Date of Lecture 29-9-2018 · missing tooth. If we have the upper or lower canine we should consider...

Faculty of Dentistry Batch of 2018

Date of Lecture 29-9-2018

Sheet Number 3

Doctor Fuad Kathim

Written By Alaa’ Nashwan

Corrected by Ruba Halasa

Reference sheets in 2013

(if present) 2

University of Jordan Cons 5 Sheet #3 Faculty of Dentistry

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Let's continue what we started talking about last lecture..

We talked about replacement of single missing tooth, and usually what we do is a

three-unit bridge; this bridge has 2 retainers, the first one is the mesial abutment

and the second one is the distal abutment, and the pontic which replaces the

missing tooth. If we have the upper or lower canine we should consider two

abutments, or we can prepare two mesial teeth "the lateral and central”, also we

talked about the use of cantilever bridge in cases where the upper lateral is

missing.

Problems associated with using the cantilever bridge are tipping, rotation and

drifting for the abutment, because in 3-unit bridge the forces are distributed on two

abutments rather than in one abutment in cantilever. "the figure below is from the book"

You must do proper assessment for the abutment before you start the preparation,

it's good idea to replace all previous amalgam or composite restoration on the

abutments, and after the removal of old restoration we decide if this tooth is

indicated for RCT or not. If a proper RCT was done for the abutment with proper

post and core the tooth can serve as abutment for the bridge.

We know that the walls for abutments should be parallel to each other, for

example if the 5 is missing the distal wall of the 4 should be parallel to mesial wall

of the 6 after preparation to have a proper path of insertion, but what if the


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abutment is tilted? Here we may cut more from the tooth structure but if the tooth

is vital there is a risk of pulp exposure; so what are the options?

1- RCT then preparation.

2- Correction for the tilted tooth orthodontically.

3- Modify the preparation or the type of retainer used, instead of doing full

coverage for the tilted abutment do three quarter prep sparing the distal part of

tooth.

A student asked a question which I couldn't hear, but this is what the doctor

answered: in case of single tooth is missing we go for doing three unit bridge,

canine is large tooth subjected to heavy occlusion, the lateral is small so it will not

serve as good abutment so that's why we prepare two mesial abutments when the

canine is missing.

When I choose the abutment I think how the forces will be distributed? Forces

should distribute equally between the distal and mesial abutments.

Replacement of multiple missing teeth

Fixed prosthodontics becomes more difficult when several teeth are missing;

problems will be encountered when restoring a single long uninterrupted

edentulous area, or multiple edentulous areas with an intermediate pier abutment

especially when anterior and posterior teeth need to be replaced

with a single fixed prosthesis.


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Here in this figure we have a tooth between

two edentulous areas and this tooth is called

"pier abutment".

The difficulty here is that I must prepare three

teeth; one of the requirements to get correct

preparation is that I have to prepare the three teeth in the figure above parallel to

each other and it's difficult to achieve this parallelism.

Under estimation of the problems involved in extensive or extended prosthesis can

lead to failure. to ensure a successful result we have to plan the prosthesis by

waxing the proposed or planned restoration on articulated diagnostic cast and then

study the case carefully.

One of the solutions for the case in figure above is to do 2 separate bridges, a 3

unit bridge on the 5, and 3 to replace the 4, fixed-movable retainer on 7 and

mobile retainer on 5, so now we have (1) fixed-fixed bridge, and (1) fixed-

movable bridge, and by this we avoid doing a long bridge.

Waxing up on the diagnostic cast is essential for the complex fixed prosthodontics

treatment, particularly where an irregular occlusal plane is to be corrected, the

vertical dimension of occlusion is to be altered and a planned supported prosthesis

is recommended or combination of fixed and removable prosthesis are to be used.


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look at this case, due to extraction and destruction of carious teeth , the patient had

such occlusion with low vertical dimension, so patient may have functional and

appearance problems so patient essentially needs to restore the vertical dimension

in order to provide space for placement of missing teeth.

