REMOVABLE PARTIAL DENTURE Flashcards
- Kennedy Classification (0.5)
Class I – bilateral edentulous areas located posterior to all remaining teeth
Class II – unilateral edentulous area located posterior to all remaining teeth
Class III – unilateral edentulous area bounded by anterior and posterior natural teeth
Class IV – a single, but bilateral edentulous area located anterior to remaining teeth
a. 6 clinical parameters for assessing potential abutment (3)
- Crown-root ratio
- Root configuration
- Periodontal ligament area
- Health and periodontium
- Endodontic consideration
- Biomechanical consideration
- Span length
- Direction of force
- Secondary abutments
- Arch Curvature
Draw the preliminary design (?)
Draw fulcrum line or rotational axis when masticatory force is acting on saddle and when saddle is being lifted (2)
d. Method of reducing stress on mucosa (2)
Extend the base of the saddle to gain more mucosal support
Use a smaller occlusal table
Indirect retainers and occlusal rests are place to gain tooth support
e. Method of reducing stress on abutment (2)
Altered cast technique
RPI/RPA
Splint the tooth
Stress breaker
f. 4 factors affecting effectiveness of Indirect retainer (2)
Indirect retainers must be positioned in properly prepared rest seats
One or more indirect retainers must be positioned perpendicular to the fulcrum line as far as possible to provide the best leverage system against dislodging forces
The effectiveness of the indirect retention will increase as the distance to the fulcrum line increases
Choose most suitable abutment tooth to place the rests for indirect retention
Rigidity of the connectors supporting the indirect retainer. All connectors must be rigid if the retainer is to function as intended.
g. 3mm high discrepancy… past paper hv (4)
Wrong jaw registration
Retake a bite registration in clinic and instruct technician remount the master cast at correct jaw relationship, adjust occlusal errors and check bite
Otto lam is wearing a denture as shown in the picture. He feels pain on biting on the left area under the denture
a. After the removal of the retained roots and some subsequent dental treatments, the dentist found that tooth 15, 17, 25, 27 and all remaining mandibular teeth can be saved. Write down the Kennedy classification for the maxillary arch. (1)
Class III Modification 2
b. The patient wants all missing teeth to be replaced. Using the correct colours, draw the
preliminary design for a cobalt-chromium denture for the maxillary arch. (3)
No more than 4 clasps, need major connector, diagonal placement of clasps
c. Write down 4 anatomical landmarks that can provide support for a mandibular free-
end saddle. (2)
Buccal shelf
Retromolar pad
Alveolar ridge
Distal abutment
d. You decided to perform a study impression for the mandibular arch of the patient. Write down instructions to the technician to request for a custom tray for the impression. (1)
Outline of the extension of the tray
Material used in impression (e.g. alginate → requires perforations on custom tray)
e. State the definition of an indirect retainer. (2)
The component of a removable partial denture that assists the direct retainer(s) in preventing displacement of the distal-extension denture base by functioning through lever action on the opposite side of the fulcrum line when the denture base attempts to move away from the tissues in pure rotation around the fulcrum line
f. Which 4 major factor determines whether an indirect retainer will be successful? (2)
Indirect retainers must be positioned in properly prepared rest seats
One or more indirect retainers must be positioned perpendicular to the fulcrum line as far as possible to provide the best leverage system against dislodging forces
The effectiveness of the indirect retention will increase as the distance to the fulcrum line increases
Choose most suitable abutment tooth to place the rests for indirect retention
Rigidity of the connectors supporting the indirect retainer. All connectors must be rigid if the retainer is to function as intended.
