PRPD Flashcards
What is the most common reason that people need a PRPD?
Age. Proportion of edentulous adults in the US is decreasing.
What are the 3 basic components of a PRPD?
Metal framework, acrylic saddles, prosthetic teeth.
What are the four basic parts of a retainer?
Rest, reciprocal clasp, retentive clasp, proximal plate.
What are some indications for a PRDP?
No fixed option is possible. Replacing missing teeth and soft tissue for esthetics. Splint periodonatlly affected teeth. Increase function and mastication. Maintain teeth alignment and arch integrity. Transition to a complete denture. Lower cost alternative to fixed.
Kennedy Class 1
Bilateral edentulous areas located posterior to the natural teeth.
Kennedy Class 2
Unilateral edentulous area located posterior to the remaining natural teeth.
Kennedy Class 3
Unilateral edentulous area with natural teeth remaining both anterior and posterior to it.
Kennedy Class 4
Single, bilateral (crosses the midline) edentulous area located anterior to the remaining teeth.
What are the steps to creating a PRDP?
Treatment plan. Study casts, design the PRDP. Final impressions, metal framework. Fit the frame, correct the frame as needed, bite registration. Set teeth. Wax try in. Deliver the prosthesis. Follow up and maintenance.
What dictates the path of insertion?
Abutment Teeth! The external surfaces and their parallelism to each other define the path the RPD framework and acrylic saddles follow until seated in the mouth.
What do abutment teeth do?
Connect the PRDP to the existing dentition.
What are the two things that keep the PRDP in the mouth and brace the abutment teeth?
Retention and Reciprocation.
Infrabulge
All the portion of the tooth apical or gingival the survey line. AKA the height of contour. You design and place a clasp arm to retain the PRDP and resist vertical displacement.
What is used to create retention.
Infrabulge clasp arm. and guide planes/plates. Resists vertical displacement.
Retentive Clasp
Infrabulge clasp arm that resists vertical displacement, keeping the PRDP in the mouth.
Suprabulge
All the portion of the tooth coronal the survey line or height of contour. Design and place a clasp, connector, or rest to “brace” the abutment tooth during the PRDP placement and removal.
What is used to create reciprocation?
A suprabulge clasp, connector or rest. Resists unwanted lateral stresses on the abutment tooth. Passive. Just above the survey line. also known as a stabilizing clasp.
What is reciprocation.
Bracing the abutment tooth during PRDP placement and removal. Lateral stress. Function of clasp design for an abutment tooth. Retentive clasp on one side and a reciprocal clasp on the other.
Clasps
Have destructive potential during the rotation of the PRDP. Use them sparingly to reduce stress.
Guide planes/plates
Frictional forces that increase retention, control stress and define the path of insertion.
Where does a stabilizing clasp go?
Just above the survey line.
Quadrilateral clasp postion.
Super stress reducer. All occlusal forces supported by abutment teeth. Kennedy class 3 and 4.
Tripod clasp position
Good stress reducer. Positions clasps on the dentate side as far from eachother as possible. Kenned 2 mods/no mods.
Bilateral clasp position
The worst stress reducer but unavoidable in conventional PRDP design. Kennedy 1 mods/no mods.
What are considered tooth force distributors?
Occlusal, cingulum, incisal rests. Direct forces in the long axis of the tooth and resist displacement toward teeth and soft tissue.
What creates support in the soft tissue?
Distal extensions should be fully extended as in a complete denture.
Support
Resistance to displacement toward teeth and soft tissue.
Stability
Resistance to displacement in a mediolateral or anteroposterior direction. It is the proper passive fit of the metal framework.
What is the occlusion of a PRPD?
Harmonious! Type of occlusion (canine-protected, group function or bilaterally balanced) depends upon the opposing occlusion.
What is a surveyor used for?
Begins the design process. Determines what tooth modifications will be needed to facilitate the design.
How does length of span affect the stress to teeth?
The longer the edentulous span, the greater the force transmitted to the abutment teeth.
How does the ridge affect stress to teeth?
The size matters. If it is large in height and width, it will withstand considerable lateral, horizontal and vertical forces. The shape matters. An inverted U is excellent. Knife edged, narrow, resorbed is bad.
How does the clasp affect stress to teeth?
