Complete Lower Dentures on 1 or 2 Implants

This study is a randomized clinical trial to compare patient satisfaction and prosthetic outcomes with lower dentures retained by one or two implants. The investigators long-term objective is to establish evidence of the cost-effectiveness of a single implant intervention for improving tolerance to complete dentures. The investigators MAIN AIM will be to investigate patient satisfaction between and within groups with mandibular dentures retained by one or two implants over five years, and SECONDARILY to investigate the survival of implants, and the frequency of events to maintain the dentures and prosthetic attachments as clinically serviceable. Furthermore, multivariate analysis can assess the prediction of patient satisfaction with implant dentures based on various possible factors including age, health, demography and socioeconomic status, number of implants, and maintenance needs. Patient satisfaction will be measured by means of Visual Analogue Scales (VAS) including a measure of overall satisfaction and various specific aspects of satisfaction such as appearance, stability and comfort of the dentures.

The CENTRAL HYPOTHESIS is that mandibular complete dentures retained by single implants are at least as satisfying to patients over a five years period as those retained by two implants for the same period.

The SECONDARY HYPOTHESES are that:

i) there is no difference over five years between groups in the survival of original implants, or in the number of events for maintenance of the dentures or implant attachments; and ii) using each treatment group as it's own control, there is no change in patient satisfaction with lower dentures retained by either one or two implants during the five year loading period.


Eligibility Criteria:
Inclusion Criteria:

* functional in English or accompanied by a responsible adult who can provide translation services
* able to consent to, and participate in, the treatment provided
* available for the duration of the study
* edentulous and with at least six month's experience with conventional complete dentures
* currently wearing conventional complete dentures that are esthetically satisfactory to the patient and technically acceptable in the judgment of the study prosthodontist(s)
* medically/psychologically suitable for implant surgery in the judgment of the study dentists

Exclusion Criteria:

* insufficient alveolar bone height for implant(s) (\< 10 mm)
* history of head and neck radiation
* systemic or neurological disease, including: American Society of Anesthesiologists (ASA) Class 3 with recently diagnosed severe systemic disease, e.g. recent (within 6 months) myocardial infarction or stroke; risks associated with bacteraemia, e.g. immune compromise, steroids, in-dwelling catheters, stents, prosthetic heart valves, etc.; Type 1 diabetes, pituitary and adrenal insufficiency, and untreated hypothyroidism; chronic granulomatous disease, e.g. tuberculosis and sarcoidosis; bone disease, e.g. histiocytosis X, Paget's disease, fibrous dysplasia; history of congenital or acquired uncontrolled bleeding, e.g. coumadin
* previous oral implant treatment
* need for additional pre-prosthetic surgery
* need for new complete dentures
* medically/psychologically unsuitable for surgery in the opinion of the study dentists