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REVIEW OF CLINICAL AND LABORATORY STAGES IN

FABRICATION OF METAL CERAMIC BRIDGES

Hello every one, this lecture added newly to the syllabus in 5th year to review clinical and laboratory stages in
fabrication of PFM bridges. You might have come across most of the information we're going to mention today in
the last semester in crown and bridges course, but this lecture will gather the information to help you to
understand the stages of PFM bridges. Most of the things we are going to discuss are based on our method in DTC -
there might be another methods (another impression, techniques, materials) – so to be familiar while you are
working on your case.

This table below will summarize all the stages of PFM bridges we are going to discuss it in details.

*shade selection is generally done in the first clinic..

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Clinic number 1

1) Examination, assessment of abutments and edentulous span and preliminary

impressions.
• History, chief complaint, dental history, medical history ( there are specific points in MH that are relevant
to bridge patients and might interfere directly to our treatment options like bleeding tendency can affect
taking impression, hypertension patient because in the retraction cord that impregnated with epinephrine,
each 2.5 mm of it has the equal amount of 4 carpules of anesthesia which is high amount, that’s why we
need to consider some medical problem such as hypertension and CVD, because epinephrine will increase
the heart rate and increase in blood pressure. Also we have to pay attention to patients who have
intolerance to supine position because tooth preparation is long procedure; like asthmatic or late
pregnancy (long compression on veins can cause some syndrome in pregnant women so be careful !!)
• extra- and intra-oral examination
• Intra-oral examination:
1. Mouth open: oral hygiene, caries, restorations, periodontal
disease, tooth mobility, length of edentulous spaces, abnormal
tooth movements (tilting or rotation)
2. Mouth closed: over-erupted teeth, Inter-arch space and
occlusion.

In bridge patient you always need to look at the abutment and

edentulous space.

Edentulous space has 2 components (horizontal- anteroposterior

space and vertical- inter-arch space) for example if the opposing
tooth is over erupted it might close the available space
so first check the edentulous space in anteroposterior manner
while the mouth is open then check the vertical space while the
mouth is closed, and both should be sufficient in order to allow
you for fabrication of the bridge.

Alginate or condensational silicon if pouring will be delayed. Sometimes we can take bite record in 1 st
visit so we can study the occlusion better and it will help in treatment planning.

2) Assessment of abutments and edentulous spaces Pic-1

• Periodontal status (no advanced periodontal disease, gingivitis,

gingival recession, inflammation)
• Angulation {very important} e.g. (pic-1) mesial tilting or drifting of the
molar occlude most of the available space so I don't have enough
space for bridge anymore and if I do aggressive preparation then I Pic-2

need elective endo or I can ask for ortho help to upright the tooth but
in this situation it is difficult to do a bridge. In (pic-2) the abutments
teeth are upright and that makes the edentulous space more
favorable for bridge fabrication.

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 • Overeruption (pic-3) overeruption of the molar almost occluded all the Pic-3
space available for the bridge and make the task more difficult; in this
case we might need the help of orthodontist for intrusion or elective
endodontics treatment and then, reshape the tooth and maybe we will
need crown lengthening.
• Caries
• Restorations : we check for any underlying caries or over hanging
restorations (the restoration need to be very good and its material
can stand occlusal force –amalgam and composite are fine
but with GIC I need to change it to stronger material).
• Length of span
• Inter-arch space
• X-rays to assess abutment teeth, the restoration is fine and no
underlying caries, periodontal health, pulpal health, bone level. Pic-4

e.g (pic-4) if the lower 6 is missing and 7 is the abutment I should take
x-ray to check the third molar because it might causing problem like
root resorption or caries to the 7. So if the 8 is not there, always take x-
ray to confirm the absence of the 8 or if present, to make sure that it is
not causing any problems now or later because if it is making any
problems, it will be more difficult to resolve the problem after
fabrication of the bridge than before ( remove the caries and extract the 8 before doing the bridge).

