What is the primary function of an auto matrix in dental procedures?

The primary function of an auto matrix is to come pre-sized and fit around the tooth, providing a crucial role in the restoration process. An auto matrix allows for the proper shaping of the restorative material when filling a cavity, ensuring that the material is contained and forms a proper anatomical contour that mimics the natural tooth structure. This pre-sized feature simplifies the process for the dental professional, as it saves time and increases efficiency during the placement of the matrix band.

Other functions such as holding a tooth in place during a filling, isolating the treatment area from saliva, or assisting in the x-ray imaging process, while related to dental procedures, do not accurately define the primary purpose of the auto matrix. These alternate functions are typically managed by different tools or techniques used in the dental field.