Design: Needs to be passive when PRDP is fully seated.
Length: Longer, and more flexible means less stress.
Metal: Base metals are more rigid than gold.
How does the abutment tooth surface affect stress to teeth?
Metal to metal is more friction than metal to enamel/porcelain.
How does occlusal harmony affect stress to the teeth?
Disharmony, hyperocclusion greatly increases stress.
Major Connectors (MC)
Connect parts of the prosthesis on one side of the arch to those on the opposite side. All other parts are directly or indirectly attached to it. Helps resist displacement of PRDP during function, creating cross arch stability.
What are some requirements/duties of the major connector?
Must be rigid to avoid flexure of framework that will cause stress of abutment teeth and damage to supportive structures. Protect the associated soft tissue. Provide a means for obtaining indirect retention where indicated. Provide a means for placement of one or more denture bases. Promote patient comfort.
How far away should the borders of MX MCs be away from gingival margins? Why?
Minimum of 6 mm. Need to be parallel. Or they can be over the gingiva and onto the teeth. Gingival tissue requires unrestricted superficial blood supply.
Where should the posterior limit for all MX MCs terminate?
At or anterior to the vibrating line.
At what angle should all MX MCs cross the midline. Why?
At right angles. Not diagonally. Better patient adaption, tongue acceptance and biomechanical rigidity.
What are the types of MX MCs?
Anterior/posterior palatal strap, single palatal strap, full palate, horseshoe (u-shaped)
Anterior/Posterior Strap MC
Very stable and rigid MC. Strength comes from the A/P straps that are 8 mm wide. Can be used when there is a small MX torus is present. Any kennedy class. Posterior strap should be flat, at least 8 mm wide and located as far posteriorly as possible, but anterior to the vibrating line.
When is a single palatal strap MC indicated?
For situations with bilateral tooth support and posterior edentulous spaces. Kennedy Class 3. NOT Kennedy class 1. Perferred by patients over an AP strap.
What is the minimum width for a single palatal strap MC?
8 mm. Need sufficient rigidity.
Full Palate Major Connector
Uniformly thing, broad, contoured plate following the contours of and covering the majority of the palate. Readily accepted by patient, underlying tissues and tongue because of close adaptation to palate, thinness and thermal conductivity.
When is a Full Palate MC indicated?
In situation where remaining abutment tooth on either side is a canine or 1st pm. Especially in cases with severe vertical ridge resorption.
What is the least desirable MC design? Why?
U shaped, or horse shoe. Should never be used arbitrarily. Lacks rigidity, allows lateral flexure under occlusal loads, leading to torquing to abutment teeth. Useful in Class 4 PRDPs.
What are the indications for a U shaped MC?
Large inoperable torus which extends posteriorly, inhibiting placement of posterior strap.
How far below the gingiva does the Lingual Bar MC need to be?
Superior border 3 mm below the free gingival margins. Above the moving tissue (floor of the mouth) and as far as possible below gingival tissue margins.
7 mm requirement vertically from FGM to base of the bar.
What is the contour of the inferior aspect of the lingual bar MC?
Half pear contour for greatest bulk and rigidity.
What is the ideal vertical height of the lingual bar MC?
4 mm.
Which do patients prefer, the linguoplate or the lingual bar?
Lingual bar.
Linguoplate MC form.
Superiorly should follow natural curvature of the tooth contour above the cingula, not extending above middle 1/3 of teeth, and scalloped form. Razor sharp!
What is used to prevent horizontal forces against anterior teeth in the linguoplate MC for Kennedy Class 1 and 2 designs.
Terminal occlusal rests or cingulum rests associated with the plate.
When is the linguoplate MC used?
When there is NOT 7 mm of vertical height from the FGM to the floor of the mouth or other considerations such as providing stability for periodontally compromised teeth by splinting. Provision for anticipated loss of teeth which may be added to the plate.
Minor connectors (mc)
Connecting link from MC to all other PRPD components. Clasp assemblies, indirect retainers or auxiliary rests, denture base.
Transfer stresses to abutment teeth and underlying supporting tissues.
What are the 3 types of mc?
Ladder, lattice meshwork, bead retention.
What are ladder openings based upon?
The tooth being connected. IE Premolar vs molar.
