Commission on Dental Accreditation (CODA) Board Practice Exam

Reversible hydrocolloids, commonly used in dentistry for making impressions, primarily consist of agar and water. Agar is a gelatinous substance derived from red algae and has the unique property of being reversible; it can transition from a gel to a sol state upon heating. This characteristic allows it to be easily manipulated during the impression-making process.

The combination of agar and water creates a stable hydrocolloid that can capture fine details of oral structures. When heated, agar dissolves in water, forming a viscous sol, and upon cooling, it solidifies back into a gel, making it extremely useful for dental applications. The effectiveness of this material lies in its ability to change states without losing its properties, making it ideal for obtaining impressions that require accuracy and detail.

Other options listed do not accurately represent the composition of reversible hydrocolloid. Sodium alginate, though a hydrocolloid, is typically used in irreversible hydrocolloid materials rather than in reversible systems. Silica is commonly used as a filler or thickening agent in various dental materials but is not a primary component of hydrocolloids. Calcium sulfate and gelatin may have specific uses in certain contexts but do not represent the foundational ingredients of reversible hydrocolloid impression materials.