A viva, or oral examination, on the properties of impression materials in dentistry may cover various aspects of the materials used to make impressions of teeth and oral structures. Here are some potential questions and answers related to the properties of impression materials:
1. Question: What are the essential properties of an ideal impression material?
Answer: An ideal impression material should have good detail reproduction, adequate dimensional stability, appropriate flow and wetting characteristics, acceptable working and setting times, sufficient tear strength, minimal distortion upon removal, and biocompatibility.
2. Question: How do you classify impression materials?
Answer: Impression materials can be classified as elastic or non-elastic. Elastic impression materials include elastomers like silicones, polyethers, and polyvinyl siloxanes (PVS). Non-elastic materials include irreversible hydrocolloids (alginate) and reversible hydrocolloids (agar).
3. Question: Discuss the differences between hydrophilic and hydrophobic impression materials.
Answer: Hydrophilic impression materials have an affinity for water, ensuring accurate impressions in a moist environment. Silicones and polyethers are examples. Hydrophobic materials repel water and may not perform well in the presence of moisture. Polyvinyl siloxanes are generally considered hydrophobic.
4. Question: Explain the concept of working time and setting time in impression materials.
Answer: Working time is the time available for manipulating the material after it is mixed, and setting time is the time required for the material to fully set. It’s crucial to respect both times to ensure a successful impression.
5. Question: What is the purpose of adding accelerators and retarders in impression materials?
Answer: Accelerators and retarders are added to control the setting time of impression materials. Accelerators shorten the setting time, while retarders extend it. This allows practitioners to customize the working characteristics based on the specific clinical situation. Dental viva voice questions in Impression Materials
6. Question: How does the viscosity of impression materials impact their use?
Answer: The viscosity of impression materials affects their flow. Low-viscosity materials are used for fine detail reproduction, while high-viscosity materials provide bulk and stability. Some materials, like addition silicones, come in various viscosities to accommodate different clinical needs.
7. Question: Discuss the role of surfactants in impression materials.
Answer: Surfactants are added to impression materials to improve their wetting properties. This helps the material flow into the details of the oral structures, ensuring better accuracy and reproduction of surface features.
8. Question: What is the significance of dimensional stability in impression materials?
Answer: Dimensional stability refers to the ability of an impression material to maintain its size and shape over time. It is crucial to ensure that the final cast accurately represents the oral structures. Elastic materials like silicones and polyethers generally exhibit good dimensional stability.
Remember that the specific questions and depth of knowledge required may vary based on the course or program you are in. It’s essential to review your course materials and class notes to prepare thoroughly for your viva. Below are some viva questions and answers related to different types of impression materials used in dentistry:
1. Question: What are the primary types of impression materials, and how are they classified?
Answer: Impression materials are classified into elastic and non-elastic types. Elastic materials include silicones, polyethers, and polyvinyl siloxanes (PVS). Non-elastic materials comprise irreversible hydrocolloids (alginate) and reversible hydrocolloids (agar).
2. Question: Compare the advantages and disadvantages of using alginate impressions.
Answer: Alginate is a cost-effective and easy-to-use non-elastic impression material. Its advantages include simplicity, quick setting time, and minimal patient discomfort. However, it has limited dimensional stability, may shrink upon drying, and is sensitive to moisture.
3. Question: Describe the setting reaction of alginate and how it influences working time.
Answer: Alginate sets through a chemical reaction called gelation, where sodium alginate reacts with calcium ions. Working time is the time available for mixing and placing the material before it begins to set. The addition of retarders can extend the working time.
4. Question: Explain the differences between condensation silicone and addition silicone impression materials.
Answer: Condensation silicones undergo a condensation reaction, releasing byproducts like alcohol, while addition silicones set without byproducts. Addition silicones exhibit better dimensional stability, improved tear strength, and less sensitivity to moisture compared to condensation silicones.
5. Question: What are the advantages of using polyether impression materials?
Answer: Polyether materials offer excellent detail reproduction, high tear strength, and dimensional stability. They have a relatively short setting time, making them suitable for a variety of clinical situations. However, they may taste unpleasant, and moisture can interfere with the setting.
6. Question: Discuss the role of catalyst and base in the setting reaction of addition silicone impression materials.
Answer: Addition silicone impression materials consist of a base and a catalyst. The base contains a polymer, and the catalyst initiates the cross-linking reaction. The two components are mixed in equal proportions to achieve a homogenous mixture, which then sets through a hydrosilation reaction.
7. Question: How do reversible hydrocolloids differ from irreversible hydrocolloids in terms of setting and usage?
Answer: Reversible hydrocolloids, such as agar, can undergo a physical sol-gel transition repeatedly, making them reversible. Irreversible hydrocolloids, like alginate, undergo a chemical reaction during setting, making them irreversible. Agar is typically used for accurate impressions in laboratory settings due to its precision.
8. Question: Discuss the advantages of using polyvinyl siloxane (PVS) impression materials.
Answer: Polyvinyl siloxanes offer high accuracy, excellent detail reproduction, and dimensional stability. They have a hydrophobic nature, making them suitable for use in moist environments. PVS materials are available in various viscosities to accommodate different clinical needs.
