Removable Dentures both partial and full dentures can be used to replace some or all missing teeth. Dentures can be made up of different materials. The three most common materials are cobalt chrome, acrylic and valplast.
Valplast dentures are made of a material that is based on thermoplastic nylon. It is not often used but can be extremely comfortable for replacement of one or two teeth that are adjacent to each other. It however can be quite expensive and therefore isn’t used often.
Step 1: Denture Assessment and Consult
Treatment Planning and Consult
A denture consult should involve a thorough examination of the patient’s mouth including both arches and the occlusal relationships as well as pulpal, periapical and periodontal status of abutment teeth. An OPG is almost vital to have as it allows a big-picture image on the bone levels, status of current teeth and any teeth that may need to be extracted. These include periodontally compromised teeth or grossly carious teeth such as root stumps. For patients with complete edentulism an assessment of the residual ridge should be undertaken, As a removable denture is always the last part of any treatment planning, any restorative and periodontal treatment should be undertaken prior.
Taking the primary Impression
Primary impressions are usually taken on the first denture appointment. Primary impression is taken using alginate and should accurately capture the labial + lingual sulcus to allow fabrication of a special tray. An appropriate tray size selection is important.
How to Take Alginate impressions
Check the tray size in the mouth to ensure that the fit is adequate.
Mix the alginate in the correct ratio according to the manufacturer's instructions.
Place alginate into the tray using a wooden paddle pop stick.
For upper impressions, it is best to take the impression from behind with the patient sitting completely upright. Retract the upper lip with your left index and middle fingers and seat the tray into the upper arch ensuring that the rear of the tray is pressed against the palate first, then lift the anterior portion of the tray firmly up so that any anterior teeth seat firmly into the tray. Pull the upper lip over the remaining tray and wait for material to set.
For lower impressions, It is better to take impressions from the front of the patient. Again retract lips using left index and middle finger. Ask the patient to lift their tongue to the top of the palate. Insert the impression down with moderate pressure. Pull the lower lip over the tray and wait for the material to set.
Likely problems to be encountered
Some patients may have a strong gag reflex during impression taking. Ensure the patient is seated upright. Use salt or numbing mouthwash (cepacaine) prior to impression.
Multiple retakes of impression may be required. Warn patient prior to commencement.
An image of a good alginate impression.
An image showing a good full upper impression whereby all the sulci are captured. The maxillary tuberosity and retromolar pad regions are especially important for retention for acrylic full dentures.
Step 2: Secondary Impression +/- Tooth Preparation
Depending on the choice of material for denture, tooth preparation may need to be done. For Cobalt chrome dentures, rest seats may be required if there is not enough occlusal clearance. Occlusal clearance can be checked either through hand articulating the study models or for more complex patients using an articulator. Occlusal clearance needs to be ideally 0.7mm.
Taking a Secondary Impression using a Special Tray
There are three types of materials that can be used for Secondary Impression.
1. Alginate Impression
Alginates are able to be used and can capture details with relatively good accuracy. It is often used as a secondary impression due to its low cost. It is especially common for partial acrylic dentures. Ideally alginate should be poured within 1 hour of taking the impression as it is dimensionally unstable and can distort when left unpoured. It however is only suitable to be poured once. The special tray designed for alginate will need to be perforated.
A special perforated tray for a secondary alginate impression
2. Polyvinyl siloxane (PVS)
PVS is an elastomeric material and is one of the more accurate and dimensionally stable materials. It has high tear strength and can be poured multiple times without distortion. However many PVS materials have a setting time of about 4-5mins and are somewhat hydrophobic so the field needs to be relatively dry. It is often used for secondary impressions of chrome dentures especially when rest seats or overlay teeth have been prepared.
3. Polyether (PE)
Polyether is another one of the elastomeric impression materials. It is also highly accurate and dimensionally stable. It is somewhat more hydrophilic than PVS. However it has a strong odour and can get caught in tissue undercuts. It is not suitable for patients with significant hard or soft tissue undercuts.
Border Moulding
Border Moulding is the process of adapting the periphery of the special tray to the contours of the tissues and contours of the mouth. It is most often done for complete dentures but may need to be done for partial acrylic dentures that replace many missing teeth. A material such as greenstick or medium body PVS can be used for border moulding.
Border Molding Technique:
The dentist or dental assistant applies the border molding material to the borders of the custom tray. They gently press the tray into the oral tissues, adapting the material to capture the contours of the vestibule and muscles around the mouth. The material is manipulated to create an accurate representation of the soft tissue anatomy, including the frenulum, tuberosities, and peripheral extensions.
An image showing a special tray that has been border moulded with green stick.
Steps for taking a secondary impression
Check the special tray on the cast to ensure adequate extension. The flanges of the tray should not be overextended or un
Apply generous amount of the specific adhesive to the special Tray.
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