Procedure For Class II Inlay Cavity Preparation:

1. Administer anesthetic. Place extra-heavy rubber dam, retracting the interdental tissues away from the tooth so they are not injured. This retraction allows fine bevels to be placed on the gingival margins where indicated.
2. Remove previous restorations, caries and observe strength of remaining tooth structure.
3. If a "block-out" is required, apply a thin layer of calcium hydroxide over the pulpal and axial walls with a small cotton pellet. This will protect the dentin and pulp of the tooth from the toxicity of the composite, any remaining bacteria and act as a separator for easy removal of the "block-out" composite when the castings are cemented. Place retention potholes with a 35 inverted cone bur, if needed, to retain composite after the calcium hydroxide has been applied.
4. Once the calcium hydroxide has set, place composite "block-out" material into the preparation and let it harden. The use of an old bur to rough out the inlay cavity preparation in composite is recommended because the composite will dull the bur quickly.
5. Establish occlusal outline and pulpal floor depth with a new straight fissure bur. An even taper of the walls of approximately 10 degrees is established with a #56 bur for bicuspids or a #57 bur for molars.
6. Establish gingival floor simultaneously with the proximal and axial walls with the same bur as was used in step 5.
7. On the distal aspect of the tooth, place the buccoaxial and linguoaxial line angles, smooth the axial wall, sharpen line and point angles and smooth the pulpal floor with an #425 off-angle chisel (15-10-16). Note: All hand instruments should be sharp and made of carbon steel for the best results.
8. On the mesial aspect of the tooth, place the buccoaxial and linguoaxial line angles, smooth axial wall, sharpen line and point angles with a #43 off-angle chisel (15-10-16).
9. Place an even external gingival bevel on the distal with a #232 Tucker gingival margin trimmer (10-98-10-16).
10. 10. Place an even external gingival bevel on the mesial with a #233 Tucker gingival margin trimmer (10-78-10-16)
11. Create occlusal bevel with a straight fissure bur (approximately 5 degrees more taper than the occlusal walls). The occlusal bevel is used to remove any fragile enamel rods and any irregularities at the cavosurface. This will give the resultant restoration a nice flowing and more pleasing outline. The width of the occlusal bevel is not even or uniform. Steep cuspal inclines will usually not have a bevel.
12. Straighten proximal walls and cavosurface margin, if space permits, with a ½ inch medium garnet disc. If the access is not sufficient, the #42S or #43S chisel can be used.
13. At this time, retentive pins, bales and cusp coverage can be done to strengthen the tooth and/or aid in additional retention and resistance.

NOTES:

• An internal bevel is placed in most two surface Class II cavity preparations on bicuspids at the gingivoaxial line angle with a #232 gingival margin trimmer for a MO and a #233 gingival margin trimmer for a DO, prior to the planing and smoothing of the axial wall and the placement of the external gingival bevel.
• The preparation is defined with the bur and refined with hand instruments.
• An inlay preparation is always prepared first for an intracoronal casting. Onlaying of cusps is done at the end.

Rationale For Composite "Block-out" Material:

1. A more ideal and conservative outline can be made by controlling the depth of the cavity preparation.
2. Enables the operator to control the depth of the pulpal and axial walls.
3. Draw and flare of a preparation of ideal depth results in a preparation that conserves tooth structure.
4. Allows the operator to prepare very smooth, flat pulpal and axial walls with sharp proximal line angles and point angles.
5. Enables the operator to prepare and visualize a more ideal preparation from both the intracoronal and extracoronal aspects.
6. Permits a smoother preparation to be cut, thus resulting in an impression of finer detail which generally allows for a smoother, sharper die.
7. A cavity preparation of uniform depth results in a wax pattern thickness that is less affected by the shrinkage of gold on cooling.
8. A smooth, uniform preparation results in a smooth, uniform die. This allows easier removal of the wax pattern without distortion, a common cause of poorly fitting castings.
9. Smooth internal surfaces of a casting permit any tiny bubbles or fins of gold to be more easily detected and removed prior to cementation. This can ensure a more precise fit of the casting.
10. Removal of the composite "block-out" prior to cementation can assist in a more precise fitting casting by elimination of potential interference on the pulpal or occlusal surface. This also creates a secondary die space relief.
11. Composite as a "block-out' material is easier to smooth with rotary and hand instruments than other commonly used "block-out" materials.
12. The use of "block-out" material saves gold by permitting the operator instead of the laboratory technician to control the depth of the preparation both axially and pulpally.