Prostho III Lec 3 (1)

7/28/2019 Prostho III Lec 3 (1)

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CLINICAL AND LABORATORY PROCEDURES IN

CONSTRUCTION OF COMPLETE DENTURES*Complete Denture definition:

-A dental prosthesis that replaces all of the natural dentition andassociated structures (the mucosa and the bone) of maxilla and mandible.

-Most of the time it is supported by mucosa or sometimes by dental

implants.

*Objectives of complete denture

hetic.

*Steps in fabrication of complete denture:

1-Clinical examination

2-Tray selection

3-Primary impression

4-Primary cast

5-Secondary impression

6-Secondary cast


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7-Denture base fabrication and Occlusal rim

8-Articulation

9-Setting of teeth, Flasking, dewaxing and curing

10-Trimming and polishing

*First: HISTORY AND EXAMINATION FOR EDENTULOUSPATIENTS

,nameSo after you opened a file for the patient, you'll include in it his-

past dental history and why he,occupation, medical history,gender.is coming here

Q: Why do we need to examine and record the history of the patient?

1- Recognition of relevant anatomical, physiological andpsychological conditions , for example the patient might have someanatomical difficulties in his jaw that will make you unable to make asatisfactory complete denture, or if he has a psychological disorder so you

can't deal with him so you'll refer him

2-Understand significance of medical status , because medical conditionof the patient is very important.

- e.g.: if he has diabetes then you have to consider that this patient mighthave reduced salivary flow or he is taking medications that reducessaliva, or his mucosa might be more prone to trauma more than other

patients, or if he has bleeding disorders, so you have to be very careful inthe selection of the trays and taking your impressions in order not totraumatize the tissues .

3- Development of treatment plan (prescription of prosthesis) , whatyou are going to do for this patient for example if he has several difficultanatomical land marks, or a flabby ridge or a enlarged maxillarytuberosity so you might need a help from a surgeon to reduce it or youcan use special impression technique.

4- Assessment of existing dentures , so the patient is coming to you toget a new denture, so you want to investigate what was the problem with


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the old denture and why he is going to replace it? Is it about the stability,the retention, the function or the appearance? In order to avoid these

problems in the next denture.

5-Why the patient is seeking this treatment.

*Extra-oral examination

-The extra-oral examination should look for:

1- Temporomandibular joint (TMJ) : so you want to investigate if the patient is opening his mouth normally or not, is the opening sufficient to

insert the tray inside the patient mouth?

- or for example if he has pain or a problem in the TMJ you cannot proceed making complete denture for this patient, you have to refer himfor a specialist in oral medicine or in oral surgery to investigate and solvethis problem, because if you construct a complete denture for this patientyou'll aggravate the problem rather than solving it, because there may beincreased or reduced vertical dimension, so you should palpate externally

and from inside the ear: pain, clicking, limitation of movement,extreme deviation .

2- The patients face height , because it will affect the vertical dimension.

3- Any facial asymmetry including the centre line ; usually we makethe center line of the face between the two central incisors along the midline of the face and the middle of the nose and the philtrum.

-some patient might have deviated center line and you need to consider this during the try-in or delivering the denture, and the patient preferenceif he want the centre line as normal or shifted toward his mid line.

4- The lip line, some patient have short lip and some of them have longlip, so if he have short lip this means that too much of the acrylic of thedenture will be shown, or if he have long lip and you're going to constructthe conventional complete denture this means that there is going to be notmuch of the denture shown.


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-Lips also include the smile line as all these features will need to betransferred to the patients' dentures.

- The degree of over closure will also need to be assessed and this will

help with deciding on how you want to make the denture.

-this means if the patient has deep overbite, for example if the patientcloses his mouth there is no space between the upper and the lower edentulous ridge, and this means that you are not allowed to increase thevertical dimension very much, so it need to be assessed and this will helpwith deciding on how you want to make the denture.

-All of these points are concentrating of the extra oral examinations; whatabout intra oral examination?

*Intra-oral Examination

-You need to examine in the patient mouth by eyes and fingers, weexamine:

1- Soft tissue : to see if there is a trauma for example or any important

lesion to know if you need to refer him.2- Salivary flow : to see if the saliva is normal or increased or reduced soyou might have an underlining medical problem.

3- Sulcus depth: as it affects the retention of your denture, if he has flatridge for example and no sulcus, then you expect your denture to havereduced amount of retention, so you consider that, for example by takingspecial impression technique or telling your supervisor that this patient isnot suitable for me at this level.

