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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 post core restoration.
Academic year II
Faculty Stomatology

 

 

Poltava 2011

 

Actuality of the theme: Complete absence of crown of the tooth are a result of trauma or caries and its complications. But the if roots of the destroyed teeth are yet strong enough and not staggered, as well as their paradontium, these roots can be used for crowns restoration. 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 classify different constructions of post core restoration.

- To define and ground a indication and contra-indication to post core restoration.

- To distinguish the clinical and laboratory stages of post core restoration making.

- To explain positive and negative properties of post core restoration.

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. Post core restoration, determinations of concept, basic elements.

2. Classification of post core restoration.

3. A indication and contra-indication are to application of different post core restoration.

4. Features of preparation of root for post core restoration making.

5. A role of auxiliary methods of inspection is in preparation of root to post core restoration making.

6. The clinical and laboratory stages of post core restoration by Richmond making .

7. The clinical and laboratory stages of post core restoration by Ilina-Markosian making .

8. The clinical and laboratory stages of post core restoration by Katz making .



9. The clinical and laboratory stages of post core restoration by Ahmedov making.

10. The clinical and laboratory stages of post core restoration by Logan making.

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 making of the post core restoration.

2. sequence and maintenance of the clinical stages of making of post core restoration.

3. sequence and maintenance of the laboratory stages of making of post core restoration.

Content of the topic:

Single-root teeth, and sometimes teeth with several roots can be replaced by pin teeth which are however unsuitable for mandibular incisors with a thin root compressed on both sides and a narrow canal.

Pin teeth are made according to commonly accept­ed clinical and technical practice.The pin is the main means of fixation of the tooth in the root. When replacing a single-root tooth the artificial crown is adequately secured to the root if the pin is the same length as the crown or longer. The pin should also be thick enough to resist lateral pressure falling on the crown during mastication. Experience has shown that it should be at least 1.0 to 1.2 mm thick. For adequate resistance to lateral pressure the walls of the root at the entrance to the canal should be at least 2.0 mm thick. Since the root and its canal are narrowed toward the apex, the pin should be conical, i. e. have a wide base at the entrance to the canal and taper gradually to a sharp tip. In addition, it should be resistsnt to bending and shaped so that it does not twist about its longitudinal axis.

Pin teeth replacing teeth with several roots may have more than one pin, the number depending on whether the root canals are obstructed or are parallel to each other. When two or more pins are incorporated in a crown they can be made shorter and thinner in accordance with the length and width of each root.

The part of the pin tooth adjoining the root should come within the area protruding above the gin­gival margin. Sometimes the part of the root in the gingival pocket can also be utilized.

According to construction and method of fixation in the root, three main types of pin teeth are distin­guished; (1) simple, (2) with an inlay, and (3) with an external ferrule.

The group of simple pin teeth includes Logan's crown,a monolithic metal or plastic crown, and crowns made of metal in combination with plastic material or porcelain. A pin tooth with an inlay differsfrom the simple design in that a rather wide square cavity is prepared at the entrance into theroot canal in which the cast pin with an inlay is fastened. The distinguishing feature of the third type of a pin tooth is its supporting component consisting of a pin and a ferrule or cap gripping the portionof the tooth protruding above the gum. Pinand cap form a single whole.

LOGAN'S CROWNS

Logan's crowns are factory produced porcelain crowns with a pin used to restore maxillary ante­rior teeth. The pin is firmly fixed in the porcelain crown or constructed separately. Expe­rience has shown that a design with a separate pin is preferable. The application of a Logan's crown involves preparation of the extragingival part of the root, dilatation of the root canal, adjustment of the pin and crown, and fastening the pin tooth on the root with phosphate cement.

Preparation of the root.— First the whole part of the root protruding from the gum is made even with a carborundum stone and to produce a favourable aesthetic effect tissues are then re­moved from the labial surface to a level with the gingival margin so that the gingival edge of the porcelain crown fits closely to the gum.

Dilatation of the root canal.— The canal is gra­dually widened by means of canal dilators, beginning with an instrument of the same diameter as the canal and changing to larger ones till a dila­tor as wide as the pin can be introduced. A canal that contains a filling is opened with a pointed fis­sure burr of the same diameter as the canal. The burr should be lightly advanced along the natural passage of the canal without force. After that canal dilators are used.

Adjustmentof the pin.— Pins for Logan's crowns are factory produced. They are made with a plate for closing the root canal and the canal in the porcelain crown. To be adjusted the part of the pin that is to be inserted into the canal is shortened till the entrance to the canal is closed with the plate.

