High Speed Drilling

2. But the major damage is caused in and on the dentine itself. Many colleagues are of the opinion that the pulp receives too much heat due to friction when turbines are used in treatment. Additional abundant cooling would avoid such a burden. As, due to the high rotation speed, both a congestion andhs_qanegative pressure occurs on the dentine, a dry (or water-less) zone is formed at the very point of drilling or grinding/milling.
3. In an edition of a German-language journal (the ZWR), SCHOLER, a Swiss colleague described trials with air and water-cooler turbines: to culminate, he discovered that already after 5-20 seconds of milling or grinding with turbines, an increase in pulp temperature by 12 degrees C (aboaut 22 degrees F0 caused irreversible damage in 60{a32a96fa760d4df88200e9380b607e1e27cc078cb403997aa41a99d92482d614}d of the pulps examined. These findings have found their confirmation in an almost identical study by HENNING and PRZTAK, who are also mentioned in the same article. This article, however, did not mention one kind of damage which is not produced thermally, but equally spell doom to the pulp, (i.e., damage from negative pressure).
As a result of the high rotation speed, turbulence are produced around the burs which produces a very high negative pressure over the dentinal tubules (according to my own most recent tests this amounts to as much as a 10 mm water column per 100,000 revolutions). This negative pressure does not increase in linear, but in exponential fashion: as a result of this state, the peritubular dentine linings, and the cylindrical odontoblastic processes are damaged or sometimes torn out, even odontoblast cores may be partially sucked into the tubules.hs_ka
(See right: Dentinal tubules under high power magnification).
Professor RAVNIK of Ljubljana in Yugoslavia was already able to prove this many years ago. This means that the metabolic processes in the enamel and dentine regions are disrupted decisively.
By way of reminder:
Approximately 5 million dentinal tubules per square centimeter (equivalent to 12 million per square inch) are located in the crown area of the pulp. This number decreases down towards the root apex, although it still amounts to approximately 1.4 million at the cement limit. One single dentinal tubule has a diameter of 1.3 to 4.5 microns.
When the drilling or grinding bur is withdrawn, so that the negative pressure ceases, the empty and now open tubules can be filled in a retrograde manner by bacteria and grinding debris, as reported in English Language electron microscope studies. The denatured protein of the destroyed odontoblastic processes and cores can be broken down porteolytically by these bacteria.
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