Dentures

Dentures
MeSH	D003778

A maxillary denture.

Occlusal view of the same maxillary denture.

Dentures, also known as false teeth, are prosthetic devices constructed to replace missing teeth, and which are supported by 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, depending on whether they are used to replace missing teeth on the mandibular arch or the maxillary arch.

Causes of tooth loss

Patients can become entirely edentulous (without teeth) for many reasons, the most prevalent being removal because of dental disease typically relating to oral flora control, i.e. periodontal disease and tooth decay. Other reasons include tooth developmental defects caused by severe malnutrition, genetic defects such as dentinogenesis imperfecta, trauma, or drug use.

Advantages

Dentures can help patients through:t

• Mastication as chewing ability is improved by replacing edentulous areas with denture teeth.
• Aesthetics because the presence of teeth provide a natural facial appearance, and wearing a denture to replace missing teeth provides support for the lips and cheeks and corrects the collapsed appearance that occurs after losing teeth.
• the improvement of pronunciation of those words containing sibilants or fricatives by replacing missing teeth, especially the anteriors enabling patients to speak better.
• improving self-esteem

Types

Removable partial dentures

Removable partial dentures are for patients who are missing some of their teeth on a particular arch. Fixed partial dentures, also known as "crown and bridge", are made from crowns that are fitted on the remaining teeth to act as abutments and pontics made from materials to resemble the missing teeth. Fixed bridges are more expensive than removable appliances but are more stable.

Complete dentures

Conversely, complete dentures or full dentures are worn by patients who are missing all of the teeth in a single arch (i.e. the maxillary (upper) or mandibular (lower) arch).

History

Around 700BC, Etruscans in northern Italy made dentures out of human or other animal teeth. These deteriorated quickly but, being easy to produce, were popular until the mid-19th century.

The oldest useful complete denture appeared in Japan, and has been traced to the ganjyoji temple in Kii Province, Japan. It was a wooden denture made of Buxus microphylla, and used by Nakaoka Tei (–20 April 1538). This wooden denture had almost the same shape as modern dentures retained by suction. It also shaped to cover each condition of teeth loss. Wooden dentures were used in Japan up until the Meiji period.

London's Peter de la Roche is believed to be one of the first 'Operators for the Teeth', men who fashioned themselves as specialists in dental work. Often these men were professional goldsmiths, ivory turners or students of barber-surgeons.

The first porcelain dentures were made around 1770 by Alexis Duchâteau. In 1791, the first British patent was granted to Nicholas Dubois De Chemant, previous assistant to Duchateau, for "De Chemant's Specification", "a composition for the purpose of making of artificial teeth either single double or in rows or in complete sets, and also springs for fastening or affixing the same in a more easy and effectual manner than any hitherto discovered which said teeth may be made of any shade or colour, which they will retain for any length of time and will consequently more perfectly resemble the natural teeth." He began selling his wares in 1792, with most of his porcelain paste supplied by Wedgwood.

In London in 1820, Claudius Ash, a goldsmith by trade, began manufacturing high-quality porcelain dentures mounted on 18-carat gold plates. Later dentures were made of Vulcanite from the 1850s on, a form of hardened rubber (Claudius Ash’s company was the leading European manufacturer of dental Vulcanite) into which porcelain teeth were set, and then, in the 20th century, acrylic resin and other plastics. In Britain sequential Adult Dental Health Surveys have shown that, in 1968, 79% of those aged 65–74 had no natural teeth;, by 1998, this proportion had fallen to 36%. ref Murray JJ. Adult dental health surveys: 40 years on. Br Dent J. 2011 Nov 11;211(9):407-8.

Fabrication of complete dentures

Modern dentures are most often fabricated in a commercial dental laboratory using a combination of a tissue shaded powder polymethylmethacrylate acrylic (PMMA) for the tissue shaded aspect, and commercially produced acrylic teeth available in hundreds of shapes and tooth colors.

The process of fabricating a denture usually begins with a dental impression of the maxilla or mandible. This impression is used to create a stone model that represents the arch. A wax rim is fabricated to assist the dentist or denturist with 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 tried in the mouth so that adjustments can be made to the Occlusion. After the occlusion has been verified by the dentist with the patient, and all phonetic requirements are met, the denture is processed.

