Page 45 - My FlipBook

RETENTION FORM 41

is gained by laying the external surrounding walls at definite angles
to the seat of the filling.
Little Retention in Enamel. It should be remembered in this
step of cavity preparation that there is very little resistance to
force in a filling Avherein retention form is provided for in enamel
walls. The enamel should be removed to a depth sufficient to get
anchorage in angles laid in dentine. A good idea of the amount
of retention form possessed by any completed cavity may be gained
if one will for the time being imagine that all enamel has been re-
moved from the tooth. The remaining cavity will still have nearly
tlie original amount of retention form. We rely upon the presence
of enamel in liable areas for resistance to recurrent caries and upon
sound dentine for retention form.