3) Preliminary impressions
• Alginate is adequate for both U and L
• C - silicone if impression pouring will be delayed
• Take impression for both arches
• Tray corrections if necessary with utility wax if the size need
some correction
• Use adhesive
• Bite registration if required for articulating the cast if you
want to study the case
• Laboratory instructions: Please pour U and L alginate
impression in plaster and wax-up (missing tooth/teeth)

Laboratory 1

Fabrication of diagnostic casts and wax-up

• Impression pouring for fabrication of diagnostic casts
• Wax up missing tooth/teeth
• Articulation if instructed of diagnostic casts and
the wax up of missing teeth to better assist the occlusion

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Clinic 2 the most important stage - do almost all things in this stage - it might took one or two visits
1) Reduction guide silicone index

• Used as tooth reduction guide through preparation

• C-silicone putty is used over wax up teeth, Tray is not required (because if I use a tray, I can't section it and
the border of the tray will hide the teeth so I can't use it to assess the tooth reduction
• Cut index half through the abutments to be prepared
• Another method? By cutting the index labiopalatally or buccolingually and then cut the facial part to 2 parts
(gingival an incisal)

2) Over impression for provisional restoration

• Used for fabrication of temporary bridge after completion of abutment teeth preparation ( I will do the
impression over waxed up teeth on the diagnostic cast{before preparation}; after finishing the preparation I
will fill the over impression with temporary bridge material and place it in the patient mouth; so the
temporary bridge material will occupy the space created by preparation and in addition, the pontic will be
in-between so I will get temporary bridge)
if I don’t have diagnostic cast -waxed teeth- then when I fill the impression, the result will be just two
separate crowns with no pontic but we don't want that because one of the functions of the temporary
bridge is occlusal stability ( to prevent any unwanted mobility of the teeth) and also for patient to expect the
final result of the case.
• C – silicone putty is used with the use universal adhesive (A- silicon is more accurate but its more expensive
and C-silicon is accurate enough for this purpose)
• Sectional tray may be used
• (Alternatives?)

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 3) Tooth preparation
• Give anaesthesia if tooth is vital
• Abutment teeth will be prepared for metal ceramic retainers/ porcelain fused to metal (PFM) retainers
• Reduce heat generation (not to cause damage to the pulp) by using copious water spray and intermittent
preparation (even if you are fast)
• Sequence of tooth preparation ( it is always better to start occlusaly
or incisally ) the advantage of starting with incisal/occlusal is that
will make the tooth shorter so reduce the chance of creating
undercut and you will be able to visualize better the preparation
• Common path of insertion

We will discuss the preparation for both anterior and posterior teeth

Tooth preparation for anterior / metal ceramic retainer

• Start with depth orientation grooves and/or reduction index to guide

you for the amount of reduction e.g. if you the diameter of the bur is 1
mm and you want 2 mm reduction incisally so you know then that you
need to insert the whole thickness of the bur twice to get 2mm
reduction
• 2 mm incisal reduction
• Facial surface should be prepared in two planes (incisal plane and gingival plane). If you prepare the tooth
according to just gingival part, you will make over contour or reduce translucency of the prosthesis because
of thin porcelain and if you prepare the tooth only according to incisal part, pulp exposure might happen.
• Shoulder finish line on labial (1.2 mm)for PFM so you need the whole thickness of the bur to be inside the
tooth, you can use reduction grooves or reduction index but as beginners start with orientation grooves.
• 0.7 – 1 mm lingual reduction incisal to cingulum depends if you want porcelain coverage (if you don’t want
porcelain coverage 0.7mm is ok, but if you want porcelain coverage you need more (1 mm). In our case, we
are going to do all porcelain coverage except the metal collar (2-3 mm above the chamfer finish line on
lingual surface).
• Chamfer finish line on lingual (o.5 mm) because we have metal collar and the margin will be from metal.

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Tooth preparation for anterior metal ceramic retainer – use the right bur!
When you prepare teeth you need to know the right bur for each step.
(Pic-A) you can see color coded bur. you will use blue color and green that you
have, and red one for finishing.

1) Incisal reduction and labial finish line ► shoulder (parallel or tapered)

the doctor prefer the taper because it is easier to work with, if you use taper you just put it in parallel aspect
to the tooth and that will create the minimum taper you need in the tooth, while as in the parallel one you
need to change the angulation of the bur to create the minimal taper you need. So we use the taper flat end
for incisal and shoulder finish line.
2) Lingual reduction above the cingulum ► football or flame shape bur

3) Proximal contact ►fine needle bur for accessing the proximal area

4) Lingual reduction below cingulum and chamfer line ►classical torpedo bur or
you can use any bur with round end, but if you assume the tip of the bur is 1 mm so you
just insert half of the bur as you know chamfer need 0.5 mm and it easier than torpedo bur.

