On edge chipping testing and some personal perspectives on the state of the art of mechanical testing

Abstract

Objective The edge chipping test is used to measure the fracture resistance of dental restoration ceramics and resin composites. This paper focuses on the progress of evaluating chipping resistance of these materials and also on the progress of standardization of this test method. This paper also makes observations about the state of the art of mechanical testing of ceramic and composite restorative materials in general. Interlaboratory comparative studies (“round robins”) are recommended. Methods An edge chipping machine was used to evaluate dozens of materials including porcelains, glass ceramics, aluminas, zirconias, filled resin-composites, new hybrid ceramic-resin composites, laminated composite ceramics, and even polymethyl methacrylate based denture materials. Force versus distance data were collected over a broad range with different indenters. Several chipping resistance parameters were quantified. Results Older restorative materials such as feldspathic porcelains and veneering materials had limited chipping resistance, but more modern ceramics and filled composites show significant improvements. A yttria-partially stabilized zirconia had the greatest resistance to chipping. Much of the early work on edge chipping resistance of brittle materials emphasized linear force versus distance trends obtained with relatively blunt Rockwell C indenters. More recently, trends for dental restorative materials with alternative sharper indenters have been nonlinear. A new phenomenological model with a simple quadratic function fits all data exceptionally well. It is loosely based on an energy balance between indenter work and fracture and deformation energies in the chipped material. Significance Although a direct comparison of our laboratory scale tests on idealized simple geometries to clinical outcomes has not yet been done, anecdotal evidence suggests the procedure does produce clinically relevant rankings and outcomes. Despite the variations in the trends and indenters, comparisons between materials can easily be made by chipping convenient block-shaped specimens with sharp conical 120°, Vickers, or Rockwell C indenters at a defined edge distance of 0.5 mm. Broad distance ranges are recommended for trend evaluation. This work has provided important information for standardization.

Edge chipping resistance and flexural strength of polymer infiltrated ceramic network and resin nanoceramic restorative materials

“…Quinn 17 showed the RNC material to have superior edge chipping resistance followed by the LRGC material, a feldspathic porcelain, and finally the PICN material. His rankings are in agreement with the results of the present study, although the a1 and a2 coefficients are not always comparable.…”

“…Finally, although recommendations for edge chipping testing have been developed, a specification has not yet been established. 17 accessed by following the link in the citation at the bottom of the page.…”

“…17 This type of testing can be performed on both layered and monolithic ceramic materials. 17 The load at which fracture occurs depends on many factors, including the shape and sharpness of the indenter, the angle of the applied force, the angle of the specimen's edge, the distance from the edge, and the material's mechanical properties.…”

“…16 As a response to chipping being a clinical issue, the edge chipping test is emerging as a new tool to characterize dental restorative materials. 17 For this test, chips are formed by advancing an indenter into a material near an edge with commercial edge-chipping machines or a customized assembly on a universal testing machine. 17 This type of testing can be performed on both layered and monolithic ceramic materials.…”

“…17 For this test, chips are formed by advancing an indenter into a material near an edge with commercial edge-chipping machines or a customized assembly on a universal testing machine. 17 This type of testing can be performed on both layered and monolithic ceramic materials. 17 The load at which fracture occurs depends on many factors, including the shape and sharpness of the indenter, the angle of the applied force, the angle of the specimen's edge, the distance from the edge, and the material's mechanical properties.…”