RPD Definitions + Lectures Flashcards
Definition of a removable partial denture
It is a dental device that restores one or more,
but not all the natural teeth and associated structures, its retention and support are provided by the natural teeth (dental implants) and/or mucosa (and under it the bone). It occupies more space in the mouth than the teeth, the mucosa and the edentulous ridge are also covered, it is connected to the natural teeth, and the patient himself can remove and insert it.
Parts of RPD (4)
1• Base plate: saddles, connectors, occlusal rests
2• Artificial teeth,
3• Artificial gingiva
4• Retainers:
1) Clasp,
2) Precision attachment (Sliding PA, Bar attachment, Telescopic crown, Ball attachment, joint attachment)
Tasks of the RPD (3)
1• To restore the functions of the masticatory system (eating, speaking, esthetics of the face – including teeth and gum)
2• To prevent the further damage to the masticatory system (migration and tilting of the teeth, elongation of the opposing teeth, overloading the teeth, damage to TMJ–prophylactic function)
3• It has to provide static and dynamic occlusion, evenly distribute the chewing force to the remaining teeth and the mucosal bony base
Indications for RPD (10)
1• The number, distribution, position of the teeth in dental arch,
2• Caries and/or periodontal status don’t allow making a fixed denture (or it is not practical to make one).
3• Long bounded saddle, free end saddle.
4• Splinting is necessary.
5• Great atrophy/defect of the edentulous ridge.
6• Patient’s request.
7• Young age (under 18), later fixed denture or implant is possible.
8• General physical or mental status of the patient (tooth preparation can’t be carried out)
9• Temporary treatment before or after implantation
10• FF classes: 2A, 2A/1, 2B, 3, All Kennedy classes
Contraindications for RPD (4)
1• Patient may faint, spastic - epileptic seizures
2• Bad general condition of the patient
3• Lack of care, patient is unable to clean the denture
4• Special occupations –diver, test pilot, opera singer, artist
Advantages relating to fixed denture (5)
1• Treatment is reversible
2• Cleaning is simple
3• Support of the lips can be better (missing alveolar process is also replaced)
4• It can be generally modified after tooth extraction (extra artificial tooth can be fitted)
5• Relatively cheap
Disadvantages compared to fixed denture (8)
1• It occupies and covers bigger area,
2• It can be uncomfortable,
3• Plaque more frequently may accumulate on the surface,
4• Vomiting/Wretching reflex,
5• Occasional relining due to changes in the bony base,
6• Patients relate it to old age
7• Clasp – unesthetic,
8• Crown preparation maybe necessary for fixed-removable dentures
Requirements for making an RPD (6)
1• Remaining teeth and artificial teeth have to create a functional unit;
2• It must not overload the abutment teeth and mucosa-bony base;
3• It must not harm the teeth, periodontium, mucosa and bone base;
4• It must not change the character of the face;
5• It must not change the habitual OVD and articulation;
6• It must not impair the hygiene of the mouth
Forces affecting the denture
• vertically: --loading (chewing) --lifting (weight of the upper denture, sticky food) • horizontally: --chewing
what is the chewing force
• It is the force of all the muscles which elevate the mandible. The force arises b/w the 2 jaws. The average value is 300- 400N, depending on age, sex, status of dentition, and muscles. There may be great differences (acrobats)
Support of prosthesis
• The transmission of vertical components of chewing force to the tissues of the mouth, and the resistance of these tissues to this force. In other words: The foundation on which the denture rests, and which resists displacement towards the tissues. It comprises the hard and soft tissues that bear the loads of mastication and clenching applied to the denture.
Methods of support (3)
1• Dental, periodontal: fixed prosthesis or removable bridge
2• Mucosal: full denture, traditional RPD with acrylic base plate without occlusal rests
3• Dento-mucosal, muco-dental: RPD, supported also on teeth
Axis of rotation
a connecting line between the supporting points on the
abutment teeth adjacent to the edentulous ridge around which the denture can rotate or rock.
Primary rotation axis
a connecting line between the supporting points on the abutment teeth adjacent to the edentulous ridge. After inserting the denture it may become a real or actual rotational axis.
Secondary rotation axis
a line between the supporting points of a tooth neighboring and a tooth non-neighboring the edentulous ridge
Clasp line/support line
a line connecting two occlusal rests of the RPD in an arch segment
Load line
connects the centric stops in an arch segment. It should be orally from the line of support to avoid the generation of lifting forces on the prosthesis.
Lever/loading arm
is equal to the distance connecting a possible axis of rotation and a point of loading.
The distance between the impact point of the loading force and the axis of the rotation;
the length of the line segment mounted perpendicular on the rotational axis (and) starting from the loading point.
