lecture 3 - components of rpd Flashcards
1
Q
what are the components of rpd? (A-F)
A
A) Major Connector
B) Rests
C) Direct Retainer
D) Minor Connector
E ) Guide Plane
F ) Indirect Retainer
2
Q
Resistance to removal from the tissues or teeth.
A
- Retention
3
Q
Resistance to movement in a horizontal direction (anterior-posteriorly or mesio- laterally.
A
- Stability
4
Q
Resistance to movement towards the tissues or teeth.
A
- Support
5
Q
- The unit of a removable partial denture that connects the parts of one side of the dental arch to those of the other side.
- Its principal functions are to provide unification and rigidity to the denture.
A
Major Connector
6
Q
- A unit of a partial denture that connects other components (i.e. direct retainer, indirect retainer, denture base, etc.) to the major connector.
- The principle functions of minor connectors are to provide unification and rigidity to the denture.
A
Minor Connector
7
Q
A unit of a partial denture that provides retention against dislodging forces.
A
Direct Retainer
8
Q
- A direct retainer is commonly called
a ‘______’ or ‘_______’ and is composed of four elements: _________________
A
clasp
clasp unit
a rest,
a retentive arm,
a reciprocal arm
a minor connector.
9
Q
A unit of a Class I or II partial denture that prevents or resists movement or rotation of the base(s) away from the residual ridge.
A
Indirect Retainer
10
Q
The indirect retainer is usually composed of one component, a ______
A
rest
11
Q
- The unit of the denture that rests on the foundation tissues and to which prosthetics teeth are attached.
- Attaches the prosthetic teeth to the denture base retention minor connector which attaches the base to the major connector.
A
Denture Base
12
Q
- Are artificial teeth used on a denture to substitute for natural teeth.
- By substituting for missing natural teeth, prosthetic teeth provide esthetics and masticatory functions.
A
Prosthetic Teeth
13
Q
COMPONENTS OF A PARTIAL DENTURE (6)
A
1) Major Connector
2) Minor Connector
3) Direct Retainer
4) Indirect Retainer
5) Denture Base
6) Prosthetic Teeth
14
Q
The unit of a removable partial denture that connects the various parts of the denture.
A
MAJOR CONNECTORS
15
Q
what are the principal functions of major connectors?
A
unification
rigidity
16
Q
Functions of a Major Connector (3)
A
- Unification
- Stress Distribution
- Cross-Arch Stabilization (Counter leverage)
17
Q
A major connector unites all other components of a partial denture so that the partial denture acts as one unit.
A
UNIFICATION
18
Q
– By unifying all elements of a partial denture the major connector can distribute functional loads to all abutment teeth, so that no one abutment is subjected to extreme loading.
A
STRESS DISTRIBUTION
19
Q
– Unification of the direct retainers with the denture bases aids in distributing forces between both the teeth and the mucosa.
A
STRESS DISTRIBUTION
20
Q
– By uniting one side of the arch to the other bracing elements on one side of the arch can aid in providing stability to the other. This can aid in dissipating twisting and torqueing forces.
A
CROSS-ARCH STABILIZATION (Counter-leverage)
21
Q
– It is necessary to ensure that the partial denture functions as one unit.
– If the denture flexes, stress distribution and cross arch stabilization can be compromised since different portions of the denture can move independent of the others.
A
Rigidity
22
Q
Major connectors should not enter into undercut areas unless tissue impingement can be avoided by changing the selected path of insertion or by using minor undercut blockout.
A
Non-Interference with the Soft Tissues
23
Q
This can be minimized by locating the margins of the connectors at the prescribed distance from the free gingival margin and by taking care that the presence of minor connectors, clasp arms and major connectors does not create “traps” or large concavities where food can collect.
A
Food Impaction
24
Q
– The margins of the major connector should have a smooth transition from connector to tissue so as to minimize the _________.
– All line angles and edges should be ______ and ______.
– Borders should not be placed in locations where they might interfere with speech.
– Bulk should be reduced enough so as not to interfere with speech or appearance, yet thick enough to ensure rigidity.
