Removable sos

Question 1

Partial Denture Prosthodontics
Clinical and laboratory stages

Answer 1

1. Primary impressions
2. Fabrication of study casts (diagnostic casts)
3. Fabrication of wax bases and occlusal rims
4. Preliminary jaw relationship registration
5. Mounting primary casts on articulator
6. Surveying primary casts
7. RPD design
8. Fabrication of custom impression trays
9. Tooth preparations
10. Secondary impressions
11. Fabrication of secondary casts (working casts)
12. Metal framework fabrication
13. Metal framework trial insertion
14. Definitive jaw relationship registration
15. Mounting secondary casts on articulator
16. Selection of tooth mould & shade
17. Tooth setup
18. Trial insertion
19. Processing and finishing of the RPD
20. Placement

Question 2

Required information
For RPDs:

Answer 2

1. Case identifier
2. Type of prosthesis
3. Teeth to be replaced
4. All components of RPD design
5. Material(s)
6. Tooth mould (where relevant) and shade
7. Every little detail of the design that will drive you mad if it turns up in any way different to what you had in mind!!!
8. Treatment stage
9. Confirmation of disinfection
10. Date (and time) work is required

Question 3

Briefly explain the steps you would follow to reach a differential diagnosis when a complete denture patient using their current set of dentures for 6 months complains they are unable to use these dentures and wish to have a new set.

Answer 3

1. Patient interview: listen carefully to the patient’s complain and understand exactly what type the patient’s complain refers to, by asking the right questions
2. Examine the patient extra orally and intra orally with and without the existing dentures in situ
3. Examine the existing dentures out of the mouth
4. Correlate what the patient reports to what is observed clinically. If what the patient reports cannot be correlated to what is observed clinically, the most likely cause is that you have missed something important (therefore return to questioning the patient or repeat the clinical examination) or that the patient has unrealistically high expectations

Question 4

Replacing existing complete dentures

Treatment options: previous dentures were not successful

If no problem can be identified, the options are:

Answer 4

Treatment options: previous dentures were not successful

If no problem can be identified, the options are:

1. repeat the interview and clinical examination
2. do nothing
3. refer to specialist (not an option if you are the specialist!)
4. consider implant treatment
5. palliative care and/or psychological support

Question 5

Replacing existing complete dentures

Treatment options: previous dentures were not successful

If the problem is diagnosed, the options are:

Answer 5

Treatment options: previous dentures were not successful

First, diagnose the problem:

• listen to the patient
• ask the right questions
• correlate the nature and magnitude of the problem to what is observed clinically

If the problem is diagnosed, the options are:

1. repair or modification to confirm the diagnosis or as main treatment
2. new CDs, aiming to address the problem
3. consider implant prosthodontics

Question 6

Replacing existing complete dentures

Replacing existing complete dentures
Treatment options: previous dentures were successful

Answer 6

Treatment options: previous dentures were successful

1. Do nothing
2. Repair or modify existing dentures
3. New CDs
4. Copy dentures

Question 7

RPD design step by step

Answer 7

1. Select path of insertion and survey cast
2. Mark teeth to be replaced
3. Indicate positions and depth of undercuts
4. Plan support (rests / saddles)
5. Plan retention (direct retainers)
6. Plan stability (bracing arms)
7. Join all components with the simplest major connector possible
8. Assess the design for indirect retention
9. Verify undercuts and modify the direct retainers if needed
10. Review overall design and modify if needed

Question 8

Tooth preparations:

Answer 8

• GUIDE PLANE PREPARATIONS

1. The required height of the guide plane is 3mm
2. Aim to remove less than 0.5mm of enamel
3. Guide planes also serve for reciprocation
4. The intended function of the guide plane determines the location of the preparation on the abutment tooth

• IMPROVING SURVEY LINES
• CREATING SPACE FOR MINOR CONNECTORS
• REST SEAT PREPARATIONS

Posterior tooth rest seat preparations: occlusal rests on premolar and molar teeth

1. minimum of 1mm reduction and taper into the adjacent fossa
2. there is no need to extend the rest seat beyond 1/3rd of the medio-distal width of the tooth

• CREATING RETENTIVE UNDERCUTS-> addition of composite resin

Question 9

Rests should always be placed in specifically designed and prepared rest seats onto the teeth, for the following reasons:

Answer 9

1. to achieve the most favourable distribution of the occlusal forces: as close as possible to the centre of rotation of the abutment tooth and down the long axis of the tooth
2. to avoid horizontal component forces being applied on anterior abutment teeth due to the inclined plane action
3. to avoid occlusal interferences
4. to avoid food trapping

Question 10

Complete Denture Prosthodontics
Clinical and laboratory stages

Answer 10

1. Primary impressions
2. Study cast fabrication
3. Custom tray fabrication
4. Secondary impressions
5. Working cast fabrication
6. Fabrication of record bases and wax occlusion rims
7. Jaw relationship registration
8. Mounting working casts on articulator
9. Artificial tooth setup
10. Trial insertion
11. Processing and finishing
12. Placement and check record
13. Review (and check record)

Question 11

Preference is for permanent, heat polymerised PMMA bases; clinical benefits far outweigh risk of processing deformation during second processing cycle if the materials are handled according to manufacturers’ instructions.

