Matrix Band Placement

Back to Class II Amalgam Restoration

The Universal (Tofflemire) matrix system is used in Class II restorations. The primary function of the matrix is to restore anatomic proximal contours and contact areas. A properly placed matrix should:

• Be rigid against the existing tooth structure
• Establish proper anatomic contour
• Restore correct proximal contact relation
• Prevent gingival overhang
• Be able to be easily removed

Armamentarium

Tofflemire Matrix Retainer
Matrix bands
(narrow or wide; usage depends on depth of gingival cavosurface margin)
Wedges
Cotton Pliers
Scissors
Knife

Class II Amalgam Restoration

Procedure

1. Try the wedge.
2. Burnish the matrix band.
3. Place the matrix band into the retainer.
4. Fit the matrix onto the tooth.
5. Place the wedge.
6. Tighten the matrix band around the tooth.

Try the wedge.

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Use of a wedge with the matrix band serves two purposes:

1. Helps to compress the matrix band against the tooth structure to create a tighter seal, preventing gingival overhang.
2. Provides slight separation between the teeth, compensating for the thickness of the matrix band, and thus helping to create a tight contact between the finished restoration and the adjacent tooth (otherwise, when matrix band is removed, a space equaling the thickness of the matrix band would exist between the restored proximal surface and the adjacent tooth).

Prior to placing the matrix band, place a wedge in the gingival embrasure to check the relationship between the occlusal surface of the wedge and the gingival cavosurface margin. In order for a wedge to be effective during amalgam placement, it should fit tightly against the tooth and its occlusal surface should extend above the gingival cavosurface margin, creating a tight seal.

To place the wedge, stretch the rubber dam tightly to allow it to seat more gingivally and keep it from getting caught by the wedge. After placing the wedge, use the blunt end of the cotton pliers to push it into place.

If the wedge fits tightly against only a portion of the gingival proximal surface, fit a slightly larger wedge and use a knife to contour the side of the wedge facing the proximal surface, so that it fits snugly around the entire gingival proximal surface. For example, this contouring of the wedge is often required when restoring the mesial surface of the maxillary first premolar, due to the mesial concavity that exists in its cervical portion.

If the wedge fits tightly against the tooth but it’s occlusal surface is too high above the gingival cavosurface margin, a knife can again be used the trim the occlusal surface of the wedge so that it extends just above the gingival cavosurface margin.

Fig. 17-85: Modified triangular (i.e., anatomic) wedge. A, Depending on proximal convexity, triangular wedge may distort matrix contour. B, A sharp-bladed instrument may be used to modify the triangular steepness of the wedge. C, Modified and unmodified wedges compared. D, Properly modified triangular wedge prevents distortion of matrix contour.

Class II Amalgam Restoration

Burnish the matrix band.

The flat matrix band must be burnished, or shaped, to achieve a contour facilitating its proper adaptation to the tooth structure. Begin by folding a paper towel several times and placing it on the benchtop; this provides a more cushioned surface for burnishing. Hold the matrix band in place on the paper towel and use a burnisher or the blunt end of an instrument, such as an examination mirror, to rub against matrix band back and forth. This will introduce a curvature into the matrix band.

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Class II Amalgam Restoration

Place the matrix band into the retainer.

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To prepare the retainer to receive the band, turn the long knob to move the locking vise all the way down to the head of the retainer. Then turn the short knob to loosen the retaining screw (the retaining screw should disengage from the sliding body).

Fold the band to form a loop; notice that when the band is folded, one edge has a smaller circumference than the other; this design accomodates the difference in tooth circumferences at the contact and gingival levels. There are two main rules for correct placement of the matrix system on the tooth:

1. Open end of the retainer head is ALWAYS placed toward the gingiva.
2. Smaller circumference of the band is always placed toward the gingiva.

Based on the two rules above, the following is also true:

• The occlusal edge of the matrix band must be placed in the retainer with the occlusal edge facing the retainer.
• In the LRQ & ULQ, the screw side of retainer is faces the buccal surface of the tooth; in the URQ & LLQ, the flat side of the retainer faces the buccal surface of the tooth.

These rules serve as a guide to how the matrix band must be positioned in the retainer. With the rules in mind, place the two ends of the band in the slot of the locking vise (occlusal edge of the band facing the retainer) and position the band in the correct slot of the head, such that the rules above will be satisfied. Turn the small knob clockwise, lowering the screw into the vise and thus locking the matrix band within the retainer.

Class II Amalgam Restoration |

Fit the matrix onto the tooth.

The band should be seated around the tooth such that:
1. The occlusal portion of the band extends 1.5  2.0 mm above the marginal ridge of the adjacent tooth and the cavosurface marginthis allows for proper condensation of the amalgam in the marginal ridge area.
2. The gingival portion of the band extends 0.5 mm below the gingival CSM.

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In certain situations, it may be difficult to achieve the proper fit in the gingival area, such as when a gingivally located carious lesion necessitates gingival overextension of the cavosurface margin. In such situations, while the band may fit correctly on the affected side, proper fit around the unaffected proximal surface (eg., in a DO prep, the mesial tooth surface may by impeded by the interdental papilla. To facilitate proper fitting of the matrix, it may be necessary to trim the matrix band at the unaffected proximal surface. Be sure to always trim the gingival, rather than the occlusal portion of the matrix band.

Class II Amalgam Restoration |

Tighten the matrix band around the tooth.

To tighten the matrix band around the tooth, turn the long knob; this will pull the matrix band up along with the sliding body, thus decreasing the diameter of the matrix band and tightening it around the tooth. Tighten the matrix as much as possible around the tooth; this allows for proper amalgam condensation and contour development.

To check that the explorer is tightly adapted to the gingival surface, use an explorer and try as hard as possible to place the tip between the matrix band and the gingival cavosurface margin; you should not be able to do so. This also helps to remove any unsupported enamel left in the area.

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Place the wedge, once it is seated tightly in the gingival embrasure, loosen the matrix band slightly by turning the knob 1/4 of a turn. This prevents the matrix band from being too tight, which may lead to an open contact and may hinder proper condensation of the amalgam into the proximal cavosurface margin areas

Finally, use a spoon excavator or burnisher to burnish the matrix band to the adjacent proximal contact area.

Class II Amalgam Restoration |