10 Questions
What is the primary purpose of taking an impression in dentistry?
To create a negative record of the oral tissue
What type of trays are used for primary impressions?
Stock trays
What is the desirable property of impression material that ensures it is not affected by oral fluids?
Not affected by oral fluids
What is the step that follows impression in the process of making dental appliances?
Gypsum
What is the purpose of special trays in impression taking?
Used for secondary impressions
What is the desirable property of impression material that ensures it is easy to use?
Easily manipulated
What is the step that precedes gypsum in the process of making dental appliances?
Impression
What is the primary material used for making the artificial gingiva in removable dentures?
Acrylic resin
What is the desirable property of impression material that ensures it is suitable for use in the oral cavity?
Biologically acceptable
What is the primary purpose of using gypsum in the process of making dental appliances?
To create a model of the oral structure
Study Notes
Making Impressions
- Elastomers don't adhere well to the tray, so an adhesive should be applied and allowed to dry before making an impression.
- METHODS OF MAKING IMPRESSIONS: Single Mix Technique, Multiple Mix Technique, and Reline Technique (Two-Stage Technique or Putty Wash Technique).
Non-Elastic Impression Materials
- Plaster of Paris: • Setting time: 5 minutes • Very low viscosity, records surface details accurately • Good dimensional stability • Rigid once set, unable to record undercuts • Patient experiences a dry sensation due to its water-absorbing nature
- Impression Compound: • High viscosity, low flow, and poor reproduction of surface details • Not used to record undercuts, as it's rigid once cooled • Can be reused for the same patient • Sufficient body to support itself, especially in peripheral portions
Reline Technique (Two-Stage Technique or Putty Wash Technique)
- Uses a special tray for peripheral seal
Classification of Impression Materials
- According to the Type of Reaction (Manner of Hardening): • Hardening by chemical reaction: Plaster, Zinc-oxide and eugenol, Alginate, Rubbers • Hardening by physical reaction: Impression compound, Agar
- According to Behavior After Setting: • Elastic: Easy to remove from undercuts • Non-elastic
- According to Use: • Dentulous or partially edentulous patient • Edentulous patient
- According to Accuracy: • 1ry impression (using stock tray): Impression compound, Alginate • 2ry impression (using special tray): Plaster, Zinc-oxide and eugenol, Agar, Rubbers
Hydrocolloids
- General Properties: • Gel strength • Dimensional changes after setting (synersis, imbibition)
- Reversible Hydrocolloids: • Agar impression material: Good accuracy, difficult manipulation
- Irreversible Hydrocolloids: • Alginate impression material: Powder and water form, easy to mix and manipulate, flexible, low cost, non-toxic, and esthetic
Ideal Material
- No ideal material, but Alginate is a popular choice
This quiz covers different methods of making impressions in dentistry, including single mix, multiple mix, and reline techniques, as well as impression materials like plaster of Paris and zinc oxide eugenol.
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