To solve this problem you have to start by collecting data, doing a diagnostic

study model articulating the upper and lower casts after doing the wax pattern then

you can study the case (e.g. if you are considering veneers, discussing the wax up

with the patient is a good idea)

When you design a fixed bridge for multiple missing teeth you have to consider

these influencing factors;

A) Overloading of abutment teeth:

-The ability of the abutment teeth to accept applied forces without drifting or

becoming mobile must be estimated and has a direct influence on prosthodontics

treatment plan. These forces could be particularly severe during parafunctional

grinding, heavy occlusion and clenching, and the need to eliminate them becomes

obvious during restoration of such a damaged condition.

The first point you have to consider in order to avoid overloading abutment is the

direction of forces; whereas the magnitude of the forces is difficult to regulate, a

well fabricated FPD can distribute these forces in the most favorable way,

directing them in the long axis of abutment teeth. When we have multiple missing

teeth it's not always necessary to do full coverage, sometimes it's good to modify

the preparation. (in case of sound mesial and distal abutments, 2 or 3 quarter preps

may be a good option)


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The second point you must consider avoiding overloading abutment is the root

surface area; Ante's law suggested in 1926 that it was unwise to provide a fixed

partial denture when the root surface area of the abutment was less than the root

surface area of the teeth being replaced.

- Surface area of the root of the abutments should be equal or more than

the surface area of the root of the missing teeth.

Imagine if we have missing first molar, and the surface areas of second premolar

and second molar are more than surface area of first molar. which is a good case.

But in case of two teeth missing (second premolar and first molar), compare their

surface area to the surface area of first premolar and second molar. the root surface

area for the 7 & 4 should be equal or more than the surface area of the teeth to be

replaced (5 & 6 so you have to study the case carefully you may need to do

preparation on canine and premolar)


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This

table is from the book showing the root surface area for each tooth, not to

memorize of course but to understand the idea.

Third point you need to consider is Root shape and angulations, also an

important factor; When the tooth support is borderline, the shape of the roots and

their angulations should be considered. A molar with divergent root will provide

better support than molar with conical root and little or no inter-radicular bone. So

when the tooth has more than one root and the inter-radicular bone between roots

is more, it will serve as good abutment. Imagine a tree with only one root and

other one with multiple divergent roots, surely the second one is more strongly

attached to the ground same principle is applied to the teeth.

Periodontal disease should be considered; after horizontal bone loss from a

periodontal disease the periodontal ligament tissue supported root surface area can

be reduced because of conical shape of most roots when one third of root length

has been exposed half of the supporting area is lost.

so when a third of periodontal ligament of root are loss and bone loss occur, it will

cause loss of about half of a root support because it’s a conical shape root.

Ex. when we calculate the surface area of this third it's about a half of the surface

area of the whole root.

In addition, the forces applied to the supporting bone are magnified, because of

greater leverage associated with length of the clinical crown plus potentially

abutment need to be carefully assessed where significant bone loss has occurred.


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B) Length of edentulous span:

All fixed partial denture flex slightly when subjected to load, the longer the span

the greater the flexion, the relationship between deflection and length of the span

is not simply linear but varies with cube of length of the span.

So, when we have long span even if we did good preparation the patient will keep

visiting us complaining from de-cementation of the prosthesis and we need to re-

cement; why? Any type of bridges tends to deflect upon function; this deflection is

not simply linear. When I had one pontic in my prosthesis let’s suppose that the

deflection would be “X” when I had two pontics the cube of 2 is 8, so the amount

of deflection would be “8X”, when I had three pontics the amount of deflection

would be “27X” . This large deflection would present clinically by de-

cementation or fracturing of porcelain.

Excessive flexing under occlusal load may cause failure of long span fixed partial

denture it can lead to fracture of porcelain veneer, breakage in connector area of

the retainer or unfavorable tissue response, this renders the prosthesis prognosis

poor.

Replacement of multiple anterior teeth:

-Special consideration in this situation includes problems with appearance and the

need to resist laterally directed tipping forces.


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-The 4 mandibular incisors can usually be replaced by simple fixed partial denture

with a retainer on each canine, in the lower it's not usually necessary to include the

premolar; Final restoration is 6 unit bridge replace 4 lower anterior teeth.

