الرحيم الرحمن الله بسم

REMOVABLE PROSTHODONTICS 2

-2ND LAB-

During this week, we will do the wire bending on the teeth. It is the reverse from last year where they did the wire bending exercise (on paper) first, before applying them on the teeth (cast). But since the students didn’t bring their instruments last week, so we will do the exercise as homework after doing the wire bending on the teeth during the lab. This is due to the limited time in this semester.

Today we are going to start the steps for the provisional partial denture. Also known as:-

1. Interim 2. Transitional 3. Temporary 4. Acrylic - as the provisional prosthesis is made up from acrylic. (Another material; the

stainless steel wire).

Stainless steel wire is made up from iron plus a variety of other elements. It’s known as 18/8 stainless steel.

18 stands for 18% of chromium – to reduce corrosion 8 stands for 8% of nickel The remainder 74% is mainly iron as a basic material.

Chromium sacrifices itself to prevent corrosion. Form layer of chromium oxide on the surface and protect the underlying iron. So that it doesn’t rust inside the patient’s mouth.

Acrylic partial denture is actually made up of:-

1. Heat cure acrylic or Cold cure acrylic2. Denture teeth – which also from acrylic3. Stainless steel wire

Meanwhile, metal framework partial denture can be made up of:-

1. Any cast dental alloy - Usually cobalt chromium or nickel chromium.2. Heat or cold cure acrylic3. Denture teeth4. In some cases, we also have rod wire (e.g. stainless steel)

Generally, for this week lab, we will talk about:-

1. Provisional partial denture step (fabrication) Before we make a partial denture, we actually have to draw a design first.

2. Block-out and surveying In order to draw the design, we need to know the topography of the teeth and

the cast. We need to know shape of the cast. (surveying) As a dentist, we can’t just make the partial denture like the complete denture

(which goes in and out direction only). Partial denture have undercut on the teeth itself and often in the soft tissue, or

bony undercut presence in the mouth.

TYPE OF UNDERCUT

Favourable Undercut

Help in retention for the denture which depends on a great degree

on mechanical retention (wire which goes around the teeth).

The wire will go into in undercut. Below the maximum bulging of

the teeth.

Unfavourable Undercut

Prevent the insertion and removal of the prosthesis

Usually on lingual surface of the teeth

The problem is we can’t just determine these undercut by simply looking at it by eye. Need to use an instruments; dental surveyor. Which tell us where’s the undercut is on the cast. These will be more accurate as the teeth have a very small and tiny scale. Using eye estimation will not be so accurate.

We’ll also talk about block-out (blocking the undercut)3. Wire bending principle

We’ll learn how to bend clasps using the stainless steel wire. And also the exercises (on the paper sheet) which we’ll do it as a homework.

The things we need during this week lab:-

Loop forming pliers. Wire cutter CD marker – mark the undercuts and on the wire while you’re working.

THE STEPS OF PARTIAL DENTURE FABRICATION –(Dr Esam explained it quickly)

1. Take primary impression. 2. Pour the primary cast.3. On the primary cast, we fabricate a custom tray.

The custom tray; slightly differs (from the complete denture). The spacer has a different shape and the stopper at difference locations.

The thickness of spacer:-i. Edentulous area : 1 layer thick

ii. Dentate area : 2 layers thick Tray used is perforated type for the retention; as we’ll going to use an elastic type

material:-i. Alginate

ii. Silicone iii. Polyether iv. Polysulphide

4. Using this tray, in edentulous area we can do the border molding (just like in a complete denture). Elsewhere we don’t need to do it.

5. Take the final impression.6. Pour up the final impression to fabricate the final cast. (stone secondary final cast)

p/s: we’ll received either maxillary or mandibular final cast; Kennedy class 2 modification 1 to work on with. There are mirror images of each other.

SURVEYING AND BLOCK-OUT

The next step in fabrication will be surveying. We need to know where’s the undercut is.

After determining where the unfavorable undercut are, we need to block-out these unfavorable undercuts.

There are part of undercuts on the lingual surface which will prevent the insertion and removal of the denture.

Remember that all teeth have undercut. If the acrylic goes into the undercut, it will stick inside. We won’t be able to get it out. Or

if we do able to get it out, we probably won’t able to get it in again.