Processing a denture is usually performed in a lost-wax process whereby the form of the final denture, including the acrylic denture teeth, is invested in stone. This investment is then heated, and the wax is removed through a sprue when it melts. The remaining cavity is then either filled by forced injection or pouring of the uncured denture acrylic. After a curing period, the stone investment is removed, the acrylic is polished, and the denture is complete.

Problems with complete dentures

Problems with dentures include the fact that patients are not used to having something in their mouth that is not food. The brain senses this appliance as "food" and sends messages to the salivary glands to produce more saliva and to secrete it at a higher rate. This will only happen 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 soft tissues mucosa (denture bearing soft tissue). A few denture adjustments for the days following insertion of the dentures can take care of this issue. 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 the dentist's control. In such cases, an implant supported palateless denture may have to be constructed). Sometimes there could be a gingivitis under the full dentures, which is caused by accumulation of dental plaque.

One of the most common problems for new full upper denture wearers is the loss of taste.

Another problem with dentures is keeping them in place. There are three rules governing the existence of removable oral appliances: support, stability and retention.

Prosthodontic principles of dentures

Support

Support is the principle that describes how well the underlying mucosa (oral tissues, including gums and the vestibules) keeps the denture from moving vertically towards the arch in question, and thus being excessively depressed and moving deeper into the arch. For the mandibular arch, this function is provided by the gingiva (gums) and the buccal shelf (region extending laterally (beside) from the posterior (back) ridges), whereas in the maxillary arch, the palate joins in to help support the denture. The larger the denture flanges (part of the denture that extends into the vestibule), the better the support and stability. 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.

Stability

Stability is the principle that describes how well the denture base is prevented from moving in the horizontal plane, and thus from sliding side to side or front and back. The more the denture base (pink material) runs in smooth and continuous contact with the edentulous ridge (the hill upon which the teeth used to reside, but now consists of 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 just a result of patient anatomy, barring surgical intervention (bone grafts, etc.).

Retention

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 full maxillary 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 saving his or her bone from wearing away. Implants can also help with the retention factor. Instead of merely placing the implants to serve as blocking mechanism against the denture 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. Options available include a metal Hader bar or precision balls attachments, among other things.

Complications and recommendations

The fabrication of a set of complete dentures is a challenge for any Dentist/Denturist, including those who are experienced. There are many axioms in the production of dentures that must be understood; ignorance of one axiom can lead to failure of the denture case. In the vast majority of cases, complete dentures should be comfortable soon after insertion, although almost always at least two adjustment visits will be necessary to remove 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 a model of the patient's edentulous (toothless) gums. The dentist must 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, and for this reason it may be in the patient's best interest to seek a specialist, either a prosthodontist or perhaps even a denturist, to make the denture. A general dentist may do a good job, but only if he or she is meticulous and usually he or she must be experienced.

The maxillary denture (the top denture) is usually relatively straightforward to manufacture so that it is stable without slippage.

A lower full denture should or must be supported by 2-4 implants placed in the lower jaw for support. A lower denture supported by 2-4 implants is a far superior product than a lower denture without implants, because

1) It is much more difficult to get adequate suction on the lower jaw.
2) The functioning of the tongue tends to break that suction, and
3) 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, it is quite difficult or even impossible to do so.

In any case, implant supported dentures provide 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.

Some patients who believe they have "bad teeth" may think it is in their best interests to have all their teeth extracted and full dentures placed. However, statistics show that the majority of patients who actually receive this treatment wind up regretting they did so. This is because full dentures have only 10% of the chewing power of natural teeth, and it is difficult to get them fitted satisfactorily, particularly in the mandibular arch. Even if a patient retains one tooth, that will contribute to the denture's stability. However, retention of just one or two teeth in the upper jaw does not contribute much to the overall stability of a denture, since a full upper denture tends to be very stable, in contrast to a full lower denture. It is thus advised that patients keep their natural teeth as long as possible, especially their lower teeth.

Denture Care

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 by chemical or mechanical denture cleaners.