Page 192 - My FlipBook

188 OPERATIVE DENTISTRY

moisture in porcelain filling is only required to preserve the sliade
of the tooth substance to be imitated in the fused filling.
Those to Which Dryness Is Most Essential are silicate, cohesive
gold, cement amalgam and gutta-percha, named in the order of the
importance of the demands. It is true that all of these excepting
silicate may be successfully manipulated under moist conditions,
but the effort is greater and the certainty of success is materially
decreased.
The Exclusion of Moisture for Sterilization and the prevention
of infection is imperative in the last stages of cavity preparation,
as it is physically impossible to properly perform the toilet of the
cavit}^ and properly sterilize the same when flooded or even under
moist Conditions.
The Proper Treatment of Pulp Canals cannot be accomplished
when flooded by the oral fluids to say nothing of the introduction
of a permanent root filling. The saliva is at all times impregnated
with various forms of bacteria. Its presence invites failure by pre-
venting sterilization of canals already septic and permitting the
re-infection of those already sterile.
Cavity Walls, and particularly the beveled margins, must be
freshly cut and planed after being moistened before the introduc-
tion of a filling, as this is the only means of having an absolutely
clean surface. We may resort to absorbing and evaporating the
moisture from the walls and margins of a cavity, but there will
invariably be left a residue or film upon the surface which is solu-
ble in the oral fluids. No amount of pressure in introducing the
filling, be it rubber, amalgam or cohesive gold, will displace the
moisture absorbed by the cavity surfaces, hence we have this layer
cf moisture or sediment intervening the filling and cavity. This
will be exchanged in course of time for that upon the outside
carrying with it bacteria and the products of fermentation or lac-
tic acid and secondary caries is the result. Bacteria, which are the
active agents of caries, will go where moisture will not, and the
lactic acid which they secrete will go where the space is too small
for the bacteria. It will therefore be readily seen that a moist sur-
face or one coated with a residue of an evaporated mixture,'
whether medicine or saliva, intervening between a filling and a
cavity Avail, becomes a large passage way for the greatest enemy
to tooth substance—lactic acid.
A Better View of the Cavity Is Obtained When Dry, as its out-
lines become more distinct and its size and shape better defined.