PROSTHO RPD: Recent Episodes
Dr. Mayakha Mariam
PARTS
1. MAJOR CONNECTOR
2. DIRECT RETAINER
3. MINOR CONNECTOR
4. INDIRECT RETAINER (if the prosthesis has distal extension)
5. BASE
MAJOR CONNECTORS
Definition:- It is a part of CPD (cast partial denture) that connects the component from one side of the arch to the other side.
Major connecter A rigid part of the partial denture casting that unites the rests and another part of the prosthesis to the opposite side of the arch.
FUNCTION
1. Unification of all other components
2. Stress distribution
3. Cross arch stabilization
Property of— rigidity, which is why it is always placed on a rigid surface
Maxillary
o anterior extension — 6 mm from palate gingival margin
o Posterior border — anterior vibrating line
Mandibular anterior border — 3 mm from lingual gingiva
MAXILLARY MAJOR CONNECTORS: -
A. Complete Palate Major Connector
i. Best major connector
ii. Like CD
iii. There is a plate covering the entire plate, this acts as the major connector.
iv. When all post teeth missing, class 1
v. Periodontally compromised remaining teeth,
vi. Shallow vault cases, small mouth, flat or flabby ridges.
vii. Almost anywhere and everywhere
B. Anterior—Posterior Bar
i. Sharp design
ii. Most rigid after complete palate
C. Horse — Shoe
i. Least preferred as it is least rigid
ii. Patient with palatal torus
D. Single palatal bar
a. Posterior palatal bar or strip used with: Kennedy class3.
E. Single palatal strap
F. Unshaped palatal connector
G. Combination of anterior—posterior palatal strap
Maxillary RPD major connectors may be beaded to — produce positive contact with the tissue
All major connectors should cross the midline at a right angle
Q. Refractory cast To fabricate a removable partial casting requires making a second cast of high heat investment material this cast.
MANDIBULAR MAJOR CONNECTOR
o Upper border 3 mm from gingival
o Lower border 1st step to design
LINGUAL BAR
o Most commonly used
o Lingual bar is short & thick - used in wide lingual sulcus & lingual frenum is low
o However, there are certain cases where we cannot use lingual bar
i. Shallow vestibule
ii. Lingually high frenal attachment
iii. Alveolar ridge resorption
iv. Lingual tori
v. Severe vertical resorption
LINGUAL PLATE
a. Can use in above conditions
b. When teeth are periodontally weak also giving splint effect
c. Need for the addition of one or more anterior teeth
d. When teeth lingually inclined
Q. Lingual plate is long & thin - used in shallow sulcus, high lingual frenum, & for splinting mobile
anterior teeth.
LABIAL BAR
DIRECT RETAINERS
a. Intracoronal (tooth prepared)
o Precision attachement- Female on the removable part nd male on the fixed part.
o Class III, Class IV
o Considering aesthetics- because no clasps
b. Extracoronal
o More common
o Should encircle the tooth at least 180 degree
PARTS OF CLASP
Retentive Arm- Retention*
a. Orginates from the occlusal third and terminates in the cervical third
b. Placed on the buccal aspect
c. The retentive terminal engages the undercut – ie apical to the highest point of contour / the survey line.
d. Rest of the clasp has to be above the hight of contour.
e. It has tapering thickness when you talk about shape
f. It has to be sated passively, ie no force when already seated, and be only active or provide retention when dislodging forces are applied.
Reciprocal Arm- Stability*
a. Is placed on the lingual aspect
b. It originates from the occlusal third and terminates above the highest point of contour
c. Doesn’t have to engage in any undercut
d. Resists lateral movement of the prosthesis
e. Counteracts the force produced by clasp/ retentive arm
f. Resists potential orthodontic movement of the abutment
Body/Minor connector = stability*
Rest = support* to entire arm
Shoulder = connects the parts of clasp assembly, function – stability
SUPRABULGE – COMES / ORIGINATES FROM
ABOVE THE BULGE
Akers
Ring
Combination
Embrasure
C clasp , akers clasp , circumferencial, supra bulge, three quarter clasp
Universal type of clasp
Can be used in almost all cases
Only disadvantage is - mobility
Ring clasp
Lingually tilted tooth, Kennedy class 2,
Isolated PM cases
When the undercut is near the proximal plate side, the clasp will have to go all around and engage in there.
Sometimes there is only one seat, or they might add an additional seat on the opp side as well
Also, they could add an additional arm from the meshwork coming infrabulge way, and soldered perpendicular to the lingual part of the arm to provide more stability.
