Cleaning is not a government benefit, so if the patient has dental insurance, it depends on the contract between the dentist and the insurance company. An insurance company might limit coverage for cleaning to, say, $300. In that case, billing for $450 would simply result in a limited payment from the insurance company. On the other hand, the insurance might cover up to $450 – that is all spelled out in the contract between the dentist and insurance company. Either way, it is legal to submit a bill for whatever amount the dentist wants.
Some things would make this practice illegal. One would be fraud, where the dentist claims that a service was performed but it was not. Another would be breach of contract with the patient. For example, your contract might say "since you have insurance, we will only charge you 20% ergo $90 for the cleaning, and we also give you a pair of airpods at no cost to you", but then he also charges you the $150 that the insurance company did not cover – that would be breach of contract between you and the dentist. It might also be breach of contract w.r.t. the insurance company, where it is frequently stipulated exactly how much the dentist can charge the patient. Of course if the dentist has no contractual relation with the insurance company (is out of network), that is not a consideration.
On the third hand, the fine print might say that you are responsible for any charges not covered by insurance, in which case again the dentist will end up charging you for the airpods, but this possibility is covered in the contract. Then, representing the airpods as "free" is (possible) deceptive advertising, which is also illegal (even though it's not fraud).
It is a legal business practice to offer a discount (and take a loss) in order to recruit new customers, which is the generous interpretation of the practice.
