Health Insurance Re-apply waiting period

Try with another provider who will cover this pre-existing illness. 
If you don't disclose it, and at a later stage insurance company gets to know about this (e.g. from medical records after your hospitalization), then you won't get the claim and may even be blacklisted. Now with NHCX coming into pipeline, patients data will be shared amongst insurers, so blacklisting from one insurance will mean that every other insurance company will get to know about it.
So better take a policy from another company who will cover this PED, or who agrees to cover this PED after 2 or 4 years. Premium may be high but you will have peace of mind and stress free life (which is the reason why you are buying an insurance).

Try Acko, they advertise that they will cover all PED for additional premium.
I bought Acko insurance 5 months back for my elderly parents and had decent experience with them at the time of claim approval.

@spantktm321
I am using Acko car insurance since last 5-6 years. But never required to file a claim.
A friend who was using acko car insurance told me he had a very good experience.

Now coming to health ins, i purchased Acko for my parents in May.
Paid around 59k premium for 25L coverage of mom (64 yrs) and dad (66 yrs).
They arranged online consultation for both. For dad they arranged home sample collection too.
Within few days I got the policy.
In Oct end my mom suffered from dengue and her platelets dropped. Got her admitted through this policy. When hospital sent for insurance approval, the acko guys asked 3 queries to the hospital and hospital replied after few hours each time. Finally the insurance was approved on the 2nd day. At the time of discharge, got insurance final approval in around 4 hrs. Did not have to pay a single rupee from the pocket. They covered everything including consumables and non medical expenses like patient diet, medical records charge, admission charge, etc

@Avadhoota I explored other options but most insurances denied to cover my dad since he had crossed 65 years.

@kukdookoo I bought directly from acko website. there was no PED in this case. Plan name is Acko standard health plan, you can check out the benefits on their website. New policy, not ported.

@hpsinha If a company blacklists a person out of vengeance/mischief, then individual can approach grievance redressal mechanism of IRDAI (mostly companies will deny claim but will not blacklist until they have really strong reason/evidence). I am not aware about your second question (RCT/Dental issues)