definition - national university crown.pdf · pin modified three quarter crown steps involved in...

Definition

The partial veneer crown is a conservative restoration that involves less tooth destruction than a full crown.

Intact tooth surface are not covered if it is not important to the retention, strength, or cosmetic result of the final restoration.

Advantages

• Conservation of tooth structure.

• The margin accessible for finishing & cleaning.

• Less restoration margin so less gingival irritation.

• More easily seated during cementation than full crowns

• No interference during electrical pulp testing.

Disadvantage

• Less retention and resistance than full coverage crowns. This could be compensated for by adding grooves for retention.

Indications

• Restore posterior teeth that have moderate amount of tooth structure loss with the buccalsurface intact.

• Used as retainers for FPD

• Used to alter the occlusal surface for prosthesis.

Indications

• Anterior partial crowns are used as retainers to re- establish the anterior guidance

• Splinting teeth with sufficient bulk

Indications

Contraindications

Can not be used on the following situations:-

1. Short clinical crowns

2. Retainers for long FPD

3. RCT teeth

4. Active caries & periodontal disease.

Types of Partial Crowns

- Anterior ¾ Crown

- Pin Modified ¾ Crown

The Anterior Crown

- Maxillary posterior ¾ crown

- Modified ¾ crown

- Maxillary ¾ crown with proximal boxes

- Seven-eighths crown

- Reverse three-quarter crown

- The proximal half crown

The Posterior

Crown

Maxillary PosteriorThree-quarter Crowns


• Is a partial veneer crown in which the buccalsurface is left uncovered.

• It is the most commonly used partial veneer crown.

• The occlusal finish line on a maxillary tooth ends near the bucco-occlusal angle.

• Esthetic.• It can be used on maxillary posterior teeth,

where esthetic demands are moderate and reasonable.


Clinical Tooth Preparation Steps:-

Occlusal reduction

• The same as for full metal crown

• Start with guiding grooves


Clinical Tooth Preparation Steps:-

Occlusal reduction

• The grooves will extend through the occlusobuccalline angle, but they will be only 0. 5 mm deep there.


Occlusal reduction

• Occlusal reduction is completed by removing the tooth structure between the grooves

• The depth decreases at the occluso- buccal line angle to minimize the display of metal


Occlusal reduction

• Next the functional cusp bevel is made


Axial reduction


Axial reduction

• First reducing the lingual surface with a torpedo diamond.

• The cut extends interproximally on each side as far as possible without touching the adjacent teeth.


Axial reduction

• A chamfer finish line is formed


Axial reduction

• A smooth transition to the proximal surface is made ( rounded internal line angles).


Axial reduction

• Proximal access with a short needle diamond in an up and down 'sawing" motion until contact with the adjacent tooth is broken and space is produced for larger instruments.


Axial reduction

• The gingivofacial angle should not be underextended; it is the most likely area of a three-quarter crown to fail "


Axial reduction

• Proximal grooves are approximately the size of a no. 171L bur

• about 0.5 mm occlusalto the chamfer


Axial reduction

• Should be placed as far facially as possible without undermining the facial surface

• Paralleling the long axis of a posterior tooth.

• 4mm occluso-cervical height.


• A flare is a flat plane that removes equal amounts of the facial wait of the groove and the outer surface of the tooth.


• It is cut from the groove outward with the tip of a flame diamond to prevent overextension


• The flare should not cause display of metal

• The flare should be smoothed with a carbide bur matching the configuration of the flame diamond


Failure to place a flare will result in undermined enamel


• The occlusal offset, a 1.0-mm-wide ledge on the lingual incline of the facial cusp,

• Is made with a no. 171L bur.

• It forms an inverted "V" that lies a uniform distance from the finish line.

• It provides space for the metal

¾ Crowns

Three-quarter crownwith proximal boxes

• Are more retentive than a standard preparation with grooves, but boxes are very destructive.

• Used only if there has been proximal caries or previous restorations.

Three-quarter crownfor mandibular molars & premolars

(Modified Three Quarter Crown)

Very similar to preparations on maxillary tooth except

The location of the occlusalfinish line on the facial surface is gingival to occlusal contacts (occlusalshoulder) which gives the same function as the occlusal offset.

Modified Three Quarter Crown

Very similar to preparations on maxillary tooth except

• No need for an offset on the lingual inclines of the buccal cusps

(Modified Three Quarter Crown)

The Seven-Eighths Crown

• Is a three-quarter crown whose vertical distobuccal margin is positioned slightly mesial to the middle of the buccai surface.


