CATEGORIES:

Biology Chemistry Construction Culture Ecology Economy Electronics Finance Geography History Informatics Law Mathematics Mechanics Medicine Other Pedagogy Philosophy Physics Policy Psychology Sociology Sport Tourism

Tasks for independent work during preparation to practical classes.

Ministry of Public Health of Ukraine

Higher State Educational Establishment of Ukraine

"Ukrainian Medical Stomatological Academy"

"Approved"

at the meeting of the department

propedeutics of Prosthodontics

Head of the department

Associate Professor, Korol D.M. _________

"_____"_______________ 20___

RECOMMENDATIONS

FOR STUDENTS’ independent WORK

during the preparation to practical classes

Academic discipline	Propedeutics of Orthopaedic stomatology
Module 1	Propedeutics of Orthopaedic stomatology
Intensional module 3	Basic technologies of dentures fabrication
Theme of the lesson	Technology of of metal – ceramic bridges
Academic year	II
Faculty	Stomatology

Poltava 2011

Actuality of the theme: Clear knowledge of construction features indications and contra-indications to their application, clinical and laboratory stages of making largely determine end-point of treatment – restoration of a form and function of masticatory system.

Specific targets:

- to define a indications to metal - ceramic bridges making;

- to define a contra-indication to metal – ceramic bridges making;

- to analyse the features of preparation of teeth for metal - ceramic bridges making;

- to distinguish the sequence of the clinical stages at making of metal - ceramic bridges;

- to distinguish the sequence of the laboratory stages at making of the metal - ceramic bridges;

- to explain positive and negative properties of the metal - ceramic bridges.

2. Base level of training:

Names of previous disciplines	Acquired skills
1. Anatomy	Determination of blood supply and innervation of dental-maxilla apparatus.
2. Physiology	Determination of the mechanism of movement of the lower jaw and the muscles, which set it in motion.
3. Histology	The ability to determine features of dental-maxilla apparatus tissues.

Tasks for independent work during preparation to practical classes.

4.1. Recommendations for students’ independent work and album for independent work of students.

4.2 Theoretical questions to the lesson:

1. Indications to making of the metal - ceramic bridges.

2. Contra-indications to making of the metal - ceramic bridges.

3. Features of teeth preparation for metal - ceramic bridges.

4. Clinical stages of metal - ceramic bridges.

5. Laboratory stages of metal - ceramic bridgesmaking.

6. Errors and complications which arise up during making of the metal - ceramic bridges.

7. Positive properties of the metal - ceramic bridges.

8. Negative properties of the metal - ceramic bridges.

9. Composition, properties and applications of metals and plastics which are used for making of metal - ceramic bridges.

10. Auxilliary materials which are used for making of the metal - ceramic bridges.

4.3. Practical works (tasks) that are executed at the lesson:

By means of diagnostic models, thematic patients demonstratively examined students:

1. indication and contra-indication to metal - ceramic bridge making.

2. sequence and maintenance of the clinical stages of metal - ceramic bridge making.

3. sequence and maintenance of the laboratory stages of metal - ceramic bridge making.

Content of the topic:

This technique consists of

Clinical step. Teeth preparation, obtaining an accurate impression of the prepared tooth

Laboratory step. 1.making a cast from the impression

2. waxing (on cast a wax pattern that resembles the shape of the final restoration is shaped

3. casting. A mold is made around the wax pattern with a refractory investment material. When the investment has set, the wax is vaporized in an electric furnace. The hollow mold is then filled with molten casting alloy, reproducing every detail of the wax pattern

4. The metal casting is retrieved, excess metal is removed, and after polishing, the cast restora tion is ready for clinical evaluation .

Clinical step. Fitting

Laboratory step. Vineering.

Clinical step. Cementation

Clinical step.1

Teeth preparation and impression taking.

An accurate impression is essential for successful fixed prostheses. Obtain gingival retraction where a preparation is subgingival via use of appropriate thickness of retraction cord or occasionally using electrosurgery.