A
obtrusiveness
smooth and rounded
25
how to avoid tissue impingement? (2)
by changing the selected path of insertion
by using minor undercut blockout
26
Requirements of a Major Connector
1. Rigidity
2. Non-Interference with the Soft Tissues
3. Food Impaction
4. Unobtrusive
27
* This is the most commonly used mandibular major connector.
* It should be used whenever possible unless there are advantages that can be obtained from another major connector.
Lingual Bar
28
– flat on tissue side
– convex or tear-drop on tongue side
– 1/2 pear shape, with thin edge toward teeth.
Lingual Bar
29
occluso-gingival width of lingual bar
4mm
30
thickness of lingual bar
1.5 to 2mm
31
Lingual Bar:
– The inferior border should be as low as the ______________ and tissue reflections of the floor of the mouth will permit, as determined by observing functional movements of the tongue.
– The superior border should be
___________________. For hygienic reasons the superior border should still be kept as far from the gingival margin as possible.
lingual frenum
at least 3mm below the free gingival margin
32
* consists of a lingual bar plus an extension over the cingulum of anterior teeth.
* This mandibular major connector should only be considered in those rare instances where a lingual bar cannot be used.
Lingual Plate
33
Lingual Plate:
* Most often, this occurs when there is a __________ of the mouth, a prominent __________ or __________ that would be impinged upon by a lingual bar, if it was made with adequate height and distance from the free gingival margin.
* The lingual plate has also been advocated for extensive distal extension cases with ______________ (i.e. little resistance to horizontal rotational tendencies).
high floor
lingual frenum or lingual tori
severe vertical resorption of ridges
34
o A ________ or _______ area must be prepared at each end of the anterior segments of the lingual plate.
o This prevents excessive forces being directed facially by movements of the distal extension base.
o Any areas where the connector crosses the gingival tissue must be _______ to prevent impingement caused by the movement of the lingual plate.
vertical stop or rest
relieved
35
The connector consists of a lingual bar plus a secondary bar resting above the cingulum of the anterior teeth.
Continuous Bar Retainer / Kennedy Bar / Double Lingual Bar
36
The ____________ supposedly acts as an indirect retainer and performs a role in the horizontal stabilization of periodontally-involved teeth.
secondary bar
37
* The performance of these functions is questionable. Additionally, this major connector can create a food trap between the two bars.
* The use of this type of connector is not encouraged.
Continuous Bar Retainer / Kennedy Bar / Double Lingual Bar
38
Major connectors in the upper arch should terminate ___________ from the gingival crest tissues.
6.0 mm or more
39
* provides maximum rigidity and minimum bulk.
* The strength of this connector lies in the fact that the anterior and posterior sections are joined together by longitudinal connectors on either side.
* Each component braces the other against possible torque and flexure.
Anterior-Posterior Palatal Strap
40
* particularly indicated when maximum tissue support is required.
* In particular it should be the major connector of choice in long distal extension cases or where six or less anterior teeth remain.
Full Palatal Plate
41
* ______________ It should be selected where the primary abutments are periodontally involved, requiring maximum stress distribution.
* It should be fabricated of a uniformly thin metal plate with accurate anatomic reproduction of the ______ configuration (improves strength and rigidity). It should cover the same area as a complete denture posteriorly.
Full Palatal Plate
rugae
42
* The large surface area of contact with the mucosa improves the potential for retention (what type of connector is this?__________).
* Connectors of this type are generally of cast metal. However, an acrylic resin plate may be used in ___________.
Full Palatal Plate
interim prostheses
43
* This type of connector can be Wide (strap) or narrow (bar) depending upon its location or the need for strength or support of the denture.
Maxillary Major Connectors Palatal Strap (or Bar)
44
* It should only be used in tooth supported cases where no other connector can be used. It is usually objectionable due to its bulk. It should never be used in cases involving distal extensions or replacement of anterior teeth since it must be made to bulky for rigidity.
palatal bar
45
From a biomechanical standpoint, it is a poor connector and should never be used unless absolutely necessary. To be rigid, the horseshoe connector must have bulk in the rugae area where the tongue requires freedom.
