Prosthodontics Flashcards
What is torus palatine? (1.5)
A harmless bony growth on the middle of the roof of the hard palate. Can vary in size
What is the prosthetic significance of torus palatine? (1)
Can’t use palatal strap for maxillary RPD – need to remove by surgery or use other type of strap.
What is the management of torus palatine? (1.5)
Surgery to remove; leave it; make sure the RPD doesn’t touch that area
How do you assess teeth used as denture abutment?
- Endodontic status (Vital / root-filled)
- Periodontal status (no mobility or advanced recession, bone loss < 1/3 of total length of roots)
- Restoration status (quality and quantity) (structural integrity, remaining sound tooth structure)
- Crown root ratio
- Crown angulation, inclination
- Opposing teeth
- Morphology, number, divergence of root
What is reciprocation? (2)
The mechanism by which lateral forces generated by a retentive clasp passing over a height of contour are counterbalanced by a reciprocal clasp passing along a reciprocal guiding plane (reciprocating element may be: retentive arm of clasp; lingual plating; combination of mesial and distal minor connectors) (like (2); remember reciprocation when displaced occlusally; bracing when denture is fully seated)
What is the function of resurveying the master cast? (1)
To know the final path of placement, the location of retentive areas, and the location of remaining interference. (The master cast has tooth preparation on it!)
Compare between base line and tripod in surveying (3marks)
Both are used to record the degree of tilt of the cast. The base line is recording three lines on the sides of the cast; the tripod is marking three points on the teeth at the same horizontal plane at a specific degree of tilt (easier to transfer to another cast?)
Why are two colours of articulating paper used when checking the fitting and occlusion of RPD? (1)
Static occlusion; dynamic occlusion (during horizontal excursion)
Compare and contrast lingual bar and lingual plate (4)
No answer
Critically assess the existing denture.
- Retention / support / stability / occlusion / aesthetics / OH
- Defective components: tooth wear / fracture of clasp / missing tooth / crack
Outline labstages for Co-Cr framework fabrication after the stage of master cast surveying
- Block out unwanted undercut on the master cast after designing the outline
- Place spacer for acrylic retention mesh
- Duplication of master cast for refractory model and another duplicated model (use agar x2)
Impression material
Refractory material (phosphate bonded investment)
Strengthen refractory model by drying at 200 degree for 45 mins and soaking in beeswax at 140 degree for 15 s
- Outline design on refractory model and make wax pattern
- Sprueing attached to wax pattern
- Apply detergent on wax surface (to avoid bubbles being trapped)
- Embedding the cast in casting ring and ring liner
- Pour phosphate bonded investment
- Wax burnout at 900 - 1000 degree (also allow expansion to compensate metal cooling contraction)
- Co-Cr is melted by electromagnetic induction (in a centrifuge via centripetal force (directed to center)) or by flame at “reducing zone” and moulded to the cast
- Cooling → remove investment → sandblast with Al2O3 → remove sprueing → electrolytic polish
- Wrought wire clasps may be soldered
- Check fitting and occlusal dimension on duplicated model (not master cast)
- Final polishing –> delivery
Upon framework try-in, an occlusal interference was found on a rest seat, but the rest seat is very thin already. What could have caused this?
- Insufficient tooth preparation
- Impression errors
- Technical and processing errors during framework fabrication
What are the problems associated with design of removable partial denture with free-end saddle? (5)
Inadequate retention Uneven support Insufficient stability Oral discomfort Damage to support tissue
Explain why inadequate retention is associated with design of removable partial denture with free-end saddle?
Absence of most distal abutment
Only rely on muscular control and mucosal coverage
Though indirect retention can resist rotational movement, its effectiveness is highly depends on the distance between rest and axis of rotation / saddle (poor if in extreme SDA case)
Explain why Uneven support is associated with design of removable partial denture with free-end saddle?
Support is derived from remaining teeth and mucosa covering posterior edentulous saddles
Mucosa itself may not be uniform in its thickness and displaceability all over the residual ridge
(Cause: impression can’t record anatomical form of teeth and physiologic form of soft tissue simultansously → that’s why the need for altered cast technique
Explain why Insufficient stability is associated with design of removable partial denture with free-end saddle?
Poor support and direction retention
Absence of most distal abtument for retentive clasp placement
In case with resorbed ridge, resistance to lateral and horizontal force is reduced
Explain why Oral discomfort is associated with design of removable partial denture with free-end saddle?
Factors include fragile or resorbed underlying ridge, uneven support, inadequate retention and stability
Explain why Damage to support tissue is associated with design of removable partial denture with free-end saddle?
Abutment teeth may be subjected to torque forces coming from the clasps and aggravated by rotational movement of denture base
Resorption of underlying ridge without relining can further exert damaging torque forces and in turns periodontal destruction of abutment
Poor support and stability may accelerate ridge resorption and induce tissue inflammation
What are the concerns of selection of path of insertion in this case (Kennedy Class IV)? (5)
- Zero tilt surveying
Dead spaces found on anterior edentulous space, flange can’t be used
More retentive as MB undercut present (No need to build undercut with composite)
Simpler to do
- Posterior tilt
Eliminate dead spaces anteriorly, and saddle / flange can make better contact to abutment tooth in better appearance
When labial flange is used, bony undercut is avoided as insertion of denture is not along a path a right angle to occlusal plane
Insufficient MB undercut, but can build with composite
What are the advantages of posterior tilt?
- Remove anterior dead space, mesial to the abutment teeth
* Avoid soft tissue undercut for a full labial denture flange
What are the disadvantages of posterior tilt?
Undercuts appear on DB of posterior teeth
• Poor aesthetics (Thicker 2/3 retentive arm on mesial side which is more visible)
• Complicated design as the undercut is on DB
Image available on doc p72
What is the purpose of aesthetic try-in? (1)
- Check aesthetic with patients
- Assist framework fabrication (facilitate position of retention, strengthening pin, metal backing)
- Production of silicone index for teeth set up
What is the thickness of “shimstock”? (1)
- 12 micron
The aesthetic try-in was fit to the patient’s mouth. However, at the delivery, there is 3 mm occlusal discrepancy found on the master cast. What will be your advice to the laboratory? (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