Or: the distance between the occlusal contact point of furthest artificial tooth from the axis and the rotation axis.
Resistance arm
the distance between the furthest clasp tip of the retentive arm and the rotational axis. The length of the line segment mounted perpendicular on the rotational axis starting from the furthest clasp finger.
Area/poligon of support
The area that is bounded by the occlusal rests, or the area determined by the lines of support. Line of support connects the occlusal rests of an arch segment. The polygon of support connects all lines of support. The supporting area must be as big as possible.
To establish such an area at least 3 supports are needed.
Area of load
The edentulous ridge outside of the supporting area. The smaller the loading area the more stable the RPD is.
Torque
is moment or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. The torque is the product of the applied force and the length of the lever. Mathematically, torque is defined as the product of force and the lever-arm distance, which tends to produce rotation. Loading force x length of loading arm = resistance force x length of resistance arm.
Base plate
that part of the denture which is laying on the mucosa. Its parts: saddles, connectors, occlusal rests. It transmits the chewing load to the oral tissues, unites the parts of the partial denture: artificial teeth, flange, and retainers.
• must have suitable strength to withstand chewing force and parafunctional forces, no deformity, precise attachment on the mucosa of the palate
• Thickness:
–Co-Cr alloy -> min. 0.6-0.9 mm
–noble metals (gold) -> thicker
Décolletage
is a feature of the RPD, when the base plate does not cover the marginal gingiva.
Minimum distances between base plate and marginal gingiva:
UPPER denture: 5-6mm,
LOWER denture: 4-5mm
The saddle
is that part of the partial denture, which rests on or covers the edentulous ridge and carries the artificial teeth, artificial gingiva and the anchors/retainers. It transmits the functional load to the mucosal-bony base in case of mixed and mucosal support.
Types of saddle
bounded saddle and free-end saddle
Tasks of the saddle (3)
1• bear the flange and artificial teeth
2• transmit the functional load to the mucosal- bony base (mixed and mucosal support)
3• take part in the retention of the denture
The characteristics of the saddle
- It should cover maxillary tuberosity and retromolar pad (in case of free end saddle), thus the distribution of load is better and the denture is stabilized against horizontal dislodgment, and can be relined
- The distal third of the saddle should be relieved (free end saddle, we should not replace the second molar)
Major connector
is the part of a partial denture that connects components on one side of the dental arch with those on the opposite side. It is that part of the denture to which all other components are attached. In the upper jaw it takes part in the support of the RPD, in the lower it has no such function.
• The biggest reduction in case of pure dental support
• It should be stable
• It should not interfere w/ speaking or eating
Types of maxillary major connector (4)
1• Palatal strap/butterfly shaped/midpalatal bar
2• Horseshoe shaped plate/U shaped
3• Anterior and posterior bar/ring form/skeletal
4• Full palatal plate
Palatal strap/butterfly shaped/midpalatal bar:
Indications (2)
Advantages (5)
Characteristics (4)
1• In case of missing posterior teeth
2• In case of a bulky/big torus palatinus it is not recommended
1• it’s rigid enough and has sufficient resistance to deformation
2• it doesn’t cover the rugae palatini
3• it doesn’t impair speech, sense of heat, and taste
4• it connects the saddles on a site, where the chewing force is the biggest
5• well tolerated by patients
1• It should be symmetrical with midsagittal plane
2• It should cross median palatine suture perpendicular
3• Minimum width 8 mm
4• Minimum thickness 0.7-0.8 mm, in case of flat palatal vault it may be thin, in case of a gothic (high) palatal vault, it has to be thicker, but narrower
Horseshoe shaped plate/U shaped:
Indications (1)
Advantages (2)
Disadvantages (1)
1• In case of missing front teeth
1• Provides good stability
2• Advantageous in case of a big torus palatinus and in case of a strong retching reflex
1• rugae palatini are covered, it covers greater area than the palatal strap
Anterior and posterior bar/ring form/skeletal:
Indication (2)
Advantages (1)
Disadvantages (1)
Characteristics (1)
1• In case of multiple bounded saddles, when mainly dental support is given
2• It may not be used in case of long edentulous saddles, because due to its small size the framework may deform
1• smaller segment of the palate is covered
1• Its mesial part may interfere with speech, because of its location and the bars should be obviously thicker than the plate to be rigid enough
1• It has to be planned symmetrical to the midsagittal plane
Full palatal plate:
Indication (1)
Advantages (4)
Disadvantages (2)
1• In case of great edentulous ridges, when only few teeth are present
1• It can bear great functional load, provides maximum mucosal support
2• No deformation
3• It resists the most to the horizontal dislodging forces
4• It can be modified easily after incidental tooth removal
1• The connector is heavier than the other forms
2• Patient may not tolerate it well
Types of mandibular major connector (4)
1• Lingual bar/Sublingual bar
2• Dental bar/Cingulum bar
3• Kennedy bar
4• Vestibule bar/Labial bar
Lingual bar/Sublingual bar:
Definition
Requirements (5)
Cross section
Dimensions of cross section
Distance from marginal gingiva
Distance from the mucosa
• It is the major connector of the lower RPD, it connects the saddles, its shape is a teardrop in cross section
1• It is placed almost always lingually but if teeth are tilted lingually, it can be placed buccally (rare occasion)
2• It is vertically positioned generally. It may be oblique or horizontal in case of shallow floor of the mouth
3• It should not lie on the marginal gingiva
4• It should neither interfere with the function of the floor of the mouth nor disturb its movements
5• must be stable and rigid
- Cross section: teardrop/flattened egg
- Dimensions of cross section: 3x2mm
- Distance from marginal gingiva: 4-5mm
- Distance from the mucosa: 0.2-0.3mm
Dental bar/Cingulum bar:
Indication (4)
Contraindication (5)
Size
• Indication:
1- when limited distance is present between the marginal gingiva and the mucolingual fold, shallow floor of the mouth.
