Partial Veneer Crowns , Inlays and Onlays

Dr shabeel pn

Anterior Partial VeneersAnterior Partial Veneers

A partial veneer has been described as a restoration covering two or more surfaces of a tooth.

There are three types of partial veneer crowns:1. Three quarter crown2. Seven eight crown 3. Mesial half crown All other forms of partial veneers are considered variations of the three basic types.

Three quarter crown – covers three surfaces of the crown leaving one surface intact.

Seven eighth crown – used in maxillary molars and premolars. It encompasses seven eighth the gingival circumference of the tooth.

Mesial half crown – is a three quarter crown rotated 90o, preserving the distal surface of the tooth. This preparation design is primarily indicated for the distal retainer of a mandibular FPD with a tilted molar abutment.

Indications For Partial Veneers:

1) Intact or minimally restored teeth.

2) Teeth with crown length that is average or exceeds average.

3) Teeth with normal anatomic crown form, ie, without cervical constriction.

4) Anterior teeth with adequate labio-lingual thickness

Contra-indications:

1. High caries rate2. Short teeth 3. Non vital teeth4. Deep cervical abrasion5. Teeth with extensive core restorations6. Bell shaped teeth (severe cervical constriction)7. Thin teeth

Advantages:

► Conserves tooth structure► Easy access to margins for finishing (for dentist)► Less gingival involvement than with complete cast crown► Aesthetics are superior to that of the complete crowns► Electric pulp testing can be done on the intact surface► Complete seating of the restoration can be easily verified.

Disadvantages:

Retention is less than that of complete veneer crown

Skilful preparation is crucial to avoid metal display

Preparation is limited to teeth with normally shaped, average length clinical crown.

It is not indicated for use in cases of non vital teeth

Steps for Preparation of Tooth for Partial Veneer Steps for Preparation of Tooth for Partial Veneer CrownsCrowns

There are seven steps for tooth preparation for partial veneer crowns:1.Occlusal or Incisal reduction2. Lingual reduction3. Inter-proximal reduction4. Proximal box or Groove placement5. Occlusal or incisal offset placement6. Facial bevel7. Finishing the preparation

The technique for each step may vary according to whether the tooth is in the maxilla or in the mandible. In the following discussion the tooth that is being considered is the maxillary canine.

Armamentarium:Armamentarium:

• Narrow (0.8mm) round tipped , tapered diamond – For bulk reduction• Regular size (1.2mm) round tipped tapered diamond or carbide – Finishing• Wheel shaped diamond - Bulk reduction• Tapered and straight carbide fissure burs - preparation of boxes, ledges and pinhole finalisation.• Small round carbide bur• Finishing stones• Inverted cone carbide bur – preparation of incisal offset

1 ) Incisal Reduction:1 ) Incisal Reduction:

Depth orientation grooves are placed at about 1 – 1.5mm depth. Using tapered round ended diamond bur reduce the incisal edge 1mm at 45o to the long axis of tooth.Follow the facial contour of the tooth And uniformly remove 1 – 1.5mm of enamel Design of incisal bevel should prevent contact with opposing teeth and incisal margin

2) Lingual Reduction:2) Lingual Reduction:

Accomplished in two stages:

a. Lingual surface reduction –

Depth orientation groove placed Football or wheel shaped diamond bur used to reduce lingual surface.Slight ridge left running incisogingivally along the centre of the lingual surface.Clearance with opposing tooth is atleast 0.7 – 1mm Do not over reduce cingulum

b. Lingual gingival reduction -

• Using tapered round ended diamond, a chamfer of 0.5mm deep is made at the cervical finish line.

• Reduction parallels long axis of the preparation (in this case the incisal two thirds of the labial surface)

The path of placement of the restoration must be accurately determined before axial reduction

Mesiodistally it should be parallel to the long axis of the tooth , buccolingually , it should parallel the middle third or incisal third of the tooth.

to enhance the retention and resistance form, a slightly exaggerated chamfer is placed in the lingual aspect and a guiding groove is placed in the middle of the lingual surface

3)3) Inter proximal reduction:Inter proximal reduction: Three steps are involved ;

a) Using a 169L carbide bur, reduce the proximal surface by moving bur from lingual to the facial surface. Position bur so that the tip of the bur is further facial than the shank. Do not break contact with the adjacent teeth. The facial line angles must remain intacet to provide aesthetically pleasing results

b) Using a narrow chamfer diamond, establish a light chamfer finis line on the proximal surface

a) Using a hatchet instrument, the contact with the adjacent tooth is broken to establish labial proximal extensions. A flame shaped bur is used to finish the flare. Axial reduction is now complete

4) Proximal grooves:4) Proximal grooves:

These are placed as far labially as possible without undermining the labial enamel plate

First groove is begun by cutting a 1mm deep template with a 170L bur. This groove is extended gingivally in increments to the full length.

