انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية طب الاسنان
القسم ترميم ومعالجة الاسنان
المرحلة 3
أستاذ المادة احمد غانم مهدي الهلال
4/27/2011 2:38:10 PM
Preparation of the 3\4 crown
It is a cast restoration which covers 3\4 of crown (occlusal, incisal, palatal & proximal leaving the labial or buccal surface unprepared) it tends to be less retentive & less resistant to displacement compared with full metal & full veneer crown.
Uses:
1. as a retainer for short span bridge.
2. as a single restoration.
3. as a splint in anterior teeth
Indications:
1. The teeth with a clinical crown of sufficient length & thickness labiolingually.
2. Teeth which have good axial relation with adjacent teeth.
3. Good oral hygiene.
4. Teeth with minimum or without caries on buccal or labial surface.
Contraindication:
1. Short teeth (short clinical crown).
2. Poor oral hygiene.
3. Poor axial alignment & relationship.
4. Tooth with extensive caries.
5. as a retainer for long span bridge.
Advantages of 3\4 crown
1. Tooth structure is saved.
2. Better esthetic than other types of crown.
3. Vitality test can be done on the unprepared tooth surface.
4. Less chance of periodontal irritation because all the margins of the crown are supragingival.
5. Complete seating of the crown can be easily seen by direct observation.
Disadvantages :
1. Difficulty in preparation compared to other types of crowns.
2. There is more possibility of recurrent caries along the cavosurface line angle.
3. There is a possibility of metal display especially in the lower anterior and posterior teeth.
Preparation of 3\4 crown on the anterior teeth:-
1. Lingual reduction:
It is done by two steps similar to other types of crowns.
2. Incisal termination:
For the maxillary anterior teeth a lingo – incisal bevel is placed using a diamond bur at 35 degree to the lingual surface, this preparation shouldn t be extended labially to prevent the showing of metal. For the lower anterior teeth a reveres bevel is placed on the labial surface to cover the incisal edge in order to protect the area of unsupported enamel from the fracture & prevent the dislodgment of the crown.
3. Proximal area:
This is prepared similar to the full veneer crown but care should be taken to avoid breaking of the contact of the labial surface.
For retention; two proximal grooves should be placed parallel to the incisal 2\3 of the labial surface using a carbide fissure bur to get the longest groove for better retention & to avoid over cutting to the labial surface resulting in poor esthetic (metal display). The groove should be placed at the junction of the labial & middle third of the proximal surface & parallel to each other, the base of the groove should be 0.5mm above the chamfer finishing line, the mesial & distal grooves should be connected with an incisal offset. The advantage of the incisal offset is improvement of the strength of the casting at this area & reinforcement of the margin by connecting the tow proximal groove together with mechanical strut.
Differences in preparation of upper & lower posterior teeth:-
1. the occlusal finishing line of the maxillary teeth terminate near the buccocclusal junction while in the lower teeth the finishing line is 1mm gingival to the lowest occlusal contact with upper teeth because the buccal cusp in lower teeth is a functional cusp which should be cover by gold.
2. In the upper teeth there should be an offset, in the lower teeth there is no offset but there is bucco-occlusal shoulder (i.e. more reduction).
Difference between anterior & posterior teeth preparation:
In the anterior teeth the retentive proximal groove should be parallel to the incisal 2\3 of the labial surface while in the posterior teeth it is parallel to the long axis to get the longest groove for better retention of the crown.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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