Anterior Palatal Plate / U-Shaped / Horse-Shoe / Palatal Connector
46
* Without sufficient bulk, the _____________ becomes flexible and allows movement posteriorly. In distal extension partial dentures where posterior tooth support is nonexistent, movement is particularly noticeable and is traumatic to the residual ridge causing continual irritation during function.
* The anterior palatal plate should only be prescribed where the ___________ prohibits the use of other connectors.
U-shaped design
torus palatinus
47
Functions of Minor Connectors
1) Provide unification and rigidity.
2) Provide stress distribution by transferring stresses from the major connector to other parts of the partial denture and from the partial denture to the abutment teeth.
3) Act as bracing elements through contact with guiding planes opposing the retentive arms.
4) Maintain a path of insertion via contact with guiding planes.
48
BASIC TYPES OF MINOR CONNECTORS
a) Minor connectors placed into embrasures between two adjacent teeth.
b) Gridwork minor connectors that connect the denture base and teeth to the major connector.
49
* Minor connectors placed into embrasures between two adjacent teeth should be somewhat _______ shaped in cross section to minimize intrusion into the tongue or vestibular spaces, while still providing adequate bulk for rigidity (a).
* A minor connector should join the major connector at a ___________ and cover as small an area of tissue as possible (b). The juncture to the major connector should be _______ (arrow) not sharp (X) unless the juncture includes an acrylic finish line.
* _______ should be placed on the master cast so that the minor connector does not lie directly on the soft tissue (c).
triangular
right angle
rounded
Relief
50
These minor connectors are adjacent edentulous spaces and usually connect the major connector to a clasp assembly as well.
Gridwork minor connectors
51
* Gridworks can be an open lattice work or mesh type. Both types are acceptable if correctly designed.
o The _________ tends to be flatter, with more potential rigidity. Conversely, it has been shown provide less retention for the acrylic if the openings are insufficiently large.
mesh type/ mesh gridwork
52
* Gridworks can be an open lattice work or mesh type. Both types are acceptable if correctly designed.
o The _________ has superior retentive potential, but can interfere with the setting of teeth, if the struts are made too thick or poorly positioned.
lattice type/ open lattice work
53
* Minor connectors originating from the gridwork in an edentulous area usually take the form of ________________ (proximal plates) that make broad contact with prepared guiding planes.
* These proximal plates may or may not terminate in an occlusal rest, depending on the partial denture design. The plate is shifted slightly towards the ________ to increase rigidity, enhance reciprocation and improve esthetics.
vertical metal plates
lingual
54
The gridwork on a mandibular distal extension should extend about ______________________________ but not on the ascending portion of the ridge mesial to the pad.
2/3 of the way from abutment tooth to retromolar pad
55
Maxillary distal extension gridworks should extend ___________________. However, the junction or finishing line of the maxillary major connector should extend fully to point to the hamular notch area so that the acrylic resin base can be extended into this area and provide a smooth transition from the connector to the base.
at least 2/3 of the length of the ridge to the hamular notch
56
Mandibular distal extension gridworks should have a ____________ at their posterior limit. This is an extension of the metal through the relief wax providing direct contact with the ridge.
If there is none, the framework can be bent or displaced during the pressure packing of the mold with stiff doughy acrylic resin. If this occurs, the framework could resume its normal shape after deflasking, and the denture would subsequently lift off the tissue. Rocking of the denture base and clasp apparatus would result, and the occlusion would be high. A _______, in theory, prevents framework deformation and its consequences.
“tissue stop"
tissue stop
57
the ability of a removable partial denture to resist dislodging forces during function.
RETENTION
58
Retention depends upon several factors: (6)
(1) Adhesion, cohesion, interfacial surface tension and atmospheric pressure,
(2) Gravity,
(3) Frictional retention (guiding planes, bracing elements),
(4) Indirect retention,
(5) Direction of dislodging force relative to the path of placement,
(6) Mechanical retention.
59
* a unit of a removable partial denture that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissues.
