A conventional treatment shows the dentist only what the naked eye permits. Under the microscope the same tooth is examined at twenty-five times its size, and the work changes accordingly.
Magnification makes it possible to open canals that are invisible on an X-ray, retrieve an instrument broken during an earlier treatment, spot hairline cracks and early decay before they spread, and correct root canals that failed the first time. It also means removing less healthy tooth: a smaller opening is enough to reach the canal.
The same discipline carries into repair work. A tooth rebuilt at magnification with tooth-coloured filling material follows the anatomy it started with rather than an approximation of it, in one appointment and without grinding the tooth down for a crown.