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Past Prosthodontics MCQ Part 4
1.Which of the following is a shrink free ceramic
- Emax
- Dicor
- Dicor MGC
- Cerestore
ANSWER d
DICOR MGC
This is a machinable glass ceramic composed of fluorosilicate mica crystals in a glass matrix. It has greater flexural strength than cast dicor . They have shown to be softer than conventional feldspathic porcelain and produce less abrasive wear of the opposing tooth structure than cerec mark I but causes more wear than cerec markII
Cerestore – 1st commercially available shrink free ceramic
- Shrink-free Ceramics
- CERESTORE system
- The application of an all ceramic crown employing a unique shrink-free alumina substrate with specially formulated porcelain veneers (cerestore system) offers a viable alternative to both the metal ceramic crown and traditional PJC.
- The development of the advanced alumina ceramic substrate allows the construction of highly durable all ceramic restorations with exceptional fit.
- The shrink free- ceramic can be formed directly on the master die, producing extreme accuracy of fit.
- A master die made from a special epoxy resin die materia, which is heat stable and undergoes permanent controlled expansions during curing.
- The ceramic substrate supplied as dense pellet of the compacted shrink free formulation is heated until it is flowable (160oC) and then transferred by pressure into a suitable mold directly on the master die. After it sets, the green substrate is removed from die and sintered/controlled firing is carried out resulting in zero shrinkage of the ceramic
2. Metal oxides used in porcelain
- In improves strength
- To improve bonding with porcelain
- Impart colour
- All the above
ANSWER c
The porcelain is manufactured in a variety of colors that are produced from the addition of metal oxides to create the different colors (shades) that will match the teeth.
Oxides are used in pottery and ceramics for a number of reasons. They can be used as fluxes, glass formers, and colorants. Fluxes lower the temperature at which a ceramic body melts when fired. Some examples of fluxing oxides are lead, sodium or zinc.
3. A patient had to undergo enucleation of the eye- ball and its contents due trauma. Following the surgery the volume of socket appears shrunken and the patient is seeking prosthetic treatment. What type of ocular prosthesis is best suited for this case?
- Buried
- Buried,semi-integrated
- Semi buried, integrated
- Hydroxyapatite implant
ANSWER c
Enucleation with Implants
Implants are inserted within the Tenon's capsule, and the aim is:
- To provide a mobile base for the prosthesis to pivot upon.
- To prevent bony deformity of the orbital wall (i.e. contracted socket) in children.
- To maintain orbital socket in adults.
Types of Implants
- Buried implants
- Non-integrated: It is an acrylic sphere, which is inserted within the Tenon's capsule to maintain shape of the eyeball. The recti muscles are tied in a cruciate manner over the implant.
- Semi-integrated: It has holes or tunnels in which the four recti muscles are tied separately.
- Semi-buried implants (integrated): It is partially buried and partially exposed implant. In its exposed part, the posterior surface of the prosthesis could be exactly fitted. Though it is capable of affording the best movement of the prosthesis, in the majority of the cases, there is infection and extrusion of the implants. It is not used nowadays.
4. A patient was rehabilitated with an extraoral prosthesis. He was satisfied with the esthetics earlier, but now notices discoloration and worn edges after few months of use. Which is the most probable material used to fabricate the prosthesis?
- PVC
- Polyurethane
- Polyethylene
- Silicone
ANSWER b
POLYURETHANE POLYMERS
- Polyurethane can be used in maxillofacial prosthetics.
- Fabrication of a polyurethane prosthesis requires accurate proportioning of three components.
- The material is placed in a stone or metal mold and allowed to polymerize at room temperature.
- Although a polyurethane prosthesis has a natural feel and appearance, it is susceptible to rapid deterioration and fungus growth.
5. Why are maxillary posterior teeth placed buccal to alveolar ridge in complete denture?
- To set teeth in neutral zone
- To balance the cusp-ridges
- To prevent ridge resorption
- To increase buccal corridor
ANSWER c
MAXILLARY ARCH
- The maxillary teeth should be labial and buccal to the residual edentulous ridge if they are to be placed in the neutral zone and occupy the position of their predecessors.
- Bone reduction usually occurs on the labial and buccal areas of the maxillary residual ridge. Consequently, the residual edentulous ridge is usually palatal to the original location of the natural teeth.
- Maxillary posterior teeth are placed buccal to alveolar ridge in complete denture to prevent ridge resorption (option 3), is more appropriate answer than to set teeth in neutral zone (option 1).
