Page 94 - My FlipBook

78 THE TREATMENT OF TEETH

occur in this part after filling, a step extension is
cut across the cutting edge.
Access to these cavities is obtained by separation,
and by cutting away part of either the labial or the
lingual wall. The methods of access apply equally
well to all methods of preparation. Small round
or oblong cavities are prepared in a similar way by
either the old or the new method, straight walls
and a flat floor being usually readily obtained ; and
the formation of sharp angles, or in the older method,
the making of a little groove around the cavity, is
readily accomplished with an inverted cone bur or
suitable excavator.
In cavities on the apjDroximal sides of bicuspids
and molars, it is usually necessary to convert them
into approximo - occlusal cavities, if gold is to be
satisfactorily used. This is effected by cutting away
the overhanging enamel and dentine at the occlusal
part, and making the cavity into one of three walls.
In the older method the absence of the occlusal wall
was counterbalanced by cutting a distinct groove,
about one sixty-fourth of an inch deep, along the
palatal and buccal walls, at the line of junction with
the floor, extending from the occlusal enamel to the
cervical wall ; and if the lateral walls were also
slightly convex, or sloping inwards, the retainage
was considered sufiicient. The cervical margin was