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INTRODUCTION & Extra-coronal TERMINOLOGY restorations Part I: General Partial considerations coverage restorations
Partial coverage restorations as we said before, these are restorations that used to restore just a portion of the clinical crown. And are classified according to retention, as: 1. by grooves : ¾, R3/4, ½, 7/8 crowns (= restorations). 2. by pins (pin-ledge). 3. Modified type (grooves + pins).
¾ crown : is a partial coverage restoration that restoresthe occlusal surface(or incisal edge), and threeaxial surface of the clinical crown (the facial orbuccal surface is not included). this type is indicated for upper anterior andposterior teeth. and it can be prepared on a lower posteriorteeth too with little difference in thepreparation.
Reversed ¾ crown : is a partial coverage restoration that restores the occlusal surface(or incisal edge), and three axial surface of the clinical crown (the lingual surface is not included). this type is indicated for lower posterior teeth. And it is useful for server lingual indications.
Mesial ½ crown : is a partial coverage restoration that restores the occlusal surface(or incisal edge), the mesial surface and a portion of the facial or lingual surfaces. this type is indicated for mesially tilted tooth.
7/8 crown : is a partial coverage restoration that restores the all surfaces of the clinical crown except the mesiobuccal cusp remains intact. this type used only for the maxillary first molar teeth.
Pin-ledge is a technique that employs parallel long pins prepared in the lingual or palatal surface of the clinical crown, in order to increase retention of the restoration.
These restorations used theboth grooves and pins toimprove retention.
Partial coverage restorations •Indications the partial coverage restorations are used: 1. for both anterior and posterior teeth. 2. when the coronal portion is intact. 3. when there is a good crown length. 4. as a retainer for FPD (short edentulous span). 5. when there is a minimum occlusal stress.
Partial coverage • Contraindications restorations the partial coverage restorations arecontraindicated :1. when maximum retention is required.2. in case of a thin or short clinical crown.3. for patient with high caries index.4. when there is active periodontal disease.5. in case of mal formed tooth, e.g. Bellshaped canine.
Partial coverage • Advantages restorations 1. preservation of tooth structure. 2. more esthetic than full coverage restorations. 3. the finish line is easy to place. 4. less periodontal irritation due to the less contact with the tissues. 5. pulp damaged is reduced.
Partial coverage • Disadvantages restorations1. less retentive than the full coverage.2. difficultly of placing the grooves and pins properly.3. in some restorations, the metal is displayed and this is not acceptable by the patient.
The ¾ crown is : a. a restoration that restores the all surfaces of the clinical crown except the mesiobuccal cusp remains intact. b. a technique that employs parallel long pins prepared in the lingual or palatal surface of the clinical crown. c. a restoration that restores the occlusal surface and three axial surface of the clinical crown without including the buccal surface in the preparation.* In which cases, the partial coverage restorations are contraindicated?