These are the most common types of denture – full ones (Figure 16.36) for edentulous patients and partial ones (Figure 16.37) for patients with any number of missing teeth up to one tooth short of being edentulous. The material used for their construction, and that of removable orthodontic appliances too, is either pink or transparent acrylic.
Figure 16.36 Full denture.
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Acrylic consists of a powder called a polymer and a liquid called a monomer. When mixed together, they form a plastic mass which has the consistency of dough. This sets into a hard acrylic by a process called curing. Curing is effected by heating the dough slowly in a special flask in an oven, or by adding a catalyst which allows it to cure at room temperature. These two methods of curing are known respectively as heat curing and cold curing.
Heat-cured acrylic is used for dentures and orthodontic appliances, and the curing process is carried out by a technician in the laboratory. Cold-cured acrylic (also called self-cured or autopoly- merised acrylic) can be used by the dentist at the chair side to make temporary crowns, and to carry out denture repairs. It is also used by the technician for the construction of special trays to take accurate second impressions.
As dentures are removable prostheses, their retention must be adequate to keep them in posi- tion in the mouth during speech and chewing, but weak enough so that the patient can easily remove the device from their mouth as they wish, say for cleaning purposes. The level of retention achieved relies on the following factors.
•
A suction film of saliva developing between the denture and the patient’s soft tissues.•
A post-dam along the back border of the denture, to help the suction film to develop.•
An accurate design and fit of denture, to allow the film to develop adequately.•
Use of any natural undercuts in the patient’s mouth, such as the alveolar ridges or any suitably shaped natural teeth.•
Use of stainless steel clasps around standing teeth with partial dentures, to increase the retention of the denture by the clasps gripping the teeth and preventing it from being dislodged by normal soft tissue movements (Figure 16.38).Sometimes no natural undercuts are present so the patient’s own teeth are adjusted to provide them, in the following ways.
•
Use of a crown to change the overall shape of the tooth.•
Use of composite build-ups to provide a retentive area for clasps to engage.•
Shape change of an existing restoration for similar reasons.With edentulous patients, the alveolar ridges can be changed surgically, to improve retention and comfort.
Figure 16.37 Partial denture on model.
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•
Alveoplasty – changing the shape of the existing ridge, such as by the removal of gross undercuts which would prevent the denture being seated.•
Flat ridges can be built up by the addition of artificial bone substitutes under the mucoperiosteum, to increase natural retention by creating a ridge that the denture can sit on.•
Alveolectomy – the surgical removal and smoothing of sharp ridges to allow comfortable wearing of the denture.Denture construction
Usually, acrylic dentures are made in four or five stages, with each stage being returned to the technician at the laboratory between patient appointments. The dentist prepares and records the details of the patient’s oral cavity, and the technician uses these records to construct the dentures to fit that patient’s mouth. Each laboratory stage is returned to the dentist for the next clinical stage to be recorded in the patient’s mouth, until the end result – the acrylic dentures, with or without clasps, are produced for fitting.
The stages are as follows, although not every stage is required in every case.
•
First impressions – using stock trays and alginate impression material (see Figure 16.3);the tooth shade and shape (mould) are often decided at this stage too. The impressions are correctly disinfected, as described previously, and suitably wrapped for dispatch to the laboratory.
•
Laboratory – study models are cast in plaster of Paris from the impressions, and special acrylic impression trays are custom made from them if required – in simple cases, the first impression may be accurate enough for denture construction to proceed.•
Second impression – using special trays and either alginate or elastomer impression material to produce a very accurate impression, and the tooth shade and mould may be chosen at this stage if not already recorded.•
Laboratory – working models are cast in dental stone and wax occlusal rims are constructed on them.•
Bite registration – the existing, or required, occlusal face height of the patient is measured using a Willis bite gauge (Figure 16.39), and recorded on the occlusal rims by warming them or Figure 16.38 Denture clasp example.507
using bite registration paste to stick them together. The rims then hold the models in the correct position and angulation for the dentures to be constructed (Figure 16.40).