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 Tooth preparation for posterior /metal ceramic retainer

• Use depth orientation grooves or reduction index

• Occlusal reduction:
1.5 mm non-functional cusp, 2 mm functional cusp ,
it is important to maintain the occlusal morphology
(planar) not flat surface for better retention,
resistant, surface area , structural durability.
• 2 mm functional cusp bevel
for structural durability because here I need
increased thickness of the material in order
to stand for occlusal forces applied on the functional cusp
• Shoulder finish line on facial (1.2 mm)
gingival bevel on the facial part is optional and it used if you plan to have very fine metal margin because in
old days they claim that the marginal fit of porcelain is not that good so for better marginal fit it is better to
have this bevel and have the margin from metal like very fine metal collar but new studies shows marginal
fit with porcelain (if the technical work is good) can be good as the metal fit so no need for gingival bevel
anymore because if you use it; it will compromise aesthetic it will appear specially on the facial side so it's
better to be avoided and have shoulder finish line on the facial surface
• Chamfer finish line on lingual (o.5 mm)

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Tooth preparation for posterior /metal ceramic retainer

A) Occlusal reduction ► round end tapered bur maintain occlusal morphology and do it
as planar reduction, after doing occlusal reduction you use the same bur but the fine one (red one) to
smoothen it and remove any roughness that may interfere with complete seating of the restoration
later on
B) Facial reduction ► flat end (tapered or parallel) bur for the creation of shoulder
finish line for facial reduction.

After facial reduction you can do either lingual or inter proximal reduction but usually we start lingual

C) Proximal reduction ► short needle easier then long needle in posterior teeth
D) Lingual reduction and chamfer finish line ► torpedo or round end (tapered
or parallel) but with half of the bur inside the tooth for 0.5 mm chamfer reduction.

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 4) Checking common path of insertion
After finishing the preparation you should check that you don’t have undercut and have common path of
insertion. the easiest way is to place the mirror against the 1st abutment until the image of the 1st abutment
is centered on the mirror then using finger rest, make sure your hand is steady and move the mirror to the
posterior abutment if you fined the posterior abutment is also centered and can be seen in the mirror then
that means you have common path of insertion. While if you need to change the angulation of the mirror to
see the second abutment, that means you have undercut and you need to find where these undercuts and
modify them and create common path of insertion.
You can also see directly from facial that mesial of first abutment with the mesial of second abutment and
check there is no undercut and then distal with distal

5) Tissue control and finish line exposure

• Finish line must be clearly reproduced in impression for precise marginal fit and if I don’t have finish line
on the cast the technician won't be able to know where to place the margin of the restoration
• Gingival retraction is unnecessary of supra gingival preparations if can be easily seen on the impression ,
it is required when I have equal-gingival or sub-gingival preparation
• Finish line exposure can be achieved by:
1. Chemical e.g. Expasyl it is a paste contain aluminum chloride and calin. these two materials will work
together to retract the tissue and stop the bleeding ( good specially for veneers)
2. Mechanical e.g. copper band around the abutment tooth to push the gingival tissue away from finish
line, plain cotton cord
3. Chemicomechanical: the one you will use combined (retraction cord + hemostatic chemicals) which will
control the fluids and cause hemostasis gingival retraction. (the method we will be using)
4. Surgical: Rotary curettage with the bur and electro surgery.

EXPASYL

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Chemicomechanical gingival retraction

• Combination of pressure packing, enlargement of gingival sulcus (by packing the cord) and control of
fluid (by hemostatic agent)
• Examples of hemostatic chemicals are epinephrine, aluminum potassium sulfate, aluminum
chloride, and ferric sulphate
• Use epinephrine impregnated retraction cords with caution especially in patients with
cardiovascular disease and hypertension

Epinephrine – facts:

• Causes an elevation of blood pressure and increased heart rate

• Maximum dose for healthy adult is 200 Mg (0.2 mg)
• Amount absorbed with each 2.5 mm impregnated retraction cord is 71 Mg that is one third of
maximum dose for healthy adult (nearly equal to epinephrine in 4 carpules of local anaesthetic with
1:100000 epinephrine) but for cardiac patient the maximum dose is 40Mg so one retraction cord has
twice the amount recommended for cardiac patient. So it is better to be avoided in cardiac pt.