* It is usually composed of a retentive arm, a reciprocal (bracing) element or arm, a rest and a minor connector.
direct retainer
60
* Retention is derived by placing a __________ into an undercut area so that it is forced to deform upon vertical dislodgment.
* Resistance of the clasp to deformation generates retention.
clasp arm
61
Requirements of Direct Retainers
1. Support
2. Reciprocity
3. Stability
4. Retention
5. Encirclement of greater than 180° of the tooth
6. Passivity
62
resistance to gingival displacement (occlusal rests).
Support
63
During placement and removal of the partial denture, the retentive arm flexes over the height of contour and generates energy. At this point the rigid reciprocal arm should contact the guiding plane and prevent orthodontic movement from taking place.
Reciprocity
64
resistance to lateral movement (reciprocal arms, minor connectors).
Stability
65
retentive arms located in undercuts on the abutments.
Retention
66
prevents the prosthesis from moving away from the tooth.
Encirclement of greater than 180° of the tooth
67
at rest, a direct retainer should not exert force against a tooth.
Passivity
68
Clasps for tooth-borne partial dentures (Class III, IV) have one function – _______________________________________
Since there is little or no rotation caused by tissue ward movement of the edentulous area (as happens in distal extension cases) stress releasing properties are usually not required.
These clasps can also be used in modification spaces for tooth and tissue supported removable partial dentures (Class I, II).
to prevent dislodgment of the prosthesis without damage to the abutment teeth.
69
* The most simple and versatile clasp (clasp of choice in tooth-borne cases)
* Clasp assembly has one retentive
arm opposed by a reciprocal arm originating from the rest.
Circumferential (Akers) Clasp
70
* The retentive arm begins above the height of contour, and curves and tapers to its terminal tip, in the ___________ of the tooth, well away from the gingiva.
gingival 1/3
71
* The bracing arm is in the _________ of the tooth, and is broader occluso-gingivally, does not taper and is either entirely above the height of contour or completely on a prepared guiding plane – it should never be designed into an undercut, as it is a rigid element.
middle 1/3
72
The junction of maxillary major connector with the gridwork should be approximately _____________ to an imaginary line along the lingual surfaces of the replacement denture teeth.
3 mm medial
73
Circumferential (Akers) Clasp Advantages (3)
o Excellent bracing qualities.
o Easy to design and construct.
o Less potential for food accumulation below the clasp.
74
Circumferential (Akers) Clasp Disadvantages (3)
o More tooth coverage than bar clasps.
o More metal is displayed than with bar or combination clasps.
o Adjustments are difficult or impossible due to the half round nature of the clasp.
75
* Encircles nearly the entire abutment tooth.
* Usually used with mesially and lingually tilted mandibular molars
* The undercut is on the same side as the rest seat (i.e. adjacent to edentulous span)
* Should always be used with a supporting strut on the non-retentive side with an auxiliary occlusal rest on the opposite side. Omission of the supporting strut will allow the clasp arm to open and close with minimum or no reciprocation.
* Use a cast circumferential clasp with lingual retention and buccal bracing, in preference to a ring clasp whenever possible, unless a severe tilt of the tooth will not permit.
Ring Clasp
76
Ring Clasp Advantages (2)
o Excellent bracing (with supporting strut).
o Allows use of an available
undercut adjacent to edentulous area.
77
Ring Clasp Disadvantages (3)
o Covers a large area of tooth surface, therefore requiring meticulous hygiene.
o Very difficult to adjust due to the extreme rigidity of the reciprocal arms.
o The lower bracing arm should be at least 1 mm from the free gingival margin and relieved to prevent impingement of the gingival tissues.
78
Ring Clasp Contraindication
Excessive tissue undercuts prevent the use of a supporting strut.
79
* Used in a quadrant where no edentulous area exists, or where a distal approach clasp cannot be used on the most posterior tooth (i.e. No usable retentive undercut).
