Matrix Systems for Restorative Dentistry

Learning Outcomes

On completion of this chapter, the student will be able to achieve the following objectives:

Performance Outcomes

On completion of this chapter, the student will be able to achieve competency standards in the following skills:

Electronic Resources

Additional information related to content in Chapter 49 can be found on the companion Evolve Web site.

and the Multimedia Procedures DVD

Key Terms

AutoMatrix (aw-toe-MAY-triks) Matrix system designed to establish a temporary interproximal wall for the restoration of a tooth surface without the use of a retainer.

Celluloid (SEL-yoo-loid) strip Clear plastic strip used to provide a temporary interproximal wall for the restoration of an anterior tooth surface.

Cupping Form created by a concave tooth surface that has not been contoured properly.

Matrix (MAY-triks) Foundation that binds or holds the dental material and tooth together during the setting process.

Mylar (MYE-lahr) Brand name for clear plastic strip used to provide a temporary wall for restoration of an anterior tooth.

Overhang Excess restorative material that extends beyond the cavity margin.

Palodent (PAL-uh-dent) Small, oval-shaped matrix made of stainless steel used interproximally during tooth restoration.

Universal retainer Dental device used to hold a matrix band in place during restoration of a class II cavity.

Wedge Wooden or plastic triangular device placed in the embrasure to provide the contour needed when a class II lesion is restored.

When a tooth is prepared for a class II, III, or IV restoration, at least one interproximal wall of the tooth has been removed. A matrix system creates a temporary interproximal wall for the amalgam, composite resin, or intermediate restorative material to be placed against (Fig. 49-1). (The plural term for matrix is matrices.) Besides acting as a temporary wall, the matrix system has additional functions such as the following:

Placement and removal of the matrix system may be a legal expanded function in the state in which you are practicing. Pay special attention to the type of tooth preparation, the type of matrix system to be prepared and placed, and the techniques of placement and removal.

Posterior Matrix Systems

The matrix system most commonly used today for the class II restoration is the universal retainer and matrix band. To avoid unnecessary delays in a procedure, the assistant will have the retainer and band assembled at the beginning of the procedure.

Universal Retainer

The universal retainer, also referred to as the Tofflemire retainer, is a mechanical device that holds the matrix band snugly in position. This type of retainer is positioned from the buccal surface of the tooth that is being restored.

If during tooth preparation, the interproximal wall extends onto the buccal surface, a contra-angle retainer has been designed with a slight bend in the body to accommodate positioning from the lingual surface.

Matrix Band

The matrix band is made of a thin flexible stainless steel material. The two designs of the matrix band most commonly used are the universal band and the extension band (Fig. 49-2). The universal band is selected for the class II preparation when the proximal “box” is prepared to a minimum depth and width and the cusps are intact. The extension band is selected for the deeper class II preparation requiring gingival extensions to compensate for the loss of a cusp, because insufficient height of a universal band will not exceed the height of the occlusal surface of the tooth as required.

The matrix band is designed in such a way that when the ends of the band are brought together, the band will form a circle. One side of the circumference (perimeter or outside edge) of the circle will be smaller than the other side. The circumference guides you in placing the band as follows:

• The smaller circumference of the band is the gingival edge and is always positioned toward the gingiva.

• The larger circumference of the band is the occlusal edge and is always positioned on the tooth facing the occlusal part of the tooth.

Components of a Universal Retainer

1 Spindle: Internal screwlike pin that fits into the diagonal slot to hold the ends of the matrix band. When the retainer is assembled, the spindle point must be clear of the slot while the band is slid into the slot, and then tightened.

2 Outer guide slots: Also known as guide channels; these are located at the end of the retainer and serve as channels to guide the loop of the matrix band. The channel selected is determined according to the quadrant that is being treated.

3 Outer knob: Used to tighten or loosen the spindle within the diagonal slot; this holds the matrix band securely in the retainer. To tighten the spindle, turn the outer knob away from you. To loosen the spindle, turn the outer knob toward you. Be careful not to turn it too far, or the diagonal slot vise will fall off the spindle. If this happens, insert the end of the spindle into the diagonal slot vise, and turn the outer knob away from you.

4 Inner knob: Used to increase or decrease the size of the matrix band loop. The size of the loop formed by the band depends on the tooth to be restored. When the band is placed over the tooth, the size of the loop circumference should be larger than the tooth, and the band should be tightened after placement.

5 Diagonal slot: Slot within the boxlike structure used to position the ends of the matrix band into the vise; the retainer is always positioned in the mouth with this slot facing toward the gingiva.

Contouring

In preparation for use, the center of the matrix band should be contoured (shaped) in the proximal contact area, so the final restoration will have proper contact with the adjacent tooth. To contour the band, place the band on a paper pad. Using a burnisher or an end of the mirror handle, rub against the inner surface of the band until the ends begin to curl (Fig. 49-3).

See Procedure 49-1.

1 What cavity classifications use a posterior matrix system?

2 What is the plural of matrix?

3 What is used to hold a posterior matrix band in position intraorally?

4 When a matrix band is placed on the tooth, where is the smaller circumference of the band placed?

5 What instrument is commonly used to contour the matrix band?

PROCEDURE 49-1  

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