•
Laboratory – models in their recorded face height positions are mounted onto an articulator, so the technician can construct the wax try-in dentures in these correct horizontal and vertical positions.•
Try-in – wax try-ins with the actual acrylic teeth mounted in them (Figure 16.41) are inserted and checked for accuracy of fit and occlusion, as well as shade; any major inaccuracies will result in new records being taken and a retry being requested.•
Laboratory – stainless steel clasps are added as necessary, then the try-ins on their models are sealed into flasks and the wax is replaced by heat-cured acrylic to form the final dentures, which are then cleaned and polished to provide a shiny outer surface to the denture.•
Fit – acrylic dentures are inserted in the patient’s mouth and checked for comfort, fit and aesthetics, then specific denture care information is given.Each stage of the denture construction in the surgery involves the use of specific instruments, materials and equipment which the dental nurse must be able to recognise and lay out at each appointment. They are summarised in Tables 16.5–16.9.
Figure 16.39 Willis bite gauge in position to record occlusal face height.
Figure 16.40 Wax rims on working models.
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The work ticket information must be duplicated onto the patient record card or the computerised notes, so that if the ticket itself is ever lost or misplaced, the relevant details are still available.
The handling and aftercare of the impressions are as for fixed prostheses.
Figure 16.41 Try-in stage of lower full denture.
Table 16.5 First impressions: instruments, materials and equipment
Item Function
Stock impression
trays To be sized and used to take the initial impressions, so that special trays can be constructed – they may be upper and/or lower, and edentulous or dentate
Alginate impression material and room - temperature water
To be mixed, loaded into the trays and inserted to produce the initial impressions
Shade and mould
guides To determine the colour and shape of the denture teeth, to be as close in appearance to any remaining teeth as possible
Work ticket or docket (Figure 16.42)
To record the patient and dentist details, the denture design and base material to be used, the tooth shade and mould, the type and position of any clasps, and the return date
Table 16.6 Second impressions: instruments, materials and equipment
Item Function
Study models and special trays To take the more accurate second impressions where required, to produce the working models
Alginate or elastomer impression
material To take the more accurate second impressions
Work ticket To record the next stage request and the return date
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If changes are required to the prostheses they must be requested at this point, as once the flask- ing process has been carried out, no further changes can be made and the whole construction process would have to be started again.
Any concerns that the patient may have must be identified and discussed at this point, and resolved to the satisfaction of both the patient and the dentist.
Table 16.8 Try-in
Item Function
Try-in prostheses To determine if fit, occlusion and aesthetics are correct before finishing the dentures
Heat source To warm the wax and make adjustments, as necessary Le Cron carver
(Figure 16.44) To make fine adjustments to the try-in, as necessary
Wax knife To warm and smooth the wax after adjustments, as necessary Shade and mould
guides To check or alter the shade or mould, as necessary Pink sheet wax For addition to the try-in, as necessary
Patient mirror To allow the patient to view the try-ins and decide if they are happy with the appearance, before completion of the dentures Work ticket To record any changes required for a retry, or to record the fit
return date
Table 16.7 Bite registration: instruments, materials and equipment
Item Function
Wax bite rims Adjusted in height so that correct face height of the patient can be recorded
Heat source
(Figure 16.43a) To warm the hand instruments and rims for adjustment Wax knife
(Figure 16.43b) To remove or add additional wax to the rims, as necessary Bite registration
paste (optional) To be mixed and applied to the rims, so that they are held in the correct position once set
Pink sheet wax
(Figure 16.43c) For addition to the rims, as necessary Willis bite gauge
(see Figure 16.39) To record the desired occlusal face height in edentulous patients, where no natural teeth remain as a guide Work ticket To record the next stage request and return date
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Instructions are given on the wear, care and cleaning of the new dentures, as follows.