Embrasure Clasp
2 Akers clasp hugging both teeth on right and left like a father hugging his two sons with both of his arms
Need 2 occlusal rest and has only 1 body
Kennedy class II
Multiple Clasp – circlet
o Periodontally compromised
o 2 occlusal rest and 2 body
Combination Clasp
o Distal extension cases
o Abutment tooth with severe undercut
INFRABULGE- COMES FROM BELOW THE BULGE
I bar
T bar
Modified T bar
Y bar
Bar clasp (Gingivaly approaching clasp/ infrabulge)
Anterior canines in maxillary
Aesthetic situations
Most retentive
Because canines have very less undercuts.
Contraindication
o When there is not enough vestibular depth
o When there is undercut in that area – coz it will engage there while removal, and traumatize the tissue, hurt the patient
CLASP ASSEMBLIES
RPI system
R-Rest (always mesial), P-proximal plate, I- I bar
MO, distally, buccally
RPA / RPC system
R-Rest (always mesial, P-proximal plate , A-akers retentive arms (Always wrought wire)
Aker’s retentive — made of wrought wire.
Q. Occlusal rest for support (resist vertical forces)
Wrought alloy wire * -
o Advantages of wrought wire over cast wire flexibility &
o Gives less pressure onto the teeth less irritant to abutment.
o Used for periodontally compromised and endo treated abutment
o more flexible
o soldered onto the framework
Cobalt-Chromium metal –
o Metal alloy used to make the framework
o For reciprocal arm
KENNEDY’S CLASSIFICATION:-
CLASS 1
BILATERAL EDENTULOUS AREA LOCATED POSTERIOR
TO BOTH REMAINING NATURAL TEETH
CLASS II
UNILATERAL EDENTULOUS AREA LOCATED POSTERIOR
TO THE REMAINING NATURAL TEETH
CLASS III
SINGLE EDENTULOUS AREA BOUNDED BY NATURAL TEETH
BOTH ANTERIORLY AND POSTERIORLY TO IT
CLASS IV
SINGLE EDENTULOUS AREA THAT CROSSES
THE MIDLINE AND IS ANTERIOR TO THE REMAINING NATURAL TEETH
INDIRECT RETAINER
Most commonly used in Kennedy class I, II & IV -ie. Distal extension cases
They have the most tipping tendency and need both tooth + tissue support
Resistance by preventing lifting off of the distal extension through First order liver principle
(see-saw principles)
The rest should be fabricated at 90 degrees away and anterior to the fulcrum line
Should be placed as far as possible from fulcrum line.
Types: auxillary rest — google (PM/canine)
-- o Lingual plate major connector + indirect retainer
-- o Canine extension from mesial rest
REST SEAT:-
TYPES OF RESTS:
1. Occlusal —Post —triangular/saucer shape (apex towards centre, base – margin ridge)
2. Cingulum - Maxillary canine and anteriors, contraindicated on mand incisors
3. Incisal rest - Mandibular canine and incisors
FUNCTION – resist vertical fracture
PREPARATION OF REST SEAT:-
o Shape of rest seat spoon or square.
o Triangle or saucer shape
o Apex towards the centre
o Depth = 2.5 mm
o Base towards the marginal ridge
o Slanting preparation following the anatomy
Rest Fabrication
o Rest and tooth angle = less than 90°, ie; acute angle
o Rest thickness = 2mm
2.5 mm at centre
1.5mm at the margin
- If poor manufacture — fracture of rest and
- If improper centric relation — fracture of the marginal ridge
Then do industrial brasing or welding
MINOR CONNECTOR / DENTURE BASE CONNECTOR
The part that connects the denture base to the major connector
Metal RPD — minor connector
Acrylic RPD — denture base connector * accordingly choose
Path of insertion of RPD: perpendicular to the occlusal plane.
Rebasing removes all or part of the fitting surface to add acrylic.
Q. Denture base connecter The part of a removable denture that forms a structure of metal struts that engages and unites the metal casting with the resin forming the denture base.
APPLEGATES RULE
- Classification should follow the extraction
- If a 3rd molar is missing & not to be replaced — not considered
- If a 2nd molar is missing & not to be replaced — not considered
- If a 3rd molar is precut and not to be used as an abutment — not to be considered
- Most posterior always determines the classification
- Edentulous area other than determining the class — mods and are designated by their numbers
- The extend of modification is not considered, only the number.
- No modification for class IV
Indirect retainers principal action — minimize movement of the base away from supporting tissue
ADD-ONS:
Cusp – fossa occlusion —full mouth reconstruction
Gento toxicity — primary test
Tek-scan — quantitative analysis for occlusion
Shim stock — adjustment of the contact point (WTH)
C factor — the ratio of bonded to unbonded tooth surface [not vice versa OK]