Matrices and Wedges

What is the function of a matrix in a cavity preparation?

1. Provides a missing wall.

2. Prevents cervical overhang of the restorative material.

3. Provides needed contact with the adjacent tooth.

4. Imputes a smooth surface to the restoration.

What are the desirable properties of a matrix?

A matrix should be:

1. Sufficiently rigid for adequate condensation.

2. Flexible enough for proper adaptation to the tooth surface.

3. Thin to facilitate easy contact with the adjacent tooth.

4. Non-adhesive to the tooth or restorative material.

5. Capable of transmitting light

6. Easy to place and remove.

7. Reasonably priced.

What are the two main types of matrices?

1. Metallic Matrices: Used for amalgam or direct gold fillings.

Types :

• Sectional (e.g., custom-made mechanical Ivory no. 1)

• Circumferential (e.g., Tofflemire, Automatrix, T-band).

2. Non-metallic Matrices: Made of Cellulose acetate. Used for tooth-colored filling materials. (e.g., composite or GIC restorations). They could be in strips or crown form. Cellulose acetate strips are stabilized by wedge.

What are the characteristics of metallic matrices?

1. Stabilized by mechanical retainers.

2. Sufficiently pliable for shaping proximal surfaces.

3. Thin for easy removal and adaptation.

4. Typically made of carbon or stainless steel with varying thickness (e.g., 0.0015”).

What are cellulose acetate matrices used for?

They are used for tooth-colored filling materials such as composite and GIC restorations.

They can come in strips or crown forms and are stabilized by wedges.

What are the two classifications of retainers?

1. Encircling (Circumferential): Fully encompasses the tooth.

2. ¾ Type (Unilateral or Partially Encircling): Used in Mesio-Occlusal or Disto-Occlusal preparations with tight interdental spaces (e.g., Ivory no. 1).

Give examples of encircling retainers.

1. Bonnalie

2. Ivory no. 8

3. Tofflemire

4. Inox

Example of ¾ retainers?

Ivory no. 1

Give 3 examples of self retained bands

1. T- bands

2. Copper bands

3. Automatrix

What is Automatrix, and what is its advantage?

Automatrix is a self-retained matrix band system. Its advantage is high visibility due to the absence of a bulky retainer.

How should a matrix be placed around a tooth?

• It should have a larger diameter occlusally than gingivally.

• Should fit snugly around the tooth.

• Extend beyond the cavosurface margin of the prepared cavity.

• Extend 1mm above the adjacent marginal ridge.

• Should be properly wedged.

Tofflemire is the most the most popular is also referred to as the universal retainer.

What is a wedge, and what are its functions?

A wedge is a piece of wood, plastic, or metal with an acute angle used for tightening the matrix against the gingival cavosurface margin of a cavity.

Functions:

1. Prevents cervical overhang of the restorative material.

2. Improves proximal contact.

3. Assists in rubber dam retention.

4. Protects interdental papillae.

What are the desirable properties of a wedge?

1. Available in varying shapes and sizes to fit the cervical embrasure accurately.

2. Rigid enough to support the matrix.

3. Easy to apply and remove.

4. Radiopaque for detection if left behind.

5. Should not break or splinter.

6. Available in bright colors contrasting with oral tissues.

What are the different types of wedges?

1. Wooden or plastic, with different colors and sizes.

2. Custom-made or proprietary.

3. Reflecting wedges used in Class II composite restorations to minimize microleakages due to polymerization shrinkage.

Where are wedges usually applied?

Wedges are usually applied on the buccal aspect, but in cases where it’s not possible, they can be applied from the lingual aspect, especially in the upper jaw.

What should you check for when placing a wedge?

Ensure that it is not possible to insert a caries probe between the matrix band and the cervical margin when the wedge is properly applied.

What are the steps for removing a matrix band?

1. Loosen the retainer.

2. Remove the wedge.

3. Remove the retainer.

4. Gently ease out the matrix band without fracturing the filling, especially at the isthmus.

What should be done after removing the matrix band?

• The axial and gingival areas should be properly contoured as they become more accessible.

• Reproduce the marginal ridge to be the same height as the adjacent tooth.

• Establish the contact point just below the marginal ridge.

• Check for high spots using articulating paper or by asking the patient to occlude gently and move the lower jaw side to side.