The block-out should not done too much as it will result in a too loose denture. Determining where the unfavourable undercut is important; in order to block it out, so that we have a single path of insertion and removal.

Block-out is done using a gypsum products usually dental plaster. (Dental stone also can be use. It’s doesn’t matter)

DENTAL SURVEYING Locate where’s the favourable and unfavourable undercuts.

The area that needed to be blocked-out:-

i. Small area on the lingual part.ii. Proximal part; mesially and distally

It’s almost the mesial and distal surfaces are parallel to each other.

Never put the block-out in the area where we want to put the clasps. If these areas are blocked-out, we’ll lose our favourable undercut which mean we’ll lose our retention.

On the other hand, we also can mark and locate the favourable undercut which is on the outside (labial surface) where we’re going to put our clasps.

P/s: we said that favourable undercut is considered on the labial surface; meanwhile the unfavourable undercut is on the lingual surface. Actually, it’s not a general rule. Sometimes we reverse them (favourable is on lingual and unfavourable on the labial). But just for this lab, we’ll consider:-

Favourable undercut = labial surface Unfavourable undercut = lingual surface and proximal surface

To sum up every things; when doing the surveying (locate favourable and unfavourable undercut), we will also mark a line on the teeth to indicate the maximum convexity of the teeth. After the surveying, we’ll blocked-out the unfavourable undercut. Finally, now we are ready to do the wire bending (final thing that we do during this week). After the wire is in its place, we’ll need the base plate and the teeth. So we’ll do the waxes shape, and setting the teeth (these will be done during another week). After the teeth are in its place, we’re going to process the denture in a similar technique as a complete denture (flasking, packing, and curing). We’ll end up with a mold that is packed and give us an acrylic denture.

DENTAL SURVEYOR

Purposes of dental surveyor: -

i. To determine the path of insertion and the path of removal of the prosthesis. (main purposes)

ii. To locate the favourable undercut and unfavourable undercut. –so we need to mark the area of maximum convexity of the teeth.

Dental surveying Block-out unfavourable undercut Wire bending

Waxes shape (for the base plate)Setting the teeth

Processing the partial denture just like the complete denture.Except they have less teeth

A = Vertical arm Can go up and down to adapt to the cast.

B = Horizontal arm It is adjustable and can be rotate.

C = Vertical mandrel –where the surveying tools are attached. Also can go up and down. It is spring loaded. The chuck of this mandrel is similar to the chuck on a handpiece.

D = Surveying instruments/surveying tools.

E = Universal table – Has three projections to hold the cast. Free movement in 3 dimensions. Have a tilt –anterior posterior, right left or any combination between them. If the table is tilt to the front; the denture is going to come in from the back. If the table is tilt to the back; the denture coming in from the front. If the table is tilt to the patient’s left; the denture coming in from the patient’s

right. (No need to understand that much so far because actually during this lab we’ll

going to work almost entirely at 0 tilt. We’ll learn much more about it later)

F = Base –at the bottom. It’s attached to two things. Universal table Surveying apparatus which is A, B, C.

There is no cutting involve. The instrument is used to determine where the undercut is, to shape and so on.

SURVEYING INSTRUMENTS/SURVEYING TOOLS

Analyzing rod

Make no marks and no measurements. It’s only a reference line. (acts just like a ruler) Represent the path of removal and insertion. The

direction of the analyzing rod is the direction of removal and insertion of prosthesis. (This is done after we get the correct tilt which we’re not going to do it for this lab as we’ll going to use 0 tilt.)

A = part that held to the mandrel B = vertical part that we used to analyze.

Graphite Marker

It’ll mark or draw on the teeth. (survey line) Designed to draw at the side, not at the tip of the end.

(it draws around the side of the tooth) It supposes to draw two lines; draws on the teeth

which represent the maximum convexity. And also draw on the gingival. (Refer the figure on how it was used)

In case of unfavourable undercuts, any region between the two lines should be blocked-out. Or in other word, any area below the maximum convexity line, should be blocked-out.

A = metal sheath so that the graphite won’t break. B = graphite marker just like a pencil.

Undercut gauge

Used to measure the undercuts. Looks like analyzing rod but it has something like a

disc at the end of it. Each one measures at a different depth.