* Two rests, two retentive arms, and two bracing arms
Embrassure Clasp (Double Akers)
80
* ____________ with definite shoulders to prevent weakening of clasp arms, separation of teeth and food impaction
* Buccal and lingual proximal areas must be opened (i.e. Blend with axial contours, reduce height of contours, round occluso-axial line angles)
* Use ____________ – prone to distortion.
* Use embrasure clasp with discretion – use another clasp if possible.
Double rests
minimum retention
81
Embrasure Clasp (Double Akers) Advantage (1)
o Allows placement of direct retainer where none could otherwise be placed (especially contralateral to the edentulous span on a Class II case).
82
Embrasure Clasp (Double Akers) Disadvantages (2)
o Extensive interproximal reduction is usually required.
o Covers large area of tooth surface - hygiene considerations.
83
* The retentive area (undercut) is adjacent the occlusal rest.
* The upper arm is a minor a connector giving rise to tapered lower arm.
C Clasp / Hair-pin / Reverse Action
84
C Clasp Advantage (1)
Allows use of undercut adjacent to edentulous space.
85
C Clasp Disadvantage (5)
o Almost impossible to adjust.
o Non-esthetic.
o Difficult to fabricate so the upper portion of the retentive arm clears the opposing occlusion.
o Covers extensive tooth surface and acts as a food trap.
o Insufficient flexibility on short crowns due to insufficient clasp arm length.
86
Tooth and tissue borne situations (Class I & II) require special attention in direct retainer selection, due to stresses created by ________________ of the prostheses.
When the denture bases are placed under function, rotation occurs about the rest seats of the most posterior abutments.
Excessive occlusal forces on the distal-extension portion of the denture could cause a _________________ on the abutment teeth unless direct retainers are designed with stress-breaking capabilities.
rotational movements
torqueing action
87
Stress releasing clasp assemblies include: (3)
1. the bar clasp with mesial rest (e.g. RPI)
2. the RPA clasp
3. the combination clasp
88
The components of RPI clasp assembly are:
o "R" - rest (always mesial)
o "P" - proximal plate
o "I" - I-bar (retentive arm)
89
The _____________ is located in the mesio-lingual embrasure but is not in contact with the adjacent tooth (prevents wedging).
minor connector
90
The proximal plate (essentially a wide minor connector) is located on a guide plane on the ______ surface of the tooth.
distal
91
The __________ of the proximal plate is located at the bottom of the guide plane (at approximately the junction of the occlusal and middle third of the guide plane).
superior edge
92
The _________ is located on the buccal surface of the premolar and on the mesio-buccal surface of the canine. It originates at the gridwork and approaches the tooth from the gingival direction.
I-bar clasp
93
The bend in the I-bar should be located _________________________. This distance will prevent food entrapment and provide the length for the necessary flexibility in the clasp arm. The clasp is usually cast and is placed just below the height of contour line.
at least 3 mm. from the gingival margin
94
The guiding plane is a parallel surface prepared on the ___________________ surface of the tooth. The guiding plane extends lingually enough so that, along with the mesial rest, it can prevent lingual migration of the tooth. It is approximately _______ in height.
occlusal one third of the distal
2 to 3 mm
95
Contraindications to the R.P.I. Clasp (4)
(1) Insufficient depth of the vestibule. (The inferior border of the I-bar must be located at least 4 mm. from the gingival margin.)
(2) No labial or buccal undercut on the abutment.
(3) Severe soft tissue undercut.
(4) Disto-buccal undercut (less than 180° encirclement).
96
* This clasp assembly is similar to the RPI design except a circumferential clasp (Akers) is used instead of the I- bar.
* This clasp arises from the proximal plate and terminates in the mesio-buccal undercut.
* It is used when there is insufficient vestibule depth or when a severe tissue undercut exists.
R–P-A Clasp
97
The combination clasp is similar to the cast circumferential clasp with the exception that the retentive arm is fabricated from a _____________ (platinum-gold-palladium alloy or chrome-cobalt alloy).
round wrought wire
98
The proponents of the mesial rest concept (i.e. RPI, RPA designs) believe that the use of the clasp assembly with a disto-occlusal rest (in a distal extension case) could lead to distal tilting and possible loss of the abutment tooth.
