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2) A) Describe the design features of various crown preparations.

B)Describe the clinical stages in making conventional bridges.There are 3 major types of conventional bridges: Fixed-fixed, fixed-movable and cantilever.

Various factors need to be taken into account when deciding which type to choose:

-Position of the bridge in the mouth

-Status of the possible abutment teeth

-Length of span

-Occlusion

-cleansability

-Appearance

-Depending on the individual patient and the clinical situation, the clinician should be able to judge

whether the abutment teeth should have full gold, metal-ceramic or all ceramic crowns

When constructing bridge:

-take impressions in either alginate/silicone of both upper and lower arches and pour these to be

used as study casts.

- It is also useful to take face bow record and patient's ICP record so that study casts can be

articulated.

-study casts can be used to do trial preparations and diagnostic wax up of the bridge in order to

show to the patient as of how the bridge might appear in the final stage.

-photograph of the patient's dentition

In preparation stage,-Take putty matrices for the tooth/teeth to be prepared

-Local anesthetic to be administered if teeth are vital, or as needed, depending on clinical situation

-shades match

-Prepare the abutment teeth. As two or more teeth are being prepared, they need to have a

common path of insertion, therefore every corresponding surfaces need to be parallel and no

undercuts. Paralleling can be done by using one eye, viewing from as far as possible, or by using a

large intraoral mirror. Straight probe can be used to detect undercuts and over-tapering.

- The amount of reduction on abutment teeth will depend on the type of crown chosen:

* Full gold crown: at least 0.5mm reduction on all aspect with chamfer margin

* All ceramic crown: approximately 1 to 1.5mm reduction with shoulder margin

* Metal-ceramic crown: Palatal aspect is usually covered by only metal, therefore the palatalreduction should be about 0.5mm with chafer margin while the other aspects of the tooth being

reduced by approximately 1.5mm to accommodate metal and porcelain with a shoulder margin

-In some cases, depending on the occlusion and space available, only minimal occlusal reduction is

needed.

-When possible, margin should be supragingival, preferably by about 1mm.

- The taper should be ideally 6*, but less than 12* is acceptable

Once preparation complete, take an accurate working impression, usually with custom tray using

either:

- Single viscosity technique, with polyether(eg. Impregum) or medium body addition cured silicone

(eg. Aquasil), which is syringed on the prepared teeth and tray.

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- double viscosity technique, in which lighter viscosity material syringed around abutment and

heavier viscosity material in special tray.

Temporary bridge:

- Use putty matrix with trim or protemp.

- trim and polished after it set.- fit and check occlusion, the cement with temporary cement.

Impression and occlusal record need to be disinfected before sending to the lab.

Final appointment:

- temporary bridge removed, make sure no cement remains on teeth

-Bridge is tried in. The fit must be checked, making sure there are no gaps, overhanging margins,

deficiencies and tightness in fitting. Floss can be used to check proximal contact. Occlusion should be

checked.

-Patient can be shown of the bridge to ensure he/she is happy with the appearance.

- Cementation with either GIC, zinc phosphate, resin-based cement or zinc polycarboxylate cement.-OHI reinforcement.

3. What methods are available for replacement of four upper incisors lost in an accident in an

otherwise intact and unrestored dentition?

Few options:

1. Do nothing

In any situation, this is always an option if patient accept the appearance and do not wish for any

treatment. But most patient will definitely want some replacement, whether it is for aesthetic

reason, functions as of biting and chewing or for speech.

2. Partial removable denture

Patient can either opt for acrylic denture or cobalt chromium denture. An acrylic denture would be

advised if the patient has poor periodontal health, high caries risk or there are poor prognosis teeth

in his/her remaining dentition that might need extraction and addition of replacement teeth at later

stage. However, since this patient has all other intact teeth and unrestored dentition, we can

assume that he/she has good oral hygiene and low caries risk. Thus, a cobalt chromium denture

would be more beneficial to him/her as it will gain more stability and support from the teeth and

provide a better flexibility in denture design.

For acrylic denture:

*Advantages: simple, quicker and cheaper fabrication, more esthetically pleasing, reparable

*disadvantages: Cover whole palate which may not be tolerated by patient (also plaque retentive),

not always retentive, quite low in strength, prone to fracture

For Cobalt-chromium:

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*Advantages: lighterand thinner in section and cover less palate which may be more comfortable for

patient, less plaque trap, usually more retentive and stable than acrylic, conduct heat and cold which

provides sensation to patient while eating and improve their satisfaction.

*disadvantages: more expensive, complex, time consuming and technique sensitive, less esthetically

pleasing due to metal framework

3. Bridge

In this situation, the best option might be conventional fixed-fixed 6 unit bridge with 2 upper

canines as abutments. Metal-ceramic bridge is preferable than all ceramic as it has superior strength

and relatively esthetic. The pontics could be ridge-lap design or saddle as these look more tooth-like

and it is important in anterior region. The disadvantage of doing conventional bridge is that it causes

irreversible tooth destruction

4. Implants

the last option would be implant-retained prostheses. Advantage of implants have over partial

denture or bridge is that they have good long term prognosis, they can function like a natural tooth

and implant is an independent restoration, so it does not affect the rest of the dentition. butimplants have some drawbacks in that they are very costly and require lengthy tretment, and is

technique sensitive treatment.