The impact of maxillary osteotomy on speech outcomes in cleft lip and palate: an evidence-based approach to evaluating the literature.

Objective : To undertake a critical and systematic review of the literature on the impact of maxillary advancement on speech outcomes in order to identify current best evidence. Design and Main Outcome Measures : The following databases were searched: PubMed, CINAHL, and The Cochrane Controlled Trials Register. In addition, reference lists were hand searched for additional articles. Using a predefined framework and set criteria, evidence was evaluated using the assignment of levels of evidence (at least Level III on the evidence hierarchy), calculation of post-hoc power (≥ 0.8), effect size (Cohen's d ≥ 0.5), and adaptation of the parameters as set out by The Cochrane Collaboration. Results : Of the 40 studies identified, the majority (68%) fell within Level III.ii, representing cohort-type studies and a fifth (20%) within Level IV, the weakest form of evidence. Power and effect size calculations were only possible in 9 studies for different speech outcomes, and only seven studies met the set criteria for best evidence. Accordingly, current best evidence for articulation exists only for a noncleft population, is conflicting for resonance and nasalance, and is mixed for velopharyngeal function depending on which instrumental measure is used. Conclusions : There is an obvious need for further prospective research in the field with strong speech methodology such as the undertaking of interrater and intrarater reliability, adequate follow-up, and sufficient sample sizes based on a priori power analyses. Methodologic issues are discussed and recommendations made.