Which procedure involves the use of a matrix system during restorative work?

The placement of posterior composite fillings is a procedure that commonly utilizes a matrix system, which is essential for restoring proper contour and contact points between adjacent teeth. The matrix helps to provide a temporary mold for the composite material during placement, preventing the filling from losing shape and ensuring accurate replication of the tooth's anatomy.

In posterior fillings, especially in class II restorations, a matrix band is used to create a wall against which the composite can be packed. This is crucial for achieving a sealed restoration that functions well in occlusion and maintains the integrity of the interproximal space. The matrix system allows for better adaptation of the filling material to the tooth structure, leading to improved function and aesthetics.

Other procedures listed do not typically involve the use of a matrix system. For instance, root canal treatments focus on removing infected pulp tissue and cleaning the tooth's canal system, which does not require a matrix. Extraction involves the removal of teeth, so a matrix system is unnecessary. The application of sealants is straightforward and does not typically demand a matrix, as the sealant is applied directly onto the tooth surface without the need for shaping or forming a filling structure.