Prosthodontics | Impression Materials | INBDE, ADAT

Summary

In this video, Ryan delves into dental impression materials, crucial for prosthodontics and board exams. He covers tissue management, including fluid control and tissue displacement, and details the various impression materials: aqueous hydrocolloids (reversible agar and irreversible alginate) and non-aqueous elastomers (polysulfide rubber, condensation silicone, polyether, and addition silicone/PVS). Key points include the materials' properties, setting times, and how to handle them to avoid distortions like imbibition and syneresis. The video also emphasizes critical information for board questions and practical tips for clinicians.

Takeaways

• 🦷 Tissue management is crucial for dental impressions and involves fluid control and tissue displacement to provide clear access to the crown prep.
• 🧪 Fluid control can use local measures like cotton rolls and suction, while tissue displacement often employs retraction cords and medicaments like aluminum chloride or epinephrine.
• 🚫 Electrosurgery can be used for tissue management but is contraindicated for patients with implanted devices like pacemakers.
• 📊 Dental impression materials are categorized into aqueous hydrocolloids and non-aqueous elastomers, each with unique properties and applications.
• 🔄 Reversible hydrocolloid, like agar, changes phases with temperature and is highly accurate but requires a complex procedure.
• 🌡 Irreversible hydrocolloid, alginate, is quick-setting and commonly used but has the lowest accuracy among the discussed materials.
• ⏱ Factors affecting setting and working times of hydrocolloids include water temperature and the ratio of water to powder.
• 💧 Imbibition and syneresis are phenomena that can distort hydrocolloid impressions and should be avoided for accurate dental models.
• 🌡 Polysulfide rubber is an elastomeric material that leaves a water byproduct and is prone to syneresis, requiring prompt pouring after impression.
• 🍺 Condensation silicone leaves an alcohol byproduct and can cause shrinkage, highlighting the importance of pouring timing to prevent distortion.
• 💧 Polyether is hydrophilic, stable but easily influenced by water and humidity, making it prone to imbibition and challenging to remove from the patient's mouth.
• 🌟 Addition silicone (PVS) is the premium choice with no byproducts, excellent fine detail, and dimensional stability, but is inhibited by sulfur in latex gloves and rubber dam.

Q & A

What are the two main components of tissue management in taking dental impressions?

The two main components of tissue management in taking dental impressions are fluid control and tissue displacement. Fluid control involves managing saliva and gingival crevicular fluid, while tissue displacement involves moving the tissues to provide clear access to the crown prep for a clean and accurate impression.

What are some local measures used for fluid control in dental impressions?

Local measures for fluid control include the use of cotton rolls, suction, and anti-style gags. These methods help isolate the area and manage fluids like saliva and gingival crevicular fluid.

What is the purpose of using retraction cords in dental impressions?

Retraction cords are used to displace the tissue, specifically to stretch the circumferential fibers of the periodontal apparatus out of the way. This helps in obtaining a clean and accurate impression by placing the cords right under the margin of the prepared crown.

What medicaments can be used to impregnate retraction cords to prevent bleeding?

Medicaments such as aluminum chloride, iron sulfate, or epinephrine can be used to impregnate retraction cords. These substances help in promoting hemostasis, preventing bleeding which can interfere with the impression process.

Why is electrosurgery not always recommended for tissue displacement in dental impressions?

Electrosurgery is contraindicated in certain patients, such as those with implanted pacemakers or insulin pumps, because the electrode must not contact the teeth. This makes it a less universally applicable method for tissue displacement.

What are the two main categories of impression materials discussed in the video?

The two main categories of impression materials discussed are aqueous hydrocolloids and non-aqueous elastomers. Aqueous hydrocolloids are water-based materials mixed with water, while non-aqueous elastomers are elastomeric impression materials that do not involve mixing with water.

What is the difference between reversible and irreversible hydrocolloids?

Reversible hydrocolloids, like agar, can change between a sol phase (solution) and a gel phase by changing temperature, allowing them to be reused. Irreversible hydrocolloids, like alginate, cannot change back into a different phase once set and are used for single-use impressions.

Why is alginate not recommended for taking final impressions for a crown or bridge?

Alginate is not recommended for taking final impressions for a crown or bridge because it has the worst accuracy among the materials discussed. It is acceptable for diagnostic impressions but not for those requiring high accuracy.

What factors can influence the setting time and working time of hydrocolloids like alginate?

The setting time and working time of hydrocolloids can be influenced by the temperature of the water used and the water to powder ratio. Hotter water or using less water can decrease the setting time, while colder water or increasing the water to powder ratio can increase it.

What is the significance of imbibition and syneresis in relation to hydrocolloid impression materials?

Imbibition is the absorption of water, which can cause the impression to swell and distort. Syneresis is the loss of water, causing the impression to shrink and distort. Both phenomena can negatively affect the accuracy of the impression and the model poured from it.

What are the characteristics of polyether impression material that make it prone to distortion?

Polyether impression material is hydrophilic, meaning it loves water and can swell up and be affected by the relative humidity in the room. This makes it prone to imbibition and distortion. Additionally, it is very stiff once set, making it difficult to remove from the patient's mouth and prone to breaking teeth from the cast.

Why is addition silicone (PVS) considered the best impression material despite its high cost?

Addition silicone (PVS) is considered the best impression material because it offers the best fine detail, elastic recovery, and dimensional stability. It has no byproducts and is very stable, allowing for a longer time before pouring is necessary. However, it is inhibited by sulfur in latex gloves and rubber dams, which is a clinically significant factor.