dental clinic income tax

if his total Income does not exceed the basis exemption limit then he's not required to file return.
however he needs to maintain a file for all the expense vouchers incurred such as light phone mobile stationery salary etc...
Also receipts book need to be maintained for money received from patients.A bank account in the name of the clinic needs to be opened

Yes, agreed. But in case you wish to declare income u/s. 44ADA, most of the records not mandatory, except aggregate of professional fees charged.