Oral appliances (OAs) hold the lower jaw forward to reduce obstructive sleep apneas. Some OA designs allow mouth opening, which influences the forward positioning of the lower jaw. The aim of this pilot study was to compare the efficacy of an adjustable, custom-made OA (NarvalA (R)) in its original design, which allowed mouth opening, with the same OA with elastic bands that restricted mouth opening. Consecutive patients with an apnea-hypopnea index (AHI) of aeyen15 were randomized to start with an OA either with or without elastic bands in a single-blinded, crossover, pilot study. The patients underwent acclimatization and titration. After 3 weeks use of each device, they had renewed sleep apnea recordings and responded to questionnaires. Washout periods took place between the tests. Ten subjects with a median AHI of 19.7 (interquartile range (IQR) 17.3 to 31.8) were included. The AHI decreased to 3.1 (IQR 1.5-14.7) (p < 0.01) with the OA and to 5.1 (IQR 2.4-14.3) (p < 0.01) with the OA with elastic bands, with no difference between them (p = 0.7). The two subjects with severe obstructive sleep apnea (OSA) almost halved their supine AHI with, as compared to without, elastic bands. The majority of the patients preferred to use the elastic bands. This pilot study indicates that elastic bands markedly reduced the supine AHI in two subjects with severe sleep apnea as compared to without elastic bands. The majority of the patients preferred the use of elastic bands, although no significant difference in the AHI was observed with versus without the elastic bands in the whole sample.