1 arrow : 0.25mm 2 arrows : 0.50mm 3 arrows : 0.75mm

Wax/plaster Trimmer (chisel)

Use to trim any excess of plaster during block-out procedure.

A = cut at the end B = cut at the side

Some dental surveyors are more advanced which we can attach handpiece to them. So we’re able to use burs to trim things on the cast. We’ll learn them in more advanced dentistry when we want to make things very parallel in the metal (for special attachment). We actually do the milling process. -just be aware with it but it’s no need for us to know it now.

PICTURES OF HOW THE SURVEYING INSTRUMENTS IS USED

Analysing Rod Graphite Marker

Undercut Gauge Wax trimmer

CLASPS PREPARATION

Where are we going to put the clasps? At the maximum convexity or in the middle or down by the gums? Actually it is a little bit more complicated than that. Dr. Esam wants us to revise our dental material.

We never put the clasps touching the gum because of:-

Hygienic reasons –if the clasps is tend to get closer to the gingival, it will form a food trap and so it is hygienically unacceptable.

Traumatic reasons –acrylic partial denture is almost always tissue supported. When the patients bite down, the clasps will start to traumatizing the gingiva (as there is no hard material preventing the denture from going down to the tissue)

Keep in mind that we need to put the clasps at least 1mm above the gingiva.

We’ll going to put the wire in the undercuts. And the wire comes in different dimensions. The wire that we’ll use today is a stainless steel wire called wrought wire. Wrought wire is flexible and its flexibility depends on:-

length diameter

From measurements and experience, we know that each type of wire should go in a specific depth of undercuts (can’t simply say that it’s in the middle or top or below). We have to know where our wire going to be (maybe by experience). Theoretically, 0.7mm or 0.8mm wrought wire should be place in 0.5mm undercut (the one that we used in the lab). There is other type of wire which should be place in 0.25mm undercut or even in 0.75mm undercuts. These clasps’s location is depends on the wires:-

flexibility length material

HOW TO MEASURE UNDERCUTS DEPTH

By using undercut gauge, we can measure the depth of the undercuts in a horizontal way (from the rod of the undercut gauge to the surface of tooth. Refer to the picture for better understanding). Below is a picture representing undercut gauge and its length at the end of it.

Remember that these undercut gauge measures in millimeter (mm) not centimeter (cm).

We want to know how much the undercut below the survey line/equatorial line. We measure the undercuts in a horizontal way (from the rod of the undercut gauge to the surface of tooth. Refer to the picture for better understanding). –it’s a depth measurement. Not the length.

Essentially, we move the surveying arm (up and down movement) until it touches the tooth. Then, we raise the surveying arm slowly until it touches the tooth from below. Just like the picture above.

After measure it up using the undercut gauge, as we’re going to place the clasp on the 0.5mm undercut, we’ll make a mark along the tooth (refer the figure above). This line will be our reference to bend the wire. Also, this will be our favourable undercut is which we place a clasp onto it. On the other hand, at the other side (lingual side), we’ll going to have unfavourable undercut. So we need to block them up.

TRIMMING

The unfavourable undercut that we blocked-out with plaster actually will be excessive. So we need to trim them up. Generally, the things we do during trimming are as figure below:-

Final result, the plaster that applies proximally, on the mesial and distal surface will be parallel to each other (which are parallel to the path of insertion and removal). Parallelism is important for easy insertion and removal of prosthesis. When the acrylic denture comes in into the space, it will fit; can be move in and out but with a space in the area of block-out.

So, again, the plaster in the final denture will become a space. If we put too much plaster, retention of the denture will be compromised. (It shouldn’t be more and it shouldn’t be less).

Finally Dr Esam start the demo….

Before we do the surveying, marking, blocking, trimming n so on… we’ll draw first the outline of the denture on the cast. We’ll not draw on the teeth yet, but it will be on the soft tissues. The denture outline will have:-

Flange –like a complete denture. Then the outline will going to the hamular notch. Include the 1st molar, meanwhile the 2nd molar is not included in the design. –so we’ll

draw a line (outline) between the 1st and 2nd molar. Posterior border –doesn’t have to be at the vibrating line. It can be further forward (as

there are no peripheral seal in this case). If we can reach it, reach it. But if we can’t, it’s ok.

When we cross the gingiva and cross the midline, it should be at right angle. There is area that is irritable and we need to cross them in a right angle as possible.