Adjustmentof the porcelain crown.— A crown of the right colour, size, and shape is chosen and the part adjacent to the root (i.e. the gingival part) is ground accordingly so that its surface fits snugly on the root, leaving no gaps. That is achieved by means of the following procedure. The surface of the root is painted black and the porcelain tooth fitted on it. Spots on the porcelain to which paint adheres are ground away with a carborundum stone. The procedure is repeated until the whole surface pressed against the root is covered in paint, which shows that tooth and root are in close contact. The pin is left in the root canal all the time, while the porcelain crowns fitted over the part that protrudes, which excludes errors in adjustment.

After the gingival part is completely adjusted the size of the crown is checked. An abnormally long crown is shortened and the medial and distal angles formed, copying the shape of the symmet­rical tooth.The last to be checked is the lingual surface of the crown which should allow occlusion of the dental rows and horizontal occlusal excursions of the lower jaw.

PLASTIC PIN TOOTH ( Ilyina-Marcosyan’s crown)

In distinction to Logan's crown a plastic pin tooth is constructed in the laboratory.

Tooth preparation is the same as for Logan's crown. The next stages are adjustment of the pin, impression taking, construction of the tooth in the laboratory, checking the accuracy of the construction, and fixation of the tooth in the root canal with cement.

The pin is made of stainless steel. When inserted into the root canal part of it should protrude above the root for fixation of the plastic crown. A cast pin can be used instead of a standard one. In that case it is modelled in wax at the same time as the pattern of the metal covering for the surface of the root, which strengthens the construction of the pin tooth and ensures an accurate fit.

After the pin has been adjusted impressions are taken and models cast to them. The crown is waxed on the model, but first the part of the pin protruding from the root is short­ened and dents are made in it for better fixation of the plastic material. The wax pattern is taken out of the model together with the tooth and invested in plaster in a casting ring to substitute plastic material for the wax. After polymerization of the plastic material the pin tooth is trimmed, filed, and polished.The fabricated restoration is fastened in the root.

A pin tooth of self-setting plastics is fabricated at a single sitting. The sequence of the procedures is as follows. The root canal is pre­pared, a pin with a root-covering plate is adjusted in itand a celluloid cap is selected, ad­justed, loaded with a self-setting plas­tics, and fitted over the tooth root. After the plas­tics sets the pin tooth is removed from the canal, the cap cut, excess amounts of plastics trimmed away, and the root canal prepared (wiped with alcohol and ether) and filled with cement, and the pin tooth is fastened in it.

Ilyina-Markosyan proposed the construction of a cast pin with an inlay to ensure better fixation in the canal and reduce the pressure exerted on the walls of the root. The lateral jolts which are most detrimental to the root are absorbed and, in addition to that, the inlay prevents the pin tooth from rotating and isolates most reliably the canal from saliva. The cavity for the inlay is formed at the entrance to the root canal. The inlay is cast (pre­ferably in a gold-platinum alloy) and the pin is made of wire which is resilient and most suitable for bearing pressure. The pin should be not short­er than the crown (1.013 1.2 cm) and 1.5 to 1.75 mm thick in its widest part.

Correct preparation of the extragingival part of the root is important. It is made concaved, straight or bevelled in relation to the tooth axis, but never bulging (so that the metal fills the defect in the tooth). With such preparation shrinkage of the metal after casting the protective plate is less signi­ficant.

PIN TOOTH WITH AN EXTERNAL FERRULE (RICHMOND'S CROWN)

A pin tooth with an external ferrule (Richmond's crown) was proposed for reinforcing the extragin-gival part of the root and isolating completely the root canal from the moisture of the oral cavity. It is made of gold or a gold-platinum alloy. The con­struction differs from those already described in the root being covered with a pressed or soldered cap inserted 0.5 to 1 mm deep under the gingival margin. A pin is introduced into the root canal and joined to the cap. On that foundation a crown of porcelain, plastics, or metal with a veneer is fabricated.

Materials for self-control:

Materials for self-control:

1. Post core restoration, determinations of concept, basic elements.

2. Classification of post core restoration.

3. A indication and contra-indication are to application of different post core restoration.

4. Features of preparation of root for post core restoration making.

5. A role of auxiliary methods of inspection is in preparation of root to post core restoration making.

6. The clinical and laboratory stages of Richmond's crown making .

7. The clinical and laboratory stages of post core restoration by Ilina-Markosian making .

8. The clinical and laboratory stages of post core restoration by Katz making .



9. The clinical and laboratory stages of post core restoration by Ahmedov making.

10. The clinical and laboratory stages of Logan's crowns making.

 

 


Date: 2016-01-14; view: 820


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