Dentures, also known as false teeth, are prosthetic devices constructed to replace missing teeth; they are supported by the surrounding soft and hard tissues of the oral cavity. Conventional dentures are removable. However, there are many different denture designs, some which rely on bonding or clasping onto teeth or dental implants. There are two main categories of dentures, the distinction being whether they are used to replace missing teeth on the mandibular arch or on the maxillary arch.
Dentures can help patients through:
- Mastication, as chewing ability is improved by replacing edentulous areas with denture teeth.
- Aesthetics, because the presence of teeth gives a natural appearance to the face, and wearing a denture to replace missing teeth provides support for the lips and cheeks and corrects the collapsed appearance that results from the loss of teeth.
- Pronunciation, because replacing missing teeth, especially the anteriors, enables patients to speak better. There is especially improvement in pronouncing words containing sibilants or fricatives.
- Self-esteem, because improved looks and speech boost confidence in the ability to interact socially.
- Fabrication of complete dentures
Modern dentures are most often fabricated in a commercial dental laboratory using a combination of tissue shaded powders polymethylmethacrylate acrylic (PMMA). These acrylics are available as heat cured or cold cured types. Commercially produced acrylic teeth are widely available in hundreds of shapes and tooth colors.
The process of fabricating a denture usually begins with an initial dental impression of the maxillary and mandibular ridges. Standard impression materials are used during the process. The initial impression is used to create a simple stone model that represents the maxillary and mandibular arches of the patient's mouth. This is not a detailed impression at this stage.
Once the initial impression is taken, the stone model is used to create a 'Custom Impression Tray' which is used to take a second and much more detailed and accurate impression of the patient's maxillary and mandibular ridges. Polyvinylsiloxane impression material is one of several very accurate impression materials used when the final impression is taken of the maxillary and mandibular ridges.
A wax rim is fabricated to assist Dr. Pollard in establishing the vertical dimension of occlusion. After this, a bite registration is created to marry the position of one arch to the other. Once the relative position of each arch to the other is known, the wax rim can be used as a base to place the selected denture teeth in correct position. This arrangement of teeth is tested in the mouth so that adjustments can be made to the occlusion. After the occlusion has been verified by Dr. Pollard and the patient, and all phonetic requirements are met, the denture is processed.
Processing a denture is usually performed using a lost-wax technique whereby the form of the final denture, including the acrylic denture teeth, is invested in stone. This investment is then heated, and when it melts the wax is removed through a spruing channel. The remaining cavity is then either filled by forced injection or pouring in the uncured denture acrylic, which is either a heat cured or cold-cured type. During the processing period, heat cured acrylics—also called permanent denture acrylics—go through a process called polymerization, causing the acrylic materials to bond very tightly and taking several hours to complete.
After a curing period, the stone investment is removed, the acrylic is polished, and the denture is complete. The end result is a denture that looks much more natural, is much stronger and more durable than a cold cured temporary denture, resists stains and odors, and will last for many years.
Cold cured or cold pour dentures, also known as temporary dentures, do not look very natural, are not very durable, tend to be highly porous and are only used as a temporary expedient until a more permanent solution is found. These types of dentures are inferior and tend to cost much less due to their quick production time (usually minutes) and low cost materials. It is not suggested that a patient wear a cold cured denture for a long period of time, for they are prone to cracks and can break rather easily. Dr. Pollard does not recommend the use of this type of denture.
- Problems with complete dentures
Problems with dentures may arise because patients are not used to having something in their mouth that is not food. The brain senses the appliance and interprets it as 'food', sending messages to the salivary glands to produce more saliva and to secrete it at a higher rate. This usually only happens in the first 12 to 24 hours, after which the salivary glands return to their normal output.
New dentures can also be the cause of sore spots as they compress the denture bearing soft tissues (mucosa). A few denture adjustments in the days following insertion of the dentures can take care of this problem.
Gagging is another problem encountered by a minority of patients. At times, this may be due to a denture that is too loose, too thick or extended too far posteriorly onto the soft palate. At times, gagging may also be attributed to psychological denial of the denture. Psychological gagging is the most difficult to treat since it is out of Dr. Pollard's control. In such cases, an implant-supported palateless denture may have to be constructed.
Sometimes there could be a gingivitis infection under the completed dentures, caused by the accumulation of dental plaque.
One of the most common problems for wearers of new upper complete denture is a loss of taste sensations.
- Prosthodontic principles
Support is the principle that describes how well the underlying mucosa (oral tissues, including gums) keeps the denture from moving vertically towards the arch in question during chewing, and thus being excessively depressed and moving deeper into the arch.
For the mandibular arch, this function is provided primarily by the buccal shelf, a region extending laterally from the back or posterior ridges, and by the pear-shaped pad (the most posterior area of keratinized gingival formed by the scaling down of the retro-molar papilla after the extraction of the last molar tooth). Secondary support for the complete mandibular denture is provided by the alveolar ridge crest.