g. You decided to use a RPA system for the RPA clasp. Draw the features of the retentive arm of an ordinary occlusally-approaching clasp and an Aker’s clasp in relation to the undercut (o) and the survey line (–). (2)
Aker’s clasp (類似occlusal approaching C clasp)
Occlusal approaching clasp: 2⁄3 above survey line
Aker’s clasps: rigid part along the survey line
h. For the RPA systems, will you prepare guiding planes on the distal surface of tooth 35 and 44? Why? (1)
No guiding plane on RPA/RPI: if there is guiding plane → saddle cannot rotate and all stress goes to abutment and torque
a. Discuss the dilemma of path of insertion of a Kennedy Class IV RPD (4)
- The anterior alveolar ridge usually has a labial undercut
- So we need to select a path of insertion that allows the flange to be smoothly placed into the undercut and reduce dead spaces on the mesial side of the abutment
- This may involve tilting the cast heels down or selecting the path of insertion before backwards
- However, surveying at this angle tends to place the undercuts on the distobuccal side of the posterior teeth therefore if occlusal clasps are placed, it may be unsightly and may complicate design as we would need indirect retention
b. Draw a preliminary design of an upper removable partial denture (missing 12 to 23) and take the patient’s mucosal condition into account (3)
c. List the factors affecting clasp arm flexibility (2)
Cross-sectional shape: if semi-circular less flexible, if circular more flexible
Length of the arm: longer arm the more flexible
Diameter of the arm: thinner arm the more flexible
Modulus of elasticity of the material of the arm: Cobalt Chromium < stainless steel < Gold (Least flexible to most flexible)
d. Reasons for altering survey line (? marks)
- Lower survey line:
- Allow the inflexible part of the clasp to be situated lower hence may avoid occlusal interference –> which may reduce deformation and more aesthetically pleasing
- Raise survey line:
- To create a retentive undercut
- So that the retentive clasp tip can be kept away from the gingival margin to avoid food trapping and impinging soft tissue
Given a panoramic radiograph, clinical photos of occlusal view of upper and lower arch.
The patient have some teeth extracted and want to replace the teeth.
a. Kennedy Classification for upper and lower arch
Class I
Given a panoramic radiograph, clinical photos of occlusal view of upper and lower arch.
The patient have some teeth extracted and want to replace the teeth.
b. Draw a preliminary design of RPD for the lower arch (41-47, 35-37 missing (?))
Given a panoramic radiograph, clinical photos of occlusal view of upper and lower arch.
The patient have some teeth extracted and want to replace the teeth.
c. Draw the axis of rotation
i. When px bite on cookies
Given a panoramic radiograph, clinical photos of occlusal view of upper and lower arch.
The patient have some teeth extracted and want to replace the teeth.
c. Draw the axis of rotation
ii. When px bite on sticky food
Given a panoramic radiograph, clinical photos of occlusal view of upper and lower arch.
The patient have some teeth extracted and want to replace the teeth.
d. Compare acrylic and co-cr as denture base materials
High modulus of elasticity, retention of pontic, soft tissue colour, thermal
a. Missing 16, 18, 26, 28, 36, 37, 38, 46, 48. kennedy class classification for upper and lower
RPD
Maxillary arch: Class III Modification 1
Mandibular arch: Class II Modification 1
b. RPD design for lower assessment of abutment tooth clinically and radiographically
c. Mechanism of RPI
The RPI system contains the rest, proximal plate and I-bar.
When an occlusal force is acting on the free end saddle, the I-bar can disengage the undercut of the tooth and travel mesially and denture base can sink deeper due to a space between the saddle and the tooth created by a shorter guide plane.
This prevents the rotation and torqueing of the abutment tooth preventing detrimental effects
A chart showing multiple missing teeth (RPD). Apparently the questions say anterior missing.
a. Kennedy classification of the missing tooth
Class IV
A chart showing multiple missing teeth (RPD). Apparently the questions say anterior missing.
b. Draw the denture design
A chart showing multiple missing teeth (RPD). Apparently the questions say anterior missing.
c. What is the difficulties for this denture design (anterior missing), how to solve it
a. Preliminary design for lower RPD (34-44 present, bilateral free-end saddle)
b. Advantage and disadvantage of using cobalt-chromium for a partial denture base over using acrylic. (5)
Advantages: high modulus of elasticity (= stiff), hence can be made thin and light and less easy to break; less retentive for Candida species reducing the risk for denture induced stomatitis, good heat conduction hence better patient sensation when eating
Disadvantages: higher cost (?); higher temperature required for fabrication; not chemically bonded to acrylic tooth; colour dissimilar to oral tissues
a. What is the Kennedy classification for the maxillary and mandibular teeth?(2marks)
Maxillary arch: Class IV
Mandibular arch: Class III Modification 2
b. Describe a partial denture for the maxillary teeth (draw + description). (4 marks)
c. What is the dilemma in choosing the path of insertion when making partial dentures for the maxillary teeth in this case? (6 marks)
- The anterior alveolar ridge usually has a labial undercut
- So we need to select a path of insertion that allows the flange to be smoothly placed into the undercut and reduce dead spaces on the mesial side of the abutment
- This may involve tilting the cast heels down or selecting the path of insertion before backwards
- However, surveying at this angle tends to place the undercuts on the distobuccal side of the posterior teeth therefore if occlusal clasps are placed, it may be unsightly and may complicate design as we would need indirect retention
- RPD: photos and study casts (Formative, 2005)
a. What are the potential problems if RPD for upper arch is used?
