Dental OSCE (Objective Structured Clinical Examination) Practice Exam

Which cement does not form a chemical bond with the tooth structure?

1. Resin-modified glass ionomer

2. Calcium hydroxide

3. Zinc phosphate

4. Glass ionomer

The correct answer is: Zinc phosphate

Zinc phosphate cement does not form a chemical bond with tooth structure. Instead, it relies on mechanical retention to adhere to the surfaces it contacts. The primary mode of action of zinc phosphate involves the physical properties of the material, such as its viscosity and the presence of small particles that can interlock with the irregularities of the tooth surface, ultimately leading to a stable mechanical bond. In contrast, resins, resin-modified glass ionomer, and glass ionomer cements all incorporate chemical bonding mechanisms. Resin-modified glass ionomers feature both ionic bonding (like traditional glass ionomer) and adhesion from resin components. Glass ionomer cements bond chemically to tooth structure through the formation of ionic bonds with the hydroxyapatite of enamel and dentin. Calcium hydroxide, while primarily used for its biological properties, can also bond with tooth structure when used as a liner, but its main role centers around pulp protection and stimulation of secondary dentin formation. Understanding these bonding mechanisms is essential in clinical dentistry, as the choice of cement can impact the longevity and effectiveness of restorations and other dental applications.