6 Flashcards
(10 cards)
T/f
When planning the extension RPD, the first point to con- sider is the location of the axis of rotation (fulcrum line). This is determined by the position of the rests, specifically the part of the rest that is closest to the edentulous area
T
T/f
The two types of RPDs (tooth-borne and extension) can also be found in patients who have lost anterior teeth. The RPD is considered tooth borne when it replaces central and lateral incisors with the canines still present (Fig 6-6a). If the tooth loss extends to the canine region, it is considered an anterior extension-base RPD
Because the portion of the rest closest to the edentulous area becomes the axis of rotation, the rest preparation on the tooth at that point should be a perfect ___ to enable ideal rotation around the fulcrum line (Fig 6-9). This rotation area should be about the size of a #__ or #8 round bur and should be highly polished.
half-sphere
6
T/f
Placement of the rest on the occlusal surface of the abutment tooth next to the edentulous area results in horizontal movement of the prosthesis at the gingival portion of the tooth
T
T/f
Little or no vertical support is obtained from the tissue next to the abutment tooth
T
T/f
As the rotation axis is moved anteriorly or away from the edentulous area, the arc of rotation becomes greater, and the forces are delivered in a more vertical direction in the edentulous extension area
T
T/f
lowering of the axis of rotation toward the gingiva also improves the direction of force, and therefore it is advisable to lower the rotation point whenever possible
T
T/f
Movement of retainers on an edentulous extension RPD in func- tion is determined by the rotation axis
T
T/f
it is not ad- visable to position the retentive tip of the retainer distal to the center of the tooth or distal to the point of greatest mesiodistal curvature of the tooth because any forward movement of the retainer may torque the tooth and harm the supporting struc- tures
T
T/f
The retentive portion of a retainer should not engage an un- dercut forward to the axis of rotation in an extension situation because that part of the prosthesis moves upward in function and tends to torque the tooth
T
