Overdenture

• Overlay Denture
• Hybrid Prosthesis
• Telescoping Denture
• Tooth Supported Denture
• Onlay dentures
• Superimposed dentures

Overdentures can be classified into 2 categories, depending on the types of abutment providing support:[7]

Retention and Stability

- If prescribing a removable prosthesis and there is limited remaining firm teeth in the dentition an overdenture may aid in retention and stability compared to that of a conventional removable prosthesis.[2]

Preventative Dentistry

- The use of an overdenture delays the process of leaving the patient completely edentulous and assists in the preservation of bone.[2]

- As a main priority for many dentists and patients, preventative dentistry is a reason for prescribing an overdenture as it retains the natural teeth for longer.[15]

Patient Anatomy

- Overdentures can be useful for patients with a severe ridge defect or bone resorption.[16]

- Patients who have unfavourable tongue positions and muscle attachment for a conventional removable prosthesis could find that an overdenture has increased retention and stability.[15]

- If the patient has a superficially placed mental nerve, then the preferential choice of treatment may be to leave certain teeth in place in order to prevent damage to the nerve and prescribe an overdenture for any aesthetic needs.[16]

Protection of Root Canal Filling

- An overdenture can be prescribed for a patient who has just had a root canal treatment completed to protect the coronal seal of the tooth if they are waiting to have fixed prosthodontics carried out on the tooth.

There are numerous advantages of overdentures when compared to conventional full or partial removable prosthesis. Overdentures can be supported and retained by natural roots left in situ or by dental implants. Implant retained dentures may be fixed or removable and are an option for the completely edentulous patient.  They offer the benefits that a root supported overdenture provides.

Proprioception

When roots are retained and used for overdentures, preservation of the periodontal membrane maintains proprioceptive impulses so the patient is aware of occlusal contacts and can control occlusal forces as they did with natural teeth.[17] Loss of proprioception is something which patients can struggle with accepting.

Bone Resorption

When teeth and roots are extracted, bone resorption ensues. This is greatest in the mandible and can be minimised by retaining roots.  Mandibular bone loss was examined by Crum and Rooney 1978 in patients with immediate complete dentures and in those with immediate overdentures on two lower canines. They found over the five years after placement 0.6mm bone loss in the overdenture group and 5.2 mm in the immediate complete dentures in the anterior part of the mandible. This reduction in bone loss enables increased stability and retention of the overdenture which has psychological and functional advantages for the patient.[18] Preservation of the alveolar ridge, especially with a lower prosthesis may improve patients comfort, chewing, phonetics and aesthetics allowing a better quality of life. A fixed implant retained denture is completely implant supported therefore further alveolar ridge resorption is avoided, unlike with a tissue supported prosthesis. An improvement in soft tissue health can also be seen.

There are a number of complications that can arise once overdentures are fitted in the mouth. These can range from post insertion tissue changes to fracture of the prosthesis.

Damage to Periodontal Tissues

The most common reason for changes within the periodontal tissues is the lack of adequate oral hygiene.[19] Plaque build up around overdenture abutments or precision attachments can lead to inflammation and hyperplasia of the gingiva. This can present as painful, red and swollen tissues, especially at the gingival margin. As a result, gingival recession may occur leading to exposure of the root surfaces to the oral environment. A study which looked at patients wearing overdentures found that the rate of tooth loss was in the order of 20% and was most commonly due to periodontal disease. Many of these failures could have been prevented with better oral hygiene methods.[20]

Tooth Decay

Any remaining tooth structure within the oral cavity is subject to developing caries and is often the result of lack of topical fluoride application, poor diet and poor oral hygiene. Caries can be found at the root face or root surface where gingival recession has occurred.[19] It is important to encourage patients to use a fluoride containing toothpaste over the denture abutments to minimise tooth surface loss and risk further infection.

Bone Resorption

Another tissue change that can result from wearing an overdenture is resorption of the alveolar bone. Although retention of a root prevents the alveolar bone from resorbing, at a distant site from the overdenture abutment the bone is susceptible to gradual resorption. This could lead to instability of the denture and uneven loading over time.[19] There is then a potential for the denture to irritate the mucosa due to repeated movement against the tissues.

Denture Stomatitis

Denture stomatitis is a common problem in full and partial denture wearers, and so can also be seen in patients wearing overdentures. It is an example of a yeast infection[21] and can arise due to various factors, for example poor oral hygiene, hyposalivation and poor diet. Common signs include ulcers, red and white patches or both.[22] It is important to encourage good denture hygiene methods and it may be necessary to provide a new denture.

Fractured Prosthesis

As well as damage to intra-oral tissues there is also a possibility of fracture of the prosthesis itself. Overdentures retained by attachments have been found to be more likely to fracture.[19] A study looking at implant retained mandibular overdentures compared the risk of fracture between one implant retained denture and two. The results showed that the incidence of denture base fracture was not significantly different between the presence of one or two implants but when a fracture did occur it was found to be in areas around the implants.[23]

A 10-year observational period found that implants which supported overdentures in the mandible had a survival rate ranging from 91.7% to 100%.[24] Furthermore, implant survival rates with respect to their attachment system were found to be best for the ball type attachment which was an average of 95.8 - 97.5%, followed by the bar and magnet ranging from 96.2 - 100% , and 91.7% respectively.[24]