These require more complex means restoring lost tooth tissue. Sometimes amalgam can still be used; in order to increase its retention small holes are cut in the tooth and pins or screws placed into them.
Badly Broken down Teeth: Gold inlays and crowns
These require more complex means restoring lost tooth tissue.Sometimes amalgam can still be used; in order to increase its retention small holes are cut in the tooth and pins or screws placed into them.
Amalgam is then built up around these aids to retention. In order to allow the amalgam to set properly before final shaping, the patient is occasionally sent away with the matrix band still in place. A copper ring modified to the tooth and gingival contour may be used for this purpose.
In situations where amalgam is not strong enough, gold or stainless steel crowns are used for the restoration of anterior teeth.
Gold inlays and Crowns
Gold provides a very strong and durable means of restoring a tooth.It is cast outside the mouth to fit the prepared tooth accurately. Inlays and crowns are used to restore teeth where much tooth tissue has been lost.
The preparation of a tooth to receive a gold inlay is similar to that of amalgam fillings, except that in this case no undercuts are allowed. The walls are made to diverge slightly occlusally, making removal of the impression possible.
After the dentist has prepared and lined the cavity he takes an impression or pattern, so that his technician can construct a gold inlay to fit the tooth. Indirect and direct techniques may be used. In the latter case a wax pattern is constructed on the tooth itself and then taken away to be processed by the technician. With the indirect technique an accurate model of the patients tooth is constructed from an impression and the wax prepared on this. In both cases the inlay is later cemented into the tooth.
Direct Techniques
Blue inlay wax is gently softened by warming and pressed into the cavity. After cooling to mouth temperature, the surface is carved with a wax carver, and smoothed with cotton wool and hot water. A metal sprue is added to aid removal of the wax pattern from the tooth and the pattern is sent to a laboratory technician. He embeds the wax impression in a refractory material (similar to plaster). This is then heated to melt the wax, the gaseous remnants of which evaporate through the sprue hole, leaving behind a cavity or mould. Molten gold is forced into this by a process of casting. After cooling, the gold is cleaned, the non-fitting surfaces are polished, and the inlay is returned to the dentist.Indirect Technique
An impression is taken of the prepared cavity using a copper ring filled with warm composition, or a tray containing rubber base or one of the elastic impression materials. The dentist also takes an impression of the opposing teeth, and the patient is asked to bite into a piece of softened pink wax to record the bite. This enables the technician to know how thick to make the occlusal portion of the gold.From these impressions the technician makes a set of models on which he then constructs the inlay, using techniques similar to those for the direct technique.
Copper Ring Technique
The correct size of copper ring is adapted to the shape of tooth and gingivae with crown scissors. The ring is filled with warm composition and pressed against the tooth until the material hardens, providing an impression of the cut tooth surface. In order to show the technician the relationship between the tooth in question and those on either side, a localizing impression is taken, using rubber base, silicone rubber, or plaster of Paris in a bridge tray.The surgery assistant must carefully pack the impression in a box so that there is no distortion, chipping, or loss on the way to the technician. The names of patient and dentist should be enclosed, together with any necessary instructions to the technician.
All of the equipment available for copper ring impression
- Selection of copper rings
- Crown scissors
- Bunsen or spirit lamp flame
- Composition and silicone rubber
- Petroleum jelly
- Bridge and other trays
- Pink bite wax.
Temporary cover
This is placed on any tooth prepared for a crown or inlay until the final restoration is ready.
1. It prevents pain due to food and air acting on exposed dentine.
2. It stops the teeth on each side and in occlusion from drifting towards the prepared tooth, into the space previously occupied by tooth tissue which has just been removed, I.e., it occupies the space which will later be filled by the final restoration.
Suitable temporary materials are quick setting zinc oxide and eugenol (possibly mixed with cotton wool), aluminum crowns, copper rings, and celluloid crown formers(anterior teeth only).
Crowns
These are constructed to resemble the natural teeth in shape and contour. Gold , porcelain, and acrylic are used, the first in sites where strength is the foremost requirement, and the others where aesthetics are more important. Stainless steel is sometimes used for deciduous teeth and for temporary crowns on fractured permanent teeth. As with inlays there are three clinical phases of construction, involving two visits to the surgery.- Preparation of the tooth
- Impression taking
- Fitting of the restoration.
Jacket Crowns
These are made to cap anterior teeth which are so badly damaged by decay that normal fillings are no longer possible.They are also used to improve the appearance of hypoplastic, discoloured, fractured, and displaced teeth.
Tooth tissue is cut away so as to leave a core of dentine. Impressions and bite are taken using techniques similar to those described for gold inlays, and a temporary crown is placed in position. The shade or color of the nearby teeth is recorded. The technician then constructs a crown, which is cemented on to the tooth with a thin mix of oxyphosphate cement.
Post crowns
With extensive destruction of tooth tissue it is no longer possible to retain a jacket crown. Under these circumstances a post crown is constructed. Most of the remaining part of the erupted tooth is cut away and a hole is drilled in the root canal for about two thirds of its length. It is, therefore, necessary to first extirpate the pulp and place a root filling in the apical one-third of the canal. Then an impression is taken of the inside of canal and a gold post is made to fit this. The top part of the post is build up to resemble a tooth stump prepared for a jacket crown, and an acrylic or porcelain crown is fitted over this core. In some cases pre-formed posts are purchased an adapted at the chairside.Stainless steel Crowns
These are used to restore badly Broken down deciduous molars, and as temporary covers on fractured permanent incisors. Caries is removed and the dentine is covered with a zinc oxide cement. All undercuts are ground away with green stones or diamond cutters, and occlusal surface is taken out of contact with the opposing tooth so as to allow a thickness of metal to be placed later in that position.A stainless steel crown of the requisite size is adapted to the gingival margin with crown scissors and pliers, and is then cemented into position.
Reference
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Last modified: 12 Jun, 2018
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