Can rapid maxillary expansion affect speech sound production in growing patients? A systematic review.

Rapid maxillary expansion (RME) may change speech sound parameters due to the enlargement of oral and nasal cavities. This study aimed to systematically review the current evidence on speech changes as a side effect of RME. An electronic search was conducted in nine databases, and two of them accessed the 'grey literature'. The eligibility criteria included clinical studies assessing orthodontic patients with maxillary transverse deficiency and the relationship with speech alterations without restricting publication year or language. Only interventional studies were included. The JBI Critical Appraisal Tool assessed the risk of bias. The initial search provided 4853 studies. Seven articles (n = 200 patients) met the inclusion criteria and were analysed. The primary source of bias was the absence of a control group in four studies. RME altered speech production by changing vowel fundamental frequency and fricative phoneme formant frequency. Shimmer and jitter rates changed in one and two studies, respectively. Two studies presented deterioration during orthodontic treatment, but speech improved after appliance removal. Despite the limited evidence, RME affects speech during and after treatment.