Final answer:
The Tofflemire retainer is the matrix system commonly used for posterior composite restorations, providing the necessary shape and support for the restorative material.
Step-by-step explanation:
The matrix system typically used with posterior composite restorations is the Tofflemire retainer. While there are various matrix systems available, the Tofflemire retainer system is quite popular as it can provide the right shape and support for the composite material being used in restorative dental procedures. It helps in creating a tight contact between the restored tooth and the adjacent teeth, ensuring a properly contoured restoration.
Other matrix systems like the Ivory Matrix System, Walser Matrix System, Ash No. 1 Matrix System, and NiTi Matrix System have their specific uses and benefits, but for posterior composite restorations, dentists often prefer the stability and reliability of the Tofflemire retainer.