Objective: The worldwide prevalence of obstructive sleep apnea (OSA) is increasing day by day and is estimated to be as prevalent as asthma and diabetes. Untreated sleep apnea can have dire health consequences and can increase risk of hypertension, diabetes, heart disease, and heart failure. Dentists are often the first professional to become aware of a potential problem since they are usually in contact with their patients more frequently than are physicians. The present study was aimed at evaluating the effect of four different mandibular advancement splints fabricated at different jaw positions on sleep parameters in patients with OSA. Method and Materials: 72 patients who fulfilled the study criteria were selected. All the patients were randomly divided into four groups of 18 patients each. All the patients in group 1 were given a mandibular advancement splint (MAS) fabricated at 60% of maximum protrusion and 4 mm of vertical opening. All the patients in group 2 were given a MAS fabricated at 60% of maximum protrusion and 6 mm of vertical opening. All the patients in group 3 were given a MAS fabricated at 70% of maximum protrusion and 4 mm of vertical opening. All the patients in group 4 were given a MAS fabricated at 70% of maximum protrusion and 6 mm of vertical opening. Results: The maximum change in all the sleep parameters was observed in group 3 when MAS was fabricated at 70% of maximum protrusion and 4 mm of vertical opening. Conclusion: The present study suggested that MAS was more effective with no patient discomfort when fabricated at 70% of maximum protrusion and 4 mm of vertical jaw separation. Schlagwörter: Apnea/Hypopnea Index (AHI), jaw position, mandibular advancement splint, obstructive sleep apnea