Anatomical limitation like torus palatinus
Use of some major connectors like ring connector can cause low tolerance and interfere tongue movement
Dead space in anterior saddle which require tilted pathway
Overerupted teeth (in this case) have to be corrected first to normal occlusal plane by enameloplasty, onlay, crown or extraction
Periodontal status, teeth malalignment (depends on case)
- RPD: photos and study casts (Formative, 2005)
b. Draw a preliminary design for an upper arch RPD
Probably class IV with torus palatinus according to the answer above
- Patient requests replacement of existing denture. Given: I/O photo of upper cobalt chromium RPD.
a. Critically assess the existing denture.
Retention / support / stability / occlusion / aesthetics / OH (plaque retentive factors) / fitness
Defective components: tooth wear / fracture of clasp / missing tooth / crack
- Patient requests replacement of existing denture. Given: I/O photo of upper cobalt chromium RPD.
b. What are the advantages and disadvantages of cobalt chromium alloy as a denture base material when compared with acrylic?
- C/O: multiple teeth lost, looking for replacements
- HPC:
- MH: clear
- DH: multiple extractions done
- E/O and I/O: (Refer to intra-oral photos and panoramic radiograph o Missing 18, 31, 32, 36, 37, 38, 41, 42
- Generalized horizontal bone loss
- Marked recession on 16 and 17
- 16 over-erupted
a. Draw the preliminary design of removable partial denture for this case
- C/O: multiple teeth lost, looking for replacements
- HPC:
- MH: clear
- DH: multiple extractions done
- E/O and I/O: (Refer to intra-oral photos and panoramic radiograph o Missing 18, 31, 32, 36, 37, 38, 41, 42
- Generalized horizontal bone loss
- Marked recession on 16 and 17
- 16 over-erupted
b. What are the problems associated with design of removable partial denture with free end saddle? (5)
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
a. What is the Kennedy classification of the denture? (1)
Upper: Class IV
Lower: Class III, modification 1 (33 is present)
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
b. What are the problems associated with the path of insertion of the maxillary denture? (8)
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
c. Draw the preliminary design for the upper and lower removable partial denture for the patient. (10)
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
d. What are the functions of guide planes?
- Increase stability
- Resist displacement
- Limit path of insertion
- Reciprocation
- Allow reciprocal to maintain continuous contact with tooth as denture is displaced occlusally, counterbalanced lateral force by retentive clasps
- Prevention of clasp deformation
- Ensure removal of denture along planned pathway
- Without guide planes tiliting or rotation of denture on removal may cause clasp to flex beyond proportional limit
- Improved aesthetics
- Provide intimate contact between saddle and abutment to minimize dead space
- Provides frictional retention
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
e. What are the essential features of guide planes? (2.5)
Minimal and fairly uniform thickness of enamel, not more than 0.5 mm Extend vertically 2-3 mm, keep as far from gingival margin as possible Follow original tooth shape, not prepared as flat surface
Parallel to the path of insertion
2/3 of the buccolingual distance
- A middle aged lady requested replacement of missing teeth with RPD
Intra-oral photographs:
- missing 11, 12, 21, 22, 31, 32, 34, 41, 42, 43, 44
- 36, 46 crowned (stainless steel crown)
f. Under what circumstances do the survey lines be raised or lowered? (1.5)
- Raised: survery line too close to gingva, at least 2mm away from gingiva
- Lowered:
- to allow placement of components more gingivally without creating an occlusal interference
- part of a retentive clasp
- reciprocal arm
- OR and Perio (Formative, 2009)
a. Draw a preliminary design of lower removable partial denture for the patients. (5)
b. Problems encountered in free ended removable partial denture. (5)
Pivot about rest/ rotational movement of saddle can be reduced by putting abutment rest mesially
Great support differential by tooth and displaceable mucosa causes saddle to sink under occlusal load. Downward movement can cause ridge resorption and pain can be reduced by using narrower false teeth
Pressure can be reduced by increasing effective saddle area (altercast technique)
Torque of abutment (displacement of free ended saddle down to displaceable mucosa creating a torque on abutment)
Problem of retention due to absence of saddle on the other side (solved by extending denture to the other
side and clasp more than one tooth by rigid clasp) guiding plane can also be employed to resist upwards movement
Patient requests replacement of existing denture made 1 year ago. Given: I/O photo of upper cobalt chromium RPD.
