Dental OSCE (Objective Structured Clinical Examination) Practice Exam

A porcelain jacket crown margin should have which type of margin?

1. Knife edge

2. Shoulder or butt joint

3. Round bevel

4. Textured finish

The correct answer is: Shoulder or butt joint

A porcelain jacket crown margin is designed to provide a strong and esthetically pleasing restoration for anterior teeth. The shoulder or butt joint margin is ideal for this type of crown because it offers a flat surface that ensures precise fit and excellent retention. This type of margin allows for better adaptation of the porcelain to the tooth structure, minimizing gaps that could harbor oral bacteria and lead to caries or periodontal issues. The flat shoulder margin also provides a more favorable aesthetic outcome because it creates a smooth transition between the tooth and the crown, enhancing the visual effects of translucency in porcelain. It allows the facial aspect of the crown to closely mimic the natural tooth. In contrast, knife edge margins can create sharp angles that may not provide sufficient strength or retention, while round bevels do not offer an adequate surface area for adhesion, making them less suitable. A textured finish is generally not appropriate for the margins of a porcelain jacket crown as it may compromise the seal between the crown and the tooth, diminishing the longevity and success of the restoration. Overall, the shoulder or butt joint margin represents the best combination of strength, retention, and aesthetics for porcelain jacket crowns.