Don’t need to go to the full depth of the sulcus. Our objective is static and stability. Don’t need to go to the full depth.

So now we have our acrylic border.

For an upper cast; we need to use the lecron carver to scribe a 0.5mm line at the posterior part where the outline is draw. It’s called a bead line. Its advantages are similar to the post dam in a complete denture.

For the lower cast, the design is slightly different. We don’t have the palate but we have the lingual area. So, the outline includes:-

2/3 of the height of retromolar pad (sulcus area). –labial and lingual flange. Don’t need to go through the full depth of sulcus.

Approximately all the retromolar pad is included. At the bounded area; draw line from the sulcus up to the distal surface of the premolar. Go up with the frenum Mesial surface of the molar. On the lingual; include the lingual sulcus and then do the lingual flange.

UPPER CAST LOWER CAST

We need to understand that the outline is draw after the dental surveying. The reason we’re doing this because we’re already know the design and it’s just to have a basic idea of where are we working.

Now, Dr. Esam starts to do the demo for dental surveying. Dental surveyor is a very expensive instrument. (It cost between 1500€ - 2000€). Have different types –simpler one are less expensive. “BEGO” It’s German company and also a very well-known company for alloys and dental instruments.

[I’ll just list them up as we had discuss them before]

1. Attach the cast to the table –tighten up the screw’s projection to hold the cast so that they don’t move. (One of the 3 projections is adjustable).

2. Attach the analyzing rod to the vertical mandrel and do the analysis. (We’ll not going to use this much as we’re working on a 0 tilt –just take a look where the undercut is).

3. Mark the maximum convexity using the carbon/graphite marker. Usually we only mark on the teeth that are involved in the design but Dr. Esam told us it’s better to mark everythings. (we even can mark the undercut on the bone and on the soft tissue). Its suppose to draw two lines.

I. On the teeth which is the maximum convexityII. On the gingival

In order to this, graphite marker must have a good shape; bevel at the end.

Space between the two lines is blocked-out.

4. Measure where is the 0.5mm undercut is. We’ll going to put a clasp on premolar, canine and molar. So, we’ll measure the undercut at these areas.

The disc of the undercut gauge will make a very small scratch which will be in between the survey line and the gingival line. And we’ll going to put the clasp on the favourable undercut here (half way between the survey line and the gingival). –facial premolar, facial canine and facial molar.

5. Do the block-out. Ideally we need to soak the cast in water but the problem is the cast will become weak. Why? Because with plaster, we want to add gypsum product to a gypsum product. It’s a good idea to have cast saturated with water because it will stick better. Moreover, if the gypsum cast is dry, it will suck the water from the new gypsum plaster (block-out material). So the new gypsum plaster will become dry and it won’t set correctly. To save time, we’ll just moisten the area where we want to add the plaster, just a small amount of water. We’ll do block out at the lingual and proximal area.

Dr Esam used tera alba/slurry water to accelerate the setting time. Slurry water is just like a super saturated solution of calcium sulphate.By using the lecron carver, we’ll approximately put the material that we mix (plaster powder + water + slurry water) on the unfavourable undercut.

I. Mesial of molarII. Lingual of molar

III. Distal of canineIV. Lingual of canineV. Distal of premolar

VI. Lingual of premolarVII. Lingual of anterior –optional

There should be no block out on the occlusal and facial surface. We can use water to smooth it down. When we look from the top, it should look almost vertical. We can remove pretty much the excess using the lecron carver. We won’t know exactly how much to put the block-out and that’s why we do the trimming on the surveyor. Before that, make sure the plaster is set enough. If not it will fall off when we do the trimming.

6. Trim away the excess using chisel. –bevel shape.I. Longer surface is toward the tooth.

II. Shorter surface is away from the tooth.

By touching the maximum convexity then it will start to cut when we brought the chisel all around the tooth. It’s almost like an analyzing rod which cut.

7. Now we’re ready to do the wire bending.

WIRE BENDING

Its good idea before we start to know where the wires were going to go. The wrought wire has two parts.

WROUGHT WIRE CLASPS

Retentive arm (clasp)

They're exposed. It's part of prosthesis

which keep the denture in place.

Will go into the 0.5mm undercut (we've discuse it earlier)

Tag Buried in the acrylic.

