Three-dimensional skeletal and dental effects of the Haas vs. hyrax type expanders in adolescent rapid maxillary expansion : Systematic review and meta-analysis.

PURPOSE: The three-dimensional dentoskeletal effects of Haas versus hyrax rapid maxillary expanders (RMEs) in adolescents with maxillary transverse deficiency remain uncertain. We conducted a systematic review and meta-analysis to compare their short-term skeletal and dental outcomes using three-dimensional measurements. Additionally, uncontrolled Haas studies were descriptively synthesized to contextualize within-group changes.

METHODS

Electronic searches (PubMed, Embase, Web of Science, Cochrane, China National Knowledge Infrastructure) up to January 2025 identified eligible clinical studies in adolescents reporting three-dimensional outcomes. Comparative studies that directly evaluated the Haas versus hyrax appliances were incorporated into the quantitative synthesis, while single-arm or self-controlled studies applying the Haas appliance were included solely in the qualitative synthesis. Primary outcomes included midpalatal suture width, first molar and premolar interdental distances, buccal and lingual alveolar bone thickness at first molars, and first molar inclination.

RESULTS

Nine studies met inclusion criteria: seven comparative studies (Haas vs. hyrax; meta-analysis), two Haas-only (narrative synthesis). Across all six evaluated outcomes, pooled analyses revealed no statistically significant differences between the Haas and hyrax expanders. Substantial heterogeneity was observed for midpalatal suture width, first molar distance, and lingual alveolar bone thickness.

CONCLUSION

Current comparative evidence does not reveal statistically significant short-term differences between the Haas and hyrax expanders concerning the evaluated three-dimensional skeletal and dental outcomes. These findings suggest that the existing evidence does not substantiate clear superiority or inferiority of the Haas appliance compared to the hyrax appliance for the assessed outcomes.