A survey of failed post-retained restorations

Survival of endodontically treated, post-restored teeth depends on a multitude of factors, all of which are practically impossible to include in a randomized, controlled clinical study. The purpose of this survey was to characterize and analyze reported failures of post-retained restorations to identify factors critical to failure and to type of failure. A questionnaire was mailed to private practitioners in Denmark with a request to complete the questionnaire whenever a patient presented with a failed post-retained restoration. Information was gathered on factors related to the patient, the tooth, the restorative materials, and the techniques. Two-hundred and sixty questionnaires were collected from 171 practitioners over a 3-year period. Functioning time until failure varied between 3 months and 38 years. Mean survival time until failure was 11 years. Of the failed restorations, 61% had functioned for 10 years or less. Fracture of the tooth was the most common type of failure reported, followed by loosening of the post and fracture of the post. Tapered posts implied an increased risk of tooth fracture compared to loosening or fracture of the post, and the relative risk of tooth fracture increased with the functioning time until failure. Fracture of the post was more common among male than female patients. On the basis of this survey of failed post-retained restorations, it was concluded that tapered posts were associated with a higher risk of tooth fracture than were parallel-sided posts

Clinical science: The influence of modification of cavity design on distribution of stresses in a restored molar

In this study, two different cavity designs were compared from a mechanical point of view: (a) an axisymmetric model of a conventional class 1 cavity preparation and restoration; and (b) an axisymmetric model of a modified cavity design. The modified design was characterized by a cavo-surface angle (c.s.a.) of approximately 90 degrees and a stepped cavity wall. Using a mathematical model, stresses were calculated by finite element analysis to compare the force distribution. It is concluded that the clinical superiority of the modified cavity design, with respect to the marginal breakdown of the amalgam restoration, can be supported by stress calculations. [Journal Article; In English; United States

Distributed crack analysis of ceramic inlays

In all-ceramic restorations, crack formation and propagation phenomena are of major concern, since they may result in intra-oral fracture. The objective of this study was calculation of damage in porcelain MOD inlays by utilization of a finite-element (FE) implementation of the distributed crack theory. Damage is defined as the parameter that describes the local decrease of stiffness caused by microdefects. In the simulated MOD ceramic inlay, the crack initiation starts at the internal occlusal surface near the pulpo-axial line angle. This initiation is invisible from the external surface and cannot be detected by the clinician. The crack initiation at the internal surface started as soon as 55-60% of the loading needed for complete fracture was reached. The use of FE techniques for calculation of the fracture in loaded ceramic inlays offers prospects for further detailed study of the crack behavior, including three-dimensional modeling and cyclic loading situations