These questions cover a range of impression materials commonly used in dentistry. Remember to refer to your course materials and textbooks for additional information and specific details related to your curriculum. Viva question and answers in dental caries
Here are some viva questions and answers related to the uses of impression materials in dentistry:
1. Question: What are the primary purposes of taking impressions in dentistry?
Answer: Impressions in dentistry serve multiple purposes, including creating accurate replicas of oral structures for the fabrication of restorations, prosthetics, and appliances. They aid in treatment planning, diagnosis, and the creation of custom dental devices.
2. Question: Discuss the role of impressions in the fabrication of fixed prostheses.
Answer: Impressions are crucial for the fabrication of fixed prostheses such as crowns, bridges, and inlays. They provide an exact replica of the prepared tooth or teeth, allowing the dental laboratory to create precise restorations that fit seamlessly in the patient’s oral cavity.
3. Question: How are impressions utilized in removable partial denture construction?
Answer: Impressions are used to capture the contours of the edentulous areas and remaining teeth in removable partial denture construction. These impressions help in the fabrication of custom-fit partial dentures that provide both esthetics and functionality.
4. Question: Explain the importance of impressions in complete denture fabrication.
Answer: Impressions are fundamental in complete denture fabrication as they capture the entire arch form and details of the edentulous ridges. Accurate impressions are critical for the creation of well-fitting complete dentures, ensuring patient comfort and proper function.
5. Question: How are impressions utilized in orthodontics?
Answer: Impressions are used in orthodontics to create study models, which aid in the diagnosis and treatment planning of orthodontic cases. They help orthodontists analyze tooth and jaw relationships, assess occlusion, and plan for the placement of braces or other orthodontic appliances.
6. Question: Discuss the role of impressions in the fabrication of mouthguards.
Answer: Impressions are used to create accurate replicas of the oral structures for the fabrication of custom mouthguards. These mouthguards provide protection during sports activities or as night guards for patients with bruxism.
7. Question: How do impressions contribute to the field of dental implantology?
Answer: Impressions play a crucial role in dental implantology by capturing the position and orientation of dental implants in relation to the surrounding structures. This information is essential for the fabrication of implant-supported restorations, ensuring proper fit and function.
8. Question: Explain the use of impressions in the diagnosis of temporomandibular joint (TMJ) disorders.
Answer: Impressions are utilized in the diagnosis of TMJ disorders by capturing the relationship between the upper and lower jaws. These impressions help in creating accurate models that aid in the analysis of occlusion, joint movements, and the planning of treatment for TMJ-related issues.
These questions cover various applications of impression materials in different dental procedures. It’s important to understand how impressions contribute to accurate diagnosis, treatment planning, and the fabrication of various dental appliances. Viva Question and Answers Related to Glass ionomer Cement!
Here are some viva questions and answers related to the classification of impression materials in dentistry:
1. Question: How are impression materials classified in dentistry, and what are the primary categories?
Answer: Impression materials are classified into two main categories: elastic and non-elastic. Elastic impression materials include elastomers like silicones, polyethers, and polyvinyl siloxanes (PVS). Non-elastic materials include irreversible hydrocolloids (alginate) and reversible hydrocolloids (agar).
2. Question: Discuss the characteristics of elastic impression materials and provide examples.
Answer: Elastic impression materials possess the ability to deform and return to their original shape. Examples include silicones (condensation and addition types), polyethers, and polyvinyl siloxanes. These materials are commonly used for detailed impressions due to their elastic nature.
3. Question: What are the properties that make irreversible hydrocolloids a non-elastic impression material?
Answer: Irreversible hydrocolloids, such as alginate, are non-elastic because they set through a chemical reaction (gelation) and do not return to their original shape once set. They are generally more suitable for single-use or preliminary impressions.
4. Question: Explain the reversible nature of hydrocolloid impression materials.
Answer: Reversible hydrocolloids, like agar, undergo a physical sol-gel transition. They can change from a sol state (liquid) to a gel state (solid) and back again, making them reusable for multiple impressions if handled properly.
5. Question: How are elastomeric impression materials further classified based on their setting reactions?
Answer: Elastomeric impression materials are classified into two main types based on their setting reactions: condensation silicone and addition silicone. Condensation silicones release byproducts during setting, while addition silicones set without byproducts. Viva Question and Answers in Denture Base Resins
6. Question: Discuss the classification of polyether impression materials and their unique characteristics.
Answer: Polyether impression materials are classified as elastomers. They exhibit high tear strength, dimensional stability, and excellent detail reproduction. Polyethers are known for their accuracy and are often used when precision is crucial.
7. Question: What role does the setting mechanism play in classifying impression materials?
Answer: Impression materials are classified based on their setting mechanisms into chemical-cure (like elastomers) and physical-cure (like hydrocolloids). Chemical-cure materials undergo a chemical reaction to set, while physical-cure materials change state through a physical process.
8. Question: How does the classification of impression materials influence their clinical applications?
Answer: The classification of impression materials dictates their characteristics, handling properties, and clinical applications. For example, elastomers are often used for detailed impressions in crown and bridge work, while hydrocolloids may be suitable for preliminary impressions in complete denture fabrication.
These questions cover the classification of impression materials and touch upon the characteristics that distinguish each type. It’s important to understand the properties of different materials to make informed decisions in clinical practice. Viva Question and Answers in Physical Properties of denture base Resins!