Free AGD Operative and Restorative Dentistry Questions and Answers — Questions and Answers
Question 1: A dentist prepares a conservative, deep Class I occlusal cavity on a mandibular molar for a composite restoration. What is the primary clinical challenge associated with the high configuration factor (C-Factor) of this preparation?
- Difficulty achieving adequate light polymerization at the pulpal floor.
- Increased polymerization shrinkage stress on the bonded interfaces. (Correct answer)
- Poor wetting of the cavity walls by the adhesive agent.
- Inability to create a well-defined hybrid layer in the deep dentin.
Correct answer: Increased polymerization shrinkage stress on the bonded interfaces.
The C-Factor is the ratio of bonded to unbonded surfaces of a restoration. A Class I preparation has a high C-Factor (typically ~5) because there are five bonded surfaces (mesial, distal, buccal, lingual, pulpal) and only one unbonded surface (occlusal). This high ratio restricts the resin's ability to flow and relieve stress during polymerization, leading to significant shrinkage stress being placed on the adhesive bonds, which can cause debonding, marginal gaps, and post-operative sensitivity.
Question 2: A patient presents with a deep carious lesion on tooth #14, approaching the pulp. After caries excavation, you decide to place a liner before the final composite restoration. Which of the following is a primary advantage of using a resin-modified glass ionomer (RMGI) for this purpose?
- It provides the highest immediate bond strength to dentin compared to any other material.
- It has a coefficient of thermal expansion identical to that of composite resin.
- It is completely insoluble and resistant to acid degradation from microleakage.
- It provides sustained fluoride release and forms a true chemical bond to the tooth structure. (Correct answer)
Correct answer: It provides sustained fluoride release and forms a true chemical bond to the tooth structure.
Resin-modified glass ionomers combine the best properties of glass ionomers and resins. Their key advantages as a liner or base include the sustained release of fluoride ions, which has a caries-inhibitory effect, and their ability to form an ionic (chemical) bond to the calcium in hydroxyapatite, in addition to the micromechanical bond from the resin component. This provides a superior seal and biocompatibility in deep preparations.
Question 3: When preparing a maxillary molar for a lithium disilicate ceramic onlay that will cover two cusps, which of the following preparation features is most critical for ensuring the long-term fracture resistance of the restoration?
- Axial walls with a minimal taper of 2-4 degrees.
- A sharp, well-defined gingival bevel.
- Broad, rounded internal line angles and adequate occlusal thickness. (Correct answer)
- A deep retentive groove placed at the axio-pulpal line angle.
Correct answer: Broad, rounded internal line angles and adequate occlusal thickness.
Ceramic materials like lithium disilicate are strong under compression but brittle and susceptible to fracture under tension. Sharp internal line angles act as stress concentration points, increasing the risk of fracture. Therefore, all internal line angles must be broadly rounded to distribute occlusal forces evenly throughout the material. Furthermore, adequate occlusal thickness (typically 1.5-2.0mm) is required to provide sufficient bulk for the material to resist functional forces.
Question 4: During the application of a total-etch (etch-and-rinse) adhesive system, what is the most significant negative consequence of aggressively air-drying the dentin after the acid-etching and rinsing step?
- It prevents the complete removal of the smear layer.
- It hyper-mineralizes the dentin surface, inhibiting resin infiltration.
- It increases the risk of post-operative thermal sensitivity due to open tubules.
- It causes the collapse of the exposed collagen fibril network, preventing hybrid layer formation. (Correct answer)
Correct answer: It causes the collapse of the exposed collagen fibril network, preventing hybrid layer formation.
In a total-etch system, phosphoric acid removes the smear layer and demineralizes the superficial dentin, exposing a network of collagen fibrils. This network must be kept hydrated and 'fluffed up' to allow the hydrophilic primer and adhesive resin to penetrate it effectively, creating the micromechanical lock known as the hybrid layer. Over-drying desiccates these fibrils, causing them to collapse into a dense mat that blocks resin infiltration, resulting in a poor seal and significantly reduced bond strength.
Question 5: Which of the following is the primary mechanism by which Silver Diamine Fluoride (SDF) arrests active carious lesions?
- Stimulating the odontoblasts to form reparative tertiary dentin.
- Forming a silver-protein conjugate that is resistant to acid and enzymatic degradation. (Correct answer)
- Creating a hypermineralized layer of fluorapatite that is 10 times harder than hydroxyapatite.
- Physically sealing the dentinal tubules with a glass-like material.
Correct answer: Forming a silver-protein conjugate that is resistant to acid and enzymatic degradation.
The primary arresting mechanism of SDF involves the silver ions. The silver is strongly antimicrobial, killing cariogenic bacteria. Furthermore, it reacts with proteins in the dentin organic matrix and bacterial debris to form a dense, dark silver-protein conjugate. This layer is highly resistant to both acid demineralization and enzymatic breakdown by bacterial collagenases, effectively halting the caries process. The fluoride component contributes to remineralization, but the silver's effect is key to the arrestment.
Question 6: A patient calls your office one week after you placed a moderately deep Class II MO composite on tooth #29. They report a sharp, brief pain only when they chew on something hard in that area. The pain disappears immediately upon release. The occlusion was checked and feels fine. What is the most probable cause?
- An air bubble trapped within the bulk of the composite material.
- A small marginal gap or void at the gingival floor of the preparation. (Correct answer)
- A premature contact on the marginal ridge in lateral excursive movements.
- A delayed hypersensitivity reaction to the BIS-GMA resin.
Correct answer: A small marginal gap or void at the gingival floor of the preparation.
The symptoms described—sharp pain on biting that disappears on release—are classic signs of a marginal defect or micro-gap, often at the gingival floor of a Class II box. When pressure is applied, fluid in the gap is forced into the dentinal tubules, stimulating the nerve via the hydrodynamic theory of pain. Upon release, the fluid moves back, sometimes causing another sharp sensation. This is often a result of polymerization shrinkage stress overcoming the adhesive bond in a high C-Factor area like the proximal box.
Free AGD Operative and Restorative Dentistry Questions and Answers
A dentist prepares a conservative, deep Class I occlusal cavity on a mandibular molar for a composite restoration.
What is the primary clinical challenge associated with the high configuration factor (C-Factor) of this preparation?