Will I be eligible for another visa exempt stamp for dental treatment in Thailand?

I would get letter from dentist and pay the $40 for tourist visa-MT medical treatment, then you’ll have no issues at Survarnabhumi Airport upon entering. Visa or no visa strongly suggest letters of appointment from dentist and proof of accommodation.

depend on your luck. better have tourist visa before coming to thailand

I would apply for a simple tourist visa.

𝗪𝗶𝗹𝗹 𝗜 𝗯𝗲 𝗲𝗹𝗶𝗴𝗶𝗯𝗹𝗲 𝗳𝗼𝗿 𝗮𝗻𝗼𝘁𝗵𝗲𝗿 𝘃𝗶𝘀𝗮 𝗲𝘅𝗲𝗺𝗽𝘁 𝘀𝘁𝗮𝗺𝗽

Sadly you're asking a question that no one on this or any other group could answer with any degree of certainty.. 😕

Now in theory, you should be able to get back in visa exempt, BUT it's gonna come down to the officer you're standing in front of when you stamp in.

I mean looks like you had two nearly back to back 60 day visa exempt entry stamps (no matter what reason they were for) and even though you didn't extend them and left before the 60 days ran out, you were coming in free stamp as a tourist. Then you want to come back in free stamp again in July/Aug for the additional dental work. Could be suspect, OR you could skate right in 🙁 it's a crap shoot..

I'd say, just to be safe, apply for the tourist visa based on medical treatment (get a letter from the treating dentist/clinic). That to me at least shows you're entering with a visa for the right reason and you shouldn't get too much scrutiny stamping in