However, if correctly designed and executed, the _____________ is as viable a treatment alternative as the mesial rest concept.
distal rest concept
99
Direct Retainer Selection is based on : (3)
A. Position of tooth undercuts, restorations, occlusion, classification of edentulous arch, tooth type.
B. Nature of the bony and soft tissue support. Is there an unfavorable:
Ø bony undercut
Ø frenal attachment
Ø vestibular depth.
C. Esthetics
100
This axis passes through rests of the most posterior abutment teeth and is called the _______________
Fulcrum Line.
101
* Most tooth borne partial dentures do not exhibit rotational movements, due to their extensive tooth support.
* However, any Class III or Class IV partial denture that has _____________ may exhibit rotational movements.
mobile abutments
102
* The fulcrum line on a Class I partial denture passes through the _________________ on either side of the arch (A and B).
* On a Class II partial denture, the fulcrum line is always ______, passing through the occlusal rest area of the abutment on the distal extension side and occlusal rest area of the most distal abutment on the other side (C).
rest areas of the most posterior abutment
diagonal,
103
* Rotation of a partial denture about the fulcrum line is prevented by _________________ placed against definite rest seats on the opposite side of the fulcrum line from the distal extension base.
* Indirect retainers should be placed as far as possible from the distal extension base so as to gain the best possible ________________ against lifting of the distal extension base.
indirect retainers
leverage advantage
104
The factors influencing the EFFECTIVENESS of an indirect retainer include: (4)
1. Proper seating of the denture.
2. Distance from the fulcrum line.
3. The rigidity of the connectors supporting the indirect retainer.
4. The effectiveness of the supporting tooth surface.
105
DIFFERENT FORMS of Indirect Retainers (3)
1) Auxiliary cingulum / incisal rests
2) Auxiliary occlusal rest
3) Lingual plates
106
Functions of Denture Base
Ø Support and retention of the denture teeth.
Ø Transmission of stresses to oral tissues - maximal coverage within anatomic limitations, accurate reproduction of supporting tissues
Ø Improve esthetics.
107
* ________________ bases are the most common types used in RPD.
* They should be routinely used in distal extension cases to allow for relining of the base to maintain mucosal support.
* Acrylic resin should make a _________ (or slightly undercut joint) with the major and minor connectors.
* If the resin is brought to a feather edge, it will distort, break or separate from the framework, causing injury to the underlying soft tissues.
Acrylic resin
butt joint
108
Advantages of Acrylic Resin Bases (3)
o Ability to reline the base as the supporting tissues change.
o Esthetically superior to metal bases.
o Ease of repair
109
Disadvantages of Acrylic Resin Bases (4)
o Dimensional stability less than metal bases.
o Lower strength than metal - long spans.
o Porous – hygiene.
o Low thermal conductivity.
110
* _______________ can be used wherever acrylic resin bases are used. However, the esthetic result can be compromised unless the metal can be veneered with sufficient thickness of acrylic.
* If an insufficient veneer is used, a ________ of the underlying metal becomes visible.
* Where single tooth replacements are placed, there is often insufficient room to fabricate a retentive gridwork.
Metal bases
greyish hue
111
3. Maxillary distal extension denture bases should terminate in the ___________.
4. Mandibular distal extension denture bases should terminate on the _________________.
hamular notches
pear-shaped retromolar pads
112
* ________________ should be used in most instances since they will not wear the opposing dentition to the same degree as porcelain teeth.
* Porcelain denture teeth cause accelerated wear of the natural dentition, particularly once the surface glaze has been broken.
* Acrylic teeth are easier to arrange, modify and adjust.
Acrylic denture teeth
113
* The selected tooth form should be selected to harmonize with the opposing teeth.
* Where the replacement teeth oppose natural dentition with minimal wear, a ________ tooth form may be indicated.
* The denture tooth is adjusted to provide room for the proximal plate, while allowing placement of the tooth close to the natural tooth for best appearance. Note on the facial surface that the denture tooth slightly overlaps the proximal plate to hide this portion of the framework.
30° or 33°
