Week 4- Matrix and Wedge

Custom Matrices

-Are rare -Special circumstances which may call for a custom matrix: ---removal of one or more cusps ---teeth with unusually long clinical crowns ---teeth without adjacent contact ---a tooth with a rubber dam clamp which interferes with placement of the band and the retainer ---teeth that involve adjacent Class II preparations simultaneously ---anterior teeth requiring Class III and IV preps -------a mylar strip matrix or a crown form may be used -preparations that extend to facial or lingual surfaces -preparations that extend to the gap formed by the band and the retainer -large amounts of tooth structure removed

Forms of Bands

-Rolled stainless steel -Precut and precontoured (various sizes) ---universal ---extension band (molar and premolar) ---pedodontic -Automatrix kit ---used without a retainer - has special applicator and remover -T-band pedo band - used without a retainer -Spot-welded bands -Copper band (tube) - used as a custom matrix

Selection of the Wedge

-Select after placement of matrix band and retainer -Should be slightly wider than distance between cervical portions of adjacent teeth in order to: ---apply pressure against the matrix and tooth ---cause slight separation of adjacent teeth

Considerations for Retainers

-Size and shape of the preparation will determine: ---band size and shape ---orientation of the retainer ---need for compound to support the band -Universal band is used when the proximal box is a minimal depth and width -Extension band is used when prep. has greater gingival extensions and when occluso-gingival dimension exceeds the height of the universal band -Prep. may include both proximal surfaces (MOD) and cusps.

Care of Matrices and Wedges

-Stainless steel matrix retainers are scrubbed, rinsed, dried and sterilized after each use. -Stainless steel matrix bands may be reused if properly sterilized and have not had their original shape changed significantly by trimming or have not become strain hardened (will not burnish). -The strip matrix is discarded after use because it is difficult to recontour and cannot be sterilized. -The wedge is discarded after use because it cannot be sterilized.

Placement of the Matrix Band

-The band should be placed in the gingival crevice about 1 mm apically to the gingival margin of the preparation. -The occlusal edge of the band should extend one to two millimeters occlusal to the marginal ridge of the adjacent tooth. If the adjacent tooth is missing extend this edge one to two millimeters occlusal to the occlusal margins of the cavity preparation.

Criteria for Matrix Retainer and Band Placement

-The slot opening of the retainer is toward the gingiva -The retainer is positioned at the facial surface of the tooth if it is a straight retainer and at the lingual surface if it is contraangled -The handle extends out from the oral cavity at the corner of the lips -The band extends approximately 1-1.5 mm below the gingival margin of the preparation -The band extends 1.5-2 mm above the occlusal surface of the tooth

Placement of the Wedge

-The wedge is seated in the largest gingival embrasure of the proximal surface being restored. -If the wedge is too large to fit the embrasures it is trimmed with a gold knife or similar instrument to fit. -The wedge is seated so that no part of it infringes on the cavity preparation. -Shorter side of the wedge is placed adjacent to gingival tissue -Point of wedge is occlusal to interdental papilla to avoid soft tissue damage. -Occlusal height of wedge should be level with the gingival wall of the preparation -MO- wedge mesial, DO- wedge distal, MOD- wedge both -An explorer tip placed against the inside of the matrix band and gingival wall should not create an opening. If so, it may be caused by: ---wedge is too narrow ---wedge is not placed with adequate force into the interproximal space ---wedge is too wide and won't pass far enough into the embrasure to be effective ---wedge is not adapted to proximal surface along entire faciolingual dimension

Wedges

-Triangular (wedge-shaped) insert used interproximally Forms: ---Uncontoured or contoured ---Wooden, plastic or metal (rare) ---Various sizes and colors -Types commonly used ---Round toothpick ---Trimmed applicator stick or match stick ---Commercially prepared triangular shaped wedges

Band selection based on:

-amount of remaining tooth structure -size and shape of preparation -proximal contacts -gingival tissue -size of the tooth -appliances restricting placement (ex. rubber dam)

The matrix band should be placed in the gingival crevice about _______ mm apically to the gingival margin of the preparation.

1

The occlusal edge of the matrix band should extend ______ millimeters occlusal to the marginal ridge of the adjacent tooth.

1-2

Matrix Uses (2)

1-Class II cavity preparation (Posterior proximal surfaces) ---Normally metal matrices 2-Class III or IV cavity preparations (Anterior proximal or incisal) ---Normal mylar or plastic matrices

Necessary Qualities of a Matrix (5)

1-Easy application and removal. 2-Should not be costly or time consuming. 3-Stable enough to withstand the stress of inserting restorative material into preparation. 4-Should produce an ideal proximal surface which will not harm the periodontium. 5-Provide sound margin to the restoration

Function of the Wedge (3)

1-In some cases the wedge helps stabilize the band. 2-Prevents excess restorative material (overhang) at the gingival margin of the restoration. 3-Wedging separates the teeth enough to compensate for the thickness of the band. This ensures a tight contact relationship after the band is removed following placement of the restorative material.

Types of Retainers (2)

1-Ivory retainer 2-Tofflemire retainer (most often used) ---straight - facial placement ---contra-angle - lingual placement ---adult size as well as deciduous size

Factors Reducing the Effectiveness of a Matrix Band (2)

1-Overuse of a stainless steel band. The band becomes strain hardened and cannot be adapted and shaped. 2-Excessive tightening of any matrix band tends to flatten the proximal contour.

Function of a Matrix (5)

1-Temporarily replaces a missing wall or walls of a cavity preparation 2-Establishes proper anatomic contour 3-Restores correct proximal contact relation 4-Prevents and excess of restorative material at the gingival margin of the restoration 5-Creates a smooth external surface for the restorative material

Components of a Matrix (3)

1-Thin metal band - provides missing tooth structure 2-Mechanical retainer - holds/ stabilizes band 3-Wedge - interproximal - adapts band to tooth

Matrix (def)

A thin metal form, usually stainless steel, adapted to a prepared cavity to supply the missing wall so the amalgam will be confined when condensed into the cavity preparation

Retainers

Supports, stabilizes and holds band in place around tooth