Let see where are these wire going to go.

Upper cast:-

1. Start from the mesiofacial margin but not from the contact area. 2. Then follow the contour of the tooth, like the survey line which called C-clasp. (but for

the molar it’s a bit longer. So it’s more like a U ).3. On the proximal, it will go half way of the gingival and occlusal. (0.5mm undercut)4. Then it will go down onto the palate. –we want it to go to area that is thick in acrylic. Its

need to be about 1.5cm long for aided in retention.

Lower cast:-

1. Just like the upper. Mesiofacial margin then to the proximal.2. Then go down and bend it toward the edentulous area. Stay away from the bottom of

sulcus so that the wire still embedded inside the acrylic. (we can make the L-bend at the end of wire but it’s not essential as we have enough length there to keep them in place)

Some notes about the wire:-

There’s something called an occlusally approaching or suprabulge clasp. And also something called gingivally approaching or infrabulge clasp. (don’t worry about

it) The type of clasp that we’re bending today is called occlusally approaching/suprabulge

clasp. The wires that we going to use for wrought wire clasp is 0.7mm or 0.8mm in diameter.

Usually in prosthodontic we’ll use 0.8mm.

When we pour an alloy, we make it very hard. If we make the metal into liquid, the atoms are in different areas. (They’re all constantly moving). When the metal is cool down, each atom will bond with another atom and will start forming a lattice (crystalline structure).

In metal, a metal crystalline is called grain. Sometimes these grains are large and sometimes small. But they have a very significance effect on the mechanical properties of the material.

CLASPCast Metal Wrought Metal

Can’t be bending, very rigid and not flexible.

Flexible

Should be at 0.25mm undercut. –because it is more rigid. If we put it in a deeper undercut, it is not flexible enough to get in and out.

Should be at 0.5mm undercut. –as it is more flexible, we can go in deeper part.

Wrought wire gold is used in 0.75mm undercut. –more flexible than stainless steel.

Gingivally approaching cast clasp can also be place in 0.5mm undercut.

Occlusally approaching wrought wire clasp is put in 0.5mm undercut.

If the metal is left to cool down slowly, we’ll give the change for the crystal to become very big.

Atoms are in different direction than the other one. So, they act slightly individually.

The cast alloy is processed (press and squeeze), so that the thickness of the cast alloy becomes a thickness of wrought alloy which is very thin.

The grains become very narrow, very thin and very long fiber. –1 grain=several meters long.

If we take this metal (when it’s cool down with those large crystals) and try to bend it, each crystal will separate from a longer line which will form a fault line. Finally it will crack. (It’ll bend a little bit but it will fail soon and it’ll break).

It doesn’t have much plasticity and elasticity. –relatively a brittle material.

Wrought wire is elastic. The problem: when we bend the wire,

we have changed the line of grain. If we bend it twice, the fiber will bend even more. Now it is less flexible and more brittle.

This information important for the wire bending. Produce a minimum number of bends (basic principle in wire bending). We don’t want the clasp to become brittle when inserted into the patient’s mouth.

Making a clasp, we should have:-

1. Loop forming pliers – good one should have beads 2 cm long. Handle about 10cm.2. Marker 3. Heavy duty wire cutters

Some pliers can use for many types of bend and some have very specific purpose. The types that we use in dentistry are generally versatile. Orthodontics uses much more pliers than prosthodontics. Pliers which can produce all of the bends that we need:-

But the pliers don’t do the works. Need to use our thumbs and finger instead. -only use the pliers edge and we’re the one who bend it to the edge.

Adam’s pliers/universal plierstwo pyramidal beads.produce a 90 bend.design by an orthodontist known as Philips Adam.we'll use them alot during the 4th year.

Loop forming pliersone bead pyramidal and one bead conical.bends wire towards the cone=curvebends wire toward pyramide = 90 angle.very flexible instruments.

RULES FOR WIRE BENDING

1. Working with a comfortable piece of wire.a. Cut the wire into sections. If it too short, we won’t able to control it (difficult to bend). If

it too long, it will keep hitting the unwanted area. For clasps, we need about 8-12cm. How to cut?

i. By holding both sections of the wire with fingers. Usually we’ll cut towards the joint (of wire cutter).

ii. Pointed it towards the floor.iii. Cover with something –lab coat, paper towel and etc.

b. It’s almost always curve as it is sold in a large coils. Rarely comes in a straight form. It’s always better to start with a straight wire. The straighter the wire, the easier it’ll be.

i. Bend the wires in the direction opposite to the curve. Use a correct plane so that we can see the curve.

ii. Keep in mind the three dimensions (3D) of where the curve is going.