2- The teeth have to be long enough
3- good periodontal health.
4- It is a continuous clasp which provides an indirect retention.
• Contraindication: 1- when there are short clinical crowns, 2- diastema, 3- lingually tilted teeth, 4- excessive bone loss around teeth, 5- long edentulous ridges.
• Size: 4 x 1.5-2.0mm
What is support remote from the saddle?
Aim
- the occlusal rest is on the remote side of the abutment tooth, or on the second tooth from the saddle.
- Primarily used in free end saddle cases
• Aim: to prevent the rotation (rocking, seesaw) and displacement of the denture away from the underlying tissues (gravity on the upper jaw, or sticky food)
Advantages of support remote from the saddle (4)
1• It provides an indirect lengthening of the saddle in mesial direction in case of distal free end saddle
2• It prevents the rotation/tilting of the denture
3• It prevents the distal tilting of the abutment tooth
4• It prevents sinking of the saddle on the distal part of the denture
Disadvantages of support remote from the saddle (4)
1• The minor connector covers the interdental papilla, difficult self- cleansing of the denture (periodontium!)
2• It needs bigger area in the mouth
3• More complicated construction
4• The connection with the saddle is not so strong, the saddle may be displaced due to horizontal forces more easily (especially in case of greatly resorbed alveolar ridge)
Indications of support remote from the saddle (5)
1• the denture may displace due to lifting force
2• the abutment has a long clinical crown
3• the opposing teeth have great chewing force
4• the edentulous ridge tolerates the load well, and the mucosa has a great compressibility
5• it is necessary to extend the saddle in mesial direction (we don’t have to reduce the number of artificial teeth in case of free end saddle)
What is support adjacent to the saddle
- the occlusal rest is close to the saddle on the abutment tooth near the edentulous saddle.
- Primarily used in tooth-bounded cases
Advantages of support adjacent to the saddle (4)
1• Minor connector (clasp stalk) doesn’t cover an extra area on the abutment tooth (good for the periodontium)
2• Tight connection with the saddle, small possibility for displacement or rotation of the saddle
3• Construction is simple
4• Minor connector is short and strong
Disadvantages of support adjacent to the saddle (3)
1• In case of distal free end saddle the denture may rotate around the rest, can sink into the mucosa
2• The abutment tooth (tooth adjacent to the edentulous ridge) may tilt in distal direction
3• In case of two-sided distal edentulous saddles the denture is not stabilized against forces and it could result in displacement away from the underlying tissues
Indirect retainer (a.k.a tilt breaker)
those elements of a partial denture which provide resistance to the rotation of the denture around the fulcrum axis. They may be the same elements as direct retainers placed on the opposite side of the fulcrum axis to that on which the displacing saddle is situated (rests, continuous clasps, connectors)
Retainer
a component of a partial denture that uses a natural tooth to resist reasonable dislodging forces which may affect the denture in function. The retainer connects the denture to the abutment tooth in a way, that the patient himself can remove the denture. Retainer can be connected to the tooth directly or through a crown or other device. The most commonly used retentive devices are clasps.
Retention of the RPD
Means the fixation of the RPD against the forces that would provoke the dislodgment, or lift of the prosthesis from its place. Retention is that property of a denture which resists the outward displacement of the denture, away from the tissues
Methods of retention?
types?