a. Critically assess the existing denture. (7) (Only photo is provided)
How to critically assess|:
Determine if denture is an upper or lower denture
Check if the major connector used is correct for the denture type
Check if there is enough rest seats, usually one missing tooth per rest seat
Check if there is a retentive clasp or reciprocal clasp, usually either one would be missing
Check if the major connector is at the correct distance from the marginal gingiva
Check if there are enough or too many clasps
Check if the base of a free end saddle is extended to the pear-shaped pads for lower and hamular
notch for upper
Check if there is indirect retention and whether the indirect retention is placed correctly
Check if RPI or RPA system is used for free end-saddle cases
Patient requests replacement of existing denture made 1 year ago. Given: I/O photo of upper cobalt chromium RPD.
b. What is the clasp on the palatal side of tooth 26? What are the functions? (3)
Reciprocal arm, above survey line, balance the force of retentive arm to prevent orthodontic movement during insertion or withdrawal of the denture, function only when the denture is not fully seated
Bracing: provide resistance to lateral displacement when the denture is fully seated
Patient requests replacement of existing denture made 1 year ago. Given: I/O photo of upper cobalt chromium RPD.
c. Draw a preliminary design of the upper RPD (5)
d. Alternative treatment option for the replacing teeth
Bridge, implant
Given: panoramic radiograph. Generalized horizontal bone loss Multiple missing teeth: 18, 16, 24, 25, 26, 27, 38, 31, 41, 42, 48 Periapical radiolucency, Furcation involvement , Tilting
a. Describe the 5 features you could observe in the panoramic radiograph.
Periapical radiolucency, Furcation involvement, tilting
Given: panoramic radiograph. Generalized horizontal bone loss Multiple missing teeth: 18, 16, 24, 25, 26, 27, 38, 31, 41, 42, 48 Periapical radiolucency, Furcation involvement , Tilting
b. No extraction is required. Draw the preliminary design for an upper removable partial
denture for the patient.
Given: an upper mirror shot showing a denture made in China no clasps or rest seats, some crowns are present.
What is the Kennedy classification?
Give a critical assessment of this denture. What are the possible complications?
Clasp: retention
Rest seat: support
Major connector
Flange
Saddle
Design
Given: an upper mirror shot showing a denture made in China no clasps or rest seats, some crowns are present.
c. Draw a preliminary design for the patient
d. What is the problem with the insertion of this denture?
- Esthetic: cant utilize the full labial flange if POI is a zero degree tilt
- Tendency to rotate in function
- Rotation resisted by clasps and rests as near to and as far away from the saddle as possible
- Difficulty in selecting the path of insertion.
- Zero tilt surveying: esthetic is compromised, dead spaces of abutment, flange cannot be used
- Posterior tilt: mechanical. DB undercut and complicated design, esthetic, clasp points backwards
- Path of insertion: from before backwards –> flange placed to labial undercut –> minimize unsightly dead spaces on the mesial of abutment teeth
Given: an upper mirror shot showing a denture made in China no clasps or rest seats, some crowns are present.
e. How would you select the prosthetic tooth?
- OR (Formative, 2011)
5 Radiographic findings from panoramic radiograph (5 marks)
a. Preliminary design for RPD (3 marks)
b. Define the term ‘support’. What components in your design contribute to support? (3
marks)
Resistance to movement of prosthesis directed towards the mucosa / edentulous ridge
Rest, saddle, major connectors like maxillary plate, lingual plate
d. What is the rationale behind for raising or lowering survey line?