Ultrapack E retraction cord the one we use (in the photo)

• Six sizes: # 000 (smallest), # 00, # 0, # 1, # 2, # 3 (largest)

• Ultrapack E is Impregnated with racemic epinephrine
(0.2 mg in each 2.5 cm)
• Knitted for better absorption of hemostatic agent ( faster and low deficient ) and help in gingival
retraction because after placement in the sulcus it will rebound and push gingival tissue away
(expansion )
• Other retraction cords can be braided or twisted
• It doesn’t make a big difference if it is knitted or braided in term of the way used but if it is twisted
you need to tighten it and twist it to make tighter before placement in the sulcus

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 Placement of retraction cord (Hints)

• Do not touch any part of the cord other than the ends (latex from gloves can inhibit polymerization
of additional silicone of the final impression)
• Impregnated cords are dipped in 25% aluminum chloride prior to insertion even if it has
epinephrine. the aluminum chloride will make the hemostatic agent more effective as twice as not
dipping in aluminum chloride.
• Don’t dip Ultrapak E in ferric sulphate because epinephrine with ferric sulphate can cause black
precipitate that compromise and adversely affect the accuracy of the impression(I am not sure I
couldn't hear it) but I read that the mix can cause temporary blue coloration or staining)
• Cord formed into U shape and slipped in the mesial interproximal area with plastic instrument
• Work then proceeds to lingual from mesiolingual to distolingual
• Tip of instrument should be inclined toward the area where the cord has already been placed, if you
do the opposite and place it toward the area which haven't been yet to be inserted, that will
displace the part of the cord that has been already inserted.
• Tip of instrument should be slightly angled toward the root (not parallel to the long access of the
tooth) this will help in packing, while if tip of instrument was parallel to the long access of the tooth
this will make excessive pushing and pressure on the gingival cervix that will resist you and the
gingival cord will go out.
• When you have excess cord overlap should occur in proximal areas because the tissue is thick in this
area and can tolerate the overlap better than buccal or palatal.
• Single vs. double cord technique.
Preparation for impression
• Retraction cord is removed after 10 mins (ferric sulphate ; 3 mins)
• Retraction cord must be slightly moist before it is removed
• In double retraction method, second cord (large one) is removed and impression is made with first
cord (small one) in place ( in single we leave it for 10 minutes and remove it before taking the impression, in
double retraction that required in very deep subgingival preparation or the gingival health is bad(inflamed and
too much bleeding) the double retraction might be helpful her we start with fine one deep in the sulcus and
then we have large one superficial on top for further pushing of gingival tissue away from finish line, if you go
for double retraction method remove the superficial one before taking the impression)
• Teeth and sulcus should be dry before injecting impression material

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 6) Final impression
• Silicones (condensational and additional) are usually used
_additional more accurate_
{it comes in different viscosities; light, medium and heavy}

• Polyether is an alternative to additional silicone (monophase)

the same material injected around the margin and on the tray
• While additional silicone (PVS) putty (heavy viscosity on the
tray{catalyst and base}) and wash (light viscosity injected in
the sulcus around the margin to record fine details specially the finish line
and the putty to support the wash as it is heavy in consistency ) will
be used for your cases (one stage technique)
• Universal adhesive should be applied onto the tray
• Light body material (wash) is first syringed in gingival sulcus around
the finish line and then on entire abutments
• While this is being done, impression tray is loaded with heavy body or putty
• Apply wash onto putty mix in tray (teeth areas) before insertion into
patient mouth
• After seating of tray, maintain dry field
• Normal setting material needs 4-5 minutes
• Bite registration (occlufast)

How you judge the impression? can you see the continuity all around the tooth this what we call flash (the
amount of impression material that capture the tooth beyond the margin). In the photo (buccal surface) you
can see the shoulder finish line is prepared while on the palatal is chamfer (it is not clear as the shoulder on
the buccal). Everything beyond this margin (material that recorded tooth structure beyond the margin) what
we call flash. Flash make the impression of a better accuracy because after taking the impression the
technician will prepare the die and trimming the die will be easy task if I have the flash. The technician will trim
all the gingival tissue apical to finish line so the flash will guide the technician where to end trimming exactly. If
we don’t have flash, it is going to be hard task and the technician might trim part of the finish line and that will
make errors in the restoration.

After taking the impression you are not going to let the patient without temporary bridge. Temporary bridge is
important for (pulp protection; prevent unwanted movement of the teeth, occlusal stability and aesthetic). we
will use over impression that we fabricated before tooth preparation and we will use bis-acrylic composite for
this purpose and cement it with temporary cement. We will continue next time..

Forgive me for any error,, best luck,, Israa Al Nassan

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