Page 96 - My FlipBook

THE TREATMENT OF TEETH
8o.
occlusal surface to produce a step, or arm-like exten-
sion, sufficiently broad and deep to counterbalance
the Avant of retention that would otherwise have
existed. Many operators adopted this step exten-
sion as a general method of practice to prevent
weakening the lateral walls by grooving or other-
wise undercutting them, and to save the time,
trouble, and uncertainty of filling these lateral
grooves or undercuts. With the exception that
the rounded or curved cervical wall was retained,
and that depressions were made at either side of
this wall, and that the end of the step was often
undercut, it will be seen that this is a near ap-
proach to the Black method.
Dr. Black's method is to make a broad, flat,
well-laterally-extended cervical wall ; to make the
lateral walls parallel to the floor ; to cut the line
of junction of these walls and the floor into sharp
angles ; to cut the step extension in every case, and
to make it with straight walls, a flat floor, and sharp
angles, and to square out, or make as distinct as
possible, the angles at the juncture of the lateral
and cervical walls. Theoretically, all methods of
bicuspid and molar preparations of approximo-
occlusal cavities weaken the walls, and may lead to
a breakdown. Any grooving or undercutting of
the lateral walls may do this ; and even if this is