A literature search indicates that since 1985 approximately 150 articles that describe various oral devices used in the treatment of sleep disorders have been published. The majority of these studies represent case series or case reports and a much smaller number are randomized controlled trials. It is generally accepted that treatment of OSA with oral appliances is a viable option for some patients with varying degrees of short- and long-term improvement and side effects. Oral appliance treatment includes, in order of decreasing usage, adjustable and nonadjustable mandibular posturing devices, anterior tongue positioners, and soft palate or uvula lifting devices. An appliance that advances the tongue, or tongue and mandible together with adjacent soft tissue, increases the posterior airway space, increases the activity of the genioglossal and lateral pterygoid muscles. It is not yet possible to predict the most advantageous appliance type for a particular patient. There are conflicting data regarding the effect of the degree of bite opening (vertical dimension of opening [VDO]) induced by oral appliances on treatment outcome. Although some studies have shown that appliances that promote an increased VDO are effective, physiologic evidence suggests that the VDO should be kept to a minimum to optimize treatment outcome. In this study, the efficacy of the of an oral appliance with minimum VDO will be tested against an appliance that increases VDO (such as twin block) based on the Epworth Sleepiness scale, Decibel readings, overall comfort of appliance for the patient, any potential side effects of either appliance. Furthermore, Computed tomographs will be taken to see the effect of the two appliances on the upper airway space of the patient with non-apnoeic snoring.