Four studies (n=412) were included.
Dental casts.
Long-term follow-up (minimum 1 year) (21 adults) found a net gain of 4.8 mm in maxillary molar transarch width and a net gain of 0.7 mm in mandibular molar transarch width when treated with RME, compared with the control group, in one study. A net increase in transarch width was also found for the maxillary first premolar (4.7 mm), the maxillary canine (2.3 mm) and the mandibular canine (0.8 mm). All measurements were taken at the lingual cervical margin.
Significantly less indirect mandibular molar and cuspid expansion was found in young adults compared with adolescents.
No significant difference was found for maximillary molar and cuspid expansion when adults were compared with adolescents.
Cephalometric radiographs.
Frontal view.
Long-term follow-up (minimum 5 years) in one study (n=42) found significantly greater maximillary intermolar width with RME (Haas appliance) in the early maturation group (Um-Um +2.7 mm) and the late maturation group (Um-Um +3.5 mm) compared with controls. Significantly greater mandibular first intermolar width with RME was found in the late maturation group (Um-Um +2.3 mm) compared with controls. No other statistically significant between-group differences were found for mandibular intermolar width change. No statistically significant between-group differences were found for maxillary insical angle.
Lateral view.
One study found no statistically significant anteroposterior dental changes with RME (Haas type expander followed by fixed edgewise treatment) compared with controls.