These are placed as a temporary measure, before the tooth is restored permanently, and are used for a variety of reasons.
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As an emergency measure to seal a cavity and prevent carious ingress.•
During endodontic treatment, as repeated access may be required to the pulp chamber over several appointments.•
During inlay construction to seal the preparation while the permanent inlay is constructed.•
To allow a symptomatic tooth to settle and become symptom free, before being permanently sealed.There are several materials available for use as a temporary restoration, some of which have other uses in dentistry – they are multi-purpose materials. Overall, they are unsuitable for use as a permanent restoration because they are too soft to chew on, are too soluble in saliva, and would not remain intact for long periods.
The key features of all temporary restorations are as follows.
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Quick mixing and placement.•
Cheap compared to permanent restorative materials.•
Easily removed from the cavity when required.•
Not strong enough to be chewed on routinely.•
Have varying degrees of adhesiveness to the tooth.•
Some contain sedative ingredients to help settle inflamed pulps.A variety of materials is available, under many trade names, but temporary restorations can generally be categorised into one of the following groups of materials.
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Zinc oxide and eugenol.•
Zinc phosphate.•
Zinc polycarboxylate.•
Gutta percha.Zinc oxide and eugenol
Presented as zinc oxide powder and eugenol liquid (‘oil of cloves’), the cement is made by mixing incre- ments of the yellowy powder to a drop of the clear eugenol liquid on a glass slab with a spatula (Figure 15.14). Older varieties of the product can be thickened if necessary by squeezing in a napkin to remove some of the eugenol liquid, otherwise full setting of the cement produced takes a few hours.
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When ready for use, the cement should be able to be rolled into a ‘sausage shape’ with the spatula, without sticking to it or smearing across the glass slab.Uses of the cement are:
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temporary filling•
non-irritant base for deep cavities•
sedative dressing for painful carious teeth and for dry sockets•
main constituent of some impression pastes, periodontal packs and root filling materials.The main advantage of the cement over other temporary restorations is that it is soothing and non-irritant to the pulp and can be safely used in deep cavities. The main disadvantage is that it used to be too soft and slow-setting to use as a foundation for a permanent filling in one visit. However, this can now be overcome by using a strengthened quick-setting proprie- tary brand such as Kalzinol. In this form it is generally regarded as a satisfactory lining for metal fillings.
Other disadvantages are that the cement is not compatible with composite filling materials, and cannot be used as a lining beneath these types of restorations. Manufacturers’ instructions must always be followed in selecting a suitable lining for any non-metallic fillings.
Also, some patients are allergic to preparations containing eugenol, although special eugenol- free alternatives are now available.
Zinc phosphate
Presented as zinc oxide powder and phosphoric acid liquid, the cement is prepared by mixing increments of the white powder to the clear liquid on a glass slab with a spatula (Figure 15.15).
Two different mixes are used.
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A thick mix of putty consistency to use as a temporary filling or a base beneath a permanent filling.•
A thin creamy mix to use for crown and inlay cementation – this is called a luting cement.Setting of the cement takes a few minutes depending on various factors.
Figure 15.14 Zinc oxide and eugenol cement – to mix.
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•
A warm slab accelerates the setting time.•
A cold slab slows down the setting time.•
A thick mix sets more quickly than a thin mix.•
A dry slab must be used as moisture accelerates setting.•
Powder contaminated by moisture in the air will set too quickly for use, so it is most important to screw the cap on tightly, immediately after using the bottle of liquid.These various factors can be used to advantage, depending on the particular use of the cement at the time. If a long setting time is required, such as when cementing a bridge, a cold dry slab can be used to give the maximum setting time possible, so that the cement can be loaded into each retainer and then fully positioning the bridge, before it begins to set.
This ability to control its setting time is the over-riding advantage of zinc phosphate cement.
Experience soon teaches a dental nurse how much powder and liquid to set out, but occasionally too little or too much powder will be put on the slab. In the former case, more powder can be added from the bottle, but the mixing end of the spatula must not be used for this purpose as it will contaminate and spoil the whole bottle. Excess unused powder may only be returned to the bottle if you are certain that it has not been contaminated by any liquid or mixed cement on the slab.
A cool thick glass slab should be used for mixing zinc phosphate cement. Thin slabs are warmed by the dental nurse’s hand and can make the cement set too quickly.
Uses of a thick mix of the cement are:
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as a temporary filling•
as a cavity base•
for blocking out undercuts in inlay and crown preparations.Uses of a thin mix of the cement are as a:
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luting cement to place inlays, crowns and bridges•
luting cement to place orthodontic bands.The main advantage of the cement is that it sets very hard within a few minutes and therefore makes a sound base for permanent fillings, and also a more durable temporary filling than zinc oxide and eugenol materials. Furthermore, its adhesive nature to dentine makes it satisfactory as a luting cement for prefabricated restorations.
Figure 15.15 Zinc phosphate cement – to mix.
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The main disadvantage is that in deep cavities it may be irritant to the pulp, as the acidic nature of the liquid component produces a mixed material with a pH of 2. In these cases, a sub- lining of calcium hydroxide is inserted onto the cavity floor beneath the zinc phosphate base cement. The alternative is to use a different base material altogether. Zinc phosphate cement is also moisture sensitive and will not adhere to a damp cavity, so good moisture control is required during its use.
Zinc polycarboxylate
Presented as white zinc oxide powder and clear, viscous polyacrylic acid liquid, or as these two components combined in the powder and sterile water as liquid (Figure 15.16). In each case the cement is prepared by mixing increments of the powder to the liquid or sterile water on either a glass slab or a waxed paper pad, with a spatula. A measure is provided by the manufacturer for exact measurement of each increment.
The advantage of using the anhydrous system with sterile water is that only one bottle of material is needed and there is no liquid to deteriorate, to be used up too soon or left over when the powder bottle is empty. Furthermore, as the polyacrylic acid liquid is viscous (thick and ‘gloopy’
in consistency), it can be difficult to dispense from the bottle and also difficult to mix. Mixing with water is much easier and quicker.
Uses of the cement are:
•
a thin mix for use as a luting cement with fixed restorations and orthodontic bands•
a thick mix for use as a cavity base•
therefore, an alternative to zinc phosphate cement.The main advantages of polycarboxylate cement are that it is less irritant than zinc phosphate cement, and far more adhesive to dentine. For these reasons many operators prefer its use to that of zinc phosphate.
The main disadvantage is that it can be rather difficult to manipulate as it is adhesive to stainless steel instruments. Excess cement must be wiped off the spatula and instruments before it fully sets, as it is difficult to remove by manual scrubbing and unlikely to be removed by the action of the ultrasonic bath.
Figure 15.16 Zinc polycarboxylate cement – to mix.
Gutta percha 435
The final material in this category is gutta percha, which is presented as preformed cones or sticks (greenstick compound) of rubber material. It only requires heat to become plasticised, but is almost obsolete now as a temporary restoration, as the previous cements described are far superior in this role.
Its main use today is as a root filling material (see later), but it is also used during vitality testing and during border contouring of impression trays during denture construction.
The main categories of temporary restorative materials, with their advantages and disadvantages outlined, are summarised in Table 15.2.