Second groove is cut parallel to the first on the opposite side.

Lingual wall of the groove has a 2 – 5 degree incisal convergence with the lingual gingival wall of the preparation.

Facial wall of the groove should be continuous with the proximal flare to contribute bulk to the facial margin.

The grooves are parallel to the incisal half or two thirds of facial surface.

Boxes may be used as substitutes for the grooves where there are existing proximal restorations or caries. Boxes must be narrow to resistant, hence lingual wall of the box shortens as it moves lingually.

The grooves are a minimum of 3mm long and terminate within 0.5mm of the gingival finish line.

5)5) Incisal grooveIncisal groove

Using 37 inverted cone bur, develop a 0.5 to 1mm groove connecting the proximal groove . This should be in the dentin and parallel to the DEJ.

Groove is not placed at the expense of the incisal edge.

6) Facial bevel:6) Facial bevel:

Using a fine, flame shaped diamond bur, develop a narrow bevel < 0.5mm on the labioincisal finish line at right angles to incisal two thirds of the facial surface.

7) Finishing the preparation7) Finishing the preparation

Using a carbide finishing bur, round the angles to ensure continuity of all the finish lines

Features of anterior three quarter crown preparation

Pin Modified Three Quarter crownPin Modified Three Quarter crown

Indications:

Undamaged anterior teeth in caries free mouth Alteration of lingual contour of the maxillary

anterior teeth or the alteration of occlusion Anterior splinting

Contra – indications:

Large pulp Thin teeth Non vital teeth Carious involvement Problems with proposed path on withdrawal of FPD

Advantages:

Minimal tooth reductionMinimal subgingival margins, hence periodontally preferableOptimum access for margin finishing and hygieneAdequate retention

Disadvantages:

Less retentive than complete coverageAlignment can prove difficultTechnically demandingNot usable on non vital teeth

Pin ledge preparationPin ledge preparation

Three designs of pin ledge preparations have been describes:

1- Conventional Pin ledge involving only the lingual surface of the tooth2 - Pin ledge with proximal slice3 – Pin ledge with a proximal groove

Conventional pin ledge preparationConventional pin ledge preparation

Lingual reduction – This is done similar to conventional anterior two third crown preparation with a few additional features. A lingual incisal bevel is prepared with a wheel bur , about 1.5mm in width. It should be parallel to the uncut incisal edge and should end lingual to the labio-incisal angle to avoid display of metal. The lingual axial wall should be parallel to the gingival two thirds of the labial surface. The chamfer finish line should stop lingual to the contact of the tooth surface adjacent to the edentulous space inorder to improve accessability to operator and patient (for maintenance)

Proximal reduction –

Only one proximal surface is prepared. The proximal surface adjacent to the edentulous ridge is only prepared. The diamond is held either parallel to the path of placement or slight lingual inclination is given. The primary purpose of this step is to provide adequate bulk of the metal in area for subsequent connector. Reduction includes contact area , but should not be extended too facially.

Ledge preparation –

Two ledges are prepared across the reduced lingual surface. The provide room for sufficient bulk of metal to ensure rigidity. The ledges are prepared parallel to the incisal edges of the tooth, as viewed from the lingual aspect and parallel to each other as viewed from the incisal aspect. Indentations are made in the two sides of the incisal ledge and slightly off centre of the cervical ledge to prevent pulp exposure when the pinholes are placed.

Pinhole preparation -

Sink pilot channels using small round bur or a small twist bur. The depth of the completed pinhole should be about 2mm. Enlarge and deepen the pilot channels with a tapered bur when the placement and orientation of the pilot channels have been found to be satisfactory. Bevel the junction between the pinhole and the ledge with a round bur slightly larger than the largest diameter of the pinhole. Inspect all areas of the preparation for smoothness and evaluate the margins

Features of pinledge anterior three quarter crown