Dento-skeletal effects produced by rapid versus slow maxillary expansion using fixed jackscrew expanders: A systematic review and meta-analysis

Background: No systematic review and meta-analysis of dento-skeletal effects following rapid maxillary expansion (RME) and slow maxillary expansion (SME) using the same jackscrew expander with different activation protocols is available. Objective: To compare dento-skeletal effects produced by RME with those induced by SME using the same fixed jackscrew expanders in growing patients. Search methods: PubMed (MEDLINE), Cochrane Library, Scopus, Embase, and OpenGrey were searched with no language or publication date restrictions. Selection criteria: Only randomized controlled trials (RCTs) were selected and the following inclusion criteria were used: growing patients in mixed or permanent dentition, with maxillary transverse discrepancy, dental crowding, and treated with fixed jackscrew maxillary expander (e.g. Hyrax, Haas) activated to achieve either RME or SME. Data collection and analysis: Data were extracted by two independent reviewers. The quality of the included RCTs was assessed according to the Cochrane risk-of-bias tool for randomized trials (RoB 2.0). For the aggregation of continuous data, the mean of the differences (MD) between treatments was used. A random effect model was applied. Results: From 4855 retrieved articles, 3 studies were selected, 1 at unclear risk and 2 at high risk of bias. Maxillary intermolar distance showed no significant differences between the two modalities of expansion [pooled MD = 0.99 mm favouring RME, with 95% confidence interval (CI) =-2.09 to 4.06, P = 0.53, I2 = 90%]. As for maxillary molar inclination measured as the angle formed by the axes passing through the disto-buccal cusps and the apexes of the palatine root of the first upper molars, it was significantly smaller in the SME group (MD =-11.51°, with 95% CI =-15.23 to-7.79, P < 0.0001). Posterior maxillary expansion was significantly greater in RME than SME (pooled MD = 0.75 mm, with 95% CI = 0.27-1.23, P = 0.002, I2 = 0%). Conclusions: Both RME and SME produce an effective dento-skeletal expansion of the maxilla. RME is slightly more effective in increasing the posterior transverse skeletal width of the maxilla while SME induces smaller molar inclination.