Guide Plane (GP)
A flat area on a tooth surface (m/d) created to follow the contour of the tooth and define the pat of insertion.
Where are GPs located?
On the mesial and distal of abutment teeth facing an edentulous space.
What are the size of GPs?
2-3 mmx2-3 mm depending on the size of the tooth.
What is the Guide plate?
Part of the framework that engages the guide plane on the tooth during insertion and removal of the PRDP.
Helps to maintain arch integrity by A/P bracing action. Resistance to horizontal forces.
Acts as secondary retainers due to frictional contact with parallel guiding planes.
Rests
Cast to fit prepared rest seats. Created in enamel or restorative materials.
What connect rests to the MC?
mcs.
What type of support do rests provide?
Vertical support. Prevent impingement of soft tissues by resisting tissue-ward movement. Direct and distribute occlusal loads to supporting abutment teeth. Preserve established occlusal relationships.
What is the shape of the occlusal rests and rest seats?
Outline should resemble a rounded triangle or spoon with apex pointing toward the center of the tooth. Should be as long as it is wide. At the marginal ridge, base of triangle should be at least 2.5 mm wide for molars and premolars. Height of marginal ridge should be reduced at least 1-2 mm to allow for bulk of metal for strength and rigidity. Floor of rest seat should be apical to the marginal ridge 1.5 mm (this is the deepest point, right under the mr is .1.0-1.2), spoon shaped and concave. Walls should be divergent.
describe the entry and exit of a rest seat.
You need to prepare the mesial facial and mesial lingual if it is being clasped. (not an edentulous space at the proximal area)
What are the options for cingulum rest seats?
Chevron shaped, or crescent shaped depression, composite resin cingulum rests, incisal rests (not frequently used)
What do you use to for rest prep refinement?
Diamond burs, finishing green stones, carborundum impregnated rubber points.
What is the order of tooth modifications?
- Create the guide planes.
- Change of survey line.
- Prepare the rests.
Describe how you create GPs.
Prepared on the m or d of abutment teeth aligned with the crest of the edentulous ridge. Extend from the marginal ridge to the JUNCTION OF MIDDLE AND CORONAL THIRDS, depending on the contour of the tooth.
Do not meat cleave. It is a gentle reshaping of enamel which follows the contour of the tooth. Curved planes.
What are the 3 ways you can change the survey line?
Enameloplasty, composite resin bonding, survey crown.
Moving survey line occlusally vs gingivally
Occlusally increases the retention apical to the line. Gingivally decreases retention apical to the line.
What indicates moving a survey line gingivally?
Red circle with lines.
What is the ideal tooth structure for rests?
Enamel, NOT dentin. Existing amalgams and composite resins are okay. Pre existing crowns are FPDs work too, but you need consent.
What is the preferred design for a minor connector?
Open lattice or ladder design.
What should the angle formed by the occlusal rest and mc from which it originates be?
Less than 90 degrees so that forces can be directed down the long axis of the abutment tooth. If the angle is greater than 90 degrees slippage could occur and orthodontic tooth movement may result.
Why don’t you want the rest seats in dentin?
Enamel is not at an increased risk for caries given appropriate oral hygiene. Dentin is.
Why do you need to inform a patient ahead of time when placing rest seats into existing restorations?
Chance of perforation and potentially needing a replacement or repair. Especially crowns.
Which is preferred for an anterior rest, incisors or canines?
Canine due to presence of a cingulum.
Cingulum rest vs incisal rest?
Cingulum preferred because there is less of a tendency to tip tooth and esthetically superior.
Intracoronal Direct retainer
A precision attachment. Prefabricated keys and keyways in the abutment crown with vertical parallel walls create frictional contact which limits movement and resists displacement.
Retention
Resistance to vertical dislodging forces. Areas apical to the height of contour are used for placement of flexible (terminal third), retentive clasp components.
What part of the retentive clasp is placed below the height of contour?
The flexible part, or terminal third.
Bracing/stability
Bracing is the resistance to the horizontal components of masticatory forces. mc’s brace and stabilize, gp’s and reciprocal clasp arms brace.
Adequate encirclement
Prevents horizontal tooth movement away from the confines of the clasp assemble. Assists in bracing. More than 180 degrees should be engaged by the clasp assembly, at the larges circumference of the tooth. Can be continuous or discontinuous contact.
