9: Restorative Procedures and Materials

CHAPTER 9 Restorative Procedures and Materials

Overview of the role of the dental nurse in restorative procedures

Dental impressions

A dental impression is an accurate representation of part or all of a person’s dentition and adjacent tissue of the mouth. A dental impression is usually made by placing an impression material into the mouth, usually in an impression tray (Figure 9.2). The impression material then sets or hardens so that, when removed from the mouth, it retains the shape of the teeth and/or mouth. It forms a ‘negative’ of a person’s teeth and adjacent soft tissues, which is then used to make a cast or model (Figure 9.3) of the dentition, usually from dental plaster. The model may be used either as a record of the person’s dentition (called a study model) or by the dental technician to make:

There are several different kinds of impression materials and their properties are described in detail below and in Chapter 12. Impressions are increasingly being made using computers, the basis of CADCAM dentistry.

The Dental Nurse’s Role in Impression Taking

You will need to offer a range of impression trays of different sizes for the clinician to select for use. Differently shaped trays are available for people with or without natural teeth (Figure 9.4). In order that the impression material once set remains firmly in position in the tray, the trays may be perforated, rim locked and/or you may need to apply a special adhesive to the tray before use. You then mix the impression material and place it in the impression tray chosen. With suitable training, dental nurses can also take certain impressions.

You must wash and disinfect the impressions once they are removed from the mouth and label them before despatching to the laboratory with a prescription:

Alginate Impression Material (‘Alginate’)

Alginate is one of the most commonly used impression materials. It is supplied as a powder, which is mixed with tap water to make a gelatinous mass. This mass then sets (hardens) rapidly. Alginate powder must be stored in a cool dry place in a tightly closed container to protect it from absorbing moisture from the air and from contamination. Shake the container before use to loosen the powder and then leave it for a few minutes before opening to let the dust settle. Powder and water measuring cups are provided by the manufacturer. Measure out the powder into the mixing bowl (Figure 9.4) and add a measured amount of tap water at room temperature (21°C). Alginates set fairly quickly; the best method of controlling the setting time is to slightly alter the temperature of the water used in the mix. The higher the water temperature, the faster the material will set.

Elastomeric Impression Materials (Elastomers, ‘Rubber Base’)

Elastomers give better impressions (more accurate and stable) than do alginates. There are three main types of elastomers:

The bases and the chemical reactors of elastomers are usually of different colours. Some products are provided in special mixing syringes. For others, you will need to lay out equal lengths of both the base material and the chemical reactor (catalyst) separately but side by side onto a special polymer paper or parchment pad. The reactor should not touch the base material until everything is ready to mix: then you mix the two pastes with a spatula in the prescribed time, until no streaks remain. A thin uniform layer of elastomer impression material is required to give the most accurate impression, so the materials are used in individually designed (custom or special tray) acrylic trays. You will need to apply a tray adhesive to prevent the impression from pulling away from the tray and distorting. Most elastomer impressions are dimensionally stable if stored dry, and thus they may be sent to the technician without a major risk of dimensional change.

Uses

Elastomers are used for making impressions of areas containing undercuts, especially for crowns, inlays, bridges, dental implants and removable and fixed partial dentures (see p. 215).

Impression Tray Set-Up (Figure 9.4)

Impression trays To carry impression materials
Impression adhesive For aiding adhesion of material to tray
Straight handpiece and acrylic trimmer (Figure 9.5) For adjustment of tray if needed
Impression material
Mixing bowl or pad
Spatula
Shade guide
Laboratory prescription (instruction) sheet and label For custom instruction to technician
Gauze swabs For damping and placing over alginate impression
Self-seal plastic bag For transporting to the laboratory
Mirror For patient to view their appearance for shade selection and ensuring face is clean

Treatment of caries

Caries prevention is discussed in Chapter 8, both the measures that the patient can take and the measures that the clinician can take (applying dental fissure sealants). Here we discuss the restoration of teeth which have been damaged by caries.

Repairing damaged or diseased teeth – making a restoration

The Dental Nurse’s Role

Moisture control and rubber dam

Moisture control is very important for two reasons:

TABLE 9.1 Damaging Effects of Moisture on the Setting of Restorations

Materials Effects of Moisture
Amalgam Expansion of material
Cement Fails to adhere to tooth structure; setting time altered
Composite Fails to adhere to tooth structure
Glass ionomer Fails to set properly

Moisture control is also crucial in endodontics to prevent spread of infection.

When preparing and placing fillings there are several ways to control moisture (Box 9.2). Use of rubber dam (or dental dam, Figure 9.6) is the most effective.

The rubber dam is a thin square of latex rubber (also available in silicone for latex-sensitive patients). To accommodate the teeth being treated, holes are made in the sheet with a rubber dam punch, and the dam is held in place on the teeth by rubber dam clamps or dental floss (Figure 9.6).

You will need to prepare the rubber dam, assist the clinician with placement and use the suction during cavity preparation or endodontics to remove debris, saliva and water. Figure 9.7 shows a selection of suction tips that can be attached to the suction machine and are placed inside mouth.

Jan 8, 2015 | Posted by in Dental Nursing and Assisting | Comments Off on 9: Restorative Procedures and Materials
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