• Is a three-quarter crown whose vertical distobuccal margin is positioned slightly mesial to the middle of the buccal surface.


• The seven-eighths crown can be used on any posterior tooth needing a partial veneer restoration where the distal cusp must be covered.

• Used on maxillary molars, but it also can be placed on mandibular premolars and molars


Advantages

1. Better resistance

2. Better esthetics

The Reverse Three-Quarter Crown

• Is used on mandibuiar molars to preserve an intact lingual surface.

• It is useful FPD abutments with severe lingual inclinations, avoiding destruction of tooth structure that would occur if a full veneer crown were used.

The Reverse Three-Quarter Crown

• The grooves at the linguoproximal line angles are joined by an occlusal offset on the buccalslope of the lingual cusps.

• Resembles a maxillary three-quarter crown because the axial surface of the nonfunctionalcusp is uncovered.

The Proximal Half Crown

• Is a three-quarter crown that is rotated 90 degrees, with the distal rather than the buccal surface left intact.

• It can be a retainer on a tilted mandibular molar FPD abutment.

The Proximal Half Crown

• Can be used only in excellent hygiene and a low incidence of interproximalcaries.

• It is contraindicated if there is a blemish on the distal surface

Anterior Three Quarter Crowns


Uses

• Well-aligned, thick, square anterior teeth with a large faciolingual bulk of tooth structure are the best candidates for three-quarter crowns

• It can be used as a retainer for short-span FPD Tooth should not have a large restoration neither caries


• Have almost been eliminated due to

1. The ease of preparing a tooth for a metal ceramic crown.

2. Displays of metal in poorly designed partial crown restorations.


• Two factors must be controlled successfully to produce a restoration with a minimal display of metal

(1) Path of insertion and groove placement

(2) Placement and instrumentation of extensions.


• The path of insertion of an anterior three-quarter crown parallels the incisal one-half to two-thirds of the labial surface, not the long axis of the tooth.


• The grooves incline lingually if the grooves incline labially, the labioincisal corners are overcut, displaying metal.


Steps involved in preparation

Lingual reduction

• A small wheel diamond is used to create a concave lingual reduction incisal to the cingulum.

• 07mm clearance from the opposing tooth is nessecary.



Incisial reduction

• Incisal reduction is done with the small wheel diamond

• It parallels the inclination of the uncut incisal edge

• Does not break through the labioincisal line angle.



Liguaxiall reduction

• The lingual axial wall is reduced with a torpedo diamond.



Liguaxiall reduction

• The diamond is kept parallel with the incisaltwo thirds of the labial surface to initiate the path of insertion of the preparation.



Linuoaxial reduction

• A Chamfer finish line is created



Proximoaxial reduction

• Proximal reduction is started with a long needle diamond.

• The axial reduction is completed and the finish line is accentuated with a torpedo diamond.



Proximal grooves

• The grooves are placed as far labially as possible without undermining the labial enamel plate.

• No 169 or 170 burs are used for groove placment



Proximal grooves

• Remember! that grooves in an anterior three-quarter crown preparation parallel the incisalone-half to two-thirds of the facial surface, unlike those in a posterior tooth, which parallel the long axis of the tooth.



Proximal grooves flare

• On the facial aspect of each groove, a flare is started at the gingival end with the thin tip of a flame diamond & finished wit a carbide to make it smooth.



Incisal offset

• The grooves are connected with an incisaloffset, staying a uniform distance from the incisal edge.



Incisal bevel

• The bevel is perpendicular to the path of insertion along the mesial incline


Incisial offsetStructural Durability

Pin Modified Three Quarter Crown

• The pin-modified three-quarter crown preserves the facial surface and one proximal surface. With minimal subgingival margins.

• Is good for repairing incisors and canines with severe lingual abrasion.

• It should not be used on teeth with caries or extensive restorations


• Pins are likely to produce less retention, and pin retained castings are less retentive than standard three quarter crowns.

• The greater the number, depth, or diameter of pins, the greater the retention


Steps involved in preparation:-

• Resemble that for a three quarter crown except:

The primary axial retention/resistance features, two grooves, are placed next to the edentulous space.




In addition to the lingual and facial proximal grooves a third, much shorter groove is placed on the opposite side of the cingulum near the vertical finish line on that surface.




A flat ledge or countersink is cut in the incisalcorner opposite the site of the proximal grooves using a no 170L bur & in the middle of the cingulum in which pin holes are placed with a no ½ round bur.


Disadvantage of the pin modified design is microleakage in the pin hole resulting in caries which will not be detected instantly.

definition - national university crown.pdf · pin modified three quarter crown steps involved in...

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