Support
Resistance to vertical seating forces and occlusal forces. Rests direct functional forces parallel to the long axis of the abutment teeth.
Passivity
The quality of inactivity of rest assumed by the teeth, tissues and prosthesis when a PRDP is in place but not under masticatory pressure.
What are the basic clasp assemble components used to achieve the 6 requirements (Support, passivity, retention, reciprocation, stability, adequate encirclement)?
Retentive arm, reciprocating arm, mc, plate, rests, guide plane.
Can rigid clasps seat?
NO! Flexibility is crucial.
What part of the clasp arm is located in the undercut area of the tooth (0.01”)?
Terminal 1/3! Just the tip! Flexes and deforms upon insertion and removal as it passes over the survey line.
For length, is long or short more flexible? Diameter?
Long. Small.
Round Retentive Arm vs Cast Half-Round
Universally flexible, may roll on tooth structure.
Flexible in one direction only. Away from and back to tooth surface.
How does taper affect flexibility of retentive arms? Type of alloy?
Uniformly taper is more flexible.
Depends on Elastic Moduli.
Describe how a reciprocal arm should contact the tooth in relation to the retentive arm?
Should contact first, as the retentive arm engages the height of contour.
What is the main example of a suprabulge clasp?
Cast circumferential claps. Also called Akers, circlet, C claps.
Half round in cross section and has low flexibility.
Does it matter which side the retentive and reciprocation is on?
No. Not in theory. Depends on the patient. Wooly likes retentive on the buccal.
What is an embrasure clasp? When is it used?
Two c clasp assemblies originating from a common mc. Used in Kennedy Class 1 or 2 with no modification spaces on the opposite side of arch to aid in clasping. Requires aggressive tooth preparation, two retentive arms, two reciprocal arms and two rests.
Back to back C clasps. Reciprocation and retention can be on either facial or lingual.
Infrabulge clasps.
Also known as bar clasps. Approaches the coronal portion of the tooth from an apical position and does not cross the height of contour when the PRDP is fully seated. Survey line is crossed only during insertion and removal. Example: I-bar, modified T bar, all BAR clasps.
In an infrabulge clasp, is the retentive clasp on the facial or lingual?
ALWAYS on the facial. The mc/mesial rest and dgp are the reciprocating elements.
What is the most common clasp in the K3?
C Clasps! Tooth borne PRDP.
What is the ideal location for supports on a K3?
Prepared rest seats on occlusal or cingulum of teeth adjacent to edentulous spaces.
How many clasps in a K3?
4! K class+1=number of clasps
What are pier abutments? What are some options for them?
Floating teeth in K3. Clasps with rests? Rests only with gps? Mesial/distal guide plates only?
What does the support for a K4 depend upon?
The length of edentulous span. Mostly tooth borne.
What should shorter edentulous spaces in K4 be treated like?
Class 3.
How many clasps in a K4?
4! Exception to the rule.
What happens with longer edentulous spaces in K4s?
The more potential for rotation around the fulcrum line, indirect retention will be required, impression technique to capture muco-osseous support.
What is the MX MC used in K4s?
AP strap or horseshoe.
What are the MX and MD MCs used in K3?
MX is palatal. MN is bar or plate.
Extracoronal retainer?
Clasp type. Frictional retention using a flexible clasp arm to engage a tooth undercut gingival to height of contour.
Extracoronal attachments?
Retention via components attached to external surface of abutment teeth interlocking with another component in the PRDP.
Direct retainers
A part of a PRDP which resist displacement of the PRDP away from the basal seat tissues, providing retention.
Secondary retention
Provided by intimate (frictional) fit of mc contact to guiding planes, denture bases to soft tissue, and MCs in MX arches (interfacial surface tension)
Tooth factors of clasp retention. Prosthesis factors.
Depth of undercut, how far terminus of clasp is placed into undercut.
Flexibility: length, diameter, shape, material.
Infrabulge clasp advantages
Minimal tooth contact, precise placement of retention contact, minimal interference with natural tooth contour. Passive functional movement of a distal extension PRDP. Reduced display of metal.
What are some issues associated with K 1 and 2?
No posterior abutment tooth. Rotation of the free end saddle in 3 planes around a fulcrum. Sagittal plane rotation causes lever forces which may result in tooth mobility and loss. C clasps on distal abutments perpetuate these problems.
What classes have the least potential for rotation and destructive forces?
K 3 and 4s.
What class has the greatest potential for rotation?
K1. Around the fulcrum line and the production of destructive forces. There is no tooth support posteriorly. The soft tissue is resilient and compresses under occlusal load creating rotation and abutment tooth stress.
Fulcrum (F)
The support point or points of the lever around which rotation occurs.
Fulcrum Line
An axis of rotation.
In PRDPs, what act as the fulcrum and fulcrum lines?
In PRDPs rests act as fulcrums. X-arch rests define a fulcrum line and the axis or axes of rotation.
E
Direction of effort or force
R
Resistance to the force or effort.
First Class Lever
What you want to avoid! Detrimental, may lead to abutment tooth mobility and instability. Fulcrum line is the axis of rotation and passes through the two most distal rests or anterior rests in K4s. Fulcrum is between Resistance and Effort. (RFE) The crowbar effect. Abutment tooth is torqued to the distal and superiorly.
What happens with C clasps during a first class lever?
Loading force causes clasp to rotate at R and retentive clasp arm tip moves occlusally during function and directs distal torquing force.
What are some problems with C clasps?
Potential for Class 1 lever with K1 and 2s if distal rest is used causing distal rotation of clasp and the compromisation of abutment teeth.
How do you fix the Class 1 lever issues with C clasps?
Control rotation through indirect retention, better fitting saddle. Design a different clasp for K1 and 2s.
What was the #1 old solution to reduce sagittal plane rotation?
More flexible clasp. Using a Combination clasp with wrought wire. The flexibility of wrought wire arms limits the torquing effect, thereby limiting rotation.
Combination Clasp (suprabulge)
Wrought wire retentive clasp arm on the facial engages a .02 undercut with a cast reciprocal clasp arm on the lingual. Distal occlusal rest and guide plate next to edentulous space. Was advocated for K1 and 2 distal abutments. The flexibility of wrought wire arms limits the torquing effect, thereby limiting rotation.
Combination Clasp advantages and disadvantages
Advantages: Flexible, adjustable, better esthetics due to lower position on tooth surface.
But….unnecessary distal torque. May be distorted by patient manipulation. May distort with function and not engage tooth at all.
What is the better solution to a class 1 lever?
Convert a class 1 lever to a class 2 lever with mesial rest clasps.
What is a second class lever?
Desirable! R and E are on the same side of F. SO: REF or FRE….F IS NOT IN THE MIDDLE. Stress releasing lever.
Why put mesial rest on distal extension abutments?
M rest creates the least force on abutment. Distal rests create more force to abutment regardless of clasp.
What type of rest and clasps exerts lest force to abutments?
M rest with WW or I bar.
How do you decrease the engaging effect?
Move fulcrum forward (M rest instead of D) and change the resistance arm.
What are the basic components of mesial rest clasps?
Mesial rest. (fulcrum!)
mc: From MC to mesial rest, functions as reciprocation..
Distal guide Plate: reciprocation and guidance.
Clasp: retention.
Modified RPA
Suprabulge Mesial Rest Clasp. Rest, proximal plate and 19 guage cast round wire clasp.
RPW
Suprabulge, Mesial Rest, proximal plate, Wrought wire.
Reverse C
Suprabulge, mesial rest, proximal plate, retention/reciprocal clasps.
RPI
Infrabulge, mesial rest, proximal plate, I bar.
Modified T
Infrabulge, mesial rest, proximal plate and mod T bar.
Indirect retention
A design concept to prevent rotation in the sagittal plane around the fulcrum line. Used in Kennedy Class 1 and 2. Used to avoid the inclined plane effect which pushes anterior teeth anteriorly. LIMITS ROTATION WHEN SADDLE IS ELEVATED (superior displacement)
What are some features that create Indirect Retention?
Occlusal or cingulum rests anterior to and perpendicular to the fulcrum line. As far as possible.
- positive rest seat.
- right angle to fulcrum line.
- As far away as possible.
Superior Displacement
Saddle is elevated. What indirect retention tries to minimize.
Inferior displacement
Rotation produced by saddle depression. Controlled through saddle fit to tissue.
When is indirect retention mandatory?
In all K1, 2, designs and some K4.
Is the lingual plate alone of a MX and MN considered an adequate indirect retainer?
NO! Must have an associated rest beneath the plate or at the terminal end to function as an indirect retainer.
For a K1 or 2, distal extension saddle, what is the first choice of clasp?
Infrabulge bar clasp: RPI or modified T bar.
When are bar clasp arms such as I bar or T bar indicated?
Tooth supported RPDs. Modification spaces in K2. DISTAL EXTENSION CASES WITH THE APPROPRIATE UNDERCUT IN K1 andK2. Need .01 undercut in cervical third that can be accessed from the gingival aspect. Best biomechanics and esthetic considerations.
When are bar clasps contraindicated?
Severe buccal/lingual tilt. Soft tissue undercuts within 3 mm of the free gingival margin because you can’t insert and remove the metal loop in a tissue undercut. Shallow buccal vestibule, you need a minimum of 3-4 mm. Prominent buccal frenum.
RPI Concept
Functional movement away from tooth under functional saddle loading. Reduces the torquing of the clasp.
What does the mc of a mesial rest provide?
Reciprocation and encirclement.
Where should the undercut exist on the guide plane?
Below it. Permits disengagement of the proximal plate under functional loading of the saddle.
How thick should the proximal guide plate be?
1-1.5 mm thick. Portion near gingival tissue is relieved and highly polished.
Where should the I Bar be placed?
Mid facial or slightly MB in the .01 undercut. NOT in a distobuccal undercut because it will not disengage under function.
Why would you use a suprabulge clasp over an infrabulge clasp?
There exist bony soft tissue undercuts or frena apical to the free gingival margin in the first 3 mm of tissue. Shallow vestibule. Patient factors that prevent them from putting them in such as parkinsons, eyesite, etc.
RPA vs RPW
Cast round wire vs. wrought wire. RPA or mod RPA is the first choice. Easy lab work and good functional movement into deeper undercut. RPW: .02 undercut, most flexible but difficult to keep in contact with tooth surface.
.01 DF undercut in gingival half of abutment tooth
T clasp or reverse c clasp.
.01 or more MF undercut in gingival half of abutment tooth with shallow vestibule.
RPA or RPW
.01 or more MidF undercut in gingival half of abutment tooth.
RPI
What color are the MC, mc and clasps in?
Brown
What are in red?
Rests, undercut, tooth mods, guiding planes.
What is in blue?
Acrylic saddle.
What color is indirect retention?
Red or brown.
What color is the lattice work for acrylic retention?
Brown
What do you submit to the lab?
Tripod master cast with no design. Study cast with PRDP.
Where are tissue rests placed?
On the most horizontal, firm tissue, not necessarily on the most posterior.
What do you adjust the framework with?
High speed and composite finishing burs or slow speed green stones.
What are common problem areas for the clinical fitting of the framework?
Guide plates, origin of circumferential clasps, under embrasure clasps, interproximal projections of lingual plates, beneath rests.
What are the cardinal rules for adjusting framework to opposing occlusion?
- Occlusal contacts existing without the framework in place should be intact with the framework seated.
- Occlusion should not be supported by occlusal rests or any part of the framework, unless specifically designed to change the VDO or occlusal plane.
- VDO should be maintained.
How thick should metal framework components be?
At least 1.0-1.2 mm.
In patients with MX and MN frameworks, what order do you adjust them?
Each independently, then with both inserted.
Are 0 degree teeth generally used in the PRDP arch?
NO. In most cases 10-22 degree teeth match the residual natural dentition.
What does the degree of cuspal inclination depend on?
The remaining natural dentition and the necessary occlusal balance required.
What is the overriding principal of occlusion?
Simultaneous bilateral contacts of opposing teeth in MI or CR.
What are the 2 basic PRDP categories?
A complete denture opposing an arch with a PRDP. Usually the MX CD.
Natural tooth anterior guidance. Ex: canine protected, group function.
What degree teeth do you use with a MX CD opposing an arch with a PRDP? K1?
