4. _Stopping of the carious cavity._ Dionis does not enumerate this operation among those intended for the preservation of the teeth. At that period, this operation was performed solely with a view to preventing the penetration into and the retention within the carious cavity of alimentary substances, and the disadvantages caused thereby. The carious process, says the author, often ceases altogether, and the pain then generally ceases also. However, as the residual cavity often becomes troublesome in various ways, among others by making the breath offensive, it is better to stop it. For this purpose, gold or silver leaf is generally made use of; but this mode of stopping is not durable, because gold or silver in leaf is apt to become loosened and fall out. It is therefore preferable, says Dionis, to make a stopping with a piece of gold or silver corresponding in size and shape to the cavity.[391] Many, he adds, prefer lead as a stopping, on account of its softness, whilst others simply use wax. 5. _The use of the file._ The indications given by Pierre Dionis for using the file do not differ from those we find in other authors. Dionis warns, however, against using the file to level down a tooth which has become lengthened through the loss of its antagonist, for after a certain time it would again project above the level of the others. 6. _Extraction._ This operation, says Dionis, ought not to be performed too lightly, but only in those cases in which it is really necessary; that is, when a tooth is the cause of insupportable pain and its crown is almost entirely worn away; when nothing remains of a tooth but its root; when a tooth is so loosened in its socket as to leave no hope of its again becoming firm; when supernumerary teeth or irregularly planted teeth give rise to inconvenience or deformity; and lastly, to remove deciduous teeth that have become loosened. The opinion that if the loosened milk teeth be not promptly extracted they cause the permanent teeth to grow irregularly, is, however, considered by Dionis to be a prejudice. Dionis strongly doubts whether a tooth that has been extracted and replanted can really take root again, as had been affirmed by Dupont, Pomaret, and other authors. This shows that Dionis had had no experience on this point.