Examine the set impression critically, paying particular attention to air blows, voids, tears and shiny surfaces (lack of flow of impression), and if necessary repeat.

In difficult cases use of impression copings or proceeding to a trial of a casting may ensure a satisfactory end result.

An impression of the opposing arch in irreversible hydrocolloid is required.

Jaw registration is essential and is usually achieved by using wax, reinforced wax or silicone rubber.

PRESCRIPTION TO TECHNICIANS

The dentist should communicate information about crown shape, shade,irregularities and design (e.g. type of margin, type of material, rest seats/undercuts/guide planes) clearly to the technician.

Laboratory step.The working (or master) cast is the replica of the prepared teeth, ridge areas, and other parts of the dental arch. The die is the positive reproduction of the prepared tooth and consists of a suitable hard substance of sufficient accuracy (usually an improved stone, resin, or metal) (Fig.1).

Fig 1 Removable die system.

The accuracy of a cast and die is a function of the completeness and accuracy of the impression. The cast cannot contain more information than the impression from which it was made.

MARKING THE MARGINS

The technician's awareness of the cavosurface margin's location is very important. By marking it with colored pencil, the technician can pinpoint this location (Fig. 18-5). The color should contrast with that of the wax that will be used (e.g., a red pencil can be used for a green wax). An ordinary lead pencil is not recommended, because it can abrade the die, its darker color can interfere with efforts to verify that the wax was properly adapted at the margin, and traces of the graphite (an antiflux) can prevent complete casting of the margins. The marked margins can be coated with low-viscosity cyanoacrylate resin and immediately blown dry. If performed properly, this procedure will add no more than a micrometer"' to the die. Although removing the excess with acetone is sometimes possible, care must be taken not to create a thick layer of cyanoacrylate, which can result in an unacceptable fit of the final cast restoration. For this reason, higher-viscosity resins should be avoided.

Materials

Inlay casting wax (the name given all wax used in forming the pattern for cast restorations) is actually composed of several waxes. Paraffin is usually the main constituent (40% to 60%). The remaining balance consists of dammar resin (to reduce flaking) plus carnauba, ceresin, or candelilla wax (to raise the melting temperature), or beeswax. Sometimes a synthetic wax is substituted for the natural material. Dyes are added to provide color contrasts.

Waxing

A step-by-step waxing technique is recommended. Each step is evaluated before proceeding to the next, which allows corrections and minimizes extra work. The finished wax patterns should be an accurately shaped anatomic replica of the original teeth. Information needed to shape the restoration correctly is derived from the contours of the unprepared tooth surface, adjacent tooth surfaces, and the opposing occlusal surfaces; however, additional in put is needed. This stems from a thorough knowledge of tooth anatomy and the ability to copy threedimensional structures accurately.

Metal Castings are objects made out of metal which are made by fabricating a hollow mold, pouring a molten metal into it, allowing the metal to solidify and separating the now solid metal casting from the mold. quenched in water so as to limit the spread of heat.

Clinical step.On receipt of a bridge from the laboratory check that: • the cast has been trimmed correctly; compare impression margin and cast margin • the neighbouring teeth on the cast have not been abraded • the crown fits the cast • the correct design features are present • the occlusion is correct • the shade looks broadly correct.

The temporary bridge should be removed from the mouth and any adherent temporary cement removed (often this requires local anaesthetic).

The bridge is tried in. The following should be carefully checked:

Marginal fit

Contact point with neighbouring teeth This should be such that interdental cleaning is possible.

Gingival emergence angle

Occlusion In all mandibular movements.

When the dentist is satisfied, the patient should be shown the bridge aesthetics and modifications made if required. When both dentist and patient are satisfied, the preparation is degreased (with alcohol), dried and the crown cemented with a permanent luting cement. If there is any doubt, it is prudent to use a temporary luting cement and review the situation. Excess cement must be removed from around the crown margin. The patient should be given oral hygiene instruction regarding the crown.

Materials for self-control:

Materials for self-control: