Lecture 1 Flashcards
What are the 3 types of RPDs? Which will we mainly deal with?
- Cast Metal Frame (90% of course)
- Acrylic
- Flexible
What are the two common metals used in a cast metal frame? Which is better?
CoCr (used more)
NiCr (used less because of nickel sensitivity)
Brief explanation of Kennedy Classifications (I-IV)
Class I - Bilateral distal extension (posterior to natural teeth)
Class II - Unilateral distal extension
Class III - Unilateral tooth bound extension
Class IV - Anterior extension area crossing midline
What are the indications for RPDs
- Edentulous area(s) too large
- Anterior region has lost alveolar tissue
- Reduced periodontal support
- Cross-arch stabilization
- No posterior abutment tooth
- Immediate tooth replacement
7.Economic considerations of patient
(True/False) Height of contour/survey line will change if the axial inclination is changed
True
Areas of tooth contour
Suprabulge - About HOC
Infrabulge - Below HOC (“undercut”)
Which number determines the classification if multiple are present?
The lowest number determines the classification
What is a modification space?
An edentulous area other than that determining the classification
(True/False) Classification should PRECEDE any extractions that might alter the original classification
False, it should follow
What are the rules governing the application of the Kennedy Classification System? How many are there?
Applegate’s Rules (8)
Do we include 3rd molars in classification? 2nd?
Not if it is missing or to not be replaced. Only if it is to be used as an abutment. If 2nd molars are missing and not replaced, they do not count either - typically do not replace 2nd or 3rd molars
The most ________(anterior OR posterior) edentulous areas always determine the classification
Posterior
Is there ever an instance of mod areas in class IV arches?
No, they would be posterior, thus take charge determining the classification
What are the 3 types of classification in the Craddock Classification?
Type 1: Mucosa-borne
Type 2: Tooth-borne
Type 3: Mucosa and tooth-borne
What should the width of the guiding planes be?
- As wide as widest portion of occlusal rest
- 1/3 bucco-lingual width
1/2 distance between cusp tips
What should the length of the guiding planes be?
Tooth supported abutments: 3-4 mm
Tooth-tissue supported abutments: 1.5-2 mm
What is the order of the survey procedure for a diagnostic cast?
1) Path of insertion is determined
- Guiding plane (parallel, flattened planes at prox/axial surfaces
- Retentive undercuts (between survey line and gingival margin, engaged by clasp - only retentive goes below)
- Interference
- Esthetics
2) Mark HOC
3) Measure/mark retentive undercut
4) Tripod cast
When establishing parallelism in a cast for the guiding planes, where is selective grinding done?
On the occlusal 1/3 - 1/2
What are typical interference areas that interrupt the path of insertion
Lingually inclined mandibular teeth
Buccally inclined maxillary teeth
Exotoses, tori
HOC too high - clasp too high
Tissue undercut area of bar clasp
Where is the survey line ideally located on a tooth? Where are the clasps located on the tooth in relation to this line?
HOC located at junction of middle and gingival 1/3
2/3 retentive clasp (rigid) above HOC, terminal 1/3 below (in gingival 1/3) (flexible) tapered
Reciprocal clasp is rigid component in middle 1/3, above HOC not tapered
What do you do if for a chosen path of insertion, the survey line?HOC is too near the occlusal surface? If it is too low with no undercuts?
Too high - Recontoured tooth to lower survey line
Too low - Surveyed crown
What is the amount of undercut for a CrCo/NiCr cast clasp?
What about for wrought wire clasp?
0.01” for CrCo/NiCr (least flexible)
0.015” for Cast Gold alloy
0.02” or 0.03” for wrought wire (most flexible)
What can you do if there is inadequate retentive undercut?
Enameloplasty to create “dimple”
Add composite
Surveyed crown
Which cast is the RPD design drawn on? What do the colors represent?
Diagnostic cast
Blue = metal framework and wrought wire clasp
Red = retentive undercut, tooth mod areas
Black = HOC, tripod marks and soft tissue undercuts
When do you make the master cast?
After mouth preparation, then resurvey (guiding planes, HOC, retentive undercuts, tripod, framework made)
Rest vs Rest Seat
Rest is the RIGID extension of the RPD that transmits force to teeth (down the long axis of the teeth) and prevents movement toward the mucosa (cervical movement)
Rest seat is the portion of the tooth prepared to receive the rest
What are the 5 types of rests?
Occlusal
Embrasure
Cingulum (Lingual)
Hooded
Incisal
Occlusal Rest Seats: describe the location, shape, width, depth
Location: mesial/distal pits, centered over marginal ridges
Shape: concave (“spoon”), triangular in shape, base being over marginal ridge
Width: 1/3 buccolingual width of tooth
1/2 width between the cusp tips
Depth: 1-1.5 mm over marginal ridge
1.5-2 mm at deepest portion in pit area
- Should be inclined forming an angle less than 90 degrees
What should the angle formed between the occlusal rest and the vertical minor connector be?
Less than 90 degrees
Describe the location and form of an Embrasure Rest Seat
Location: between two adjacent posterior teeth, used when no posterior modification space is present
Form: Occlusal rests placed adjacent without removing contact point, but allowing for adequate tooth reduction (~1 mm)
Sluiceway should be ~2 mm evaluated using two 18-gauge wire (width of adjacent rest seats) (U-shaped trough to accommodate clasp assembly)
How do we prepare a cingulum rest seat on mandibular vs maxillary teeth?
