How do you correctly punctuate this sentence? According to my dentist I need to brush my teeth for at least two minutes

Place a comma after the word 'dentist,' ((and put a period after the word 'minutes.'))

Explanation:

Why? ... because you have to separate the dependent (subordinating) clause from the independent clause - - whenever it begins the sentence.

According to my dentist, (comma) I need to brush my teeth for at least two minutes. (period)