Final answer:
A 9-year-old with an anterior crossbite should typically receive treatment that may involve a removable appliance or be observed until further tooth eruption, based on individual dental evaluation.
Step-by-step explanation:
A single tooth anterior crossbite found in a 9-year-old should typically be treated with intervention rather than waiting for self-correction. Given that the permanent dentition is in the process of establishing in a child of this age, observing until all permanent teeth, such as the cuspids, have fully erupted could be part of the treatment strategy. However, depending on the specific circumstances, a dental professional may recommend a removable appliance to correct the crossbite at this stage before the complete permanent dentition has developed. The approach to treatment would be individualized to the child's needs, assessed through clinical examination and possibly orthodontic consultation.