Department of Computerized Dentistry, University of Amsterdam, Netherlands
Corresponding author details:
Jef M Van Der Zel
Department of Computerized Dentistry
University of Amsterdam
Netherlands
Copyright:
© 2020 Van Der Zel JM..
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Patients with missing tooth structure should receive restorations that at least mimic or exceed the functional and esthetic requirements of the remaining teeth. This can be accomplished by using a strong substructure and a translucent layer of porcelain, therewith mimicking the structure of a natural tooth. The technology that is regarded as best available technology (BAT) is computer aided design (CAD) and computer aided milling (CAM) of a reduced substructure of zirconia and subsequently milling the outer contour in hardened paste glass ceramic, known as prosthetic mimetic restorations [1].However, at present most restorations produced by CAD/CAM technology are monolithic products of either color and structure graded zirconia or lithiumdisilicate glass ceramic. That the best available technology is not used has economical reasons, because direct milling of the final restoration from one block of material is easier than having to mill a second porcelain layer. The three materials involved in present restoration differ considerably in their Vickers surface hardness: zirconia in all its modifications 1200, lithium disilicate glass ceramic 700 and PRIMERO 470, while human enamel has hardness between 390 and 450. Because zirconia has four times the hardness of metal, initial concern about antagonist abrasion could with numerous studies be negated.
Most previous work conducted on the wear behavior of dental enamel has focused
mainly on wear rates and surface damage. There is, however, scarce information regarding
the subsurface damage (SSD) arising from sliding contact fatigue. Enamel probes
were submitted to cyclic contact fatigue test in off-axis mouth-motion cycling machine
with 200 N load and 2 Hz frequency in distilled water at 37°C for up to 106 cycles a
zirconia, lithiumdisilicate and PRIMERO indenter. Subsurface damage of enamel is often
covered with a smearing layer generated by wear mechanisms and rather difficult to directly
observe and detect by optical microscopy. Subsurface damage was therefore assessed
using sagittal and transverse sections of the samples and lateral, median and cone cracks
observed and quantified. Massive crack formation in enamel probes opposing monolithic
zirconia was observed. The zirconia caused twice as much crack in the enamel probe as
lithiumdisilicate and three times more cracks than the PRIMERO indenter. Both wear and
subsurface fracture in enamel are determining factors for the long-term decay of teeth. We
must fear for the subsurface integrity of zirconia opposing enamel on the long term and the
use of porcelain glass ceramics should remain the “best available technology”.
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