# Prosthodontics/Copy technique

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In prosthodontics, the copy technique (or copy dentures) refers to duplication of an existing denture(s) with or without modification of the existing denture. They are an faster alternative to a remake of complete-complete acrylic dentures.
A denture has 3 surfaces:
* Occlusal surface- the biting surface of the artificial teeth on the denture
* Fitting surface- the unpolished surface that contacts the mucosa of the denture bearing area
* Polished surface- the part of the denture which is not the biting surfaces of the teeth and which does not sit on the mucosa.
The occlusal and fitting surface can be changed by the copy technique, but to change the polished surface, a complete remake is required.
Indications:
* Satisfactory position of teeth and polished surface
* Alveolar resorption has gradually made a set of existing dentures poorly fitting, although otherwise the dentures were successful. This is particularly helpful in elderly individuals who have less ability to adapt to new dentures in terms of neuromuscular control.
* Gradual wear of the occlusal surfaces which is making chewing difficult, in an otherwise successful set of dentures
* To make a spare set of existing dentures
* To replace immediate dentures
* Deterioration of denture base materials
Advantages of copy dentures:
* Less clinical and laboratory stages than normal method of making new dentures
* Less work for dental technician
* Can make copy dentures (usually) without damaging the old ones, and without needing to take the dentures away from the patient between appointments, which may be socially awkward for them

## Clinical stage 1: Create mould of existing dentures

At the first appointment, any modifications desired are made to the existing denture:
* Gross corrections to the peripheral extension using low fusing impression compound, greenstick or acrylic border moulding material
* Add a labial flange if the existing denture was open face (if required)
* A wax wafer is used to register the occlusion. Typically due to alveolar resorption and/or wear of the existing artifical teeth, the occlusal vertical dimension of the dentures is proportioally increased. This is done by adding wax to the occlusal surfaces of the teeth. The height is added to the upper, the lower, or both.
* Choose the shade (could be the same or a new shade as required)

## Laboratory stage 1: Make replicas

* Wax or self-curing acrylic resin replicas are poured. Typically the occlusal surface is made from wax, and the fitting surface is made from acrylic
* The wax teeth are replaced with artificial teeth of the same size and shape as in the existing denture, in the required shade
* The replicas are sent back to the clinic

## Clinical stage 2: Wax try-in & wash impression

* A try-in of the replicas
* Any errors in the position of the teeth are corrected. If the errors are significant, the instructions sent back to the lab and this stage needs to be repeated
* When the replicas are deemed suitable, Wash impressions are made (a thin-layer impression using the try-in as a special tray, which identifies the small dimensional changes that have occurred as a result of alveolar resorption since the time the original denture was made). Any undercut must be removed using a bur, the periphery is reduced, and the polished surface of the replica is coated with vaseline. The wash impression are made using zinc-oxide/eugenol, low-viscosity elastomer (if soft tissue undercuts are present) or light-bodied silicone in the closed mouth technique, reproducing the occlusion.
* The post dam is marked

## Laboratory stage 2: Finish

* Stone casts are poured from the impression, preserving the functional borders
* The acrylic palate, if one was used in the upper denture, is removed and an even-thickness palate is waxed up and then the final acrylic dentures are made
* Flask, pack and finish

## Clinical stage 3: Fit

* The copied dentures are tried, and adjusted if needed
* A review appointment in about 1 week is usually booked, when typically further smoothing of any rough edges is required

## References and further reading

Heasman P, ed (2008). Master Dentistry Vol I: Restorative dentistry, paediatric dentistry and orthodontics (2nd ed.). Edinburgh: Churchill Livingstone. p. 117-119. ISBN 9780443068959.