Machining-Induced Surface & Subsurface Damage in Dental
Ceramics
Ling Yin1, Xiao-Fei Song2
1School of Engineering & Physical Sciences, James Cook Univerisity, James Cook
University, Townsville, QLD 4811, Australia;
2School of Mechanical Engineering, Tianjin University, Tianjin 300072, China
e: ling.yin@jcu.edu.au
Glass ceramics are ceramic composites containing a glass phase and one or
more embedded crystalline phases produced by controlled crystallization of certain
glasses. The crystallization is generally induced by nucleating additives with the
degree of crystallinity between 30 and 70 percent. Most glass ceramics have no or
very low porosities. They have low thermal expansion coefficients, good
biocompatibility, chemical durability, high strength and toughness, and they are
translucent.
Glass ceramics have been used in engineering applications as diverse as
radomes to protect radar equipment in the aerospace industry, microchannels in
optical fibers, large type telescope mirror blanks for ring laser gyroscopes and optical
parts, broadband optical amplification, tunable and infrared lasers, solar collectors,
ink-jet printer heads, and substrates for pressure sensors and acoustic systems in
head-phones. They are also widely applied as dental restorative materials for
crowns, bridges, inlays, onlays and veneers.
In these applications, glass ceramics need to be shaped by abrasive machining
processes, such as milling, grinding and polishing, to obtain the desired shapes and
surface quality. Because of the variety of their chemical structures and
microstructures, the mechanical properties and machinability of these materials are
different widely. For instance, feldspar and leucite glass ceramics have lower
hardness and are more machinable than the much harder alumina-infiltrated glass
ceramics. However, machinable or difficult-to-machine glass ceramics share the
common problem, i.e., they are very brittle and prone to fracture and produce
extensive machining-induced surface and subsurface damage in the materials during
the machining processes. This paper discusses the surface and subsurface damage
induced in machining of several glass ceramics using experimental and finite element
analysis approaches.
This paper briefly presented diamond machining characteristics of some glass
ceramics for dental restoations, particularly surface and subsurface damage induced
in the materials using experimental and FEA modeling approaches. The removal
features of these glass ceramics mainly controlled by brittle fracture were determined
by the material microstructure and machining parameters. The FEA modeling was
shown to be a powerful tool for the prediction of subsurface damage depths induced
in the glass ceramics, which will be very useful for conducting non-destructive
evaluation of the reliabilities of fabricated glass ceramics using diamond abrasive
tools. Further studies are needed to understand the thermal influence on the
microstructural changes using Raman spectroscopy. The mechanical-thermal
coupling effects on the FEA modelling of fracture, plastic deformation and phase
transformations in diamond machining of glass ceramics also need to be investigated.