Mathematical derivation of the minimally acceptable all-porcelain margin angle

There is limited research defining the minimally acceptable porcelain margin angle required to withstand the stresses incurred during seating a restoration. A mathematical model was derived to calculate this critical porcelain margin angle. The factors involved in margin fracture were determined to be the tensile strength of the porcelain, the axial reduction, the diameter of the tooth, the porcelain margin angle, and the seating force. As the seating force increases, the porcelain margin angle required to prevent failure also increases. Increasing either the axial reduction or the diameter of the tooth allowed the minimum porcelain margin angle to decrease.