Maxillary - cut into enamel (primary)
Mandibular - composite resin (since canine does not exhibit sufficient enamel thickness lingually (still clinical long-term success)
Form of lingual cingulum rest
Chevron “V” shaped
Slope slightly downward (<90 degrees with path of insertion)
Width of floor: 0.75-2 mm (1 IDEAL)
Inciso-apical depth: 1.0-1.5 mm
Where are hooded rests indicated? Form?
Mandibular first premolars ONLY, cannot be on distal abutments of distal extensions
1.0-1.5 mm reduction, marginal ridge to marginal ridge
What is the least desirable of all the rests? Why? Primarily used where?
Incisal Rests due to poor esthetics and occlusal interference
Mandibular canines as indirect retainers
Small, V-shaped notch
Intracoronal vs Extracoronal Direct Retainers
Intra: key/keyway (most esthetic)
high maintenance and complex
Extra: Clasp assembly, more common
Suprabulge vs infrabulge
Supra: approach undercut from ABOVE HOC (circumferential, akers, circlet)
Infra: Approached undercut from BELOW HOC (bar clasps)
Are minor connectors flexible or rigid? What is an exception to the rule?
Rigid, an exception is the approach arm (bar clasps) which connects the clasp to the framework
What are requirements of clasp assembly?
Encirclement of more than 180 degrees
Minimum of 3 points
Prevent tooth from moving away from clasp
(True/False?) Components of direct retainers should exert no force when fully seated
True, retentive clasps should only become active when forces are applied to them
Relationship between flexibility and length? How is this done? Diameter and Flexibility?
Flex=length^3 (double length = 8x more flex), this is done by curving the clasp
Flex=1/diameter^3 (double diameter, 8x less flexible)
How doe the dimensions of the terminal portion of the retentive clasp compare to the origin?
1/2 as thick (1 –> 0.5 mm)
1/2 as wide (2 –> 1 mm)
Which is more flexible… round clasp (wrought wire) or half-round (circumferential)? Why?
Round, flexes in all spatial planes, half-round flexes in one plane
What is the most logical clasp for tooth-supported RPD (Class III) Name the types of circumferential clasps (7)
Circumferential Clasps
1.) Circlet
- Class III RPD clasp of choice
2.) Embrasure Clasp (2 circlet joined at body)
- Class II and III with no modification space
- Class IV
3.) Reverse Circlet (hairpin) clasp
- Last choice for Mesially-tipped mandibular molar
4.) Ring Clasp (avoid if possible)
- Mesiolingually-tipped mandibular molar (no recip.)
5.) Reverse Circlet Clasp
- Class I, II or III (avoid if possible)
6.) Combination Clasp (Class I and II)
- Wrought retentive
Cast reciprocal
7. RPC Clasp
Class I and II
Which circumferential clasps can be used for Class I RPDs
Combination
RPC
Which circumferential clasps can be used for Class I RPDs
Combination
RPC
Which circumferential clasps can be used for Class II RPDs
Embrasure (if no mod space)
Combination
RPC
Which circumferential clasps can be used for Class III RPDs
CIRCLET (BEST)
Embrasure (if no mod space)
_______________________
Reverse Circlet
Ring
Hairpin (WORST)
Which circumferential clasps can be used for Class IV RPDs
Embrasure
What should be used to prepare an undercut?
Round-end tapered diamond
Where is the occlusal pressure concentrated in a tooth-tissue supported RPD? What causes this?
Due to the lever effect of the distal extension base, pressure is concentrated on the distal end of the base
(True/False?) There is significant advantage of altered cast impression material when compared with one-piece cast method?
False, there is not significant advantage. One-step is less prone to error
How does one mark an undercut on the master cast?
Red line NOT red dot at the approximate inferior edge of the clasp
In terms of rigidity, flexibility = _____________
Force concentration
How far away should the borders of the major connector be from the gingival margin for maxillary arch? Mandibular?
6 mm
3 mm
Needs to cross at right angles to the gingival margins
Name the 4 kinds of maxillary major connectors
- Palatal Strap (8-10 mm)
- Palatal Plate (thicker, more stable, worse phonetics, uncomfy etc.)
- Anterior-Posterior Strap - 6-8 mm, space should be 15 mm (circumvent a torus)
- Horseshoe or “U” - least rigid, used in HIGH VAULT PALATE
Beading of the maxillary cast FORM
1/2 round
1 mm deep, 1.5 mm wide
Feathers out to nothing 6 mm from free gingiva margin
Shallower over mid-palatal suture
Mandibular Major Connectors (3)
Lingual Bar (need 7 mm from ging. margin to floor of mouth) (4-5 mm tall), located 3-4 mm below free gingival margin
Lingual Plate (if can’t use bar, more rigid)
Labial Bar
What are the 3 types of Bar Clasps?
- T Clasp
- 1/2-T (DF)
- I-Bar (MF, mid-F)
Tooth-supported RPD Clasps
1.) Circlet (circumferential) most common
- Reciprocal clasp
2.) I-Bar
- MF, mid-F undercut
3.) 1/2 T-Bar
- DF undercut
- Reciprocal clasp
4.) Reverse Circlet (hairpin)
- Tissue undercut, last resort
5.) Embrasure Clasp
- Class III, IV (no mod space)
- Also class II with tooth-tissue, no mod space
Tooth-tissue supported RPD Clasps
- RPI Clasp (rest mesial, prox plate, I bar)
- RPC (A) Clasp
- Combination Clasp
- 1/2 T Clasp
- Reverse Circumferential
How far apart fo the vertical minor connectors in a RPI Clasp Assembly need to be? If not, what should be used?
5 mm, Lingual Plate if not