Clinical benefits are:

Answer 11

1. all adjustments are carried out on the permanent base at an early stage of denture construction
2. retention**, **support** and **stability** can be **assessed early on, not at the placement appointment; if lacking, there is time to make corrections before the dentures are finished
3. retentive** and **well supported bases render the jaw relationship registration (which is arguably the most critical stage) much easier and thus likely to be more accurate; same is true for the trial insertion
4. at placement the denture base and borders will hardly need any adjustment and there should be no issues relating to retention, support and stability, therefore the student may focus on the occlusion (as they should) and hygiene instructions
5. excessive trimming of the base and borders at the placement appointment can be avoided, so the patient receives a well-polished denture and does not have to endure the soul- crushing experience of witnessing a student trimming their brand new shiny denture for 2 hours

Question 12

Disadvantages of using permanent bases:

Answer 12

• extra work for the laboratory and (small) extra cost
• risk of denture base deformation occurring during the 2nd processing cycle resulting in gapping at the posterior palatal border of the maxillary denture only if the materials are mishandled and techniques are abused. Modern materials used with care will only present minimal deformation – gap has been measured to 50-100 microns at the posterior palatal border; this is negligible and has no clinical impact whatsoever on a mucosa borne prosthesis.

Question 13

Fabricate wax occlusal rims: laboratory stage
Laboratory instructions

Answer 13

Maxilla:

• labially, the wax rim should extend 7-8mm anterior to centre of incisive papilla;
• posteriorly follow the crest of the ridge and slightly buccally in the molar region (depending on degree and pattern of resorption).
• Should not extend distally beyond the second molar.
• Height of 10mm anteriorly sloping down posteriorly to about 0.8mm.
• Width of 8-10mm in the molars, 5-7mm in the premolars and 3-4mm in the incisors.
• Mandible: on the crest of the ridge, and/or slightly anterior to the crest in the anterior region, depending on degree of resorption; extending only up to 2nd molar distally, where the ridge starts to slope up towards the retromolar pad; only as high as 2/3rds of the retromolar pad posteriorly, sloping up to about 8-10mm anteriorly; width same as in the maxilla.

Question 14

Describe how you would handle an alginate impression from the moment it is removed from the patient’s mouth until it is ready to be sent to the dental laboratory. Make sure to mention both actions you must do as well as actions to avoid

Answer 14

1. Avoid leaving the impression drying on the bench for any length of time
2. Avoid leaving the impression to rest on its tissue surface for any length of time
3. Rinse the impression with cold tap water upon removal from the mouth to remove any visible contamination
4. Visually inspect and evaluate the impression
5. Disinfect the impression by spray disinfectant or by immersion.in disinfectant for no longer than 10 minutes
6. Rinse the impression again with cold tap water
7. Wrap the impression in damp tissue making sure no parts of the impression are compressed during wrapping
8. Package the impression in airtight plastic bag making sure there is no excess water in the bag

Question 15

There are several reasons why IDs cannot be considered a predictable treatment option:

Answer 15

1. Impression procedures employed in the construction of IDs are suboptimal
2. Jaw relationship registration (JRR) may be incorrect due to the condition of the remaining teeth
3. The trial insertion is carried out with an incomplete pattern of the final prosthesis
4. Presence of deep soft tissue undercuts is common
5. IDs are placed while the patient is under the effect of local anaesthesia
6. IDs are placed on a compromised foundation
7. The accuracy of fit of an ID begins to deteriorate from the moment it is first inserted
8. IDs are often placed in patients who have not had the time to come to terms with their edentulous state
9. IDs may be one’s first denture wearing experience and also the most negative one

Question 16

Component parts of RPDs: major and minor connectors, rests and rest seats:

Maxilla

Basic Design Requirements:

Answer 16

1. Rigidity
2. Free gingival margin (FGM) 6mm-> Because of blood supply or deep vascularity of the gingival crevice
3. Parallel and 90°
4. Auxiliary role in indirect retention
5. Round boarders
6. Crossing midline at 90°<=> least possible contact with the soft tissue

Question 17

Types of maxillary major connectors:

Answer 17

Single palatal bar or anterior and posterior palatal bars:

• if <8mm wide
• Bilateral edentulous spaces of short span which is entirely tooth-supported

Single Palatal Strap:

• 8 mm wide
• Bilateral edentulous spaces of short span in a tooth- supported restoration.

Anterior and posterior palatal strap:

• (8 to 10 mm) anterior and posterior palatal straps.
• Lateral palatal straps (7 to 9 mm) narrow and parallel to curve of arch;
• minimum of 6 mm from gingival crevices of remaining teeth.
• Anterior palatal strap-> never closer than 6 mm to lingual gingival crevices
• Posterior palatal connector-> posterior border located at junction of hard and soft palates and at right angles to median palatal suture and extended to hamular notch area(s) on distal extension side(s).

Complete Palatal Plate:

• covering more than half of the palate
• Posterior border-> terminates at the junction of the hard and soft palates; extended to hamular notch area(s) on distal extension side(s); at a right angle to median suture line.

U-shaped connector:

• only in those situations in which inoperable tori extend to the posterior limit of the hard palate.
• lacks the rigidity of other types of connectors.
• Anterior border areas-> at least 6 mm away from adjacent teeth

Question 18

Types of Mandibular Major Connectors:

Answer 18

Lingual bar:

• first choice
• minimum of 7-8mm height between lingual sulcus (when floor of
  the mouth is raised) and gingival margins
• 3-4mm clearance to gingival margins for hygiene + 4mm bar height

Lingual plate:

• when there is less than 8mm from gingival margins to the floor of the mouth
• not extend above the middle third of the teeth

Sublingual bar:

• when there is less than 8mm from gingival margins to the floor of the mouth
• when there is a soft tissue undercut which would require
  considerable blocking out if a lingual bar was to be used

Continuous bar +/- lingual bar:

• when the alignment of the anterior teeth would necessitate excessive blocking out of interproximal undercuts
• when there is a need for indirect retention but prefer to avoid lingual
  plate