الرحيم الرحمن الله بسم

Class II Cast Metal Restorations

What is the difference between Inlay and Onlay? Class II Inlay involves the occlusal and proximal surfaces of the posterior teeth and may cap one or more, but Not all of the Cusps.

Class II Onlay involves the proximal surfaces of the posterior teeth and caps all of the cusps.

Indications

1. Large Restorations.

2. Endodontically Treated teeth.

3. Teeth at Risk for fracture.

4. Dental Rehabilitation with cast Metal alloys.

5. Diastema closure and occlusal plane Correction.

6. Removable prosthodontic Abutment.

Contraindications

1. High Caries Rate.

2. Young patients.

3. Esthetics

4. Small Restorations.

Advantages

1. Strength.

2. Biocompatibility.

3. Low Wear.

4. Control of Contours and Contracts.

Disadvantages

1. Number of appointments and higher chair time.

2. Temporary.

3. Cost.

4. Technique sensitive.

5. Splitting force.

Initial Procedures• Occlusion• Anesthesia

Considerations for Temporary Restorations- Before preparation of the tooth, consideration must

be given to the method that will be used to fabricate the temporary restorations. Most temporary restoration techniques require the use of a preoperative impression to reproduce the occlusal, facial, and lingual surfaces of the temporary restoration to the preoperative contours.

The technique involves making a preoperative impression with an elastic impression material. Alginate impression materials may be used and are relatively inexpensive.

The preoperative impression may be made with a polyvinyl siloxane impression material if additional accuracy, stability, and durability are required (e.g., when making multiple temporaries over an extended period).

Tooth Preparation for Class II Cast Metal Inlays

Initial Preparation Carbide burs used to develop the vertical internal walls of

the preparation for cast metal inlays and onlays are plane cut, tampered fissure burs.

Suggested burs are the No. 271 and the No. 169L Throughout preparation for a cast inlay, the cutting

instruments used to develop the vertical walls are oriented to a single “ draw” path, usually the long axis of the tooth crown, so that the completed preparation has draft ( no undercuts) . The gingival –to- occlusal divergence of these preparation walls may range from 2 to 5 degrees per wall from the line of draw.

Occlusal Step• With the No.271 carbide bur held parallel to the long

axis of the tooth crown, the dentist enters the fossa/pit closest to the involved marginal ridge, using a punch cut to a depth of 1.5 mm to establish the depth of the pulpal wall.

• A general rule is to maintain the long axis of the bur parallel to the long axis of the tooth crown at all times.

• Maintaining the 1.5-mm initial depth and the same bur orientation, the dentist extends the preparation outline mesially along the central groove/fissure to include the mesial fossa/pit.

• The facial and lingual extension in the mesial pit region should provide the desired dovetail retention form, which resist distal displacement of the inlay.

• Continuing at the initial depth, the occlusal step is extended distally into the distal marginal ridge sucifficiently to exposed the junction of the proximal enamel and the dentin. While extending distally, the dentist progressively widens the preparation to the desired faciolingual width in anticipation for the proximal box preparation.

Proximal Box• Continuing with No. 271 carbide bur, the distal enamel

is isolated by cutting a proximal ditch. The mesiodistal width of the ditch should be 0.8 mm (the tip diameter of the bur).

• While penetrating gingivally, the proximal ditch is extended facially and lingually beyond the caries to the desired position of the facioaxial and linguoaxial line angles.

• Ideal extension gingivally of a minimal, cavitated lesion eliminates caries on the gingival floor and provides 0.5-mm clearance of the unbeveled gingival margin with the adjacent tooth.

• With the No. 271 carbide bur, the dentist makes two cuts, one at the facial limit of the proximal ditch and the other at the lingual limit, extending from the ditch perpendicularly toward the enamel surface.

• At this time, however, the remaining wall of enamel often breaks away during cutting, especially when high speeds are employed. If the isolated wall of enamel is still present, it can be fractured out with a spoon excavator.

• Planning the distofacial, distolingual, and gingival walls by hand instruments to remove all undermined enamel may be indicated if minimal extension is needed to fulfill an esthetic objective.

• Shallow (0.3 mm deep) retention grooves may be cut in the facioaxial and linguoaxial line angles with the No. 169L carbide bur . These grooves are indicated especially when the prepared tooth is short.

Final Preparation• Removal of Infected Carious Dentin.• Pulp Protection.

Preparation of Bevels and Flares• After the cement base ( where indicated) is completed,

the slender, flame shaped, fine-grit diamond instrument is used to bevel the occlusal and gingival margins and to apply the secondary flare on the distolingual and distofacial walls. This should result in 30-to 40-degree marginal metal on the inlay.

Capping CuspsThe facial and lingual margins on the occlusal surface frequently must be extended toward the cusp tips to the extent of existing restorative materials and to uncover caries.

• When the occlusal outline is extended up the cusp slopes more than half the distance from any primary occlusal groove (central, facial, or lingual) to the cusp tip, capping the cusp should be considered. If the preparation outline is extended two thirds of this distance or more, capping the cusp is usually necessary to (1) protect the weak, underlying cuspal structure from fracture caused by masticatory force and

(2) remove the occlusal margin from a region subjected to heavy stress and wear.

• Before reducing the surface, the operator prepares depth gauge grooves (depth cuts) with the side of the No. 271carbide bur. Such depth cuts should help to prevent thin spots in the restoration. With the depth cuts serving as guides the operator completes the cusp reduction with the side of the carbide bur. The reduction should provide for a uniform 1.5 mm of metal thickness over the reduced cusp.

Tooth Preparation for Cast Metal OnlaysThe cast metal Onlay by definition caps all of the cusps of a posterior tooth and can be designed to help strengthen a tooth that has been weakened by caries or previous restorative experiences.

It can be designed to distribute occlusal loads over the tooth in a manner that greatly decreases the chance of future fracture. It is more conservative of tooth structure than the full crown preparation, and its supragingival margins, when possible, are less irritating to the gingiva.

Initial Preparation• Using the No.271 carbide bur held parallel to the long

axis of the tooth crown, prepare a 2- mm deep pulpal floor along the central groove.

• With the side of the No. 271 carbide bur, prepare uniform 1.5 mm deep depth cuts on the remaining occlusal surface.

• The gingival-to-occlusal divergence of these preparation walls may range from 2 to 5 degrees from the line of draw.

Occlusal Step• After cusp reduction, there should be a 0.5 mm deep

occlusal step in the central groove region between the reduced cuspal inclines and the pulpal floor.

Proximal Box• The proximal box are prepared as described in the inlay

section.

Final Preparation• Removal of Infected Carious Dentin and Defective

Restorative Materials and Pulp Protection.

Preparation of Bevels and Flares• After the cement base (when indicated) is completed,

use the slender, flame-shaped, fine-grit diamond instrument to place counter bevels on the reduced cusps, to apply the gingival bevels and to create secondary flares on the facial and lingual walls of the proximal boxes.

• The bevel should be of generous width and should result in 30-degree marginal metal. The best way to judge this is always to maintain a 30 –degree angle between the side of the instrument and the external enamel surface beyond the counter bevel.

• When deemed necessary, shallow (0.3 mm deep) retention grooves may be cut in the facioaxial and the linguoaxial line angles with No.169L carbide bur.