4- Ridge anatomy : does the ridge have enough height and depth, and it'sform (firm or flabby)

5- Inter-ridge relationships: class 1, 2 or 3.

-class 1 is normal and easy-class 2 might be difficult and it's prognathic- Class 3 is the more difficult which is retrognathic.


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- If already wearing dentures: denture assessment : fit, retention, stabilityand occlusion or the patient might ask you to copy the denture if it isalready satisfactory?

-The first step in intraoral examination is to open the mouth and to look for anything abnormal, like the color, consistency and appearance of themucosa.

*Maxillary arch: the most important thing here it to look for themaxillary tuberosity (the red circles), in most patients it's normal, in someof them it's enlarged, either bony or fibrous enlargement.

- If it's enlarged it will affect your impression so you'll need aconsultation by special prosthodontist or a surgeon.

- If the enlargement is fibrous then you can do your conventionaltechnique without problems

- If it's bony you cannot do it because there will be too much undercutand this means that you have to refer the patient to oral surgery to excisesome of this bone

*Mandibular Arch : the two most important areas here we haveretromolar pad and the mylohyoid ridge.

-the retromolar pad is used for several things:1. It indicates extension of the lower complete denture, by extending to

the anterior one third of it


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2. It is important in the retention and occlusal plan, it indicates the levelof the lower occlusal plan (2/3 of retromolar pad)

- The mylohyoid ridge in some patient might be prominent and it will be

sharp, if you construct your denture in such a way the final denture willtraumatize the patient, so you need to consider that this might be a sourceof pain for the patient.

*Second: IMPRESSIONS FOR COMPLETE DENTURES

Definition : A negative likeness of the tissues so that a model can bemade from which a denture can be constructed.

-The impression material is held against the tissues and is supported by animpression tray. The material shows plastic flow in the initial stages andthen hardens.

-A model is then formed using model stone or plaster. For maximumaccuracy a 2 stage impression procedure is adapted.

-Impression with a stock tray is first taken called a primary orpreliminary impression


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*IMPRESSION TRAYS

-Two types of impressions trays are used stock and special trays *Properties:1-Must be clean and smooth

2-Must be rigid and strong

3-Should permit correct thickness of impression material to be used(3mm)

4- Handle must be shaped and attached to the tray so that it doesntdisplace the lip when the impression is taken

5- Must hold the impression material in the correct position in the mouthand consequently must cover the whole area of the jaw required in theimpression.

6- Must prevent distortion of the impression material during setting andremoval from the mouth

-Stock tray means universal tray, it's not specific for one patient, we canuse it for all patient with a similar size of the jaw, and the tray should beselected to cover all anatomical land marks, how do you check for this?

-You insert the tray inside the patient mouth (for this case the maxillaryarch) it should relief the frenum and should cover the maxillarytuberosity, the whole edentulous ridge and posteriorly the vibrating lineor the post dam area.


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-We have different sizes we have small , medium , large and X- largeSize

- If you use a small size tray then your impression will be very small and

not representing the jaw, and if you use a very large tray then you'lldistort your impression

*Types of stock tray:

1) Box trays: RPD.2) Trays for edentulous arches3) Combination trays: Distal extension base

*Disadvantages of the stock tray:

1- Variation in thickness of impression material : because they are notsuitable for the patient, the thickness for example in the anterior areamight be different from the thickness in the posterior area

2- Localized pressure on oral tissues : it might press for example on theleft side and not press on the other side.

3- Incomplete coverage of oral tissues : so sometimes you have tomodify this tray by adding some wax to it on the borders in order to reachthe full depth of the sulcus

-in this pic the patient have a deep palate that why we added wax on thisarea.


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3- Pouring of impression may be delayed: you might not send theimpression till two hours, so we can delay it not like alginate which haveto be poured in 30 mins.

*Impression compound disadvantages:

1- Does not reproduce fine surface details , and for this reasonsometimes we go for corrective alginate wash .

2- Should not be used in undercuts , because it's very stiff (rigid)material, if you use it for patient with sever maxillary undercut in themaxillary tuberosity area it will not come out and the patient will be hurt.

3- Re-softening/unhygienic , this material can be re-softened for 3 or 4times for the same patient several times in order to take the finalimpression, and this can be unhygienic.

