Which term describes the junction of two surfaces in a tooth preparation?

• A. Line Angle
• B. Point Angle
• C. Vertex
• D. Edge

Answer: (A)

The junction where two prepared surfaces meet is called a line angle. This term describes the edge formed by the intersection of two walls of a cavity, running along the contour where those surfaces meet. It contrasts with a point angle, which is formed where three surfaces come together, and with the vertex, which is the intersection point of multiple line angles at a corner. An edge isn’t the standard term used for the junction of two cavity walls, so line angle is the correct descriptor. For example, the mesio-occlusal line angle is where the mesial and occlusal walls meet.