-If a single incisor remains, it should be extracted because its retention will

unnecessarily complicate the design and fabrication of FPD, and can jeopardize

the long term results.

- the Mandibular incisors because of their small size teeth generally make poor

abutment, it is particularly important not to have over-contoured restorations on

these teeth because plaque control will be nearly impossible.

Thus the clinician may have a choice between a compromised esthetic (too thin

ceramic veneer) or pulp exposure during tooth preparation and elective Endo.

Sometimes when two centrals are missing we can do preparation on laterals they

will be good abutments, but the problem is the difficulty of having acceptable

esthetic restoration, always they become over contoured because these laterals are

too small also if we make over reduction we will end up with pulp exposure

because we need room for porcelain and we need more cutting.

Replacement of missing maxillary incisors:

The loss of several maxillary incisors is a much greater problem in term of esthetic

and providing support because of the curvature of arch, the forces directed against

the maxillary incisors which tends to tip of the abutment teeth (the canine is not

enough because there will be drifting in preparation, so you have to involve the

first premolar in preparation, so the missing upper incisors need two abutments

(canine and first premolar) at each end of a long span FPD (replacing all 4

maxillary incisors).

If anterior bone loss has been severe as can happen when teeth are lost due to

trauma or periodontal disease they may have a ridge defect. In those patient

(removable partial denture) should be considered especially when the patient has

high smile line since a fixed partial denture generally replace only the missing

tooth structure and not the supporting tissue. Sometimes we can use pink porcelain

to imitate the color of gingiva, but this is in limited scenarios.

Sequences of treatment plan:

when a patient needs have been identified and the appropriate corrected measures

have been determine, a logical sequence of steps must be decided on including the


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treatment of symptoms, stabilization of deteriorating conditions(dental caries and

periodontal disease), the definitive therapy (prosthodontics) and then a program of

follow up care .

1- Treatment of symptoms:

The relief of this discomfort accompanying an acute condition is a priority items

in planned treatment, this discomfort can be due to one or more of the following

items: Fractured tooth, acute pulpitis, acute exacerbation of chronic pulpitis, dental

abscess, acute pericoronitis or gingivitis and myofacial pain dysfunction.

Fortunately most patients candidate for fixed prosthodontics do not seek treatment

for acute conditions, the patient who comes to you for bridge construction ,does

not come with acute pulpitis or pain, his chief complaint is replacement of missing

teeth (esthetic problem).

However, they may have a specific problem which should receive immediate

attention such as anterior cracks or broken porcelain veneer or fractured

removable partial prosthesis.

2- Stabilization of deteriorating conditions:

The second step of treatment plan is stabilization of deteriorating conditions such

as dental caries and periodontal disease by removing the etiological factor,

increasing patient resistance or doing both.

Dental caries treatment is approached by a conservative manner and teeth are

restored with a proper contoured plastic material.

Periodontal disease; chronic periodontitis, with continued irreversible bone loss

should be treated as early as possible. Proper removal of plaque is possible only if

Question:

If a patient come with fractured porcelain crack , how could you deal with this case?

By adding Composite by using special bonding agent after doing etching for porcelain using

hydrofluoric acid not phosphoric acid which is weaker acid.

Question: why we do not use phosphoric acid? And why we use it on enamel and dentine?

1- Phosphoric acid reacts with hydroxyapatite crystals, the byproduct of this reaction is

washable.

2- The hydroxyapatite(Ca10(PO4)6(OH)2) have H3PO4 or phosphate which is also part of

phosphoric acid so it's not considered a foreign material and they share the same

compositions.

3- Phosphoric acid has a high molecular weight so we do not expect a more occurrence of

penetration of this acid into the dentinal tubules.

4- The PKa of phosphoric acid is weak so we do not expect the formation of hydrogen ions.

So all these are reasons for using phosphoric acid on enamel and dentine.

2013 sheet…


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the teeth are smooth and their contours allow unimpeded access to the gingival

sulci.