*Alginate- composed of Sodium alginate, calcium sulphate, trisodium phosphate

- Trays should be Perforated (perforations are means of mechanicalretention, so the alginate will go inside them and stick to the tray), whileimpression compound can be used with perforated or non-perforatedtrays.

- Sometimes we add adhesive to the tray before we mix alginate(polyamide in isoprpyl alcohol)

- Impression poured immediately ( imbibition and syneresis) within 30

minutes

- Record good surface detail with a minimum of tissue displacement

- Accuracy depends upon the accuracy of the tray

Easily distorted


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* Alginates advantages:

Excellent surface details .

Elastic: so we can use it in undercuts.

Different viscosities: we have high, medium and low thickness alginate.

*Alginates disadvantages:

Not flow in areas not supported by tray

Cannot be added: if you have a problem with you alginate impressionyou have to repeat it, but if you have problem with impression compoundyou can add to it.

Liable to distortion at laboratory .

*which impression should we take first maxillary or mandibular?

-We usually go for mandibular impression and this has been found byresearch, but for some patient you can start with the maxillary first.But if you started with maxillary you'll see:1- Increased salivation2- Retching (gagging) reflex3- Chocking by impressionSo to avoid these take the mandibular first.

-sometimes when we use impression compound it's hot, you'll mix it in 60degree and then we you will temper it

, but if you take it as 60 degrees and put it in the

patient mouth cause this will burn him, so you temper it in the temperingrubber bowel and then to the patient mouth, for these reasons if youforget to temper the impression compound and you put on the maxillayou'll burn the palate because it's a very sensitive area.

- If this has been done in the lower jaw it will not cause that trauma as if you were doing the upper jaw.


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*Preliminary Impressions

*Common faults: (lower impression )

1 Edge of the tray showing:-Incorrect centring of the tray

-Use of too large or too small tray

-Forward thrust of tongue not been countered by backward pressure onthe tray in the anterior region

2 Insufficient depth at lingual pouch:

-Short flange

-Lack of compound

-Too little force applied

-Tongue trapped

*Common faults: ( Upper impression )

Deficiency in midline of palate-Insufficient compound

-Insufficient pressure

-Compound cold

-Trapped air


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-So we opened a file for the patient, we finished the examination, we took primary impression with impression compound, what is next? I'm goingto send these to the lab, so I'll send a piece of paper to the technician to

tell him what I'm going to do, what type of stone to pour, amount of spacer, and do we need modification of the tray like perforations or not

*Diagnostic cast

-The cast that come after pouring the impression, we ask the technician to pour the impression with dental plaster, so why do we need a primarycast?

1- Analyze feasibility of various treatment measures.2- Foundation for special trays 3- Help the dentist to discuss possible treatment forms with patient ortechnician : sometimes you'll not be able to see all the anatomicalstructures inside the mouth very clearly, so once you get the impressionyou'll see it more clearly.4- Analyze occlusion and articulation : these are not for completedenture patients, these are for RPD patients.

*CASTS MATERIAL (properties of ideal cast material)

-We cannot pour impression with any type of stone, it should be:1- Compatible with all types of impression materials.2- Reasonable setting and working time: we don't need it to set for example within 2 hours, we need it to set very fast.3- Reproduce surface details.4- Exhibit surface hardness : which means that it cannot be scratched .


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*EDENTULOUS CASTS

-Posterior border of cast stops 8 mm frommaxillary tuberosity or retromolar pad

- The outer surface of the cast is trimmed toabout 3mm from the maximum convexity(Land area)

- At least 10 mm thick

*Special trays

-These are made of type of material called acrylic material, they can belight cured, or you can mix them and apply them on the flame.

-Note that on the lower special tray we have stops, and they are used to press the tray on the posterior part of the mandible, because it's difficultto stabilize the tray inside the patient mouth (Called finger rest)

*Before fabrication of the custom tray we do conditioning of theprimary cast , first of all the technician needs to draw the borders of thetray, you can see two lines on the cast below, on is black and the other isred, so the special tray material will reach these lines.


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- notice that he is adding wax, this is called block out, which is insertingwax in the undercuts, and we do this because when we cure the specialtray if these undercuts are not blocked out the tray will not come out or will be fractured.

-you can see in the picture below, the spacer which provides space for

impression material, which could be zinc oxide eugenol or silicon or alginate.