2. Use the edge of pliers and our hand to do the bending. Some of us will try to bend the wire on the cast. It won’t work. It will scratch the cast. We only bend the wire with the pliers and our thumbs and fingers only.

“If it doesn’t marked deep groove in your thumb when you’re done, you didn’t do the bending correctly” –orthodontics professor.

3. The tips of the wire (the tip at the beginning) should not touch the adjacent tooth. Atleast a millimeter away from the adjacent tooth. Any excess during bending, we can cut it out later.

4. Bends the wire following the contour of the survey line; touching the tooth. The clasp only touches the mouth in two places:-

a. Favourable undercut on the facialb. Tip at the end of the clasp. Tip of the tag. –prevent wire from going down leaving no

space between the wire and the palate during packing (which has heavy pressure).

Means; when bending the c- clasp (occlusally approaching wrought wire), it will go touching around the tooth. Proximally , when it reach the distofacial line angle (premolar for example), it will go away from the tooth by 0.5mm or 1mm but parallel to the tooth. Occlusalgingivally it will fit at 0.5mm undercuts. When it reaches the distolingual corner of the tooth, it’s going to bend down to adapt to the patient’s mouth. Before it touches the palate or edentulous ridge, there must be 1mm space between the palate and the wire. The reasons are:-

We want the wire to be sandwiched within the acrylic so that the wire will not come out during function. We also don’t want too much space in between them because this will make the acrylic become too thick.

Proximally we also have space so that in acrylic denture we’ll not scratching the wire when there is need to do the trimming. But at the same time, we can’t make the space too far away as it can interfere the adjacent tooth which we’re going to set.

Dr Esam starts showing us the way to bend the wire. (Premolar is used during demo. Premolar and canine quite similar)

Most valuable aid when bending wire; mark where we want to bend. The first thing we want to do is make a curve. Two ways to do it:-

i. Hold the tip of wire around the broad part of the conical bead. Using a thumb at one end, and then bend round. –One quick bend and the wire look smooth and still flexible.

ii. Make many small bends. But the problem is we’ll make sharp edges. After done with the bend, we’ll get small “c-shape”. We’ll check the adaptation on the

facial surface of tooth. Once we take a reference on the cast at the tip, don’t change it. Each bend will change

the wire after that.

We bend then check, bend again then check again. If we suddenly make a mistake and the clasp becomes non adapted, the mistake was at the last bend. So, go back to the last bend we made and make it straight again. We should always go back and check on the cast. If mistake happen, don’t keep going.

Mark the last point which is in contact with the tooth using sharp tip CD marker. So that we know where to bend next. In case we were at the distofacial line angle of the premolar, we need a space 0.5 mm here. So, we’ll mark just a hair away from the tooth in order to have a little bit space between the wire and the tooth.

If we want to bend exactly at the points that we marked, grasp the wire just a 1\10 millimeter before the point. If we grasp the wire exactly on the marked point, the bend will happen after that point.

In case of our curve is too small, widened them by placing the pyramidal inside the curve and the conical outside it. Then press and it will widen up.

For the retention of the clasp, at the end of the tag, we can do either “zigzag shape” or just “L shape” bend toward the cast. But the more the bends, the more complicated it is. (In lab we do the L-shape).

For the molar, the difference is; molar will have “u-shape clasp” rather than “c-shape”, which means one bend is not enough. –make a series of bends. So on the molar; we’ll have a curve then a straight line then a curve again.

In lower, wire bending is more challenging because the angle of the wire is more difficult (in the tag). –in the palate it is more horizontal but in the lower, the wire goes straight down. Becareful not to reach to the bottom of the sulcus or beyond the border of the denture. (That’s why we do the outline in the first place).

The easiest to do the wire bending is on the premolar canine molar the hardest.

pressure apply

When finish with the bending, put the utility wax at the tip end of the tag. Use small amount just to keep them in place.

-the end-

Sorry for any mistake and good luck!