Obstructive sleep apnoea (OSA) is a serious and common disorder affecting one in twenty-five men and one in fifty women over the age of 30. This breathing abnormality occurs during sleep and is characterised by snoring and episodes of sleep disturbances. The symptoms of untreated OSA (e.g. excessive daytime sleepiness), can result in significant reductions in the patients' quality of life. The key treatment modalities today include Continuous Positive Air Pressure (CPAP), surgery and the use of oral appliances (OAs). Increasingly, OAs have been advocated in the treatment of the symptoms of OSA since they offer a non-invasive form of treatment and also because patients often prefer this treatment to other treatment modalities. There is increasing evidence to support the effectiveness of OAs in the management of OSA, at least as a short term measure. What is still unclear is which types of OA are most effective and whether OAs are effective in the long term management of OSA. This randomized clinical trial aims to evaluate two differently designed OAs in terms of their effect on patients' quality of life and on the physiological symptoms of OSA (apnoea/hypopnoea index AHI). Around 45 patients with OSA will be recruited from a pool of patients referred to the dental hospital for treatment from the medical faculty. The treatment with OAs will commence after randomization to two treatment groups; follow-up examinations will take place over a period of 12 months. The results of this study will help inform practitioners and patients of the feasibility of using OAs in the long term management of OSA and help determine the most appropriate type of OAs for the management of OSA and improvement in quality of life.