MDS PREP
The most reproducible relation of the jaws that is used in fixed denture construction
1) Centric occlusion
2) Centric relation
3) Protrusive contact position
4) Lateral contact position
Prosthodontics
Answer: 2
The most reproducible relation of the jaws that is used in fixed denture
construction is Centric Relation (CR). Here's a detailed explanation of the
options provided and why Centric Relation is the correct answer:
1) Centric Occlusion (CO): This is the position of the mandible where the
incisor and posterior teeth of the maxilla and mandible are in maximum
intercuspation, meaning the teeth are in their most closed and stable contact.
It is the position that occurs when the condyles are in the most superior and
anterior position in the glenoid fossae of the temporal bones. While important
for the function of the teeth, centric occlusion is not always a reliable
reference for the construction of a fixed denture, as it can be influenced by
various factors such as tooth wear, pathology, or parafunctional habits.
Moreover, it is a dynamic relationship that can change over time.
2) Centric Relation (CR): Centric relation is the most retruded, unstrained
position of the mandible on the maxilla from which the mandible can move to the
lateral and protrusive positions. It is the basis for the articulators in
dentistry and is considered the most reproducible jaw relationship for the
fabrication of fixed dentures. CR is determined by the temporomandibular joint
(TMJ) and does not involve tooth contact. This is crucial because it provides a
consistent and predictable starting point for constructing a denture that will
function harmoniously with the TMJ and the surrounding soft tissues. It is the
position where the condyles are in a centric relation with the fossa and the
disk is properly situated, which minimizes strain and maximizes stability during
function.
3) Protrusive Contact Position: This is the position of the mandible where the
incisor or canine teeth make contact with the maxilla in a forward and downward
movement. While it is a functional movement of the jaw, it is not a stable or
reproducible position for the construction of fixed dentures because it is
highly dependent on the muscles and may not be consistent across different
individuals or even during different occasions for the same individual.
4) Lateral Contact Position: This refers to the position of the mandible during
lateral movements, where the teeth contact the maxilla on the side of the arch.
Similar to protrusive contact, it is a functional position that is influenced by
muscle activity and not a stable reference for denture construction. Lateral
movements are also not the primary focus in fixed denture construction, which is
mainly concerned with the vertical and anteroposterior relationships of the
jaws.
What is the purpose of using undercut gauges in dental surveying?
1) To identify the amount of retentive undercut
2) To measure the size of the cast
3) To contour wax patterns
4) To clean the surveyor
Prosthodontics
Answer: 1
Undercut gauges are specifically designed to measure the amount of retentive undercut available on the cast.
Posterior palatal seal is recorded when the head is bent at
1. 30 degree
2. 150 degree
3. 60 degree
4. 45 degree
Prosthodontics
Answer: 1
Posterior palatal seal is recorded when the head is bent at 30 degrees.
Porosity occuring in the bulky portions of the heat-cured acrylic complete dentures is due to
1) Insufficient pressure application during packing
2) Time lag between packing and curing
3) Directly placing the packed resin in water at 100 degree
4) Using a fluid pour technique
Prosthodontics
Answer: 3
Porosity in heat-cured acrylic dentures can occur due to several factors, but the most significant cause in this context is the direct placement of the packed resin in water at high temperatures (100 degrees Celsius). When the packed resin is subjected to such conditions, it can lead to rapid polymerization and the formation of bubbles or voids within the material, resulting in porosity. This is because the heat causes the monomer to vaporize, and if the vapor cannot escape, it leads to trapped air pockets.
The direction of the resorption of the maxillary ridge
1. Downwards and buccally
2. Upwards and lingually
3. Downwards and lingually
4. Upwards and buccally
Prosthodontics
Answer: 2
The direction of the resorption of the maxillary ridge is upwards and lingually.
Penumbra in a processed film is related to
1. Magnification
2. Sharpness of image
3. Detail of the image
4. All of the above
Prosthodontics
Answer: 4
Penumbra in a processed film is related to all of the above: magnification, sharpness of image, detail of the image.
Which of the following is least likely to occur when record bases are formed
from self-curing resins, on the master
cast of an edentulous patient without blocking out the undercuts ?
1 The borders will not be accurately reproduced
2 Record bases will exhibit instability in the patients mouth
3 The casts may be abraded when removing the record bases
4 Record bases may break when removing from the casts
Prosthodontics
Answer: 1
Explanation: When record bases are formed from self-curing
resins without blocking out undercuts, the most likely issues are instability in
the mouth, abrasion of the casts, and potential breakage of the record bases
upon removal. However, the borders of the record bases are typically
well-defined and can be accurately reproduced even if undercuts are not blocked
out. Therefore, option 1 is the least likely occurrence.
The following aslo serves in guiding path of insertion and path of removal along with guiding planes
1) Minor connector
2) Occlusal rest
3) Major connector
4) Clasps
Prosthodontics
Answer: 1
While guiding planes are the primary elements that dictate the path of insertion and removal, the minor connector also plays a role. The minor connector helps in the overall stability and retention of the RPD by linking the major connector to the abutment tooth and distributing the forces more evenly across the denture base. However, its primary function is not to guide the path of insertion and removal as much as it is to provide additional support and strength to the RPD.