محاضرات المرحله الرابعه Crown and bridge Lec .1 Dr. zainab shakir محاضرات المرحله الرابعه

Crown &bridge

Crown : It's a fixed artificial restoration of the coronal portion of a natural tooth It must restore the morphology, contour and the function of the tooth should protect the remaining tooth structures from further damage

Types of crowns(classifications) Bridge - according to coverage area Complete crown Partial crown Complete replacement Bridge

Types of crowns(classifications) Bridge - According to materials 1. Metal {Gold alloy and it's alternatives} as in full metal crown and 3/4 crown. Bridge 2.Non metal : Such as Acrylic resin or Porcelain as in jacket crown. 3. A combination: of metal and plastic materials as in full veneer crown.

Bridge It's a fixed prosthesis constructed to replace the missing [one or more] teeth.(cant remove by the patient ) The tooth that gives support to the bridge is called an abutment tooth.

Component of the bridge Connector Pontic Retainer Retainer abutment

Purposes of crown construction To restore the grossly damaged tooth, To restore the masticatory function and speech. To restore the esthetic. To maintain the periodontal health. As a retainer for the bridge.

Diagnosis: Steps in crown construction Periodontal Examination dental examination

2 Tooth Preparation: it is the cutting or instrumentation of the abutment tooth to be in a form to seat a crown on it.

3. Final impression

4. Temporary restoration (Crown), 5. Construction of working model. 6. Waxing. 7. investing, 8. Wax Elimination, 9. Casting. 10. Finishing and polishing. 11. Cementation of the restoration.

Disadvantage of crown Heat generation Over preparation cause pulp irritation or exposure lead to death of the pulp Periodontal problem ,food impaction and secondary caries might develope

Finishing line of the preparation

It's the final margin that separates between the prepared and the unprepared tooth structure. The F.L. should be smoothly continuous from one surface to the other, interfere with seating of the crown if it's poorly done.

Margin placement 1- Subgingival 2-Supragingival 3- Placing the margin within the level of the gingiva

1- Subgingival Placing the margin below the gingival tissue for these reasons:- For esthetic reason. To increase retention of short teeth. To place the margin on sound tooth structure.

2- Supragingival: Placing the margin above the gingival tissue for these reasons:- It's self cleansable area. To provide good vision for the dentist during preparation. Easy to finished. Easy to take impression Less destructive

3- Placing the margin within the level of the gingiva.

Types of finishing line Featheredge (or knife –edge) margin. Chamfer F.L. Shoulder F.L. Bevel shoulder (modification of shoulder F.L.) by beveling the margin. These different types of F.L. Depend also on the types of the crown

1- Feather edge We use pointed end tapered fissure bur to provide this type of margin. It's the most conservative type of F.L. But the margin is weak. It's easy to prepare but difficult to be detected on the cast or tooth, the gold can be burnished to this margin. It's mainly used for: I- Full Metal Crown (All the surface). 2- Lingual and proximal surfaces of full veneer crown, three quarter crown and post crown.

2. Chamfer F.L.: It is well defined F.L. That has an adequate space in the cervical region we can make the contour of the crown restoration within the contour of natural tooth. It is thick. We can use the round end tapered fissure bur for this margin. It is mainly used for: I- Full Metal Crown (All the surfaces). 2- Lingual and proximal surfaces of full veneer crown, three quarter crown and post crown.

3. Shoulder F.L. (butt shoulder): It's the least conservative type of F.L.. Shoulder F.L. is almost used with jacket (all around) since jacket is made either of porcelain or acrylic resin (brittle materials) that require enough thickness we use tapered fissure bur (diamond) with flat end.

4. Bevel shoulder F.L. By creating a bevel on the end margin of unprepared tooth structure, this is needed when we use a metal with facing material e.g. Metal- porcelain or metal-acrylic. We used gold alloy because ceramic materials when extended subgingivally are irritant to the gingiva Bevel shoulder is used on the labial surface of full veneer crown and is recommended for extremely short walls.

Factors affecting selection of F.L Type of restoration Material used in construction Amount of occlusal force (stress the restoration will bear

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