A posterior restoration, commonly known as a filling on a back tooth, requires precision when the decayed area involves a side surface. This type of filling is classified as a Class II restoration and necessitates the use of a specialized matrix system to rebuild the missing wall of the tooth. The matrix system is composed of a matrix band, which acts as the temporary wall, and a small, triangular device called a dental wedge. The wedge is a crucial component that helps ensure the final restoration is shaped correctly and seals effectively against the adjacent tooth and the gumline.
The Essential Function of the Dental Wedge
The dental wedge serves three primary functions during a posterior restoration. The most immediate function is to achieve a tight seal at the bottom of the prepared tooth surface, known as the gingival margin. If the matrix band is not held firmly against this margin, the filling material can extrude, creating an excess known as an overhang. This overhang traps plaque and frequently causes subsequent gum inflammation and bone loss.
A second function is physically stabilizing the matrix band within the interproximal space. The pressure exerted by the tightly placed wedge secures the band, preventing it from moving or collapsing as the restorative material is placed and condensed. This stabilization maintains the desired contour and shape of the new tooth surface.
The third role of the wedge is to create a minute, temporary separation between the treated tooth and the neighboring tooth, known as the wedging action. The wedge applies gentle force to slightly push the teeth apart, compensating for the thickness of the matrix band itself. When the wedge and the matrix band are removed after the filling is set, the teeth naturally spring back. This results in a tight and anatomically correct contact point with the adjacent tooth.
Precise Positioning in the Interproximal Space
The wedge is inserted into the gingival embrasure, the V-shaped space located just below the contact point. It must be seated firmly and slightly apical (toward the root) of the prepared cavity’s gingival margin. This placement ensures the wedge compresses the gum tissue and holds the matrix band snugly against the tooth structure where the filling material will end.
The wedge is typically inserted from the wider embrasure space, usually the lingual or palatal side, and pushed through until the tip slightly emerges on the opposite buccal side. The aim is for the wedge’s widest part to be positioned directly at the gingival margin. Incorrect positioning severely compromises the restoration’s quality.
If the wedge is placed too far occlusally (toward the biting surface), it can push the matrix band inward, creating an abnormal concavity in the final restoration. Conversely, if it is not seated deeply enough, it fails to seal the margin, leading to a destructive overhang. The insertion requires a controlled, snug fit that applies sufficient pressure to seal the margin without damaging the surrounding soft tissue.
Selecting the Correct Wedge Size and Material
The effectiveness of the wedge depends on selecting the correct size and material for the specific restoration. Wedges are available in a range of sizes, often color-coded, to accommodate variations in the interproximal space dimensions. The general rule is to choose the largest wedge that can be firmly seated into the embrasure without distorting the matrix band.
The two main material types are wooden and plastic. Wooden wedges, typically made from maple or birch, are rigid and absorb moisture, causing them to expand slightly after placement and enhance the marginal seal. Plastic wedges are often anatomically pre-contoured, flexible, and less absorbent, making them suitable for tight spaces. Some plastic wedges are also transparent, allowing curing light to pass through for certain composite fillings.
Choosing a wedge that is too small prevents it from achieving the necessary pressure to seal the margin or create the desired tooth separation. Conversely, a wedge that is too large or too forcefully placed can deform the matrix band, leading to an incorrect contour or causing trauma to the gum tissue. Correct selection balances the need for a tight seal and slight tooth separation with preserving the matrix band’s anatomical shape.