Complete dentures


A complete denture is a removable appliance used when all teeth within a jaw have been lost and need to be prosthetically replaced. In contrast to a partial denture, a complete denture is constructed when there are no more teeth left in an arch; hence, it is an exclusively tissue-supported prosthesis. A complete denture can be opposed by natural dentition, a partial or complete denture, fixed appliances or, sometimes, soft tissues.

Epidemiology and causes of tooth loss

There has been a decline in both the prevalence and incidence of tooth loss within the last decades; people retain their natural dentition for longer. Nonetheless, there is still a great demand for complete dentures as more than 10% of adults aged 50–64 are completely edentulous, with age, smoking status and socioeconomic status being significant risk factors. Tooth loss can occur due to many reasons, such as:
Following the loss of teeth, there occurs a resorption of alveolar bone, which continues throughout life. Although the rate of resorption varies, certain factors such as the magnitude of loading applied on the ridge, the technique of extraction and healing potential of the patient seem to affect this. The edentulous ridge can be classified according to the amount of bone in both the vertical and horizontal axes:
  • Class I: dentate
  • Class II: immediately post-extraction
  • Class III: well-rounded ridge form, adequate in height and width
  • Class IV: knife-edge ridge form, adequate in height and inadequate in width
  • Class V: flat ridge form, inadequate in height and width
  • Class VI: depressed ridge form, with some basilar loss evident
Alveolar bone resorption is an important consideration when designing complete dentures. In the absence of natural dentition, such dentures rely completely on soft tissues for their support. As a consequence, the forces exerted on the mucosa are significant and may, in turn, lead to an increased rate of bone resorption. Therefore, in order to ensure an equal distribution of forces across the mucosa, complete dentures should have maximum extensions.
Facial muscles on the cheeks and lips also lose their support as teeth are lost, contributing to an 'aged' appearance of the individual. Although complete dentures cannot prevent the loss in muscular tone, they can nevertheless provide some artificial support to mask this loss in tone. Furthermore, perhaps the most noticeable effect of tooth loss from a patient perspective is the loss in masticatory efficiency. Teeth function to help with the chewing of food, breaking it down in small pieces that can be swallowed. Denture-wearing can bring some masticatory function back to normal. It cannot, however, fully compensate for the efficiency of the natural dentition because dentures are not fixed in place like teeth are and so have to be actively controlled by the muscles and biting forces are greatly reduced as the dentures are impinging on soft tissues.

Principles of complete dentures

Complete dentures are prone to a variety of displacing forces of differing magnitude as they are resting on oral mucosa and are in close proximity with tissues that are constantly changing due to the action of muscles. Consequently, for complete dentures to be retentive and stable, the retentive forces that hold the dentures in place must be greater than the ones aiming to displace it. Obtaining maximum stability and retention is one of the biggest challenges in full denture construction.

Retention

Retention in removable prosthodontics can be defined as the resistance to vertical dislodgment that can arise from either muscular forces or physical forces. It can be gained from three different surfaces of the denture:
  1. Occlusal surface
  2. Polished surface
  3. Impression surface

    Muscular control of the dentures

The peri-oral muscles can cause displacement of the dentures. Patients can, however, learn to control and coordinate their muscles so that the forces exerted are minimised or counter-acted to prevent such displacement. With age, the ability to learn new skills and acquire some level of neuromuscular control declines. Therefore, the "training" time-frame for patients to learn how to successfully use their new complete dentures is expected to be much longer for older patients.

Transition into complete dentures

Many patients find the idea of wearing complete dentures very upsetting. Such psychological effects, together with the challenges that accompany successful prosthetic wear, can make acceptance of treatment difficult. It is, therefore, reasonable to consider different ways of transitioning into the edentate state in patients who have not yet lost all of their teeth but in which complete dentures will be required in the foreseeable future. Certain teeth can be retained in the short to medium-term with partial dentures provided in the interim so that the patient can become accustomed to denture wearing. Alternatively, if the former is not possible, consideration should be given to whether roots of teeth can be retained in strategic locations in the maxilla or mandible to help with the stability of the prostheses.

Transitional partial dentures

Teeth that can be restored despite a poor long-term prognosis may be retained to transition the patient into the edentulous state via a series of transitional partial dentures. It is important that the patient can maintain good plaque control during this period, as progression of periodontal disease will lead to further destruction of bone that will later become the foundation for denture support. Complete dentures require some level of muscular control from the patient and this process of adaptation can last for several weeks or even months. As patients age, the process of learning and memorising new skills as well as neuromuscular control becomes more challenging. Hence transitional partial dentures can provide a practice period for the musculature, before complete dentures are provided.

Overdentures

An overdenture is a prosthesis that fits over retained roots or implants in the jaws. Compared to conventional complete dentures, it provides a greater level of stability and support for the prosthesis. The mandibular jaw has significantly less surface area compared to the maxillary jaw; hence, retention of a lower prosthesis is greatly reduced. Consequently, mandibular overdentures are much more commonly prescribed than maxillary ones, where the palate often provides enough support for the plate.

Tooth supported

Retaining two or three natural teeth as retained roots can greatly improve the retention and stability of a complete denture, especially if the roots are fitted with special precision attachments. The process involves decoronation and elective root canal treatment of the overdenture abutments. For matters of simplicity for endodontic treatment provision, single-rooted anterior teeth are preferred, with the exception of lower incisors as they lack sufficient root surface area. If plaque control is satisfactory, tooth-supported overdentures can be considered as a long-term treatment option. Alternatively, if treatment fails, the roots can be extracted and the overdenture can easily be converted into a conventional complete denture.
Advantages
  • Increased retention of prosthesis
  • Reduced alveolar bone resorption and preservation of alveolar ridge
  • Reduced horizontal forces
  • Proprioception maintained
  • Improved aesthetics
    Disadvantages
  • Requires endodontic treatment of abutment teeth
  • Predisposes to dental caries and periodontal disease

    Implant supported

Although an implant-supported overdenture is not appropriate for the short-term transitioning stage into conventional complete dentures, it is an option that should be considered for the definitive treatment, given the higher stability and retention of such dentures. Despite complications, the success rate of dental implants is well established, with reports exceeding 98% in 20 years for mandibular anterior teeth. The provision of a two-implant supported overdenture in the mandibular edentulous jaw is now considered as the first choice of treatment, with patients reporting to have a significant improvement in quality of life and greater patient satisfaction when compared to conventional removable prostheses.

Immediate dentures

When clearance of the dentition is the only viable treatment option, immediate dentures can be constructed prior to the extractions and fitted once the teeth have been removed, at the same appointment. Such dentures help restore masticatory function and aesthetics whilst at the same time allowing a period for the soft tissues to heal and the bone levels to stabilise before constructing the definitive complete dentures.

Advantages

  • Restoration of aesthetics and masticatory function
  • Allow for time of adaptation as the patient gets used to their new dentures
  • Psychosocial advantages
  • Protection of wound area following extractions
  • Allow clinician to transfer jaw relationship and aesthetics from natural teeth onto immediate dentures. If immediate dentures are not provided, then following extraction of the teeth such information will be lost; hence it prevents later 'guesswork'.

    Disadvantages

  • Unpredictable fit and aesthetics – the dentures are constructed before all teeth are removed in a jaw; therefore, there is some level of guesswork involved with respect to tooth placement and the fitting surface of the denture.
  • Limited lifespan of prosthesis and relines often required – as the tissues heal following extractions, the alveolar bone starts to resorb causing the tissues to recede. Consequently, immediate dentures will require some level of maintenance, with relines of the fit surface and/or occlusal adjustments.