Journal of Dental Research, Vol 70, 44-49, Copyright © 1991 by International & American Associations for Dental Research Online Journals
Tandem-scanning microscopy of slow-speed enamel cutting interactions
T. F. Watson
Department of Conservative Dentistry, United Medical School, Guy's Hospital, London Bridge, England.
The aim of this study was to observe the subsurface microstructure of
dental enamel during cutting procedures. Real-time confocal scanning
optical microscopy, with a tandem-scanning reflected-light microscope, is
suitable for making high-resolution images of enamel prisms in intact teeth
under near-normal conditions. Blocks of enamel were held on a
micro-positioning stage and advanced toward the tip of a diamond knife. The
orientation of the samples was varied to simulate common clinical cutting
conditions. Oil immersion objectives were used with the knife rigidly
mounted in a specially made carrier. This was attached to the objective
below its end-lens. The images were recorded with a sensitive video camera
and cassette recorder for analysis of the cutting interactions at a slow
playback speed. The presence of decussating enamel prisms was particularly
effective at slowing crack propagation when loading was applied in an
appropriate direction. Residual subsurface cracking was seen when the blade
had finished cutting. This was most pronounced in regions where the enamel
prisms were cut transverse to their long axis; this was equivalent to the
preparation of the cervical margin of an approximately cavity. Where there
is surface adhesion to enamel (e.g., glass-ionomer cements), residual
subsurface cracking will produce a weakened substrate for bonding that
could have important implications for restoration longevity.
