DANB - General Chairside Assisting Dental Impression Materials Questions and Answers — Questions and Answers
Question 1: A dental assistant is preparing to take a preliminary impression for diagnostic models. Which of the following materials is most commonly used for this purpose due to its ease of use and cost-effectiveness?
- Polyvinyl siloxane (PVS)
- Polyether
- Alginate hydrocolloid (Correct answer)
- Impression compound
Correct answer: Alginate hydrocolloid
Alginate is an irreversible hydrocolloid and is the material of choice for preliminary impressions, such as those for study models, orthodontic casts, and opposing arch impressions. It is favored for these applications because it is inexpensive, easy to manipulate, and well-tolerated by patients. Polyvinyl siloxane and polyether are elastomeric materials used for final impressions requiring high accuracy, such as for crowns and bridges. Impression compound is a rigid, thermoplastic material typically used for border molding or primary impressions for edentulous arches.
Question 2: A patient has a strong gag reflex, and the dentist has requested a preliminary maxillary impression. To make the procedure more comfortable for the patient, the dental assistant should:
- Use a fast-set alginate and seat the tray from anterior to posterior. (Correct answer)
- Select a tray that is one size larger than needed to capture more detail.
- Mix the alginate with cold water to delay the setting time.
- Have the patient tilt their head backward during tray placement.
Correct answer: Use a fast-set alginate and seat the tray from anterior to posterior.
Using a fast-set alginate reduces the amount of time the tray is in the patient's mouth. Seating the tray from the anterior to the posterior allows excess material to flow forward and out of the mouth, rather than toward the patient's throat, which can trigger the gag reflex. Using colder water would prolong the setting time, and having the patient tilt their head back would increase the likelihood of material flowing down their throat.
Question 3: Which elastomeric impression material is known for its superior hydrophilicity (ability to perform well in moist conditions) and rigidity, making it a good choice for detailed impressions of crown preparations, even with slight moisture?
- Condensation silicone
- Polysulfide
- Polyvinyl siloxane (PVS)
- Polyether (Correct answer)
Correct answer: Polyether
Polyether is recognized for being the most hydrophilic of the elastomeric impression materials, which means it has a high affinity for water and can capture fine details accurately even in a moist oral environment. This property, along with its rigidity and dimensional stability, makes it ideal for impressions of crown and bridge preparations. While PVS materials have added surfactants to improve their hydrophilic properties, they are naturally hydrophobic. Polysulfide is also hydrophilic but has a longer setting time and a distinct odor.
Question 4: After taking an alginate impression, the dental assistant should immediately rinse it under cool running water and then disinfect it. What is the primary reason for wrapping the disinfected impression in a damp paper towel and placing it in a sealed bag before pouring?
- To allow the material to fully polymerize.
- To prevent distortion from syneresis or imbibition. (Correct answer)
- To remove any residual disinfectant from the surface.
- To make the impression easier to separate from the stone model.
Correct answer: To prevent distortion from syneresis or imbibition.
Alginate is a hydrocolloid material, meaning its primary component is water. It is dimensionally unstable and susceptible to changes if not handled correctly. Wrapping it in a damp towel in a sealed bag creates a 100% humidity environment, which prevents water loss (syneresis) or water gain (imbibition), either of which would cause the impression to distort. The impression should be poured as soon as possible, ideally within 10-15 minutes, to ensure accuracy.
Question 5: A dentist is using a polyvinyl siloxane (PVS) material for a final impression. The dental assistant notices that the material is taking much longer than usual to set. The use of which of the following items by the operator could have caused this setting inhibition?
- Cotton rolls
- Latex gloves (Correct answer)
- Retraction cord with aluminum chloride
- Nitrile gloves
Correct answer: Latex gloves
The setting reaction of addition silicone (PVS) materials can be inhibited by sulfur compounds. Latex gloves contain sulfur, and contact with the impression material or the prepared tooth can prevent the material from setting properly. Dental professionals should use vinyl or nitrile gloves when working with PVS materials to avoid this complication.
Question 6: When taking a final impression using a heavy body and light body system, what is the primary purpose of the light body material?
- To fill the bulk of the impression tray.
- To provide rigidity and support to the impression.
- To adhere the heavy body material to the tray.
- To flow into and capture the fine details of the preparation. (Correct answer)
Correct answer: To flow into and capture the fine details of the preparation.
Light body impression material has a low viscosity (it is very flowable), which allows it to be syringed directly onto and around the prepared tooth. Its purpose is to capture the intricate details of the preparation margins and tooth anatomy with high accuracy. The heavy body material, which is much more viscous, fills the tray and provides support and stability for the light body material.
DANB - General Chairside Assisting Dental Impression Materials Questions and Answers
A dental assistant is preparing to take a preliminary impression for diagnostic models.
Which of the following materials is most commonly used for this purpose due to its ease of use and cost-effectiveness?