Indexing Techniques in Dental Prosthetics

Indexing The Cast Introduction

After recording jaw relation the same should be transferred to the articulator for teeth arrangement and further laboratory procedures. Before mounting casts to the articulators, some modifications are done to the base of the casts for easy removal and accurate remounting. This chapter emphasizes various indexing methods and briefs about mounting procedures.

Indexing

Indexing is done on the master cast. Indexing helps in remounting the casts in the same position on the articulator after processing. Remounting is done to do selective grinding to eliminate processing errors.

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Indexing The Cast Requirements

• Indexing the cast should not weaken the cast
• Indexing should be free of undercuts
• The indexing procedure should be easy to perform
• It should permit easy removal and remounting
• It should be of use even if the base of the cast is modified.

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Indexing The Cast Types

There are two types of indexing:

1. Groove indexing
2. Notch indexing.

Indexing The Cast Armamentarium

• Master casts
• Metallic scale
• Pencil
• BP blade No. 15 with handle/paper cutter.

Groove Indexing:

In this method of indexing, “V”-shaped grooves are made across the base of the master cast.

For Maxillary Cast:

Draw two lines that are perpendicular to each other through the center of the base of the cast.

Indexing Of Master Cast

For Mandibular Cast:

Draw two lines that are on the thicker part of the cast. Draw these lines under the area of the residual ridge as that is a thicker area of the cast. Make grooves along the lines. The grooves should be 3 mm in depth and 5 mm in width. The grooves can be made with 15 No. BP blade.

Lathe mounted wheel which has been modified (sharpened) to make a “V”-shaped groove can also be used for this purpose.

Notch Indexing:

In notch indexing “V”-shaped notches are created on the base of the cast. The notch should be 3 mm deep and 5 mm wide.

For Maxillary Cast:

A total of four (04) notches are made for maxillary cast. Mark one notch in the anterior, one in the posterior, and one on either side of the maxillary cast. Make notches using BP blade number 15.

For Mandibular Cast:

A total of three (03) notches are made for mandibular cast. Mark one notch in the anterior region and two in the posterior region. Make notches using BP blade number 15.

Indexing Of Master Cast

These indexing are made before mounting the casts on the articulator. Sometimes it is necessary to reduce the size of the base of the cast to fit in the flask during the flasking procedure. During the reduction of base thickness peripheral notch indexing will be trimmed and there will be a loss of indexing.

Note: If indexing is done with grooves, trimming may reduce the size of the groove but still it can be used effectively for remounting procedures so groove indexing is preferred over notch indexing.

Indexing Of Master Cast

The mounting plaster forms a negative replica of grooves as shown below, which is used for remounting casts. The negative replica of groove indexing.