Condition analysis: After tooth extraction and correction, the gap is not completely closed, which means that the correction is unsuccessful and cannot be completed. It is impossible that the gap cannot be closed. Guidance: From the perspective of correction and maintenance, transparent retainers are more effective. Lingual retainers are generally only used on the front teeth, while transparent retainers are worn on all upper and lower teeth or teeth within the correction range. Therefore, transparent retainers are more effective.