The Evans Twin Block is usually used in the adult dentition -- when the choice has been made to accomplish the majority of orthodontic corrections required prior to using the Twin Block to correct any orthopedic problems. Vertical changes are often easier when the majority of orthodontic corrections are performed first. Because multiple ball clasps are used for retention, this appliance can be used while the patient is still in full brackets. The placement and number of ball clasps needed for a given case is dependent upon the type of orthodontic corrections needed to finalize treatment. Of course, midline expansion screws can be added, if needed.