Introduction The purpose of this study was to assess speech perturbation and adaptation for patients wearing modified C‐palatal plates (MCPPs) over time. Methods The sample consisted of 40 patients, 20 wearing MCPPs as the experimental group (age: 20.7 ± 5.8 years) and 20 patients wearing a transpalatal arch (TPA) as the control group (age: 21.5 ± 6.4 years). The sounds /t/, /d/, /s/, /n/, /r/, /tʃ/. and /j/ were recorded for each patient at six time points: immediately before (T0) and after (T1) appliance placement; then 1, 2, 3 and 4 weeks after placement (T2–T5). Acoustic analysis of pitch and voice onset time (VOT) was performed by Praat software. Repeated measures analysis of variance (RM‐ANOVA) was used to assess changes in the pitch and VOT over time and the difference between the appliances. Results With the MCPP appliance, /n/, /r/, /tʃ/ and /j/ decreased in VOT starting in the first week while /t/ and /s/ almost returned to pre‐treatment levels after 2 weeks. VOT for the /d/ sound did not change between T0 and T3, but it decreased after 3 weeks. There were no significant differences in pitch and VOT between the two groups at any time point. Conclusions Wearing an MCPP device caused patients to initially distort the articulation of several sounds, but the distortion dissipated within 1 to 2 weeks. It is recommended that patients and/or their parents be advised during pre‐treatment counselling of the possibility of temporary speech changes with MCPP placement.