Shallow cusp posterior tooth in the CD arch-10-20 degrees. You need to avoid over engaging the CD teeth to ensure stability. Set in CR.
In a K1-treat it like a CD against a CD and create a bilateral working, non-working balance. Protrusive balance can be retained with a balancing ramp.
For natural tooth anterior guidance, how do you manage occlusion?
Depends on the steepness of the incisal guidance and on MN working movement. Posterior occlusion may be group function or may have posterior disclusion. Match existing tooth forms for best intercuspation.
K3 Teeth
Arrange teeth similar to the occlusion of a natural dentition. This applies to opposing MX/MN class 3 RPDs. If you have a MN RPD opposing a MX CD, determine the MN plane of occlusion first.
K4s teeth
Anterior contacts in MI against the opposing dentition. Want light protrusive contacts. Focus on esthetics and phonetics.
What are the considerations for the removal of unerupted teeth in edentulous saddle areas?
Same as for a CD.
Amount of overlying bone, history of the tooth, evidence of pathology.
What necessitates surgery for a torus palatinus?
Size and undercuts. Most major connectors can circumvent.
Who gets torus palatinus?
20-25% of adults. Women 2 times more than men.
What determines the removal of mandibular torus?
Usually are bilateral, very thin, easily traumatized covering mucosa. SHOULD BE REMOVED. They lead to severe compromises in design, rigidity, and placement of major connector if retained.
Who get mandibular torus?
5-10% of adults. Women same as men.
What determines the removal of exostoses and undercuts?
In critical base areas of the saddle extensions, they should be removed. Path of insertion or design may compensate for some undercuts. In the absence of surgery, a partially flangeless PRDP base may be required.
When do you reduce a MX tuberosity?
When it is pendulous, hypertrophic and compromises vertical space.
When do you perform a fenectomy?
When the attachment is at the crest of the ridge, it is hypertrophic and compromises the framework, tooth placement, esthetics or saddle.
What is the best way to evaluate for a pre-prosthetic surgery?
Diagnostic casts and a surveyor as you design the PRDP.
What are the material used for frameworks?
Gold (type 4), base metal alloys such as CoCr, NiCr, commercially pure titanium.
What are more than 90% of PRDP frameworks made out of?
Base metal alloys such as CoCr and NiCr.
What are the advantages of Co-Ni-Cr alloys?
Higher strength, fatigue resistance, lighter weight, lower cost.
What are the advantages of CP titanium?
Low weight to volume. High strength to weight. High fatigue resistance. High corrosion resistance.
Why can’t you have a higher percentage than 30 for Cr in alloys?
Becomes toxic.
Percentage of Co-Cr?
30 Cr, 60 Co. Called vitallium, nobilium, wironium.
Percentage of Ni-Cr?
65-70% Ni, 17% Cr. Called Ticonium Premium 100.
Percentage of Type 4 gold?
71-74% gold. PT, PD
Which alloy has the highest density? The lowest?
Gold. Titanium.
What is the significance of density?
Low density means more casting force is required and you need special, expensive equipment. A large MX framework will have improved retention if the weight of the framework can be reduced….thus low density metal.
Which alloy shrinks the most? The least?
Titanium. Gold.
Which alloys are the hardest?
Co-Cr, Ni-Cr
What is the modulus of elasticity?
The ability to bend and not break. The higher means the more brittle. It is best when space is limited, meaning less framework bulk required. Cr is two times as stiff so less retention is required.
Highest MOE? Lowest?
Highest is Co-Cr, then Ni-Cr, Gold and Ti are similar.
Yield Strength
Base metals withstands permanent deformation. Cr is much higher than Ti or gold.
Why is hardness of base metals important?
Base metals may be more abrasive to opposing dentition if not highly polished.
Ease of adjustment?
Au and Ti
Ease of Solder?
Au
Cost effective?
Cr! 175 vs 1000+ vs 650+
Which alloy can be used with wrought wire?
ALL OF THEM!
What is a big issue with Ni?
Allergies!
What is the big issue with Beryllium?
Health risks! Need proper protective measures.
What is a concern with RPD base acrylics that has ben resolved?
The cadmium salts were a carcinogen, but were removed over 20 years ago. An alternative are heat processed clear acrylic. Lucitone 199 has no Cadmium!
