There are many points in crown and bridge work requiring particular
attention which many operators seem entirely to overlook in the
construction of this special class of work. It might be of interest to
you to turn your attention in this direction.
In the first place, the use of crowns has been abused to a great extent
by the crowning of all class of roots, some of which are only fit
to be crowned by a good, strong pair of forceps. These roots may be
divided into three classes: first, those that have been in a diseased
condition for years and have been a source of constant irritation
to their owners; second, those that are only held in by their gum
attachments; third, those whose walls have been fractured, said
fracture only extending down as far as the process.
As the result of many inquiries in regard to the class first mentioned,
I find that the majority of operators after spending weeks and even
months in careful preparatory treatment, have met with very little
success in crowning such cases. They invariably cause some annoyance
to the patient. In the majority of cases the trouble is that of
inflammation of the surrounding tissues, caused by the constant moving
of the root during the process of mastication. After a root has been
in a diseased condition for a year or more, it is questionable whether
treatment, however carefully given, will place that root in a condition
to be crowned and do the work of the original tooth.
The second class is beyond the bounds of practical dentistry, and no
operator who has any regard for his reputation will attempt this class
of crown work, unless he has a mercenary object in view.
All who have attempted the third class have made many failures. When
there is a fracture extending from the centre of the root, running down
to the process border in a slant, no crown can with any satisfaction
be properly adjusted, owing to this movable portion of the root. Were
this portion removed, the root would be placed in a position impossible
to crown. Then again, in case the crown is successfully placed, how
long will it last? Probably not more than a year. There is bound to be
a decaying of the root at the site of the fracture. From decay, that
fractured piece will soon become loosened, and the chances are that it
will in some way work its way out, and as a result, there is a cup to
accumulate food, which will cause, later on, a very offensive odor.
A case of this kind cannot be ferrelled without the results already
mentioned. Should the root be split down through its centre, then a
crown could be used without fear of any bad results, by bracing the
root with a strong ferrell made of platinum, letting it extend down to
the process border, thus avoiding the possibility of any secretions
getting in between the fractured parts. The difference between the
two cases can very readily be seen. In one case, there is a loose,
disconnected piece of tooth structure only held in place by the
membrane surrounding it. In the other case, there are two firm parts
which are firmly held in place by their bony socket.
These three classes of roots are being crowned day after day by men who
are considered competent practitioners, and their only success is the
satisfaction of knowing that they retained the root, or roots, for six
months or a year's time.
These are only some of the abuses of crown work, to say naught of teeth
which could be properly filled, that are sacrificed for crowns which
can never take the place of teeth properly filled.
Bridge work has taken the place of gold plates to a certain extent.
Still, however good a thing it may be, it also is greatly abused. In
my mind, a bridge is not a practical dentiture when it has to span
the entire arch supported only by three or four roots, or, say teeth.
It has no superiority over a gold plate in such a case, because the
latter can be kept clean, while the former can not, and the best of
bridges must be removed at times to be reset. The chief objection to a
full case of bridge is its becoming loose, which is no doubt caused by
the unbalanced movement of the roots, as pressure or weight cannot be
brought to bear upon three spans surmounting four pieces at the same
time; one piece will surely give way to the undue strain.
The abusive use of open-face crowns must not be overlooked. These
classes of crowns for bridge work should never be used, as they are
simply not practical. We have yet to see one which will last any length
of time. They have no strength nor durability. One of their weak points
is the band around the labial surface of the tooth which in course of
time cracks. Another is the free access which the secretions have to do
their work upon the cement which holds the crown in place.
We are taught that a cement filling is not a permanent one, and
especially should not be used below the gum border; but we are advised
to use open-face crowns and to set them on with cement. If cement
will not last when put into a cavity of a tooth at the gum line, we
should hardly imagine that it would last very long when only protected
by a thin gold band placed below the gum line, where secretions have
continual play at it.
Another class of bridge work which should be done away with is what
is called pin bridges, where places are bridged over, getting the
necessary support by drilling cavities into sound teeth to insert the
pins necessary to support the bridge. This is a class of work which
simply will not last, owing to the lack of proper strength required to
support a dentiture of that sort. If a good tooth must be sacrificed,
why not crown the necessary teeth and get something from the start that
will be of lasting service?
In my mind it is far better to have a bridge rest fully upon the gum
instead of having a shelf-like projection over the ridge. It is said
that the advantage gained from this class is its cleanliness, as
there is no way for the food to become lodged during the process of
mastication, as is the case with the shelf-projecting bridge. One would
naturally imagine that food could find its way underneath, between the
gum and the teeth, but strange to say, there is very little that ever
finds its way to those places.
In closing, I will offer a suggestion which may, or may not, be new to
you. It is this:
For investing material, I recommend common moulding sand, in proportion
of one-half plaster and one-half sand. After allowing the mass to
set hard, trim it down to suit the case invested, and then with a
hair-brush paint the upper surface with a solution of borax water. The
advantage of the use of sand as an investing material is that from the
change of the color of the mass from a deep yellow to a lighter shade
you can perceive the exact moment at which your case is thoroughly
dried out. The borax has the property of preventing the mass from
splitting. Its greatest qualities are its strength and non-contractible
properties, it having an advantage in this respect to pumice, asbestos
and other materials generally used for this class of work.
* * * * *
ALUMINUM.—A new process of extracting this metal has been discovered,
it is claimed, by which the metal can be produced for a few cents a
pound. Prof. Joseph M. Hirsh, Chicago, Ills., is the one whom it is
claimed has solved the problem of extracting the metal from an aqueous
solution.
Societies.