- elastic: there is a force present affecting the abutment tooth even if the patient doesn’t chew (harmful for the tooth)
types: wrought wire clasp, acrylic clasp - rigid: there is no force transmission to the abutment tooth without chewing, it doesn’t cause any harm to the tooth
types: cast clasps, precision attachments, bars, telescopic crowns
Rigid retainer
Means that the load affecting the denture is transmitted to the abutment tooth in the same size, because the connection between the saddle and the retainer is stiff, there is no movement of the denture independent from the abutment tooth. The denture can move neither in vertical, horizontal, nor in sagittal direction. Forces from any direction affecting the denture reach the abutment teeth immediately. Retention acts at the moment of load. There is no force transmission to the abutment tooth without chewing; it is the appropriate retention form.
cast clasps, PA, bars, telescopic crowns
Elastic retainer
In this case a decreased load is transmitted to the abutment teeth, because the connection between the saddle and the abutment teeth is elastic/non rigid (wrought wire clasp), the partial denture can move/dislodge independent from the abutment tooth. The fixation is not activated immediately at the time of the load.
The wrought wire clasp transmits load to the tooth also, when the denture is in a resting position and sooner or later it may cause the destruction of the parodontium of the abutment and loss of tooth.
Types of clasps (2)
- Metal clasps:
elastic (wrought wire clasps)
rigid (cast clasps) - Acrylic clasps
Cast clasp
a metal device, when in contact with a tooth, retains and/or stabilizes a partial denture. Retainer for RPD. Theoretically it provides rigid retention (clasp finger has small flexibility) Freedom of movement is only in one direction, namely along the path of insertion.
Requirements of Cast clasp (5)
1• The stop of the terminal position is clearly defined.
2• Bodily encirclement of the abutment tooth.
3• The clasp embraces about 270° the abutment tooth.
4• Gentle insertion and removal.
5• Sufficient friction, in this case with active retention
Task of Cast clasp
support and retention-to stabilize the denture against vertical and horizontal dislodging forces
Material of Cast clasp (3)
1) generally chrome-cobalt-molybdenum alloy,
2) seldom gold alloy,
3) (titanium)
Parts of the cast clasp
a. retentive arm/clasp finger/tip
b. bracing/reciprocal/guiding arm
c. Shoulder and body
e. Minor connector/clasp stalk
d. Occlusal rest
Anatomical equator
the biggest outline of the clinical crown, the most prominent part of the axial walls
Prosthetic equator
(height of contour, survey line) – the most prominent part of the clinical crown perpendicular to the path of insertion of the RPD, also called survey line, it can be determined with a surveyor. It divides the tooth in two parts:
- -occlusal from the prosthetic equator there is no undercut area, it can be used for support,
- -gingival from this line there is an undercut, which is suitable for retention.
Path of insertion
Path is a term followed by the denture from its initial contact with the surface teeth until it is fully seated.
Determined by surveyor. It helps to find undercut part for the retentive arm and parallel surfaces for the reciprocal arm
bracing/reciprocal/guiding arm
an arm of a clasp located in such a manner as to reciprocate any force arising from an opposing clasp arm on the same tooth. It stabilizes the prosthesis against horizontal bodily movement and rotation around vertical axis.
retentive arm/clasp finger/tip
a circumferential clasp arm that is a little flexible and engages the infrabulge area at the terminal end of the arm. It ends in a finger that is slender. Ensures the retention of the denture.
Occlusal rest
A unit of the partial denture that rests upon the tooth surface to provide vertical support for the denture. It provides a precise terminal stop for the clasp. Transmits the vertical chewing forces exerted on the body of the RPD to the abutment tooth. Stabilizes the denture against the abutment, and restricts displacement in the transverse and sagittal planes. Prevents vertical bodily movement. Limits rotation around sagittal and vertical axes. Due to its function it belongs to the base plate.
The position and size of rest seat
- The buccal-lingual width is about 1/3 of the distance between the cusp tips, min. 1.5-2.5mm,
- mesio-distal length 2-2.5mm,
- depth 1-1.5mm.
- The rest and the connector make a right angle.
- Spoon shaped, inside enamel or fillings
Minor connectors (clasp stalk)
Definition
Characteristics (6)
It connects the clasp to the body of the prosthesis, It transmits forces falling on the denture base to the clasp, and thereby to the abutment tooth.
• 1) cross section is rounded triangle, 2) it should be strong, 3) perpendicular to baseplate, 4) as short as possible, 5) not lie on the marginal gingiva, 6) not very close to each other
Position of minor connectors (2)
1• Connectors adjacent to the denture base (direct)
2• Connectors remote from the denture base (indirect)