Here is a legendary software whose existence needed to be proven... up to now ! This is THE ghost of the PlayStation, as Scorcher is on Japanese Sega Saturn.
According to GC documentation and catalogues, it could only be purchased by dentists to be displayed in waiting rooms or next to the dental chair. Two versions were listed : a regular Level 2 and a Level 2 "Upgrade Ban" (cheaper). Nobody has ever been able to tell the difference. GC Dental doesn't accept to answer either...
By seeking deep into web archives, there remain traces and pictures of Level 2 PC version but the picture of the PS1 version was deleted... This is the very reason why it was supposed not to have been released.
With my copy and the envelope, I can confirm that dentists could either buy Level 2 directly or buy Level 2 cheaper if they shipped back Level 1 (as an "Upgrade" version).
「デンタルIQさん2」をお買い求めいただき誠に ありがとうございます。 大変恐縮ですが、いままでお使いの「デンタル IQさんLEVEL-I」のCD-ROMをこの封筒にて ご投函いただきますようお願い申し上げます.
Thank you for purchasing「Dental IQ-san2」. We are very sorry, but please send us the 「Dental IQ-san LEVEL-1」 CD-ROM you have used so far in this envelope.
Level 1 is very rare : only a few copies have surfaced in 16 years. But Level 2 is the rarest "for sale" software... and the most expensive Japanese PS1 "for sale" title !
Since shops in Japan didn't see any copy, they are constantly offering more and more money, still thinking Level 2 & "Upgrade Ban" are different softwares... They sometimes make confusions like below...