•
A demonstration of how to insert and remove the dentures is given, with the patient then practising the techniques in front of the mirror and under the dentist’s supervision.•
Do not wear them overnight if possible, to avoid the development of oral fungal infections (thrush).•
Store them overnight in a denture pot containing water or ideally a soaking agent such as Steradent or Dentural.•
Clean after each meal if possible, using a denture brush and denture toothpaste – some ordinary toothpastes may be too abrasive for use on the acrylic teeth.•
Clean over a bowl of water, to avoid damage to the denture if it is dropped.•
Avoid soaking in bleach-based cleansers if any metal components are included in the design.•
Eat soft foods initially, while the oral soft tissues acclimatise to the prostheses.•
Take time to chew foods thoroughly, to avoid causing indigestion by swallowing large food particles.•
Harden oral soft tissues by carrying out hot salt water mouthwashes initially, otherwise the new dentures are likely to rub the soft tissues and make them sore.•
Return to the surgery if any ulceration occurs beneath the dentures, as further adjustments are likely to be required to remove high spots and deep flange edges.•
Dentate patients must continue to attend for oral health assessment at their regular recall interval, and edentulous patients are advised to attend at least once every 2 years, but ideally annually.Patients are also told that new dentures do not last forever, and their fit and appearance will be checked at each recall. Alveolar bone gradually changes its shape following the loss of teeth and the denture will eventually become too loose as resorption spaces develop beneath the fitting surface. By that time, most patients will have learned how to control a loose denture using a combination of their soft tissues and denture adhesive products such as Table 16.9 Fitting
Item Function
Completed
removable prostheses To fit, to the patient and dentist’s satisfaction Straight handpiece and
selection of trimming burs and carborundum polishing stones (Figure 16.45)
To remove any acrylic pearls or occlusal high spots before polishing and smoothing the adjusted area for comfort
Patient mirror To allow the patient to view the completed prostheses Articulating paper To identify occlusal high spots, for adjustment as
necessary
Pressure relief paste To identify high spots on the denture fitting surface, for removal as necessary
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ACME DENTAL LABORATORIES LTD. M.H.R.A. REF. CA 008044 136 WATERLOO ROAD, BURSLEM, STOKE-ON-TRENT ST6 3HB
Telephone: 01782 817621 Fax: 01782 824142
Received
Received
Received
Received DENTURES
NON STERILE DEVICE
This device conforms to the relevant requirements set out in Finish
Notes
STATEMENT.
Retry Try in Bite
RETURN DATES Trays L
THIS IS A CUSTOM MADE DEVICE FOR THE EXCLUSIVE USE OF
PVT
IND
N.H.S
I.D.Names
LABORATORY FEE
Inspected and Signed by
Please tick box Patient Mr./Mrs.
Surgery Address
Dentist Job No.
Annex I of the Medical Devices Directive
Special U Acrylic Shade Mould Teeth
Figure 16.42 Denture laboratory docket.
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Polygrip and Fixodent (Figure 16.46), but the alveolar bone changes can adversely affect appearance as the loose denture may no longer provide adequate support for the lips and cheeks. It is consequently necessary to reline the fitting surface of a denture from time to time and perhaps make other adjustments (see later). Ultimately, the denture will need to be replaced.
If the denture cleaning advice is not followed, the soft tissues covered by a denture may become inflamed and develop into a condition called denture stomatitis. This is treated with antifungal drugs such as nystatin or fluconazole, and the reiteration of suitable oral hygiene instructions.
Similarly, the dentures may become stained by products such as tea and coffee, and calculus may form on them in the same regions as for natural teeth. Patients with these problems are advised to clean the dentures by soaking in hypochlorite (for example, Milton solution) for 20 min, rinsing Figure 16.43 Pink wax, wax knife, burner.
(b) (a)
Figure 16.45 Acrylic burs (a) and stones (b).
Figure 16.44 Le Cron carver.
thoroughly and then immersing in water overnight. Dentures with metallic components should be
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soaked in non-hypochlorite disinfectants, such as Dentural, instead, otherwise the bleach-based products will cause metal corrosion.