Free AGD Fixed and Removable Prosthodontics Questions and Answers — Questions and Answers
Question 1: Which of the following features of a full coverage crown preparation is most influential in providing resistance to dislodgement from tipping forces directed obliquely to the path of insertion?
- Occlusal reduction providing 2mm of clearance.
- A heavy chamfer margin of 1.2mm.
- Axial wall height of 4mm or greater. (Correct answer)
- A total occlusal convergence of 6 degrees.
Correct answer: Axial wall height of 4mm or greater.
Resistance form prevents the dislodgement of a crown by forces directed apically or obliquely. The height of the axial walls is the most critical factor; taller walls create a smaller arc of rotation, thus preventing the crown from tipping off. [7, 10, 15] While minimal taper (convergence) is important for both retention and resistance, a preparation with tall walls can resist tipping forces even with a slightly greater taper more effectively than a short preparation with ideal taper. [14, 15] Occlusal reduction and margin design are critical for other aspects (material thickness and marginal seal, respectively) but have less impact on resistance form.
Question 2: A patient presents for a new mandibular removable partial denture (RPD) to replace teeth #19 and #30. The most posterior teeth in the arch are now #21 and #28. This is a Kennedy Class I situation. What is the primary function of placing rests on the mesial-occlusal surface of tooth #22 and the distal-occlusal surface of tooth #27?
- To provide reciprocation for the direct retainers.
- To provide indirect retention against lifting of the distal extensions. (Correct answer)
- To act as the primary vertical stops for the prosthesis.
- To guide the path of insertion and removal of the RPD.
Correct answer: To provide indirect retention against lifting of the distal extensions.
In a Kennedy Class I RPD, the fulcrum line passes through the most distal rests, in this case on teeth #21 and #28. When sticky foods or other forces lift the posterior denture bases, the prosthesis rotates around this fulcrum line. Rests placed anterior to the fulcrum line, such as on the canines or premolars (#22 and #27), act as indirect retainers to counteract this rotational movement and prevent the denture from lifting away from the tissues. [6, 20] While all rests provide some vertical support, the primary function of these specific rests is indirect retention. [4, 20]
Question 3: When designing a pontic for a fixed partial denture in the maxillary anterior region where esthetics and hygiene are both high priorities, which pontic design is generally considered the most appropriate choice?
- Sanitary (Hygienic)
- Saddle (Ridge-Lap)
- Ovate
- Modified Ridge-Lap (Correct answer)
Correct answer: Modified Ridge-Lap
The modified ridge-lap pontic is widely used because it provides excellent esthetics by lapping the facial aspect of the ridge while having a convex, cleansable tissue surface that allows for easy cleaning with dental floss. [8, 9] The saddle/ridge-lap pontic has a large, concave contact with the ridge, making it unhygienic. [8] The sanitary pontic is hygienic but highly unaesthetic. The ovate pontic offers superior esthetics but typically requires surgical site preparation to be ideal and can be more difficult for some patients to clean. [9, 13, 17]
Question 4: A patient with new complete dentures complains that their teeth make a distinct 'clicking' sound when they are speaking. This clinical finding is most commonly associated with which of the following errors?
- Incorrect centric relation record.
- Excessive vertical dimension of occlusion (VDO). (Correct answer)
- Use of acrylic teeth instead of porcelain teeth.
- Inadequate posterior palatal seal.
Correct answer: Excessive vertical dimension of occlusion (VDO).
When the vertical dimension of occlusion (VDO) is excessive, there is insufficient interocclusal rest space, also known as 'freeway space'. [19, 22] This lack of space causes the maxillary and mandibular teeth to contact prematurely and 'click' during speech, particularly during the production of sibilant sounds like 's'. [19, 23] An inadequate posterior palatal seal would affect retention, and an incorrect centric relation would cause occlusal interferences during chewing, but clicking during speech is the classic sign of excessive VDO. [29, 30]
Question 5: Which of the following luting agents provides its strongest and most durable bond to tooth structure primarily through micromechanical interlocking after acid etching and requires a multi-step application protocol?
- Adhesive Resin Cement (Correct answer)
- Resin-Modified Glass Ionomer (RMGI) Cement
- Zinc Phosphate Cement
- Polycarboxylate Cement
Correct answer: Adhesive Resin Cement
Adhesive resin cements achieve high bond strengths by creating a micromechanical interlock with the tooth surface. This is accomplished by acid etching the enamel and dentin to create microporosities, followed by the application of a primer and/or bonding agent that flows into these spaces and is then polymerized. The cement then bonds to this hybrid layer. [24] In contrast, RMGI and polycarboxylate cements bond via a chemical, acid-base reaction and chelation to calcium, while zinc phosphate has no chemical bond and relies on mechanical friction. [26, 27]
Question 6: A patient requires a Kennedy Class III removable partial denture to replace missing teeth #19 and #20. The design includes a mesial-occlusal rest on tooth #21 and a distal-occlusal rest on tooth #18. What is the primary purpose of these rests?
- To provide indirect retention for the prosthesis.
- To provide reciprocation against the retentive clasps.
- To provide vertical support against occlusal forces. (Correct answer)
- To enhance the esthetics by closing small gaps.
Correct answer: To provide vertical support against occlusal forces.
The primary and most fundamental function of any rest in a removable partial denture is to provide vertical support for the prosthesis. [1, 2, 3] Rests transmit occlusal forces along the long axes of the abutment teeth, preventing the denture from settling into the soft tissues and maintaining the established occlusal relationships. [4, 5] Indirect retention is a concern for extension base RPDs (Class I and II), not for a tooth-supported Class III case. Reciprocation is provided by other components like a reciprocal arm or plating.
Free AGD Fixed and Removable Prosthodontics Questions and Answers
Which of the following features of a full coverage crown preparation is most influential in providing resistance to dislodgement from tipping forces directed obliquely to the path of insertion?