will get the above results).

Now we reached our topic in the video, the operator dipped the retraction cord in haemostatic agent (strengodent as Dr read it) then he took the excessive by gauze and then he applied it, and the ways to do that is many, you can use a probe or a plastic instrument with flat end, also there is some instruments the tip of it is irregular ( to catch the cord to push it or other things flat like plastic instruments you could (مخرمةuse either ( بيمشي كله ) but you should be experience in this process.

Make the cord as a loop, the Dr himself found that if you hold the two ends and you give it a bit of stress ( شوي شديتو ) then you push it, it will slip all inside the tissues, when you push you keep pushing backward means you started from a point you keep pushing toward the starting point with the same direction don’t make like this (I don’t know what he meant by

this but the result of making this this is pulling out the cord from the tissues ), then you cut the excess and you push what remains inside.

As we noticed in the video the operator had a space to prepare mesial to the tooth structure beneath the amulgum and that’s what Dr told us about, that without retraction cord we can`t prepare beneath the gingiva, and regarding the astringent we may put it on

the retraction cord as above or it come in a form of tip and you rub it against the tooth structure to control the bleeding, and as we said before use the hemodent which is a less powerful haemostatic agent than astringent to clean the remaining debris, also you control the moisture using cotton roll lingually, then piece of cotton dipped in a haemostatic agent (hemodent as we said) to clean the tooth and then see how nice and clear tooth structure finish line beneath the amulgum restoration.

One asked about the ferule and the Dr answered that it will be covered more in post crown course.

Now one of the advantages of tissue displacement is that it will enable us to do another

step which is margination, when the gum is away you can see the finish line obviously so you can see the entire finish line to make sure that the finish line is clear all around with the thickness that you want, then you do the final step which is the finishing to remove all the rough areas using either fine grid diamond bur or use a used bur ( كثيريعني مستخدمة it will not take much from the tooth it`s something like polishing, so you remove all (ماحيهsharp areas.

And you do roundation for the cusps because these sharp areas can cause problems to you, any sharp area in the impression may cause voids and when the technician cast it if we got the impression maybe he will not pour it properly because it`s very thin, even if all these things continued good ( االمور كل زبطت لو حتى يعني ) later on even on the crown when he work on these sharp edges he might break them, even if he continue ( مشاها رد )

there will be another chance that in the future after cementation it will be stress areas on the cement, so there is many advantages to remove the sharp areas.

Finally the operator checked for any sharp edges by probe and by howly (spelling not sure)

instrument he did finishing for the finish line or you can use tungsten carbide bur, then he cleaned the area and prepared for the impression, so by now we finished the first step which is the tissue management and the tooth was ready for impression, now as the finish line was clear to the operator he had two choices either taking the impression with the retraction cord in its place, or removing it and do syringing directly.

Then the operator started with the impression (the Dr didn’t about what he did but he

explained what we use in our clinics) by gun we load the light body of silicon on the finish line and on the tooth because its flowable and the heavy body (putty) on the tray so this is the technique the same concept with different material (from the material that operator used).

The operator used a gauze to control the moisture because as you know silicon is hydrophobic material (can`t work properly with saliva and blood), so we use regular viscosity or heavy putty on the tray and why is that means (why we don’t load the tray also with light body?) is because if we load it with light body it will flow and there will be much excess and it may enter in the patient`s mouth, so it will force against the light body (remember it’s the same material with two viscosities, the difference is only in the filler).

The Dr mentioned a clinical point that when you do syringing with the gun always keep material in front of and behind the tip of the gun which means don’t drag the material behind, so you start with bollous of impression then you keep syringing where there is material in front and in the back of the tip.

Then the operator continued syringing the light body for all the occlusal surfaces for all

teeth because its more accurate than the heavy body, so we need the more accurate light body on all the teeth because the die is not the only thing important, we

need our impression to be accurate on all teeth even those on the other side because these teeth after pouring the impression will be articulated against the opposing arch and if

the other teeth were not accurate this means that your mounting will be wrong and

the occlusal surface shape of the crown will be wrong, so don’t be as one of the students who asked the Dr "I want to make a bridge, can I get sectional impression?" and of

course the answer is no, you should get full arch impression.

Finally he removed the impression and he inspected the impression, and here the Dr pointed in the video on the impression and pointed on depression in it, and that depression is the finish line and the part of the impression which is coming upward toward us and has irregularities is the material that entered subgingivally beneath the finish line.

I found the picture beside on the net I think it can help

you understand.

This is the finish line

One of the students asked about all the previous process and that it will take long time to do it, and the Dr answered that it’s a step by step, applying retraction cord will not take 10 minutes and finishing will not take more than 2 minutes also drying doesn’t take time so it will not take long time, but if your preparation was bad it will take long time.

The Dr showed us another video, we saw in it how the nurse was removing the

retraction cord and the operator following here directly with the impression material and

that is to prevent any leakage of fluid or blood in the place of retraction cord, so you need someone to help you with this.

Now one should ask why here the operator removed the retraction cord while in the previous case he didn’t?

Will this depends on the case, for example if you put the retraction cord and still the finish line is not clear you should remove the retraction cord because when you remove it there will be space so the impression will be better, but if you put the retraction cord and the finish line became clear and you are afraid that if you removed the cord there will be bleeding and you are working on posterior teeth it will be better to take the impression without removing it.