- With zinc oxide eugenol we don't need a spacer , we don't need aspace below the tray, but with alginate and silicon they are thick so weneed two layers of wax to provide enough space for it to prevent tearing

-Notice in the picture that the spacer wason the anterior ridge, we don't need aspacer posteriorly, why? Because theanatomy of the anterior one is flabby sowe need spacer.


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-Now , there is an important thing that the technician should know ,thatthe special tray borders shouldnt reach the full

depth of the sulcus ,it should be 2 mm awayfrom the full depth of the sulcus (not like thestock tray that reach the the full depth of thesulcus .

-why do we leave that space? Because we willdo border molding and in another word to bedistinctive from stock tray so it will be specificto that patient.

-Sometimes the tray is 2 mm away from the borders of full depth of thesulcus , once you put it inside the patient mouth it reaches the full depthof the sulcus , why is that ? because most of primary impression that wesend it to the technician - are over extended , so to solve this we put thetray inside the patient mouth and we give a pencil and put a mark on it to

be 2 mm away from the full depth, then cut the tray by trimmer or acrylic bur to be in the suitable distance.


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-After that we will start the first procedure of secondary impression that is border molding.

- in this procedure we will use a material like impression compound or

material called green stick (molding stick) , it the same of impressioncompound its thermoplastic material , contain wax and resin but it differsfrom it by the amount of fillers ( we can put impression compound in arubber container that contain 60 C water but green stick we can't dependon water to soft it , we put it on the flame because the amount of filler init is more , so softening on flame then apply on the borders)

-These borders should be very accurate, why? bcz they are representingthe borders of the final denture ( if border molding accurate your

secondary impression will be accurate , your secondary cast accurate andyour final denture will be accurate) .

*How to check that our border molding is accurate?

-look inside the patient mouth , it reach the full depth of the sulcus , andtry to remove the tray : for the upper , if your border molding is accuratethe tray will not come out because we closed the peripheral seal ( after wedo border molding the air will be under the tray and we closed on it so

there will be negative pressure ) , in the lower the same thing but in mostcases lower retention( 75% )not like upper retention (100% )because of two reasons:

1- The flat lower ridge so it's difficult to close on the air and get negative pressure

2- The second thing is the movement of the tongue will prevent alsonegative pressure, so if we can apply 75% negative pressure this will begood.


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-we put utility wax on the borders of the tray then we bring boxing wax(red) and make a sealing on the tray and pour it by dental stone, why isthat?

-bcz the secondary cast (master cast) should tolerate pressure, so it should be accurate and made from strong material.

- Now we will put record blocks on the master cast.

- Record block has two parts:

1) Denture base (acrylic material that reach the full depth of the sulcus onthe upper or lower)

2) Wax rim on the top of it (representing upper teeth and lower teeth).


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- We can use the acrylic resin to made denture base. Shellac andcompound was in the past and can be distorted by the mouth temperature.

- The requirement of record base:


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*NOTEs:

- The labial surface of anterior teeth supports the lips and is between 10 -12mm labial to incisive papilla

- The centre of the last molar is nearly opposite the centre of thetuberosity and its buccal surface is 3-5mm buccal to centre of tuberosity

- On average, the distance from the functional sulcus to incisal edge of centrals is about 20mm and to the occlusal surface of first molar is about

18mm. in another meaning, the record blocks will come from lab, we willcare about the dimensions of the wax it s hould be ant 3-5 mm,

premolar area 5-7 mm and posterior area 8-10 mm in width


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- The functional depth of sulcus should be 22 mm in incisal area and posterior 8 mm. this is for upper.

-If the difference is so far away from the correct one we need to send it back to the technician

*For lower record blockfunctional depth anteriorly 15 -18 mm, and thewax should reach 2/3 of the retromolar pad area. The rest dimensions likethe upper nearly.


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*JAW RELATIONS:

- Centric occlusion :( its tooth to tooth relationship) Static tooth contactsin maximum intercuspation (termination of masticatory closure).

- Centric relation: (the most used term, bone to bone relation) mostretruded position of mandible to maxilla from which lateral movementcan be made at a given degree of jaw separation

- Vertical dimension: the distance between alveolar process of maxillaand mandible in centric relation

- Occlusal plane: the position and angle of a plane to which the occlusalsurfaces of teeth relate

*The relations that we will use:1-Orientation relation : relation to the cranium2-Vertical relation : amount of jaw separation3-Horizontal relation : anterio-posterior and lateral relations - when weneed to use hotplate we will begin with the upper

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Prostho III Lec 3 (1)