- So, the following are essential for stabilizing the condition:

Replacements of defective restoration, removal of carious lesion, recontouring of

Over-contoured crowns (especially in the furcation area) and oral hygiene

instructions and then start the definitive treatment.

Several therapeutic proposal may be applicable for a single patient and may range

in complexity from minimum restoration treatment with regular maintenance to

full mouth prosthodontic reconstruction proceeded by orthognathic surgery or

orthodontic treatment.

So first we control the acute condition, then stabilization then we start the

definitive treatment (removable or fixed). It's very important to start with making

wax pattern in order to study the case, predict the treatment outcome, show the

patient what's the final result would be and study how much space you have for

the prosthesis (could the space accommodate two teeth or a single tooth?), and

study it on the articulator.

Usually surgical procedures are scheduled first, followed by periodontics,

endodontics, orthodontics, fixed prosthodontics, (from restoration of a single tooth

to rehabilitation of the entire mouth), and finally removable prosthodontics.

Fixed Prosthodontics is only initiated after the preceding modalities have been

completed, this will permit modification of the original plan if unforeseen

difficulties surface during treatment.

for example; a tooth is indicated for RCT, porcelain core and then it will serve as

abutment, but after caries removal we find that it's non-restorable so now we have

to change treatment plan.

Occlusal adjustment are often necessary before the initiation of the fixed

prosthdontics, where extensive prosthodontics are to be provided, an accurate and

well tolerated occlusal relationship may be obtainable only if the discrepancy

between intercuspal position and centric relation is eliminated first.

The correct sequence of Tx is to start with correction of occlusion, followed by

anterior restorations, then posterior restorations, complex restorations then follow

up.

Further explanation; if a patient came complaining from missing anterior teeth and

posterior teeth also she has occlusal problems (deflection while attempting

maximum intercuspation position) the correct treatment steps are the above

mentioned, the doctor just repeated them.


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If both anterior and posterior teeth are to be restored, anterior teeth are usually

done first because they influence the border movement of the mandible and thus

the shape of occlusal surface of the posterior teeth.

We must start with anterior in order to create the anterior guidance as we said and

then go back for posterior restoration.

If the posterior teeth are restored first a subsequent change in the lingual contour

of the anterior teeth could require considerable adjustment of the posterior

restoration.

Restoring the opposing posterior segment at the same time is often advantageous,

this permits the development of efficient occlusal scheme through the application

of an additive wax technique, so one side of the mouth should be completed before

the other side treatment.

If I have lower and upper segment need bridges at the same side we create the

bridges at the same time so do impressions, put the models on the articulator then

make a wax pattern,

So we will have a proper occlusal relation, and a good space for what will be

added of restorative materials and we can do a proper marginal ridge to cuspal

relationship.

Restoring all four posterior segments at the same time might lead to considerably

more complications for the patient and the dentist including fracture of breaking of

the provisional restorations, discomfort with bilateral local anesthesia and

difficulties in confirming the accuracy of jaw relationship recordings.

Complex prosthodontics:

Carefully planned treatment sequencing is particularly important when complex

prosthodontic treatments involving alteration of the vertical dimension or a

combination of fixed and removable prostheses are required.

When patient has many missing teeth, loss of vertical dimension, wearing in teeth,

so how to treat this step by step?

Proper examination, vitality testing, periodontal chart, diagnostic casts and wax

pattern, ask the patients about their expectations, then think and evaluate the

abutments and how the force distribution would be, think about the periodontal

condition how much bone do you have, the oral hygiene is important it will

determine if the patient motivated or not.

So, consider all these when you're going to put your treatment plan.


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The doctor showed a case of a patient who has wearing of the teeth, loss in the

vertical dimension; how do we know that VOD has lost? By looking to patient

profile, we need to restore the vertical dimension by using night guard and

occlusal splint and creating a space and then start our restorations; crowning for

anterior teeth (upper and lower) and then the posterior restorations.

Always follow these steps for any case and don't forget the regular follow up

visits.

Follow up

A specific program of follow up care and regular recall is an essential part of the

treatment plan, The aim is to monitor dental health, identify the signs of disease

early, and initiate prompt corrective measures as necessary. The first lecture done Take a breath

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