There is also another technique which is the double retraction cord where you use

two retraction cords above each other, you put first very small size cord (size 00) then

you put (size 1) on top of it so there will be two retraction cords beneath the finish line,

then before taking the impression you remove only the larger size and you take the impression above the smaller size which prevent bleeding or seepage of fluids, finally

you should always check that there no remnants of impression material .

That is the material that entered beneath the finish

line

By now we finished watching videos and the Dr started passing on the remaining slides, saying that it’s a revision and you can read it by yourself.

Remember in fixed prosthodontics we use only rubbers which are below

"Mun: did you see how this lecture is easy, just 5 pages and you will finish"

Classifications:

According to elasticity:

According to viscosity:

Available materials:

Polysulphide:

Base:

Short chain Thiokol polymer.

Used extensively in building industry where it is supplied as a one pack and setting takes place under atmospheric oxygen (weeks). This is regarding using in building not in clinic

In dentistry, setting is brought about by oxidizing agent (lead dioxide)

Molecule of water is produced for every link that is made. (condensation)

Objectionable odor

Long setting time (9 minutes) so it`s one of its problems

High shrinkage because of its water byproduct so it will cause dimensional changes

High tear resistance so it go out from undercut without tearing (maybe it’s the only advantage)

High permanent deformation.

Actually the Dr didn’t ever use polysulfide because of its bad properties (bad smell in addition to above bad properties)

Polyether:

Base:

Polyether polymer with imine group

Plasticizer & Inert filler

Activator:

Aromatic Sulphonate

Plasticizer & Inert filler

Short working time

Less permanent deformation than polysulfide but not as low as silicones.

Stiff (very rigid) not while polymerizing but once it set (polymerized), the Dr mentioned a story about this point, when he was training he took an impression for an implant with polyether because its rigid (the impression material for implant should be rigid), so when pulled the impression he pulled the bridge on the other side from its place because this material is very rigid, so if there is a lot of undercuts bridges or whatever block it with wax then take the impression

The least dimensional change except the addition type silicone, so it’s the best after addition silicon (regarding stability) because it doesn't have byproducts.

Absorb water (like alginate) so between the impression and pouring make sure that it`s away from water.

It`s hydrophilic so if your tissue management is not very good you can use it, unlike silicone which is hydrophobic.

Silicone Rubber:

Condensation Type

Base:

Hydroxyl terminated Dimethyl siloxane (reactive OH).

Catalyst:

Alkyl silicate.

Different viscosities produced by different MW of Dimethyl siloxane and the concentration of the filler.

Condensation reaction producing alcohol. Resulting in dimensional change occuring mainly during the first 24 h.(remember its very good and accurate material but dimensionally not stable)

Addition Type (Polyvinylsiloxane):

Prepolymer of polydimethyl siloxane in which some of the methyl groups are replaced by vinyl groups in one paste and with hydrogen in the other paste.

Catalyst: Platinum containing compound (chloroplatinic acid).

Addition reaction producing no by products.

Increase in Temperature and Moisture increases the reaction.

Early when they first introduced it (1950’s), gaseous hydrogen was produced as a result of the cross linking reaction. Mechanism is unclear !(side reaction of the hydroxil group ? Or a reaction of the catalyst with moisture??), but in the new products they got rid of this problem.

Comparison of elastomers:

� Setting time - Polysulfides (longest)> Silicones > Polyethers

� Tear strength - Polysulfides > Silicones > Polyethers

� Stiffness - Polyethers > Silicones > Polysulfides

� Dimensional Change - Cond Silicone (the worst)> Polysulfides > Polyethers > Addition Silicone

The Dr pointed to main indications, if you want to do crown and bridge work use

the best material (addition sillicon), for implant use polyether, for complete denture use either addition silicon or use ZOE as you do in the clinic because we

don’t need it to be elastic or you may use polyether but the technique is different

(with one shot you do border molding), for partial dentures use addition silicone or alginate (but take care of its dimensional changes), so by now you are not excused if you were asked about them in viva exams.

Packaging & Techniques:

The material may come as putty (معجونة), or heavy body or light body and the difference between them is in the filler and they differ in the flowability, the heavy body on the tray and light body on the crown.

Trays:

Routinely we don’t use custom trays, we use stock trays and the best tray is the one who covers the teeth and is rigid, notice for example the silicone, the spacer in it

is not that important (we want spacer if we use heavy body but the light body don’t need much spacer same as ZOE).

The more important thing is that the tray should be rigid, because if you want to use heavy body or putty with the red tray which is flexible (look to the lower picture right)the tray will deflect and the impression will be deflected (because silicon is accurate if the impression deflected it will remain deflected).

You could use custom tray if you have big mouth and you don’t have stock tray that cover all teeth, but not for the purposes of thicknesses because silicon is accurate in either thin or thick sections and at the end there is no dimensional changes.

This was previously important when they were using the condensation type, because as you lower the amount of material in the impression you lower the amount of dimensional changes.

Stainless steel perforated trays(metal)(left)Polytrays (Polycarbonate/Yellow) (middle)Orthodontic impression trays(red) (right)

Disinfection:

DISINFECTANTS FOR IMPRESSION MATERIALS:

Glutaraldehyde:

� - Indicated for all impression materials except hydrocolloids

Phenols:

� - Indicated for polysulfide rubber base only (so you will never use it because the Dr didn’t ever use polysulfide)

Iodophors and NaOCl:

� - Indicated for all impression materials.

The end

Normal thanks to saleh alqadi for hearing a one word in the record

Any feedback is partially welcomed

Good luck for everyone in the next uncountable exams

Done by: muntaser ghassan toffaha.