Free NDEB Prosthodontics and Restorative Dentistry Questions and Answers — Questions and Answers
Question 1: A patient presents with a completely edentulous maxilla opposing natural mandibular anterior teeth and a bilateral distal-extension removable partial denture. The patient exhibits significant resorption of the premaxilla, papillary hyperplasia of the palate, and supra-eruption of the mandibular incisors. Which of the following is the most accurate diagnosis for this clinical presentation?
- Combination Syndrome (Correct answer)
- Paget's Disease of Bone
- Fibrous Dysplasia
- Tori Mandibularis Exacerbation
Correct answer: Combination Syndrome
Combination Syndrome, first described by Ellsworth Kelly, presents with a characteristic pattern of signs resulting from the specific occlusal forces generated by an edentulous maxilla opposing natural mandibular anterior teeth. These signs include loss of bone from the anterior maxillary ridge, overgrowth of the maxillary tuberosities, papillary hyperplasia of the hard palate, extrusion of the mandibular anterior teeth, and bone loss under the mandibular partial denture bases.
Question 2: When preparing an endodontically treated molar for a full coverage crown, what is the most critical factor for ensuring long-term resistance to fracture and dislodgement of the restoration?
- Using a fiber post
- Achieving a 2.0 mm ferrule effect (Correct answer)
- Selecting a high-strength ceramic material
- Creating a deep chamfer margin
Correct answer: Achieving a 2.0 mm ferrule effect
The ferrule effect is the 360-degree collar of sound tooth structure that a crown encircles coronal to the margin. A ferrule of 1.5 to 2.0 mm in height is widely considered a critical determinant for the long-term success of restoring an endodontically treated tooth, as it provides resistance to fracture by bracing the tooth against functional lever forces. While post type, material choice, and margin design are important, the presence of an adequate ferrule has the most significant impact on fracture resistance.
Question 3: A clinician is preparing a maxillary first molar for a full gold crown. To ensure adequate retention and resistance form, what is the ideal total occlusal convergence (taper) of the axial walls?
- 0-2 degrees
- 20-25 degrees
- 6-10 degrees (Correct answer)
- 15-20 degrees
Correct answer: 6-10 degrees
While perfectly parallel walls would offer maximum theoretical retention, they are clinically impossible to create without causing undercuts. A total occlusal convergence (the sum of the taper on opposing walls) of 6 to 10 degrees is widely accepted as the clinical ideal. This taper allows for the restoration to seat completely while providing sufficient parallelism to resist dislodgement from functional forces.
Question 4: A patient requires a removable partial denture for a mandibular arch that is missing all teeth posterior to the second premolars on both sides. According to Kennedy's classification, how would this edentulous situation be classified?
- Class II
- Class IV
- Class III
- Class I (Correct answer)
Correct answer: Class I
Kennedy's classification is a system used to categorize partially edentulous arches. A Kennedy Class I describes a situation with bilateral edentulous areas located posterior to the remaining natural teeth. This is the most common classification for free-end or distal-extension cases.
Question 5: Which of the following occlusal schemes is most frequently recommended for complete dentures to enhance stability during parafunctional movements and accommodate patients with resorbed ridges?
- Canine guidance
- Lingualized occlusion (Correct answer)
- Group function
- Anterior guidance
Correct answer: Lingualized occlusion
Lingualized occlusion is an occlusal scheme where the maxillary lingual cusps articulate with the central fossae of the mandibular teeth. This setup centralizes occlusal forces, minimizes tipping forces, and provides bilateral balance, which is highly advantageous for denture stability, especially in patients with significant ridge resorption. Canine guidance and group function are concepts primarily applied to natural dentition and fixed prosthodontics and can create destabilizing forces in complete dentures.
Question 6: When selecting an elastomeric impression material for a multi-unit fixed partial denture, which material offers the best combination of dimensional stability, detail reproduction, and elastic recovery, making it a gold standard for precision?
- Polyvinyl siloxane (PVS) (Correct answer)
- Condensation silicone
- Polysulfide
- Irreversible hydrocolloid
Correct answer: Polyvinyl siloxane (PVS)
Polyvinyl siloxane (PVS) is considered a gold standard for fixed prosthodontics due to its superior properties. It undergoes an addition polymerization reaction with no by-products, leading to excellent dimensional stability. It also has high tear strength and the best elastic recovery of the elastomers, ensuring the impression is not distorted upon removal from the mouth.
