In this video we visit Dr Tony Johnson, Dental Technician, in the dental laboratory to observe how dentures are made.
You will see the skills of the dental technician, the specialist equipment used, and some of the materials we have been learning about so far on the course.
The construction of dentures requires a patient to attend a number of visits to the dentist, with the dental technician making a sequence of models, trays and ‘try-ins’ before the completed dentures are fitted. The following is a brief overview of the steps required to provide a set of dentures for a patient, and the video shows you each step in the dental laboratory (with the time it is shown in the video in brackets).
1) The dentist takes the primary impressions of the patient’s mouth using an impression material contained in a stock tray (a pre-made impression tray that comes in a number of sizes, and the dentist will use the size that best fits the patient’s mouth).
2) The impressions are given to the dental technician, who casts plaster models from the impressions. These are called the primary models.
3) The technician will make customised impression trays for the patient using the primary models that will provide much more accurate impressions. These are called special trays and allow for a much better quality impression to be taken by fitting the mouth closely, and providing an even support for the impression material (think of it as the difference between ‘off the peg’ and tailored clothes). (1:00)
4) The dentist will take new impressions using the special trays and send them to the dental technician.
5) The technician will cast up the new models, and these are the working models that the dentures will be constructed on.
6) Before the dentures can be made, registration blocks are first constructed. These are made from wax (often with a resin-base for rigidity). The blocks are made to occupy the space in the mouth where the dentures will be and provide means of recording where the teeth will need to be placed. (2:55)
7) The registration blocks are placed into the patient’s mouth and the dentist adjusts them for height (recording where the upper and lower teeth will meet), and contour so that they mimic as closely as possible the patient’s missing teeth. The blocks are returned to the technician.
8) The models and registration blocks are mounted onto an articulator: a device that mimics the patient’s jaw movements. (6:12)
9) Pre-made acrylic teeth are placed into the blocks, keeping everything aligned within the boundaries defined by the dentist during step 7. The upper anterior teeth are usually placed first. The lowers and posterior teeth are placed after. (6:48)
10) Denture teeth are placed in such a way that there is usually always a bilateral (each side) contact between the upper and lower denture, to stop them tipping during talking and chewing. This is called balanced occlusion and is different to what is found naturally.
11) The denture is waxed up, using wax to make the soft tissue areas mirror as closely as possible natural gums. (7:15)
12) The dentures are returned to the dentist at this point for a try-in, where they are checked for fit, function and aesthetics. Any changes required are relatively simple to do as the denture is made from soft wax.
13) The completed denture, on its plaster model, is placed into a 2-part mould called a flask. Plaster of Paris is poured over the dentures in such a way that the mould can later be separated. A separating medium called sodium alginate acts as a separating skin to allow the mould to later come apart again. (8:45)
14) The wax dentures, still in the closed flasks are placed into hot water to melt the wax. The flask is then opened gently, and the remaining wax washed away with further hot water to leave a mould containing the acrylic teeth embedded with it. (9:50)
15) The mould is filled with pink acrylic-resin dough, closed and compressed until it is cured. The curing takes place in hot water and takes a few hours. (10:20)
16) The now acrylic dentures are retrieved from the flasks, which requires the use of saws and chisels. (11:55)
17) The dentures are fitted back onto the articulator to be ground in where any increased height in the denture from the moulding process is corrected. (13:55)
18) The dentures are cleaned, polished and returned to the dentist for fitting.
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