INBDE (Integrated National Board Dental Examination) Practice Exam

Primary resistance form is a key factor in achieving a successful and long-lasting restoration. It refers to the shape and positioning of the preparation walls that provide stability and resistance to displacement during functional forces. Rounded internal line angles and a 90 degree cavosurface margin can contribute to optimal resistance form. Option A is incorrect because while converging internal line angles may aid in retention, they can weaken the structure and compromise resistance form. Option C is incorrect because while parallel walls may aid in resistance form, a 90 degree cavosurface margin is not ideal as it can create stress concentration and lead to failure. Option D is incorrect because undercuts may aid in retention, but they can also increase the risk of fracture and do not contribute to resistance form.