A dentist usually uses: 

The correct answer is a concave mirror.

Key Points

• A dentist uses a concave mirror to examine the teeth.
• Concave mirrors provide a magnified and upright image of the teeth, which helps in detailed examination.
• The curved surface of a concave mirror helps in focusing light, providing better illumination in the oral cavity.
• Concave mirrors are preferred because they allow dentists to see a larger area of the mouth clearly.

Additional Information

• Convex Mirror:
  • A convex mirror diverges light rays and is used for a wider field of view, such as in vehicle side mirrors.
  • It provides a smaller, upright, and diminished image, which is not suitable for dental examination.
• Plane Mirror:
  • A plane mirror reflects light without altering the size of the image.
  • It provides a virtual, upright image of the same size as the object, but it does not magnify, making it less useful for detailed dental work.
• Plano-Convex Mirror:
  • A plano-convex mirror is typically used in focusing applications, such as in telescopes and laser systems.
  • It is not used in dental practices due to its specific focusing properties.
• Optical Properties:
  • Concave mirrors converge light rays to a focal point, allowing for magnification of the image.
  • Convex mirrors and plane mirrors do not offer the same level of magnification and focus required for dental examinations.