The maxillary arch receives primary support from the horizontal hard palate and the posterior alveolar ridge crest. The larger the denture flanges (that part of the denture that extends into the vestibule), the better the stability (another parameter to assess fit of a complete denture). Long flanges beyond the functional depth of the sulcus are a common error in denture construction, often (but not always) leading to movement in function, and ulcerations (denture sore spots).
Stability is the principle that describes how well the denture base is prevented from moving in a horizontal plane, and thus sliding from side to side or front to back. The more the denture base (pink material) is in smooth and continuous contact with the edentulous ridge (the hill upon which the teeth used to reside, but now only residual alveolar bone with overlying mucosa), the better the stability. Of course, the higher and broader the ridge, the better the stability will be, but this is usually a result of patient anatomy, barring surgical intervention (bone grafts, etc.).
Retention is the principle that describes how well the denture is prevented from moving vertically in the opposite direction of insertion. The better the topographical mimicry of the intaglio (interior) surface of the denture base to the surface of the underlying mucosa, the better the retention will be (in removable partial dentures, the clasps are a major provider of retention), as surface tension, suction and friction will aid in keeping the denture base from breaking intimate contact with the mucosal surface.
It is important to note that the most critical element in the retentive design of a maxillary complete denture is a complete and total border seal (complete peripheral seal) in order to achieve 'suction'. The border seal is composed of the edges of the anterior and lateral aspects and the posterior palatal seal. The posterior palatal seal design is accomplished by covering the entire hard palate and extending not beyond the soft palate and ending 1–2 mm from the vibrating line.
Implant technology can vastly improve the patient's denture-wearing experience by increasing stability and preventing bone from wearing away. Implants can also aid retention. Instead of merely placing the implants to serve as blocking mechanism against the denture's pushing on the alveolar bone, small retentive appliances can be attached to the implants that can then snap into a modified denture base to allow for tremendously increased retention. Available options include a metal "Hader bar" or precision balls attachments.
- Complications and recommendations
The fabrication of a set of complete dentures is a challenge for any dentist. There are many axioms in the production of dentures that must be understood; ignorance of one axiom can lead to failure of the denture. In the vast majority of cases, complete dentures should be comfortable soon after insertion, although almost always at least two adjustment visits are necessary to remove the cause of sore spots.
One of the most critical aspects of dentures is that the impression of the denture must be perfectly made and used with perfect technique to make an accurate model of the patient's edentulous (toothless) gums. Dr. Pollard may use a process called border molding to ensure that the denture flanges are properly extended. An array of problems may occur if the final impression of the denture is not made properly. It takes considerable patience and experience for a dentist to know how to make a denture.
Once the laboratory receives dental impressions of the patient's mouth, the laboratory creates plaster molds from them. The laboratory uses the molds to create the wax rims used to register the patient's bite. These wax rims are returned to Dr. Pollard, who uses them to register the patient's bite. Dr. Pollard may assist the patient in choosing the correct size of teeth for the dentures, or simply make the selection himself. Once bite registration is completed and the teeth are selected for the dentures, the wax rim is usually returned to the dental laboratory in order to have the denture teeth set into the wax.
Once the teeth are set into the wax rim, the result is a prefinished denture that looks almost like the finished product. This prefinished denture is usually returned to Dr. Pollard and the patient usually has a chance to approve the setup and to try the denture before it is finished. After approval by the patient, Dr. Pollard returns the pre-denture to the laboratory for final processing. The finished denture is the returned for delivery to the patient.
The maxillary denture (the top denture) is usually relatively straightforward to manufacture so that it is stable without slippage.
A lower complete denture should or must be supported by two to four implants placed in the lower jaw for support. An implant-supported lower denture is far superior to a lower denture without implants, because:
It is much more difficult to get adequate suction on the lower jaw.
The functioning of the tongue tends to break that suction, and
Without teeth the ridge tends to resorb and provides the denture less and less stability over time. It is routine to be able to bite into an apple or corn-on-the-cob with a lower denture anchored by implants. Without implants, this is quite difficult or even impossible.
In any case, implant-supported dentures have several advantages over conventional dentures. They offer improved comfort due to less irritation of the gums, confidence due to less risk of slipping out, and appearance due to less plastic required for retention purposes. Patients with implant-supported dentures have increased chewing efficacy and can speak more clearly.
In cases where a patient needs a complete upper and lower set of dentures, costs can be reduced by having a conventional non-implanted upper denture, since retention of upper dentures is much easier to achieve, and an implanted lower denture, since lower dentures tend not to fit as well otherwise.
Daily cleaning of dentures is recommended. Plaque and tartar can build up on false teeth, just as they do on natural teeth. Cleaning can be done using chemical or mechanical denture cleaners.