Summary of answers to all objectives of removable prosthodontics syllabus for Dentistry. Appropriate for final year undergraduate dentistry question and answer overview. In accordance with board exams for removable prosthodontics.
REMOVABLE PARTIAL DENTURES
Basic concepts of RPDs:
1. stability: resistance to horizontal, lateral and torsional forces (most important).
All components of an RPD, except the retentive clasp tip, contribute
to stability.
2. support: resistance to vertical seating forces provided by rests and denture bases.
3. retention: resistance to vertical dislodging (least important)-direct and indirect retainers.
Kennedy’s classification of RPDs:
-class I: bilateral edentulous areas located posterior to the remaining natural teeth.
-class II: a unilateral edentulous area located posterior to the remaining natural teeth.
-class III: a unilateral edentulous area with natural teeth natural teeth remaining both anterior and posterior to
it.
-class IV: a single, but bilateral (crossing the midline), edentulous area located
anterior to the remaining natural teeth.
-Applegate’s rules for applying the Kennedy classification:
-rule 1: the classification should follow, not precede extractions.
-rule 2: if a 3rd molar is missing and not to be replaced, it’s not considered in the classification.
-rule 3: if a 3rd molar is present and not to be used as an abutment, it’s not
considered in the classification.
-rule 4: if a 2nd molar is missing and not to be replaced, it’s not considered in the classification.
-rule 5: the most posterior area always determines the classification.
-rule 6: edentulous areas other then those determining the classification are
referred to as modifications and are designated by their #.
-rule 7: the extent of the modification is not considered, only the number of
additional edentulous areas.
-rule 8: there are no modification areas in a KIV.
The lever systems:
-Class I: the “see-saw”
-resistance – fulcrum – effort
-resistance is the clasp
-fulcrum is the terminal rest
-effort is downward force on the distal extension
-like KII, where resistance is on the contralateral side of the arch from the fulcrum
and effort
-Class II: the “wheel-barrel”
-fulcrum – resistance – effort
-effort is upward force on the distal extension
-otherwise, the clasp would disengage
-like KI
-Class III: the “fishing pole”
-fulcrum – effort – resistance
-does not occur in RPD design
-TMJ muscles and teeth act as a class III lever
-cantilever: when fulcrum and resistance are connected on the same body
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, Major connectors:
A major connector connects one side of the dental arch to the other side. It’s the primary component of the RPD (the majority of
rigidity).
4 mandibular major connectors:
1. lingual bar
2. lingual plate
3. continuous bar retainer
4. labial bar
-lingual bar:
-should be 4mm from gingival margin
-should be ½ pear shaped and 4mm thick occl/gingivally (greatest bulk should be
in the inferior 1/3) and 2mm thick anteroposteriorly.
-should be above movable tissues (vestibule must be 7mm)
-inferior border should be slightly rounded so it does not impinge on the lingual
tissue when denture base is rotated inferiorly under occl loads
-lingual plate:
-use if you have a vestibule less than 5mm
-indications: (4)
-high lingual frenum
-class I situations where ridges have undergone excessive vertical
resorption
-to stabilize periodontally weakened teeth
-when anticipating possible replacement of mandibular anterior teeth
-labial bar:
-should be 3mm below gingival margins
-indications: (2)
-use with lingually inclined mandibular anterior teeth
-can use with large lingual tori
4 maxillary major connectors:
1. posterior palatal strap
2. U-shaped or horse-shoe
3. anterior-posterior palatal strap
4. full palatal plate
-all should be 6mm from gingival margin
-borders should be beaded and 1mm wide
-posterior palatal strap:
-should be 8-12mm wide
-needs bulk for rigidity
-good to use for tooth-borne restorations of bilateral edentulous short span
-U-shaped palatal connector
-the least desirable---can be used if a large inoperable palatal torus in present and
occasionally when several anterior teeth are missing
-3 principal objections of this connector:
1. lack of rigidity
2. the design fails to provide good support characteristics
3. bulk for rigidity results in increased thickness for areas most frequented by the tongue
-A-P palatal strap
-structurally the most rigid palatal connector
-can be used in almost any maxillary RPD
-least objectionable to the patient and least harmful to adjacent tissues
-palatal plate
-thin, broad palatal coverage
-reproduces contours of the patient’s palate
Minor connectors
2
, 2 functions of minor connectors:
1. to transfer functional stress to the abutment teeth
2. to transfer the effect of the retainers, rests, and stabilizing components to the rest of the denture
-minor connectors should be 1.5mm thick
-when they join major connectors, they should be in a rounded acute angle to increase gingival exposure
-distance between minor connectors should be 5mm
-it should be thickest toward the lingual surface, tapering toward the contact area
-the minor connector for the mandibular distal extension base should extend posteriorly about 2/3 the length
of the edentulous ridge
-tissue stops:
-are integral parts of minor connectors designed for retention of the acrylic resin bases
-they provide stability to the framework during the stages of transfer and
processing
-finish lines:
-the finish line junction should take the form of an angle of less than 90°,
therefore, being somewhat undercut
Rests and rest seats:
-primary purpose: to provide vertical support for the RPD
-it maintains established occlusal relationships by preventing settling of the denture
-prevents impingement of soft tissues
-directs and distributes occlusal loads to abutment teeth
-form of the occlusal rest and rest seats:
1. The outline form should be a “rounded” triangular shape with the apex toward the center of the
occlusal surface.
2. It should be as long as it is wide and the base of the triangular shape should be at least 2.5mm for
both molars and premolars.
3. The marginal ridge of the abutment tooth at the site of the rest seat must be lowered to permit a
sufficient bulk of metal for strength and rigidity. This means that a reduction of the marginal ridge
of about 1.5mm is usually necessary.
4. The floor of the occlusal rest should be apical to the marginal ridge and be concave or spoon
shaped (no sharp edges or line-angles in the prep).
5. The angle formed by the occlusal rest and the vertical minor connector from which it originates
should be less than 90°.
Direct Retainers (clasps):
-they counteract dislodging forces at right angles to the occlusal plane.
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