Thanks for reading my first article where I wish to begin to explain the broad aspect of a dental technician and what we do. My first article will be basic but at the end I will explain the ins and outs of dentures, crowns, gold teeth and the general line of prosthetics.
I begin with what they use to make the actual impression which we as technicians work on.
Impression Materials:
An Impression material is a substance or combination of substances used for making an impression or negative reproduction.
Some ideal properties of impression materials include:
• Must be free of poisonous or irritating ingredients.
• The material must be able to set uniformly without any concentration of stress that will cause it to warp.
• It must accurately reproduce in detail the surface area of the tissues.
• Must possess elasticity so that it can reproduce undercut areas without distortion.
• Must be compatible with cast and die materials.
• Should be simple to manipulate,
• It must be dimensionally stable.
Rigid Impression Material
Zinc Oxide Impression Paste
Impression pastes are used in conjunction with specially prepared impression trays, which are made of modeling compound. The paste is used as a thin film or “wash” and thus provides surface detail to the impression.
The paste only supplies the surface detail to the impression and thus is mainly used for full denture impression where the patient has no existing natural teeth.
Composition
The active ingredients of impression pastes are zinc oxide (a fine white powder) and oil of cloves or eugenol (an aromatic oily liquid). Balsam and resins are added in various proportions.
These substances are dispensed in separate tubes with the eugenol paste generally being brown in color.
Application
Impression pastes are applied using impression trays where a small amount of paste is applied evenly over the impression tray. The tray is inserted into the patient’s mouth and the initial setting is impressed. Optimal care must be taken when removing the tray from the patient’s mouth to ensure the impression is successful.
Decontamination
Impression trays are decontaminated by placing them a solution for a set amount of time, normally 3 minutes. These solutions are normally diluted with water and the trays are place into the solution.
Some examples of solutions that could be used include:
• Dilute Hypochlorite
• Chlorine Dioxide
• Milton’s Solution
Great care must be taken to ensure the trays are thoroughly rinsed under running water after decontamination.
Storage
Zinc Oxide Impression Paste has no serious storage precautions but the storage area must remain below 30⁰ Celsius.
Dimensional Stability
The set material is not strong and must be handles carefully to avoid damage. It may be stored for a short time without change if it is kept in water to prevent drying out and cracking.
Aqueous Elastomers
Aqueous Irreversible Hydrocolloids
Irreversible hydrocolloid can be used in preliminary impressions, provisional crown-and-bridge impressions, study models, opposing dentition impressions. Alginates are used for impressions in orthodontic models, sports mouth guards, and bleaching trays.
Composition
A formula for an alginate impression material powder is:
Potassium Alginate
Diatomaceous
Calcium sulphate
Trisodium phosphate
When mixed with water a chemical reaction takes place between these substances.
The alginate reacts with the calcium sulphate to produce an elastic gel structure of insoluble calcium alginate.
Application
Application of alginates requires a metal tray and when mixed with water the substance is applied evenly onto the tray. The tray is then inserted into the patient’s mouth on either maxillary or mandibular and the impression is taken. The tray must remain in the patient’s mouth until the alginate is of a soft rubbery consistency.
Decontamination
Alginate Impressions are disinfected much the same way as zinc oxide impressions. The tray is placed into a diluted solution containing a disinfectant substance for 3 minutes and then rinsed thoroughly under running water.
Storage
Alginate Impression material should be stored in a cool, dry place below 30⁰ Celsius.
The end result is a perfect working working model;
References: HLTDETOO1 Diploma of dental technology book 1
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