A Photoelastic and Dynamic Studies on Pin-Restoration

Abstract

The Purpose of this Two-Dimensional Photoelastic studies are based on getting the solution for dynamical answers in planning of pin-restration. The most important factors in pin-restration are length, size, numbers, and location of pins. These factors are Discussed in this investigations. Under the influence of pin length and size for stress concentrations were reported in part I. Under the influence of a space between two pins for stress concentrations were reported in part II. In part III, I studied and discussed about the infiuence of pin location for stress concentration in specimen. As the results of these efforts, the following conclusionand clinical application are obtained.1) When appling the compress force on pin axis, the resistance of specimen for load was decreased and the compress stress was increased in pin apex area. These findings were caused by the pin closer to outer surface, the thickness of specimen became thinner from outer surface to the pin. The stress concentrations under pin apex region were varnished toward the outer surface. Futther more, the stress fringes were increased in the region of pin apex conected to outer surface. These findings of increased stress in thinn specimen area were indicated that the fracture in this region. From all of these findings and the results in part I, I could summarize that increased of the force applied on a pin axis, the pin should be placed in tooth least same distance of pin diameterinside from the outer surface.2) When appling the perpendicular bending force on pin axis from outer surfacce of specimen, the resistance of specimen for load was decreaied, and the moment of force and spling back action of pin were increased. These findings were caused by the pin closer to outer surface, the thickness of specimen became thinner from outer surface to the pin. The changing of stress concentrations in specimen was found that the compress stress was increased on the top side pin, and was decreased under side of pin neck. Tensile stress in outer surface of specimen and stress fringes which collected from outer surface of specimen to the top side of pin apex were found. These findings of increased stress in thinn specimen area were indicated that the fracture in this region. From all these findings and the results in part I, I could summarized that in case of the force applied to a. pin perpendiculary from outer surface to the pin, the pin should be placed in tooth least twice more of pin diameter inside from the outer surface.3) When appling the perpendicular bending force on pin axis to outer surgace, the resistance of specimen for load was decreased, and the moment of force was increased, also thinn outer surface area getting the bending force directry from pin. These findings were caused by the pin closer to outer surface, the thickness of specimen became thinner from side of pin to outer surface. The compress stress under side of pin neck, top side of apex, and under side of apex were decreased. Tensile stress under side of apex and compress stress in outer surface of specimen were extremely increased within this region. From all of these findings and the results of part I, I could summarized that in case of the force applied to a pin perpendiculary to outer surface of specimen, the pin should be placed in tooth least four times of pin diameter inside from the outer surface.4) More greater stress concentration was found in case of appling the bending force to outer surface of specimen than the same force was applied from outer direction.5) From all of these findings, the followin conclusion are obtained.Planning of the pin-restration should be discussed about the direction of applied force and the amount of the force, all of these be based upon the sever condition.In the small pin-restration, the location of pin should be inside from outer surface as same distance as the diameter of pin.