- Raising
- Allow retentive clasp’s rigid part placed above survey line and retentive one third placed below survey line without sinking into gingivae and cause trauma
- Allow reciprocal arm place in correct position that has similar displacing distance with retentive arm (also can be achieved by lowering survey line)
- Lowering
- Prevent occlusal interference
- Prevent deformation of clasp as clasp is prevented from moving down the tooth by contacting occlusal surface
Perio Given I/O photos of upper occlusal, lower occlusal and frontal view. 22 pontic, 23 abutment.
Upper missing 16 or 18?
And missing 26. Lower missing 35-38, 45-48. Spacing for lower incisors and gingival recession
a. Classification for lower RPD based on 1. Number of edentulous spans 2. What type of support (2)
Class I bilateral free end saddle, 2 edentulous spans, tooth and mucosal support
Perio Given I/O photos of upper occlusal, lower occlusal and frontal view. 22 pontic, 23 abutment.
Upper missing 16 or 18?
And missing 26. Lower missing 35-38, 45-48. Spacing for lower incisors and gingival recession
b. Describe ways to minimize rotation of free end saddle towards the mucosa (3)
Altered cast technique
Smaller / narrower occlusal table
Full base extension to full functional depth of sulcus, cover pear-shaped pad, reach retromyolohyoid area
Perio Given I/O photos of upper occlusal, lower occlusal and frontal view. 22 pontic, 23 abutment.
Upper missing 16 or 18?
And missing 26. Lower missing 35-38, 45-48. Spacing for lower incisors and gingival recession
c. Describe the movements of the components in RPI during occlusal loading (3)
Mesial rest: unchanged
Proximal plate: downward
I-Bar: mesial buccal
Information given: A faulty RPD Design of upper arch of replacement of 21,22,23
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
a. What is the Kennedy Classification? (1)
Class III
Information given: A faulty RPD Design of upper arch of replacement of 21,22,23
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
b. Critically assess the RPD. (4)
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
Information given: A faulty RPD Design of upper arch of replacement of 21,22,23
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
c. Draw your preliminary design. (3)
Information given: A faulty RPD Design of upper arch of replacement of 21,22,23
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
d. What are the concerns of selection of path of insertion in this case? (5)
Information given: A faulty RPD Design of upper arch of replacement of 21,22,23
Discrepancy: Major connector: lingual bar
Retention: only recriprocal arm present on 17 and 27. No clasp. Support: absence of rest seat to support saddle.
Indirect retention (cingulum rest on 23 and molars) not properly positioned.
e. What are the function of Rest seats? (3)
Indirect retention
Protect interproximal interface between saddle and abutment
Support
Maintain components in correct position
Prevent overeruption
Distribution of horizontal forces
- Clinical photo presented the lower occlusal view. Missing 36,37,38,46. Mesially tilted 47. Big DO amalgam on 45. (Summative, 2014)
a. Draw the preliminary design of the RPD (5)
- Clinical photo presented the lower occlusal view. Missing 36,37,38,46. Mesially tilted 47. Big DO amalgam on 45. (Summative, 2014)
b. What are the associated anatomical landmarks in the free-end saddle? (6)
Posteriorly: pear-shaped pad, which is the most distal keratinized mucosa but not extend retromolar pad
Buccally: full functional depth of buccal sulcus and extent to buccal shelf, which is the primary denture
bearing area
Lingually: full function depth of lingual sulcus and extent to retromyolohyoid area to achieve stability
- Clinical photo presented the lower occlusal view. Missing 36,37,38,46. Mesially tilted 47. Big DO amalgam on 45. (Summative, 2014)
c. What are the assessment for the potential abutment teeth? (6)
Endodontic status (Vital / root-filled)
Periodontal status (no mobility or advanced recession, bone loss not exceed one-third of total length of roots)
Restoration status (quality and quantity)
Crown root ratio
Crown angulation, inclination
Opposing teeth
Morphology, number, divergence of root
- Clinical photo presented the lower occlusal view. Missing 36,37,38,46. Mesially tilted 47. Big DO amalgam on 45. (Summative, 2014)
d. Assess the 45 and 47 for the difficulties as being the abutment teeth (4)
45: Weakness of marginal ridge of amalgam restoration for rest seat, restoration easy to be fracture off due to repeated lateral force and low resistance of restoration, removal of amalgam may expose pulp and need RCT, while endo-treated tooth is much more weak and tend to fracture
47: Tilted molar present with high unfavorable survey line can cause occlusal interference, deformation of clasp
