CHAPTER 9 Restorative Procedures and Materials
Restorative dentistry forms a major part of the workload of general dentistry, being the branch of dentistry involved in treatment of the common dental diseases – dental caries and periodontal disease, and their sequelae, including loss of teeth. Thus the specialty of restorative dentistry includes endodontics, periodontics and prosthodontics. Prosthodontists are also sometimes called ‘conservative clinicians’.
A dental restoration (filling) is used to restore the tooth shape (morphology) and function. Restorations have to be custom-made for every patient, because each patient presents with a unique colour, shape and size of their teeth and relationship of their upper and lower jaws. Each patient also has their own unique aesthetics, depending on the colour, size and shape of their teeth, face and jaws and tone of their facial muscles.
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 CAD–CAM dentistry.
Primary impressions, which are the initial impressions, are often taken using alginates (p. 214) in a stock impression tray (see Figure 9.4). The resulting cast is then used by the dental technician to make a special tray. Then a secondary impression is made – using a more accurate impression material such as an elastomer (p. 215) – in the special tray.
FIGURE 9.4 Items required for an alginate impression: (A) stock impression trays; (B) scoop for measuring out alginate powder; (C) water measure; (D) plastic mixing bowl with alginate powder; (E) plaster spatula; (F) wax knife; (G) mouth mirror; (H) laboratory prescription (instruction) sheet and label; (I) gauze for keeping the impressions moist; and (J) plastic bag to put the impressions in for sending to the laboratory.
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.
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.
To keep moist, wrap the impression in damp gauze or, if the impression must be stored for a short period of time, place it in a humidor in which the relative humidity is 100%. The cast should be poured soon after the impression is removed from the mouth.
Alginates are satisfactory for taking primary impressions and for many of the impressions required in prosthetic work. But they can also distort due to syneresis (separation of liquid from the gel), imbibition etc. So for the more accurate impressions, as are required for crowns and bridges (see later), other impression materials such as elastomers are used.
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.
|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|
|Mixing bowl or pad|
|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|
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.
|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|
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.
BOX 9.2 Methods of Moisture Control
FIGURE 9.6 Rubber dam equipment: (A) rubber dam punch; (B) rubber dam clamp; (C) rubber dam frames; (D) dental floss; (E) a selection of rubber dam clamps; (F) rubber dam sheet; (G) rubber dam napkin; and (H) dry dam.
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.
FIGURE 9.10 Instruments used for cavity preparation and amalgam restorations: (A) mouth mirror; (B) straight probe; (C) tweezers; (D) excavators; (E) amalgam condensers (pluggers); (F) amalgam burnisher; (G) amalgam carvers; and (H) flat plastic instrument.
The main aim is to remove all of the decayed parts of the tooth but at the same time avoid damage to the underlying dental pulp. Once the clinician has prepared the cavity, the pulp is protected by applying a lining cement with an instrument called a ‘plastic’ (labelled H in Figure 9.10).
Cements are described in Chapter 12. They are usually prepared by the dental nurse. Several cements are supplied in capsules containing pre-proportioned powder and liquid. These are not only convenient but ensure consistent powder/liquid ratios and thus predictable setting times and ultimately the lining strength.