How Prosthodontic Procedures Are Done-Part II
Management of Tissue
Different methods can be used for the management of tissue and the most common technique is management by retraction cord. Retraction cords are available in different sizes and may be braided or twisted. The retraction cord is used by pushing it gently into the depth of gingival margin with the help of a cord-packing instrument. It is then used to pack the gingival margin while encircling the tooth.
The retraction cords are chemically treated with certain agents like aluminum chloride, ferric sulphate, potassium sulphate, or zinc sulphate. These chemicals increase the tissue contraction by causing swelling of the collagen fibers in the tissues surrounding the capillaries. The expanded collagen increases pressure on the capillaries, which in response, are constricted along with the contraction of tissues. This whole process of the contraction of tissues allows entrance of the impression material beneath the gingival margin, thereby facilitating a proper and exact impression.
Preparation of Final Impression
Materials for final impression are prepared once the tissues have been managed. Dentists select the final impression material according to their preference. Mostly, dentists favor monophase material with single-viscosity because it is easy to mix and produces fine detail. Combination of different viscosities (medium, heavy, or putty like) can also be used with wash-type material but the technique requires completion in two steps. The selection of materials needs elaborate consideration, taking into account the number of helping hands available for mixing and loading the impression material into a syringe or an impression tray.
An automixer can be used to prepare the impression material, which after preparation is disinfected and then undergoes a thorough examination by the dentist. The dentist makes sure that all necessary and fine details have been captured by the impression. It is very important that the impression records clear image of the margins otherwise the dyes fabricated with the help of this impression will not be read properly by the technician at the dental laboratory. Subsequently, the permanent prosthesis will be ill fitting and the entire process of recording the impression will have to be repeated including the gingival retraction.
A bite registration must also be recorded as soon as the impression is complete and elastomeric material that is highly viscous is used. The bite registration must be disinfected before sending it to the laboratory.
Creation of Provisional Restoration
After the completion of the final impression process, provisional coverage for temporary restoration is needed. Different materials and methods can provide provisional coverage. They can be preformed or custom-made. The materials used include preformed polymer, preformed polycarbonate, and aluminum. Crowns made of stainless steel are more useful for adults.
Technicians at the dental laboratory can also make provisional restoration by using the pretreatment cast. Laboratory made provisional restorations do save time and dental visits are also reduced but the cost of treatment is increased. These restorations are more useful when they are to be worn for a longer duration of time.
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