5.6 Bases, Liners, Matrices, and Wedges

Small setup choices shape the restoration

Bases, liners, matrices, and wedges are common treatment preparation topics because they connect anatomy, materials, and sequence. They are not random accessories. They help the dentist protect tooth structure, manage deep preparations, create missing walls, and shape restorative material. The RDA's job is to prepare and support the needed system under dentist direction.

A liner is generally a thin material placed in selected areas for protection, sealing, or therapeutic purpose as determined by the dentist. A base is usually thicker and may provide insulation, support, or replacement of missing dentin depending on the material and clinical situation. The assistant may prepare the selected material, delivery device, pad, or mixing instrument according to instructions. The dentist decides whether a base or liner is indicated.

A matrix provides a temporary wall when a proximal surface is missing. Without a proper matrix, restorative material may spread beyond the intended contour or fail to establish a contact area. Matrix systems include retainers and bands, sectional rings and bands, clear strips for anterior restorations, and other office-specific systems. The RDA should know that the band, retainer or ring, and wedge work together.

Key components

Wedges are easy to underestimate. A wedge can press the matrix against the gingival margin, reduce the chance of overhang, stabilize the band, and create slight tooth separation that helps restore contact after the matrix is removed. If a question describes a proximal restoration with a gap at the gingival margin, the wedge is a likely issue. If the wedge is too large, too small, missing, or unstable, the assistant should recognize that contour and margin control are at risk.

The RDA also watches timing and contamination. Some bases and liners set chemically or by light. Some are dispensed through tips that must stay clean. Matrix bands and wedges contact the oral field and become contaminated after try-in or placement. A used band or wedge should not be returned to clean stock. If a band is dropped on the floor before placement, replace it.

Do not turn preparation knowledge into independent treatment decisions. The exam may ask what the RDA should have ready when the dentist requests a liner, or what is missing from a matrix setup. It should not lead the assistant to decide that a tooth needs a liner without dentist direction. The safest answer keeps the RDA in the role of preparation, communication, and support.

Study these items as systems. A base or liner needs the selected product, delivery method, timing, and field control. A matrix needs the band or strip, stabilizer, wedge, and instruments for placement and removal. A good setup prevents overhangs, open contacts, delays, and contamination. That is exactly the kind of functional knowledge the California RDA exam is built to sample.